Palynological evidence for a southward shift of the North Atlantic Current at ~2.6 Ma during the intensification of late Cenozoic Northern Hemisphere glaciation

Abstract

The position of the North Atlantic Current (NAC) during the intensification of NorthernHemisphere glaciation (iNHG) has been evaluated using dinoflagellate cyst assemblages and foraminiferal geochemistry from a~260 kyr interval straddling the base of the Quaternary System from two sites: eastern North Atlantic Deep Sea Drilling Project Site 610 in the path of the present NAC and central North Atlantic Integrated Ocean Drilling Program Site U1313 in the subtropical gyre. Stable isotope and foraminiferal Mg/Ca analyses confirm cooling near the marine isotope stage (MIS) G7-G6 transition (2.74 Ma). However, a continued dominance of the dinoflagellate cyst Operculodinium centrocarpum sensu Wall and Dale (1966) indicates an active NAC in the eastern North Atlantic for a further 140 kyr. At MIS 104 (~2.60 Ma), a profound dinoflagellate cyst assemblage turnover indicates NAC shutdown in the eastern North Atlantic, implying elevated atmospheric pressure over the Arctic and a resulting shift in the westerlies that would have driven the NAC. These findings challenge recent suggestions that there was no significant southward shift of the NAC or the Arctic Front during iNHG, and reveal a fundamental climatic reorganization near the base of the Quaternary.

Glacial induced closure of the Panamanian Gateway during Marine Isotope Stages (MIS) 95–100 (∼2.5 Ma)

“…Major oceanic reorganization due to the restriction of surface water masses occurred during the Pliocene. However, the final closure did probably not occur until the latest Pliocene or even Early Pleistocene (Jackson et al, 1993). In this study, we have tested the hypothesis that sea level lowstands of 60-90 m during the first major G-IG cycles (MIS 95-100; ∼2.5 Ma) after intensification of NHG (e.g., Lourens et al, 2010;Miller et al, 2012) temporarily closed the Panamanian Gateway.…”

“…As relatively cool waters from the East Pacific no longer entered the Caribbean, the Caribbean could warm up intensifying the Gulf Stream, increasing heat and salt transport towards high northern latitudes (Haug et al, 2001a;Steph et al, 2006;Groeneveld et al, 2008). Completion of the tectonic closure probably did not occur until ∼2 Ma, when a mass migration of tropical rain forest animals occurred from South America toward the north (Jackson et al, 1993).…”

“…High-resolution records for specific key periods, however, are still relatively sparse. Time intervals which have been studied in more detail include Marine Isotope Stage (MIS) M2 (De Schepper et al, 2009, 2013, the Mid Piacenzian warm interval (Dowsett et al, 1996(Dowsett et al, , 2009Robinson et al, 2008), MIS 102-G14 (Bartoli et al, 2006;Bailey et al, 2013;Hennissen et al, 2014), and the first larger glacial-interglacial (G-IG) cycles after the intensification of NHG, MIS 95-100 (∼2.5 Ma; Lisiecki and Raymo, 2005;Becker et al, 2005;Bolton et al, 2010aBolton et al, , 2010bLourens et al, 2010;Friedrich et al, 2013). During glacial MIS M2 productivity in the North Atlantic is hypothesised to have been strongly dependent on nutrients from the East Pacific, which were transported into the Atlantic through the Panamanian Gateway (Schneider and Schmittner, 2006;De Schepper et al, 2013).…”

Response to “Comment on ‘The transition on North America from the warm humid Pliocene to the glaciated Quaternary traced by eolian dust deposition at a benchmark North Atlantic Ocean drill site’, by David Lang et al.”

“…3 ¼ First time that Arctic air temperatures tend towards Last Glacial Maximum values (Brigham-Grette et al, 2013). 4 ¼ First excursion of the polar front in the glacial North Atlantic Ocean south of~53 N (Hennissen et al, 2014). MIS ¼ marine isotope stage.…”

Pliocene environmental change in West Africa and the onset of strong NE trade winds (ODP Sites 659 and 658)

“…The results of the iNHG are apparent in the North Atlantic by the southward diversion of the North Atlantic Current during glaciations (Naafs et al, 2010;Hennissen et al, 2014). These authors studied SSTs of the North Atlantic in combination with aeolian terrestrial input from North America.…”