Evidence for Shelf Acidification During the Onset of the Paleocene‐Eocene Thermal Maximum

Abstract

A transect of paleoshelf cores from Maryland and New Jersey contains an ~0.19‐ to 1.61‐m‐thick interval with reduced percentages of carbonate during the onset of the Paleocene‐Eocene Thermal Maximum (PETM). Outer paleoshelf cores are barren of nannofossils and correspond to two minor disconformities. Middle paleoshelf cores contain a mixture of samples devoid of nannofossils and those with rare specimens characterized by significant dissolution (i.e., etching). The magnitude of the decrease in carbonate cannot be explained by dilution by clastic material or dissolution resulting from the oxidation of organic matter during early diagenesis. The observed preservation pattern implies a shoaling of the calcite compensation depth and lysocline to the middle shelf. This reduced carbonate interval is observed during the onset of the PETM on other continental margins raising the possibility that extreme shoaling of the calcite compensation depth and lysocline was a global signal, which is more significant than in previous estimates for the PETM. An alternative scenario is that shoaling was restricted to the northwest Atlantic, enhanced by regional and local factors (eutrophication from rivers and microbial activity associated with warming) that exacerbated the impact of acidification on the shelf.

Environmental and Geomorphological Changes on the Eastern North American Continental Shelf Across the Paleocene‐Eocene Boundary

“…Benthic foraminiferal (Stassen et al, ) and pollen (Willard et al, ) studies provide additional evidence for an early Eocene shelf flooded with terrestrial material and nutrients. Malformed calcareous nannoplankton provide evidence for rare ecophenotypical responses to sea surface warming and eutrophication (Bralower & Self‐Trail, ), and a shelf‐wide interval of reduced carbonate suggests that the lysocline shoaled to the middle shelf (Bralower et al, ). Considered together, these data point to an increase in temperature, precipitation, ocean acidification, erosion, and sedimentation along the U.S. mid‐Atlantic continental shelf in the earliest Eocene.…”

Ecological Changes in the Nannoplankton Community Across A Shelf Transect During the Onset of the Paleocene‐Eocene Thermal Maximum

“…The assemblage record at CD is interrupted by a 1.61‐m interval (222.39–224.00 m) with virtually no carbonate and very rare and poorly preserved nannofossils. This low carbonate interval (LCI) is observed in sections across the paleoshelf (Bralower et al, ). There are distinct changes in the assemblage across the LCI at CD (Figure ).…”

“…Abundance of nannofossil genera at CD and bulk carbonate δ 13 C (from Bralower et al, ). (a) Percentages of common taxa.…”

“…At Wilson Lake and Bass River, 300 specimens were counted (Gibbs, Bralower, et al, ; Gibbs, unpublished data). Sections were correlated using bulk carbonate δ 13 C values (John et al () for Bass River and Wilson Lake, Self‐Trail et al () for South Dover Bridge, Self‐Trail et al () for MCBR, and Bralower et al () for CD). Because Toweius is the dominant species in all sections besides MCBR and small fluctuations in the abundance of this taxon can cause significant changes in the abundance of other taxa, we estimate percentages of all taxa based on the percentage of the non‐ Toweius fraction when correlating trends in different sections.…”

“…Many studies have been devoted to the investigation of deep-sea PETM records, including characterization of geochemical and biotic changes during the event (e.g., Pak & Miller, 1992;Ravizza et al, 2001;Thomas et al, 2002;Nunes & Norris, 2006;Penman et al, 2014;Sluijs et al, 2007;Sluijs et al, 2014). These studies show that sediments that record the onset of the PETM in the deep sea are highly condensed, and possibly incomplete, as a result of shoaling of the lysocline and calcite compensation depth (e.g., Zachos et al, 2005;Colosimo et al, 2006;Bralower et al, 2014Bralower et al, , 2018. Consequently, there has been increasing focus on paleoshelf sections that contain highly expanded and more complete records of the onset of the event (e.g., Gibson et al, 1993; Bybell & Self-Trail, 1995;Sluijs et al, 2007;John et al, 2008;Scheibner & Speijer, 2008;Self-Trail et al, 2012;Stassen et al, 2012;Self-Trail et al, 2017).…”