Mobilization of old terrestrial carbon in the North Pacific realm caused by permafrost thawing, sea-level rise and ice-sheet melting during the last deglaciation

• Main Authors: Winterfeld, Maria, Meyer, Vera, Mollenhauer, Gesine, Dummann, Wolf, Köhler, Peter, Hefter, Jens, Lembke-Jene, Lester, Wacker, Lukas, Mc Intyre, Cameron, Haghipour, Negar, Tiedemann, Ralf, Gersonde, Rainer, Kokfelt, Ulla
• Format: Conference Object
• Language: unknown
• Published: 2017
• Subjects: Bering Sea; Brooks Range; Ice; Ice Sheet; permafrost; Yukon river; Yukon
• Online Access: https://epic.awi.de/id/eprint/45544/; https://hdl.handle.net/10013/epic.51816

The last deglaciation was characterized by rising concentration in atmospheric CO2 (CO2atm) and a decrease in its radiocarbon content (Δ14Catm). Mobilization of 14C-depleted terrestrial organic carbon, which was previously frozen in extensive boreal permafrost soils, might have contributed to both changes, and was potentially caused by coastal erosion during deglacial sea-level rise and warming. Since parts of this potentially mobilized organic carbon was reburied in marine sediments, records of accumulation of terrigenous biomarkers and their compound-specific radiocarbon ages can provide insights into the timing and controls on permafrost decomposition. We present data from three marine sediment cores, two cores off the Amur River draining into the Sea of Okhotsk, and one core from the Northeastern Bering Sea adjacent to the Bering shelf (one the largest shelf areas flooded during the deglaciation) receiving input from the Yukon River. During the Last Glacial Maximum all catchments were completely covered with permafrost. Today, the Amur drainage basin is free of permafrost while the Yukon catchment is covered by discontinuous permafrost. All sites show three distinct deglacial maxima (at 16.5, 14.5, 11.5 ka BP) in accumulation of old terrigenous biomarkers (5-20 kyr old at the time of deposition). The peaks occurred during meltwater pulses suggesting that sea-level rise remobilized old terrestrial carbon from permafrost on the flooded shelfs. In the Bering Sea fossil, mature organic matter, mobilized by erosion of organic rich rocks during the retreat of Brooks Range glaciers and the Laurentide ice sheet additionally contributed to the first peak via increased fluvial runoff. Deglacial changes in abundance ratios of long-chain n-alkanes record gradual changes in vegetation type and wetland extent in the Amur-river catchment. Since wetland expansion is closely linked to permafrost thaw this implies that permafrost decomposition in the Amur drainage basin was a gradual process. By contrast sea-level rise caused ...