A high quantity of well-dated, high-resolution, continuous geoarchives is
needed to connect palaeoenvironmental reconstructions with
socio-environmental and cultural transformations in a geographically
heterogeneous region such as southern Greece. However, detailed and
continuous palaeoclimatic and palaeoenvironmental archives from the NE
Peloponnese are still sparse. Here, we present two new palaeolake archives
of Pheneos and Kaisari covering the last 10 500 and 6500 years,
respectively. For the last 5000 years, we compare them with sediment
records from adjacent Lake Stymphalia and the Asea valley by applying the
same set of sedimentological, geochemical, and statistical analyses to all
four lacustrine archives.
Continuous geochemical X-ray fluorescence (XRF) core scanning records
provide evidence for hydrological variations and environmental changes since
the Early Helladic period (5050 BP), the beginning of the Bronze Age in
Greece. We hereby focus on different spatial scales to estimate the validity
range of the proxy signals. Ten elements were selected (Al, Si, K, Ca, Ti,
Mn, Fe, Rb, Sr, Zr) for a principal component analysis. The clr(Ca/Ti) was
chosen as the most meaningful proxy, reflecting varying input of
carbonaceous vs. clastic input, which may be linked to changes in the
hydrological conditions. Our results show phases when permanent lake water
bodies existed (ca. 5000–3600 cal BP) as well as phases with periodic
desiccation of the lakes during younger times. While Pheneos and Kaisari
show a drying trend during the transition phase from the Late Helladic
period to the Proto-Geometric period (ca. 3200–2800 cal BP), Stymphalia
and Asea show a rather short dry peak around 3200 cal BP followed by a
wetter phase.
Although all our geoarchives show evidence for drier phases, their timing
and duration display considerable site-to-site differences which may be
explained by site-specific responses in individual ecosystems. Age
uncertainties, however, may likewise explain some deviations, as the dating
is based on bulk sediment samples including potential unknown reservoir
effects.
The high regional geographical diversity within the Peloponnese combined
with the dating challenges in the limestone-rich area and the variation in
our data testify that any hypothetical mono-causal connection between
palaeoenvironmental changes in a single geoarchive and contemporaneous
societal transformations across the Peloponnese would be an
oversimplification.
Kurzfassung
Eine hohe Anzahl gut datierter, hochaufgelöster und kontinuierlicher
Geoarchive wird benötigt, um Paläoumweltrekonstruktionen mit
sozial-ökologischen und kulturellen Transformationen in einer
geographisch heterogenen Region wie Südgriechenland zu verknüpfen.
Aktuell sind solch detaillierte und durchgängige Paläoklima- sowie
Paläoumweltarchive auf der NO Peloponnes jedoch spärlich.
In dieser Arbeit stellen wir kontinuierliche Proxydaten für zwei neue
Umweltarchive aus den Paläoseen Pheneos und Kaisari vor, welche die
letzten 10 500 bzw. 6500 Jahre abdecken. Für den Zeitraum der letzten
5000 Jahre vergleichen wir diese mit Sedimentkernen des angrenzenden Sees
Symphalia sowie des Asea Tals, indem wir für alle vier lakustrinen
Archive die gleichen sedimentologischen, geochemischen und statistischen
Analysen durchführen.
Röntgenfluoreszenz-Kernscandaten liefern Hinweise auf hydrologische
Schwankungen und Umweltveränderungen seit der frühhelladischen Zeit
(5050 BP), dem Beginn des Bronzezeitalters in Griechenland. In dieser
Arbeit konzentrieren wir uns auf verschiedene räumliche Skalen, um den
Gültigkeitsbereich der Proxysignale abzuschätzen. Eine
Hauptkomponentenanalyse wurde auf Basis von zehn geochemischen Elementen
(Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr) durchgeführt. Das zentrierte
log-Verhältnis clr(Ca/Ti) wurde als aussagekräftigster Proxy
identifiziert, welcher den veränderlichen Eintrag von
calciumcarbonathaltigem zu klastischem Material widerspiegelt, der wiederum
auf Veränderungen in den hydrologischen Bedingungen
zurückgeführt werden kann. Unsere Ergebnisse zeigen Phasen, in denen
dauerhafte Seen an den untersuchten Standorten existierten (ca. 5000–3600 cal BP) sowie Phasen – vor allem in jüngerer Zeit – in denen es
zu periodischer Austrocknung der Seen kam. Während Pheneos und Kaisari
beispielsweise eine Trockenphase während der Übergangszeit der
späthelladischen zur protogeometrischen Periode (ca. 3200–2800 cal BP) erkennen lassen, zeigen Stymphalia und Asea eine eher kurze Trockenphase
um 3200 cal BP gefolgt von einer längeren feuchteren Phase.
Auch wenn alle untersuchten Geoarchive klare Anzeichen für Trockenphasen
liefern, variieren sowohl der Zeitpunkt als auch die Dauer erheblich, was
auf standortspezifische Reaktionen der einzelnen Ökosysteme
zurückgeführt werden kann. Unsicherheiten in den Altersmodellen
können gleichwohl einige Abweichungen erklären, da die
Radiokarbondatierungen auf Basis von Gesamtsedimentproben durchgeführt
wurden, welche einen potenziellen, unbekannten Reservoireffekt beinhalten
können.
Die hohe räumliche Diversität innerhalb der Peloponnes Halbinsel in
Kombination mit den Datierungsunsicherheiten in einem kalkhaltigen
Karstgebiet und den Schwankungen in den Datensätzen deuten darauf hin,
dass das Herstellen monokausaler Verbindungen zwischen
Paläoumweltschwankungen in einem einzelnen Geoarchiv und zeitgleichen
sozialen Transformationen auf der Peloponnes eine zu starke Vereinfachung
der Forschungshypothesen zur Konsequenz hat.Highlights.
Multi-proxy investigation of Middle to Late Holocene hydrological development
from four (palaeo)lake sediment sequences.
Proxy signals are discussed on three different spatial scales.
High regional to local variability of palaeoclimatic proxies across the
Peloponnese peninsula.
citationstatementSeguin, J., Avramidis, P., Haug, A., Kessler, T., Schimmelmann, A., and Unkel, I.: Reconstruction of palaeoenvironmental variability based on an
inter-comparison of four lacustrine archives on the Peloponnese (Greece) for
the last 5000 years, E&G Quaternary Sci. J., 69, 165–186, https://doi.org/10.5194/egqsj-69-165-2020, 2020.Introduction
The eastern Mediterranean can be considered a region of high importance
for palaeoenvironmental research, as it experienced a long history of
cultural development and human–environment interaction throughout the Middle
to Late Holocene (Izdebski et al.,
2016; Roberts et al., 2011).
Middle to Late Holocene environmental archives often provide records on
palaeoenvironmental changes containing a combination of natural climatic and
anthropogenic signals, which are often not easy to disentangle. From
southern Greece and the Peloponnese, high-resolution environmental archives
covering this time period are still relatively sparse or often discontinuous
(Finné et al., 2011; Gogou et al., 2016; Luterbacher et al., 2012,
McCormick et al., 2012; Atherden
and Hall, 1994; Izdebski et al., 2016; Jahns, 1993).
Lake sediments record climatic changes as well as local catchment-specific
processes (Roberts
et al., 2008). However, each lake responds differently to global, regional,
or local influences, depending on its size and catchment settings
(Meyers and Lallier-Vergès, 1999). To distinguish
local from regional or even hemispheric climatic signals, a combination of a
larger number of geoarchives and an analysis of multiple proxies seems more
promising (Finné et al., 2019).
Although there are an increasing number of studies on eastern Mediterranean
palaeoenvironmental archives that have been published most recently
(Emmanouilidis
et al., 2018, 2019; Finné et al., 2017; Katrantsiotis et al., 2018,
2019; Masi et al., 2018; Rothacker et al., 2018), they do not provide a
uniform picture of the climatic and environmental changes through the Middle to
Late Holocene, and sometimes they are inconsistent with archaeological or
historical data (Finné et al., 2019). Most reconstructions
of Holocene climatic variations in the Mediterranean are based on one single
palaeoenvironmental archive, leading to very heterogeneous and often even
divergent results when being compared to each other
(Finné
et al., 2011; Luterbacher et al., 2012). This calls for the need for not
only multi-proxy approaches on one palaeoenvironmental archive, but also
multi-archive approaches that use the same methods and proxies at different
study sites.
Map of the study area in the NE Peloponnese. (a) Overview of the Peloponnese with the location of selected cities and archaeological sites (red), lacustrine (dark green) and lagoonal (light green) sediment archives, and speleothem archives (purple). (b) Topographic map of the poljes area with the location of the coring sites
(green) and settlements (black). Black lines trace the surface hydrological
catchments. Contour lines are drawn in increments of 100 m. Photo locations
A–C from Fig. 2 have been indicated by a dotted square and yellow stars.
Here, we present a combined approach of four lake sediment archives from the
northeastern and central Peloponnese (Greece), namely from Lake Stymphalia
and from the valleys of Asea, Pheneos, and Kaisari (Fig. 1), which hosted
lakes of different extent in the past. Human presence in the study area is
proven since Neolithic times but has been relatively sparse and remains
widely unexplored except for the Classical–Hellenistic periods and the last
200 years
(Seguin
et al., 2019; Walsh et al., 2017). Due to its mountainous topography with
elevations of up to 2400 m only a few kilometres away from the coast, the
Peloponnese displays a high climatic heterogeneity with significant
precipitation and temperature gradients from west to east and from the coast
to the mountain ranges. Hence, palaeoclimate records across the Peloponnese
are prone to reveal different patterns on a spatially comparatively limited
scale (Katrantsiotis et al., 2019).
The concept of spatial scales is a fundamental working technique in physical
geography and climatology (Lauer and Bendix, 2006; Wanner,
1986). The scales however are not uniformly used and may differ according to
the studied landforms, climate phenomena, and processes. In this study, we
distinguish micro-, meso-, and macroscales and define them as follows: (1) the microscale covers local lake catchment-specific signals and processes,
(2) the mesoscale describes the regional climate on the NE Peloponnese with
an approximate diameter of 102 km (Wanner, 1986), and (3) macroscale signals reflect changes on the supra-regional level, here the
eastern Mediterranean. Given the proximity of our selected
palaeoenvironmental archives to each other and the similar geological and
geomorphological setting, we suppose that they experienced similar
mesoscale climatic conditions. We investigate each archive with the same
geochemical and sedimentological analytical tools, notably XRF core
scanning, to reveal the differences and similarities in the proxy records
that help us to disentangle local (microscale) from regional (mesoscale)
signals. A concordance in the course of the same proxy at the different
sites would suggest that the proxy reflects an overarching signal of
regional environmental or climatic change (macroscale). If the proxy shows
no agreement between the sites, this may hint towards local site-specific
effects or a mismatching of the data due to dating uncertainties
(Roberts et al., 2016).
Earlier studies on Lake Stymphalia
(Heymann
et al., 2013; Seguin et al., 2019) showed that the lake reacted sensitively
to environmental and hydrological changes as well as to human disturbances,
notably during the last 2500 years. A sediment core from the Asea valley
provided a record on the hydrological variability in the area of the last
6500 years (Unkel et al., 2014), however in
lower resolution than the Stymphalia record.
In this study, we aim to (1) provide geochemical proxies for two new
sediment sequences from palaeolakes Pheneos for the last 10 500 years and
Kaisari for the last 6500 years and (2) compare the last 5050 years with the
same proxies from nearby Stymphalia and Asea to reconstruct and investigate
climatic and environmental changes since the beginning of the Helladic
period (for references to cultural periods see Table S3 in the Supplement). This is a period
when the Greek societies were already sedentary and achieved major advances
in social, economic, and technological skills (Bintliff, 2012). By directly
juxtaposing records from four sites, we provide a more profound picture of
the environmental and climatic history of the Peloponnese, going beyond the
capabilities of a climate reconstruction based on a single lake record.
