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1.	Blunden, Jessica, et al. (author) State of the Climate in 2012 2013 In: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 94:8, s. S1-S258 Journal article (peer-reviewed)abstract For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.
2.	Achberger, Christine, 1968, et al. (author) State of the Climate in 2011 2012 In: Bulletin of the American Meteorological Society. - 0003-0007. ; 93:7 Journal article (peer-reviewed)abstract Large-scale climate patterns influenced temperature and weather patterns around the globe in 2011. In particular, a moderate-to-strong La Nina at the beginning of the year dissipated during boreal spring but reemerged during fall. The phenomenon contributed to historical droughts in East Africa, the southern United States, and northern Mexico, as well the wettest two-year period (2010-11) on record for Australia, particularly remarkable as this follows a decade-long dry period. Precipitation patterns in South America were also influenced by La Nina. Heavy rain in Rio de Janeiro in January triggered the country's worst floods and landslides in Brazil's history. The 2011 combined average temperature across global land and ocean surfaces was the coolest since 2008, but was also among the 15 warmest years on record and above the 1981-2010 average. The global sea surface temperature cooled by 0.1 degrees C from 2010 to 2011, associated with cooling influences of La Nina. Global integrals of upper ocean heat content for 2011 were higher than for all prior years, demonstrating the Earth's dominant role of the oceans in the Earth's energy budget. In the upper atmosphere, tropical stratospheric temperatures were anomalously warm, while polar temperatures were anomalously cold. This led to large springtime stratospheric ozone reductions in polar latitudes in both hemispheres. Ozone concentrations in the Arctic stratosphere during March were the lowest for that period since satellite records began in 1979. An extensive, deep, and persistent ozone hole over the Antarctic in September indicates that the recovery to pre-1980 conditions is proceeding very slowly. Atmospheric carbon dioxide concentrations increased by 2.10 ppm in 2011, and exceeded 390 ppm for the first time since instrumental records began. Other greenhouse gases also continued to rise in concentration and the combined effect now represents a 30% increase in radiative forcing over a 1990 baseline. Most ozone depleting substances continued to fall. The global net ocean carbon dioxide uptake for the 2010 transition period from El Nino to La Nina, the most recent period for which analyzed data are available, was estimated to be 1.30 Pg C yr(-1), almost 12% below the 29-year long-term average. Relative to the long-term trend, global sea level dropped noticeably in mid-2010 and reached a local minimum in 2011. The drop has been linked to the La Nina conditions that prevailed throughout much of 2010-11. Global sea level increased sharply during the second half of 2011. Global tropical cyclone activity during 2011 was well-below average, with a total of 74 storms compared with the 1981-2010 average of 89. Similar to 2010, the North Atlantic was the only basin that experienced above-normal activity. For the first year since the widespread introduction of the Dvorak intensity-estimation method in the 1980s, only three tropical cyclones reached Category 5 intensity level-all in the Northwest Pacific basin. The Arctic continued to warm at about twice the rate compared with lower latitudes. Below-normal summer snowfall, a decreasing trend in surface albedo, and above-average surface and upper air temperatures resulted in a continued pattern of extreme surface melting, and net snow and ice loss on the Greenland ice sheet. Warmer-than-normal temperatures over the Eurasian Arctic in spring resulted in a new record-low June snow cover extent and spring snow cover duration in this region. In the Canadian Arctic, the mass loss from glaciers and ice caps was the greatest since GRACE measurements began in 2002, continuing a negative trend that began in 1987. New record high temperatures occurred at 20 m below the land surface at all permafrost observatories on the North Slope of Alaska, where measurements began in the late 1970s. Arctic sea ice extent in September 2011 was the second-lowest on record, while the extent of old ice (four and five years) reached a new record minimum that was just 19% of normal. On the opposite pole, austral winter and spring temperatures were more than 3 degrees C above normal over much of the Antarctic continent. However, winter temperatures were below normal in the northern Antarctic Peninsula, which continued the downward trend there during the last 15 years. In summer, an all-time record high temperature of -12.3 degrees C was set at the South Pole station on 25 December, exceeding the previous record by more than a full degree. Antarctic sea ice extent anomalies increased steadily through much of the year, from briefly setting a record low in April, to well above average in December. The latter trend reflects the dispersive effects of low pressure on sea ice and the generally cool conditions around the Antarctic perimeter.
3.	Pipko, I.I., et al. (author) Interannual variability of air-sea CO2 fluxes and carbon system in the East Siberian Sea 2011 In: Biogeosciences. ; 8, s. 1987-2007 Journal article (peer-reviewed)abstract Over the past couple of decades it has become apparent that air-land-sea interactions in the Arctic have a substantial impact on the composition of the overlying atmosphere (ACIA, 2004). The Arctic Ocean is small (only ~4 % of the total World Ocean), but it is surrounded by offshore and onshore permafrost which is thawing at increasing rates under warming conditions, releasing carbon dioxide (CO2) into the water and atmosphere. The Arctic Ocean shelf where the most intensive biogeochemical processes have occurred occupies 1/3 of the ocean. The East Siberian Sea (ESS) shelf is the shallowest and widest shelf among the Arctic seas, and the least studied. The objective of this study was to highlight the importance of different factors that impact the carbon system (CS) as well as the CO2 flux dynamics in the ESS. CS variables were measured in the ESS in September 2003 and, 2004 and in late August–September 2008. It was shown that the western part of the ESS represents a river- and coastal-erosion-dominated heterotrophic ocean margin that is a source for atmospheric CO2. The eastern part of the ESS is a Pacific-water-dominated autotrophic area, which acts as a sink for atmospheric CO2. Our results indicate that the year-to-year dynamics of the partial pressure of CO2 in the surface water as well as the air-sea flux of CO2 varies substantially. In one year the ESS shelf was mainly heterotrophic and served as a moderate summertime source of CO2 (year 2004). In another year gross primary production exceeded community respiration in a relatively large part of the ESS and the ESS shelf was only a weak source of CO2 into the atmosphere (year 2008). It was shown that many factors impact the CS and CO2 flux dynamics (such as river runoff, coastal erosion, primary production/respiration, etc.), but they were mainly determined by the interplay and distribution of water masses that are basically influenced by the atmospheric circulation. In this contribution the air-sea CO2 fluxes were evaluated in the ESS based on measured CS characteristics, and summertime fluxes were estimated. It was shown that the total ESS shelf is a net source of CO2 for the atmosphere in a range of 0.4 × 1012 to 2.3 × 1012 g C.
4.	Semiletov, I. P., et al. (author) Carbon transport by the Lena River from its headwaters to the Arctic Ocean, with emphasis on fluvial input of terrestrial particulate organic carbon vs. carbon transport by coastal erosion 2011 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:9, s. 2407-2426 Journal article (peer-reviewed)abstract The Lena River integrates biogeochemical signals from its vast drainage basin, and the integrated signal reaches far out over the Arctic Ocean. Transformation of riverine organic carbon (OC) into mineral carbon, and mineral carbon into the organic form in the Lena River watershed, can be considered to be quasi-steady-state processes. An increase in Lena discharge exerts opposite effects on total organic (TOC) and total inorganic (TCO(2)) carbon: TOC concentration increases, while TCO(2) concentration decreases. Significant inter-annual variability in mean values of TCO(2), TOC, and their sum (total carbon, TC) has been found. This variability is determined by changes in land hydrology which cause differences in the Lena River discharge. There is a negative correlation in the Lena River between TC in September and its mean discharge in August; a time shift of about one month is required for water to travel from Yakutsk to the Laptev Sea. Total carbon entering the sea with the Lena discharge is estimated to be almost 10 Tg C yr(-1). The annual Lena River discharge of particulate organic carbon (POC) can be as high as 0.38 Tg (moderate to high estimate). If we instead accept Lisytsin's (1994) statement that 85-95% of total particulate matter (PM) (and POC) precipitates on the marginal filter, then only about 0.03-0.04 Tg of Lena River POC reaches the Laptev Sea. The Lena's POC export would then be two orders of magnitude less than the annual input of eroded terrestrial carbon onto the shelf of the Laptev and East Siberian seas, which is estimated to be about 4 Tg. Observations support the hypothesis of a dominant role for coastal erosion (Semiletov, 1999a, b) in East Siberian Arctic Shelf (ESAS) sedimentation and the dynamics of the carbon/carbonate system. The Lena River is characterized by relatively high concentrations of the primary greenhouse gases, dissolved carbon dioxide (CO(2)) and methane (CH(4)). During all seasons the river is supersaturated in CO(2) compared to the atmosphere, by up to 1.5-2 fold in summer, and 4-5 fold in winter. This results in a significant CO(2) supersaturation in the adjacent coastal sea. Localized areas of dissolved CH(4) along the Lena River and in the Lena delta channels may reach 100 nM, but the CH(4) concentration decreases to 5-20nM towards the sea, which suggests that riverborne export of CH(4) plays but a minor role in determining the ESAS CH(4) budget in coastal waters. Instead, the seabed appears to be the source that provides most of the CH(4) to the Arctic Ocean.
