SedGeo: Eocene carbonate accumulation in the north-central Pacific Ocean: new insights from Ocean Drilling Program Site 1209, Shatsky Rise

Joyeeta Bhattacharya and Gerald R. Dickens
Major climate transitions and perturbations in global carbon cycle are known to have occurred during the Eocene, between 56 and 34 million years ago (Ma). A series of carbon isotope excursions (CIEs) mark variations in the global carbon cycle and changes in climate through early Eocene. Paleocene-Eocene Thermal Maximum(PETM) ca. 56 Ma is the most pronounced and well documented of these events expressed as a clay rich layer in many deep-sea sections, resulting from widespread carbonate dissolution on the seafloor, which is in turn re-lated to shoaling of the carbonate compensation depth (CCD) and lysocline. Other CIEs of early Eocene had similar response. However, response of these geologically ‘instantaneous’ hyperthermals differ from long-term warmth (multi-million-year time scale) of the Early Eocene Climate Optimum (EECO) in terms of sea-floor carbonate accumulation. Following the termination of EECO, earth’s climate transitioned into long-term cooling.Pronounced fluctuations in CCD of equatorial Pacific are known to have occurred during middle-late Eocene as well, whose global extent and origin are still unresolved. Most proxy records either span the interval of early Eocene or document particular climatic events in Eocene, which significantly limits visualizing the long-term Eocene climate change and response of open marine carbonate preservation. The present study documents change in carbonate dissolution and carbonate mass accumulation rate through the entire Eocene (56–34 Ma)at ODP Site 1209 on Shatsky Rise, north-central Pacific and ties it to a stable carbon and oxygen isotope record.Our study determines the correlation between deep-sea carbonate dissolution and carbon cycling process during the dynamic climate regime of Eocene. A strong correlation between magnitude of CIEs and intensity of dissolution for early Eocene hyperthermal events appears to significantly weaken for multiple dissolution events in middle-late Eocene, thereby indicating fundamental difference in their causal mechanism.

Bhattacharya, J., & Dickens, G. R. (2020). Eocene carbonate accumulation in the north-central Pacific Ocean: New insights from Ocean Drilling Program Site 1209, Shatsky Rise. Sedimentary Geology, 105705.

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