Carbon geochemistry of plankton-dominated samples in the Laptev and East Siberian shelves: contrasts in suspended particle composition

Tesi, Tommaso; Geibel, M. C.; Pearce, Christof; Gershelis, Elena; Vonk, Jorien E.; Karlsson, Emma; Salvadó, Joan A.; Kruså, Martin; Bröder, Lisa; Humborg, Christoph; Semiletov, I. P.; Gustafsson, Örjan

doi:10.5194/os-13-735-2017

Cited by 13 publications

(15 citation statements)

References 68 publications

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“…In general, terrOC may be divided into terrOC from the active layer (topsoil) and Pleistocene Ice-Complex Deposits (ICD) by combining δ 13 C and Δ 14 C. However, establishing the topsoil Δ 14 C endmember is complicated by the fact that it is influenced by the cross-shelf net transport time, which is so far only constrained for the eastern Laptev Sea . One caveat of using only δ 13 C as a source marker, on the other hand, is its relatively poorly constrained value for the marine end-member (e.g., Belicka & Harvey, 2009;Tesi et al, 2017), which is reflected in the comparatively large uncertainty of 2.6‰. The spread between marine and terrigenous sources, especially for ICD, is larger for Δ 14 C (−50‰ ± 12‰ for marine, −232‰ ± 147‰ for topsoil and −966‰ ± 45‰ for ICD; Tesi, Muschitiello, et al, 2016), resulting in a higher precision of the dual carbon isotope approach.…”

Section: Source Apportionmentmentioning

confidence: 99%

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

Bröder

Andersson

Tesi

et al. 2019

Global Biogeochemical Cycles

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Ongoing permafrost thaw in the Arctic may remobilize large amounts of old organic matter. Upon transport to the Siberian shelf seas, this material may be degraded and released to the atmosphere, exported off‐shelf, or buried in the sediments. While our understanding of the fate of permafrost‐derived organic matter in shelf waters is improving, poor constraints remain regarding degradation in sediments. Here we use an extensive data set of organic carbon concentrations and isotopes ( n = 109) to inventory terrigenous organic carbon (terrOC) in surficial sediments of the Laptev and East Siberian Seas (LS + ESS). Of these ~2.7 Tg terrOC about 55% appear resistant to degradation on a millennial timescale. A first‐order degradation rate constant of 1.5 kyr −1 is derived by combining a previously established relationship between water depth and cross‐shelf sediment‐terrOC transport time with mineral‐associated terrOC loadings. This yields a terrOC degradation flux of ~1.7 Gg/year from surficial sediments during cross‐shelf transport, which is orders of magnitude lower than earlier estimates for degradation fluxes of dissolved and particulate terrOC in the water column of the LS + ESS. The difference is mainly due to the low degradation rate constant of sedimentary terrOC, likely caused by a combination of factors: (i) the lower availability of oxygen in the sediments compared to fully oxygenated waters, (ii) the stabilizing role of terrOC‐mineral associations, and (iii) the higher proportion of material that is intrinsically recalcitrant due to its chemical/molecular structure in sediments. Sequestration of permafrost‐released terrOC in shelf sediments may thereby attenuate the otherwise expected permafrost carbon‐climate feedback.

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Section: Source Apportionmentmentioning

confidence: 99%

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

Bröder

Andersson

Tesi

et al. 2019

Global Biogeochemical Cycles

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“…For the Laptev Sea shelf, a fraction of the surface water DIC used for marine production is derived from terrestrial dissolved organic carbon (DOC) and particulate organic carbon (POC) remineralized in shelf waters and transported from land (Tesi et al, 2017;Alling et al, 2012). Based on these data we use an isotope end-member composition of −23.0 ‰ for marine organic matter in the Laptev Sea.…”