5.	Anderson, Leif G, 1951, et al. (author) East Siberian Sea, an Arctic region of very high biogeochemical activity 2011 In: Biogeosciences. ; 8, s. 1745-1754 Journal article (peer-reviewed)abstract Shelf seas are among the most active biogeochemical marine environments and the East Siberian Sea is a prime example. This sea is supplied by seawater from both the Atlantic and Pacific Oceans and has a substantial input of river runoff. All of these waters contribute chemical constituents, dissolved and particulate, but of different signatures. Sea ice formation during the winter season and melting in the summer has a major impact on physical as well as biogeochemical conditions. The internal circulation and water mass distribution is significantly influenced by the atmospheric pressure field. The western region is dominated by input of river runoff from the Laptev Sea and an extensive input of terrestrial organic matter. The microbial decay of this organic matter produces carbon dioxide (CO2) that oversaturates all waters from the surface to bottom relative to atmospheric level, even when primary production, inferred from low surface water nutrients, has occurred. The eastern surface waters were under-saturated with respect to CO2 illustrating the dominance of marine primary production. The drawdown of dissolved inorganic carbon equals a primary production of ~0.8 ± 2 mol C m−2, which when multiplied by half the area of the East Siberian Sea, ~500 000 km2, results in an annual primary production of 0.4 (± 1) × 1012 mol C or ~4 (± 10) × 1012 gC. Microbial decay occurs through much of the water column, but dominates at the sediment interface where the majority of organic matter ends up, thus more of the decay products are recycled to the bottom water. High nutrient concentrations and fugacity of CO2 and low oxygen and pH were observed in the bottom waters. Another signature of organic matter decomposition, methane (CH4), was observed in very high but variable concentrations. This is due to its seabed sources of glacial origin or modern production from ancient organic matter, becoming available due to sub-sea permafrost thaw and formation of so-called taliks. The decay of organic matter to CO2 as well as oxidation of CH4 to CO2 contribute to a natural ocean acidification making the saturation state of calcium carbonate low, resulting in under-saturation of all the bottom waters with respect to aragonite and large areas of under-saturation down to 50 % with respect to calcite. Hence, conditions for calcifying organisms are very unfavorable.
6.	Clement Kinney, J., et al. (author) On the circulation, water mass distribution, and nutrient concentrations of the western Chukchi Sea 2022 In: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 18:1, s. 29-49 Journal article (peer-reviewed)abstract Substantial amounts of nutrients and carbon enter the Arctic Ocean from the Pacific Ocean through the Bering Strait, distributed over three main pathways. Water with low salinities and nutrient concentrations takes an eastern route along the Alaskan coast, as Alaskan Coastal Water. A central pathway exhibits intermediate salinity and nutrient concentrations, while the most nutrient-rich water enters the Bering Strait on its western side. Towards the Arctic Ocean, the flow of these water masses is subject to strong topographic steering within the Chukchi Sea with volume transport modulated by the wind field. In this contribution, we use data from several sections crossing Herald Canyon collected in 2008 and 2014 together with numerical modelling to investigate the circulation and transport in the western part of the Chukchi Sea. We find that a substantial fraction of water from the Chukchi Sea enters the East Siberian Sea south of Wrangel Island and circulates in an anticyclonic direction around the island. This water then contributes to the high-nutrient waters of Herald Canyon. The bottom of the canyon has the highest nutrient concentrations, likely as a result of addition from the degradation of organic matter at the sediment surface in the East Siberian Sea. The flux of nutrients (nitrate, phosphate, and silicate) and dissolved inorganic carbon in Bering Summer Water and Winter Water is computed by combining hydrographic and nutrient observations with geostrophic transport referenced to lowered acoustic Doppler current profiler (LADCP) and surface drift data. Even if there are some general similarities between the years, there are differences in both the temperature-salinity and nutrient characteristics. To assess these differences, and also to get a wider temporal and spatial view, numerical modelling results are applied. According to model results, high-frequency variability dominates the flow in Herald Canyon. This leads us to conclude that this region needs to be monitored over a longer time frame to deduce the temporal variability and potential trends. © 2022 Jaclyn Clement Kinney et al.
7.	Feng, X., et al. (author) Multi-molecular tracers of terrestrial carbon transfer across the pan-Arctic : comparison of hydrolyzable components with plant wax lipids and lignin phenols 2015 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:15, s. 4841-4860 Journal article (peer-reviewed)abstract Hydrolyzable organic carbon (OC) comprises a significant component of sedimentary particulate matter transferred from land into oceans via rivers. Its abundance and nature are however not well studied in Arctic river systems, and yet may represent an important pool of carbon whose fate remains unclear in the context of mobilization and related processes associated with a changing climate. Here, we examine the molecular composition and source of hydrolyzable compounds isolated from sedimentary particles derived from nine rivers across the pan-Arctic. Bound fatty acids (b-FAs), hydroxy FAs, n-alkane-alpha,omega-dioic acids (DAs) and phenols were the major components released upon hydrolysis of these sediments. Among them, b-FAs received considerable inputs from bacterial and/or algal sources, whereas omega-hydroxy FAs, mid-chain substituted acids, DAs, and hydrolyzable phenols were mainly derived from cutin and suberin of higher plants. We further compared the distribution and fate of suberin- and cutin-derived compounds with those of other terrestrial biomarkers (plant wax lipids and lignin phenols) from the same Arctic river sedimentary particles and conducted a benchmark assessment of several biomarker-based indicators of OC source and extent of degradation. While suberin-specific biomarkers were positively correlated with plant-derived high-molecular-weight (HMW) FAs, lignin phenols were correlated with cutin-derived compounds. These correlations suggest that, similar to leaf-derived cutin, lignin was mainly derived from litter and surface soil horizons, whereas suberin and HMW FAs incorporated significant inputs from belowground sources (roots and deeper soil). This conclusion is supported by the negative correlation between lignin phenols and the ratio of suberin-to-cutin biomarkers. Furthermore, the molecular composition of investigated biomarkers differed between Eurasian and North American Arctic rivers: while lignin dominated in the terrestrial OC of Eurasian river sediments, hydrolyzable OC represented a much larger fraction in the sedimentary particles from Colville River. Hence, studies exclusively focusing on either plant wax lipids or lignin phenols will not be able to fully unravel the mobilization and fate of bound OC in Arctic rivers. More comprehensive, multi-molecular investigations are needed to better constrain the land-ocean transfer of carbon in the changing Arctic, including further research on the degradation and transfer of both free and bound components in Arctic river sediments.
8.	Grinko, A. A., et al. (author) Sediment Organic Matter in Areas of Intense Methane Release in the Laptev Sea : Characteristics of Molecular Composition 2020 In: Russian Geology and Geophysics. - 1068-7971 .- 1878-030X. ; 61:4, s. 456-477 Journal article (peer-reviewed)abstract We present results of study of the molecular composition of organic matter (OM) in the bottom sediments of the Laptev Sea by gas chromatography-mass spectrometry, isotope gas chromatography-mass spectrometry, and Rock-Eval pyrolytic analysis. The OM of all collected sediment samples shows a significant terrigenous contribution. Compounds that are biomarkers of methanotrophic microorganisms arc also found. A positive correlation between the contents of the studied biomarkers and the contents of pelite and total organic carbon is observed at the sites with documented intense methane bubbling. For example, the average content of C30 hopenes at the methane stations is twice higher than that at the background ones. The average content of C32 alpha beta-hopanes in sediment samples from the methane seepage area is 1.5 tunes higher than that at the background stations. We suggest that the increased C30 alpha beta-hopane content (similar to 1.5 times higher within the methane seepage area) and the decreased more index relative to the C31 hopane index are due to the inflow of OM of petroleum origin. The presence of biphenyl in sediments indicates its petroleum origin, which supports our assumption of the migratory nature of petroleum hydrocarbons in the methane seepage area. Triterpenoids found in the sediment OM indicate diagenetic bacterial transformation of OM in the methane seepage areas, which shows that methane has been released for a long time. We assume the intense activity of the consortium of methanotrophs and sulfate reducers in the methane seepage areas.