Regional setting
The three karst poljes Pheneos, Stymphalia, and Kaisari are located in the
northeastern Peloponnese at the southern base of the Mt. Ziria (also known as Kyllini)
(2374 m) limestone massif at an elevation of ca. 600 m above sea level
(Fig. 1).
The Stymphalia Polje, extending approximately 13 km from west to east,
comprises the only remaining natural permanent lake of the Peloponnese, Lake
Stymphalia (37.85∘ N, 22.46∘ E), as well as the
archaeological site of the Hellenistic town of Stymphalos
(Walsh et al., 2017; Williams, 1983; Williams and Gourley,
2005). The total catchment area today is approximately 217 km2, excluding subsurface water flow of the Ziria karst
system (Nanou and Zagana, 2018). The larger Stymphalia
catchment (∼182 km2) and the smaller Kaisari
catchment in the NE (∼35 km2) were connected
in the early 20th century CE by an artificial tunnel
(Knauss, 1990; Morfis and Zojer, 1986). Formerly, Lake
Stymphalia drained via one main sinkhole (katavothre), which was encased in
concrete in the 19th century (Morfis and Zojer, 1986).
Today, water is pumped away for agricultural purposes via the Hadrianic
aqueduct that was built around 130 CE and reactivated in the 19th
century CE. Since the building of the aqueduct, lake level and size have varied
considerably over time
(Seguin et al., 2019).
Geologically, the Stymphalia Polje is located in the limestone and dolomite-dominated Gavrovo–Tripoli and Olonos–Pindos geotectonic zones, where karst
features are abundant. Outcrops of the metamorphic phyllite–quartzite
series, Neogene and Pleistocene conglomerates and marls, schists, and
Quaternary deposits can be found mainly in the west and southwest
(IGME, 1982, 1970; Morfis and Zojer,
1986).
The Kaisari Polje (37.93∘ N, 22.55∘ E, ca. 730 m a.s.l.) stretches ca. 7 km from the SW to NE directions. Morfis
and Zojer (1986) considered it to be part of the Stymphalia Polje and called it
valley of Klimenti, which is a village north of the village of
Kesario/Kaisari (Fig. 1). It contained a small lake in former times, which
was drained in the 1880s for agricultural purposes. The catchment geology of
the Kaisari Polje is more homogeneous and consists of Neogene marls and
conglomerates (Morfis and Zojer, 1986).
To the west of the Stymphalia Polje, crossing the Geronteion Pass in the
Mavrovouni mountain ridge (rising up to 1600 m), the Pheneos Polje
(37.85∘ N, 22.33∘ E) is located at approximately
700 m a.s.l. It is 28 km long and max. 13 km wide, with a catchment area of
approximately 235 km2 (Knauss, 1990;
Morfis and Zojer, 1986). The ancient site of Archea Pheneos at the NW end of
the polje (Fig. 1) was mainly inhabited during the Middle Helladic (ca.
4050–3650 BP).
Photos of the Pheneos Polje. Locations are indicated in Fig. 1.
(a) Aerial perspective with southwestward view on the eastern bay of the Pheneos Polje. (b) Side view on palaeoshorelines in the eastern bay close to Amigdalia. (c) Top-down view into the eastern katavothre contained in a
concrete construction. The metal grille allows the discharge of water and
prevents blockage. To the right, humans for scale (photos: Joana Seguin, 2017;
Ingmar Unkel, 2019).
Morfis and Zojer (1986) divide the Pheneos polje into an
eastern and a western bay. It consists of two main hydro-tectonic systems
containing 87 springs and seven sinkholes (Morfis and Zojer,
1986). In this karstic environment, subsurface flow is of high importance
for the hydrological system (Nanou and Zagana, 2018). Today, no
perennial Lake Pheneos exists anymore and the water drains through trenches
to the eastern katavothre (Fig. 2a). Most katavothre were anthropogenically
regulated and the polje floor is no longer inundated, thus creating more
space for agricultural land. Only during wet winter months may a small
ephemeral/seasonal lake develop in the western bay (Morfis
and Zojer, 1986). Today, the eastern katavothre is surrounded by a
concrete construction to prevent it from blocking (Fig. 2c).
Knauss (1990) refers to different historical scholars who
recount that it was blocked in the past more than once, causing inundations
and high lake level stands, but they also report periods with complete
desiccation of the polje. During the Ottoman period, the drainage system was
purposely blocked in the 1820s, leading to a 39 km2 large and
42.5 m deep lake, which was reopened by an earthquake in 1834
(Knauss, 1990).
Geologically, the Pheneos Poljes is similar to Stymphalia. It is likewise
located in the limestone- and dolomite-dominated Gavrovo–Tripoli and
Olonos–Pindos zones. Outcrops of the metamorphic phyllite-quartzite series,
Neogene and Pleistocene conglomerates and marls, schists, and Quaternary
deposits are also present (IGME, 1982,
1970; Morfis and Zojer, 1986).
The Asea valley is located in central Arcadia, close to Tripoli
(Peloponnese) and about 50 km south-southwest of Stymphalia. Contrary to the
geomorphologically closed poljes, the Asea valley, although located on the
southwestern margin of the large Tripoli polje, is hydrographically
connected to the catchments of the rivers Alpheios and Eurotas, both
draining into the Ionian Sea, and thus Asea represents a natural
thoroughfare (Unkel et al., 2014). Archaeological information for the site
from Palaeolithic to early modern times is available from a field survey in
the 1990s (Forsén and Forsén, 2003). Geologically, Asea belongs to
the Gavrovo–Tripoli zone, characterized by carbonate rocks and some clastic
flysch (IGME, 2002,
1992; Morfis and Zojer, 1986; Unkel et al., 2014).
Materials and methods
The methods applied equal the analyses of the sediment cores from Stymphalia
(STY1) and Asea (Asea-1) (Heymann
et al., 2013; Seguin et al., 2019; Unkel et al., 2014; Table 1), which
allows detailed comparisons with our newly recovered records Pheneos (PHE1)
and Kaisari (KES2).
Overview of coring sites discussed in this study.
IDLocationCoreCoordinatesElevationCatchmentPresented coreacronym(m a.s.l.)sizelength1StymphaliaSTY137.84944∘ N, 22.46056∘ E610182 km2324 cm2KaisariKES237.94558∘ N, 22.57641∘ E73035 km2350 cm3PheneosPHE137.85114∘ N, 22.33510∘ E710235 km2390 cm4AseaAsea-137.37603∘ N, 22.26592∘ E630500 cmSediment coring
Fieldwork at the former lake sites of Kaisari and Pheneos was conducted in
spring 2017. At the time of coring, both sites were drained and covered by
pastures and non-vegetated field, thus being accessible for land-based
vibracore drilling. Following a test coring using an open system (A cores),
two parallel cores (B and C) for each site with a vertical offset of 50 cm
were retrieved in 1 m sections of 55 mm diameter using inliner tubes
deployed in a piston corer (Stitz type). PHE1 (37.85114∘ N,
22.33510∘ E; 390 cm total length) was cored in the eastern bay of
the Pheneos Polje in proximity to the eastern katavothre. Two corings were
taken from the Kaisari Polje, and we here present results from KES2
(37.94558∘ N, 22.57641∘ E; 350 cm total length), which
is assumed to have been closer to the former lake depocentre. The sediment
cores were kept in their sealed inline PVC tubes and transported to Kiel
University (Germany), where they were stored at +4∘C in a
cooler.
Sedimentology and geochemistry
After the cores from Pheneos and Kaisari had been split, they were described
in terms of lithology, sediment texture, structure, and colour according to
Munsell soil colour charts (Munsell, 2000). A master depth
scale was established for each site based on a compilation of overlapping
parallel cores using the RGB colour values. The core sections were visually
correlated using distinct marker layers.
Fresh and smooth core surfaces of the archive half cores were prepared for
line-scan photography (resolution: 143 ppcm cross-core and down-core,
shutter time: 5 ms) and subsequently analysed geochemically via
non-destructive X-ray fluorescence (XRF) scans using an Avaatech XRF core
scanner (Richter et al., 2006) and
an attached colour line-scan camera. The defined overlapping intervals in
the parallel cores were scanned in two runs with 10 kV (exposure time of 10 s at 750 µA) and 30 kV (exposure time of 20 s at 2 mA, using a
Pd thick filter) at a resolution of 5 mm. Combining the data into a
continuous sequence and data cleaning were done in R version 3.5.1
(R Core Team, 2019). Cleaning of the dataset, i.e. the removal of
explicit outliers and refilling of the missing values by linear
interpolation, was done manually prior to statistical processing. Voids in
the sediment, e.g. in PHE1 275–300 cm and in the topmost parts of both
cores, were not filled with interpolated data. We selected 10 elements that
were measured in all cores (10 kV: Al, Si, K, Ca, Ti, Mn, Fe; 30 kV: Rb, Sr,
Zr) for detailed analyses along the sediment sequence. The XRF scanning
results are expressed as element intensities that were transformed into
centred log ratios (Weltje et al., 2015). Unlike element intensities,
centred log ratios of elemental pairs minimize measurement variation caused
by sample geometry, physical properties, and the closed-sum effect
(Weltje and Tjallingii, 2008).
Centred log ratio (clr) transformed data were also used for multivariate
statistical operations.
Data exploration was conducted by statistical analyses using the open-source
programme R (R version 3.4.2; R Core Team, 2019). For each study
site, we applied a standardized and rotated principal component analysis
(PCA) to the geochemical elements to reduce the dimensions that explain the
variability in the dataset in the first place and secondly to explore the
relationship between the different elements and their distribution within
the sedimentary units. These principal components (PCs) do not have absolute
units but reflect relative changes in the chemical composition over time.
Element correlations of all elements acquired by XRF scanning were explored
by biplots (Aitchison and Greenacre, 2002), which show the
correlation of each element with respect to the main variance in the data
indicated by principal components. For each lake ecosystem, the
interpretation of element ratios as proxies for palaeoenvironmental
variation needs to be explored and validated individually prior to
multi-site comparisons (Xu et al., 2010).
For discrete samples from KES2 and PHE1, the grain size distribution
<2 mm was measured on air-dried samples (ca. 0.3 g, n=21) every
30 cm using a laser particle analyser Malvern Mastersizer 2000. The samples
were pretreated with hydrogen peroxide (H2O2, 35 %) to remove
the organic matter, and the dispersant agent sodium pyrophosphate
(Na4P2O7) was added to avoid aggregation of particles. At
least one measurement was conducted per previously identified lithological
unit. The grain size distribution was categorized according to the DIN EN
ISO 14688-1 nomenclature and indicated in volume percent (Figs. 4 and 5).
However, grain size determination via laser diffraction on carbonate-rich
sediments is known to be difficult (Murray, 2002), and
thus it only provides general guidance here. In addition to laser
diffraction, we use clr(Zr/Rb) as an indicator for variation in grain size
of the clastic input (Figs. 4, 5), where lower values reflect finer-grained,
clay-size particles (Dypvik and Harris, 2001).
Additionally, samples for carbon and nitrogen analyses were taken at the
same intervals. The concentrations of total carbon (TC), total inorganic
carbon (TIC), and total nitrogen (TN) were determined on dried and powdered
samples using a Euro EA (elemental analyser). We calculated total organic
carbon (TOC) concentrations in dry sediment by subtracting TIC from TC. The
TOC/TN ratio was calculated to indicate the origin of the sedimentary
organic matter. While values for autochthonous organic matter, such as algal
biomass, are low, generally ranging between 4 and 10, land-plant organic
matter eroded into the lake shows values higher than 10 and vascular plants
even higher than 20 (Meyers, 2003).
Radiocarbon dating and Bayesian modelling
The radiocarbon dates used here from Stymphalia are published in Heymann et
al. (2013) and Seguin et al. (2019) while those from Asea are published in Unkel et al. (2014).
The chronologies of the new sediment cores from Pheneos and Kaisari (Table 2) are based on accelerator mass spectrometry radiocarbon (14C)
measurements performed at the Poznań Radiocarbon Laboratory.
