Diatom records and tephra mineralogy in pingo deposits of Seward Peninsula, Alaska

Accepted Manuscript Diatom records and tephra mineralogy in pingo deposits of Seward Peninsula, Alaska

Olga Palagushkina, Sebastian Wetterich, Boris K. Biskaborn, Larisa Nazarova, Lutz Schirrmeister, Josefine Lenz, Georg Schwamborn, Guido Grosse PII: DOI: Reference:

S0031-0182(16)30833-1 doi: 10.1016/j.palaeo.2017.04.006 PALAEO 8258

To appear in:

Palaeogeography, Palaeoclimatology, Palaeoecology

Received date: Revised date: Accepted date:

9 December 2016 30 March 2017 4 April 2017

Please cite this article as: Olga Palagushkina, Sebastian Wetterich, Boris K. Biskaborn, Larisa Nazarova, Lutz Schirrmeister, Josefine Lenz, Georg Schwamborn, Guido Grosse , Diatom records and tephra mineralogy in pingo deposits of Seward Peninsula, Alaska. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Palaeo(2017), doi: 10.1016/j.palaeo.2017.04.006

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ACCEPTED MANUSCRIPT Diatom records and tephra mineralogy in pingo deposits of Seward Peninsula, Alaska Olga Palagushkina (1), Sebastian Wetterich (2), Boris K. Biskaborn (2)*, Larisa Nazarova (1,2,3), Lutz Schirrmeister (2), Josefine Lenz (2,3), Georg Schwamborn (2), Guido Grosse (2, 3)

Kazan Federal University, Institute of Management, Economics and Finance, Kazan,

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(1)

Russia (2)

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([email protected])

Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Department of

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Periglacial Research, Potsdam, Germany

([email protected], [email protected], [email protected], (3)

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[email protected])

University of Potsdam, Institute of Earth and Environmental Science, Potsdam, Germany

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([email protected])

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* Corresponding author: [email protected]

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Keywords  Microalgae assemblages

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 Palaeoenvironments  Thermokarst

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 Late Quaternary  Permafrost

Highlights  We present palaeolake archive from remote pingo deposites in western Alaska  Diatoms reveal climate conditions enabling thermokarst 42,000 years ago  Climate and volcanic tephra events had significant impact on the palaeoecology  High precipitation and seasonal temperature gradients enabled glacial thermokarst

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ACCEPTED MANUSCRIPT Abstract Vast areas of the terrestrial Subarctic and Arctic are underlain by permafrost. Landscape evolution is therefore largely controlled by climate-driven periglacial processes. The response of the frozen ground to late Quaternary warm and cold stages is preserved in permafrost sequences, and deducible by multi-proxy palaeoenvironmental approaches. Here,

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we analyse radiocarbon-dated mid-Wisconsin Interstadial and Holocene lacustrine deposits preserved in the Kit-1 pingo permafrost sequence combined with water and surface sediment

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samples from nine modern water bodies on Seward Peninsula (NW Alaska) to reconstruct thermokarst dynamics and determine major abiotic factors that controlled the aquatic

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ecosystem variability. Our methods comprise taxonomical diatom analyses as well as Detrended Correspondence Analysis (DCA) and Redundancy Analysis (RDA). Our results

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show, that the fossil diatom record reflects thermokarst lake succession since about 42 14C kyr BP. Different thermokarst lake stages during the mid-Wisconsin Interstadial, the late Wisconsin and the early Holocene are mirrored by changes in diatom abundance, diversity,

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and ecology. We interpret the taxonomical changes in the fossil diatom assemblages in combination with both modern diatom data from surrounding ponds and existing

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micropalaeontological, sedimentological and mineralogical data from the pingo sequence. A

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diatom-based quantitative reconstruction of lake water рН indicates changing lake environments during mid-Wisconsin to early Holocene stages. Mineralogical analyses indicate presence of tephra fallout and its impact on fossil diatom communities. Our comparison of modern and fossil diatom communities shows the highest floristic similarity of

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modern polygon ponds to the corresponding initial (shallow water) development stages of thermokarst lakes. We conclude, that mid-Wisconsin thermokarst processes in the study area

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could establish during relatively warm interstadial climate conditions accompanied by increased precipitation due to approaching coasts, whilst still high continentality and hence high seasonal temperature gradients led to warm summers in the central part of Beringia.

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Introduction 2

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Intense landscape dynamics in Arctic and Subarctic regions underlain by permafrost, which are presently observed and to a large extent triggered by climate, will most likely accelerate in the future. The current Arctic warming promotes intensified permafrost thaw, which has similar warm periods in the Quaternary past. Ongoing permafrost research on palaeoclimate and permafrost responses focuses on Arctic lowlands in Beringia; the landmass that connected the Eurasian and North American continents during the Wisconsin glacial

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period, enabling floral, faunal and human migration (Hopkins 1959). Permafrost deposits, which aggraded during cold stages in non-glaciated region of Beringia, as well as permafrost

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degradation facies from warm stages, such as lacustrine thermokarst deposits, provide insights

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into past environmental conditions and periglacial landscape dynamics. The interplay between late Quaternary climate variations and Beringian periglacial landscapes is archived in fossil,

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sedimentary and ground-ice properties of permafrost deposits.

The Seward Peninsula (NW Alaska) is located close to the central part of the former Bering Land Bridge (Fig. 1), and here permafrost research focused on modern (Jones et al.,

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2011) and Holocene (Hopkins and Kidd, 1988; Jones MC et al., 2012; Farquharson et al.,, 2016; Lenz et al., 2016b, Bouchard et al., 2017) thermokarst lake dynamics while older

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records of permafrost degradation and lake development during e.g. interstadial intervals of the last Glacial have rarely been studied (Lenz et al., 2016a).

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Alaskan areas underlain by permafrost host a wide range of surface water body types (Smith et al., 2007; Grosse et al., 2013; Muster et al., 2013). Small ephemeral polygonal ponds represent important freshwater resources in Arctic periglacial lowlands, which provide

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essential habitats for the fauna and flora (Frolova et al., 2013, 2014). Small pond types developed to larger thermokarst lakes when ice-rich permafrost began to thaw during

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lateglacial warming about 13 to 10 thousand years before present (kyr BP) (e.g. Kaufmann et al., 2004). Sediments deposited in both, polygonal ponds and thermokarst lakes represent archives of past environmental conditions, recorded by ecological indicators, such as microalgae (diatoms) and geochemical proxies, such as the mineralogical sediment composition (Palagushkina et al., 2012, 2014; Meyer et al., 2015; Fritz et al., 2016). In Arctic areas affected by climate warming, permafrost thaw leads to a rapid and dynamic change of the periglacial landscape and thermokarst lakes often experience drainage (Jones et al., 2011). When a lake is drained completely, the unfrozen zone (talik) below the lake and the exposed lacustrine and water-rich sediments gradually refreeze, new ground ice forms, and new vegetation and soils develop on the exposed surfaces (Jones BM et al., 2012; Lenz et al., 3

ACCEPTED MANUSCRIPT 2016a, 2016b). Under some refreezing conditions, hydrostatic pingos can form and heave the frozen lacustrine sediments and post-drainage soils several meters above the surrounding terrain (Mackay 1978). The usually conically-shaped pingos may reach diameters of up to 300 meters and heights of up to 60 meters (French, 2007). Subsequent erosion, e.g. at the coast, exposes the strata preserved in the pingo and enables sampling of the former lacustrine and terrestrial sediments without the need for coring of the lake basin. Hence pingo deposits provide access to lacustrine thermokarst sequences, which can contain valuable information

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on late-Quaternary palaeoenvironmental history (Hyvärinen and Ritchie, 1975). Additionally, pingo growth and decay rates, age, and distribution on the landscape were used to reconstruct

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past periglacial landscape conditions (Flemal, 1976; Grosse et al., 2007).

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Freshwater diatoms are well-established bioindicators of modern ecological conditions and are used to reconstruct past environmental dynamics, especially in northern boreal regions

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(Solovieva et al., 2008, 2015), where other aquatic bioindicators are less abundant (Palagushkina et al., 2012; Pestryakova et al., 2012).

Here we combine new results from diatom and mineral analyses with published

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cryolithological, geochronological, and palaeontological data from the Kit-1 pingo sequence exposed at the north coast of the Seward Peninsula, Alaska (Wetterich et al., 2012). Our

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objective is to deduce past thermokarst lake conditions and Beringian landscape dynamics from the mid-Wisconsin (> 42.000 years ago) to early Holocene (< 8000 years ago) times by

Study site

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2

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ecological and statistical analyses of past diatom assemblages and tephra mineralogy.

The study area on the northern Seward Peninsula (Fig. 1) in Alaska is underlain by continuous permafrost exceeding 90 m thickness (Jorgenson et al., 2008) and is located west and east of the Kitluk River mouth on the Chukchi Sea coast (Fig. 2). Here, the modern climate is characterised by long cold winters and short cool summers with low precipitation (mean annual air temperature –5.7 °C, mean January air temperature –19.2 °C, mean July air temperature 12.6 °C, mean annual precipitation 254 mm at Kotzebue Climate Station 19712000; Alaska Climate Research Center, 2008). The growing season for tundra and shrub vegetation at the coast spans from May to September. The periglacial landscape in the study area is shaped by Yedoma uplands, thermokarst basins containing lakes and pingos, thermo4

ACCEPTED MANUSCRIPT erosion valleys, and polygonal tundra. Small (meters to decameters in diameter) and shallow polygonal ponds (not exceeding 2 m water depth) located at the bottom of thermokarst basins are classified as intrapolygonal or interpolygonal ponds, or larger coalesced thaw ponds (Table 1). The vegetation in and around these ponds mainly consists of Carex aquatilis, Eriophorum angustifolium, and Sphagnum. The bottom substrate comprises muddy sediments with varying amounts of sand and organic material. The sedimentary record of the pingo exposure near the Kitluk River mouth (Kit-1)

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consists of four units, which were classified according to their sedimentological and cryolithological properties and contain palaeoenvironmental records between 42,500 ± 660

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and 8,070 ± 20 14C kyr BP (Fig. 3; Wetterich et al., 2012). The northern Seward Peninsula is

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also known to have been coated by tephra fallout from nearby phreatomagmatic eruptions associated to the formation of several maar lakes during the Pleistocene, e.g. at the Last Glacial Maximum (ca. 18 14C

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et al., 1996; Goetcheus and Birks, 2001; Lenz et

al., 2016b) and possibly around 45-40 kyr BP (Lenz et al., 2016a). The input of volcanic material may have affected the hydrochemical and lake sediment properties at that time. Such

3.1

Materials and methods

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effects may have influenced the aquatic ecosystem and hence the diatom community.