9.	Ingri, J., et al. (author) Fractionation of iron isotopes during estuarine mixing in Ob, Yenisey and Lena freshwater plumes 2009 In: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 73:13 Journal article (other academic/artistic)
10.	Kosmach, D. A., et al. (author) Methane in the surface waters of Northern Eurasian marginal seas 2015 In: Doklady. Chemistry. - 0012-5008 .- 1608-3113. ; 465, s. 281-285 Journal article (peer-reviewed)abstract More than 12 000 measurements of the dissolved methane (CH4) concentrations in the surface waters of Northern Eurasian marginal seas (Barents, Kara, Laptev, Chukchi, and Bering Seas, Sea of Okhotsk, and Sea of Japan) during two marine expeditions (September-October 2011 and 2012) show that all seas are CH4 source to the atmosphere, but the Laptev and East Siberian seas demonstrate the strongest signal.
11.	Lobkovsky, L. I., et al. (author) Recent geological-geomorphological processes on the east Arctic shelf : Results of the expedition of the icebreaker Oden in 2014 2015 In: Oceanology. - 0001-4370 .- 1531-8508. ; 55:6, s. 926-929 Journal article (peer-reviewed)abstract Results obtained by the International Arctic marine expedition (SWERUS-C3) in June to October of 2014, using advanced seismoacoustic equipment, confirmed the wide distribution of potentially hazardous exogenic geological-geomorphological natural processes on the eastern Arctic shelf of Russia. In Arctic seas, serious hazards are represented by ice exaration and its consequences must be taken into consideration when developing oil and gas fields on the shelf. Many areas with anomalous gas saturation of sediments and gas seeps established in the region under consideration may represent global hazard: further increases in methane emissions may represent global risks. The minimization of these and other geological risks in constructing different technogenic objects on the shelf should be a first-priority task in the economic development of the Arctic region.
12.	Vonk, J. E., et al. (author) Activation of old carbon by erosion of coastal and subsea permafrost in Arctic Siberia 2012 In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 489:7414, s. 137-140 Journal article (peer-reviewed)abstract The future trajectory of greenhouse gas concentrations depends on interactions between climate and the biogeosphere(1,2). Thawing of Arctic permafrost could release significant amounts of carbon into the atmosphere in this century(3). Ancient Ice Complex deposits outcropping along the similar to 7,000-kilometre-long coastline of the East Siberian Arctic Shelf (ESAS)(4,5), and associated shallow subsea permafrost(6,7), are two large pools of permafrost carbon(8), yet their vulnerabilities towards thawing and decomposition are largely unknown(9-11). Recent Arctic warming is stronger than has been predicted by several degrees, and is particularly pronounced over the coastal ESAS region(12,13). There is thus a pressing need to improve our understanding of the links between permafrost carbon and climate in this relatively inaccessible region. Here we show that extensive release of carbon from these Ice Complex deposits dominates (57 +/- 2 per cent) the sedimentary carbon budget of the ESAS, the world's largest continental shelf, overwhelming the marine and topsoil terrestrial components. Inverse modelling of the dual-carbon isotope composition of organic carbon accumulating in ESAS surface sediments, using Monte Carlo simulations to account for uncertainties, suggests that 44 +/- 10 teragrams of old carbon is activated annually from Ice Complex permafrost, an order of magnitude more than has been suggested by previous studies(14). We estimate that about two-thirds (66 +/- 16 per cent) of this old carbon escapes to the atmosphere as carbon dioxide, with the remainder being re-buried in shelf sediments. Thermal collapse and erosion of these carbon-rich Pleistocene coastline and seafloor deposits may accelerate with Arctic amplification of climate warming(2,13).
13.	Anderson, Leif G, 1951, et al. (author) Export of calcium carbonate corrosive waters from the East Siberian Sea 2017 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14:7, s. 1811-1823 Journal article (peer-reviewed)abstract The Siberian shelf seas are areas of extensive biogeochemical transformation of organic matter, both of marine and terrestrial origin. This in combination with brine production from sea ice formation results in a cold bottom water of relative high salinity and partial pressure of carbon dioxide (pCO(2)). Data from the SWERUS-C3 expedition compiled on the icebreaker Oden in July to September 2014 show the distribution of such waters at the outer shelf, as well as their export into the deep central Arctic basins. Very high pCO(2) water, up to similar to 1000 mu atm, was observed associated with high nutrients and low oxygen concentrations. Consequently, this water had low saturation state with respect to calcium carbonate down to less than 0.8 for calcite and 0.5 for aragonite. Waters undersaturated in aragonite were also observed in the surface in waters at equilibrium with atmospheric CO2; however, at these conditions the cause of undersaturation was low salinity from river runoff and/or sea ice melt. The calcium carbonate corrosive water was observed all along the continental margin and well out into the deep Makarov and Canada basins at a depth from about 50 m depth in the west to about 150 m in the east. These waters of low aragonite saturation state are traced in historic data to the Canada Basin and in the waters flowing out of the Arctic Ocean north of Greenland and in the western Fram Strait, thus potentially impacting the marine life in the North Atlantic Ocean.
14.	Anderson, Leif G, 1951, et al. (author) Out-gassing of CO2 from Siberian Shelf seas by terrestrial organic matter decomposition 2009 In: Geophys. Res. Lett.. ; 36 Journal article (peer-reviewed)abstract The Siberian shelf seas cover large shallow areas that receive substantial amounts of river discharge. The river runoff contributes nutrients that promote marine primary production, but also dissolved and particulate organic matter. The coastal regions are built up of organic matter in permafrost that thaws and result in coastal erosion and addition of organic matter to the sea. Hence there are multiple sources of organic matter that through microbial decomposition result in high partial pressures of CO2 in the shelf seas. By evaluating data collected from the Laptev and East Siberian Seas in the summer of 2008 we compute an excess of DIC equal to 10 · 1012 g C that is expected to be outgassed to the atmosphere and suggest that this excess mainly is caused by terrestrial organic matter decomposition.
15.	Anderson, Leif G, 1951, et al. (author) Shelf-Basin interaction along the East Siberian Sea 2017 In: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 13:2, s. 349-363 Journal article (peer-reviewed)abstract Extensive biogeochemical transformation of organic matter takes place in the shallow continental shelf seas of Siberia. This, in combination with brine production from sea-ice formation, results in cold bottom waters with relatively high salinity and nutrient concentrations, as well as low oxygen and pH levels. Data from the SWERUS-C3 expedition with icebreaker Oden, from July to September 2014, show the distribution of such nutrient-rich, cold bottom waters along the continental margin from about 140 to 180 degrees E. The water with maximum nutrient concentration, classically named the upper halocline, is absent over the Lomonosov Ridge at 140 degrees E, while it appears in the Makarov Basin at 150 degrees E and intensifies further eastwards. At the intercept between the Mendeleev Ridge and the East Siberian continental shelf slope, the nutrient maximum is still intense, but distributed across a larger depth interval. The nutrient-rich water is found here at salinities of up to similar to 34.5, i.e. in the water classically named lower halocline. East of 170 degrees E transient tracers show significantly less ventilated waters below about 150 m water depth. This likely results from a local isolation of waters over the Chukchi Abyssal Plain as the boundary current from the west is steered away from this area by the bathymetry of the Mendeleev Ridge. The water with salinities of similar to 34.5 has high nutrients and low oxygen concentrations as well as low pH, typically indicating decay of organic matter. A deficit in nitrate relative to phosphate suggests that this process partly occurs under hypoxia. We conclude that the high nutrient water with salinity similar to 34.5 are formed on the shelf slope in the Mendeleev Ridge region from interior basin water that is trapped for enough time to attain its signature through interaction with the sediment.
