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  • 1. Alling, Vanja
    et al.
    Sanchez-Garcia, Laura
    Porcelli, Don
    Pugach, Sveta
    Vonk, Jorien E.
    van Dongen, Bart
    Morth, Carl-Magnus
    Anderson, Leif G.
    Sokolov, Alexander
    Andersson, Per
    Humborg, Christoph
    Semiletov, Igor
    Gustafsson, Orjan
    Nonconservative behavior of dissolved organic carbon across the Laptev and East Siberian seas2010In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 24Article in journal (Refereed)
    Abstract [en]

    Climate change is expected to have a strong effect on the Eastern Siberian Arctic Shelf (ESAS) region, which includes 40% of the Arctic shelves and comprises the Laptev and East Siberian seas. The largest organic carbon pool, the dissolved organic carbon (DOC), may change significantly due to changes in both riverine inputs and transformation rates; however, the present DOC inventories and transformation patterns are poorly understood. Using samples from the International Siberian Shelf Study 2008, this study examines for the first time DOC removal in Arctic shelf waters with residence times that range from months to years. Removals of up to 10%-20% were found in the Lena River estuary, consistent with earlier studies in this area, where surface waters were shown to have a residence time of approximately 2 months. In contrast, the DOC concentrations showed a strong nonconservative pattern in areas with freshwater residence times of several years. The average losses of DOC were estimated to be 30%-50% during mixing along the shelf, corresponding to a first-order removal rate constant of 0.3 yr(-1). These data provide the first observational evidence for losses of DOC in the Arctic shelf seas, and the calculated DOC deficit reflects DOC losses that are higher than recent model estimates for the region. Overall, a large proportion of riverine DOC is removed from the surface waters across the Arctic shelves. Such significant losses must be included in models of the carbon cycle for the Arctic Ocean, especially since the breakdown of terrestrial DOC to CO2 in Arctic shelf seas may constitute a positive feedback mechanism for Arctic climate warming. These data also provide a baseline for considering the effects of future changes in carbon fluxes, as the vast northern carbon-rich permafrost areas draining into the Arctic are affected by global warming.

  • 2. Feng, Xiaojuan
    et al.
    Gustafsson, Örjan
    Holmes, R. Max
    Vonk, Jorien E.
    van Dongen, Bart E.
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Yunker, Mark B.
    Macdonald, Robie W.
    Wacker, Lukas
    Montlucon, Daniel B.
    Eglinton, Timothy I.
    Multimolecular tracers of terrestrial carbon transfer across the pan-Arctic: C-14 characteristics of sedimentary carbon components and their environmental controls2015In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 29, no 11, p. 1855-1873Article in journal (Refereed)
    Abstract [en]

    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.

  • 3. Fisher, Rebecca E.
    et al.
    France, James L.
    Lowry, David
    Lanoisellé, Mathias
    Brownlow, Rebecca
    Pyle, John A.
    Cain, Michelle
    Warwick, Nicola
    Skiba, Ute M.
    Drewer, Julia
    Dinsmore, Kerry J.
    Leeson, Sarah R.
    Bauguitte, Stéphane J.-B.
    Wellpott, Axel
    O’Shea, Sebastian J.
    Allen, Grant
    Gallagher, Martin W.
    Pitt, Joseph
    Percival, Carl J.
    Bower, Keith
    George, Charles
    Hayman, Garry D.
    Aalto, Tuula
    Lohila, Annalea
    Aurela, Mika
    Laurila, Tuomas
    Crill, Patrick M.
    McCalley, Carmody K.
    Nisbet, Euan G.
    Measurement of the 13C isotopic signature of methane emissions from Northern European wetlands2017In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224Article in journal (Refereed)
    Abstract [en]

    Isotopic data provide powerful constraints on regional and global methane emissions and their source profiles. However, inverse modeling of spatially-resolved methane flux is currently constrained by a lack of information on the variability of source isotopic signatures. In this study, isotopic signatures of emissions in the Fennoscandian Arctic have been determined in chambers over wetland, in the air 0.3 to 3 m above the wetland surface and by aircraft sampling from 100 m above wetlands up to the stratosphere. Overall the methane flux to atmosphere has a coherent δ13C isotopic signature of -71 ± 1‰, measured in situ on the ground in wetlands. This is in close agreement with δ13C isotopic signatures of local and regional methane increments measured by aircraft campaigns flying through air masses containing elevated methane mole fractions. In contrast results from wetlands in Canadian boreal forest further south gave isotopic signatures of -67 ± 1 ‰.Wetland emissions dominate the local methane source measured over the European Arctic in summer. Chamber measurements demonstrate a highly variably methane flux and isotopic signature, but the results from air sampling within wetland areas show that emissions mix rapidly immediately above the wetland surface and methane emissions reaching the wider atmosphere do indeed have strongly coherent C isotope signatures. The study suggests that for boreal wetlands (>60°N) global and regional modeling can use an isotopic signature of -71‰ to apportion sources more accurately, but there is much need for further measurements over other wetlands regions to verify this.

