Response and Recovery of Surface Ocean Carbonate Chemistry in the Mid-latitude North Atlantic During the PETM

Marcus Gutjahr1,2, Philip F. Sexton3, Andy Ridgwell4, Eleni Anagnostou1, Paul N Pearson5, Heiko Palike6, Richard D Norris7, Ellen Thomas8 and Gavin L Foster9, (1)University of Southampton, Southampton, United Kingdom, (2)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (3)The Open University, School of Environment, Earth and Ecosystem Sciences, Milton Keynes, United Kingdom, (4)University of California Riverside, Department of Earth and Planetary Sciences, Riverside, United States, (5)University College London, School for Earth and Ocean Sciences, London, United Kingdom, (6)MARUM, Bremen, Germany, (7)Scripps Institution of Oceanography, La Jolla, CA, United States, (8)Wesleyan University, Middletown, United States, (9)University of Southampton, School of Ocean and Earth Science, Southampton, United Kingdom
Abstract:
With more than 3,000 Gt of carbon released over ≤10 ka [1-3], the Paleocene-Eocene Thermal Maximum (PETM) arguably represents our closest geologic analogue for the long-term effects of present-day and future fossil fuel carbon combustion. The PETM carbon isotopic excursion (CIE) was initiated at ~55.9 Ma [4] and lasted for ~170 ka [5]. This event was associated with pronounced ocean acidification, recently reported to amount to a drop in oceanic mixed-layer pH on the order of 0.3 pH units at the central North Pacific Shatsky Rise [6].

Here, a new boron isotope record (expressed in δ11B) will be presented from mixed-layer dwelling foraminiferal species Morozovella subbotinae across the PETM from DSDP Site 401 in the North Atlantic. We convert the δ11B data into mixed layer pH, complemented by elemental records and new carbon and oxygen isotope data generated from the same samples. Our records cover the time interval from about 300 ka prior to the CIE to more than 400 ka after the CIE. The bulk carbonate content decreased from 80 to 30 wt% at the onset of the CIE, but calcareous microfossils in the interval show no signs of carbonate dissolution [7, and this study].

We find significantly lowered pH for almost 100 ka following the CIE onset and furthermore, no complete post-PETM recovery of surface ocean pH to pre-PETM values, likely tracing the longer-term climatic trajectories leading to the subsequent Eocene Thermal Maximum 2 (ETM 2) [8]. Based on this surface ocean pH record, atmospheric CO2 concentrations over the PETM are estimated using the GENIE Earth System Model [9, 10].

References

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