Mid-Miocene Carbon Isotope Maximum: Marine Versus Terrestrial Carbon Burial
Abstract
A prominent, middle Miocene (17.5 to 13.5 Ma) carbon-isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13C depleted organic carbon in marine sediments or enhanced carbon burial in peat/lignite deposits on land. We use a multi-proxy approach including estimates of paleoproductivity based on benthic foraminiferal accumulation rates, elemental ratios (Ba/Al, P/Al), the δ13C of bulk sedimentary organic matter, dissolution indices, and a geochemical model to test whether or not an increase in marine productivity can explain the observed positive shift in middle Miocene δ13C records. Our results indicate that marine paleoproductivity in the Atlantic Ocean is not related to the benthic foraminiferal δ13C excursion. The numerical box model confirms that marine productivity cannot account for the δ13C maximum. The model shows that sequestration of 1.5×1018 mol C in the terrestrial realm over a period of 3 myr leads to a 0.9 permil δ13C increase in the deep ocean, which is near to the observed records. Therefore, an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean's carbon pool with 13C, which is consistent with coeval lignite deposits worldwide. The δ13C values of bulk sedimentary organic matter parallel the δ13C of dissolved inorganic carbon as reflected by benthic foraminiferal δ13C values suggesting no significant change in atmospheric pCO2 levels over the investigated period. These results are consistent with other geochemical studies highlighting the importance of factors other than, or in addition to, pCO2 in mid- Miocene climatic warmth.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMPP33A1525D
- Keywords:
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- 4806 Carbon cycling (0428);
- 4825 Geochemistry;
- 4912 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615;
- 4805)