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Global cooling accelerated by early late Eocene impacts?

¹ Free University, Faculty of Earth Sciences, De Boelelaan 1085, 1081 HV Amsterdam, Netherlands
² Utrecht University, Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3585 CD Utrecht, Netherlands
³ Osservatorio Geologico di Coldigioco, 62020 Frontale (MC), Italy
⁴ University College London, Department of Geological Sciences, Gower Street, London WC1E 6BT, UK

At Ocean Drilling Program Site 689 (Maud Rise, Southern Ocean), ¹⁸O records of fine-fraction bulk carbonate and benthic foraminifers indicate that accelerated climate cooling took place following at least two closely spaced early late Eocene extraterrestrial impact events. A simultaneous surface-water productivity increase, as interpreted from ¹³C data, is explained by enhanced water-column mixing due to increased latitudinal temperature gradients. These isotope data appear to be in concert with organic-walled dinoflagellate-cyst records across the same microkrystite-bearing impact-ejecta layer in the mid-latitude Massignano section (central Italy). In particular, the strong abundance increase of Thalassiphora pelagica is interpreted to indicate cooling or increased productivity at Massignano. Because impact-induced cooling processes are active on time scales of a few years at most, the estimated 100 k.y. duration of the cooling event appears to be too long to be explained by impact scenarios alone. This implies that a feedback mechanism, such as a global albedo increase due to extended snow and ice cover, may have sustained impact-induced cooling for a longer time after the impacts.

Key Words: Eocene • meteorites • climate effects • ODP Site 689

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