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Abstract. We report the results of amino acid racemization (AAR) analyses of aspartic acid (Asp)and glutamic acid (Glu) in the planktic Neogloboquadrina pachyderma, and the benthic Cibicidoides wuellerstorfi, foraminifera species collected from sediment cores from the Arctic Ocean. The cores were retrieved at various deep-sea sites of the Arctic, which cover a large geographical area from the Greenland and Iceland seas (GIS) to the Alpha and Lomonosov ridges in the central Arctic Ocean. Age models for the investigated sediments were developed by multiple dating and correlation techniques, including oxygen isotope stratigraphy, magnetostratigraphy, biostratigraphy, lithostratigraphy, and cyclostratigraphy. The extent of racemization (D/L values) was determined on 95 samples (1028 subsamples) and shows a progressive increase downcore for both foraminifera species. Differences in the rates of racemization between the species were established by analysing specimens of both species from the same stratigraphic levels (n=21). Aspartic acid (Asp) and glutamic acid (Glu) racemize on average 16 ± 2 % and 23 ± 3 % faster, respectively, in C. wuellerstorfi than in N. pachyderma. The D/L values increase with sample age in nearly all cases, with a trend that follows a simple power function. Scatter around least-squares regression fits are larger for samples from the central Arctic Ocean than for those from the Nordic Seas. Calibrating the rate of racemization in C. wuellerstorfi using independently dated samples from the Greenland and Iceland seas for the past 400 ka enables estimation of sample ages from the central Arctic Ocean, where bottom water temperatures are presently relatively similar. The resulting ages are older than expected when considering the existing age models for the central Arctic Ocean cores. These results confirm that the differences are not due to taxonomic effects on AAR and further warrant a critical evaluation of existing Arctic Ocean age models. A better understanding of temperature histories at the investigated sites, and other environmental factors that may influence racemization rates in central Arctic Ocean sediments, is also needed.
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Amino acid racemization in Quaternary foraminifera from the Yermak Plateau, Arctic Ocean
Abstract. Amino acid racemization (AAR) geochronology is a powerful tool for datingQuaternary marine sediments across the globe, yet its application to ArcticOcean 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 racemization is higher in this area, orinaccurate age models were used to constrain the sediment ages. This studyinvestigates racemization rates in foraminifera from three well-datedsediment 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 asparticacid (Asp) and glutamic acid (Glu) were separated in samples of theplanktic foraminifer Neogloboquadrina pachyderma and the benthic species Cassidulina neoteretis to quantify the extent ofracemization. In total, 241 subsamples were analysed, extending back tomarine oxygen isotope stage (MIS) 7. Two previously published powerfunctions, which relate the extent of racemization of Asp and Glu inforaminifera to sample age are revisited, and a comparison is made betweenthe ages predicted by these calibrated age equations and independentgeochronological constraints available for the cores. Our analyses reveal anexcellent match between ages predicted by a global compilation ofracemization rates for N. pachyderma and confirm that a proposed Arctic-specificcalibration curve is not applicable at the Yermak Plateau. These resultsgenerally support the rates of AAR determined for other cold bottom watersites and further highlight the anomalous nature of the purportedly highrate of racemization indicated by previous analyses of central Arcticsediments.
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- Award ID(s):
- 1855381
- PAR ID:
- 10167279
- Date Published:
- Journal Name:
- Geochronology
- Volume:
- 1
- Issue:
- 1
- ISSN:
- 2628-3719
- Page Range / eLocation ID:
- 53 to 67
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/gchron-1-53-2019
