Vigorous exchange between the Indian and Atlantic oceans at the end of the past five glacial periods

Abstract

The magnitude of heat and salt transfer between the Indian and Atlantic oceans through 'Agulhas leakage' is considered important for balancing the global thermohaline circulation. Increases or reductions of this leakage lead to strengthening or weakening of the Atlantic meridional overturning and associated variation of North Atlantic Deep Water formation. Here we show that modern Agulhas waters, which migrate into the south Atlantic Ocean in the form of an Agulhas ring, contain a characteristic assemblage of planktic foraminifera. We use this assemblage as a modern analogue to investigate the Agulhas leakage history over the past 550,000 years from a sediment record in the Cape basin. Our reconstruction indicates that Indian-Atlantic water exchange was highly variable: enhanced during present and past interglacials and largely reduced during glacial intervals. Coherent variability of Agulhas leakage with northern summer insolation suggests a teleconnection to the monsoon system. The onset of increased Agulhas leakage during late glacial conditions took place when glacial ice volume was maximal, suggesting a crucial role for Agulhas leakage in glacial terminations, timing of interhemispheric climate change and the resulting resumption of the Atlantic meridional overturning circulation.

Opal burial in the equatorial Atlantic Ocean over the last 30 ka: Implications for glacial‐interglacial changes in the ocean silicon cycle

“…[49] Several studies of the Southeast Atlantic have concluded that the supply of Agulhas water to the Atlantic was reduced substantially during glacial times [Flores et al, 1999;Kuhn and Diekmann, 2002;Peeters et al, 2004;Franzese et al, 2006]. Furthermore, as the Agulhas system and the Drake Passage are the two primary avenues for return flow to the North Atlantic [Gordon et al, 1992], the glacial reduction in supply of Agulhas water may have been compensated for by increased supply via the Drake Passage.…”

Insight into the latest Messinian (5.7–5.2Ma) palaeoclimatic events from two deep-sea Atlantic Ocean ODP Sites

“…sensus Peeters et al, 2004) at ODP Site 1088 do not increase in relative abundance and therefore the warming cannot be attributed to increased circulation of warm Agulhas water at the site. This observation is similar to those made in a micropalaeontological study of site TNO57-21 over the last deglaciation (Barker et al, 2009).…”

“…10 seaway during the late Quaternary can be found in Peeters et al, (2004), andin O'Neil et al, (2007) for the middle Pleistocene.…”

“…Peeters et al, (2004) found it living at intermediate depths (at ~600 meters water depth) and associated with a ring of Indian Ocean water that had been transferred into the South Atlantic via the "Agulhas leakage". At the end of the Messinian, the Isthmus of Panama had shoaled to less than 500 m so that the periodic occurrence in the Atlantic Ocean of this rare species could only be related to its re-introduction via the Agulhas area (Collins et al, 1996).…”

Spatio-temporal characteristics of Agulhas leakage: a model inter-comparison study

“…Over 2-4 decades the warm salty water that enters the South Atlantic is advected northwards (Ruhs et al 2013;Weijer et al 2001), its influence on the buoyancy balance affects deep water formation, the AMOC and thus global climate. Paleoceanographic studies and foram assemblages indicate that fluctuations in the strength of AL are linked to the glacial/interglacial cycles and periods of variable AMOC (Peeters et al 2004;Caley et al 2014). With the potential of increasing leakage to warm the climate (Beal et al 2011), the importance of the Agulhas system and its role in the global climate and circulation makes understanding the drivers of variability very important.…”