Paradox of the peak-PCIM (Paleocene carbon isotope maxima; ∼57.8 Ma) and abrupt global warming

Author(s): Harper, D. T.; Hoenisch, B.; Zachos, J. C.
Author Affiliation(s): Primary:
University of California-Santa Cruz, Ben Lomond, CA, United States
Columbia University, United States
Volume Title: AGU 2015 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2015; American Geophysical Union 2015 fall meeting, San Francisco, CA, Dec. 14-18, 2015. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Paleocene Carbon Isotope Maxima (PCIM; ∼57.8 Ma) represents a major transition in global δ13C during the late Paleocene, when the long-term positive trend in δ13C reversed from positive to negative. The peak-PCIM (∼57.7 Ma) has been tightly resolved in new high-resolution, astronomically-tuned benthic isotope records from IODP Sites 1209 (Pacific) and 1262 (Atlantic), which show the final phase of δ13C enrichment as abrupt (∼1 ppm in <100 kyrs) and coinciding with a 0.5 ppm decline in benthic δ18O indicative of 2-3°C of bottom water warming, effectively marking the onset of a gradual 8 Myr long warming trend [Littler et al., EPSL 2014]. Typically, during the Paleogene on orbital time scales, warming is observed during intervals of δ13C depletion, consistent with release of isotopically light carbon to the atmosphere. This event, which has the appearance of a bifurcation in the long-term coupling of climate system and the carbon cycle, poses an interesting paradox as any rapid carbon release to the atmosphere should, in theory, create a negative excursion because all of the major carbon sources are isotopically light, whether volcanic outgassing, weathering/oxidation of organic carbon, or methane release [Dunkley-Jones et al., Phil. Trans. R. Soc. A 2010]. If global, there are several testable mechanisms that may explain the shift including increase in burial flux of light carbon, a reduction in heavy carbon burial flux, or a large-scale circulation change perhaps associated with the transition of a major oceanic gateway. Using trace metal (B/Ca and Mg/Ca) and stable isotope (δ11B, δ18O, and δ13C) geochemistry, here we establish the nature of the peak-PCIM at sites from 3 different ocean basins (IODP Sites 690, 1209, and 1262) and begin to test several of the possible mechanisms for change. Mg/Ca in mixed-layer planktonic foraminifera show 2-3°C of sea surface warming coinciding with, and abrupt as, the benthic carbon isotope enrichment at all sites. Bottom water [CO32-], as indicated by B/Ca in benthic foraminifera, abruptly increases by 30-40 µmol/kgsw. While this may indicate a change in bottom water circulation, surface B-based proxies also respond with a positive shift during the peak-PCIM indicating a slight increase in surface pH and highlighting the global nature of the event.
Year of Publication: 2015
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; C-13/C-12; Carbon; Cenozoic; Climate change; Global change; Global warming; Isotope ratios; Isotopes; Leg 198; Leg 208; North Pacific; Northwest Pacific; ODP Site 1209; ODP Site 1262; Ocean Drilling Program; Pacific Ocean; Paleocene; Paleogene; Shatsky Rise; South Atlantic; Stable isotopes; Tertiary; Walvis Ridge; West Pacific
Coordinates: N323900 N324000 E1583100 E1583000
S271100 S271100 E0013500 E0013400
Record ID: 2016050817
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