List of radiocarbon samples taken from PHE1 and KES2. The sampling
depths refer to the master core. Indicated 14C ages are unmodelled ages giving the 68.2 % calendar dating probability. Indicated IntCal13 ages are cal BP ages modelled with rcarbon using the IntCal13 calibration dataset (Reimer et al., 2013).
Notes: 1 Amount of remaining sample material after respective pretreatment. 2 Dates have been excluded from age–depth modelling.
For Pheneos and Kaisari, bulk sediment samples were taken for dating using
the alkali residue fraction, due to the absence of discrete organic
macro-remains during visual examination. Tephra layers supporting the
chronology could not be found in the sediments and have so far not been
reported in southern Greece for the Middle to Late Holocene in this area
(Zanchetta et al., 2011). Poor preservation
of organic matter and the high amount of reworked material and inorganic
carbon content present a considerable challenge for precise 14C dating
in the semi-arid Mediterranean (Grootes
et al., 2004; Vaezi et al., 2019; Walsh et al., 2019). As human decisions
may have a strong influence on the age–depth modelling, we present our
dating proceeding in detail in the following.
The age–depth models of Pheneos and Kaisari were produced using rbacon
(Blaauw and Christeny, 2011) with respect to the
IntCal13 calibration curve (Reimer et al., 2013)
and without applying any reservoir correction (Fig. 5).
For the Pheneos sequence, we calculated the age–depth model
PHE_03 based on eight samples (Table 2) for the complete
master core of 390 cm (Fig. 5). The analysis of the sediment sequence gave
no indications for hiatuses or erosional discontinuities, and thus a
continuous sedimentation was assumed. The lithology of the upper half of the
core however seems different and most probably reflects higher input of
terrestrial material. Four samples taken from units 7 and 8 (PHE075 –
PHE149) all show an age reversal of up to 3000 years, indicating
contamination by old detrital carbon
(Seguin et al., 2019)
and were hence excluded from the modelling process.
For the Kaisari sequence, four bulk samples were used (Table 2) along the
350 cm core (Fig. 5). The top of the sediment cores in Kaisari and Pheneos
was disturbed by agricultural activity, and the uppermost sedimentological
unit was considered to be plough horizon at both sites. Hence, it was not used
for dating, and the date of the surface was defined as the year of coring
(-67±10 BP).
For Asea, charcoal and plant remains from 30 sediment intervals were
handpicked, pretreated, and radiocarbon dated by NOSAMS at Woods Hole
Oceanographic Institution (see Table 1 in
Unkel et al., 2014). The initial
age–depth model was published in Unkel et
al. (2014); it was calculated using Oxcal 4.1 and based on IntCal09
(Reimer et al., 2009). Based on the most recent
state of knowledge and for the sake of consistency in the inter-comparison,
the model was also updated here using rbacon and IntCal13 as a calibration
curve (Reimer et al., 2013, Fig. S1). As sample
nos. 229 and 236, i.e. charcoal material, most likely gave too old of ages, we
considered them here as outliers. Sample nos. D, L, M, N, 233, and 235 were
considered too young of ages, as they contained root fragments probably
penetrating the sediment post hoc, e.g. reaching to the aquitard
(greenish grey units 2–3)” (Unkel et al.,
2014). They were likewise considered to be outliers and excluded from modelling
(Fig. S1).
For Stymphalia, the data and modelling approach is described in detail in
Seguin et al. (2019).
It is based on 45 radiocarbon measurements on 26 samples, modelled with
rbacon and calibrated using IntCal13 as the calibration curve
(Reimer et al., 2013). For bulk sediment samples,
we regarded the humic acid fraction as providing more plausible results
than the alkali residue fraction, and we applied a reservoir correction of
200±100 years. Cultural dates such as the building of the Hadrianic
aqueduct and the finding of a ceramic sherd were additionally integrated
into the modelling approach.
If not stated otherwise, mean ages were extracted for all models and used
for representation and interpretation of the geochemical proxies. In the
following, all dates are indicated as calibrated calendar years before
present (cal BP), where “present” is defined as 1950 CE with 1σ-uncertainty ranges according to Mook and van der Plicht (1999).
ResultsLithostratigraphy and geochemistry
The lithology of the Stymphalia core STY1 is presented by Heymann et al. (2013) and Seguin et al. (2019). The upper 324 cm was distinguished into 20
lithological units (units 54–70b). The colours are generally brighter in
the upper half; a distinct blackish layer (unit 62) separates the upper
brownish units from the lower, darker greyish units (Seguin et al., 2019).
Similar to the other sites, the sequence presents fine sediments dominated
by silt. Contrary to the other cores, shell fragments of Bithynia sp. and Valvata sp. gastropods
appear frequently.
For the Asea core, 11 lithological units were differentiated, and the
sequence has a fine texture of clay to silt size particles with few
intercalations of smaller carbonate clasts and isolated pebbles. The colours
range from very dark greyish brown at the bottom to dark olive brown at the
top, generally becoming brighter towards the top except for the blackish
unit 9 (Unkel et al., 2014).
Pheneos
Core PHE1 stretches over 390 cm and nine lithological units (Fig. 3, Table S1). The upper 19 cm is missing due to unconsolidated material and core
compaction. Due to an unfortunate match of coring depths of parallel lower
core segments, a void exists at 276–290 cm.
PHE1 composite core log with pictures (a), master core profile (b), lithological units (c), and overview of different proxies plotted
against depth. Age scale is adapted to depth scale. Depths where samples for
14C dating were taken are marked by red dots. (d) RGB colour values
(blue, green, red). (e) TOC (black line) and TOC/TN (red dotted line). (f) TIC (circles) together with counts per second (cps) of calcium (dark blue
line). (g) Titanium (in cps). (h) Iron (in cps). (i) Log ratio of Zr/Rb. (j) Log ratio of Ca/Ti. (k) Granulometry. For orientation, boxes with
lithological units (l) and cultural periods (m) are indicated (for
abbreviations and temporal classification of cultural periods see Table S3
and Weiberg et al., 2016).
KES2 composite core log with pictures (a), master core profile (b), lithological units (c), and overview of different proxies plotted
against depth. Age scale is adapted to depth scale. Depths where samples for
14C dating were taken are marked by red dots. (d) RGB colour values
(blue, green, red). (e) TOC (black line) and TOC/TN (red dotted line). (f) TIC (circles) together with calcium (dark blue line, in 1000 × cps). (g) Titanium (in 1000 × cps). (h) Iron (in 1000 × cps). (i) Log ratio of Zr/Rb. (j) Log ratio of Ca/Ti. (k) Granulometry. For orientation, boxes with
lithological units (l) and cultural periods (m) are plotted to the right
(for abbreviations and temporal classification of cultural periods see Table S3 and Weiberg et al., 2016).
Bayesian age–depth models for Pheneos (a). Kaisari (b). The
models were constructed using the R package rbacon (Blaauw and Christeny, 2011).
The blue tie bars indicate the 14C age distributions (see Table 2). Outliers are plotted in red and were excluded from modelling
(explanation in the text). The greyscale of the line graph reflects the
likelihood: the darker the more likely the model passes through that age.
The red dotted line follows the mean ages. The core lithologies are plotted
to the left.
Colours range from 10YR 3/1 to 10YR 5/3 (Munsell, 2000) with brown
and dark yellowish brown colours characterizing the sediments. The lower
part of the core is generally darker than the upper half, except for the
bright unit 1 (Fig. 3). The transitions between the units are all gradual
and do not show signs of abrupt changes. Visible organic debris is absent
except for some modern roots in the plough horizon (unit 9). Very few
mollusc shell fragments were found in units 6 to 8. The TOC content varies
between 0.2 wt %, at the boundary between units 1 and 2, and
2.3 wt % in the uppermost unit (Fig. 3). The existence of numerous
carbonate concretions within the rather fine matrix of the sediment in
several intervals of the core is characteristic and points towards at least
seasonal desiccation and initiation of soil formation. A higher number of
carbonate concretions with diameters <0.5 cm occurs in units 1 and
4. TIC (ranging from 0.6 to 4.0 wt %) and Ca contents follow a similar
trend, showing the highest values in unit 1 and low values in units 2 and 5.
Total nitrogen (TN) ranges from 0.04 to 0.16 wt % with an average of
0.08 wt %. The TOC/TN ratio ranges from 4.8 to 21.6, indicating varied
mixing of aquatic algae and terrestrial vascular plant material
(Meyers, 2003). Units 2 and 4 show the lowest
TOC/TN ratios, suggesting a greater input of autochthonous aquatic algae.
The grain size distribution ranges from fine to medium silt; it has a mean
clay content of 20.4 vol %, a mean silt content of 78.1 vol %, and a
mean sand content of only 1.5 vol %. The uppermost unit 9 is of
homogeneous brown colour and has an exceptionally high clay content
>30 vol %, which may be linked to alteration and compression
by agricultural use of the area. Due to this modern anthropogenic
alteration, unit 9 is excluded from any palaeoenvironmental interpretation.
Kaisari
The core KES2 has a length of 350 cm, while the upper 34 cm of
unconsolidated material is missing. Most analyses including XRF scanning
exclude the upper 50 cm, as the material was too loose to meet the scanning
prerequisites. KES2 was subdivided into seven lithological units (Fig. 4,
Table S2). No laminations are visible, all unit boundaries are gradual and
do not show any sign of abrupt changes, hiatuses, or event layers. Overall,
the core looks very homogeneous; yellowish brown to olive-brown colours
(10YR 4/4 to 2.5Y 5/3; Munsell, 2000) are dominant. Reddish
mottled sections with a higher Fe content suggest that the coring spot
periodically dried out and oxidation processes occurred. However, fractures,
layers of gypsum, or carbonate nodules, which could indicate desiccation or
soil formation, are absent. With the beginning of unit 6, few patches of
reddish material appear, which suggests the selective input of reddish soils
present in the catchment. Macro-remains are likewise largely absent except
for some roots in the plough horizon (unit 7) and sporadic, small shell
fragments in the lower part of the core. Intact gastropod shells – abundant
in Lake Stymphalia – are absent here. The sediment sequence has a fine,
silty texture composed of a varying mixture of clay (mean =21.5 vol %) and silt (mean =77.5 vol %); sand content was
<1 vol %. TOC varies between 1.0 wt % and 2.2 wt %. TN is similar
to Pheneos and ranges from 0.06 wt % to 0.13 wt % with an average of
0.09 wt %. TOC/TN ratios are in the range of 14–27, which – in
contrast to Pheneos – indicates a predominantly or exclusively terrestrial
source of organic matter with a higher input of vascular plants (TOC/TN>20) in units 2 to 4.
Core chronologies and sedimentation rates
The 390 cm long Pheneos core covers a total time span of 10 500 years (Fig. 5a). On average, the sedimentation rate for the whole sequence was
calculated at approximately 0.37 mm yr-1, being lowest between
4500 and 6500 cal BP with ca. 0.16 mm yr-1, slightly increasing to 0.32 mm yr-1
between ca. 4800 and 3300 cal BP, and further increasing to ca. 0.53 mm yr-1
during the last 3000 years.
Based on the age–depth model KES2_01 (Fig. 5b), we calculated
the average sedimentation rate to be approx. 0.54 mm yr-1 with a slightly
higher accumulation rate (0.78 mm yr-1) between 3800 and 2800 cal BP.
For Asea, the initial age–depth model by Unkel et al. (2014) was updated
by a more sophisticated modelling approach. Now, the 500 cm long core covers
a time span of 5400 years. Our new age–depth model shifted towards younger
ages by up to 1000 years compared to the Unkel-2014 model, especially
during the third millennium cal BP (Fig. S1). According to the new
age–depth model (Asea_9), the average sedimentation rate for
Asea is calculated to 0.92 mm yr-1. For the period 3000–3600 cal BP, the
rate is considerably lower with approximately 0.3 mm yr-1.