Fieldwork

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We obtained and analysed water and bottom sediment samples from nine modern water bodies (sample codes: EB-01 to EB-09, Table 1) in the surroundings of the studied Kit-

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1 pingo sequence in July 2008 (Fig. 2). We analysed various chemical and environmental parameters in each pond of which 21 were available for all sites in the present investigation and were included in statistical analyses (Table 1, ESM 1). The surface of the upper 10 m of the approximately 16-m-high Kit-1 exposure was removed to describe and sample clean sediment and ground-ice structures in frozen state. Four sediment units (A to D) were defined by Wetterich et al., (2012). Their main characteristics are summarised in the lithological profile in Figure 3.

3.2

Geochronology 5

ACCEPTED MANUSCRIPT The accelerator mass spectrometry (AMS) facilities at the Keck Carbon Cycle AMS Facili

Univ si

of Califo nia, I vin , USA and h

oznań Radioca bon Labo a o

Adam Mic i wicz Univ si , oznań, oland ca i d ou

adiocarbon dating of selected

fossil plant remains. Santos et al., (2007) and Goslar et al., (2004), respectively, provide details on the applied laboratory procedures. Wetterich et al., (2012) provide a comprehensive discussion of the dating results, explaining that single dates are rejected from the chronological model (Fig. 3) because the location of the dated organic material was reversed

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during thermokarst formation and pingo growth. Sample Kit-1-18 of unit B dated to 14.3 14C kyr BP is considered as reworked material attributed to an ice-wedge cast penetrating into

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mid-Wisconsin sediments. Further age reversals of unit B are understood as redeposited 14

C kyr

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organic material (samples Kit-1-12, Kit-1-16, Kit-1-19 dated to >45, 48 ± 3 and >50

BP, respectively) that entered the expanding thermokarst lake due to shore erosion and thaw

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slumping of older deposits in which the lake developed. Outlier samples that have been reworked by thermokarst processes are indicated in brackets in Figure 3. In small young lakes, reworking of permafrost sediments results in significant input

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older sediment organic matter to the near-shore lake bottom and,repeated age reversals in thermokarst lake deposits are commonly reported in palaeolimnological studies in permafrost

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regions (e.g. Hopkins and Kidd, 1988; Murton, 1996, Biskaborn et al., 2013).

Chemical analyses

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We conducted hydrochemical analyses after passing the water through a celluloseacetate filter with a pore size of 0.45 μm. Sampl s fo cation analysis were then acidified with

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nitric acid (HNO3), while samples for anion analysis and residue samples were kept untreated and stored in a cool place. The element (cation) content of the water was determined by inductively coupled plasma optical emission spectrometry (ICP-OES, Perkin-Elmer Optima 3000 XL), while the anion concentration was measured by ion chromatography (IC, Dionex DX-320) in the laboratories of the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) in Germany. Bicarbonate concentrations were calculated from the alkalinity measurements in the field and additionally checked the concentrations by titration with 0.01 M hydrochloric acid (HCl) using an automatic titrator (Metrohm 794 Basic Titrino). We determined electrical conductivity (EC) and pH values in the field using a WTW 340i device equipped with appropriate sensors (EC: Tetracon 325 and pH: SenTix 41). 6

ACCEPTED MANUSCRIPT To track changes in the mineral composition and influx of volcanic particles, we analysed 27 samples of the pingo record (Kit-1-1 to Kit-1-27) using X-ray diffraction (XRD) on non-textured pulverised bulk samples at AWI. Standard XRD measurements were performed with a Philips PW1820 goniometer applying Cobalt- o assium alpha CoKα radiation (40 kV, 40 mA) as outlined in Petschick et al. (1996). In the resulting XRD pattern, h ho izon al scal is conv n ionall p s n d as h °2θ an l , which ma s h coh

nc

between the wavelength and the angle of the incident beam and the lattice spacing in the

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crystal structures (Petschick et al., 1996). Mineral peaks with their Ångstrom values (10Å = 1nm) corresponding to the lattice spacing are placed along the horizontal scale. The vertical

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scale is the intensity of diffracted radiation where counts of peak areas can be calculated using

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XRD processing software MacDiff 4.0.7 (freeware developed by R. Petschick in 1999). Individual bulk mineral contents were expressed as percentages of bulk sediment XRD

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counts. The main clay minerals illite, kaolinite, and chlorite form their own group in this respect. Our assessment of the main mineral components included ratios of the areas below their respective peaks. The following minerals (and peaks) were used: quartz (4.26 Å),

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feldspars, i.e. plagioclase (3.18 Å) and orthoclase (3.24 Å), pyroxenes (2.92-3.0 Å), and calcite (3.04 Å). In addition, the clay minerals illite (10 Å) (001, basal reflections), and

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kaolinite and chlorite (7.1 Å) were evaluated (Vogt et al., 2001). Contents of each clay mineral group in the sample are expressed as relative weight percentage using the weighing

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factors introduced by Biscaye (1965). The XRD method is semi-quantitative with accuracy

Diatom analyses

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between 5 and 10% (Gingele et al., 2001).

We collected a total of nine surface sediment samples from modern ponds and 27 samples from the Kit-1 pingo profile and processed them for diatom analysis, following the standard technique for diatom slide preparation in a water bath described by Battarbee et al., (2001), using 30% hydrogen peroxide (H2O2), 37% HCl, 1% ammonium (NH4+) for removal of carbonates and organics, and Naphrax diatom mounting medium. Diatom frustules (valves) were examined at 1000x magnification using an Axioplan Zeiss light microscope equipped with an oil-immersion objective. We identified and counted up to 500 valves per sample in modern pond sediments and up to 300 valves in pingo sediments. Diatom data were converted into percent relative abundances. We defined taxa with abundances of ≥10% and ≥5% as dominants and subdominants, respectively. Diatoms were identified at the lowest possible 7

ACCEPTED MANUSCRIPT taxonomic level following different diatom floras, mainly Krammer and Lange-Bertalot (1986-1991), and agreed with modern taxonomy as given in the AlgaeBase database (Guiry and Guiry 2015; ESM 2). The coefficient of floristic similarity of taxa composition was calculated according to Sorensen and Czekanovsky (Magurran, 1992), and expressed in percentages. Biogeographical and ecological characteristics of the taxa with respect to preferences of habitat and pH, water salinity as well as changes in the ice cover duration and the

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spring/autumn turbulence period were described following Van Dam (1994), Fallu et al. (2000) and Barinova et al. (2006) and other sources from case studies.

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We used Detrended Correspondence Analysis (DCA, detrended by segments, rare taxa

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downweighted) to explore the main pattern of taxonomic variation in the diatom data and to determine the lengths of the compositional gradients, from which we decided whether

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unimodal or linear statistical techniques would be the most appropriate for the data analysis (Birks 1995; Nazarova et al., 2015). The gradient length of taxa scores for DCA axis 1 was less than 2 standard deviation units, indicating that numerical methods based on the linear

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response model are more appropriate to assess the variation structure of the diatom assemblages (ter Braak 1994; ter Braak 1995). We used variance inflation factors (VIFs) to

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identify intercorrelated variables. Environmental variables with a VIF > 20 were eliminated, beginning with the variable with the largest inflation factor, until all remaining variables had aa and Šmilau

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values < 20

2002a). By this criterion, we deleted EC, Al3+, Fe3+,

Mn2+, Na+, Sr2+, Cl-, and HCO3- from further analysis. We assessed the relationships between diatom distribution and remaining

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environmental variables using a set of Redundancy Analyses (RDAs) with each environmental variable as the sole constraining variable, and calculated the percentage of the

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variance explained by each variable. The statistical significance of each variable was tested by a Monte Carlo permutation test with 999 unrestricted permutations (ter Braak 1990). In order to further explore the relationship between modern analogues and the pingo fossil sequence we combined and analysed the data usin a ‘ im - ac ’ RDA with the pingo samples plotted passively (Nazarova et al., 2013a). Ordination was performed by vegan package (Oksanen et al., 2013) in the R environment (Venables et al., 2015). RDA uses scaled species data (scaled to equal variance of species abundance). We completed the reconstruction of pH using the combined diatom based pH inference model (WA-PLS, 2 component, R2 jack = 0.80, RMSEPjack = 0.42), which comprises 627 samples and 652 taxa from lakes in the pH range 4.32-8.4. (EDDI, European 8

ACCEPTED MANUSCRIPT Diatom Database, 2001). The reconstruction was performed online using untransformed data with boot-strapped cross-validation. To verify the quantitative pH reconstruction, we additionally characterized the hydrochemical regime of the studied waters by qualitative interpretation of the diatom dataset following Alekin (1970) and Kitaev (2007) among other case studies. To assess the reliability of the diatom based pH reconstruction we performed several tests. Following the modern analogue technique described in Birks et al. (1990), and Juggins

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(2001) we performed a MAT analysis using online EDDI software as a measure of the flo is ic ma ch b w n h fossil sampl and i ’s clos s analo s in h

ainin s . Sampl s

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with dissimilarity larger than the 5% threshold in the modern data are frequently considered

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as having no good analogues in the modern calibration dataset (Birks et al., 1990; Birks, 1995, 1998; Velle et al., 2005). But as precise interpretation of analog measure is difficult Juggins

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(2001) suggests that any fossil sample that lies beyond a value of 100-150 has no close analogs in the training set. This estimate is based on the distribution of dissimilarities within the training set (Jones and Juggins, 1995). Output from the verification analysis can also help

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to identify no-analog samples. Percentage abundances of the taxa that are absent or rare in the modern calibration data set were calculated (Engels et al., 2010; Nazarova et al., 2013b;

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Solovieva et al., 2015) and less reliability was placed on pingo samples in which more than 5% taxa were not represented in the modern calibration data or more than 5% of taxa were

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rare in modern calibration dataset (i.e. Hill's N2 less than 5) (Heiri and Lotter, 2001; Heiri et al., 2003; Self et al., 2015). Goodness-of-fit statistics derived from a canonical correspondence analysis (CCA) of the modern calibration data and down-core passive

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samples with pH as the sole constraining variable was used to assess the fit of the analysed down-core assemblages to pH (Birks et al., 1990; Birks, 1995, 1998; Heiri and Lotter, 2001;

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Nazarova et al., 2017). This method allows to assess how unusual are the fossil assemblages in respect to the composition of the training set samples along the gradient of interest. Fossil samples with a residual distance to the first CCA axis larger than the 90th and 95th percentile of h

sidual dis anc s of all h mod n sampl s w

and a ‘v

poo fi ’ wi h pH,

sp c iv l

id n ifi d as sampl s wi h a ‘poo fi ’

Birks et al., 1990). The significance of the

reconstructions was also evaluated using the palaeoSig package (Telford, 2011) in R (R Development Core Team, 2013) with 999 random reconstructions. Following Telford and Birks (2011), a reconstruction is considered statistically significant if it explains more of the variance in the fossil data than 95% of reconstructions that are derived from random environmental variables. 9

ACCEPTED MANUSCRIPT DCA, RDA and CCA w

p fo m d usin CANOCO 4.5

aa and Šmilau

2002a,

b). Stratigraphic diagrams were produced using C2 version 1.5 (Juggins, 2007).

