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Cenozoic seawater Sr/Ca evolution

Sosdian, Sindia, Lear, Caroline Helen, Tao, Kai, Grossman, Ethan, O'Dea, Aaron and Rosenthal, Yair 2012. Cenozoic seawater Sr/Ca evolution. Geochemistry Geophysics Geosystems 13 (10) , Q10014. 10.1029/2012GC004240

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Abstract

Records of seawater chemistry help constrain temporal variations in geochemical processes that impact the global carbon cycle and climate through Earth’s history. Here we reconstruct Cenozoic seawater Sr/Ca (Sr/Casw) using fossil Conus and turritellid gastropod Sr/Ca. Combined with an oxygen isotope paleotem- perature record from the same samples, the gastropod record suggests that Sr/Casw was slightly higher in the Eocene ($11.4 ` 3 mmol/mol) than today ($8.54 mmol/mol) and remained relatively stable from the mid- to late Cenozoic. We compare our gastropod Cenozoic Sr/Casw record with a published turritellid gas- tropod Sr/Casw record and other published biogenic (benthic foraminifera, fossil fish teeth) and inorganic pre- cipitate (calcite veins) Sr/Casw records. Once the uncertainties with our gastropod-derived Sr/Casw are taken into account the Sr/Casw record agrees reasonably well with biogenic Sr/Casw records. Assuming a seawater [Ca] history derived from marine evaporite inclusions, all biogenic-based Sr/Casw reconstructions imply decreasing seawater [Sr] through the Cenozoic, whereas the calcite vein Sr/Casw reconstruction implies increasing [Sr] through the Cenozoic. We apply a simple geochemical model to examine the implications of divergence among these seawater [Sr] reconstructions and suggest that the interpretation and uncertainties associated with the gastropod and calcite vein proxies need to be revisited. Used in conjunction with records of carbonate depositional fluxes, our favored seawater Sr/Ca scenarios point to a significant increase in the proportion of aragonite versus calcite deposition in shelf sediments from the Middle Miocene, coincident with the proliferation of coral reefs. We propose that this occurred at least 10 million years after the seawater Mg/Ca threshold was passed, and was instead aided by declining levels of atmospheric carbon dioxide.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: G Geography. Anthropology. Recreation > GC Oceanography
Q Science > QE Geology
Uncontrolled Keywords: gastropods; seawater chemistry; strontium
Additional Information: Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/1525-2027/ (accessed 20/02/2014).
Publisher: American Geophysical Union.
ISSN: 1525-2027
Funders: NSF
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Feb 2020 13:47
URI: http://orca.cf.ac.uk/id/eprint/39119

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