So far, the upper 5 m of the Stymphalia STY-1 core has been studied
geochemically in high resolution (Seguin et al., 2019; Heymann et al.,
2013). The most recent age–depth model was calculated for the upper 324 cm,
indicating a basal age of 8500 cal BP (Seguin et al., 2019). This gives an
average sedimentation rate of 0.38 mm yr-1 for the total sequence. For the
period 8500–2000 cal BP, the rate is calculated to be approximately 0.2 mm yr-1. It rises to 0.4 mm yr-1 around 195 cm and strongly increases to more
than 2 mm yr-1 at 165 cm. For the uppermost 50 cm, a lowering of the
sedimentation rate to 0.7 mm yr-1 was calculated (Seguin et al., 2019).
Asea-1 shows a consistently higher average sedimentation rate than the other
three sites (Fig. 7). For 6500–3500 cal BP, the sedimentation rate in
STY1 and PHE1 is similar and increases in younger times. For KES2, the
sedimentation rate stays relatively constant over the whole period, which
can mainly be attributed to the lowest available number of radiocarbon
dates.
In the following, we compare and interpret all four archives
palaeoenvironmentally for the last 5000 years, since the beginning of the
Helladic period (Table S3), a period when the Greek societies were sedentary
and generally achieved major advances in social, economic, and technological
skills (Bintliff, 2012).
Statistical analyses of the geochemical data
The principal component analysis, based on clr-transformed data, revealed
comparatively similar patterns for all for sites (Fig. 6). The first two
principal components (PC1 and PC2) for each site account for >65 % of the variance in the respective dataset. For Stymphalia, PC1
explains 62.5 % of the variance and is negatively associated with Ca and
Sr and positively associated with elements in clastic materials. For Kaisari
and Asea, the relationship is similar and PC1 explains 43 % and 46.1 % respectively (Fig. 6). For Pheneos, PC1 also spans the axis between
carbonate and terrigenous assemblages (53.1 %), but Sr appears more
distant from Ca and closer to Si, indicating an additional non-carbonaceous
Sr source, e.g. feldspars (Kylander et al., 2011).
Generally, the loadings of Ca and Sr in carbonates are closely bound
together and point to one axis direction, while the loadings of elements
such as Al, Fe, K, Rb, Si, Ti, and Zr in clastic material show a wider
spread of directions, but largely point to the opposite direction of the
carbonates, indicating a high negative correlation (Fig. 6). The influence of
K is the most variable in the four archives and more strongly influences
PC2. Mn plots perpendicular to most of the other elements, indicating that it
is influenced by an independent process.
Principal component analyses (PCA) for all study sites. (left)
Variable correlation circles of PCA of the XRF data for each site displaying
correlation between PC1 (Dim1) on the x axis and PC2 (Dim2) on the y axis. (right) Distribution of sample points in the
PC1–PC2 scatter plot for each site. The samples are coloured according to
their depth in the sediment core from purple (surface) to red (maximum
depth). The point density for STY1 is highest because data resolution is
1 mm. For the interpretation, the reader is referred to the text.
A colouration of the point cloud by depth (Fig. 6) visualizes the geochemical
evolution of the lake ecosystem and intervals where general geochemical
changes become visible or abrupt changes are revealed. For Asea, for
example, the upper lithological unit has not been interpreted
palaeoenvironmentally, because post-depositional processes have caused the
precipitation of carbonate nodules (Unkel et al., 2014). This can be
observed in an abrupt shift in the biplot towards very Sr- and Ca-rich samples
(Fig. 6).
For a comparison of all sites, the clr(Ca/Ti) ratio, showing higher
correlations for all sites, seemed to be more suitable to depict this
relationship than clr(Rb/Sr), which was applied as a palaeoenvironmental proxy
for Stymphalia (Seguin
et al., 2019). It was thus compared to PC1 and plotted over time (Fig. S3)
to demonstrate similarities and to illustrate the highest fluctuations of
geochemical proxies in the respective dataset.
DiscussionArchive comparison on the spatial scale
Our analyses of the four sediment cores revealed considerable variation
within the proxies, which shows that the landscape in NE Peloponnese has
changed significantly over the last 5000 years. Changes in the proxies can
be interpreted on different spatial and temporal scales. Microscale changes
occur due to local forcing that only influences one lake catchment and hence
is not visible in the neighbouring poljes. They may also hint towards
anthropogenic activities in the respective valley. Archaeological evidence
at the study sites, however, is limited to specific periods. Human activity
within the lake catchments certainly had an impact on erosion processes and
water availability
(Seguin et al., 2019),
but archaeological information is often lacking and it is not always evident
to differentiate clearly anthropogenic and natural drivers in the
geochemical record of the sediment. On a mesoscale, we find regional,
climatic similarities across the Peloponnese visible in all four sites,
while macroscale changes can be linked to over-regional climatic phenomena
also visible in further proxy records from Greece and adjacent regions.
All study sites represent shallow lacustrine environments that were not
permanently waterlogged during the respective period, but rather show phases
of periodic or episodic desiccation. Although Pheneos, Stymphalia, and
Kaisari are located in the immediate proximity (Fig. 1) and may have experienced
the same climatic changes, the sedimentary facies vary significantly due to
differences in catchment size, lake size and depth, and geology. Common
features of all sites are a relatively low organic carbon content and the
very low abundance of sand-sized particles within the grain size
distribution. Fine-grained silty clay and clayey silt dominate the Pheneos
and Kaisari sequences. Sand and coarse matrix (>2 mm) are almost
absent with the exception of carbonate nodules in PHE1 (Fig. 4). No event
layers were identified, and boundaries between the sedimentary units are
exclusively gradual in Pheneos and Kaisari. Combined with the dominance of
fine material, this indicates rather constant deposition of sediment under
relatively stable or gradually changing conditions and excludes the
existence of slumped units deposited during extreme precipitation events or
earthquakes. Accordingly, the sediment sequence in Kaisari only shows very
slight variations in the geochemical proxies (Fig. 4). The catchment and the transport distance from the slopes to the coring spot are much
smaller, and the input of terrestrial detritus is thus higher compared to
Pheneos or Stymphalia. Comparatively stable counts of terrigenous elements
suggest that the input of clastic detritus was relatively constant during
the Middle and Late Holocene, which is likewise supported by the rather stable
sedimentation rate.
Comparison of age–depth models for all four study sites. Solid
lines indicate the mean age of the respective model, while the dotted lines
indicate the ±2σ probability range. The shaded area reflects
the possible age–depth distribution range.
A comparison of all four age–depth models (Fig. 7) shows a generally higher
resemblance for the age–depth curves for the three poljes surrounding Mt. Ziria, while the model for Asea shows a significantly higher sedimentation
rate. While Stymphalia and Pheneos have similar sedimentation rates in the
lower part (>3800 cal BP), Kaisari shows an overall more
constant and slightly higher deposition rate, which can be ascribed to the
softer and more easily erodible marl sediments in the catchment and the
smaller lake size, where allochthonous detrital material from the slopes
reaches the coring site more easily. In Stymphalia, a strong increase in the
sedimentation rate related to anthropogenic activity was observed around
1200 cal BP (Seguin et
al., 2019). In Pheneos, age constraints for the upper 185 cm are
unfortunately weak, and we link the age reversals in unit 7 to higher input
of old, terrestrial carbon, which may have been caused by increased erosion
caused by human activity. Contrary to Stymphalia, we did not apply a
reservoir correction to the chronologies for Pheneos and Kaisari, because
this varies site specifically and may even change over time
(Grimm et al., 2009; Stein et al.,
2004). Due to the old carbon effect, it is more likely that the
age–depth models for Kaisari and Pheneos indicate too old ages than the
opposite (Grootes et al., 2004; Olsson, 1991). To account for discrepancies
in the chronologies (see also Fig. S2), we restrict the analysis of variation in
the dataset to the centennial scale and do not trace direct links between
palaeoenvironmental and societal changes.
The 390 cm long Pheneos sediment sequence covers the last 10 500 years,
while the bottom of the 350 cm long Kaisari core (KES2) was dated to 6500 cal BP. Both lakes have experienced at least periodic desiccation during the
last 5000 years, which is indicated by the absence of visible organic macro
remains, the low TOC content, and the carbonate nodules in Pheneos
and the strongly mottled nature of the sediment in Kaisari suggesting
turbation. Due to the non-stratified lithology with oxidized patches, low
preservation of organic remains, and the absence of indications for anoxic
conditions, the sediments of both palaeolakes suggest relatively shallow
water levels and high water level fluctuations with a well-mixed and
ventilated water column.
For all our study sites, the first principal component (PC1) explains the
variation between carbonate-rich and mineral-rich assemblages (Fig. 6).
Similar elemental distributions in PC1 have been found in Greece
(Katrantsiotis et al., 2018) and in Tibet (Ramisch et al., 2018). We
interpret these fluctuations as hydro-climatic variations. Intensified
carbonate precipitation (low values of PC1) occurs during warm and dry
summers, while the input of clastic material (high values of PC1) may be
enhanced during wetter periods
(Croudace
and Rothwell, 2015; Heymann et al., 2013; Katrantsiotis et al., 2018). We
use PC1 as the main palaeoenvironmental proxy in the following, as it represents
all carbonate and siliciclastic elements by their loadings and thus is more
representative than a ratio, based on only two elements, although the
clr(Ca/Ti) reflects the same bipolar distribution between carbonate
precipitation and terrigenous input and depicts similar trends (Fig. S3).
Palaeoenvironmental reconstruction on the temporal scale
Changes in water level and water availability may be attributed to climatic
fluctuations as well as to human interference. The intensity and spatial
distribution of human activities however is highly variable over time. There
is much evidence that human activity in the Peloponnese increased with
the introduction of Helladic economies
(Weiberg et al., 2016). While low activities
are assumed for most of the Final Neolithic (archeologically constrained for
the period 6450–5150 BP), a population boom is inferred for ca. 4750 BP followed by another decline around 4350 BP
(Weiberg et al., 2019). No explicit information
is available on human impact in the studied valleys for the Early Helladic
period. The onset of the Early Helladic period and thus the Greek Bronze Age
in southern Greece is archaeologically defined at 5050 BP
(Weiberg et al., 2016), and it can generally
be assumed that human activity in the study area existed throughout the
entire analysed period with varying intensities. According to
Sadori et al. (2011), vegetation
changes before ca. 4000 cal BP can be linked to climatic rather than
anthropogenic forcing, which was locally restricted. The possible impacts of
climatic changes on sedentary communities are a key topic in palaeoclimatic
research in the eastern Mediterranean; they may have been one factor
contributing to the downturn of societies, as intensely discussed for the
Late Helladic Mycenaean palatial period (Drake, 2012; Finné et al.,
2017; Kaniewski et al., 2013; Knapp and Manning, 2016; Knitter et al., 2019;
for cultural phases see Table S3).
In the following, we present our data chronologically divided into three
different periods; the limits were set according to the boundaries of
cultural periods of southern Greece as defined by
Weiberg et al. (2016), to underpin the
significance of human–environment interaction in the study area.
Early to Middle Helladic (5050–3650 cal BP)
For the Early to Middle Helladic period, our geochemical proxies generally
indicate wetter conditions. In Pheneos, phases of blackish sediment colour
with higher Fe content and slightly higher TOC content hint towards less
oxygenated phases, in which the non-composed organic matter and reduced iron
minerals, e.g. iron sulfides, most probably cause the blackish colouration.