4 4.1

Results Hydrochemistry of modern diatom host waters The investigated modern periglacial waters are low in phosphorus and represent ultra-

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oligotrophic ecosystems with slightly acidic to neutral pH. Their ECs range mostly from 130 to 260 µS сm-1, pointing to low mineralisation (Table 1). The ion composition is dominated

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by Na+ or Na+ + Mg2+ and Cl-. One exception is pond ЕВ-06 with an EC of 494 µS сm-1, a

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moderate mineralisation, dominated by Mg2+ and HCO32-, and neutral to slightly alkaline рН. The silica content ranges from values below 1 mg l-1 (ЕВ-01 to EB-05) to values slightly above 1 mg l-1 (ЕВ-06, EB-07, ЕВ-08, EB-09) reaching maximum concentrations of 2.85 mg

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l-1 in sample EB-09 (ESM 1).

Modern and fossil diatom taxonomy

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We found a total of 192 diatom taxa in both the pingo sequence and in modern pond

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sediments (ESM 2). In 22 pingo samples we recorded 156 diatom taxa, while in assemblages of nine modern ponds we identified 104 taxa. The floristic similarity between the modern and the fossil diatom assemblages is 53.8%. Our comparison of modern and fossil diatom

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communities using RDA time tracking indicates that fossil assemblages of unit B (late midWisconsin) and unit D (early Holocene) are most closely related to the modern record

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(coefficients of taxonomic similarity reach 26%; Fig. 5B).

Diatom assemblages from modern ponds are composed of predominantly cosmopolitan, benthic, alkaliphilic taxa, rather indifferent to water salinity, temperature, and velocity. However, we also found acidophilic, halophobic and arctic-alpine taxa in the modern data set. Most dominant diatom taxa belong to fragilarioid and achnanthoid genera and Tabellaria. Diatom species with occurrences of ≥5 % in at least one sample are shown in Figure 4. Eunotia arcus, E. naegelii, Nitzschia frustulum, and Pinnularia streptoraphe were found only in modern deposits but not in the fossil pingo record (ESM 2). A set of RDAs constrained to individual environmental variables and Monte Carlo permutation tests reveal that three variables explain significant proportions (p<0.05) of 10

ACCEPTED MANUSCRIPT variance in the data set: sulphate (SO42-) explains 17.3%, pH explains 16.9%, and Si4+ explains 13.2%. Eigenvalues of the RDA axes 1 and 2 of these three variables equal 0.207 and 0.127, explaining 51.2% and 31.6% of variance in the data, respectively (Fig. 5A). Juggins (2013) suggests that a ratio of axes 1 and 2 eigenvalues (λ1/λ2) less than 1 indicates that potential factors affecting assemblages besides the explored variables have not been assessed. In our case, λ1/λ2 is 1.62 λ1/λ2 = 0.207/0.127 , which indica s ha h mos impo an explanatory variables are most likely included. Statistical analyses have shown that 20 diatom

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species from modern ponds EB-01, EB-06, and EB-08 are strongly associated with high pH and high concentrations of Si4+ and SO42-, and another 22 species, i.e. Tabellaria fenestrata,

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E. bilunaris, E. flexuosa, E. naegelii, E. pectinalis, Fragilariforma virescens are commonly

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present under conditions of lower pH and SO42- as found in samples EB-02 to EB-05, EB-07, and EB-09 (Fig. 5A).

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The most abundant diatom taxa in the fossil and the modern samples are Staurosirella pinnata (Kit-1-1, Kit-1-2 and ЕВ-01, EB-02), Fragilariforma virescens (Kit-1-11, Kit-1-12 and ЕВ-02 to EB-04, EB-07), Fragilaria capucina (Kit-1-9 and ЕВ-01, EB-04, EB-06, EB-

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09), Achnanthidium minutissimum (Kit-1-1, Kit-1-2 and ЕВ-01, EB-04), Tabellaria fenestratа (Kit-1-11 and EB-12, ЕВ-05, EB-08, EB-09), and T. flocculosa (Kit-1-11, Kit-1-12 and ЕВ-

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03 to EB-05) (Fig. 5B). Generally, planktonic and benthic-planktonic taxa are more abundant in the fossil pingo record than in the modern pond assemblages (Table 2).

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The fossil diatoms of the early Holocene unit D reflect neutral to slightly alkaline ecological conditions with higher mineralisation while the late mid-Wisconsin diatoms of unit B point to conditions from neutral-alkaline with high mineralisation to slightly acidic with

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lower mineralisation.

Mineralogy

The mineral composition in the Kitluk pingo profile shows overall little variation across

the

sediment

layers

(Fig.

6).

For

example,

the

quartz-over-feldspar

(plagioclase+orthoclase) ratio ranges around 0.8 with minimum and maximum values differing by ± 0.3. There is minor variation in the orthoclase-over-plagioclase ratio around a mean of 0.2. One peak at 11.7-11.8 m above sea level (a.s.l.) is conspicuous, with values up to 0.4. Very little change is visible in the occurrence of calcite and pyroxenes across the layers with ratios smaller than 0.2 (pyroxenes-to-all, calcite-to-all). The clay mineral composition shows a fairly constant dominance of illite over kaolinite+chlorite. For comparison, ratios of 11

ACCEPTED MANUSCRIPT the main mineral phases in other sediment records with interpreted sediment change can have sharp increases up to 8 (Vogt, 2009).

4.4

Stages of thermokarst lake development inferred by diatoms

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4.4.1 pH reconstruction The statistical application of the combined European Diatom Database (European Diatom Database, 2001) dataset resulted in fluctuations of reconstructed pH estimates (Fig. 7)

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from lowest values between 6.1 and 6.3 in the middle part of the mid-Wisconsin thermokarst

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lake sediment section (unit B, samples Kit-1-12 and Kit 1-11, heights 12.0 to 12.5 m a.s.l.) and to highest values between 7.7 and 7.9 in the upper part of the late Wisconsin thermokarst lake sediment section (unit B, samples Kit-1-10 to Kit-1-7, heights 12.9 to 13.7 m a.s.l.),

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while intermediate pH values were reconstructed for the latest Wisconsin and the early Holocene sections.

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A reconstructed environmental value is likely to be more reliable if the fossil sample has a close modern analogue in the modern training-set (ter Braak, 1995; Juggins and Birks, 2012). MAT showed that only 2 samples (Kit-1-7, 1-9) have no close analog in the training

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set (Fig. 8). Mos of h dia om axa hav N2≥5 in h

ainin s , suppo in

h quan i a iv

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diatom-based pH reconstruction (Brooks and Birks, 2001). However, five abundant taxa have N2<5 in the training set: Diploneis elliptica (max 5.6% in Kit-1-10), Epithemia adnate (max 7.3% in Kit-1-4), Hantzschia amphioxys (max 7,9% in Kit-1-9), Pinnularia borealis

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var.rectangularis (15.6% Kit-1-1), Pinnularia brevicostata (max 8.8% Kit-1-7), Only in the sample Kit-1-4 more than 5% of the taxa are absent in the training set and rare taxa reach

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more than 5% in the samples Kit 1-4, 1-5, 1-6, and 1-9. Goodness-of-fit statistics revealed, that only three samples have a `good fit` (Kit-1-1, 1-3, 1-4), and the remaining samples have a `very poor fit` with pH. 26 out of 156 identified taxa are absent from the modern data set. However, these rare taxa mainly form minor components of the assemblage with single or at less than 2% occurrences. Only Pinnularia borealis var. rectangularis and Sellaphora stroemii were present at higher abundances but solely in the uppermost pingo sediment layer of Kit-1. Analysis using the Telford and Birks (2011) method indicated that the pH reconstruction was not statistically significant. However, as it was shown by Luoto et al. (2014) this may result from the size of the calibration dataset (627 lakes and 652 taxa). The 12

ACCEPTED MANUSCRIPT bigger size of the training set increases the variability in the environmental variable of interest, so that reconstructions fail the Telford–Birks test, although these reconstructions strongly and significantly correlate to reconstructions based on a smaller training set which passed through the Telford–Birks test (Luoto et al., 2014). There is li l

mpi ical vid nc of a

la ionship b w n ‘fi ’ b w n fossil and

training-set samples and increased error or unreliability, provided fossil taxa are wellrepresented in the training-set (Juggins and Birks, 2012). Experiments with simulated data

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suggest that methods, with the exception of MAT, perform well under mild non-analogue situations (ter Braak et al., 1993, ter Braak, 1995). Reconstructions for samples with mild

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non-analogue situations should probably be treated with caution, although as long as the

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majority of taxa in the fossil samples are present in the training set there are no apriori

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reasons for suspecting the reconstructions to be in error (Juggins, 2001).

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4.4.2 Early mid-Wisconsin taberite (unit A)

The lowermost sediment unit A (ca. 42.5 to 42.3 14C kyr BP, samples Kit-1-27 to Kit1-21) represents the talik of the former thermokarst lake below the lacustrine sediments.

D

Hence unit A represents an unfrozen zone within the permafrost ground below the lake that

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refroze after drainage of the lake. Therefore, diatoms are practically lacking (Fig. 7). Only the uppermost samples (Kit-1-22 and Kit-1-21) of unit A at the transition to the lacustrine unit B mirror an initial development of diatom flora, comprising Actinocyclus sp., Denticula

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kuetzingii, Ellerbeckia arenaria, Fragilaria capucina, and Pinnularia brevicostata. These cosmopolitan taxa are mainly benthic, alkaliphilic, and indifferent to salinity and water

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velocity (Lange-Bertalot, 2011). The total number of diatom valves found in the samples was too low to further use this sample in the statistical analyses or reconstruction.

4.4.3 Late mid-Wisconsin thermokarst lake sediments (unit B) The sediment unit B (ca. 42.3 to 31.4

14

C kyr BP, samples Kit-1-20 to Kit-1-7)

accumulated in the lacustrine milieu of a developing thermokarst water body until about 31.4 14

C kyr BP. From 9.5 to 10.4 m a.s.l. diatom findings are rare (Fig. 7). Most species belong to

the genus Cymbella, while Denticula kuetzingii and Navicula radiosa are also present.

