NORTH ATLANTIC OCEAN SEA SURFACE TEMPERATURES DURING THE MIDDLE TO LATE MIOCENE, 18-8 MILLION YEARS AGO

The Middle to Late Miocene was a period of climactic transition. During the Miocene Climactic Optimum (MCO; 17-14.7 million years ago [Ma]), ocean temperatures were approximately 3-4°C warmer than current ocean temperatures. The planet then experienced a period of global cooling, during which permanent ice sheets formed in East Antarctica (14.7-12.8 Ma). Despite the transition’s climactic importance, there are few reconstructions of the surface and thermocline temperature changes during this period, with records particularly scarce in the North Atlantic Ocean. Records of surface temperature variations in the North Atlantic Ocean are essential in understanding the relationship of temperature changes on Atlantic Meridional Overturning Circulation, the production of North Atlantic Deep Water, and Meridional thermal gradients. Here we present new data from trace metals analyses of surface-dwelling foraminifera (Globigerinoides quadrilobatus)together with new planktonic and published benthic foraminiferal oxygen and carbon stable isotopic from Deep Sea Drilling Project Site 563 (33°N). We measured Mg/Ca in G. quadrilobatus, providing independent estimates for the North Atlantic Ocean’s surface temperatures. A decrease in Mg/Ca by approximately 1.1 mmol/mol associated with the end of the MCO indicates a decrease in sea surface temperature by approximately 4-5°C. Oxygen isotope data fromsurface-dwelling foraminifera show a 1.5‰ decrease from 14.7-12.8 Ma. Of this, 0.5‰ can be attributed to changes in the oxygen isotopic composition of seawater due to permanent ice sheet formation in East Antarctica. Using the 0.25‰/°C gradient,the remaining 1.0‰ correlates to a cooling of 4°C. Thus, Mg/Ca estimated temperatures at DSDP Site 563 are consistent with the oxygen isotope data.

Further stable isotopes and trace elements analyses of surface-dwelling foraminifera are needed to extend the records of the North Atlantic sea surface temperature in DSDP 563 during the Miocene.