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Impact of the Miocene Carbonate Crash (13-8 Ma) on Bulk Carbonate δ44/40Ca in the Eastern Equatorial Pacific

Regnier, Alexa Marie
http://rave.ohiolink.edu/etdc/view?acc_num=osu168329735635357

Abstract Details

2023, Master of Science, Ohio State University, Earth Sciences.
The Miocene epoch, a period of dynamic global changes, ranged from 23.03 to 5.33 million years ago (Ma). Global temperature was between 3 and 7 ˚C higher than today, but atmospheric carbon dioxide (CO2) concentrations were thought to be ~400-600 ppm, only slightly more elevated than modern values (but significantly more than preindustrial levels). This, combined with heightened global sea levels, makes the Miocene a possible analog for future climate warming scenarios. Between 13.5 and 8.2 Ma during the so-called “carbonate crash”, sediment carbonate content (weight % CaCO3) dropped in all major tropical ocean basins. Many hypotheses attempt to explain the mechanisms behind the crash, including potential shifts in the chemical makeup of weathered materials or a reorganization of deep-water circulation patterns that changed silicate and carbonate deposition. Here, calcium (Ca) isotopes are examined to understand better how the major geologic marine Ca sink was impacted by the crash. For this study, 55 deep sea bulk carbonate sediment samples were obtained from the International Ocean Discovery Program (IODP) Expedition 320/321, Sites U1337 and U1338, located in the eastern equatorial Pacific (EEP). Samples ranged in age from 17 to 7 Ma, allowing for high-resolution ~200 kyr spacing. An analysis of changes in marine Ca isotopes (δ44/40Ca) shows an overall increase of about 0.2 ‰ over the mid to late-Miocene which is consistent with biogenic carbonate records from other tropical basins. The relationship between bulk carbonate Sr/Ca and δ44/40Ca indicates that post-depositional modification plays a minor role in the δ44/40Ca increase at Sites U1337 and U1338, and therefore the record likely reflects primary δ44/40Casediment. The increase in δ44/40Ca also agrees with an existing marine barite record from the EEP. However, the magnitude of change between the bulk carbonate record differs from the seawater δ44/40Ca marine barite record between 15 and 10 Ma, indicative of a short-lived change in Ca isotopic fractionation. Published fluid inclusion data points to a decrease in seawater Ca content during this time, and published radiogenic Sr records indicate a shift in isotopic composition of the weathering flux toward increased granitic input. The decrease in seawater Ca content and increase in seawater δ44/40Ca hint at a decrease in the weathering (input) on long-term scales that is larger than any decrease in the sedimentation (output) flux. Together, the changes in Ca isotopic fractionation, Ca fluxes (amount and composition), and seawater Ca concentration are consistent with a reduction of deep-sea carbonate deposition that may have significantly impacted the marine Ca cycle during the Miocene
Elizabeth Griffith (Advisor)
Andréa Grottoli (Committee Member)
Matthew Saltzman (Committee Member)
93 p.
Earth; Geochemistry; Geology; Marine Geology
calcium; calcium cycle; geochemistry; Miocene; carbonate crash; paleoceanography

Recommended Citations

Citations

  • Regnier, A. M. (2023). Impact of the Miocene Carbonate Crash (13-8 Ma) on Bulk Carbonate δ44/40Ca in the Eastern Equatorial Pacific [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu168329735635357

    APA Style (7th edition)

  • Regnier, Alexa. Impact of the Miocene Carbonate Crash (13-8 Ma) on Bulk Carbonate δ44/40Ca in the Eastern Equatorial Pacific. 2023. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu168329735635357.

    MLA Style (8th edition)

  • Regnier, Alexa. "Impact of the Miocene Carbonate Crash (13-8 Ma) on Bulk Carbonate δ44/40Ca in the Eastern Equatorial Pacific." Master's thesis, Ohio State University, 2023. http://rave.ohiolink.edu/etdc/view?acc_num=osu168329735635357

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.