13

ACCEPTED MANUSCRIPT Between 10.4 and 11.4 m a.s.l., the sediments practically lack diatom findings although other lacustrine fossils such as molluscs and ostracods were preserved (Fig. 7). Starting at a height of 11.7 m a.s.l. the fossil record increases as shown by high numbers of counted diatom valves and identified taxa. At 12 and 12.5 m a.s.l., the number of diatom taxa reaches 32 and 36 per sample, respectively. Dominant taxa are Aulacoseira subarctica (≤37.5%), Cyclotella rossii (≤15%), Tabellaria fenestrata (≤11%), and Tabellaria flocculosa (≤10%) (Fig. 7). Planktonic taxa dominate. Halophobic taxa decrease while halophilic taxa

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increase in number even though salinity-indifferent taxa prevail. Here we found alpinecosmopolitan and cosmopolitan taxa and the highest percentage taxa known for their main

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occurrence in boreal regions, i.e. Cyclotella iris and Aulacoseira subarctica (Gibson et al.,

SC

2003; Barinova et al., 2006).

Taxa indifferent to temperature and water velocity dominate, but still-water taxa also

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occur. The quantitative reconstruction of low pH values between 6.2 to 6.3 can also be verified qualitatively by high percentages of acidophilic taxa (Fig. 7). Above 12.5 to 13.7 m a.s.l. the species richness increases to 48. Dominant taxa are

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Amphora libyca (≤ 28%), Amphora pediculus (≤10%), Cymbopleura incerta (≤14%), Aneumastus tuscula ( (≤ 13%), and Pinnularia brevicostata (≤10%) (Fig. 7). Planktic taxa are

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replaced by benthic taxa pointing to a decrease in water depth likely induced by greater evaporation and/or lake drainage. Consequently, halophilic taxa, which react to higher ion

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content in the water increase in numbers. Alkaliphilic taxa also increase, and the reconstructed pH varies from 6.3 to 7.7 (Fig. 7). Boreal taxa disappear and are replaced by cosmopolitan

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taxa.

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4.4.4 Late Wisconsin shallow (polygonal) water sediments (unit C) Sediment unit C (ca. 19

14

C kyr BP, samples Kit-1-6 to Kit-1-4) discontinuously

covers the underlying unit B. The number of found diatom taxa varies between 28 and 43 (Fig. 7). Most of the identified taxa are cosmopolitan, temperature-indifferent, and benthic. Dominant taxa are Epithemia adnata (≤16%), Aneumastus tuscula (≤12%), and Eunotia praerupta (≤10% each) (Fig. 7). Mesohalobic and benthic taxa increase, associated with occurrence of water-velocity-indifferent taxa or taxa that prefer streaming water. The reconstructed pH for unit C varies between 7 and 7.8 (Fig. 7).

14

ACCEPTED MANUSCRIPT 4.4.5 Early Holocene thermokarst lake sediments (unit D) The uppermost exposed sediment unit D was radiocarbon-dated to the early Holocene (ca. 8.4 to 8.1

14

C kyr BP, samples Kit-1-3 to Kit-1-1). Here, the taxonomic richness reach

highest values of up to 52 taxa. Most dominant taxa are Fragilaria capucina (≤81%) and Staurosirella pinnata (≤48%) (Fig. 7). Cosmopolitan, benthic taxa make up as much as 92% of the assemblages. Temperature-indifferent, water-velocity-indifferent, salinity-indifferent,

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5.1

Discussion

Modern diatom ecology

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5

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halophilic taxa prevail. The reconstructed pH indicates values between 6.7 and 7.2 (Fig. 7).

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According to previous investigation in Arctic freshwaters recent factors influencing diatom species composition include lake-water pH, conductivity, nutrients, dissolved organic carbon, water temperature, and habitat availability (Smol et al., 2005; Rühland et al., 2008;

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Biskaborn et al., 2012; Rouillard et al., 2012). Eunotia taxa are commonly acidophilous

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species found at low Ca2+ and Mg2+ concentrations and have lower optima for HCO3+CO3 (Van Dam 1994; Potapova and Charles 2003). Hence, we assume that рН valu s of 6.2 o 7 (except for lake EB-06) and low EC (180 to 262 µS cm-1) in modern waters are reflected in

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findings of Eunotia arcus, E. naegelii, Nitzschia frustulum, and Pinnularia streptoraphe. Vice versa, if calcium increases the alkalisation of host waters, many calciphobic and acidophilic taxa of the Eunotia and Pinnularia genera disappear (Stenina 2008). This could be the case

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for EB-01 and EB-02.

5.2

Palaeoenvironmental reconstructions Assuming that the lack of diatoms is not a preservation-phenomenon, only the

uppermost horizon in unit A is interpreted to represent the development of a shallow water basin sufficient for diatom growth. We assume that unfavourable conditions for diatoms prevailed both due to severe climate conditions and abiotic sedimentary factors such as high sediment input from shoreline disturbances and rapidly changing morphological settings. 15

ACCEPTED MANUSCRIPT When thaw subsidence and lake deepening became more important than the lateral thermokarst processes, quieter limnogeological conditions allowed the development of the lake ecosystem and pioneering diatoms established prior to ostracodes, molluscs and Characeae (Fig. 7). Hence, according to the radiocarbon dates (Fig. 3), the initial thermokarstlake formation during the mid-Wisconsin can be assigned to about 42.5 to 42.3

14

C kyr BP,

which predates the onset of thermoersosional processes as interpreted by Wetterich et al. (2012). The presence of the fresh-to-brackish-water genus Actinocyclus indicates salinisation

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via evaporation of the initial thermokarst lake because any influence of seawater on the diatom flora is highly unlikely due to the remoteness of the coast from our site during that

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period of lower sea level. The other taxa indicate shallow and oligotrophic conditions and low

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water temperature.

The late mid-Wisconsin thermokarst lake (ca. 42 to 31.4 14C kyr BP) is characterised

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by a rising number of Cymbella genera in the deeper part of unit B indicating better conditions for diatom growth. Longer open-water periods and longer growing seasons, sufficient for the development of more complex forms, resulted in more diverse aquatic

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habitats available for diatoms (Biskaborn et al., 2012). A longer growing season promoted the extension of the littoral area with substrates, including vegetation such as mosses, to maintain

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the development of Cymbella genera (Douglas and Smol, 2010; Paul et al., 2010). Inflow of substrates from the catchment area especially promoted development of Cymbella

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cymbiformis and Cymbella cistula, which are calciphilous taxa with relatively high optima for nutrients, HCO3+CO3 and Si4+ (Potapova and Charles 2003, Çelekli and Kül ö lüoğlu 2007). The presence of Hantzschia amphioxys in records after tephra sedimentation indirectly

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reflects slightly acidic and disturbed, shallow water with moss cover at the bottom (LangeBertalot, 2011). During the same period and until the early Holocene, Charophytes started to

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inhabit the lake. Charophyta are submerged macroalgae occurring in various types of terrestrial aquatic environments, preferring freshwater lakes where they occupy sites of depths ranging from 1 to 40 m and tolerate a wide pH (5.2 to 9.8) gradient. They are frequently found in lakes with high concentration of dissolved carbonates and then playing an important role in water body functioning. They often dominate at initial stages of succession and possess more competitive advantage over vascular plants when water level fluctuates (Caisová and Gabka 2009). The presence of Charophytes fossils in sediments (gyrogonites and encrustations) indicates that the lake remained unfrozen for at least three months during summer seasons, because this is the time required for the algae to complete a full growth cycle (Apolinarskaa et

16

ACCEPTED MANUSCRIPT al., 2011). The existence of a developed lake ecosystem also supports a permanent presence of ostracods and mollusks in the samples from unit B (Fig. 7). The shift in diatom dominants in the upper part of unit B probably indicates a reduction in minerogenic input and the development of stable lake conditions, allowing an increase of planktonic taxa, generally pointing to increased water depth. Replacement of Hantzschia amphioxys by more complex diatom assemblages dominated by Aulacoseira and Cyclotella taxa is indicative of further climate amelioration (Hoff et al.,, 2015; Biskaborn et

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al., 2016). The slight change from planktonic Aulacoseira to Cyclotella taxa is consistent with a decrease in the duration of ice cover with recent warming, increased open water periods, and

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related limnological changes (Paul et al., 2010). Furthermore, Aulacoseira taxa are heavily

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silicified and therefore require turbulent water conditions (Rühland and Smol, 2005). The presence of Fragilariforma virescens and Eunotia taxa are indicative of circumneutral to

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slightly acidophilic conditions (Paul et al., 2010). The dominance of Amphora genera in the uppermost part of unit B reflects higher conductivity and ion contents, i.e. carbonate in littoral habitats (Bigler et al., 2006) under conditions of attenuated hydrodynamics during colder

In unit C (ca. 19

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periods (Pushkar and Cherepanova, 2011). 14

C kyr BP), the high abundance of benthic diatom taxa indicates

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shallow water conditions. Higher ion content is reflected by increased mesohalobic taxa; i.e. dominance of Epithemia adnata and Aneumastus tuscula in confirms higher water EC during

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this period (Potapova and Charles, 2003). We assume that a shift occurred from lake conditions to ponding water of a remnant lake or polygonal ponds after the lake drained. The occurrence of water-velocity-indifferent taxa or taxa that prefer streaming water might

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furthermore indicate very shallow and hence unstable water conditions where wind can induce considerable water movement. Hence, in unit C, the previously existing thermokarst

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lake of mid-Wisconsin origin successively transformed into another lake type, resembling modern polygon ponds with similar shallow-water conditions. The indication of very shallow water in addition to the late Wisconsin age of this horizon confirm the previous interpretation by Wetterich et al. (2012) that unit C accumulated in a polygon tundra landscape under coldclimate glacial conditions. Lake conditions were re-established within the preserved basin during the early Holocene warming (unit D, ca. 8.4 to 8.1

14

C kyr BP). Comparing the early Holocene lake

with the mid-Wisconsin lake we can deduce higher air temperatures in the early Holocene, because Aulacoseira subarctica dominates in the mid-Wisconsin deposits. A. subarctica is a species that is associated with lower temperatures, low-light conditions, and turbulent waters 17

ACCEPTED MANUSCRIPT (Rühland et al., 2015). We attribute the occurrences of A. subarctica and Cyclotella rossii to cooler climatic conditions, whereas the shift towards Staurosirella pinnata found in the early Holocene deposits may be in that context related to increased temperatures (Kumke et al., 2004, Wolfe et al., 2000, Wilson et al., 2012). Moreover, the distinct change in the diatom assemblage, expressed by the newly established dominance of fragilarioid taxa indicates that the ecological state of the lake changed markedly at the Pleistocene-Holocene boundary. This change is strongly related to the development of interglacial catchment vegetation and soil

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properties. This is i.e. reflected by the lack of early Holocene Сharophytes findings, pointing to increasing inflow of phosphorus and humic substances causing unfavorable conditions for

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Сharophytes vegetation (Apolinarskaa et al., 2011). Similar characteristics of diatom

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assemblages, i.e. the predominance of small benthic fragilarioid taxa, starting to occupy upcoming early Holocene lake basins have been observed in Siberian studies by Biskaborn et

Tephra and its impact on lacustrine environments

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5.3

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al. (2012).

