Interhemispheric Climatic Effects from Pliocene Contrictions of Tropical Oceanic Seaways

Abstract:

The climatic roles of the constrictions of the Central American Seaway (CAS) and the Indonesian Seaway have been shown to be of global relevance during the Pliocene epoch. It was assumed that the constriction of the CAS reached a critical threshold during the early Pliocene (~4.8-4 Ma) and model simulations predicted a warming of the Northern Hemisphere and a cooling of the Southern Hemisphere, which climatic effects are known as “Panama hypothesis”. The constriction of the Indonesian seaway had profound climatic effects on the surrounding ocean areas during ~4-3 Ma, with possible effects for the Northern Hemisphere Glaciation. We here present combined measurements of Mg/Ca and δ¹⁸O from planktic foraminifera to reconstruct sea surface temperatures and changes in salinities in both hemispheres during the Pliocene epoch. Within ~4.8-3.9 Ma our reconstructions support the Panama hypothesis with a simultaneous sea surface cooling and freshening of ~2-3 °C of southern hemisphere sites, when North Atlantic Site 552A indicate a warming and more saline conditions. After ~3.9 Ma, our data is in contrast to an ongoing restriction of the CAS and rather suggest that the constriction of the Indonesian Seaway might have reduced the Atlantic thermohaline circulation, leading to significant cooling in the North Atlantic Ocean.