Deciphering global cooling of the mid-latitude oceans and its implication for the ocean circulation and climate during the early Pliocene (~5-3.5 Ma)
Final Report Abstract
The DFG-project intended to study the effect of the Pliocene tectonic constriction and subsequent closure of the Central Amercian Seaway on the remote North and South Atlantic ocean areas. Previous studies constrained the timing of the closure of the seaway and its effects on the Caribbean and E Pacific ocean areas. We here tested whether the expected strenghtening of the Atlantic Meridional Overturning Circulation warmed the North Atlantic and at the same time cooled the South Atlantic. Model simulations previously termed this phenomenon as „heat piracy“ of the Northern Hemisphere. In the framework of this project we generated combined foraminiferal Mg/Ca-derived sea surface temperatures (SST) and stable oxygen isotopes (δ18O) dataseries from North and South Atlantic ODP/DSDP sites for the Pliocene time period of ~5.5-3 Ma. Results from Sites 552 and 516A show that the reconstructed SSTMg/Ca and changes in sea surface salinites (δ18Oseawater) from both the North and South Atlantic sites are inversely correlated over the entire time period pointing to a close seesaw pattern across hemispheres. The similarity of the interhemispheric sea surface temperature and salinity gradients to a South Atlantic benthic δ13C record, which approximates strength variability of North Atlantic Deep Water, suggests that our reconstructed changes in the upper North and South Atlantic oceans indeed retrace past changes in the Atlantic Meridional Overturning Circulation. At ~5.3 Ma, our proxy data point to a weakening of the Atlantic Meridional Overturning Circulation, which corresponds to the end of the Messinian Salinity Crises. Our data further support earlier studies including various model simulations, which suggested a strengthening of the AMOC during 4.8-3.8 Ma that led to warmer and more saline conditions in the upper North Atlantic and cooler and fresher conditions in the upper South Atlantic in direct response to the tectonical constriction/closure of the Central Amercian Seaway. During 3.8-3 Ma, our data imply a gradual weakening of the Atlantic Meridional Overturning Circulation, which we partly relate to the tectonic constriction of the Indonesian Seaway. High-resolution (millenial-scale) SSTMg/Ca and changes in surface salinities from Site 610A elucidate this climatic effects of a weakened AMOC on the intensification of the Northern Hemisphere Glaciation during 4-3.3 Ma. „Wie der Nordatlantik zum Wärmepirat wurde“ http://www.scinexx.de/wissen-aktuell-21082-2017-01-24.html „Wie der Nordatlantik zum Wärmepirat wurde“ https://www.geomar.de/news/article/wie-der-nordatlantik-zum-waermepirat-wurde/ „Wie der Nordatlantik zum Wärmepirat wurde“ https://www.innovations-report.de/html/berichte/geowissenschaften/wie-der-nordatlantik- zum-waermepirat-wurde.html „How North Atlantic became a “heat pirate“ https://blog.divessi.com/how-north-atlantic-became-a-heat-pirate-2337.html
Publications
- (2017) Pliocene oceanic seaways and global climate. Scientific Reports 7
Karas, C., Nürnberg, D., Bahr, A., Groeneveld, J., Herrle, J. O., Tiedemann, R., deMenocal, P.
(See online at https://doi.org/10.1038/srep39842)