Independent of environmental changes across the Wisconsin and the early Holocene,

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the similar distribution of mineral phases in the Kit-1 pingo sediment succession suggests a

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stable source area over time for the terrestrial minerogenic sediment supply. This implies that the study site likely received contributions largely from local sources. Minor mineral variations in the sediment layers may be explained by hydrodynamic sorting during

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transportation and deposition rather than by a provenance changes. One exception occurs at 11.7-11.8 m a.s.l., where a negative peak in the quartz-to-feldspar curve and a major positive

AC

peak in the orthoclase-to-feldspar ratio (Fig. 6) indicates a tephra layer. This layer also reveals a prominent magnetic susceptibility peak but is poorly dated with an age identified as outlier (Fig. 3) due to reworking and admixing of old carbon close to the 14C age determination limit (Wetterich et al., 2012). Nevertheless, based on similar observations by Lenz et al. (2016a) we assume that the tephra most likely can be linked to an eruption of the South Killeak Maar at about 42 kyr BP. The latest major volcanic event on the northern Seward Peninsula is the Devil Mountain Maar eruption that caused tephra covering a Last Glacial Maximum palaeosol dated to ca. 18

14

C kyr BP (21,570 cal yr BP; Goetcheus and Birks 2001). The tephra layer in the

Kit-1 pingo sequence at 13.9-14.1 m a.s.l. possibly matches this eruption in terms of the height-to-age function in the exposed lithological units. The tephra is close to two dates from 18

ACCEPTED MANUSCRIPT plant remains at 13.5 m of about 32

14

C kyr BP (Fig. 3) indicating a hiatus in sediment

succession prior to the tephra event. Moreover, the accurate identification of volcanic eruptions in the Kit-1 pingo sequence is still under debate. If there was an immediate geochemical change in the deposits, either due to ash fallout or water-transported tephra, the mineral signature produced by the XRD method does not resolve this event. Further tephrochronological analyses revealed very similar geochemical composition of tephra in depths of 13.9-14.1 m a.s.l. (Kit-1-6) and 11.7-11.8 m a.s.l. (Kit-1-13) (Lenz et al., 2016b).

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Both tephra layers are also geochemically similar to a 1-m-thick tephra layer in depths of 1.55-2.43 m a.s.l. in the Kit-64 record (informal name: GG basin) of a drained basin core

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dated to the South Killeak Maar eruption as well as in tephra layers of the Devil Mountain

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Maar eruption detected in the drained lake basin core of Kit-43 (in depths of 3.48-3.49 m a.s.l. and 2.00-2.01 m a.s.l.; Lenz et al., 2016b). The geochemical similarity of tephra in this area of

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evidently different ages indicates the same geological setting of the Cape Espenberg maars. Begét et al. (1996) point out that the phreatomagmatic explosions that formed the maar lakes were related to basaltic volcanism in the region, which may lead to conspicuous pyroxene or

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feldspar signals we found in these tephra layers. Even though the Kitluk sediment record shows no drastical mineral changes, ecological changes due to tephra accumulation affected

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the abundance of the diatom flora at the site. In fact, the lower tephra layer (at 11.7-11.8 m a.s.l.) marks the beginning of a distinct increase in the number of diatom species, whereas the

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upper tephra layer (at 13.9-14.1 m a.s.l.) marks a phase when, after a short-term increase of diatom abundance, the total number of diatom species decreased in the overlying sediment layers. The tephra events may thus have played a role in controlling the diatom record,

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possibly by nutrient supply. In the nearby Kit-43 record of a drained thermokarst lake basin, however, it was found that other aquatic microfossil (ostracods) were mostly absent in core

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sections where (partly redeposited) tephra was noted, suggesting unfavourable living conditions for aquatic organisms in such dynamic environments (Lenz et al., 2016b).

5.4

Wisconsin to Holocene environmental change and thermokarst dynamics Thermokarst lake initiation and expansion in northern high latitudes are largely

associated with periods of warming and wetting which were particularly prevalent during the Pleistocene-Holocene transition (Kaplina and Lozhkin, 1979; Walter et al., 2007). Over the Deglacial and Holocene thermokarst lake dynamics with initation, expansion, and drainage contributed to the atmospheric carbon budget my mobilizing or sequestering carbon in these 19

ACCEPTED MANUSCRIPT lake environments (Walter Anthony et al.,, 2015). In fact, several climate fluctuations were reconstructed for the mid-Wisconsin in eastern Beringia between 80 and 30 kyr BP with conditions warmer than present (Schweger and Matthews, 1985). The Kit-1 diatom record indicates thermokarst lake initiation during the midWisconsin interstadial, around 42.5 to 42.3 about 31.4

14

14

C kyr BP, and its further development until

C kyr BP. Although general warm temperatures peaked between 35 and 33

14

C

kyr BP, high regional interstadial variability was recorded in western and eastern Beringia

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(Anderson and Lozhkin, 2001, Wetterich et al., 2014). The study of Kit-1 also highlights periods of wetting during glacial periods. Lacustrine and peatland sequences of mid-

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Wisconsin age indicating wetter conditions were previously reported for the Seward Peninsula

SC

by Hopkins and Kidd (1988) and Lenz et al. (2016b). Probably, the more continental position of the study site in the central area of Beringia during the Wisconsin glacial period due to

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generally low sea levels resulted in strong seasonal temperature gradients. Within the Wisconsin glacial, however, stadials and interstadials were accompanied by regional sea level shifts. Approaching coasts during interstadials likely caused increased precipitation and hence

MA

local intensification of thermokarst processes during relatively warm summers. Warmer than present air temperatures for Alaska and western Canada at 11.3 ± 1.5 cal

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kyr BP were suggested even though the time-transgressive pattern in North-America introduced by Kaufman et al. (2004) was revised by Kaufman et al. (2016) as being more

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variable with a less clear spatial pattern. Edwards et al. (2016) show that highly dynamic surface processes associated to thermokarst have shaped the landscape during the early Holocene. Kaufmann et al. (2016) suggest that thermokarst as well as peatland initiation

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peaked between 11 and 10 cal kyr BP in eastern Beringia, most likely in response to changing seasonality rather than solely increased summer temperatures. Wetterich et al. (2012) confirm

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the much warmer than present conditions during the early Holocene at the study site highlighting the presence of several plant species in macrofossils of the Kit-1pingo record that are well beyond their modern range. Furthermore, Kaufman et al. (2016) conclude that simultaneous low lake levels during the early Holocene, which at first seems to contradict evidences of lake and peatland formation at that time, point towards the major role of seasonal distribution of precipitation: Low winter precipitation may have decreased lake levels and increased peatland development by paludification, while high summer precipitation promoted peatland development.

20

ACCEPTED MANUSCRIPT 6

Conclusions

The present diatom-based reconstruction of lake stages completes and broadens the previously interpreted periglacial landscape development and allows a more detailed look into thermokarst-lake dynamics during the interstadial mid-Wisconsin, the stadial late-Wisconsin, and the interglacial conditions during the early Holocene. The discussion of our results can be

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concluded as follows:

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 Statistical analysis reveal highest similarity of diatom data from modern polygon ponds to the corresponding initial (shallow water) development stages of thermokarst

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lakes.

 The diatom data records the thermokarst onset at about 42.5

14

C kyr BP within the

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uppermost part of unit A, which predates the former interpretation of Wetterich et al. (2012).

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 The qualitative diatom analysis and the application of quantitative reconstruction of hydrochemical parameters showed that the pingo sequence underwent several phases of both thermokarst and intensified ecosystem diversity that were related to climate

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variability and the influence of volcanic tephra on the hydrochemical regime.

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 Pleistocene thermokarst processes at the Kitluk River mouth in the Northern Seward Peninsula could establish during interstadials, facilitated by both, increased precipitation due to approaching coasts and still high continentality causing high

7

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seasonal temperature gradients.

Acknowledgments

Th fi ldwo

was financiall suppo

d b NSF

an №0732735, DFG

SCHI 530/7-1, WE 497 4390/2-1, and KI 849/2-1, and NASA

an № NNX08AJ37G.

Furthermore, the study contributes to the German-Russian p oj c s DFG 3622/16-1 and M F

an s №

an № HE

an № 01DJ14003. The study was additionally supported by personal

grants to O. Palagushkina (DAAD grants № A0972849, A1104289), JL (dissertation stipend by University of Potsdam and the Christiane Nüsslein Volhard Foundation), LN and OP are 21

ACCEPTED MANUSCRIPT supported by the Russian Science Foundation (Grant 16-17-10118) by the subsidy allocated to Kazan Federal University for the state assignment in the sphere of scientific activities, GG (ERC № 338335 . We thank Hanno Meyer and Frank Kienast for help in the field, as well as CH2M Hill Polar Services, Katey Walter Anthony, as well as Curtis Nayokpuk and Fred Goodhope from Shishmaref for logistical support. The US National Park Service kindly permitted this work in Bering Land Bridge National Preserve. The paper greatly benefited by comm n s and lan ua

co

c ions f om Candac

O’Conno

of Alas a

References

NU

8

SC

RI

PT

Fairbanks).

Univ si

Alaska Climate Research Center (2008) Online source, last visited in June 2014.

MA

http://climate.gi.alaska.edu

Alekin OA (1970) Osnovy gidrokhimii (Basics of Hydrochemistry). Gidrometeoizdat,

PT E

D

Leningrad [in Russian]

Anderson PM and Lozhkin AV (2001) The Stage 3 interstadial complex (Karginskii/middle Wisconsinan interval) of Beringia: variations in paleoenvironments and implications for

CE

paleoclimatic interpretations, QSR, 20(1-3), 93-125

Antoniades D, Douglas MSV, Smol JP (2005) Quantitative estimates of recent environment

AC

changes in the Canadian High Arctic inferred from diatoms in lake and pond sediments. J Paleolimnol 33: 349-360 Apolina s aa K,

ł cha b M,

u aczc A

Carophytes (Characeae): Can calcifi d

2011

CaCO3 sedimentation by modern

mains and ca bona

δ13C and δ18O record the

ecological state of lakes? Stud Lim Tel 5: 55-66

Barinova SS, Medvedeva LA, Anisimova OV (2006) Bioraznoobrazie vodoroslei indikatorov okruzhayushchei sredy (Biodiversity of algae-indicators of the environment). Pilies Studio, Tel Aviv [in Russian] 22

ACCEPTED MANUSCRIPT

Battarbee RW, Jones VJ, Flower RJ, Cameron NG, Bennion H, Carvalho L, Juggins S (2001) Diatoms. In: Smol JP, Birks HJB, Last WM (Eds.), Tracking Environmental Change Using Lake Sediments. Kluwer Academic Publishers, Dordrecht, Netherlands, pp. 155–202. JE, Hopkins DM, Charron SD (1996) The largest known maars on Earth,

PT

Seward Peninsula, northwest Alaska. Arctic 49: 62-69

Bigler C, Barnekow L, Heinrichs ML, Hall RI (2006) Holocene environmental history of

RI

Lake Vuolep Njakajaure (Abisko National Park, northern Sweden) reconstructed using

SC

biological proxy indicators. Veget Hist Archaeobot 15: 309-320

NU

Birks HJB (1995) Quantitative palaeoenvironmental reconstructions. In: Maddy D, Brew JS (eds) Statistical Modelling of Quaternary Science Data Vol. XII. Cambridge Quaternary

MA

Reasearch Association, Cambridge, pp 161-254

Birks HJB (1998) Numerical tools in palaeolimnology — progress, potentialities, and

D

problems. J Paleolimnol 20: 307–332.

