Calcium isotope composition of Morozovella over the late Paleocene–early Eocene

Ocean acidification (OA) during the Paleocene-Eocene thermal maximum (PETM) likely caused a biocalcification crisis. The calcium isotope composition (δ44/40Ca) of primary carbonate producers may be sensitive to OA. To test this hypothesis, we constructed the first high-resolution, high-precision planktic foraminiferal δ44/40Ca records before and across the PETM. The records employ specimens of Morozovella spp. collected from Ocean Drilling Program Sites 1209 (Shatsky Rise, Pacific Ocean) and 1263 (Walvis Ridge, Atlantic Ocean). At Site 1209, δ44/40Ca values start at –1.33‰ during the Upper Paleocene and increase to a peak of –1.15‰ immediately before the negative carbon isotope excursion (CIE) that marks the PETM onset. Values remain elevated through the PETM interval and decrease into the earliest Eocene. A shorter-term record for Site 1263 shows a similar trend, although δ44/40Ca values are on average 0.22‰ lower and decrease shortly after the CIE onset. The trends support neither diagenetic overprinting, authigenic carbonate additions, nor changes in the δ44/40Ca value of seawater. Rather, they are consistent with a kinetic isotope effect, whereby calcite δ44/40Ca values inversely correlate with precipitation rate. Geologically rapid Ca isotope shifts appear to reflect the response of Morozovella to globally forced changes in the local carbonate geochemistry of seawater. All data combined suggest that the PETM-OA event occurred near the peak of a gradual reduction in seawater carbonate ion concentrations during a time of elevated atmospheric pCO2, potentially driven by North Atlantic igneous province emplacement.

Kitch G. D., Jacobson A. D., Harper D. T., Hurtgen M. T., Sageman B. B. & Zachos J. C., in press. Calcium isotope composition of Morozovella over the late Paleocene–early Eocene. GeologyArticle (subscription required).

0 Responses to “Calcium isotope composition of Morozovella over the late Paleocene–early Eocene”

  1. Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,442,665 hits


Ocean acidification in the IPCC AR5 WG II

OUP book