Section: Marine Versus Terrestrial End-member Partitioning Of Carbon mentioning

confidence: 99%

“…Generally, marine productivity in the Laptev Sea is low and controlled by the nutrients derived from Atlantic water, but spring outflow from the Lena River provides an additional temporary land-derived nutrient source (Pivovarov et al, 1999;Sakshaug et al, 2004;Nitishinsky et al, 2007;Bourgeois et al, 2017) during late spring ice melt (Raymond et al, 2007). Terrestrially derived nutrients can also directly affect marine productivity by new production, or indirectly due to plankton production from remineralized, terrestrially derived dissolved organic carbon and particulate organic carbon Tesi et al, 2017). In the eastern East Siberian and Chukchi seas, the inflow of nutrient-rich Pacific water supports higher marine primary productivity (e.g., Grebmeier et al, 2006).…”

Section: Marine Versus Terrestrial Organic Matter Contributionmentioning

confidence: 99%

Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment

et al. 2018

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Abstract. The Siberian Arctic Sea shelf and slope is a key region for the degradation of terrestrial organic material transported from the organic-carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O 2 microelectrode profiling; intact sediment core incubations; 35 S-sulfate tracer experiments; pore-water dissolved inorganic carbon (DIC); δ 13 C DIC ; and iron, manganese, and ammonium concentrations from 20 shelf and slope stations. This data set provides a spatial overview of sediment carbon mineralization rates and pathways over large parts of the outer Laptev and East Siberian Arctic shelf and slope and allows us to assess degradation rates and efficiency of carbon burial in these sediments. Rates of oxygen uptake and iron and manganese reduction were comparable to temperate shelf and slope environments, but bacterial sulfate reduction rates were comparatively low. In the topmost 50 cm of sediment, aerobic carbon mineralization dominated degradation and comprised on average 84 % of the depthintegrated carbon mineralization. Oxygen uptake rates and anaerobic carbon mineralization rates were higher in the eastern East Siberian Sea shelf compared to the Laptev Sea shelf. DIC / NH + 4 ratios in pore waters and the stable carbon isotope composition of remineralized DIC indicated that the degraded organic matter on the Siberian shelf and slope was a mixture of marine and terrestrial organic matter. Based on dual end-member calculations, the terrestrial organic carbon contribution varied between 32 and 36 %, with a higher contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation of the measured degradation rates using isotope end-member apportionment over the outer shelf of the Laptev and East Siberian seas suggests that about 16 Tg C yr −1 is respired in the outer shelf seafloor sediment. Of the organic matter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C yr −1 is degraded by anaerobic processes, with a terrestrial organic carbon contribution ranging between 0.3 and 0.5 Tg yr −1 .

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“…The significant correlation (r 2 0.75, P < 0.05) between the dissolved O 2 uptake and anaerobic carbon degradation by sulfate reduction with a slope of 6.1 ± 1.1 (Fig. 7) reflects the coupling of oxygen uptake to the oxidation of reduced inorganic metabolites (FeS and H 2 S) produced during sulfate reduction (e.g., Glud, 2008;Jørgensen and Kasten, 2006;Thamdrup, 2000;Berg et al, 2003). The percentage of the inverse of this slope, 16.4 %, is slightly lower than the 23 % reported for oxygenated coastal and continental shelf sediment (Canfield et al, 2005) but is consistent with the notion that a substantial amount of the buried organic matter in Siberian shelf sediment is oxidized anaerobically.…”

Section: Coupled Terminal Electron-accepting Processesmentioning

confidence: 99%

“…where f terr and f mar are the respective mass fractions of terrestrial and marine-derived organic carbon and δ 13 C terr OC and δ 13 C marine OC reflect the isotope composition of these end-members. For the Laptev Sea shelf, a fraction of the surface water DIC used for marine production is derived from terrestrial dissolved organic carbon (DOC) and particulate organic carbon (POC) remineralized in shelf waters and transported from land (Tesi et al, 2017;Alling et al, 2012). Based on these data we use an isotope end-member composition of −23.0 ‰ for marine organic matter in the Laptev Sea.…”

Section: Marine Versus Terrestrial End-member Partitioning Of Carbon mentioning

confidence: 99%

Responses to referees 1 and 2

Brüchert¹

2017

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Carbon geochemistry of plankton-dominated samples in the Laptev and East Siberian shelves: contrasts in suspended particle composition

Cited by 13 publications

References 68 publications

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment

Responses to referees 1 and 2

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