Assessing offsets between the δ13C of sedimentary components and the global exogenic carbon pool across early Paleogene carbon cycle perturbations

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doi: 10.1029/2011GB004224
Author(s): Sluijs, Appy; Dickens, Gerald R.
Author Affiliation(s): Primary:
Utrecht University, Department of Earth Sciences, Utrecht, Netherlands
Volume Title: Global Biogeochemical Cycles
Source: Global Biogeochemical Cycles, 26(4). Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0886-6236
Note: In English. 139 refs.; illus., incl. 1 table
Summary: Negative stable carbon isotope excursions (CIEs) across the Paleocene-Eocene thermal maximum (PETM; ∼56 Ma) range between 2 ppm and 7 ppm, even after discounting sections with truncated records. Individual carbon isotope records differ in shape and magnitude from variations in the global exogenic carbon cycle through changes in (1) the relative abundance of mixed components with different δ13C within a measured substrate, (2) isotope fractionation through physiological change, and (3) the isotope composition of the carbon source. All three factors likely influence many early Paleogene δ13C records, especially across the PETM and other hyperthermal events. We apply these concepts to late Paleocene-early Eocene (∼58-52 Ma) records from Lomonosov Ridge, Arctic Ocean. Linear regression analyses show correlations between the δ13C of total organic carbon (TOC) and two proxies for the relative contribution of terrestrial organic components to sediment TOC: the branched and isoprenoid tetraether index and palynomorphs. We use these correlations to subtract the terrestrial component from δ13CTOC and calculate marine organic matter δ13C. The results show that the magnitude of the CIE in δ13CTOC across the PETM is exaggerated relative to the magnitude of the CIE in δ13CMOM by ∼3ppm due to increased contributions of terrestrial organic carbon during the event. Collectively, all carbon isotope records across the PETM and other major climate-carbon cycle perturbations in Earth's history are potentially biased through one or more of the above factors. Indeed, it is highly unlikely that any δ13C record shows the true shape and magnitude of the CIE for the global exogenic carbon cycle. For the PETM, we conclude that CIE in the exogenic carbon cycle is likely <4ppm, but it will take additional analyses and modeling to obtain an accurate value for this CIE.
Year of Publication: 2012
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; C-13/C-12; Carbon; Carbon cycle; Cenozoic; Eocene; Expedition 302; Geochemical cycle; IODP Site M0004; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Organic compounds; Paleocene; Paleocene-Eocene Thermal Maximum; Paleogene; Stable isotopes; Tertiary; Total organic carbon
Coordinates: N875200 N875200 E1361100 E1361100
Record ID: 2014008967
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