  • 4. Giesler, Reiner
    et al.
    Mörth, Carl-Magnus
    Karlsson, Jan
    Lundin, Erik J.
    Lyon, Steve W.
    Humborg, Christoph
    Spatiotemporal variations of pCO2 and δ13C-DIC in subarctic streams in northern Sweden2013In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, no 1, p. 176-186Article in journal (Refereed)
    Abstract [en]

    Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO2 (pCO2) and in stable isotopic composition of dissolved inorganic carbon (δ13C-DIC) in subarctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest and tundra and differences in bedrock. We found that all streams generally were supersaturated in pCO2 with an average concentration of 850 µatm. The variability in pCO2 across streams was poorly related to vegetation cover, and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream pCO2 or δ13C-DIC. Stream water pCO2 values were highest during winter base flow when we also observed the lowest δ13C-DIC values, and this pattern is interpreted as a high contribution from CO2 from soil respiration. Summer base flow δ13C-DIC values probably are more affected by in situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO2 and quantify their relative importance.

  • 5. Karlsson, A.
    et al.
    Theorin, M.
    Abrahamsson, K.
    Distribution, transport, and production of volatile halocarbons in the upper waters of the ice-covered high Arctic Ocean2013In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, no 4, p. 1246-1261Article in journal (Refereed)
    Abstract [en]

    Volatile halogenated compounds (CHBr3, CH2Br2, CHBr2Cl, and CH2ClI) were measured in the water column and in sea ice brine across the Arctic Ocean, from Barrow, Alaska, to Svalbard, during the Beringia 2005 expedition (August-September) with RV/IB Oden. High concentrations of brominated compounds (up to 42 pmol kg(-1) of bromoform) were found under multiyear ice in the surface waters over the Makarov Basin and the Lomonosov Ridge, near the North Pole. Even higher concentrations (bromoform up to 160 pmol kg(-1)) were found in sea ice brine. We propose that the high load of riverine dissolved organic matter that is transported in the Transpolar Drift is a main factor responsible for the high concentration of brominated volatile compounds found in sea ice brine and upper waters and that cycles of freezing and thawing during the transport enhance the transfer of halocarbons to the seawater. The iodinated compound (CH2ClI) showed a completely different distribution with highest concentrations in water of Pacific origin in the mixed layer and upper halocline of the northern Canada Basin and over the Alpha Ridge. In the southern Canada Basin, low concentrations of halocarbons were found in upper waters. Higher concentrations in water of Pacific origin, especially on the continental shelf, indicate production in the shelf regions, likely in the Chukchi Sea and the East Siberian Sea.

  • 6. Salvadó, Joan A.
    et al.
    Bröder, Lisa
    Andersson, August
    Semiletov, Igor P.
    Gustafsson, Örjan
    Release of Black Carbon From Thawing Permafrost Estimated by Sequestration Fluxes in the East Siberian Arctic Shelf Recipient2017In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 31, no 10, p. 1501-1515Article in journal (Refereed)
    Abstract [en]

    Black carbon (BC) plays an important role in carbon burial in marine sediments globally. Yet the sequestration of BC in the Arctic Ocean is poorly understood. Here we assess the concentrations, fluxes, and sources of soot BC (SBC)—the most refractory component of BC—in sediments from the East Siberian Arctic Shelf (ESAS), the World’s largest shelf sea system. SBC concentrations in the contemporary shelf sediments range from 0.1 to 2.1 mg g−1 dw, corresponding to 2–12% of total organic carbon. The 210Pb-derived fluxes of SBC (0.42–11 g m−2 yr−1) are higher or in the same range as fluxes reported for marine surface sediments closer to anthropogenic emissions. The total burial flux of SBC in the ESAS ( 4,000 Gg yr−1) illustrates the great importance of this Arctic shelf in marine sequestration of SBC. The radiocarbon signal of the SBC shows more depleted yet also more uniform signatures (−721 to −896‰; average of −774 ± 62‰) than of the non-SBC pool (−304 to −728‰; average of −491 ± 163‰), suggesting that SBC is coming from an, on average, 5,900 ± 300 years older and more specific source than the non-SBC pool. We estimate that the atmospheric BC input to the ESAS is negligible ( 0.6% of the SBC burial flux). Statistical source apportionment modeling suggests that the ESAS sedimentary SBC is remobilized by thawing of two permafrost carbon (PF/C) systems: surface soil permafrost (topsoil/PF; 25 ± 8%) and Pleistocene ice complex deposits (ICD/PF; 75 ± 8%). The SBC contribution to the total mobilized permafrost carbon (PF/C) increases with increasing distance from the coast (from 5 to 14%), indicating that the SBC is more recalcitrant than other forms of translocated PF/C. These results elucidate for the first time the key role of permafrost thaw in the transport of SBC to the Arctic Ocean. With ongoing global warming, these findings have implications for the biogeochemical carbon cycle, increasing the size of this refractory carbon pool in the Arctic Ocean.

