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.
Highlights
Dating Quaternary marine sediments from the Arctic Ocean has been a long-standing problem, and a number of studies (e.g. Backman et al, 2004; Stein, 2011; Alexanderson et al, 2014) highlight the challenges of establishing firm chronologies for these sediments
The extent of racemization generally increases with depth in both N. pachyderma and C. neoteretis samples, and this conforms to the expected diagenetic behaviour of amino acids in foraminifera
Differences in the rates of Amino acid racemization (AAR) (16 % for Asp and 23 %– 26 % for glutamic acid (Glu) – Fig. 7) between N. pachyderma and C. neoteretis tests from the same depths are similar to those documented in other AAR studies (e.g. King and Neville, 1977; Kaufman et al, 2013)
Summary
Dating Quaternary marine sediments from the Arctic Ocean has been a long-standing problem, and a number of studies (e.g. Backman et al, 2004; Stein, 2011; Alexanderson et al, 2014) highlight the challenges of establishing firm chronologies for these sediments. Dating Quaternary marine sediments from the Arctic Ocean has been a long-standing problem, and a number of studies Amino acid racemization (AAR) geochronology was first applied to Arctic Ocean sediments in the pioneering studies of Sejrup et al (1984) and later in that of Macko and Aksu (1986). Sejrup et al (1984) used AAR results to challenge the prevailing view of slow (mm kyr−1) sedimentation rates On the other hand, Macko and Aksu (1986) found that AAR chronology of sediments from the Alpha Ridge supported the accepted ages established by the use of these two dating techniques, supporting arguments for slow sedimentation rates in this region.
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