Comment on cp-2022-67

Abstract

Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the last glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs. Long-chain n-alkyl lipids and lignin phenols are two types of biomarkers excellently suited for the reconstruction of terrestrial higher plant vegetation, as they are derived from epicuticular waxes and from the major rigidifying material of higher plants. For the Okhotsk and Bering Seas off the mouths of the Amur and Yukon rivers, respectively, published records reported the temporal variations of n-alkyl lipid accumulation recording mostly erosive processes. Surface runoff, vegetation type, and degree of organic matter degradation as reflected by lignin have not been investigated so far. Here, we present new lignin phenol records from marine sediment cores and compare them with previously published lipid biomarker data from these two subarctic marginal seas. We find that in the Yukon Basin, vegetation change and wetland expansion began already in the early deglaciation (ED, 14.6–19 ka BP). This timing is different from observed changes in the Okhotsk Sea reflecting input from the Amur Basin, where wetland expansion and vegetation change occurred later in the Preboreal (PB). In the two basins, angiosperms contribution and wetland extent all reached maxima during the PB, both decreasing and stabilizing after the PB. We also find that the permafrost of the Amur Basin began to become remobilized in the PB. Retreat of sea-ice coupled with increased sea-surface temperatures in the Bering Sea during the ED might have promoted early permafrost mobilization. In both records, accumulation rates of lignin phenols and lipids are similar, suggesting that under conditions of rapid sea-level rise and shelf flooding, both types of terrestrial biomarkers are delivered by the same transport pathway.