Pacific Institute of Geography, Far Eastern Branch of the Russian Academy of Sciences

The sizes of major sources and sinks of atmospheric methane (CH 4 ), an important greenhouse gas, are poorly known. CH 4 from north Siberian lakes contributes ∼1.5 teragrams CH 4 year −1 to observed winter increases in atmospheric CH 4 concentration at high northern latitudes. CH 4 emitted from these lakes in winter had a radiocarbon age of 27,200 years and was derived largely from Pleistocene-aged carbon.

Abstract Ongoing climate warming in the Arctic will thaw permafrost and remobilize substantial terrestrial organic carbon (OC) pools. Around a quarter of northern permafrost OC resides in Siberian Yedoma deposits, the oldest form of permafrost carbon. However, our understanding of the degradation and fate of this ancient OC in coastal and fluvial environments still remains rudimentary. Here, we show that ancient dissolved OC (DOC, >21,000 14 C years), the oldest DOC ever reported, is mobilized in stream waters draining Yedoma outcrops. Furthermore, this DOC is highly biolabile: 34 ± 0.8% was lost during a 14 day incubation under dark, oxygenated conditions at ambient river temperatures. Mixtures of Yedoma stream DOC with mainstem river and ocean waters, mimicking in situ mixing processes, also showed high DOC losses (14 days; 17 ± 0.8% to 33 ± 1.0%). This suggests that this exceptionally old DOC is among the most biolabile DOC in any previously reported contemporary river or stream in the Arctic.

Polar ice-core records suggest that an arctic or boreal source was responsible for more than 30% of the large increase in global atmospheric methane (CH4) concentration during deglacial climate warming; however, specific sources of that CH4 are still debated. Here we present an estimate of past CH4 flux during deglaciation from bubbling from thermokarst (thaw) lakes. Based on high rates of CH4 bubbling from contemporary arctic thermokarst lakes, high CH4 production potentials of organic matter from Pleistocene-aged frozen sediments, and estimates of the changing extent of these deposits as thermokarst lakes developed during deglaciation, we find that CH4 bubbling from newly forming thermokarst lakes comprised 33 to 87% of the high-latitude increase in atmospheric methane concentration and, in turn, contributed to the climate warming at the Pleistocene-Holocene transition.

The magnitude of future CO 2 ‐induced climate warming is difficult to predict because of uncertainties in the role of ecosystems and oceans as CO 2 sources and sinks. Siberia has extensive areas (1 × 10 6 km 2 ) of deep (up to 90 m) deposits of organic‐rich frozen loess (wind‐blown silt) that accumulated during the Pleistocene but have not been considered in most global carbon (C) inventories. Similar deposits occur less extensively in Alaska. Recent warming at high latitudes causes this permafrost (permanently frozen ground) to thaw, raising questions about the fate of C in thawing permafrost. Here we show that Siberian loess permafrost contains a large organic C pool (∼450 GT—more than half the quantity in the current atmosphere) that decomposes quickly when thawed, and could act as a positive feedback to climate warming.

We examined the age and structural composition of dissolved organic carbon (DOC) transported in the Kolyma River, two large tributaries and several small upland and lowland streams in 2003. The sampling took place under ice through the winter and included the spring flood period. Radiocarbon measurements of the DOC indicated that the bulk of the annual DOC flux was modern in origin (Δ 14 C > 100‰) and pyrolysis‐gas chromatography/mass spectroscopy techniques showed high concentration of terrestrial lignin monomers consistent with vigorous leaching of surface horizons during the spring thaw. By September 2003 however, little terrestrial lignin was present and the radiocarbon age became significantly older (Δ 14 C < 0‰) indicating that the mechanism of DOC generation transitions from surface to deeper soils or other terrestrial sources of old, previously stabilized C.

