Olga Borisova

Peatlands of the Western Siberian lowlands: current knowledge on zonation, carbon content and Late Quaternary history

The Western Siberian lowlands (WSL) are the world’s largest high-latitude wetland, and possess over 900,000 km 2 of peatlands. The peatlands of the WSL are of major importance to high-latitude hydrology, carbon storage and environmental history. Analysis of the existing Russian data suggests that the mean depth of peat accumulation in the WSL is 256 cm and the total amount of carbon stored there may exceed 53,836 million metric tons. A synthesis of published and unpublished radiocarbon dates indicates that the peatlands first developed at the end of the Last Glacial, with a rapid phase of initiation between 11,000 and 10,000 cal yr BP. Initiation slowed after 8000 cal yr BP and reached a nadir at 4000 cal yr BP. There has been renewed initiation, particularly south of 621N, following 4000 cal yr BP. The initial development of peatlands in the WSL corresponds with the warming at the close of the Pleistocene. Cooling after 4000 Cal yr BP has likely led to increased permafrost and increased peatland development particularly in central and southern regions. Cold and dry conditions in the far north may have inhibited peatland formation in the late Holocene. r 2002 Elsevier Science Ltd. All rights reserved.

Radiocarbon dated Pinus sylvestris L. wood from beyond tree-line on the Kola Peninsula, Russia

Radiocarbon dates were obtained from 24 samples of Pinus sylvestris L. (Scots pine) wood recovered from sites beyond the modern conifer tree-line on the Kola Peninsula of Russia. Twenty-one of the samples came from the shallow waters and eroding peats at the edges of two small lakes at 68°439N, 35°109E, located north of the modern conifer tree-line. Three samples came from a small pond located above the modern elevational limits of Pinus sylvestris at 68°259N, 35°199E. The radiocarbon dates indicate that pine trees grew approximately 20 km north of the mapped modern limits of the species from 6680 BP to 3830 BP. Pine trees were also growing some 40 m above their modern elevational limits between 5890 BP and 3450 BP. Nineteen of the samples date from 6680 BP to 5070 BP, suggesting that the density of trees north of the modern tree-line was greatest between 7000 and 5000 BP. The timing of tree-line advance and greatest density on the Kola Peninsula are in agreement with the results of similar studies from northern Fennoscandia which indicate that maximum northern and elevational extension of tree-line occurred between 7000 BP and 4000 BP. The general agreement between tree-line reconstructions suggests that the climatic changes that promoted mid-Holocene tree-line extension along the North Atlantic margins in northern Fennoscandia propagated eastward to the Kola Peninsula. The late timing of initial pine expansion on the Kola and in adjacent northern Fennoscandia remains problematic and may relate to lower winter insolation, temperature regimes in the adjacent oceans or slow rates of migration.

Fluvial response to the Late Valdai/Holocene environmental change on the East European Plain

Abstract The relicts of large meandering paleochannels are found throughout the territory of the periglacial zone of the last (Valdai=Weichselian) glaciation on the Russian Plain, on the lower levels of river terraces and on the floodplains. Channel widths of so-called macromeanders can be 15 times larger than the recent meanders on the same rivers. Paleolandscape and paleohydrological reconstructions show that such periglacial river channels were formed under the conditions of high spring water flow, up to eight times greater than modern discharges, when the flow coefficient was close to 0.9–1.0 due to the existence of permafrost. Also, summers were dry and streams lacked ground water supply. Permafrost degradation increased soil permeability in the spring and increased ground water flow during summer, causing a decrease of annual flow 12,000–14,000 years BP in the southern periglacial zone, and up to 8500 years BP in the northern periglacial zone. In the taiga zone, an annual flow in the recent river basins is about 80–85% of that found in the periglacial zone in the east, and 30–60% of that in the west. In the east of the broad-leaved forest zone, it is about 40–50% of that of the periglacial zone, and 20–25% in the western part of the broad-leaved forest zone. In the eastern steppe and forest steppe, the modern annual flow is about 40–60% of that of the periglacial zone and about 10% in the western part of steppe and forest steppe zones. As a result, large periglacial channels were abandoned and transformed into floodplain lakes and bogs. The Holocene channels have much smaller channel widths and meander lengths, formed under conditions of lower annual flows and much steadier flow regime.

Estimates of methane emission during the last 125,000 years in Northern Eurasia

The concentration of methane in the atmosphere has varied considerably during the last 125,000 years. Boreal wetlands represent one of the main sources of methane emissions into the atmosphere, the rate of which is largely controlled by climate. Changes in climate (mainly in the duration of the frost-free period) and in the extent of wetlands presumably caused variations in the methane production from boreal ecosystems. We chose Northern Eurasia to estimate both climatic changes and the area of methane-producing ecosystems, as it plays a leading role in methane emission. Palaeobotanic and palaeocryological data were used for the reconstruction. The two most recent warm stages: the Holocene Optimum (5500–6000 years BP) and the Last Interglacial Optimum (ca. 125,000 years BP) were studied. During these warm periods, both an area of tundra and the proportion of the wetlands within the boreal forest zone were considerably reduced. On the other hand, a longer frost-free period and higher precipitation would have caused higher methane production. The precipitation rise was apparently in part compensated by an increase in potential evaporation due to higher summer temperatures. Compared to methane emissions of about 9×106 t per year from modern forests of Northern Eurasia, emissions amounted to 86 and 44% of modern values for the region during the Holocene Optimum and Last Interglacial Optimum respectively. Under the greenhouse warming expected early in the 21st century, the climatic conditions may lead to a considerable increase of methane emission.