In combination with low Ca content, this generally indicates phases of lower
evaporation and more permanent water saturation around 5100–3600 cal BP
(unit 5; Fig. 4). This is further supported by TOC/TN ratios of ±12,
which indicate a mix of terrestrial and aquatic organic matter
(Meyers and Ishiwatari, 1993). It thus
seems as if during this period, wetter conditions prevailed and the eastern
Pheneos Bay was covered by a permanent lake. In Kaisari, the geochemical
proxies and the lower TOC/TN ratio at 260 cm also indicate wetter conditions
at the same time, but generally a higher variability. Asea shows very stable
conditions over the period 5000 to 3400 cal BP with two short, dry pulses
around 4900 and 4700 cal BP and a general tendency towards increasingly
wetter conditions. The PC1 in Stymphalia likewise depicts wetter conditions
approximately until 4200 cal BP, when it reaches stable mean values for the
following 250 years. This is in agreement with a humid period reported from
Agios Floros (Fig. 8g; Norström et al., 2018) as
well as with results from a marine sediment core from the NE Aegean Sea
(Triantaphyllou et
al., 2016) indicating continuous warm and humid conditions between 5.5 and
4.0 kyr BP terminating with the “4.2 kyr” climate event.
Comparison of the PC1 proxies (a–d, this study) with other regional records for the last 5000 years. (e) Gialova PC1
(Katrantsiotis et al., 2018). (f) Lerna δD23 (reversed; Norström et al., 2018). (g) Agios Floros δD23 (reversed; Norström et al., 2018). (h) Mavri Trypa δ18O (reversed; Finné et al., 2017). (i) Thassos Cave δ18O, Skala Marion (reversed, Psomiadis et al., 2018). (j) Closani Cave, Romania, autumn–winter precipitation
(Warken et al., 2018). (k) Regional mean and uncertainty range of the Balkan model based on 10,
notably sedimentary, archives from the Balkan region
(Finné et al., 2019). Horizontal dotted lines depict the
respective mean values for each dataset. Vertical reddish shaded bars
indicate periods with potentially drier or warmer climatic conditions (RWP: Roman Warm Period; MWP: Medieval Warm Period).
The 4.2 kyr event is often described as a period of increased aridity and
drought conditions in large parts of the Mediterranean (Finné
et al., 2011; Isola et al., 2019; Kaniewski et al., 2018) and has recently
been set as a time marker for the onset of the Late Holocene
(Walker et al., 2019). In the Asea record, the event is
completely absent (Unkel et al., 2014) and not
clearly visible in our other three records either (Fig. 8a–d). In
Stymphalia, PC1 may indicate a slight tendency towards drier conditions,
while Pheneos and Kaisari show more prominent short-term fluctuations on a
microscale level, representing higher fluctuations in the respective lake
levels.
Late Helladic to Archaic (3650–2429 cal BP)
The Middle Helladic to mid-Late Helladic cultural period (ca. 4050–3300 cal BP) appears as a relatively stable phase at all four sites, which is
supported by reconstructions from Lake Lerna
(Katrantsiotis et al., 2019) and Agios Floros
(Norström et al., 2018), although they have a much
lower resolution. Following this more stable phase, several Peloponnesian
records provide evidence for an aridification trend starting around 3300 cal BP. Changes in the geochemical proxies occur gradually; the most
significant shift occurs in Pheneos and Kaisari around 3300–3200 cal BP. The input of terrigenous elements (e.g. Ti, Zr, K) decreases, while
carbonate content increases (Figs. 4, 5). Although elements in siliciclastic
material decrease in concentration, the accumulation rate indicates an
increase which may derive from more intensified carbonate precipitation
during drier conditions. This is supported by the bright yellowish brown
colour of the sequences and reddish oxidized patches in the sediment,
suggesting episodic desiccation. Climatologically, this can be interpreted
as warmer summers leading to more evaporation and carbonate precipitation
and lower input of allochthonous sediment due to less intense precipitation.
While Pheneos and Kaisari depict rather continuous shifts that peak in 3000 cal BP, Asea and Stymphalia show two minor dry spells around 3200
and 2900 cal BP while the conditions in between seem wetter (Fig. 8a–d).
This pattern looks similar to the records from Gialova and Lerna (Fig. 8e,
f; Katrantsiotis et al.,
2018; Norström et al., 2018). The differences in the
reaction may be explained by age uncertainties, a diverging resilience in
the respective ecosystems, or differing sedimentation processes. The
considerable drying trend observed in Pheneos and Kaisari is generally in
line with the Agios Floros record, Mavri Trypa, and Closani Cave, Romania
(Fig. 8g, h, j; Finné
et al., 2017; Katrantsiotis et al., 2015; Warken et al., 2018).
Nevertheless, as the radiocarbon dates in Pheneos show age reversals for
this period, it cannot be excluded that the material here has been reworked
by relocation and transport and that the geochemical proxies do not depict a
climatic signal for the respective time period.
The rapid climate change interval, as defined by Mayewski et al. (2004) for
3500–2500 cal BP, is characterized by pronounced but heterogeneous
climatic shifts in many regions across the Mediterranean and Europe. Scaling
up to the meso-level, some authors see a significant climate event at 3200 cal BP (3.2 kyr event) and relate it to cultural changes at the end of the
Late Helladic period (Table S3), also understood as the end of the Greek
Bronze Age (Drake,
2012; Finné et al., 2017; Kaniewski et al., 2013; Weiberg et al., 2016).
Other studies find more evidence of a climatic shift around 2800 cal BP (2.8 kyr event; Neugebauer
et al., 2015; van Geel et al., 2014), temporally related to the onset of the
Greek Early Iron Age. The temporal and spatial diversity in the results of
various studies shows that climatic changes proclaimed on a macroscale
could be regionally very different and reveal very heterogeneous (local)
conditions. This seems to be particularly the case during this time
interval, while studies for other Holocene climate events, such as the 8.2 kyr or the 4.2 kyr events, reveal more homogeneous manifestations on the different scales (Bini
et al., 2019; Isola et al., 2019; Zanchetta et al., 2016).
Several proxies confirm a drying trend in Greece at the end of the Late
Helladic period
(Emmanouilidis
et al., 2018; Finné et al., 2017; Katrantsiotis et al., 2018, 2019;
Warken et al., 2018). While other studies indicate an overall drying trend
for ca. 3000–2000 cal BP, with a short break of one wetter phase or two
separate dry phases, as observed for example at Agios Floros or Thassos Cave, Skala
Marion, NE Greek island
(Norström et al., 2018;
Psomiadis et al., 2018). The juxtaposition of climate records shows that the
end of the Late Helladic period was a period of high climatic instability,
during which the majority of the records for southern Greece indicate a
shift towards generally drier conditions, but with high intra-regional
variability (Finné et
al., 2011). We reason that based on the heterogeneous data, even on a mesoscale, one needs to examine studies critically that draw a direct causal
link between climate fluctuations and cultural decline. In the records
presented here, we mostly see gradual changes in the environmental proxies
for the last 5000 years and suggest that climatic fluctuations in the NE
Peloponnese have not been as rapid or drastic to cause a societal downturn.
However, this may also partly be an effect of how the climatic signal is
stored in the sediment; as these lakes did not produce varves or laminated
sediments, we need to consider the possibility that proxy signals have been
smoothed out over a few years. Nevertheless, as we detect no severe climatic
events in any of our records, we assume that climatic changes may have been
only one factor in a multi-causal relationship influencing cultural
transformations.
Human-induced vegetation clearing also increases erosion and may cause
similar signals in the sediment like an increase in precipitation and
surface run-off. Thus, the shifts observed in Pheneos and Kaisari around
3300–3200 cal BP could likewise be explained by anthropogenic forcing.
Late Helladic activity is attested for the Stymphalia Polje only by some
pottery sherds (Williams, 2013). In the Kaisari Polje, Late
Helladic settlement activity is attested by pottery at the northern fringe
of the plain, and later there is some evidence of human activity in Archaic
and Classical times (Lolos, 2011). For Asea, we know about human
activity due to an archaeological survey (Forsén and
Forsén, 2003), but we do not have any clear evidence from excavations to
distinguish human and climate influences in the record
(Unkel et al., 2014). In the Pheneos Polje,
pottery from the Late Helladic period to Early Iron Age (ca.
3150–2650 BP) was found in archaeological surveys, but without clear
stratigraphical information (Erath, 1999; Howell,
1970; Tausend, 1999). According to Knauss (1990), there
should be a Late Helladic artificial channel crossing the Pheneos Polje in
order to control the Aroanius River and prevent it from flooding the
southern and eastern plain. He hypothesizes extensive Mycenaean
hydro-engineering constructions according to which our coring spot would be
located in a polder area that was subject to controlled flooding and could
otherwise be used for agricultural purposes, as it is used today. However,
such constructions have never been proven by archaeological excavations, and
we do not see any clear evidence for such extensive human activity in our
sediment record. A human influence on the shift in the geochemical proxies
(PC1, Ca/Ti, Fe, C/N) around 3300 cal BP in Pheneos cannot be confirmed, as
archaeological evidence is lacking. As the proxy signal is contemporaneous
to changes in Kaisari and other records from the region, we conclude that it
more likely reflects a climatic drying event around 3200 cal BP. However,
due to the immanent age uncertainties, we are not able to contribute to the
debate on narrowing down when exactly that period started.
Classical–Hellenistic to Medieval period (2429–490 cal BP)
Climate reconstruction for the last 2400 years is challenging in the four
archives, as we see strong human impact and desiccation processes that
additionally affect the geochemical proxies
(Seguin et al., 2019; Unkel et al., 2014).
Overall, increasingly dry conditions seem to prevail in the area. During the
last 2800 years, the sediment structure of PHE1 looks more similar to KES2;
carbonate nodules are absent and high TOC/TN values of 21.6 around 2700 cal BP (150 cm) show that the eastern Pheneos Bay received more terrestrial
influence. We assume that for several centuries the eastern Pheneos Bay was
shaped by relatively dry conditions and was not covered by a considerably
deep lake, but most likely regularly fell dry periodically. This is further
supported by stronger oxidizing conditions and high variation in Ca
content, notably in unit 7, reflecting the alternation between
well-waterlogged and relatively dry environmental conditions. An alternative
explanation for the variability in carbonates could be the agricultural use
of the area during the Classical–Hellenistic and Roman periods
(2429–1650 cal BP), but clear archaeological evidence for that is
lacking. This pattern can be interpreted as a lasting transformation in the
valley ecosystem starting around 3000 cal BP. The Ca peaks hereby suggest
dry phases with strong authigenic carbonate precipitation, but due to age
uncertainties and potential reworking of the material in this period, we
cannot link the peaks to any specific drought periods.
During the Classical–Hellenistic periods around 2200 cal BP, the Asea record
starts to be influenced by pedogenic processes and the occurrence of
carbonate nodules, which may indicate desiccation
(Unkel et al., 2014). At the same time, Lake
Lerna experiences its driest phase (Katrantsiotis et al.,
2019). Stymphalia and Kaisari show more stable conditions during this phase.
For Kaisari, the PC1 proxy indicates slightly wetter conditions between
2200–1700 cal BP, a phase often referred to as part of the Roman Warm
Period (RWP; Luterbacher et al., 2012), which is
in agreement with other proxies from the region
(Boyd,
2015; Finné et al., 2014; Weiberg et al., 2016).
In the eastern Mediterranean, these trends are also reflected in the
modelling approach by Finné et al. (2019) and the
records used therein (Fig. 8k). The Dark Ages Cold Period or Late Antique
Little Ice Age period (ca. 1550–1200 BP; Büntgen et al., 2016;
Helama et al., 2017), prominent in the Stymphalia record around 1200 cal BP
by high variation in water availability
(Seguin et al., 2019), is
hardly visible in Pheneos and Kaisari. Pheneos and Kaisari, however, show a
short phase with moderately wetter conditions from 1050 to 850 cal BP,
which is in agreement with Gialova Lagoon (Fig. 8e; Katrantsiotis et al., 2018) and Closani Cave (Fig. 8j; Warken et al., 2018).
Historical sources report the existence of a large lake in Pheneos in
1895 CE, which was completely dried up by 1901 CE (Knauss,
1990). These strong changes cannot be observed in the sediment sequence, as
the poljes have been completely drained and used for agricultural purposes
since the 1930s CE. Hence, the uppermost 46–50 cm in the Pheneos and
Kaisari cores shows signs of ploughing (Figs. 3, 4, Tables S1, S2), and the
palaeoenvironmental signals for the last ca. 700 years have been destroyed.