PT E

Birks HJB, Juggins S, Line JM (1990) Lake water chemistry reconstruction. In: Mason, B.J. (Ed.), The Surface Waters Acidification Programme. Cambridge University Press,

CE

Cambridge, pp. 301–313.

Biscaye PE (1965) Mineralogy and sedimentation of recent deep-sea clay in the Atlantic

AC

ocean and adjacent seas and oceans. GSA Bull 76: 803-832.

Biskaborn BK, Herzschuh U, Bolshiyanov D, Savelieva L, Diekmann B (2012) Environmental variability in northeastern Siberia during the last similar to 13,300 yr inferred from

lake

diatoms

and

sediment-geochemical

parameters.

Palaeogeography

Palaeoclimatology Palaeoecology 329: 22-36.

Biskaborn B, Herzschuh U, Bolshiyanov D, Schwamborn G, Diekmann B (2013) Thermokarst processes and depositional events in a tundra lake, Northeastern Siberia. Permafrost and Periglacial Processes 24, 160-174. 23

ACCEPTED MANUSCRIPT

Biskaborn BK, Subetto DA, Savelieva LA, Vakhrameeva PS, Hansche A, Herzschuh U, Klemm J, Heinecke L, Pestryakova LA, Meyer H, Kuhn G, Diekmann B (2016) Late Quaternary vegetation and lake system dynamics in north-eastern Siberia: Implications for seasonal climate variability. Quaternary Science Reviews 147, 406-421.

Bouchard F, MacDonald LA, Turner KW, Thienpont JR, Medeiros AS, Biskaborn BK,

PT

Korosi J, Hall RI, Pienitz R, Wolfe BB (2017). Paleolimnology of thermokarst lakes: a

s Cha ac a , Cha oph a in h Cz ch R public:

SC

Caisová L, Gąb a MG 2009 Cha oph

RI

window into permafrost landscape evolution. Arctic Science. DOI: 10.1139/AS-2016-0022

NU

Taxonomy, autecology and distribution. Fottea 9(1): 1-43

Douglas MSV, Smol JP (2010) Freshwater diatoms as indicators of environmental change in the high Arctic. In: Smol JP, Stoermer EF (eds) The Diatoms: Applications for the

MA

Environmental and Earth Sciences, 2nd edition. Cambridge University Press, Cambridge, pp

D

249-266

Edwards M, Grosse G, Jones B, MacDowell P (2016) The evolution of a thermokarst-lake

PT E

landscape: Late Quaternary permafrost degradation and stabilization in interior Alaska. Sedimentary Geology, 340, 3-14. doi:10.1016/j.sedgeo.2016.01.018.

CE

Engels S, Helmens KF, Vӓliranta M, Brooks SJ, Birks HJB (2010) EarlyWeichselian (MIS 5d and 5c) temperatures and environmental changes in northern Fennoscandia as recorded by

European

AC

chironomids and macroremains at Sokli, northeast Finland. Boreas 39: 689-704.

Diatom

Database

(2001)

Online

source,

last

visited

in

June

2014.

http://craticula.ncl.ac.uk/Eddi/jsp/datasetdesc.jsp?DatasetId=pH

Fallu MA, Allaire N, Pienitz R (2000) Freshwater diatoms from northern Québec and Labrador (Canada). Bibliotheca Diatomologica. Gebr. Borntraeger, Berlin, Volume 45: 1-200

24

ACCEPTED MANUSCRIPT Farquharson, L., K. W. Anthony, N. Bigelow, M. Edwards, and G. Grosse (2016) Facies analysis of yedoma thermokarst lakes on the northern Seward Peninsula, Alaska. Sedimentary Geology, 340, 25-37, doi:10.1016/j.sedgeo.2016.01.002.

Flemal RC (1976) Pingos and pingo scars: Their characteristics, distribution, and utility in reconstructing former permafrost environments. Quat Res 6: 37-53

PT

French HM (2007) The Periglacial Environment, England, Wiley. pp. 458

RI

Fritz M, Wolter J, Rudaya N, Palagushkina O, Nazarova L, Obu J., Rethemeyer J., Lantuit H.,

SC

Wetterich S. 2016. Holocene ice-wedge polygon development in the northern Yukon, Canada.

NU

QSR 147: 279-297.

Frolova LА, Nazarova L, Pestryakova L, Herzschuh U (2013) Analysis of the Effects of Climate-Dependent Factors on the Formation of Zooplankton Communities that Inhabit

MA

Arctic Lakes in the Anabar River Basin. Contemporary Problems of Ecology 6(1): 1–11.

D

Frolova L, Nazarova L, Pestryakova L, Herzschuh U (2014) Subfossil cladoceran from sediment in thermokarst lakes in northeastern Siberia, Russia and their relationship to

PT E

limnological and climatic variables. Journal of Paleolimnology 52 (1): 107-119.

Gibson CE, Anderson NJ, Haworth EY (2003)Aulacoseira subarctica: taxonomy, physiology,

CE

ecology and palaeoecology. European Journal of Phycology 38.2: 83-101.

AC

Gingele FX, De Deckker P, Hillenbrand CD (2001) Clay mineral distribution in surface sediments between Indonesia and NW Australia - source and transport by ocean currents. Mar Geol 179: 135-146

Goetcheus VG, Birks HH (2001) Full-glacial upland tundra vegetation preserved under tephra in the Beringia National Park, Seward Peninsula, Alaska. Quat Sci Rev 20: 135-147

Goslar T, Czernik J, Goslar E (2004) Low-energy

14

C AMS in Poznan radiocarbon

Laboratory, Poland. Nucl Instr Methods Phys Res B 223-224: 5-11

25

ACCEPTED MANUSCRIPT Grosse G, Jones B, Arp C (2013) Thermokarst lakes, drainage, and drained basins. In: Shroder JF (ed) Treatise on Geomorphology. Academic Press, San Diego, vol. 8, pp 325-353.

Guiry MD, Guiry GM (2015) AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; visited on 18 September 2015.

Grosse G, Schirrmeister L, Siegert C, Kunitsky VV, Slagoda EA, Andreev AA, Dereviagyn

PT

AY (2007) Geological and geomorphological evolution of a sedimentary periglacial landscape in northeast Siberia during the Late Quaternary. Geomorphology 86: 25-51

RI

Hopkins DM (1959) Cenozoic History of the Bering Land Bridge, Science: 129 (3362): 1519-

SC

1528.

NU

Heiri O, Lotter AF, (2001) Effect of low counts sums on quantitative environmental reconstructions: an example using subfossil chironomids. J Paleolimnol 26: 343–350.

MA

Heiri O, Lotter AF, Hausmann S, Kienast F (2003). A chironomid-based Holocene summer

D

air temperature reconstruction from the Swiss Alps. The Holocene 13: 477–484.

Hill MO (1973) Diversity and evenness: a unifying notation and its consequences. Ecology

PT E

54: 427-432.

Hoff U, Biskaborn B K, Dirksen V, Dirksen O, Kuhn G, Meyer H, Nazarova L, Roth A,

CE

Diekmann B (2015). Holocene Environment of Central Kamchatka, Russia: Implications from

AC

a multi-proxy record of Two-Yurts Lake. Global and Planetary Change. 134: 101-117.

Hopkins DM (1988) The Espenberg maars: A record of explosive volcanic activitiy in the Devil mountain - Cape Espenberg area, Seward Peninsula, Alaska. In: Schaaf JM (ed) The Bering Land Bridge National Preserve: An archeological survey. National Park Service, Alaska Regional Office Resources Management Report AR 0014, vol. 1, pp 262-321

Hopkins DM, Kidd JG (1988) Thaw lake sediments and sedimentary environments. In: 5th International Permafrost Conference. Tapir, Trondheim, pp 790-795

26

ACCEPTED MANUSCRIPT Hyvärinen H, Ritchie JC (1975) Pollen stratigraphy of Mackenzie pingo sediments, N.W.T., Canada. Arc Alp Res 7: 261-272

Juggins S, Birks HJB (2012) Quantitative environmental reconstructions from biological data. In: Birks H JB, Lotter AF, Juggins S, Smol JP (eds.) Tracking Environmental Change Using Lake Sediments. Springer Netherlands, 5: 431-494,

PT

Jones BM, Grosse G, Arp CD, Jones MC, Walter Anthony KM, Romanovsky VE (2011) Modern thermokarst lake dynamics in the continuous permafrost zone, northern Seward

SC

RI

Peninsula, Alaska. J Geophys Res 116: G00M03

Jones BM, Grosse G, Hinkel KM, Arp CD, Walker S, Beck RA, Galloway JP (2012)

NU

Assessment of pingo distribution and morphometry using an IfSAR derived DSM, western Arctic Coastal Plain, northern Alaska. Geomorphology 138: 1-14

MA

Jones MC, Grosse G, Jones BM, Walter Anthony KM (2012) Peat accumulation in a thermokarst-affected landscape in continuous ice-rich permafrost, Seward Peninsula, Alaska.

D

J Geophys Res 117: G00M07

PT E

Jones V, Juggins S (1995) The construction of a diatom-based chlorophyll a transfer function and its application at three lakes on Signy Island (maritime Antarctic) subject to differing

CE

degrees of nutrient enrichment. Freshwater Biology 34: 433-445.

Jorgenson MT, Yoshikawa K, Kanevskiy M, Shur YL, Romanovsky V, Marchenko S, Grosse

AC

G, Brown J, Jones BM (2008) Permafrost characteristics of Alaska. In: Kane D, Hinkel K (eds) Proceedings of the Ninth International Conference on Permafrost. University of Alaska, Fairbanks, AK, pp 121-122

Juggins S (2001) The European Diatom Database User Guide. Version 1.0. October 2001.