16.	Andersson, P.S., et al. (author) The importance of river water inflow and shelf sediment-sea water exchange in the East Siberian Sea for the Nd isotopic composition of Arctic Ocean water 2009 In: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 73:13, Suppl. 1, s. A41- Journal article (other academic/artistic)abstract With data generated from cruises to the Canada Basin in 2000, to the Eurasian and Central Arctic Ocean basins in 2001, to the Fram Strait in 2002 and to the Chuckchi Sea in 2005 we now have a good general view of the distribution and isotopic composition of Nd (εNd) in the Arctic Ocean [1, 2]. The restricted Arctic Ocean basin is surrounded by large continental shelves, covering more than 50% of its total area.Distinct from other oceans, with surface water Nd depletion, there is throughout the Arctic a pattern of high Nd concentrations, up to 58pM, at the surface that gradually diminish with depth to 15-18pM in the deep waters. A range of isotopic variations across the Arctic and within individual depth profiles reflects the different sources of waters. The dominant source of water and Nd is the Atlantic (εNd= -10.7). Radiogenic isotope Nd signatures can be traced in Pacific water flowing into the Canada Basin and further into the Eurasian Basin (up to εNd= -6.5). The variation of εNd and concentration in the Arctic Ocean suggest that Nd input from rivers and shelf sediments is also of great importance.Improving our understanding of the vast Siberian Shelves influence on Nd and trace element behaviour in the Arctic Ocean was one of the main objectives of the International Siberian Shelf Study 2008 (ISSS-08). The ISSS-08 cruise recovered filtered water (<0.2µm), particles and sediments from the Laptev and East Siberian Seas as well as estuarine and river water from Lena, Indigirka and Kolyma. Crucial processes, including loss of river water Nd in the estuarine region and shelf sediment-sea water exchange will be discussed in terms of controlling the Nd concentration and isotopic composition of sea water.[1] Andersson et al. (2008) GCA 72, 2854-2867. [2] Porcelli et al. (2009, in press) GCA. (2009, in press)
17.	Andersson, P.S., et al. (author) The importance of river water inflow and shelf sediment-sea water exchange in the East Siberian Sea for the Nd isotopic composition of Arctic Ocean water 2009 In: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 73:13 Journal article (other academic/artistic)
18.	Bröder, Lisa, et al. (author) Historical records of organic matter supply and degradation status in the East Siberian Sea 2016 In: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 91, s. 16-30 Journal article (peer-reviewed)abstract Destabilization and degradation of permafrost carbon in the Arctic regions could constitute a positive feedback to climate change. A better understanding of its fate upon discharge to the Arctic shelf is therefore needed. In this study, bulk carbon isotopes as well as terrigenous and marine biomarkers were used to construct two centennial records in the East Siberian Sea. Differences in topsoil and Pleistocene Ice Complex Deposit permafrost concentrations, modeled using delta C-13 and Delta C-14, were larger between inner and outer shelf than the changes over time. Similarly, lignin-derived phenol and cutin acid concentrations differed by a factor of ten between the two stations, but did not change significantly over time, consistent with the dual-carbon isotope model. High molecular weight (HMW) n-alkane and n-alkanoic acid concentrations displayed a smaller difference between the two stations (factor of 3-6). By contrast, the fraction for marine OC drastically decreased during burial with a half-life of 19-27 years. Vegetation and degradation proxies suggested supply of highly degraded gymnosperm wood tissues. Lipid Carbon Preference Index (CPI) values indicated more extensively degraded HMW n-alkanes on the outer shelf with no change over time, whereas n-alkanoic acids appeared to be less degraded toward the core top with no large differences between the stations. Taken together, our results show larger across-shelf changes than down-core trends. Further investigation is required to establish whether the observed spatial differences are due to different sources for the two depositional settings or, alternatively, a consequence of hydrodynamic sorting combined with selective degradation during cross-shelf transport.
19.	Charkin, A. N., et al. (author) Seasonal and interannual variability of sedimentation and organic matter distribution in the Buor-Khaya Gulf : the primary recipient of input from Lena River and coastal erosion in the southeast Laptev Sea 2011 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:9, s. 2581-2594 Journal article (peer-reviewed)abstract Climate warming is amplified in the land-sea system of the East Siberian Arctic, which also holds large pools of vulnerable carbon in permafrost. This coastal area is strongly influenced by sediment and carbon transport from both its large rivers and extensive erosion of Pleistocene permafrost along its coastline. This study is investigating the coastal fate of the sediment and organic carbon delivered to the Buor-Khaya Gulf, which is the first recipient of the overwhelming fluvial discharge from the Lena River and is additionally receiving large input from extensive erosion of the coastal ice-complex (permafrost a. k.a. Yedoma; loess soil with high organic carbon content). Both water column suspended particulate matter (SPM) and surface sediments were sampled at about 250 oceanographic stations in the Gulf in this multi-year effort, including one winter campaign, and analyzed for the distribution and sorting of sediment size, organic carbon content, and stable carbon isotope signals. The composition of the surface sediment suggests an overwhelmingly terrestrial contribution from both river and coastal erosion. The objective of this paper is to improve our understanding of the seasonal (i.e., winter vs summer) and interannual variability of these coastal sedimentation processes and the dynamics of organic carbon (OC) distribution in both the water column SPM and the surface sediments of the Buor-Khaya Gulf. Based on data collected during several years in the period 2000-2008, two different sedimentation regimes were revealed for the Buor-Khaya Gulf, the relative importance of each at a given time depend on hydrometeorological conditions, the Lena River water discharge and sea-ice regime: Type 1 erosion-accumulation and Type 2 accumulation. The Type 1 erosion-accumulation sedimentation regime is typical (2000-2006) for the ice-free period of the year (here considered in detail for August 2005). Under such conditions terrigenous sources of SPM and particulate organic carbon (POC) stem predominantly from river discharge, thermal erosion of coastal ice-complex and remobilized bottom sediments. The Type 2 accumulation sedimentation regime develops under ice-covered conditions, and only occasionally during the ice-free period (August 2008). In Type 2 winter, combined terrigenous and marine-biogenic SPM and POC sources are dominating due to relatively low overall terrigenous input (April 2007). In Type 2 summer, river alluvium becomes the major SPM and POC source (August 2008). The water column SPM and POC loadings vary by more than a factor of two between the two regimes. This study underscores the necessity of multi-year investigations to better understand the functioning of the primary recipient of terrestrially expulsed matter in the East Siberian Arctic.
20.	Chuvilin, E., et al. (author) In-situ temperatures and thermal properties of the East Siberian Arctic shelf sediments : Key input for understanding the dynamics of subsea permafrost 2022 In: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 138 Journal article (peer-reviewed)abstract Significant reserves of methane (CH4) are held in the Arctic shelf, but the release of CH4 to the overlying ocean and, subsequently, to the atmosphere has been believed to be restricted by impermeable subsea permafrost, which has sealed the upper sediment layers for thousands of years. Our studies demonstrate progressive degradation of subsea permafrost which controls the scales of CH4 release from the sediment into the water-atmospheric system. Thus, new knowledge about the thermal state of subsea permafrost is crucial for better understanding of the permafrost -hydrate system and associated CH4 release from the East Siberian Arctic Shelf (ESAS) – the broadest and shallowest shelf in the World Ocean, which contains about 80% of subsea permafrost and giant pools of hydrates. Meanwhile, the ESAS, still presents large knowledge gaps in many aspects, especially with respect to subsea permafrost distribution and physical properties of bottom sediments. New field data show that the ESAS has an unfrozen (ice-free) upper sediment layer, which in-situ temperature is −1.0 to −1.8 °C and 0.6оС above the freezing point. On one hand, these cold temperature patterns may be related to the presence of subsea permafrost, which currently primarily occurs in the part of the ESAS that is shallower than 100 m, while ice-bearing sediments may also exist locally under deeper water in the Laptev Sea. On the other hand, the negative bottom sediment temperatures of −1.8 °C measured on the Laptev Sea continental slope sediments underlying water columns as deep as down to 330 m may result from dissociation of gas hydrates or possibly from dense water cascading down from the shelf. In contrast, data collected on recent expeditions in the northern Laptev shelf, zones of warmer bottom temperatures are coinciding with methane seeps, likely induced by seismic and tectonic activity in the area. These warm temperatures are not seen in the East Siberian Sea area, not even in areas of methane seeps, yet with little seismic activity.The thermal conductivity and heat capacity of bottom sediments recorded in the database of thermal parameters for the ESAS areas mainly depend on their lithification degree (density or porosity), moisture content, and particle size distribution. The thermal conductivity and heat capacity average about 1.0 W/(m·K) and 2900 kJ/(m3·K), with ±20% and ±10% variance, respectively, in all sampled Arctic sediments to a sub-bottom interval of 0–0.5 m.
