Evidence for high sea-surface temperatures during the early Aptian OAE 1a in the Boreal Realm

The early Aptian was characterized by the widespread occurrence of anoxia in the oceans, known as Oceanic Anoxic Event (OAE) 1a. Intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric CO2 concentrations, culminating in greenhouse conditions (e.g., Hochuli et al., 1999; Jenkyns, 2003; Erba et al., 2010). OAE 1a can, therefore, be considered as a past “natural experiment” important to understand the evolution of our future climate. Paleotemperature estimates for OAE 1a are, however, predominantly based on bulk oxygen-isotopes, which are susceptible for diagenetic overprinting, while TEX86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections. We reconstructed for the first time sea-surface water (SST) temperatures based on the TEX86 paleothermometer from an OAE 1a section from the middle northern latitudes (39° N paleolatitude). We find a SST rise starting prior to OAE 1a and reaching a maximum during the event with SSTs around 31–34 °C, 4–9 °C higher than those of older Hauterivian - lower Aptian sediments from the same sedimentary basin (Mutterlose et al., 2014). The end of OAE 1a is marked by relatively lower SSTs around 30 °C. These observations are supported by belemnite-based oxygen isotope data and calcareous nannofossils. Our integrated data set clearly indicates that ‘super greenhouse’ conditions prevailed during OAE 1a at northern latitudes. SSTs are similar to those estimated for coeval low latitudinal sites, suggesting that an equable warm climate, with reduced latitudinal gradients, characterized the early Aptian. References Erba, E., Bottini, C., Weissert, J.H. & Keller, C.E. (2010): Calcareous nannoplankton response to surface-water acidifi cation around Oceanic Anoxic Event 1a: Science, v. 329, p. 428–432. Hochuli, P.A., Menegatti, A.P., Weissert, H., Riva, A. Erba, E. & Premoli Silva, I. (1999): Episodes of high productivity and cooling in the early Aptian Alpine Tethys: Geology, v. 27, p. 657– 660. Jenkyns, H.C. (2003): Evidence for rapid climate change in the Mesozoic–Palaeogene greenhouse world: Philosophical Transactions of the Royal Society of London, Series A, v. 361, p. 1885– 1916. Mutterlose, J., Bottini, C., Schouten, S. & Sinninghe Damsté, J.S. (2014) : High sea-surface temperatures during the early Aptian Oceanic Anoxic Event 1a in the