The rocky, barren beach and palaeoshorelines (Fig. 2b) on the flanks in the
southern part of the Pheneos basin point towards higher lake level stands at
some point in the recent past. Their exact age is unknown, but in
combination with the historically reported high stand in 1821–1834 CE,
due to the destruction of all katavothre by the retreating Turkish troops
(Knauss, 1990), the absence of rock coatings on the boulders,
and the sparse vegetation around them, we may assume that they were formed
during that short period. Yet, Pausanias, travelling through Greece in the
2nd century CE, already mentioned the existence of “mountains marks up
to which, it is said, the water rose” (Paus. 8.14.1), which suggests that
the existence of shorelines could also be older than expected. A closer
investigation of these features is needed to give more precise information
on their formation.
Research to better understand soil development and erosion processes in the
research area is crucial to understand landscape development with respect to
the increasing anthropogenic land use. Decreasing the age uncertainties in
the chronologies, e.g. by finding datable organic macro-remains or
independent age markers, would facilitate the study of socio-environmental
interactions. Further studies on the transformation of the landscape and
land-use activities would additionally call for pollen analysis, although
pollen preservation is extremely low (Walsh
et al., 2017) or sometimes non-existent as the authors' own (unpublished) test samples
from Stymphalia have shown.
Conclusions
Our comparative analysis of PC1 proxy responses between neighbouring lakes
improved the palaeoclimatic interpretation compared to single-site studies
such as Stymphalia and Asea. Based on the geochemical analysis of the four
study sites, we identified different phases when permanent lake water bodies
existed at all sites (ca. 5000–3600 cal BP), as well as phases when the
lakes episodically or at least seasonally dried out (around 3200 cal BP or
during the last 1000 years), contributing to closing a gap in the
understanding of water availability in the northern and central Peloponnese
during culturally important periods. Our analyses show that Kaisari has
never been a deep permanent lake over the last 5000 years, but regularly
dried out. Due to its small size and the comparatively homogeneous
catchment, it seems not very suitable as a high-resolution
palaeoenvironmental archive. In Pheneos, phases with a more permanent lake
water body were identified for the Mid-Holocene (5100–3600 cal BP),
while the Late Holocene was likewise characterized by regular desiccation.
There is an indication of a shift towards drier conditions around 3000 cal BP in the Pheneos and Kaisari records; however, due to dating uncertainties,
especially in the Pheneos record, there is a high uncertainty in the exact
timing of this dry period. On the other hand, according to the Stymphalia
record, the main drying trend started after 2800 cal BP, culminating at
around 2200 cal BP, which is in accordance with other records from the
Peloponnese (Fig. 8a, e, f). Human impact cannot be excluded as an
alternative explanation, as this falls into the time of the Late Helladic
period with intensifying human activity, but this requires more
archaeological evidence in combination with palaeoenvironmental
investigations. We did not see any dramatic shift in the proxies, which
would hint towards rapid climatic changes with a severe impact on the human
population, but we rather noticed gradual variations. We thus suggest that
climatic changes may have been only one factor in a multi-causal interaction
network that contributed to but did not cause social transformations,
contrasting the hypothesis of a climate-induced Late Bronze Age collapse
(Drake, 2012).
Another plausible hypothesis would be that these basins integrate the
climate signal over the catchment and thus may be less useful to pick up
short-term variation in the way they are recorded in speleothems (Finné
et al., 2014, 2017).
Interpreting proxy records on different spatial scales is promising to
identify different, nested signals, which allows a more holistic
understanding of landscape changes. Our study shows that geoarchives in
mesoscale proximity to each other show similar trends and respond generally
in a similar way to climate variations on the next larger scale. However,
the mountainous landscape and the specific karst morphology of the
Peloponnese cause a significant modulation in the response of the archives
to climate, environmental, and human forcing on a local valley scale. The
uncertainty ranges of the radiocarbon-based chronologies of more than 100 years, both in most geoarchives and in the archaeological record of the
Peloponnese, as well as the difficulties of the assumption of an appropriate
reservoir effect, inherent to the dating of bulk sediment samples, limit the
extent to which conclusions on cause and effect within the interaction
between humans and their environment can be drawn.
Data availability
Primary datasets for the sites Kaisari and Pheneos have been submitted to PANGAEA: 10.1594/PANGAEA.921425 (Seguin et al., 2020a) and 10.1594/PANGAEA.921424 (Seguin et al., 2020b).
The supplement related to this article is available online at: https://doi.org/10.5194/egqsj-69-165-2020-supplement.
Author contributions
JS carried out the lab work, statistical analyses, and interpretation of the data.
JS wrote the manuscript with contributions from all authors, above all from
IU and TK. IU and AH are project investigators and designed the project. PA
supported the sampling and field campaigns of Pheneos and Kaisari and
contributed to the interpretations. TK and AH provided information on
archaeological finds. AS contributed Asea data. All authors have read and
approved the final version of the manuscript.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
We kindly thank the two reviewers for their valuable comments that helped to
improve an earlier version of the manuscript. Furthermore, we thank our
following colleagues and students for their invaluable support in the field:
Dimitris Bassukas, Alexandros Emmanouilidis, Konstantinos Nikolaou, and Jan Weber. Sophia Dazert and McKenzie Elliott are acknowledged for support and assistance during laboratory work. Special thanks are due to Thomas Birndorfer, who was instrumental in creating the map in Fig. 1. The project was carried out with the relevant permits from Greek authorities, the Institute of Geology and Mineral Exploration of Greece (IGME), and the Water Management Body of the Decentralized Prefecture
of Peloponnese, Western Greece and the Ionian Islands.
Financial support
This research has been supported by the Collaborative Research Centre 1266 “Scales of Transformation – Human-environmental interaction in prehistoric and archaic societies” of the German Research foundation (DFG, project number 2901391021).
Review statement
This paper was edited by Elisabeth Dietze and reviewed by two anonymous referees.
ReferencesAitchison, J. and Greenacre, M.: Biplots of compositional data, J. R. Stat.
Soc. C-Appl., 51, 375–392, 10.1111/1467-9876.00275, 2002.Atherden, M. and Hall, J. A.: Holocene pollen diagrams from Greece, Hist.
Biol., 9, 117–130, 10.1080/10292389409380493, 1994.Bini, M., Zanchetta, G., Perşoiu, A., Cartier, R., Català, A., Cacho, I., Dean, J. R., Di Rita, F., Drysdale, R. N., Finnè, M., Isola, I., Jalali, B., Lirer, F., Magri, D., Masi, A., Marks, L., Mercuri, A. M., Peyron, O., Sadori, L., Sicre, M.-A., Welc, F., Zielhofer, C., and Brisset, E.: The 4.2 ka BP Event in the Mediterranean region: an overview, Clim. Past, 15, 555–577, 10.5194/cp-15-555-2019, 2019.
Bintliff, J. L.: The Complete Archaeology of Greece, from Hunter-Gatherers to
the Twentieth Century AD, Blackwell-Wiley, Oxford, UK, New York, USA, 2012.Blaauw, M. and Christeny, J. A.: Flexible paleoclimate age-depth models
using an autoregressive gamma process, Bayesian Anal., 6, 457–474,
10.1214/11-BA618, 2011.
Boyd, M.: Speleothems in Warm Climates?: Holocene records from the Caribbean
and Mediterranean. Dissertation, Stockholm University, Stockholm, Sweden, 2015.Büntgen, U., Myglan, V. S., Ljungqvist, F. C., Mccormick, M., Cosmo, N.
Di, Sigl, M., Jungclaus, J., Wagner, S., Krusic, P. J., Esper, J., Kaplan,
J. O., Vaan, M. A. C. De, Luterbacher, J., Wacker, L., Tegel, W., and
Kirdyanov, A. V.: Cooling and societal change during the Late Antique Little
Ice Age from 536 to around 660 AD, Nat. Geosci., 9, 231–237,
10.1038/NGEO2652, 2016.
Croudace, I. W. and Rothwell, R. G.: Micro-XRF Studies of Sediment Cores,
edited by: Croudace, I. W. and Rothwell, R. G., Springer Netherlands,
Dordrecht, the Netherlands, 2015.Drake, B. L.: The influence of climatic change on the Late Bronze Age
Collapse and the Greek Dark Ages, J. Archaeol. Sci., 39, 1862–1870,
10.1016/j.jas.2012.01.029, 2012.Dypvik, H. and Harris, N. B.: Geochemical facies analysis of fine-grained
siliciclastics using Th/U, Zr/Rb and (Zr+Rb)/Sr ratios, Chem. Geol.,
181, 131–146, 10.1016/S0009-2541(01)00278-9, 2001.Emmanouilidis, A., Katrantsiotis, C., Norström, E., Risberg, J.,
Kylander, M., Sheik, T. A., Iliopoulos, G., and Avramidis, P.: Middle to late
Holocene palaeoenvironmental study of Gialova Lagoon, SW Peloponnese,
Greece, Quatern. Int., 476, 46–62, 10.1016/j.quaint.2018.03.005,
2018.Emmanouilidis, A., Unkel, I., Triantaphyllou, M., and Avramidis, P.:
Late-Holocene coastal depositional environments and climate changes in the
Gulf of Corinth, Greece, Holocene, 30, 77–89,
10.1177/0959683619875793, 2019.
Erath, G.: Archäologische Funde im Becken von Pheneos, in: Pheneos und
Lousoi. Untersuchungen zu Geschichte und Topographie Nordostarkadiens,
edited by: Tausend, K., Frankfurt am Main, Germany, 199–237, 1999.Finné, M., Holmgren, K., Sundqvist, H. S., Weiberg, E., and Lindblom, M.:
Climate in the eastern Mediterranean, and adjacent regions, during the past
6000 years – A review, J. Archaeol. Sci., 38, 3153–3173,
10.1016/j.jas.2011.05.007, 2011.Finné, M., Bar-Matthews, M., Holmgren, K., Sundqvist, H. S.,
Liakopoulos, I., and Zhang, Q.: Speleothem evidence for late Holocene climate
variability and floods in Southern Greece, Quaternary Res.,
81, 213–227, 10.1016/j.yqres.2013.12.009, 2014.Finné, M., Holmgren, K., Shen, C.-C., Hu, H.-M., Boyd, M., and Stocker,
S.: Late Bronze Age climate change and the destruction of the Mycenaean
Palace of Nestor at Pylos, edited by J. P. Hart, PLoS One, 12, e0189447,
10.1371/journal.pone.0189447, 2017.Finné, M., Woodbridge, J., Labuhn, I., and Roberts, C. N.: Holocene
hydro-climatic variability in the Mediterranean: A synthetic multi-proxy
reconstruction, Holocene, 29, 847–863, 10.1177/0959683619826634,
2019.
Forsén, J. and Forsén, B.: The Asea Valley Survey. An Arcadian
Mountain Valley from the Palaeolithic Period until Modern Times, Paul
Åströms Förlag, Stockholm, Sweden, 2003.Gogou, A., Triantaphyllou, M., Xoplaki, E., Izdebski, A., Parinos, C., Dimiza, M., Bouloubassi, I., Luterbacher, J., Kouli, K., Martrat, B., Toreti, A., Fleitmann, D., Rousakis, G., Kaberi, H., Athanasiou, M., and Lykousis, V.: Climate variability and socio-environmental changes in the northern Aegean (NE Mediterranean) during the last 1500 years, Quaternary Sci. Rev., 136, 209–228, 10.1016/j.quascirev.2016.01.009, 2016.Grimm, E. C., Maher, L. J., and Nelson, D. M.: The magnitude of error in
conventional bulk-sediment radiocarbon dates from central North America,
Quaternary Res., 72, 301–308, 10.1016/j.yqres.2009.05.006, 2009.Grootes, P. M., Nadeau, M.-J., and Rieck, A.: 14C-AMS at the Leibniz-Labor:
radiometric dating and isotope research, Nucl. Instrum. Meth. B, 223–224, 55–61, 10.1016/j.nimb.2004.04.015, 2004.Helama, S., Jones, P. D., and Briffa, K. R.: Dark Ages Cold Period: A
literature review and directions for future research, Holocene, 27,
1600–1606, 10.1177/0959683617693898, 2017.Heymann, C., Nelle, O., Dörfler, W., Zagana, H., Nowaczyk, N., Xue, J., and Unkel, I.: Late Glacial to mid-Holocene palaeoclimate development of
southern Greece inferred from the sediment sequence of Lake Stymphalia
(NE-Peloponnese), Quatern. Int., 302, 42–60, 10.1016/j.quaint.2013.02.014,
2013.Howell, R.: A Survey of Eastern Arcadia in Prehistory, Annu. Br. Sch.