21.	Cooke, M.P., et al. (author) Bacteriohopanepolyol biomarker composition of organic matter exported to the Arctic Ocean by seven of the major Arctic rivers 2009 In: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 40:11, s. 1151-1159 Journal article (peer-reviewed)abstract Bacteriohopanepolyols (BHPs) are a diverse group of membrane lipids produced by a wide variety of bacteria and can be used as molecular biomarkers for bacterial processes and populations in both modern and ancient environments. A group of BHPs, including adenosylhopane and structurally related compounds, have been identified as being specific to soils, enabling the transport of terrestrial organic matter (terrOM) to the marine realm to be monitored. Estuary surface sediment samples were obtained from the five Great Russian Arctic Rivers (GRARs: Ob, Yenisey, Lena, Indigirka and Kolyma) and river sediments were obtained from two North American Rivers (Yukon and Mackenzie). Analysis of the BHP signatures, using high performance liquid chromatography-tandem mass spectrometry (HPLC-MSn), indicated the presence of 15 different BHPs originating from a variety of different bacteria, as well as a significant presence of terrestrially derived OM. Total BHP abundance and the contribution of the "soil-marker" BHPs to the total BHP pool increased eastwards among the GRAR sediments. This suggests increasing terrestrial OM or increased preservation of OM as a result of shorter periods of permafrost thawing. The North American rivers showed greatly differing BHP levels between the Yukon and Mackenzie rivers, with a greater BHP input and thus a relatively higher soil OM contribution from the Yukon. The Indigirka River basin in the eastern Siberian Arctic appeared to be the epicentre in the pan-Arctic BHP distribution trend, with the highest "soil-marker" BHPs but the lowest tetrafunctionalised BHPs. Aminobacteriohopanepentol, an indicator of aerobic methane oxidation, was observed in all the sediments, with the source being either the marine environment or methane producing terrestrial environments.
22.	Elmquist, M., et al. (author) Pan-Arctic patterns in black carbon sources and fluvial discharges deduced from radiocarbon and PAH source apportionment markers in estuarine surface sediments 2008 In: Global Biogeochem. Cycles. ; 22, s. 1-13 Journal article (peer-reviewed)
23.	Feng, Xiaojuan, et al. (author) Differential mobilization of terrestrial carbon pools in Eurasian Arctic river basins 2013 In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:35, s. 14168-14173 Journal article (peer-reviewed)abstract Mobilization of Arctic permafrost carbon is expected to increase with warming-induced thawing. However, this effect is challenging to assess due to the diverse processes controlling the release of various organic carbon (OC) pools from heterogeneous Arctic landscapes. Here, by radiocarbon dating various terrestrial OC components in fluvially and coastally integrated estuarine sediments, we present a unique framework for deconvoluting the contrasting mobilization mechanisms of surface vs. deep (permafrost) carbon pools across the climosequence of the Eurasian Arctic. Vascular plant-derived lignin phenol C-14 contents reveal significant inputs of young carbon from surface sources whose delivery is dominantly controlled by river runoff. In contrast, plant wax lipids predominantly trace ancient (permafrost) OC that is preferentially mobilized from discontinuous permafrost regions, where hydrological conduits penetrate deeper into soils and thermokarst erosion occurs more frequently. Because river runoff has significantly increased across the Eurasian Arctic in recent decades, we estimate from an isotopic mixing model that, in tandem with an increased transfer of young surface carbon, the proportion of mobilized terrestrial OC accounted for by ancient carbon has increased by 3-6% between 1985 and 2004. These findings suggest that although partly masked by surface carbon export, climate change-induced mobilization of old permafrost carbon is well underway in the Arctic.
24.	Feng, Xiaojuan, et al. (author) Multimolecular tracers of terrestrial carbon transfer across the pan-Arctic : C-14 characteristics of sedimentary carbon components and their environmental controls 2015 In: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 29:11, s. 1855-1873 Journal article (peer-reviewed)abstract Distinguishing the sources, ages, and fate of various terrestrial organic carbon (OC) pools mobilized from heterogeneous Arctic landscapes is key to assessing climatic impacts on the fluvial release of carbon from permafrost. Through molecular C-14 measurements, including novel analyses of suberin- and/or cutin-derived diacids (DAs) and hydroxy fatty acids (FAs), we compared the radiocarbon characteristics of a comprehensive suite of terrestrial markers (including plant wax lipids, cutin, suberin, lignin, and hydroxy phenols) in the sedimentary particles from nine major arctic and subarctic rivers in order to establish a benchmark assessment of the mobilization patterns of terrestrial OC pools across the pan-Arctic. Terrestrial lipids, including suberin-derived longer-chain DAs (C-24,C-26,C-28), plant wax FAs (C(24,26,2)8), and n-alkanes (C-27,C-29,C-31), incorporated significant inputs of aged carbon, presumably from deeper soil horizons. Mobilization and translocation of these old terrestrial carbon components was dependent on nonlinear processes associated with permafrost distributions. By contrast, shorter-chain (C-16,C-18) DAs and lignin phenols (as well as hydroxy phenols in rivers outside eastern Eurasian Arctic) were much more enriched in C-14, suggesting incorporation of relatively young carbon supplied by runoff processes from recent vegetation debris and surface layers. Furthermore, the radiocarbon content of terrestrial markers is heavily influenced by specific OC sources and degradation status. Overall, multitracer molecular C-14 analysis sheds new light on the mobilization of terrestrial OC from arctic watersheds. Our findings of distinct ages for various terrestrial carbon components may aid in elucidating fate of different terrestrial OC pools in the face of increasing arctic permafrost thaw.
25.	Fripiat, F., et al. (author) Influence of the bordering shelves on nutrient distribution in the Arctic halocline inferred from water column nitrate isotopes 2018 In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 63:5, s. 2154-2170 Journal article (peer-reviewed)abstract The East Siberian Sea and contiguous western Arctic Ocean basin are characterized by a subsurface nutrient maximum in the halocline, generally attributed to both Pacific inflow and intensive remineralization in shelf bottom waters that are advected into the central basin. We report nitrogen and oxygen isotopic measurement of nitrate from the East Siberian Sea and western Eurasian Basin, in order to gain insight into how nitrate is processed by the microbial community and redistributed in the Arctic Ocean. A large decoupling between nitrate delta N-15 and delta O-18 is reported, increasing and decreasing upward from the Atlantic temperature maximum layer toward the surface, respectively. A correlation between water and nitrate delta O-18 indicates that most of the nitrate (> 60%) at the halocline has been regenerated within the Arctic Ocean. The increase in nitrate delta N-15 correlates with the fixed N deficit, indicating a causal link between the loss of fixed N and the delta N-15 enrichment. This suggests that a significant share of benthic denitrification is driven by nitrate supplied by remineralization and partial nitrification, allowing residual delta N-15-enriched ammonium to diffuse out of the sediments. By increasing nutrient concentrations and fixed N deficit in shelf bottom waters, this imprint is attenuated offshore following advection into the halocline by nitrate regeneration and mixing. Estimation of the sedimentary isotope effect related to benthic denitrification yields values in the range of 2.4-3.8 parts per thousand, with its magnitude driven by both the degree of coupling between remineralization and nitrification, and fixed N concentrations in shelf bottom waters.
