Delivery of aged terrestrial organic matter to the Laptev Sea during the last deglaciation

Abstract. Arctic warming is causing rapid thawing of permafrost, which holds about 1.25 times as much carbon as currently is present in the atmosphere. The ongoing Arctic warming and projected sea level rise are expected to accelerate permafrost thaw, leading to the reintroduction of ancient, previously frozen organic carbon into the contemporary carbon cycle. The degradation of permafrost and the consequent release of greenhouse gases into the atmosphere are considered one of the most significant positive climate feedback mechanisms that could potentially intensify global warming trends. Studying carbon release from permafrost thawing during the last deglaciation provides a perspective that can help refine the anticipated climate-permafrost feedback. However, the timings, magnitude and mechanisms of carbon release from thawing permafrost are still poorly understood, primarily because of the limited number of deglacial records that document carbon mobilization occurrences. In the present study we analyzed a high-resolution marine sediment record close to the Lena River outflow located on the Laptev Sea continental slope, close to the paleo-shoreline during the Last Glacial Maximum, and we provided a continuous record of the last 16 kyr. Biomarkers and radiocarbon dating of terrestrial materials have been used to reconstruct deglacial permafrost thaw events. We integrated mass accumulation rate data from the core site with the depositional ages of terrigenous biomarkers to identify the occurrence of past massive permafrost degradation and mobilization. We found that the highest accumulation of strongly pre-aged terrigenous biomarkers coincided with peaks in rapid sea-level rise, suggesting that permafrost carbon delivered to the core site was mobilized mainly by coastal erosion. Superimposed on the coastal signal, a significant freshwater discharge event was documented at about 13 kyr BP, characterized by low mass accumulation rates of terrigenous biomarkers and relatively young pre-depositional ages compatible with surface runoff-derived terrigenous material. This study further adds to the limited datasets on the age of deglacial permafrost-derived carbon accumulating on the Arctic shelves and offers valuable insights into the future behavior of permafrost carbon soils in the context of a warming climate.