Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard–Oeschger events

Relative timing of precipitation and ocean circulation changes in the western equatorial Atlantic over the last 45 ky

“…Together with 5 two other recent studies (Gottschalk et al, 2015 ;Henry et al, 2016), these results demonstrate that all stadials of the last 45 ky were not only characterized by decreases in flow rate and extension of northern-sourced waters below 3800 m depth, but also by decreases in mid-depth water mass transport in the western equatorial Atlantic.…”

“…On the one hand, increases in Pa/Th during each stadial of the last glacial have been observed at a very deep western North Atlantic site located at ~42 °N and 4500 m depth (Henry et al, 2016). On the other hand, reconstructions of water corrosiveness in a South Atlantic core located at ~44°S and 3800 m depth indicate the absence of northern-sourced deep water at that site during stadials, whereas nearly all interstadials of the last 60 ky are characterized by incursions of northern-sourced deep water into the deep South Atlantic (Gottschalk et al, 2015). Together with these 10 independent results, our results indicate that decreases in both the flow rate and extension of northern-sourced deep waters during stadials were not limited to very dense waters circulating at 3800 m or deeper, but also affected water mass transport above 2350 m in the western equatorial Atlantic.…”

The dynamics of cold events

“…Katrin J. Meissner 8 find that similar oceanographic changes occurred during both Heinrich stadials and stadials not associated with massive iceberg discharge (yellow star at core site). Renssen et al 9 find that cooling during the Younger Dryas was partially caused by a weakening of North Atlantic Deep Water formation, in this case by the rerouting of melt water from glacial Lake Agassiz (green arrows), but changes in the position and strength of the westerlies (purple arrows) and a decrease in solar radiation reaching the Earth's surface also contributed to climate change during this event.…”

“…Looking farther back in time, Gottschalk et al 8 find a close correlation between major Atlantic overturning reorganizations and transitions between warm interstadials and cold stadials. They reconstruct carbonate ion concentrations at 3,370 m water depth in the sub-Antarctic Atlantic, using the B:Ca ratios of benthic foraminifera and sedimentary dissolution indicators.…”

“…Changes in the Atlantic meridional overturning circulation (AMOC) and associated heat transport are most commonly invoked as the main cause for the observed cooling 3 , but other mechanisms have been suggested 4 , particularly for the Younger Dryas [5][6][7] . Writing in Nature Geoscience, Gottschalk et al 8 show evidence for the pivotal role played by the Atlantic Ocean during the transitions between cold stadials and warm interstadials over the past 62,000 years. Also writing in Nature Geoscience, Renssen et al 9 identify roles for changes in ocean circulation, radiative forcing from dust or solar irradiance, and atmospheric circulation during the Younger Dryas cold event.…”