Method of paleogeographical analogues in paleohydrological reconstructions

Abstract One of the main problems of quantitative paleohydrology is a discrepancy between very high (even catastrophic) reconstructed discharges in the paleorivers and the results of the majority of precipitation reconstructions in the same territory. To resolve the problem it is necessary to find the closest recent analogue to the hydrological regime of a paleoriver and to calculate the main hydrological and climatic parameters of the former flow with the help of this analogue. This approach to paleohydrological reconstructions is the method of paleogeographical analogues based on two assumptions: (1) similar hydrological regimes were characteristic for the paleorivers in similar paleolandscapes; (2) the hydrological regime of a paleoriver within some paleolandscape would be similar to that of a present-day river in the same type of landscape. Quantitative paleohydrological reconstruction by paleogeographical analogy calculates a wide range of paleohydrological and paleoclimatic parameters, such as maximum discharge and its return period; mean maximum discharge; mean annual discharge; volume of the floodwave; winter and annual precipitations. A study of the Khoper River paleochannel with a discharge 7 times exceeding the modern one indicates that the paleochannel formation was caused mainly by periglacial conditions with continuous permafrost and very sparse vegetation, while the rainfall increase was only two-fold. The relative errors in calculations of hydrological parameters for the present-day rivers using their modern analogues are mainly within ±10%, and up to 40%. The relative errors of palaeohydrological reconstructions are probably closer to the latter value.

U.S.‐Russia venture probes Siberian peatlands' sensitivity to climate

The extent to which northern peatlands respond to or influence climate change is an unresolved question in Arctic science. Recent studies in Alaska, Canada, and Fennoscandia have raised concerns that northern peatlands, while currently a net sink or minor source of atmospheric CO2 , may become a significant CO2 source under a warming climate. Expanding peatlands emit methane but sequester atmospheric carbon through long-term accumulation of undecomposed plant matter. Drier conditions may reverse this process by increasing temperatures and lowering the peatland water table, causing anaerobic decomposition of stored peat and subsequent outgassing of CO2.While this process would likely reduce methane emissions and possibly enhance C uptake from increased soil nutrient mineralization rates [Oechel and Vourlitis, 1994], many scientists now believe that warming and drying of northern peatlands will liberate stored C for uptake by the atmosphere and biosphere.

Greenhouse warming and the Eurasian biota: are there any lessons from the past?

Abstract Climate models predict a rise in global mean temperature of around 2–4°C by the end of the next century, with far greater rises in the high latitudes. Mean annual temperature rises of 6–8°C are predicted for 65°N, and as much as 10–12°C for above 70°N. There can be little doubt that such changes will have profound effects on boreal and arctic ecosystems, both through the temperature effects themselves and through associated changes in water balance. There is abundant evidence of climatic change in the high latitudes from the last 2.4 million years of the Quaternary. In a succession of glacial-interglacial cycles, high latitude temperatures seem to have fluctuated overall by about the same amount as is projected for the next century. Perhaps it is possible to use our knowledge of such past changes to understand what might happen to the high latitude ecosystems once the future greenhouse warming gets under way? There are many potential pitfalls in using data from the past to attempt to predict the future. In addition to the limitations in the data, there are also many important differences in the rate and setting of changes that should be borne in mind. With regard to climatic time-scale, the biogeographical patterns which we observe for the past are far more likely to represent equilibrium situations than those which we will observe in the future. Equilibrium data can itself be useful in that it provides indications of the distribution of climate conditions towards which the Earth will move. For example, it provides support for the notion that the climatic models are indeed correct in predicting that the strongest warming will occur in the high latitudes. Even following the relatively slow climate changes of the Quaternary high latitudes, there is abundant evidence of disequilibrium in tree species migrations, lasting for millennia in some cases. The survival of nearly all the high-latitude forms of plants and animals known from the Pleistocene fossil record—despite the repeated climatic fluctuations—may provide reassuring evidence of their future resilience. However, the extinctions of many large arctic mammals at around the time of the most recent warming phase may provide warning of what will occur in the future to certain species whose populations are already depleted by human activity. The exceptions to this pattern of gradual change are the sudden climatic shifts which have occurred in the North Atlantic region on several occasions during the late Quaternary. These may offer the closest analogues that we have to the effects of a future greenhouse warming on high-latitude plant and animal communities. It seems that some groups of organisms, such as insects, molluscs and water plants were able to respond rapidly to the climate warming, perhaps on the timescale of decades. However, tree populations were left far behind and took centuries or milennia to catch up with the changed climate, resulting in unfamiliar ecological scenarios in the mid and high latitudes.

