The Paleocene – Eocene Thermal Maximum: Temperature and Ecology in the Tropics

Abstract:

Various records across the Paleocene – Eocene Thermal Maximum (PETM) have established approximately 5 °C of additional surface and deep ocean warming, superimposed on the already warm latest Paleocene. The PETM is further characterized by a global negative stable carbon isotope excursion (CIE), poleward migration of thermophilic biota, ocean acidification, increased weathering, photic zone euxinia and intensified hydrological cycle. Reconstructed temperatures for the PETM in mid and high-latitudes regularly exceed modern open marine tropical temperatures. Constraints on absolute tropical temperatures are, however, limited.

We studied the PETM in a sediment section from the Nigerian sector of the Dahomey Basin, deposited on the shelf near the equator. We estimate sea surface temperatures by paired analyses of TEX₈₆, and Mg/Ca and δ¹⁸O of foraminifera from the Shagamu Quarry. These show Palaeocene temperatures of ~33 °C and SSTs rose by 4 °C during the PETM based on TEX₈₆. During the PETM, intermittent photic zone euxinia developed based on the presence of the biomarker isorenieratane. Interestingly, during peak warmth, dinoflagellate cyst abundances and diversity are remarkably low.

From our new data and evidence from modern dinoflagellate experiments, we conclude that thermal stress was the main driver for this observation. We derive that endothermal and most ectothermal nektonic and planktonic marine eukaryotic organisms could not have lived in the surface waters in this part of the tropics during the PETM.