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The Northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The arctic-boreal natural environments play a crucial role in the global climate via the albedo change, carbon sources and sinks, as well as atmospheric aerosol production via biogenic volatile organic compounds. Furthermore, it is expected that the global trade activities, demographic movement and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but is also able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX is setting a research approach where large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land–atmosphere–aquatic–society continuum in the Northern Eurasian region. We introduce here the state of the art of the key topics in the PEEX research agenda and give the future prospects of the research which we see relevant in this context. more...

Although the climate development over the Holocene in the Northern Hemisphere is well known, palaeolimnological climate reconstructions reveal spatiotemporal variability in northern Eurasia. Here we present a multi-proxy study from north-eastern Siberia combining sediment geochemistry, and diatom and pollen data from lake-sediment cores covering the last 38,000 cal. years. Our results show major changes in pyrite content and fragilarioid diatom species distributions, indicating prolonged seasonal lake-ice cover between ~13,500 and ~8900 cal. years BP and possibly during the 8200 cal. years BP cold event. A pollen-based climate reconstruction generated a mean July temperature of 17.8 �C during the Holocene Thermal Maximum (HTM) between ~8900 and ~4500 cal. years BP. Naviculoid diatoms appear in the late Holocene indicating a shortening of the seasonal ice cover that continues today. Our results reveal a strong correlation between the applied terrestrial and aquatic indicators and natural seasonal climate dynamics in the Holocene. Planktonic diatoms show a strong response to changes in the lake ecosystem due to recent climate warming in the Anthropocene. We assess other palaeolimnological studies to infer the spatiotemporal pattern of the HTM and affirm that the timing of its onset, a difference of up to 3000 years from north to south, can be well explained by climatic teleconnections. The westerlies brought cold air to this part of Siberia until the Laurentide icesheet vanished 7000 years ago. The apparent delayed ending of the HTM in the central Siberian record can be ascribed to the exceedance of ecological thresholds trailing behind increases in winter temperatures and decreases in contrast in insolation between seasons during the mid to late Holocene as well as lacking differentiation between summer and winter trends in paleolimnological reconstructions. more...

We present a systematic compilation of previously published Holocene proxy climate records from the Arctic. We identified 170 sites from north of 58 degrees N latitude where proxy time series extend back at least to 6 cal ka (all ages in this article are in calendar years before present - BP), are resolved at submillennial scale (at least one value every 400 +/- 200 years) and have age models constrained by at least one age every 3000 years. In addition to conventional meta-data for each proxy record (location, proxy type, reference), we include two novel parameters that add functionality to the database. First, "climate interpretation" is a series of fields that logically describe the specific climate variable(s) represented by the proxy record. It encodes the proxy-climate relation reported by authors of the original studies into a structured format to facilitate comparison with climate model outputs. Second, "geochronology accuracy score" (chron score) is a numerical rating that reflects the overall accuracy of C-14-based age models from lake and marine sediments. Chron scores were calculated using the original author-reported C-14 ages, which are included in this database. The database contains 320 records (some sites include multiple records) from six regions covering the circumpolar Arctic: Fennoscandia is the most densely sampled region (31% of the records), whereas only five records from the Russian Arctic met the criteria for inclusion. The database contains proxy records from lake sediment (60 %), marine sediment (32 %), glacier ice (5 %), and other sources. Most (61 %) reflect temperature (mainly summer warmth) and are primarily based on pollen, chironomid, or diatom assemblages. Many (15 %) reflect some aspect of hydroclimate as inferred from changes in stable isotopes, pollen and diatom assemblages, humification index in peat, and changes in equilibrium-line altitude of glaciers. This comprehensive database can be used in future studies to investigate t more...

Thermokarst activity is a widespread arctic feature in Arctic periglacial regions. The highly dynamic relationships between limnogeological processes, permafrost degradation/aggradation and climate change, however, are yet not fully understood. To gain insight into the complex nature of climatic and non-climatic processes in the Arctic, we investigated palaeoenvironmental archives in a thermokarst landscape setting at Lake El’gene-Kyuele (71°17'N, 125°34'E, 157 m a.s.l.) in the tundra of northeastern Siberia. The lake is about 3 km long and 0.5 km wide with a maximum water depth of 10.5 m. It is located 125 km southwest of Tiksi near the Lena Delta, on the southern part of the watershed between the Lena and Olenek rivers. The waterbody is cutting into Holocene alas and Pleistocene Ice Complex sediments. In the latter case, thaw slumps occur associated with increased sediment transport. We analysed grain-size distributions, organic matter contents, elemental and mineralogical compositions, stable carbon isotopes, and plant macrofossils in sediment cores from the bottom and the shoreline of the lake. Sr/Rb ratios (related to feldspar and illite) serve as high-resolution grain-size proxies, Br correlates with the TOC content, and the Fe/Mn ratio reflects the degree of oxidisation. Radiocarbon dated samples indicate that the Late Pleistocene was affected by fire, which potentially triggered the initiation of thermokarst processes. A number of fine sand layers with the maximum age of ~10.9 cal. kyr BP is linked to depositional events associated with thaw slump activity on the thermokarst slopes. Besides the general dependence on hydroclimate variability, repeated phases of fine sand input and retrogressive thaw slumping indicate a close linkage with the orthogonally oriented patterns of the ice-wedge networks in the ice-rich permafrost within the catchment area. During the early Holocene Thermal Maximum (HTM) the lake rapidly expanded surrounded by forest or forest tundr more...

