Premium
Diagenetic Attenuation of Carbon Isotope Excursion Recorded by Planktic Foraminifers During the Paleocene‐Eocene Thermal Maximum
Author(s) -
Kozdon Reinhard,
Kelly D. Clay,
Valley John W.
Publication year - 2018
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1002/2017pa003314
Subject(s) - diagenesis , excursion , geology , carbonate , isotopes of carbon , paleontology , mineralogy , carbon fibers , total organic carbon , chemistry , materials science , organic chemistry , composite number , political science , environmental chemistry , law , composite material
Earth surface temperatures warmed by ~5 °C during an ancient (~56 Ma) global warming event referred to as the Paleocene‐Eocene thermal maximum (PETM). A hallmark of the PETM is a carbon isotope excursion (CIE) signaling the release of massive amounts of 13 C‐depleted carbon into the ocean‐atmosphere system, but substrate‐specific differences in the CIE magnitude are a source of uncertainty for estimating the mass of carbon emitted. Here we report that secondary ion mass spectrometry (SIMS)‐based in situ measurements of δ 13 C in minute (7 μm) domains of planktic foraminifer shells (Ocean Drilling Program Site 865, central Pacific Ocean) yield a CIE that is ~2‰ larger than that delineated by conventional “whole‐shell” δ 13 C values for this same PETM record. SIMS‐based measurements on diagenetic crystallites yield δ 13 C values (~2.8‰) that fall between those of pre‐CIE and CIE planktic foraminifer shells, indicating that the crystallites are an amalgamated blend of pre‐CIE and CIE carbonates. This suggests that diagenesis shifts the whole‐shell δ 13 C compositions of pre‐CIE and CIE foraminifers found in samples straddling the base of the PETM interval toward the intermediate δ 13 C composition of the crystallites, thereby dampening the amplitude of the isotopic excursion. The diagenetic process envisioned would be most consequential for carbonate‐rich PETM records that have suffered chemical erosion of pre‐CIE carbonate. Given that the domains targeted for SIMS analysis may not be pristinely preserved, we consider the 4.6‰ excursion in our SIMS‐based δ 13 C record to be a conservative estimate of the full CIE for surface ocean dissolved inorganic carbon.