River runoff decrease in North-Eurasian plains during the Holocene optimum

Three stages were identified in the development of meandering rivers and the formation of floodplains with natural levees in Northern Eurasia: the development of rivers with size larger than that of the modern ones; the development of rivers smaller than the modern ones; and the development of rivers of the present-day morphodynamic type. Small oxbows of the second stage are widespread in the floodplains of lowland rivers in Northern Eurasia. The largest amount of floodplain segments with such oxbows can be seen in the forest zone, mostly in the coniferous forests of northeastern European Russia. The available radiocarbon datings show that river channel were significantly decreasing in size and the steepness of meanders was increasing during the Atlantic period of the Holocene. Data on changes in the size of river channels were used to evaluate the ratios between paleo- and modern discharges and to construct a map of difference between runoff depths in the Holocene optimum and in the present and assess changes in water runoff volume. The discharges in the basins of the Vyatka and middle Irtysh accounted for as little as 40–50% of their current values. North, east, and west from those basins, the ratio of ancient and present-day discharges increases. During the Holocene optimum, water runoff from the northern megaslope of the East European Plain was ∼180 km3/year, which is 30% less than the present runoff from the same drainage area. The annual runoff in Volga basin was ∼134 km3, which is almost half as large as the present value. The runoff in Don and Dnieper basins during the Holocene optimum was 40% less, and that in the Ob and Irtysh basin was 30% less than the present one. If we accept the hypothesis that the Holocene optimum was a climate analogue of global anthropogenic warming of the mid-XXI century, the obtained estimates of the state of water resources in Northern Eurasia acquire great prognostic importance.

Climate-induced changes in surface runoff on the North-Eurasian plains during the late glacial and Holocene

Abandoned rivers (large paleochannels and meanders) are common on river floodplains and low terraces on the East European and West Siberian plains. They are 10–15 times greater in size than the present-day river channels. The large paleochannels are dated back to 11–15 thousand radiocarbon years B.P. (the Late Glacial period). Based on the hydraulic and morphometric relationships for present-day rivers and the method of paleogeographic analogs, the surface runoff during the Late Glacial period was quantitatively reconstructed by the morphometric parameters of large paleochannels. The reconstructed surface runoff exceeded the present values by 1.4 times on the northern mega-slope of the East European Plain (the Northern Dvina, Mezen, and Pechora river basins), by 2.3 times on its southern mega-slope (the Volga, Don, and Dnepr basins), and twofold in West Siberia (the Ob basin). The large surface runoff volumes can be explained by the landscape and climate conditions, including the high coefficients of runoff (due to the permafrost), the increased proportion (and, conceivably, the amount) of snowfall, and, hence, the respective increased intensity of spring floods. The transformation of large Late-Glacial paleorivers due to climate warming at the beginning of the Holocene is a likely scenario of the surface runoff development within the present-day permafrost zone at the ongoing human-induced climate warming. A general decrease in surface runoff and its more uniform intra-annual distribution would result in the reduced size of rivers in the middle Siberia, Yakutia, and northeastern Russia.

18. Indications of short-term climate warming at the very end of the Eemian in terrestrial records of Central and Eastern Europe

Geochemical and palynological studies of lacustrine sediments from the standard Eemian-Early Weichselian profiles Grobern, Neumark-Nord and Klinge (Germany, Central Europe) document at least two warming events during the transition from the Eemian to the Early Weichselian. The first pronounced warming phase takes place towards the very end of the Eemian Interglacial during pollen assemblage zone E7, just before the actual transition into the Weichselian Glacial period. Its amplitude is not on the scale of the Eemian climatic optimum, but is comparable with the conditions found in the first Early Weichselian Interstadial (Brorup). An additional event of climatic amelioration was detected within the period of the first Weichselian Stadial (Herning). In the high-resolution Eemian-Early Weichselian limnic sequence from Ples in the Upper Volga region (Russia, Eastern Europe), we also found indications of climate warming events at the very end of the Eemian during pollen assemblage zone E7 and within the Herning Stadial recorded both in palynological and in geochemical records. Furthermore, the δ18O results of the new Greenland ice core presented by the North Greenland Ice Core Project (NGRIP) members record ‘a hitherto unrecognised warm period initiated by an abrupt climate warming about 115 000 years ago (towards the end of the Last Interglacial), before glacial conditions were fully developed’. In this paper, we discuss possible correlations between our terrestrial results in Central and Eastern Europe and their possible connection to the NGRIP record. It appears that both in Central and Eastern Europe and in Greenland, warming phases towards the end of the Last Interglacial preceded the final transition to glacial conditions. Thus, natural warming episodes during the end of the Last Interglacial appear to be a global phenomenon for the Northern Hemisphere.