Constraints on Earth System Functioning at the Paleocene‐Eocene Thermal Maximum From the Marine Silicon Cycle

Type Article
Date 2020-05
Language English
Author(s) Fontorbe Guillaume1, 2, Frings Patrick J.3, 4, de La Rocha Christina L., Hendry Katharine R.5, Conley Daniel J.1
Affiliation(s) 1 : Department of Geology Lund University Lund, Sweden
2 : GEOMAR Helmholtz Centre for Ocean Research Kiel Kiel ,Germany
3 : Section 3.3 Earth Surface Geochemistry GFZ German Research Centre for Geosciences Potsdam, Germany
4 : Department of GeosciencesSwedish Museum of Natural History Stockholm ,Sweden
5 : School of Earth Sciences University of Bristol Bristol , UK
Source Paleoceanography and Paleoclimatology (2572-4517) (American Geophysical Union (AGU)), 2020-05 , Vol. 35 , N. 5 , P. e2020PA003873 (22p.)
DOI 10.1029/2020PA003873
Keyword(s) Paleocene‐Eocene Thermal Maximum, silicon biogeochemical cycle, silicon isotopes, weathering
Abstract

The Paleocene‐Eocene Thermal Maximum (PETM, ca. 56 Ma) is marked by a negative carbon isotope excursion (CIE) and increased global temperatures. The CIE is thought to result from the release of 13C‐depleted carbon, although the source(s) of carbon and triggers for its release, its rate of release, and the mechanisms by which the Earth system recovered are all debated. Many of the proposed mechanisms for the onset and recovery phases of the PETM make testable predictions about the marine silica cycle, making silicon isotope records a promising tool to address open questions about the PETM. We analyzed silicon isotope ratios (δ30Si) in radiolarian tests and sponge spicules from the Western North Atlantic (ODP Site 1051) across the PETM. Radiolarian δ30Si decreases by 0.6‰ from a background of 1‰ coeval with the CIE, while sponge δ30Si remains consistent at 0.2‰. Using a box model to test the Si cycle response to various scenarios, we find the data are best explained by a weak silicate weathering feedback, implying the recovery was mostly driven by nondiatom organic carbon burial, the other major long‐term carbon sink. We find no resolvable evidence for a volcanic trigger for carbon release, or for a change in regional oceanography. Better understanding of radiolarian Si isotope fractionation and more Si isotope records spanning the PETM are needed to confirm the global validity of these conclusions, but they highlight how the coupling between the silica and carbon cycles can be exploited to yield insight into the functioning of the Earth system.

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How to cite 

Fontorbe Guillaume, Frings Patrick J., de La Rocha Christina L., Hendry Katharine R., Conley Daniel J. (2020). Constraints on Earth System Functioning at the Paleocene‐Eocene Thermal Maximum From the Marine Silicon Cycle. Paleoceanography and Paleoclimatology, 35(5), e2020PA003873 (22p.). Publisher's official version : https://doi.org/10.1029/2020PA003873 , Open Access version : https://archimer.ifremer.fr/doc/00627/73939/