About 10,000 years ago, when the million-year-long Pleistocene epoch gave way to the ongoing Holocene epoch, much of the world's ecosystems changed. In what is now northern Siberia, vast numbers of large animals, among them mammoths, woolly rhinoceroses, and yaks, both thrived on and nurtured the steppes that, compared to other northern regions of the world, remained relatively unscathed from the repeated advances and retreats of ice sheets. Even so, the steppes there gave way to silt, dust, and ice-based tundra landscapes dominated in some places by forests and in others by mosses. The large animals disappeared. [Sergey Zimov][1], director of the Northeast Science Station in Cherskii in the Republic of Sakha (Yakutia), argues that climate change may not have been the primary reason behind the demise of this Pleistocene ecosystem. Instead, he says changing hunting practices wiped out the large animals whose absence led to the ecosystem shifts. He and his colleagues now are reintroducing bison, Yakutian horses, and other animals, eventually even tigers, in an attempt to reconstitute the Pleistocene ecosystem. The experiment will test the hypothesis that humans, rather than climate change, caused the ecosystem shift at the beginning of the Holocene. The stabilization of the northern tundra soils that this reconstitution could bring also could prevent the release of vast amount of carbon now sequestered in the Siberian soils but in danger of being released in the warmer times projected for the future. All essays appearing in this series can be found online at [www.sciencemag.org/sciext/globalvoices/][2] * * * [1]: http://www.sciencemag.org/cgi/content/full/308/5723/796 [2]: http://www.sciencemag.org/sciext/globalvoices/

We quantified the relative influence of maternal fidelity to feeding grounds and natal fidelity to breeding grounds on the population structure of humpback whales Megaptera novaeangliae based on an ocean-wide survey of mitochondrial (mt) DNA diversity in the North Pacific. For 2193 biopsy samples collected from whales in 10 feeding regions and 8 breeding regions during the winter and summer of 2004 to 2006, we first used microsatellite genotyping (average, 9.5 loci) to identify replicate samples. From sequences of the mtDNA control region (500 bp) we identified 28 unique haplotypes from 30 variable sites. Haplotype frequencies differed markedly among feeding regions (overall F ST = 0.121, ST = 0.178, p < 0.0001), supporting previous evidence of strong maternal fidelity. Haplotype frequencies also differed markedly among breeding regions (overall F ST = 0.093, ST = 0.106, p < 0.0001), providing evidence of strong natal fidelity. Although sex-biased dispersal was not evident, differentiation of microsatellite allele frequencies was weak compared to differentiation of mtDNA haplotypes, suggesting male-biased gene flow. Feeding and breeding regions showed significant differences in haplotype frequencies, even for regions known to be strongly connected by patterns of individual migration. Thus, the influence of migratory fidelity seems to operate somewhat independently on feeding and breeding grounds over an evolutionary time scale. This results in a complex population structure and the potential to define multiple units to conserve in either seasonal habitat.

Whereas evolutionary inferences derived from present-day DNA sequences are by necessity indirect, ancient DNA sequences provide a direct view of past genetic variants. However, base lesions that accumulate in DNA over time may cause nucleotide misincorporations when ancient DNA sequences are replicated. By repeated amplifications of mitochondrial DNA sequences from a large number of ancient wolf remains, we show that C/G-to-T/A transitions are the predominant type of such misincorporations. Using a massively parallel sequencing method that allows large numbers of single DNA strands to be sequenced, we show that modifications of C, as well as to a lesser extent of G, residues cause such misincorporations. Experiments where oligonucleotides containing modified bases are used as templates in amplification reactions suggest that both of these types of misincorporations can be caused by deamination of the template bases. New DNA sequencing methods in conjunction with knowledge of misincorporation processes have now, in principle, opened the way for the determination of complete genomes from organisms that became extinct during and after the last glaciation.

Transport of dissolved organic carbon (DOC) from land to water is an important but poorly known component of northern carbon cycles. We examined seasonal patterns of arctic river DOC flux, focusing on the largely uncharacterized snowmelt period. High‐intensity sampling of the Kolyma River showed rapid increases in DOC concentration during peak discharge, yielding unique DOC‐water flux relationships compared to summer, fall and winter. Our annual DOC flux estimates were 31% higher than previous estimates for the basin based on few or no snowmelt samples. Synthesis of the sparse literature show that 55% of arctic river DOC flux occurs during snowmelt. Biogeochemical characterizations of DOC in large rivers are usually done after snowmelt runoff, and are thus unrepresentative of most DOC transported to the Arctic Ocean. Finally, the proportion of annual DOC flux at snowmelt is considerably higher than for water, suggesting that cold season production is an important but little known process regulating arctic DOC transport.

