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- Semiletov, I. P., et al.
(författare)
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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
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 8:9, s. 2407-2426
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Pipko, I.I., et al.
(författare)
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Interannual variability of air-sea CO2 fluxes and carbon system in the East Siberian Sea
- 2011
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Ingår i: Biogeosciences. ; 8, s. 1987-2007
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Tidskriftsartikel (refereegranskat)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.
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