Boron proxy evidence for surface ocean acidification & elevated pCO2 during the PETM

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Author(s): Penman, Donald E.; Zachos, James C.; Honisch, Barbel; Eggins, Stephen; Zeebe, Richard E.
Author Affiliation(s): Primary:
University of California at Santa Cruz, Earth and Planetary Sciences, Santa Cruz, CA, United States
Lamont-Doherty Earth Observatory, United States
Australian National University, Australia
University of Hawaii at Manoa, United States
Volume Title: Goldschmidt 2011 abstract volume
Source: Mineralogical Magazine, 75(3), p.1619; Goldschmidt 2011, Prague, Czech Republic, Aug. 8-14, 2011. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Note: In English
Summary: The Paleocene-Eocene Thermal Maximum (∼55 Ma) is recognized as a rapid (<10 ka) input of a large mass (∼4500-6000 GtC) of 12C-enriched carbon into the ocean-atmosphere system. Patterns of CaCO3 dissolution at the suggest that this was accompanied by a rapid decrease in ocean pH, followed by a gradual recovery phase. A further result of such modeling studies is the suggestion of an 'overshoot' or supersaturated ocean phase after the recovery, when the carbonate lysocline deepened to below its Paleocene depth and surface water carbonate saturation states rose to above pre-excursion levels. In an effort to quantify changes in the carbonate chemistry of surface waters and infer potential effects on calcifying organisms and Mg/Ca and δ18O-based temperature estimates, we have measured B/Ca and Mg/Ca in mixed-layer planktic foraminifers from IODP site 1209 in the Pacific and sites 1262 and 1263 in the Atlantic. Previous work at these sites has documented large increases (∼50%) in Mg/Ca ratios in the mixed-layer planktic foraminifer species M. velascoensis and A. soldadoensis consistent with 5 to 6°C of sea surface warming. Our B/Ca measurements in both species suggest a large drop in surface water pH and [CO3=] coincident with the rise in temperature at the onset of the carbon isotope excursion, followed by a gradual recovery to pre-excursion levels. The latter feature, coupled with the rise in total alkalinity caused by the dissolution of CaCO3 is taken as evidence of an overshoot phase starting ∼100 ka after the onset of the event. We are currently measuring boron isotopes in the same taxa in order to quantify the pH changes suggested by the B/Ca data. Additionally, we plan to measure B/Ca and δ11B in thermocline-dwelling planktic species in order to examine the depth-dependence of the pH changes. Estimating the magnitude of the pH drop at the onset of the event will facilitate calculations of the mass and rate of carbon input that triggered the PETM, as well as the magnitude of change in atmospheric pCO2 levels and Paleogene climate sensitivity.
Year of Publication: 2011
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Acidification; Alkaline earth metals; Atlantic Ocean; Atmospheric pressure; B/Ca; Boron; Calcium; Carbon dioxide; Cenozoic; Climate change; Experimental studies; Foraminifera; Geochemistry; Invertebrata; Leg 198; Leg 208; Magnesium; Marine environment; Metals; Mg/Ca; Microfossils; North Pacific; Northwest Pacific; ODP Site 1209; ODP Site 1262; ODP Site 1263; Ocean Drilling Program; PH; Pacific Ocean; Paleo-oceanography; Paleocene-Eocene Thermal Maximum; Paleoclimatology; Paleoecology; Paleogene; Planktonic taxa; Protista; Shatsky Rise; South Atlantic; Tertiary; Walvis Ridge; West Pacific
Coordinates: N323900 N324000 E1583100 E1583000
S271100 S271100 E0013500 E0013400
S283200 S283200 E0024700 E0024700
Record ID: 2012093616
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland