G04_06

Export of pre-aged carbon to the Bay of Biscay at the end of the LGM

Queiroz Alves E¹, Wang Y², Hefter J¹, Grotheer H¹, Zonneveld K³, Mollenhauer G^1,3

¹Alfred Wegener Institute (AWI), Bremerhaven, Germany, ²NORCE Norwegian Research Centre, Bergen, Norway, ³MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany

The last deglaciation was the most recent relatively well-documented period of pronounced and fast climate warming. As such, it holds important information for our understanding of the climate system. Notably, the mechanisms leading to rapid atmospheric CO₂  changes during this period are incompletely defined. While research into terrestrial organic carbon reservoirs has been instrumental in exploring the possible sources of atmospheric CO₂ during these periods of rapid change, the underlying processes are not yet fully understood. Here we investigate the mobilization of organic carbon to the Bay of Biscay at the mouth of  the English Channel, where an enhanced terrigenous input has been reported for the last glacial-interglacial transition.  We have established an accurate and robust chronological framework for this deposition, showing enhanced rates of sediment accumulation from approximately 20.2 to 15.8 cal ky BP. The compound-specific radiocarbon  dating of n-alkanoic acids isolated from the sedimentary archive disclosed the deposition of pre-aged carbon with pre-deposition ages of up to ca. 30,000 yr, constituting the first direct evidence for the presence of ancient organic matter at the core location.  In the light of what has been reported for other regions with present or past permafrost conditions on land, this result points to the possibility of permafrost and/or petrogenic carbon export to the ocean, caused by processes that likely furthered the observed changes in atmospheric CO₂.