Athens, 65, 79–127, 10.1017/S0068245400014702, 1970.
Institute of Geology and Mineral Exploration of Greece (IGME): Geological
Map of Greece, 1 : 50 000 (Sheet Nemea), Athens, Greece, 1970.
Institute of Geology and Mineral Exploration of Greece (IGME): Geological
Map of Greece, 1 : 50 000 (Sheet Kandila), Athens, Greece, 1982.
Institute of Geology and Mineral Exploration of Greece (IGME): Geological
Map of Greece, 1 : 50 000 (Sheet Megalopolis), Athens, Greece, 1992.
Institute of Geology and Mineral Exploration of Greece (IGME): Geological
Map of Greece, 1 : 50 000 (Sheet Kollinai), Athens, Greece, 2002.Isola, I., Zanchetta, G., Drysdale, R. N., Regattieri, E., Bini, M., Bajo, P., Hellstrom, J. C., Baneschi, I., Lionello, P., Woodhead, J., and Greig, A.: The 4.2 ka event in the central Mediterranean: new data from a Corchia speleothem (Apuan Alps, central Italy), Clim. Past, 15, 135–151, 10.5194/cp-15-135-2019, 2019.Izdebski, A., Pickett, J., Roberts, N., and Waliszewski, T.: The
environmental, archaeological and historical evidence for regional climatic
changes and their societal impacts in the Eastern Mediterranean in Late
Antiquity, Quaternary Sci. Rev., 136, 189–208,
10.1016/j.quascirev.2015.07.022, 2016.Jahns, S.: On the Holocene vegetation history of the Argive Plain
(Peloponnese, southern Greece), Veg. Hist. Archaeobot., 2, 187–203,
10.1007/bf00198161, 1993.Kaniewski, D., Van Campo, E., Guiot, J., Le Burel, S., Otto, T., and
Baeteman, C.: Environmental Roots of the Late Bronze Age Crisis, PLoS One,
8, 1–10, 10.1371/journal.pone.0071004, 2013.Kaniewski, D., Marriner, N., Cheddadi, R., Guiot, J., and Van Campo, E.: The 4.2 ka BP event in the Levant, Clim. Past, 14, 1529–1542, 10.5194/cp-14-1529-2018, 2018.Katrantsiotis, C., Norstro m, E., Holmgren, K., Risberg, J., and Skelton, A.:
High-resolution environmental reconstruction in SW Peloponnese, Greece,
covering around the last c. 6000 years: Evidence from Agios Floros fen,
Messenian plain, Holocene, 26, 188–204,
10.1177/0959683615596838, 2015.Katrantsiotis, C., Kylander, M. E., Smittenberg, R. H., Yamoah, K. K. A.,
Hättestrand, M., Avramidis, P., Strandberg, N. A., and Norström, E.:
Eastern Mediterranean hydroclimate reconstruction over the last 3600 years
based on sedimentary n-alkanes, their carbon and hydrogen isotope
composition and XRF data from the Gialova Lagoon, SW Greece, Quaternary Sci.
Rev., 194, 77–93, 10.1016/j.quascirev.2018.07.008, 2018.Katrantsiotis, C., Norström, E., Smittenberg, R. H., and Finne, M.:
Climate changes in the Eastern Mediterranean over the last 5000 years and
their links to the high-latitude atmospheric patterns and Asian monsoons,
Global Planet. Change, 175, 36–51,
10.1016/j.gloplacha.2019.02.001, 2019.Knapp, A. B. and Manning, S. W.: Crisis in Context: The End of the Late Bronze
Age in the Eastern Mediterranean, Am. J. Archaeol. 120, 99–149,
10.3764/aja.120.1.0099, 2016.
Knauss, J.: Der Graben des Herakles im Becken von Pheneos und die
Vertreibung der stymphalischen Vögel, Athenische Mitteilungen, 105, 1–52, 1990.Knitter, D., Hamer, W., Günther, G., Seguin, J., Unkel, I., Kessler, T.,
Weiberg, E., Duttmann, R., and Nakoinz, O.: Land use patterns and climate change – a modeled scenario of Late Bronze Age in Southern Greece, Environ.
Res. Lett., 14, 125003, 10.1088/1748-9326/ab5126, 2019.Kylander, M. E., Ampel, L., Wohlfarth, B., and Veres, D.: High-resolution
X-ray fluorescence core scanning analysis of Les Echets (France) sedimentary
sequence: new insights from chemical proxies, J. Quaternary Sci., 26,
109–117, 10.1002/jqs.1438, 2011.
Lauer, W. and Bendix, J.: Klimatologie. Das geographische Seminar, 2,
Westermann, Braunschweig, Germany, 2006.
Lolos, Y. A.: Land of Sikyon. Archaeology and History of a Greek City-state,
American School of Classical Studies at Athens, Princeton, NJ, USA, 2011.Luterbacher, J., García-Herrera, R., Akcer-On, S., Allan, R.,
Alvarez-Castro, M.-C., Benito, G., Booth, J., Büntgen, U., Cagatay, N.,
Colombaroli, D., Davis, B., Esper, J., Felis, T., Fleitmann, D., Frank, D.,
Gallego, D., Garcia-Bustamante, E., Glaser, R., Gonzalez-Rouco, F. J.,
Goosse, H., Kiefer, T., Macklin, M. G., Manning, S. W., Montagna, P.,
Newman, L., Power, M. J., Rath, V., Ribera, P., Riemann, D., Roberts, N.,
Sicre, M.-A., Silenzi, S., Tinner, W., Tzedakis, P. C., Valero-Garcés,
B., van der Schrier, G., Vannière, B., Vogt, S., Wanner, H., Werner, J.
P., Willett, G., Williams, M. H., Xoplaki, E., Zerefos, C. S., and Zorita,
E.: A Review of 2000 Years of Paleoclimatic Evidence in the Mediterranean,
in: The Climate of the Mediterranean Region, edited by: Lionello, P., Elsevier, 87–185, 10.1016/C2011-0-06210-5, 2012.
Manning, S. W.: Chronology and terminology, in: The Oxford Handbook of the
Bronze Age Aegean (Ca. 3000–1000 BC), edited by: Cline, E. H.,
Oxford University Press, Oxford, UK, 11–28, 2010.Masi, A., Francke, A., Pepe, C., Thienemann, M., Wagner, B., and Sadori, L.: Vegetation history and paleoclimate at Lake Dojran (FYROM/Greece) during the Late Glacial and Holocene, Clim. Past, 14, 351–367, 10.5194/cp-14-351-2018, 2018.Mayewski, P. A., Rohling, E. E., Curt Stager, J., Karlén, W., Maasch, K.
A., Meeker, L. D., Meyerson, E. A., Gasse, F., van Kreveld, S., Holmgren,
K., Lee-Thorp, J., Rosqvist, G., Rack, F., Staubwasser, M., Schneider, R. R., and Steig, E. J.: Holocene Climate Variability, Quaternary Res., 62,
243–255, 10.1016/j.yqres.2004.07.001, 2004.McCormick, M., Büntgen, U., Cane, M. A., Cook, E. R., Harper, K., Huybers, P., Litt, T., Manning, S. W., Mayewski, P. A., More, A. F. M., Nicolussi, K., and Tegel, W.: Climate change during and after the roman Empire: reconstructing the past from scientific and historical evidence. J. Interdiscip. Hist., 43, 169–220, 10.1162/JINH_a_00379, 2012.Meyers, P. A.: Applications of organic geochemistry to paleolimnological
reconstructions: A summary of examples from the Laurentian Great Lakes, Org.
Geochem., 34, 261–289, 10.1016/S0146-6380(02)00168-7, 2003.Meyers, P. A. and Ishiwatari, R.: Lacustrine organic geochemistry-an
overview of indicators of organic matter sources and diagenesis in lake
sediments, Org. Geochem., 20, 867–900, 10.1016/0146-6380(93)90100-P,
1993.
Meyers, P. A. and Lallier-Vergès, E.: Lacustrine sedimentary organic
matter records of Late Quaternary paleoclimates, J. Paleolimnol., 21,
345–372, 1999.Mook, W. G. and van der Plicht, J.: Reporting 14C activities and
concentrations, Radiocarbon, 41, 227–239, 10.1017/S0033822200057106,
1999.
Morfis, A. and Zojer, H.: Karst Hydrogeology of the Central and Eastern
Peloponnesus (Greece), Steir. Beitr. zur Hydrogeol., 37/38, 1–301, 1986.
Munsell, A. H.: Munsell Soil Color Charts, Munsell Color, Grand Rapids, Michigan, USA,
2000.Murray, M. R.: Is laser particle size determination possible for
carbonate-rich lake sediments?, J. Paleolimnol., 27, 173–183,
10.1023/A:1014281412035, 2002.Nanou, E.-A. and Zagana, E.: Groundwater Vulnerability to Pollution Map for
Karst Aquifer Protection (Ziria Karst System, Southern Greece), Geosciences,
8, 125, 10.3390/geosciences8040125, 2018.Neugebauer, I., Brauer, A., Schwab, M. J., Dulski, P., Frank, U.,
Hadzhiivanova, E., Kitagawa, H., Litt, T., Schiebel, V., Taha, N., and
Waldmann, N. D.: Evidences for centennial dry periods at ∼3300 and ∼2800 cal. yr BP from micro-facies analyses of the
Dead Sea sediments, Holocene, 25, 1358–1371,
10.1177/0959683615584208, 2015.Norström, E., Katrantsiotis, C., Finné, M., Risberg, J.,
Smittenberg, R. H., and Bjursäter, S.: Biomarker hydrogen isotope
composition (δD) as proxy for Holocene hydroclimatic change and
seismic activity in SW Peloponnese, Greece, J. Quaternary. Sci., 33, 563–574,
10.1002/jqs.3036, 2018.Olsson, I. U.: Accuracy and precision in sediment chronology, Hydrobiologia,
214, 25–34, 10.1007/BF00050928, 1991.Psomiadis, D., Dotsika, E., Albanakis, K., Ghaleb, B., and Hillaire-Marcel,
C.: Speleothem record of climatic changes in the northern Aegean region
(Greece) from the Bronze Age to the collapse of the Roman Empire,
Palaeogeogr. Palaeocl., 489, 272–283,
10.1016/j.palaeo.2017.10.021, 2018.Ramisch, A., Tjallingii, R., Hartmann, K., Diekmann, B., and Brauer, A.:
Echo of the Younger Dryas in Holocene Lake Sediments on the Tibetan Plateau,
Geophys. Res. Lett., 45, 11154–11163, 10.1029/2018GL080225,
2018.R Core Team: R: A language and environment for statistical computing, R
Foundation for Statistical Computing, Vienna, Austria, available
from: https://www.r-project.org/ (last access: 30 June 2020), 2019.Reimer, P. J., Baillie, M. G. L., Bard, E., Bayliss, A., Beck, J. W.,
Blackwell, P. G., Bronk Ramsey, C., Buck, C. E., Burr, G. S., Edwards, R.
L., Friedrich, M., Grootes, P. M., Guilderson, T. P., Hajdas, I., Heaton, T.