The origin of pottery is among the most important questions in Old World archaeology. The author undertakes a critical review of radiocarbon dates associated with the earliest pottery-making and eliminates a number of them where the material or its context are unreliable. Using those that survive this process of ‘chronometric hygiene’, he proposes that food-containers made of burnt clay originated in East Asia in the Late Glacial, c . 13 700-13 300 BP, and appeared in three separate regions, in Japan, China and far eastern Russia, at about the same time.

Abstract We estimated the abundance of humpback whales in the North Pacific by capture‐recapture methods using over 18,000 fluke identification photographs collected in 2004–2006. Our best estimate of abundance was 21,808 (CV = 0.04). We estimated the biases in this value using a simulation model. Births and deaths, which violate the assumption of a closed population, resulted in a bias of +5.2%, exclusion of calves in samples resulted in a bias of −10.5%, failure to achieve random geographic sampling resulted in a bias of −0.4%, and missed matches resulted in a bias of +9.3%. Known sex‐biased sampling favoring males in breeding areas did not add significant bias if both sexes are proportionately sampled in the feeding areas. Our best estimate of abundance was 21,063 after accounting for a net bias of +3.5%. This estimate is likely to be lower than the true abundance due to two additional sources of bias: individual heterogeneity in the probability of being sampled (unquantified) and the likely existence of an unknown and unsampled breeding area (−8.7%). Results confirm that the overall humpback whale population in the North Pacific has continued to increase and is now greater than some prior estimates of prewhaling abundance.

The organic carbon stock in permafrost is of increasing interest in environmental research, because during the late Quaternary a large pool of organic carbon accumulated in the sedimentary deposits of arctic permafrost. Because of its potential to degrade and release organic carbon, the organic‐matter inventory of Yedoma Ice Complex deposits is relevant to current concerns about the effects of global warming. In this context, it is essential to improve the understanding of preserved carbon quantities and characteristics. The paper aims to clarify the Yedoma Ice Complex origin, and to develop an approach for volumetric organic‐matter quantification. Therefore, we analyzed the grain size and the organic‐matter characteristics of the deposits exposed at the stratigraphic key site Duvanny Yar (lower Kolyma River, northeast Siberia). A distinct bimodal grain‐size distribution confirms a polygenetic origin of the frozen sediments from a floodplain environment. The total organic‐carbon content averages 1.5 ± 1.4 wt% while the volumetric organic‐carbon content averages 14 ± 8 kg/m 3 . However, large‐scale extrapolations for Yedoma Ice Complex deposits in general are not reasonable yet because of their rather unclear spatial distribution. We conclude that Yedoma Ice Complex formation at Duvanny Yar was dominated by water‐related (alluvial/fluvial/lacustrine) as well as aeolian processes. The total organic‐carbon content of the studied deposits is low if compared to other profiles, but it is still a significant pool.

The large radiocarbon database now established for Paleolithic sites in Siberia and the Russian Far East can be used to build up a picture of relative population size in these regions. We consider the time period of ca. 46,000 to 12,000 B.P. for which we have assembled and critically studied 437 radiocarbon dates. All dates from individual sites that fall within 1,000 14 C years are considered as a single event and called occupation episode. The results of our analysis show that the number of 14 C dates until ca. 28,000 B.P. is small and increases at ca. 28,000–20,000 B.P, and dates decrease in frequency for the ca. 20,000–16,000 B.P. time range. It is after ca. 16,000 B.P. that we see a substantial rise in the number of 14 C dates. In terms of the relative size of Siberian Paleolithic populations based on the frequency of occupation episodes, population density was small until ca. 36,000 B.P. Subsequently, population size increased gradually at ca. 36,000–16,000 B.P., and the growth rate became almost exponential at ca. 16,000–12,000 B.P. The number of occupations from ca. 20,000 to 18,000 B.P. did not decrease, running counter to arguments that Siberia was completely or considerably depopulated during the Last Glacial Maximum.

