Amino acid racemization in Quaternary foraminifera from the Yermak Plateau, Arctic Ocean

Abstract

Abstract. Amino acid racemization (AAR) geochronology is a powerful tool for dating Quaternary marine sediments across the globe, yet its application to Arctic Ocean sediments has been limited. Anomalous rates of AAR in foraminifera from the central Arctic were reported in previously published studies, indicating that either the rate of racemization is higher in this area, or inaccurate age models were used to constrain the sediment ages. This study investigates racemization rates in foraminifera from three well-dated sediment cores taken from the Yermak Plateau during the 2015 TRANSSIZ (TRansitions in the Arctic Seasonal Sea Ice Zone) expedition on RV Polarstern. D and L isomers of the amino acids aspartic acid (Asp) and glutamic acid (Glu) were separated in samples of the planktic foraminifer Neogloboquadrina pachyderma and the benthic species Cassidulina neoteretis to quantify the extent of racemization. In total, 241 subsamples were analysed, extending back to marine oxygen isotope stage (MIS) 7. Two previously published power functions, which relate the extent of racemization of Asp and Glu in foraminifera to sample age are revisited, and a comparison is made between the ages predicted by these calibrated age equations and independent geochronological constraints available for the cores. Our analyses reveal an excellent match between ages predicted by a global compilation of racemization rates for N. pachyderma and confirm that a proposed Arctic-specific calibration curve is not applicable at the Yermak Plateau. These results generally support the rates of AAR determined for other cold bottom water sites and further highlight the anomalous nature of the purportedly high rate of racemization indicated by previous analyses of central Arctic sediments.