Juggins S (2007) C2 Version 1.5 User Guide. Software for ecological and palaeoecological data analysis and visualisation. Department of Geography, University of Newcastle, Newcastle upon Tyne

27

ACCEPTED MANUSCRIPT Juggins S (2013) Quantitative reconstructions in palaeolimnology: New paradigm or sick science? Quat Sci Rev 64: 20-32

Kaplina TN and Lozhkin AV (1980) Age of alass deposits of the Maritime Lowland of Yakutia, International Geology Review, 22(4), 470-476

Kaufman DS, Ager TA, Anderson NJ, Anderson PM, Andrews JT, Bartlein PJ, Brubaker LB,

PT

Coats LL, Cwynar LC, Duvall ML, Dyke AS, Edwards ME, Eisner WR, Gajewski K, Geirsdóttir A, Hu FS, Jennings AE, Kaplan MR, Kerwin MW, Lozhkin AV, MacDonald GM,

RI

Miller GH, Mock CJ, Oswald WW, Otto-Bliesner BL, Porinchu DF, Rühland K, Smol JP,

SC

Steig EJ, Wolfe BB (2004) Holocene thermal maximum in the western Arctic (0-180°W),

NU

Quat Sci Rev, 23(5-6), 529-560

Kaufman DS, Axford YL, Henderson ACG, McKay NP, Oswald WW, Saenger C, Anderson RS, Bailey HL, Clegg B, Gajewski K, Hu FS, Jones MC, Massa C, Routson CC, Werner A, –

A

systematic

review

of

MA

Wooller MJ, Yu Z (2016) Holocene climate changes in eastern Beringia (NW North America) multi-proxy

Quat

Sci

Rev

(in

press),

D

doi:10.1016/j.quascirev.2015.10.021

evidence.

PT E

Kitaev SP (2007) Osnovi limnologii dlya hidrobiologov i ikhiologov (Basics of limnology for hydrobiologists and ichthyologists). Karelian Research Centre, Russian Academy of Sciences,

CE

Petrozavodsk [in Russian]

Krammer K, Lange-Bertalot H (1986-1991) Bacillariophyceae, vol. 2 (1–4). In: Ettle H.,

AC

Gerloff J., Heyning H., Mollenhauer D. (eds). Süsswasserflora von Mitteleuropa (Freshwater flora of Europe). Gustav Fischer Verlag, Stuttgart, Jena [in German]

Kumke T, Kienel U, Weckström J, Korhola A, Hubberten H-W (2004) Inferred Holocene palaeotemperatures from diatoms at Lake Lama, Central Siberia. Arc Ant Alp Res 36: 626636

Lange-Bertalot H, Hofmann G, Werum M (2011) Diatomeen im Süßwasser - Benthos von Mitteleuropa, Ganter Verlag, 908 p. ISBN: 3906166929

28

ACCEPTED MANUSCRIPT Lenz J, Grosse G, Jones BM, Walter Anthony KM, Bobrov A, Wulf S, Wetterich S (2016a) Mid-Wisconsin to Holocene permafrost and landscape dynamics on the northern Seward Peninsula, Northwest Alaska, based on a drained lake basin core. Permafrost Periglac 27: 5675

Lenz J, Wetterich S, Jones BM, Meyer HM, Bobrov A, Grosse G (2016b) Evidence of multiple thermokarst lake generations from an 11 800-years-old permafrost core on the

PT

northern Seward Peninsula, Alaska. Boreas, 45(4), 584-603, doi: 10.1111/bor.12186

RI

Luoto TP, Kaukolehto M, Weckstrӧm J, Korhola A, Väliranta M (2014) New evidence of

SC

warm early-Holocene summers in subarctic Finland based on an enhanced regional

NU

chironomid-based temperature calibration model. Quat. Res. 81: 50–62.

Mackay JR (1978) Contemporary pingos. Biul Periglacjalny 27: 133-154

MA

Magurran E (1992) Ecological diversity and its measurement. Princeton University Press,

D

Princeton

Meyer H, Chapligin B, Hoff U, Nazarova L, Diekmann B (2015) Oxygen isotope composition

PT E

of diatoms as Late Holocene climate proxy at Two-Yurts-Lake, Central Kamchatka, Russia. Global and Planetary Change 134: 118-128.

CE

Muster S, Heim B, Abnizova A, Boike J (2013) Water body distributions across scales: A

AC

remote sensing based comparison of three arctic tundra wetlands. Remote Sens 5: 1498-1523.

Nazarova L, de Hoog V, Hoff U, Diekmann B (2013a) Late Holocene climate and environmental changes in Kamchatka inferred from subfossil chironomid record. Quaternary Science Reviews 67: 81-92.

Nazarova L, Lüpfert H, Subetto D, Pestryakova L, Diekmann B (2013b) Holocene climate conditions in Central Yakutia (North-Eastern Siberia) inferred from sediment composition and fossil chironomids of Lake Temje. Quaternary International 290-291: 264-274.

29

ACCEPTED MANUSCRIPT Nazarova L, Self A, Brooks SJ, van Hardenbroek M, Herzschuh U, Diekmann B (2015) Northern Russian chironomid-based modern summer temperature data set and inference models. Global and Planetary Change 134: 10-25.

Nazarova L, Bleibtreu A, Hoff U, Dirksen V, Diekmann B (2017) Changes in temperature and water depth of a small mountain lake during the past 3000 years in Central Kamchatka

lanch

FG, Kind R, L

nd

, Minchin

R, O’Ha a R , Simpson GL,

RI

Oksanen J,

PT

reflected by chironomid record. Quaternary International doi:10.1016/j.quaint.2016.10.008

SC

Solymos P, Stevens MHH, Wagner H (2013) Vegan: Community Ecology Package, R

NU

package version 2.0-7, http://CRAN.R-project.org/package=vegan

Palagushkina OV, Nazarova LB, Wetterich S, Schirrmeister L (2012) Diatoms from sediments of water bodies of Siberian Arctic. Contemporary Problems of Ecology 5 (4): 413–

MA

422

D

Palagushkina О.V., Nazarova L. B., Frolova L.A. 2014. Diatoms from holocene sediments of the lake Bolshoy Kharbey (Bolshezemelskaya tundra, Russia). Journal of Siberian Federal

PT E

University. Biology 4 (7): 395-410.

Paul CA, Rühland KM, Smol JP (2010) Diatom-inferred climatic and environmental changes

CE

over the last 9000 years from a low Arctic (Nunavut, Canada) tundra lake. Palaeogeogr

AC

Palaeoclimatol Palaeoecol 291: 205-216

Pestryakova LA, Herzschuh U, Wetterich S, Ulrich M (2012) Present-day variability and Holocene dynamics of permafrost-affected lakes in central Yakutia (Eastern Siberia) inferred from diatom records. Quat Sci Rev 51: 56-70

Petschick R, Kuhn G, Gingele F (1996) Clay mineral distribution in surface sediments of the South Atlantic: Sources, transport, and relation to oceanography. Mar Geol 130: 203-229

Potapova M, Charles DF (2003) Distribution of benthic diatoms in U.S. rivers in relation to conductivity and ionic composition. Freshwater Biol 48: 1311-1328 30

ACCEPTED MANUSCRIPT

Pushkar VS, Cherepanova MV (2011) The Bering land bridge connecting Asia and North America was much wider than both the Alaska and Chukchi peninsulas. Quat Int 237: 32-38

Rouillard A, Michelutti N, Rosén P, Douglas MSV, Smol JP (2012) Using paleolimnology to track Holocene climate fluctuations and aquatic ontogeny in poorly buffered high Arctic

PT

lakes. Palaeogeogr Palaeoclimatol Palaeoecol 321-322: 1-15

Rühland K, Smol JP (2005) Diatom shifts as evidence for recent Subarctic warming in remote

SC

RI

tundra lake, NWT, Canada. Palaeogeogr Palaeoclimatol Palaeoecol 226: 1- 16

Rühland K, Patterson AM, Smol JP (2008) Hemispheric-scale patterns of climate-related

NU

shifts in planktonic diatoms from North American and European lakes. Glob Chang Biol 14: 1-15

MA

Rühland KM, Paterson AM, Smol JP (2015) Lake diatom responses to warming: reviewing the evidence. Journal of Paleolimnology 54: 1-35.

D

Santos GM, Southon J, Griffin S, Beaupre SR, Druffel ER (2007) Ultra small mass 14C-AMS

PT E

sample preparation and analysis at the KCCAMS Facility. Nucl Instr Methods Phys Res B 259: 293-302

CE

Self AE, Klimaschewski A, Solovieva N, Jones VJ, Andrén E, Andreev AA, Hammarlund D, Brooks SJ (2015) The relative influences of climate and volcanic activity on Holocene lake

AC

development inferred from a mountain lake in central Kamchatka. Global and Planetary Change. 134: 67-81.

Smith LC, Sheng Y, MacDonald GM (2007) A first pan-Arctic assessment of the influence of glaciation, permafrost, topography and peatlands on Northern hemisphere lake distribution Permafrost Periglac 18: 201-208

Smol JP, Wolfe AP, Birks HJB, Douglas MSV, Jones VJ, Korhola A, Pienitz R, Rühland K, Sorvari S, Antoniades D, Brooks SJ., Fallu MA, Hughes M, Keatley BE, Laing TE, Michelutti N, Nazarova L, Nyman M, Paterson AM, Perren B, Quinlan R, Rautio M, 31

ACCEPTED MANUSCRIPT Saulnier-Talbot E, Siitonen S, Solovieva N, Weckström J (2005) Climate-driven regime shifts in the biological communities of Arctic lakes. Proc Natl Acad Sci USA 102: 4397- 4402 Solovieva N, Jones VJ, Birks HJB ,Appleby PG, Nazarova L (2008) Diatom responses to 20th century climate warming in lakes from the northern Urals, Russia. Palaeogeography, Palaeoclimatology, Palaeoecology 259: 96 –106.

PT

Solovieva N, Klimaschewski A, Self AE, Jones VJ, Andrén E, Andreev AA, Hammarlund D, Lepskaya EV, Nazarova L (2015) Holocene environmental history of a small coastal lake

SC

RI

from north-eastern Kamchatka Peninsula. Global and Planetary Change. 134: 55-66.

Stenina AS (2008) Diatoms in a peatbog polluted with oil-field brines in the Kolva River

NU

Basin, Komi Republic. Contemp Probl Ecol 1: 449-453

Schweger CE and Matthews JV (1985) Early and Middle Wisconsinan environments of

D

Geogr Phys Quatern 39(3): 275-290

MA

eastern Beringia: stratigraphic and paleoecological implications of the Old Crow tephra:

Telford R, Birks HJB (2011) A novelmethod for assessing the significance of quantitative

PT E

reconstructions inferred from biotic assemblages. Quat. Sci. Rev. 30: 1272–1278.

