Deglacial records of terrigenous organic matter accumulation off the Yukon and Amur rivers based on lignin phenols and long-chain n-alkanes

Abstract

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.

Dynamic land-plant carbon sources in marine sediments inferred from ancient DNA

“…3), reflecting known phases of increased terrestrial productivity and terrestrial organic matter (OM) delivery by meltwater runoff (23; 24). Furthermore, the accumulation of land plant DNA shows the same peaks as the Lignin accumulation rate of the marine sediment core SO202-18-3/6 that is located close to SO201-2-77KL in the Bering Sea (7).…”

“…This means that plant DNA can serve as a proxy for the burial of recent plant matter and such for carbon sink on human-relevant timescales. In contrast, compound-specific radiocarbon studies indicate that common biomarkers for terrigenous matter, such as leaf waxes and lignin, originate, at least partly, from a strongly pre-aged organic carbon pool, for example, from permafrost soil (7), though biomarker-specific turnover times have been recognized (38). Hence, the lateral transport of old soils or sediments (37) may be less reflected in the plant DNA signal but this requires further research.…”

“…Hitherto, even the separation of marine (4) and terrigenous (5) carbon has been a challenge for state-of-the-art biogeochemical and isotopic methods and only very rough taxonomic information has been available. For example, lignin-biomarker patterns have been used as proxies for the relative share of gymnosperms (6) and angiosperms (7); and fatty acid compound-specific isotope signals indicate the relative share and productivity of aquatic plants (8), but cannot differentiate between coastal and freshwater taxa. Furthermore, mixing models are applied to compound-specific isotope data to discern the relative contribution of C3 and C4 plants (9).…”