Sustained imbalance in the calcium cycle and climate-ocean chemistry interactions over the Eocene-Oligocene transition from the geochemistry of large benthic Foraminifera

Author(s): Evans, David; Cotton, Laura J.; Pearson, Paul; Rosenthal, Yair; Rae, James; Müller, Wolfgang; Erez, Jonathan; Affek, Hagit P.
Author Affiliation(s): Primary:
Saint Andrews University, School of Earth and Environmental Sciences, Saint Andrews, United Kingdom
Other:
University of Florida, United States
Cardiff University, United Kingdom
Rutgers University, United States
Royal Holloway University of London, United Kingdom
Hebrew University of Jerusalem, Israel
Volume Title: Geological Society of America, 2017 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 49(6); Geological Society of America, 2017 annual meeting & exposition, Seattle, WA, Oct. 22-25, 2017. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: The Eocene-Oligocene Transition (EOT) arguably represents the most dramatic permanent shift in Earth's climate during the Cenozoic, marking the onset of an Antarctic ice sheet similar in size to modern. The transition is associated with a large drop in the carbonate compensation depth (CCD) and rapid weathering of shallow carbonate platforms as a result of a ∼100 m sea level fall. Here, we explore whether these global changes resulted in a concommitant shift in the seawater calcium concentration ([Casw]). Such reconstructions not only have the potential to inform us of changes in the processes governing the calcium cycle over the EOT, but may also have implications for the accuracy of temperature and ice volume reconstructions based on trace element systems if seawater chemistry shifted. We simultaneously reconstruct temperature and seawater chemistry based on two novel proxies: coupled Mg/Ca-clumped isotopes from shallow-dwelling large benthic foraminifera from the Tanzania Drilling Project, and the Na/Ca ratio of benthic foraminifera from DSDP Site 522 and IODP Site U1333. These data demonstrate a globally-coherent signal of calcium decrease over the transition, implying that calcium burial out-paced supply despite the weathering of carbonate platforms. A decrease in [Casw] would also serve to further draw-down CO2 across the transition, requiring a [CO32-] increase to maintain an equivalent or deeper CCD. Furthermore, our clumped-isotope temperatures highlight a substantially larger magnitude of sea surface temperature cooling compared to published Mg/Ca records. The discrepancy possibly results from a bias in the trace element data due to the Mg/Casw shift, indicating that ice volume and temperature reconstructions based on Mg/Ca may be systematically biased.
Year of Publication: 2017
Research Program: DSDP Deep Sea Drilling Project
IODP Integrated Ocean Drilling Program
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Alkaline earth metals; Angola Basin; Atlantic Ocean; Benthic taxa; Calcium; Calcium cycle; Cenozoic; Climate change; DSDP Site 522; Deep Sea Drilling Project; East Pacific; Eocene; Expedition 320; Expeditions 320/321; Foraminifera; Geochemical cycle; IODP Site U1333; IPOD; Integrated Ocean Drilling Program; Isotopes; Leg 73; Lower Oligocene; Magnesium; Marine environment; Metals; Mg/Ca; Microfossils; Na/Ca; North Pacific; Northeast Pacific; Oligocene; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Paleoenvironment; Paleogene; South Atlantic; Tanzania Drilling Project; Tertiary; Upper Eocene
Coordinates: N103100 N103100 W1382510 W1382510
S260651 S260650 W0050646 W0050647
Record ID: 2018059094
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States