Telford RJ (2011) palaeoSig: Significance Tests of Quantitative Palaeoenvironmental

CE

Reconstructions. R package Version 1.0.

AC

ter Braak CJF (1990) Update notes: CANOCO Version 3.10. Agricultural Mathematics Group, Wageningen

ter Braak CJF (1994) Canonical community ordination. Part I: Basic theory and linear methods. Ecoscience 1: 127-140

ter Braak CJF (1995) Ordination. In: Jongman RHG, ter Braak CJF, van Tongeren OFR (eds) Data analysis in community and landscape ecology. Cambridge University Press, Cambridge. pp. 69-173

32

ACCEPTED MANUSCRIPT aa

CJF, Šmilau

(2002a) CANOCO for Windows: software for community

ordination (version 4.5). Microcomputer Power, Ithaca, New York aa CJF, Šmilau Us ’s Guid : Sof wa

P (2002b) CANOCO Reference Manual and CanoDraw for Windows fo Canonical Communi

O dina ion v sion 4.5 . Mic ocompu

Power, Ithaca, New York

PT

Van Dam H, Mertens A, Sinkeldam J (1994) A coded checklist and ecological indicator

RI

values of freshwater diatoms from the Netherlands. Aquatic Ecology 28: 117-133. Velle G, Brooks SJ, Birks HJB, Willassen E (2005) Chironomids as a tool for inferring

SC

Holocene climate: an assessment based on six sites in southern Scandinavia. Quat. Sci. Rev.

NU

24: 1429–1462.

Venables WN, Smith DM and the R Core Team (2015) An introduction to R. Notes on R: A

MA

Programming Environment for Data Analysis and Graphics, Version 3.1.3. R Foundation for Statistical Computing, Vienna, http://www.R-project.org

D

Vogt C (2009) Data report: Semiquantitative determination of detrital input to ACEX sites

PT E

based on bulk sample X-ray diffraction data. In: Backman J, Moran K, McInroy DB, Mayer LA (eds) Proceedings of the Integrated Ocean Drilling Program (IODP), IODP Management

CE

International, Inc., Edinburgh, doi:10.2204/iodp.proc.302.203.2009

Vogt C, Knies J, Spielhagen RF, Stein R (2001) Detailed mineralogical evidence for two nearly identical glacial/deglacial cycles and Atlantic water advection to the Arctic Ocean

AC

during the last 90,000 years. Glob Planet Change 31: 23-44

Walter KM, Edwards ME, Grosse G, Zimov SA and Chapin, III FS (2007) Thermokarst Lakes as a Source of Atmospheric CH4 During the Last Deglaciation. Science 318(5850): 633-636

Walter Anthony KM, Zimov SA, Grosse G, Jones MC, Anthony P, Chapin III FS, Finlay JC, Mack MC, Davydov S, Frenzel P, Frolking S (2014) A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch. Nature, 511, 452–456. doi:10.1038/nature13560.

33

ACCEPTED MANUSCRIPT Wetterich S, Grosse G, Schirrmeister L, Andreev AA, Bobrov A, Kienast F, Bigelow NH, Edwards ME (2012) Late Quaternary environmental and landscape dynamics revealed from a pingo profile on Seward Peninsula, Alaska. Quat Sci Rev 39: 26-44

Wetterich S, Tumskoy V, Rudaya N, Andreev AA, Opel T, Meyer H, Schirrmeister L, Hüls M (2014) Ice Complex formation in Arctic East Siberia during the MIS3 Interstadial, Quat Sci

PT

Rev 84: 39-55

Wilson CR, Michelutti N, Cooke CA, Briner JP, Wolfe AP, Smol JP (2012) Arctic lake

SC

RI

ontogeny across multiple interglaciations. Quat Sci Rev 31: 112-126

Wolfe AP, Fréchette B, Richard PJH, Miller GH, Forman SL (2000) Paleoecology of a

NU

>90,000-year lacustrine sequence from Fog Lake, Baffin Island, Arctic Canada. Quat Sci Rev

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Table captions

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Table 1 Characteristics of the studied modern periglacial waters. Ta: air temperature, Tw: water temperature, EC: electrical conductivity

Table 2 Ecological characteristics of diatom taxa from fossil findings in the pingo sediments (Kit-1) and from modern surface samples (EB)

Table 3 Summary of major changes in the local environment and lake ecosystem with references to methods and proxies (*from Wetterich et al., 2012).

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Figure captions

Figure 1 Location of (A) the study region in NW Alaska and (B) the Seward Peninsula in more detail with notations of some geographic features mentioned in the paper. The black frame west of Cape Espenberg indicates the study location shown in detail in Figure 2

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Figure 2 Satellite imagery of the study location indicating the sampled modern ponds (upper image: sample codes EB-01 through EB-09) and the pingo exposure at the Chukchi Sea coast

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(lower image)

Figure 3 Stratigraphic scheme, cryolithological description, and radiocarbon dates of the

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studied pingo remnant exposure Kit-1, redrawn from Wetterich et al. (2012). Radiocarbon dates in brackets indicate ages that are assumed as invalid for further interpretation. Elevation

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expressed as m a.s.l. (above sea level)

Figure 4 Record of modern diatom species from polygon pond (EB-1 to EB-9) surface

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Figure 5 RDA ordination diagrams showing (A) the distribution of diatom species in modern surface sediments of nine modern waters (sample code: EB) in relation to the three most significant water chemistry parameters, and (B) the modern diatom data sets in relation to the

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three most significant water chemistry parameters, and the fossil diatom data from pingo

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exposure Kit-1 plotted passively

Figure 6 Mineral composition of the Kitluk pingo record versus depth based on XRD measurements. TPA = total peak area

Figure 7 Record of aquatic fossils from pingo exposure Kit-1. Mollusc, ostracod, and characea findings (Wetterich et al. 2012) fit into the more detailed diatom record. Diatom taxa with occurences of at least 5% in one or more samples are plotted

Figure 8 Diatom-inferred pH from exposure Kit-1 with sample-specific estimated standard errors of prediction, the percentage of identified fossil specimens not represented in the 35

ACCEPTED MANUSCRIPT modern calibration dataset, the percentage of identified fossil specimens rare in the modern calibration dataset (N2 < 5), nearest modern analogues for the fossil samples in the calibration dataset and goodness-of-fit of the fossil samples with the reconstructed variable. Vertical dashed lines indicate 5% thresholds for identified taxa not present or rare in the calibration set, the squared chord distances of 150 in the calibration set to identify samples with no good modern analogue ,and the 90th nd 95th percentile in residual distances of modern samples to spond nc Anal sis o id n if sampl s wi h a ‘poo ’ ‘and a

‘v

cons uc d va iabl . R cons uc ions f om sampl s which

poo ’ `fi wi h pH o h

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plot to the right of the dashed lines may be unreliable.

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Table 1

EB-08 EB-09

Tw [°C]

EC pH [µS cm-1]

2.0

14.0

11.3

198

6.98

Basin bottom Intrapolygon pond

8x5

0.3

14.7

13.5

253

6.57

Basin bottom Intrapolygon pond

8x5

0.3

14.9

13.3

188

6.38

1-1.5

16.1

15.4

127

6.8

6x4

0.3

15.0

13.0

188

6.28

15 x 9

1.5

9.7

11.9

494

7.59

Basin bottom Interpolygon pond

3x3

0.2

12.0

11.9

173

6.42

Basin bottom Interpolygon pond

4x4

0.5

14.5

8.5

262

6.7

Basin bottom Interpolygon pond

2x2

0.6

12.8

5.2

180

5.9

Basin margin Thaw pond Basin margin Intrapolygon pond Higher slope

Thaw pond

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EB-07

Ta [°C]

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EB-06

Depth [m]

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EB-05

Basin bottom Thaw pond

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EB-04

Size [m]

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EB-03

66,57899 164,42000 66,57783 164,42508 66,57578 164,43624 66,56680 164,44515 66,57234 164,46323 66,57989 164,41151 66,57758 164,41680 66,57859 164,41958 66,57799 164,41958

Water type

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EB-02

Location

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EB-01

°N °W

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Table 2

pH preference

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Biogeography

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Temperature preference

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Velocity preference

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63.5 10.3 12.2 32.7 7.1 25 16.7 12.2 55.8 9.0 0.6 1.3 16.0 2.6 2.6 0.6 12.2 32.1 25.6 0.6

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Salinity preference

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benthic planctonic-benthic planctonic oligohalobic: indifferent halophilic halophobic mesohalobic alkaliphilic alkalibiontic indifferent acidophilic acidobiontic boreal cosmopolitan arctic-alpine alpine-cosmopolitan holarctic indifferent cool water eurytherm warm water still water indifferent stream water aerophilic

Habitat preference

% of total taxa number pingo sediments modern sediments (Kit 1) (EB) 49.4 77.5 16.7 15.7 7.1 1.9

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Ecological groups

56.9 11.8 20.6 0.9 30.4 4.9 20.6 22.5 0.9 7.8 56.9 11.8 1 17.6 1.9 3.9 0.9 10.8 32.4 26.5 1.9

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ACCEPTED MANUSCRIPT Table 3 Sediment unit D

C

upper B

Period (14C kyr BP) Early Holocene (8.4 to 8.1)

Hiatus Late Wisconsin (19)

Hiatus Mid-Wisconsin (42.3 to 31.4)

lower B

Mid-Wisconsin (42.3 to 31.4)

A

Mid-Wisconsin (42.5 to 42.3)

Diatom proxy record highest abundance and diversity; benthic species prevail; shallow water; neutral pH

Ostracod* proxy record single findings

high abundance and diversity; benthic species prevail; shallow water; neutral pH

low abundance and diversity

high abundance and diversity; benthic species prevail; decreasing water depth; neutral pH increasing abundance and diversity; planktonic species prevail; increasing water depth; acidic pH low adundance and diversity; benthic species prevail; shallow water; neutral pH

highest abundance and diversity

D E

Pollen and plant macrofossil* proxy records birch shrub tundra with spruce stands; aquatic vascular plants and algae

M

no record

C C

A

49

Thermokarst lake

T P

I R

grass-sedge tundra-steppe; aquatic vascular plants and algae

C S U

N A

low abundance and diversity

T P E

Lacustrine environments

Polygon ponds

grass-sedge tundra-steppe; aquatic vascular plants and algae

Thermokarst lake

Birch shrub tundra and grasssedge tundra with spruce stands; aquatic vascular plants and algae

Thermokarst lake

birch-willow shrub tundra with spruce and larch stands

Initial thermokarst lake

AC

CE

PT E

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

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