26.	Gustafsson, Örjan, et al. (author) Widespread release of old carbon across the Siberian Arctic echoed by its large rivers 2011 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:6, s. 1737-1743 Journal article (peer-reviewed)abstract Over decadal-centennial timescales, only a few mechanisms in the carbon-climate system could cause a massive net redistribution of carbon from land and ocean systems to the atmosphere in response to climate warming. The largest such climate-vulnerable carbon pool is the old organic carbon (OC) stored in Arctic permafrost (perennially frozen) soils. Climate warming, both predicted and now observed to be the strongest globally in the Eurasian Arctic and Alaska, causes thaw-release of old permafrost carbon from local tundra sites. However, a central challenge for the assessment of the general vulnerability of this old OC pool is to deduce any signal integrating its release over larger scales. Here we examine radiocarbon measurements of molecular soil markers exported by the five Great Russian-Arctic Rivers (Ob, Yenisey, Lena, Indigirka and Kolyma), employed as natural integrators of carbon release processes in their watersheds. The signals held in estuarine surface sediments revealed that average radiocarbon ages of n-alkanes increased east-to-west from 6400 yr BP in Kolyma to 11 400 yr BP in Ob. This is consistent with westwards trends of both warmer climate and more degraded organic matter as indicated by the ratio of high molecular weight (HMW) n-alkanoic acids to HMW n-alkanes. The dynamics of Siberian permafrost can thus be probed via the molecular-radiocarbon signal as carried by Arctic rivers. Old permafrost carbon is at present vulnerable to mobilization over continental scales. Climate-induced changes in the radiocarbon fingerprint of released permafrost carbon will likely depend on changes in both permafrost coverage and Arctic soil hydraulics.
27.	Ingri, Johan, et al. (author) Fractionation of iron isotopes during estuarine mixing in Ob, Yenisey and Lena freshwater plumes 2009 In: Geochimica et Cosmochimica Acta. - 0016-7037 .- 1872-9533. ; 73:13, Suppl. S, s. A569- Journal article (other academic/artistic)abstract Iron isotopes were measured in suspended matter (>0.2 µm) in the Ob, Yenisey and Lena River freshwater plumes during the International Siberian Shelf Study 2008 (ISSS-08). The δ56Fe value was around zero within the Lena River and close to the river mouth, but changed to more negative values in the outer parts of the plume. In both the Ob and Yenisey plumes suspended matter in the surface water had clearly negative values whereas samples close to the bottom showed values close to zero.It has previously been suggested that total Fe in river suspended matter (>0.2µm) in boreal regions is roughly a mixture of three phases, detrital particles (δ56Fe around zero), oxyhydroxide particles (δ56Fe positive) and C-Fe particles (δ56Fe negative). We suggest that the δ56Fe pattern observed in this study is the result of relatively rapid removal of detrital particles and Fe-oxyhydroxides, leaving a suspended fraction with negative values in the surface water in the outer parts of the freshwater plumes. Hence, during estuarine mixing of suspended particles heavy iron isotopes are deposited close to the river mouth, whereas light isotopes are exported to open ocean water.
28.	Jakobsson, Martin, et al. (author) Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation 2016 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7 Journal article (peer-reviewed)abstract The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions41-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (similar to 140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.
29.	Karlsson, Emma, et al. (author) Carbon isotopes and lipid biomarker investigation of sources, transport and degradation of terrestrial organic matter in the Buor-Khaya Bay, SE Laptev Sea 2011 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:7, s. 1865-1879 Journal article (peer-reviewed)abstract The world's largest continental shelf, the East Siberian Shelf Sea, receives substantial input of terrestrial organic carbon (terr-OC) from both large rivers and erosion of its coastline. Degradation of organic matter from thawing permafrost in the Arctic is likely to increase, potentially creating a positive feedback mechanism to climate warming. This study focuses on the Buor-Khaya Bay (SE Laptev Sea), an area with strong terr-OC input from both coastal erosion and the Lena river. To better understand the fate of this terr-OC, molecular (acyl lipid biomarkers) and isotopic tools (stable carbon and radiocarbon isotopes) have been applied to both particulate organic carbon (POC) in surface water and sedimentary organic carbon (SOC) collected from the underlying surface sediments. Clear gradients in both extent of degradation and differences in source contributions were observed both between surface water POC and surface sediment SOC as well as over the 100 s km investigation scale (about 20 stations). Depleted delta(13)C-OC and high HMW/LMW n-alkane ratios signaled that terr-OC was dominating over marine/planktonic sources. Despite a shallow water column (10-40 m), the isotopic shift between SOC and POC varied systematically from +2 to +5 per mil for delta(13)C and from +300 to +450 for Delta(14)C from the Lena prodelta to the Buor-Khaya Cape. At the same time, the ratio of HMW n-alkanoic acids to HMW n-alkanes as well as HMW n-alkane CPI, both indicative of degradation, were 5-6 times greater in SOC than in POC. This suggests that terr-OC was substantially older yet less degraded in the surface sediment than in the surface waters. This unusual vertical degradation trend was only recently found also for the central East Siberian Sea. Numerical modeling (Monte Carlo simulations) with delta(13)C and Delta(14)C in both POC and SOC was applied to deduce the relative contribution of - plankton OC, surface soil layer OC and yedoma/mineral soil OC. This three end-member dual-carbon-isotopic mixing model suggests quite different scenarios for the POC vs SOC. Surface soil is dominating (63 +/- 10 %) the suspended organic matter in the surface water of SE Laptev Sea. In contrast, the yedoma/mineral soil OC is accounting for 60 +/- 9% of the SOC. We hypothesize that yedoma-OC, associated with mineral-rich matter from coastal erosion is ballasted and thus quickly settles to the bottom. The mineral association may also explain the greater resistance to degradation of this terr-OC component. In contrast, more amorphous humic-like and low-density terr-OC from surface soil and recent vegetation represents a younger but more bioavailable and thus degraded terr-OC component held buoyant in surface water. Hence, these two terr-OC components may represent different propensities to contribute to a positive feedback to climate warming by converting OC from coastal and inland permafrost into CO(2).
30.	Karlsson, Emma S., et al. (author) Contrasting regimes for organic matter degradation in the East Siberian Sea and the Laptev Sea assessed through microbial incubations and molecular markers 2015 In: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 170, s. 11-22 Journal article (peer-reviewed)abstract Compositional studies of organic matter on the East Siberian Arctic Shelf (ESAS) suggest that different terrestrial carbon pools have different propensities for transport and/or degradation. The current study combined laboratory-based microbial degradation experiments with earlier published degradation-diagnostic composition of several classes of terrestrial biomarkers on the same sediments to investigate differences and driving forces of terrestrial organic matter (TerrOM) degradation in two biogeochemically-contrasting regimes of the ESAS. The incubation-based anaerobic degradation rates were consistently higher (by average factor of 6) in the East Siberian Sea Kolyma Paleoriver Channel (ESS-KPC) (15 mu mol CO2 g OC-1 day(-1)) compared to the Laptev Sea Buor-Khaya Bay (LS-BKB) (2.4 mu mol CO2 g OC-1 day(-1)). The reported molecular markers show similarities between the terrestrial carbon pools in the two systems, but impose contrasting degradation regimes in combination with the incubation results. For the LS-BKB, there was a strong relationship between the degradation rates and the three lignin phenol-based degradation proxies (r(2) = 0.93-0.96, p < 0.01, linear regression) and two wax lipid-based degradation proxies (r(2) = 0.71 and 0.66, p < 0.05, linear regression). In contrast, for the ESS-KPC system, there was no relationship between incubation-based degradation rates and molecular marker-based degradation status of TerrOM. A principal component analysis indicated that short-chain fatty acids and dicarboxylic acids from CuO oxidation are mainly of terrestrial origin in the LS-BKB, but mainly of marine origin in the ESS-KPC. Hence, the microbial degradation in the western (LS-BKB) system appears to be fueled by TerrOM whereas the eastern (ESS-KPC) system degradation appears to be driven by MarOM. By combining molecular fingerprinting of TerrOM degradation state with laboratory-based degradation studies on the same ESAS sediments, a picture evolves of two distinctly different modes of TerrOM degradation in different parts of the ESAS system.
