Amino acid racemization in Quaternary foraminifera from the Yermak Plateau

Abstract. Amino acid racemization(AAR) geochronologyis 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 foraminiferafrom the central Arctic were reported in previously published studies, indicating that either the rate of racemizationis higher in this area, or inaccurate age models were used to constrain the sediment ages. This study investigates racemizationrates in foraminiferafrom three well-dated sediment cores taken from the Yermak Plateau during the 2015 TRANSSIZ 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 foraminifera, Neogloboquadrina pachyderm and the benthic species, Cassidulinaneoteretis to quantify the extent of racemization. In total, 241 subsamples were analysed, extending back to Marine Isotope Stage(MIS) 7. Two previously published power functions, which relate the extent of racemizationof Asp and Glu in foraminiferato sample age are revisited, and a comparison is made between the ages predicted by these calibrated age equations and independent geochronologicalconstraints available for the cores. Our analyses reveal an excellent match between ages predicted by a global compilation of racemizationrates 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 watersites, and further highlight the anomalous nature of the purportedly high rate of racemizationindicated by previous analyses of central Arctic sediments.