J., Hogg, A. G., Hughen, K. A., Kaiser, K. F., Kromer, B., McCormac, F. G.,
Manning, S. W., Reimer, R. W., Richards, D. A., Southon, J. R., Talamo, S.,
Turney, C. S. M., van der Plicht, J., and Weyhenmeyer, C. E.: IntCal09 and
Marine09 Radiocarbon Age Calibration Curves, 0–50 000 Years cal BP,
Radiocarbon, 51, 1111–1150, 10.1017/S0033822200034202, 2009.Reimer, P. J., Bard, E., Bayliss, A., Beck, J. W., Blackwell, P. G., Bronk
Ramsey, C., Buck, C. E., Cheng, H., Edwards, R. L., Friedrich, M., Grootes,
P. M., Guilderson, T. P., Haflidason, H., Hajdas, I., Hatté, C., Heaton,
T. J., Hoffmann, D. L., Hogg, A. G., Hughen, K. A., Kaiser, K. F., Kromer,
B., Manning, S. W., Niu, M., Reimer, R. W., Richards, D. A., Scott, E. M.,
Southon, J. R., Staff, R. A., Turney, C. S. M., and van der Plicht, J.:
IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0–50 ,000 Years cal BP, Radiocarbon, 55, 1869–1887, 10.2458/azu_js_rc.55.16947, 2013.Richter, T. O., Van Der Gaast, S., Koster, B., Vaars, A., Gieles, R., De
Stigter, H. C., De Haas, H., and Van Weering, T. C. E.: The Avaatech XRF Core
Scanner: Technical description and applications to NE Atlantic sediments,
Geol. Soc. Spec. Publ., 267, 39–50,
10.1144/GSL.SP.2006.267.01.03, 2006.Roberts, N., Jones, M. D., Benkaddour, A., Eastwood, W. J., Filippi, M. L.,
Frogley, M. R., Lamb, H. F., Leng, M. J., Reed, J. M., Stein, M., Stevens,
L., Valero-Garcés, B. L., and Zanchetta, G.: Stable isotope records of
Late Quaternary climate and hydrology from Mediterranean lakes: the ISOMED
synthesis, Quaternary Sci. Rev., 27, 2426–2441,
10.1016/j.quascirev.2008.09.005, 2008.Roberts, N., Eastwood, W. J., Kuzucuoğlu, C., Fiorentino, G., and
Caracuta, V.: Climatic, vegetation and cultural change in the eastern
Mediterranean during the mid-Holocene environmental transition,
Holocene, 21, 147–162, 10.1177/0959683610386819, 2011.Roberts, N., Allcock, S. L., Arnaud, F., Dean, J. R., Eastwood, W. J.,
Jones, M. D., Leng, M. J., Metcalfe, S. E., Malet, E., Woodbridge, J., and
Yiğitbaşıoğlu, H.: A tale of two lakes: a multi-proxy
comparison of Lateglacial and Holocene environmental change in Cappadocia,
Turkey, J. Quaternary Sci., 31, 348–362, 10.1002/jqs.2852, 2016.Rothacker, L., Dosseto, A., Francke, A., Chivas, A. R., Vigier, N.,
Kotarba-Morley, A. M., and Menozzi, D.: Impact of climate change and human
activity on soil landscapes over the past 12 300 years, Sci. Rep., 8,
247, 10.1038/s41598-017-18603-4, 2018.Sadori, L., Jahns, S., and Peyron, O.: Mid-Holocene vegetation history of the
central Mediterranean, Holocene, 21, 117–129,
10.1177/0959683610377530, 2011.Seguin, J., Bintliff, J. L., Grootes, P. M., Bauersachs, T., Dörfler,
W., Heymann, C., Manning, S. W., Müller, S., Nadeau, M.-J., Nelle, O.,
Steier, P., Weber, J., Wild, E.-M., Zagana, E., and Unkel, I.: 2500 years of
anthropogenic and climatic landscape transformation in the Stymphalia polje,
Greece, Quaternary Sci. Rev., 213, 133–154, 10.1016/j.quascirev.2019.04.028,
2019.Seguin, J., Avramidis, P., Haug, A., Kessler, T., Schimmelmann, A., and Unkel, I.: Geochemical and sedimentological record of sediment core KES2 retrieved from the Kaisari Polje (Peloponnese, Greece), PANGAEA,
10.1594/PANGAEA.921425, 2020a.Seguin, J., Avramidis, P., Haug, A., Kessler, T., Schimmelmann, A., and Unkel, I.: Geochemical and sedimentological record of sediment core PHE1 retrieved from the Pheneos Polje (Peloponnese, Greece), PANGAEA,
10.1594/PANGAEA.921424, 2020b.Stein, M., Migowski, C., Bookman, R., and Lazar, B.: Temporal changes in
radiocarbon reservoir age in the dead sea-Lake Lisan system, Radiocarbon,
46, 649–655, 10.1017/S0033822200035700, 2004.
Tausend, K.: Die Siedlungen im Gebiet von Pheneos, in: Pheneos und Lousoi.
Untersuchungen zu Geschichte und Topographie Nordostarkadiens, edited by:
Tausend, K., Frankfurt am Main, Germany, 331–342, 1999.Triantaphyllou, M. V., Gogou, A., Dimiza, M. D., Kostopoulou, S., Parinos,
C., Roussakis, G., Geraga, M., Bouloubassi, I., Fleitmann, D., Zervakis, V.,
Velaoras, D., Diamantopoulou, A., Sampatakaki, A., and Lykousis, V.: Holocene
Climatic Optimum centennial-scale paleoceanography in the NE Aegean
(Mediterranean Sea), Geo-Marine Lett., 36, 51–66,
10.1007/s00367-015-0426-2, 2016.Unkel, I., Schimmelmann, A., Shriner, C., Forsén, J., Heymann, C., and
Brückner, H.: The environmental history of the last 6500 years in the
Asea Valley (Peloponnese, Greece) and its linkage to the local
archaeological record, Z. Geomorphol. Supp., 58,
89–107, 10.1127/0372-8854/2014/S-00160, 2014.Vaezi, A., Ghazban, F., Tavakoli, V., Routh, J., Beni, A. N., Bianchi, T.
S., Curtis, J. H., and Kylin, H.: A Late Pleistocene-Holocene multi-proxy
record of climate variability in the Jazmurian playa, southeastern Iran,
Palaeogeogr. Palaeocl., 514, 754–767,
10.1016/j.palaeo.2018.09.026, 2019.van Geel, B., Heijnis, H., Charman, D. J., Thompson, G., and Engels, S.: Bog
burst in the eastern Netherlands triggered by the 2.8 kyr BP climate event,
Holocene, 24, 1465–1477, 10.1177/0959683614544066, 2014.Walker, M., Head, M. J., Lowe, J., Berkelhammer, M., BjÖrck, S., Cheng,
H., Cwynar, L. C., Fisher, D., Gkinis, V., Long, A., Newnham, R., Rasmussen,
S. O., and Weiss, H.: Subdividing the Holocene Series/Epoch: formalization of
stages/ages and subseries/subepochs, and designation of GSSPs and auxiliary
stratotypes, J. Quaternary Sci., 34, 173–186, 10.1002/jqs.3097, 2019.Walsh, K., Brown, A. G., Gourley, B., and Scaife, R.: Archaeology,
hydrogeology and geomythology in the Stymphalos valley, J. Archaeol. Sci.
Rep., 15, 446–458, 10.1016/j.jasrep.2017.03.058, 2017.Walsh, K., Berger, J.-F., Roberts, N., Vannière, B., Ghilardi, M.,
Brown, A. G., Woodbridge, J., Lespez, L., Estrany, J., Glais, A., Palmisano,
A., Finné, M., Verstraeten, G., Roberts, C. N., Vanniere, B., Ghilardi,
M., Brown, A. G., Woodbridge, J., Lespez, L., Estrany, J., Glais, A.,
Palmisano, A., Finné, M., and Verstraeten, G.: Holocene demographic
fluctuations, climate and erosion in the Mediterranean: A meta
data-analysis, Holocene, 29, 864–885, 10.1177/0959683619826637,
2019.
Wanner, H.: Die angewandte Geländeklimatologie – ein aktuelles
Arbeitsgebiet der physischen Geographie, Erdkunde, 40, 1–14, 1986.Warken, S. F., Fohlmeister, J., Schröder-Ritzrau, A., Constantin, S.,
Spötl, C., Gerdes, A., Esper, J., Frank, N., Arps, J., Terente, M.,
Riechelmann, D. F. C., Mangini, A., and Scholz, D.: Reconstruction of late
Holocene autumn/winter precipitation variability in SW Romania from a
high-resolution speleothem trace element record, Earth Planet. Sc. Lett.,
499, 122–133, 10.1016/j.epsl.2018.07.027, 2018.
Weiberg, E., Unkel, I., Kouli, K., Holmgren, K., Avramidis, P., Bonnier, A.,
Dibble, F., Finné, M., Izdebski, A., Katrantsiotis, C., Stocker, S. R.,
Andwinge, M., Baika, K., Boyd, M., and Heymann, C.: The socio-environmental
history of the Peloponnese during the Holocene: Towards an integrated
understanding of the past, Quaternary Sci. Rev., 136, 40–65,
10.1016/j.quascirev.2015.10.042, 2016.Weiberg, E., Bevan, A., Kouli, K., Katsianis, M., Woodbridge, J., Bonnier,
A., Engel, M., Finné, M., Fyfe, R., Maniatis, Y., Palmisano, A.,
Panajiotidis, S., Roberts, C. N., and Shennan, S.: Long-term trends of land
use and demography in Greece: A comparative study, Holocene, 29,
742–760, 10.1177/0959683619826641, 2019.Weltje, G. J. and Tjallingii, R.: Calibration of XRF core scanners for
quantitative geochemical logging of sediment cores: Theory and application,
Earth Planet. Sc. Lett., 274, 423–438,
10.1016/j.epsl.2008.07.054, 2008.Weltje, G. J., Bloemsma, M. R., Tjallingii, R., Heslop, D., Röhl, U., and
Croudace, I. W.: Prediction of Geochemical Composition from XRF Core Scanner
Data: A New Multivariate Approach Including Automatic Selection of
Calibration Samples and Quantification of Uncertainties, edited by:
Croudace, I. W. and Rothwell, R. G., Springer Dordrecht, the Netherlands, 507–534, 10.1007/978-94-017-9849-5_21, 2015.Williams, E. H.: Stymphalos: A Planned City of Ancient Arcadia, Echos du
Monde Class. = Class. Views, 27, 194–205, 1983.
Williams, H.: Archaeological Investigations at Ancient Stymphalos,
1982–2008, in: The Corinthia and the Northeast Peloponnese. Topography and
History from Prehistoric Times until the End of Antiquity, edited by:
Kissas, K. and Niemeier, W. D., Munich, Germany, 425–431, 2013.
Williams, H. and Gourley, B.: The fortifications of Stymphalos, Mouseion: Journal of the Classical Association of Canada, 5, 213–225, 2005.Xu, H., Liu, B., and Wu, F.: Spatial and temporal variations of Rb/Sr ratios
of the bulk surface sediments in Lake Qinghai, Geochem. Trans., 11, 3,
10.1186/1467-4866-11-3, 2010.Zanchetta, G., Sulpizio, R., Roberts, N., Cioni, R., Eastwood, W. J., Siani,
G., Caron, B., Paterne, M., and Santacroce, R.: Tephrostratigraphy,
chronology and climatic events of the Mediterranean basin during the
Holocene: An overview, Holocene, 21, 33–52,
10.1177/0959683610377531, 2011.
Zanchetta, G., Regattieri, E., Isola, I., Drysdale, R. N., Bini, M.,
Baneschi, I., and Hellstrom, J. C.: The so-called “4.2 event” in the
central Mediterranean and its climatic teleconnections, Alp. Mediterr.
Quat., 29, 5–17, 2016.