31.	Macdonald, R. W, et al. (author) The Arctic Ocean: budgets and fluxes 2006 In: Carbon and Nutrient Fluxes in Continental Margins: A global Synthesis. Journal article (peer-reviewed)
32.	Matsubara, Felipe, 1991-, et al. (author) Molecular-Multiproxy Assessment of Land-Derived Organic Matter Degradation Over Extensive Scales of the East Siberian Arctic Shelf Seas 2022 In: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 36:12 Journal article (peer-reviewed)abstract Global warming triggers permafrost thaw, which increases the release of terrigenous organic matter (terr-OM) to the Arctic Ocean by coastal erosion and rivers. Terrigenous OM degradation in the Arctic Ocean contributes to greenhouse gas emissions and severe ocean acidification, yet the vulnerability of different terr-OM components is poorly resolved. Here, terr-OM degradation dynamics are studied with unprecedented spatial coverage over the World's largest shelf sea system—the East Siberian Arctic Shelf (ESAS), using a multi-proxy molecular biomarker approach. Mineral-surface-area-normalized concentrations of terr-OM compounds in surface sediments decreases offshore. Differences between terr-OM compound classes (lignin phenols, high-molecular weight [HMW] n-alkanes, n-alkanoic acids and n-alkanols, sterols, 3,5-dihydroxybenzoic acids, cutin acids) reflect contrasting influence of sources, propensity to microbial degradation and association with sedimenting particles, with lignin phenols disappearing 3-times faster than total terr-OM, and twice faster than other biomarkers. Molecular degradation proxies support substantial terr-OM degradation across the ESAS, with clearest trends shown by: 3,5-dihydroxybenzoic acid/vanillyl phenol ratios, acid-to-aldehyde ratios of syringyl and vanillyl phenols, Carbon Preference Indices of HMW n-alkyl compounds and sitostanol/β-sitosterol. The combination of terr-OM biomarker data with δ13C/Δ14C-based source apportionment indicates that the more degraded state of lignin is influenced by the relative contribution of river-transported terr-OM from surface soils, while HMW n-alkanoic acids and stigmasterol are influenced by erosion-derived terr-OM from Ice Complex deposits. Our findings demonstrate differences in vulnerability to degradation between contrasting terr-OM pools, and underscore the need to consider molecular properties for understanding and modeling of large-scale biogeochemical processes of the permafrost carbon-climate feedback.
33.	Porcelli, D., et al. (author) The distribution of neodymium isotopes in Arctic Ocean basins 2009 In: Geochimica Cosmochimica Acta. ; 73, s. 2645-2659 Journal article (peer-reviewed)
34.	Pugach, Svetlana P., et al. (author) Dissolved organic matter and its optical characteristics in the Laptev and East Siberian seas : spatial distribution and interannual variability (2003-2011) 2018 In: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 14:1, s. 87-103 Journal article (peer-reviewed)abstract The East Siberian Arctic Shelf (ESAS) is the broadest and shallowest continental shelf in the world. It is characterized by both the highest rate of coastal erosion in the world and a large riverine input of terrigenous dissolved organic matter (DOM). DOM plays a significant role in marine aquatic ecosystems. The chromophoric fraction of DOM (CDOM) directly affects the quantity and spectral quality of available light, thereby impacting both primary production and ultraviolet (UV) exposure in aquatic ecosystems. A multiyear study of CDOM absorption, fluorescence, and spectral characteristics was carried out over the vast ESAS in the summer-fall seasons. The paper describes observations accomplished at 286 stations and 1766 in situ high-resolution optical measurements distributed along the nearshore zone. Spatial and interannual CDOM dynamics over the ESAS were investigated, and driving factors were identified. It was shown that the atmospheric circulation regime is the dominant factor controlling CDOM distribution on the ESAS. This paper explores the possibility of using CDOM and its spectral parameters to identify the different biogeochemical regimes in the surveyed area. The analysis of CDOM spectral characteristics showed that the major part of the Laptev and East Siberian seas shelf is influenced by terrigenous DOM carried in riverine discharge. Western and eastern provinces of the ESAS with distinctly different DOM optical properties were also identified; a transition between the two provinces at around 165-170 degrees E, also consistent with hydrological and hydrochemical data, is shown. In the western ESAS, a region of substantial river impact, the content of aromatic carbon within DOM remains almost constant. In the eastern ESAS, a gradual decrease in aromaticity percentage was observed, indicating contribution of Pacific-origin waters, where allochthonous DOM with predominantly aliphatic character and much smaller absorption capacity predominates. In addition, we found a stable tendency towards reduced concentrations of CDOM and dissolved lignin and an increase in spectral slope and slope ratio values eastward from the Lena River delta; the Lena is the main supplier of DOM to the eastern Arctic shelf. The strong positive correlation (r = 0.97) between dissolved organic carbon (DOC) and CDOM values in the surface shelf waters influenced by terrigenous discharge indicates that it is feasible to estimate DOC content from CDOM fluorescence assessed in situ using a WETStar fluorometer. This approach is reliable over the salinity range of 3 to 24.5. The fact that there is little difference between predicted and observed parameters indicates that the approach is justified. The direct estimation of DOM optical characteristics in the surface ESAS waters provided by this multiyear study will also be useful for validating and calibrating remote sensing data.
35.	Rosen, P. O., et al. (author) Ice export from the Laptev and East Siberian Sea derived from O-18 values 2015 In: Journal of Geophysical Research-Oceans. - : American Geophysical Union (AGU). - 2169-9275 .- 2169-9291. ; 120:9, s. 5997-6007 Journal article (peer-reviewed)abstract Ice export from the vast Arctic Siberian shelf is calculated using O-18 values and salinity data for water samples collected during the International Siberian Shelf Study between August and September 2008 (ISSS-08). The samples represent a wide range of salinities and O-18 values due to river water inputs and sea ice removal. We estimate the fraction of water that has been removed as ice by interpreting observed O-18 values and salinities as a result of mixing between river water and sea water end-members as well as to fractional ice removal. This method does not assume an ice end-member of fixed composition, which is especially important when applied on samples with large differences in salinity. The results show that there is net transport of ice from both the Laptev and the Eastern Siberian Seas, and in total 3000 km(3) of sea ice is exported from the shelf. The annual total export of ice from the entire region, calculated from the residence time of water on the shelf, is estimated to be 860 km(3) yr(-1). Thus, changes in ice production on the shelf may have great impact on sea ice export from the Arctic Ocean.
36.	Sanchez-Garcia, Laura, et al. (author) Characterisation of Three Regimes of Collapsing Arctic Ice Complex Deposits on the SE Laptev Sea Coast using Biomarkers and Dual Carbon Isotopes 2014 In: Permafrost and Periglacial Processes. - : Wiley. - 1045-6740 .- 1099-1530. ; 25:3, s. 172-183 Journal article (peer-reviewed)abstract Arctic amplification of climate warming is intensifying the thaw and coastal erosion of the widespread and carbon-rich Siberian Ice Complex Deposits (ICD). Despite the potential for altering long-term carbon dynamics in the Arctic, the susceptibility of organic carbon (OC) to degradation as the ICD thaw is poorly characterised. This study identifies signs of OC degradation in three Siberian ICD regimes of coastal erosion through elemental, isotopic and molecular analyses. The degree of erosion appears to determine the extent of degradation. The moisture-limited and beach-protected ICD bluff near Buor-Khaya Cape, characterised by thermokarst mounds (baydzherakhs), represents a dormant regime with limited ongoing degradation. Conversely, the more exposed ICD scarps on eroding riverbanks (Olenek Channel, Lena Delta) and coastal slopes (Muostakh Island) showed more pronounced signs of ongoing OC decay. Different parameters suggest that degradation can partially explain the shift of the OC signature with C-14 age in the thawing ICD. Exposure time, degree of erosion, slope gradient and moisture conditions appear to be key factors determining the degradation propensity of OC in exposed ICD. These field results document the lability of OC in ICD upon thaw and illustrate the potential for transferring old OC into the rapidly cycling atmosphere-biosphere carbon pools.
37.	Semiletov, I., et al. (author) East Siberian Shelf Study Alleviates Scarcity of Observations 2009 In: EOS. - : American Geophysical Union (AGU). - 0096-3941 .- 2324-9250. ; 90:17, s. 145- Journal article (peer-reviewed)abstract The East Siberian Arctic Shelf (ESAS) is the world's largest continental shelf and also the most understudied part of the Arctic Ocean. Composed of the Laptev Sea, the East Siberian Sea, and the Russian section of the Chukchi Sea, the ESAS is characterized by tundra discharge through the Lena, Indigirka, and Kolyma rivers; coastal erosion; methane seeps from subsea permafrost reservoirs; and the formation of water masses that spread throughout the Arctic Ocean. The region, which has experienced a 4°C springtime positive air temperature anomaly for 2000–2005 compared with preceding decades, is also of particular interest for its carbon-climate couplings.