The territory of Siberia is of crucial importance for the study of early human dispersal and the peopling of the New World. A Siberian Paleolithic Radiocarbon Database has been compiled. The Database allows us to compile a chronolgical framework for human colonization of Northern Asia. There are 446 14 C dates for 13 Middle and 111 Upper Paleolithic sites older than around 12,000 BP. Seventeen percent of the dates were obtained by the accelerator mass spectrometry (AMS) technique, and the remaining 83% are conventional. From the viewpoint of the spatial distribution of the 14 C-dated sites, the majority of these are located at the Yenisey River Basin, Transbaikal, and the Altai Mountains. The general outline of the Upper Paleolithic colonization of Siberia is given here. The earliest traces of modern human occupation are dated to around 43,000–39,000 BP in the southern part of Siberia. It seems that by around 13,000 BP, almost all of northern Asia, including the extreme northeastern Siberia had been colonized by modern humans. We discuss some controversial problems that have provoked heated debates in current Russian archaeology. Notable among these are the surprisingly early AMS dates for the Early Upper Paleolithic, the age of the Dyuktai culture of Yakutia, the problem of human presence in Siberia at the time of the Last Glacial Maximum (20,000–18,000 BP), and the timing of the initial settling of the Chukchi Peninsula and northeastern Siberia.

Turbic Cryosols (permafrost soils characterized by cryoturbation, i.e., by mixing of soil layers due to freezing and thawing) are widespread across the Arctic, and contain large amounts of poorly decomposed organic material buried in the subsoil. This cryoturbated organic matter exhibits retarded decomposition compared to organic material in the topsoil. Since soil organic matter (SOM) decomposition is known to be tightly linked to N availability, we investigated N transformation rates in different soil horizons of three tundra sites in north-eastern Siberia and Greenland. We measured gross rates of protein depolymerization, N mineralization (ammonification) and nitrification, as well as microbial uptake of amino acids and NH4+ using an array of 15N pool dilution approaches. We found that all sites and horizons were characterized by low N availability, as indicated by low N mineralization compared to protein depolymerization rates (with gross N mineralization accounting on average for 14% of gross protein depolymerization). The proportion of organic N mineralized was significantly higher at the Greenland than at the Siberian sites, suggesting differences in N limitation. The proportion of organic N mineralized, however, did not differ significantly between soil horizons, pointing to a similar N demand of the microbial community of each horizon. In contrast, absolute N transformation rates were significantly lower in cryoturbated than in organic horizons, with cryoturbated horizons reaching not more than 32% of the transformation rates in organic horizons. Our results thus indicate a deceleration of the entire N cycle in cryoturbated soil horizons, especially strongly reduced rates of protein depolymerization (16% of organic horizons) which is considered the rate-limiting step in soil N cycling.

The radiocarbon reservoir age correction values (R) for the Russian Far East are estimated as 370 ± 26 yr for the northwestern Sea of Japan, and 711 ± 46 yr for the southern Kurile Islands.

Recent increases in the seasonal amplitude of atmospheric carbon dioxide (CO2) at high latitudes suggest a widespread biospheric response to high-latitude warming. The seasonal amplitude of net ecosystem carbon exchange by northern Siberian ecosystems is shown to be greater in disturbed than undisturbed sites, due to increased summer influx and increased winter efflux. Increased disturbance could therefore contribute significantly to the amplified seasonal cycle of atmospheric carbon dioxide at high latitudes. Warm temperatures reduced summer carbon influx, suggesting that high-latitude warming, if it occurred, would be unlikely to increase seasonal amplitude of carbon exchange.