  • 7. Sanchez-Garcia, Laura
    et al.
    Alling, Vanja
    Pugach, Svetlana
    Vonk, Jorien E.
    van Dongen, Bart
    Humborg, Christoph
    Dudarev, Oleg
    Semiletov, Igor
    Gustafsson, Orjan
    Inventories and behavior of particulate organic carbon in the Laptev and East Siberian seas2011In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 25Article in journal (Refereed)
    Abstract [en]

    Fluvial and erosional release processes in permafrost-dominated Eurasian Arctic cause transport of large amounts of particulate organic carbon (POC) to coastal waters. The marine fate of this terrestrial POC (terr-POC), water column degradation, burial in shelf sediments, or export to depth, impacts the potential for climate-carbon feedback. As part of the International Siberian Shelf Study (ISSS-08; August-September 2008), the POC distribution, inventory, and fate in the water column of the extensive yet poorly studied Eurasian Arctic Shelf seas were investigated. The POC concentration spanned 1-152 mu M, with highest values in the SE Laptev Sea. The POC inventory was constrained for the Laptev (1.32 +/- 0.09 Tg) and East Siberian seas (2.85 +/- 0.20 Tg). A hydraulic residence time of 3.5 +/- 2 years for these Siberian shelf seas yielded a combined annual terr-POC removal flux of 3.9 +/- 1.4 Tg yr(-1). Accounting for sediment burial and shelf-break exchange, the terr-POC water column degradation was similar to 2.5 +/- 1.6 Tg yr(-1), corresponding to a first-order terr-POC degradation rate constant of 1.4 +/- 0.9 yr(-1), which is 5-10 times faster than reported for terr-DOC degradation in the Arctic Ocean. This terr-POC degradation flux thus contributes substantially to the dissolved inorganic carbon excess of 10 Tg C observed during ISSS-08 for these waters. This evaluation suggests that extensive decay of terr-POC occurs already in the water column and contributes to outgassing of CO2. This process should be considered as a geographically dislocated carbon-climate coupling where thawing of vulnerable permafrost carbon on land is eventually adding CO2 above the ocean.

  • 8. Sperlich, Peter
    et al.
    Schaefer, Hinrich
    Fletcher, Sara E. Mikaloff
    Guillevic, Myriam
    Lassey, Keith
    Sapart, Celia J.
    Rockmann, Thomas
    Blunier, Thomas
    Carbon isotope ratios suggest no additional methane from boreal wetlands during the rapid Greenland Interstadial 21.22015In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 29, no 11, p. 1962-1976Article in journal (Refereed)
    Abstract [en]

    Samples from two Greenland ice cores (NEEM and NGRIP) have been measured for methane carbon isotope ratios (delta C-13-CH4) to investigate the CH4 mixing ratio anomaly during Greenland Interstadial (GI) 21.2 (85,000 years before present). This extraordinarily rapid event occurred within 150 years, comprising a CH4 mixing ratio pulse of 150 ppb (similar to 25%). Our new measurements disclose a concomitant shift in delta C-13-CH4 of 1 parts per thousand. Keeling plot analyses reveal the delta C-13 of the additional CH4 source constituting the CH4 anomaly as -56.8 +/- 2.8 parts per thousand, which we confirm by means of a previously published box model. We propose tropical wetlands as the most probable additional CH4 source during GI-21.2 and present independent evidence that suggests that tropical wetlands in South America and Asia have played a key role. We find no evidence that boreal CH4 sources, such as permafrost degradation, contributed significantly to the atmospheric CH4 increase, despite the pronounced warming in the Northern Hemisphere during GI-21.2.

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