38.	Sparkes, R. B., et al. (author) GDGT distributions on the East Siberian Arctic Shelf : implications for organic carbon export, burial and degradation 2015 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:12, s. 3753-3768 Journal article (peer-reviewed)abstract Siberian permafrost contains a globally significant pool of organic carbon (OC) that is vulnerable to enhanced warming and subsequent release into the contemporary carbon cycle. OC release by both fluvial and coastal erosion has been reported in the region, but the behaviour of this material in the Arctic Ocean is insufficiently understood. The balance between OC deposition and degradation on the East Siberian Arctic Shelf (ESAS) influences the climate-carbon cycle feedback in this area. In this study we couple measurements of glycerol dialkyl glycerol tetraethers (GDGTs) with bulk geochemical observations to improve knowledge of the sources of OC to the ESAS, the behaviour of specific biomarkers on the shelf and the balance between delivery and removal of different carbon pools. Branched GDGT (brGDGT) concentrations were highest close to river mouths, yet low in 'ice complex' permafrost deposits, supporting recent observations that brGDGTs are mostly delivered by fluvial erosion, and may be a tracer for this in complex sedimentary environments. BrGDGT concentrations and the branched and isoprenoidal tetraether (BIT) index reduced quickly offshore, demonstrating a rapid reduction in river influence. Stable carbon isotope ratios changed at a different rate to the BIT index, suggesting not only that OC on the shelf is sourced from fluvial erosion but also that erosion of coastal sediments delivers substantial quantities of OC to the Arctic Ocean. A model of OC export from fluvial, coastal and marine sources is able to recreate the biomarker and bulk observations and provide estimates for the influence of fluvial and coastal OC across the whole shelf. The model shows that coastal erosion delivers 43 % of the OC and 87 % of the mineral sediment to the ESAS, but that rivers deliver 72 % of brGDGTs, indicating that brGDGTs can be used as a proxy for river-derived sediment.
39.	Sparkes, Robert B., et al. (author) Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic Shelf 2016 In: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 10:5, s. 2485-2500 Journal article (peer-reviewed)abstract Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis-gas chromatography-mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r(2) = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (C-14(OC)) which, when coupled with previous measurements, allows us to produce the most comprehensive C-14(OC) map of the ESAS to date. Combining the C-14(OC) and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river-ocean transects of surface sediments transition from river-dominated to coastalerosion-dominated to marine-dominated signatures.
40.	Tesi, Tommaso, et al. (author) Massive remobilization of permafrost carbon during post-glacial warming 2016 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7 Journal article (peer-reviewed)abstract Recent hypotheses, based on atmospheric records and models, suggest that permafrost carbon (PF-C) accumulated during the last glaciation may have been an important source for the atmospheric CO2 rise during post-glacial warming. However, direct physical indications for such PF-C release have so far been absent. Here we use the Laptev Sea (Arctic Ocean) as an archive to investigate PF-C destabilization during the last glacial–interglacial period. Our results show evidence for massive supply of PF-C from Siberian soils as a result of severe active layer deepening in response to the warming. Thawing of PF-C must also have brought about an enhanced organic matter respiration and, thus, these findings suggest that PF-C may indeed have been an important source of CO2 across the extensive permafrost domain. The results challenge current paradigms on the post-glacial CO2 rise and, at the same time, serve as a harbinger for possible consequences of the present-day warming of PF-C soils.
41.	van Dongen, B.E., et al. (author) Contrasting lipid biomarker composition of terrestrial organic matter exported from across the Eurasian Arctic by the five great Russian Arctic rivers 2008 In: Global Biogeochem. Cycles. ; 22, s. 1-14 Journal article (peer-reviewed)
42.	Vonk, Jorien Elisabeth, et al. (author) Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea. Other publication (other academic/artistic)
43.	Vonk, Jorien E., et al. (author) Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea 2010 In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 7:10, s. 3153-3166 Journal article (peer-reviewed)abstract Climate warming in northeastern Siberia may induce thaw-mobilization of the organic carbon (OC) now held in permafrost. This study investigated the composition of terrestrial OC exported to Arctic coastal waters to both obtain a natural integration of terrestrial permafrost OC release and to further understand the fate of released carbon in the extensive Siberian Shelf Seas. Application of a variety of elemental, molecular and isotopic (delta C-13 and Delta C-14) analyses of both surface water suspended particulate matter and underlying surface sediments along a 500 km transect from Kolyma River mouth to the mid-shelf of the East Siberian Sea yielded information on the sources, degradation status and transport processes of thaw-mobilized soil OC. A three end-member dual-carbon-isotopic mixing model was applied to deduce the relative contributions from riverine, coastal erosion and marine sources. The mixing model was solved numerically using Monte Carlo simulations to obtain a fair representation of the uncertainties of both end-member composition and the end results. Riverine OC contributions to sediment OC decrease with increasing distance offshore (35 +/- 15 to 13 +/- 9%), whereas coastal erosion OC exhibits a constantly high contribution (51 +/- 11 to 60 +/- 12%) and marine OC increases offshore (9 +/- 7 to 36 +/- 10%). We attribute the remarkably strong imprint of OC from coastal erosion, extending up to similar to 500 km from the coast, to efficient offshoreward transport in these shallow waters presumably through both the benthic boundary layer and ice-rafting. There are also indications of simultaneous selective preservation of erosion OC compared to riverine OC. Molecular degradation proxies and radiocarbon contents indicated a degraded but young (Delta C-14 ca. -60% or ca. 500 C-14 years) terrestrial OC pool in surface water particulate matter, underlain by a less degraded but old (Delta C-14 ca. -500% or ca. 5500 C-14 years) terrestrial OC pool in bottom sediments. We suggest that the terrestrial OC fraction in surface water particulate matter is mainly derived from surface soil and recent vegetation fluvially released as buoyant organic-rich aggregates (e. g., humics), which are subjected to extensive processing during coastal transport. In contrast, terrestrial OC in the underlying sediments is postulated to originate predominantly from erosion of mineral-rich Pleistocene coasts (i.e., yedoma) and inland mineral soils. Sorptive association of this organic matter with mineral particles protects the OC from remineralization and also promotes rapid settling (ballasting) of the OC. Our findings corroborate recent studies by indicating that different Arctic surface soil OC pools exhibit distinguishing susceptibilities to degradation in coastal waters. Consequently, the general postulation of a positive feedback to global warming from degradation of permafrost carbon may be both attenuated (by reburial of one portion) and geographically displaced (degradation of released terrestrial permafrost OC far out over the Arctic shelf seas).
44.	Vonk, Jorien E., et al. (author) Preferential burial of permafrost-derived organic carbon in Siberian-Arctic shelf waters 2014 In: Journal of Geophysical Research Oceans. - 2169-9275. ; 119:12, s. 8410-8421 Journal article (peer-reviewed)abstract The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4-13 C-14-ky in surface PM and 5.5-18 C-14-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost.
45.	Wild, B., et al. (author) Quantity, origin and degradation state of organic matter in subsea permafrost on the East Siberian Arctic shelf 2019 In: Conference Proceedings, 29th International Meeting on Organic Geochemistry. - : European Association of Geoscientists & Engineers. - 9789462823044 Conference paper (peer-reviewed)abstract Based on a unique set of three drill cores, we characterize the quantity, origin and degradation state of organic matter through the subsea permafrost with higher resolution across the current thaw front, to improve our understanding of its vulnerability to decomposition upon thaw.
46.	Winiger, Patrik, et al. (author) Source apportionment of circum-Arctic atmospheric black carbon from isotopes and modeling 2019 In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:2 Journal article (peer-reviewed)abstract Black carbon (BC) contributes to Arctic climate warming, yet source attributions are inaccurate due to lacking observational constraints and uncertainties in emission inventories. Year-round, isotope-constrained observations reveal strong seasonal variations in BC sources with a consistent and synchronous pattern at all Arctic sites. These sources were dominated by emissions from fossil fuel combustion in the winter and by biomass burning in the summer. The annual mean source of BC to the circum-Arctic was 39 +/- 10% from biomass burning. Comparison of transport-model predictions with the observations showed good agreement for BC concentrations, with larger discrepancies for (fossil/biomass burning) sources. The accuracy of simulated BC concentration, but not of origin, points to misallocations of emissions in the emission inventories. The consistency in seasonal source contributions of BC throughout the Arctic provides strong justification for targeted emission reductions to limit the impact of BC on climate warming in the Arctic and beyond.

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