Permafrost thaw in the Arctic driven by climate change is mobilizing ancient terrigenous organic carbon (OC) into fluvial networks. Understanding the controls on metabolism of this OC is imperative for assessing its role with respect to climate feedbacks. In this study, we examined the effect of inorganic nutrient supply and dissolved organic matter (DOM) composition on aquatic extracellular enzyme activities (EEAs) in waters draining the Kolyma River Basin (Siberia), including permafrost-derived OC. Reducing the phenolic content of the DOM pool resulted in dramatic increases in hydrolase EEAs (e.g., phosphatase activity increased >28-fold) supporting the idea that high concentrations of polyphenolic compounds in DOM (e.g., plant structural tissues) inhibit enzyme synthesis or activity, limiting OC degradation. EEAs were significantly more responsive to inorganic nutrient additions only after phenolic inhibition was experimentally removed. In controlled mixtures of modern OC and thawed permafrost endmember OC sources, respiration rates per unit dissolved OC were 1.3-1.6 times higher in waters containing ancient carbon, suggesting that permafrost-derived OC was more available for microbial mineralization. In addition, waters containing ancient permafrost-derived OC supported elevated phosphatase and glucosidase activities. Based on these combined results, we propose that both composition and nutrient availability regulate DOM metabolism in Arctic aquatic ecosystems. Our empirical findings are incorporated into a mechanistic conceptual model highlighting two key enzymatic processes in the mineralization of riverine OM: (i) the role of phenol oxidase activity in reducing inhibitory phenolic compounds and (ii) the role of phosphatase in mobilizing organic P. Permafrost-derived DOM degradation was less constrained by this initial 'phenolic-OM' inhibition; thus, informing reports of high biological availability of ancient, permafrost-derived DOM with clear ramifications for its metabolism in fluvial networks and feedbacks to climate.

During the Last Glacial Maximum (LGM), atmospheric CO 2 concentration was 80–100 ppmv lower than in pre‐industrial times. At that time steppe‐tundra was the most extensive biome on Earth. Some authors assume that C storage in that biome was very small, similar to today's deserts, and that the terrestrial carbon (C) reservoir increased at the Pleistocene‐Holocene transition (PHT) by 400–1300 Gt. To estimate C storage in the entire steppe‐tundra biome we used data of C storage in soils of this biome that persisted in permafrost of Siberia and Alaska and developed a model that describes C accumulation in soils and in permafrost. The model shows a slow but consistent C increase in soil when permafrost appears. At the PHT, C‐rich frozen loess of Europe and South of Siberia thawed and lost most of its carbon. Soil carbon decreases as tundra‐steppe changes to forest, steppes and tundra. As a result, over 1000 Gt C was released to the atmosphere, oceans, and other terrestrial ecosystems. The model results also show that restoring the tundra‐steppe ecosystem would enhance soil C storage, while providing other important ecosystem services.

Pleistocene Yedoma permafrost contains nearly a third of all organic matter (OM) stored in circum-arctic&#13;\npermafrost and is characterized by the presence of massive ice wedges. Due to its rapid formation by&#13;\nsediment accumulation and subsequent frozen storage, Yedoma OM is relatively well preserved and highly&#13;\nbiologically available (biolabile) upon thaw. A better understanding of the processes regulating Yedoma&#13;\ndegradation is important to improve estimates of the response and magnitude of permafrost carbon&#13;\nfeedbacks to climate warming. In this study, we examine the composition of ice wedges and the influence of&#13;\nice wedge thaw on the biolability of Yedoma OM. Incubation assays were used to assess OM biolability,&#13;\nfluorescence spectroscopy to characterize the OM composition, and potential enzyme activity rates to&#13;\nexamine the controls and regulation of OM degradation.We show that increasing amounts of ice wedge melt&#13;\nwater in Yedoma-leached incubations enhanced the loss of dissolved OM over time. This may be attributed&#13;\nto the presence of low-molecular weight compounds and low initial phenolic content in the OM of ice&#13;\nwedges, providing a readily available substrate that promotes the degradation of Yedoma OC. The physical&#13;\nvulnerability of ice wedges upon thaw (causing irreversible collapse), combined with the composition of ice&#13;\nwedge-engrained OM (co-metabolizing old OM), underlines the particularly strong potential of Yedoma to&#13;\ngenerate a positive feedback to climate warming relative to other forms of non-ice wedge permafrost.