Intra‐Valve Elemental Distributions in Arctic Marine Ostracodes: Implications for Mg/Ca and Sr/Ca Paleothermometry

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Maximiliano Rodriguez, John M. Doherty, Ho Lai Hilary Man, Rujian Wang, Wenshen Xiao, Baochun Zhou, Benoit Thibodeau, Christelle Not
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2021
• Subjects: Arctic Ocean; bottom water temperature; Mg/Ca; ostracod; Sr/Ca; trace element distribution; Geophysics. Cosmic physics; QC801-809; Geology; QE1-996.5; Arctic; Chukchi Sea; Chukchi; Sea ice
• Online Access: https://doi.org/10.1029/2020GC009379; https://doaj.org/article/900c6fa413274033b30531b04b5a0905

Abstract Reconstructing intermediate and bottom‐water temperature in the Arctic Ocean is key for understanding paleoclimatic phenomena, such as the region's interactions with warm Atlantic waters, stratification, and sea‐ice dynamics. However, benthic proxy archives are sparse throughout the Arctic circle compared to lower latitudes. Trace‐element ratios (E/Ca) derived from ostracodes, a group of bivalved microscopic crustaceans, have shown promise in this regard. Samples for E/Ca measurements typically require rigorous cleaning prior to analysis, and signs of contamination are routinely monitored through the presence of other trace elements such as Al, Fe, and Mn, which are associated with suspected sources of overprinting. However, there has not yet been an intra‐valve investigation of all of these trace elements, which may hinder our ability to effectively identify geochemical overprinting. Here, we present several elemental concentration and E/Ca ratio measurements in two ostracode genera, Krithe and Polycope, extracted from Chukchi Sea sediment samples. We further investigate the intra‐valve distribution of elements within single shells of adult and juvenile specimens using electron probe microanalysis (EPMA). Our findings suggest that brushing and bleach treatments may not be effective for completely eliminating clays from the edges of valves, which can bias paleoclimatologically relevant trace‐element proxies such as Mg/Ca ratios, particularly in the case of incomplete or small samples with low amounts of calcite material. In addition, we report the first trace‐element data from the genus Polycope, which shows potential as a new Arctic paleotemperature archive.