In August 2010 the paleolimnological expedition Lena 2010 has been carried out in the area close to the Lena Delta. The aim of the expedition was to study lakes located in the area of tundra and taiga, and the selection of core sediments. Studies carried out within the framework of a larger project SibLake to reconstruct climatic changes in northern Eurasia during the Pleistocene and Holocene. During the conference we will present the results of field studies. more...

In 2009 a collaborative German-Russian expedition realised an ecological and limnogeological survey along a north-south transect in arctic Siberia. The field studies included 14 thermokarst lake-sites reaching from the Arga region at 73° N within the Lena delta (Laptev Sea regioin) to the Lena hinterland at 69° N crossing the treeline. Based on the findings of this pre-survey (e.g. significant high sedimentation rates) a follow-up expedition in 2010 was undertaken to continue the paleolimnological studies at Lake El'gene Kyuele (71°18,04' N, 125°34,15' E) in the middle part of the transect and Lake Kyutyunda (69°37,89' N, 123°39,42' E) near the southernmost position of the transect. During this expedition longer sediment cores up to 8 m could be retrieved using an Uwitec piston corer system from a platform. Additionally the catchment area and the lake bathymetry were analysed.El'gene Kyuele has a length of 2.9 km and a width of 0.5 km. The lake bottom shows a strong relief with a maximum water depth of 10.5 m. The small catchment area reveals intensive thermokarst processes of the surrounded deeply loesslike sediments (Yedoma). The elongated shape corresponding to the regional geological structure of the bedrock also indicates a tectonic component influencing the thermokarst lake genesis.We intend to compare the sedimentological and paleoenvironmental regimes of 4 selected lakes of the transect in order to gain informations about temporal environmental changes in the gradient from the north to the south. Our main questions are: How much is the thermokarst erosion influencing the sedimentological regime? Is the lake bathymetry only controlled by thermokarst subsidence processes? Is there a paleoclimate signal triggering the detrital input events? To answer this questions bio-geochemical, geochemical and grain-size studies were conducted on several sediment cores along the selected lakes of the transect.The aim of the research project is to understand and reconstruct more...

Yakutia (Russia, northeastern part of Eurasia) represents one of Earths most extreme climatic settings in the worldwith deep-reaching frozen ground and a semiarid continental climate with highest seasonal temperature contrastsin the northern hemisphere. The amplitude of temperature variations around the year sometimes exceeds 100oC.There are few examples of quantitative palaeoecological studies in Siberia and these data have to be tested byquantitative studies from other sites in this region, inferred from different proxies and using regional calibrationdatasets and temperature models that are still lacking. Chironomid midges (Insecta, Diptera, Chironomidae) havebeen widely used to reconstruct past climate variability in many areas of Western Europe and North America. Achironomid-mean July air temperature inference model has been developed, based on a modern calibration set of200 lakes sampled along a transect from 110° to 159° E and 61° to73° N in northern Russia. The inference modelwas applied to sediment cores from 2 lakes in the Central Yakutia in order to reconstruct past July air temperatures.The lacustrine records span mid- to late Holocene. The downcore variability in the chironomid assemblages and thecomposition of organic matter give evidence of climate-driven and interrelated changes in biological productivity,lacustrine trophic states, and lake-level fluctuations. Three phases of the climate development in Central Yakutiacan be derived from the geochemical composition of the lake cores and according to the inferred from chironomidassemblages mean July air ToC. Content of organic matters reached maximal values in the period between 7000-4500 yBP. Sedimentation rate is especially high, numerous molluscs shells are found in sediments. All this alongwith the reconstructed air temperature confirmed that Mid Holocene optimum in Central Yakutia took place in thisperiod with the maximal temperatures up to 4oC above present day ToC. Strong faunistic changes take more...

In 2008 a joint German-Russian project POLYGON was proposed as potential contribution to the APEX research network (Jakobsson et al. 2008). Here, we present the project outline whose realisation will hopefully start in summer 2009.Permafrost regions are more strongly affected by ongoing global warming than regions elsewhere on this planet. Polygon ponds, mires and cryosols in wetland landscapes underlain by permafrost are common components of the Arctic Siberian lowlands. The landscapes of the polygonal tundra wetlands are sensitive to environmental and climate change, but such research suffers by large uncertainties in observations. However, permafrost degradation leads to changes in element and energy fluxes, affects relief and hydrology, and has a tremendous ecological impact.A proposed joint German-Russian project aims on investigating polygonal tundra wetlands in a gradient transect comprising three representative sites across the northeast Siberian lowlands in the Lena Delta (72 °N, 126 °E), and in areas of the lower Indigirka river (70 °N, 147 °E) and the lower Kolyma river (68 °N; 161 °E). Using an interdisciplinary approach, modern, sub-recent, and fossil environments will be characterised and compared in order to understand temporal and spatial environmental dynamics in relation to climate change.The proposed POLYGON project aims at answering three interrelated questions:(i) How do polygon ponds, cryosols, and permafrost in the polygonal tundra of the northeast Siberian Arctic lowlands interact and how have they reacted on climate change on seasonal, annual, decadal, centennial, and millennial time scales?(ii) Does the biotic and abiotic states and interactions in polygonal wetlands differ along the climatic gradient from the Lena River region to the Kolyma River region?(iii) How will the components of the polygonal tundra wetlands change when permafrost degrades due to climate change?Cryological, limnological, pedological and ecological features will be c more...

Udgivelsesdato: 2008