Sources and Fluxes of Carbon Buried on Subaqueous Delta of Lena River and Inner Shelf of Laptev Sea (Russian Arctic)

Eugene Karabanov¹, Janiel Rivera¹, Douglas Williams¹, Michael Kuzmin², Valeryi Buchunskyi², and Alexander Mamontov^2
1 University of South Carolina, Columbia, SC
² Institute of Geochemistry, Siberian Branch of Russian Academy of Sciences, Irkutsk, Russia

Cores from the Laptev Sea inner shelf (30-70km from delta), were analyzed for TOC, TN and δ¹³C to understand the variation of river export over time, amount and origin of carbon in sediments of Lena River's prodelta and shallow Laptev Sea. Alternated fluvial and marine units were found along the cores and 17 fluvial events were diagnosed that are extended to the Laptev Sea up to 34.5-47.5km, which were accumulated during the last 2,000yrs, based on ¹⁴C dating of marine bivalves. TOC concentration in fluvial units fluctuate significantly (0.7-4%) depending on grain-size and distance from the delta, while TOC concentration in marine units is uniform (1.8-2.2%). δ¹³C fluctuate from 25.6 to 27.9‰ in fluvial and from 25.7 to 26.9‰ in marine units, revealing its predominantly terrestrial origin. A value of δ¹³C is in good agreement with isotopic composition of Lena River suspended matter and sediments of Laptev Sea. Data exhibits that TOC stored in sediments close to the delta, became isotopically heavier (20.1-24.9‰), showing plankton origin of organics buried in sediments 30-47km from the delta at 11-17m water depth. Apparently, these organics originated from shallow water plankton blooming during summer. The delta is surrounded by 15-20km wide belt of sediments with a predominantly non terrestrial TOC that contains more planktonic TOC then suspended matter of Lena River and shelf sediments. Collected cores represent the time interval covered the Late Holocene and carbon isotopic composition is uniform throughout time, showing consistent pattern of sources and fluxes of carbon during last 2000yrs.