title: Extreme warmth and heat-stressed plankton in the tropics during the Paleocene-Eocene Thermal Maximum.
abstract: Global ocean temperatures rapidly warmed by ~5°C during the Paleocene-Eocene Thermal Maximum (PETM; ~56 million years ago). Extratropical sea surface temperatures (SSTs) met or exceeded modern subtropical values. With these warm extratropical temperatures, climate models predict tropical SSTs >35°C-near upper physiological temperature limits for many organisms. However, few data are available to test these projected extreme tropical temperatures or their potential lethality. We identify the PETM in a shallow marine sedimentary section deposited in Nigeria. On the basis of planktonic foraminiferal Mg/Ca and oxygen isotope ratios and the molecular proxy [Formula: see text], latest Paleocene equatorial SSTs were ~33°C, and [Formula: see text] indicates that SSTs rose to >36°C during the PETM. This confirms model predictions on the magnitude of polar amplification and refutes the tropical thermostat theory. We attribute a massive drop in dinoflagellate abundance and diversity at peak warmth to thermal stress, showing that the base of tropical food webs is vulnerable to rapid warming.
authors.affiliation: Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, Netherlands.
authors.forename: Joost
authors.initials: J
authors.lastname: Frieling
authors.affiliation: Geologische Bundesanstalt, Neulinggasse 38, A 1030 Wien, Austria.
authors.forename: Holger
authors.initials: H
authors.lastname: Gebhardt
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47906, USA.
authors.forename: Matthew
authors.identifier: 0000-0002-2771-9977
authors.initials: M
authors.lastname: Huber
authors.affiliation: Department of Geology and Mineral Sciences, University of Ilorin, P.M.B. 1515, Kwara State, Nigeria.
authors.forename: Olabisi A
authors.initials: OA
authors.lastname: Adekeye
authors.affiliation: Department of Geology and Mineral Sciences, University of Ilorin, P.M.B. 1515, Kwara State, Nigeria.
authors.forename: Samuel O
authors.initials: SO
authors.lastname: Akande
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, Netherlands.; NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, and Utrecht University, 't Horntje, Texel, Netherlands.
authors.forename: Gert-Jan
authors.identifier: 0000-0002-7256-2243
authors.initials: GJ
authors.lastname: Reichart
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, Netherlands.
authors.forename: Jack J
authors.identifier: 0000-0003-3601-9072
authors.initials: JJ
authors.lastname: Middelburg
authors.affiliation: Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, Netherlands.; NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, and Utrecht University, 't Horntje, Texel, Netherlands.
authors.forename: Stefan
authors.identifier: 0000-0001-9200-8269
authors.initials: S
authors.lastname: Schouten
authors.affiliation: Marine Palynology and Paleoceanography, Laboratory of Palaeobotany and Palynology, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Heidelberglaan 2, 3584CS Utrecht, Netherlands.
authors.forename: Appy
authors.initials: A
authors.lastname: Sluijs
mesh_terms: D005580:Fossils; D057232:Global Warming; D018869:Heat-Shock Response / Q000502:physiology*; D010933:Plankton / Q000502:physiology*
keywords: PETM; Plankton; SST; Tropics; dinoflagellate; heat; heat stress; paleocence - eocene; polar amplification; temperature proxy