Deep water flow speed and surface ocean changes in the subtropical North Atlantic during the last deglaciation

Climate fluctuations during the last deglaciation have been linked to changes in the North Atlantic Meridional Overturning Circulation (MOC) through its modulation of northward marine heat transport. Consequently, much research into the causes of rapid climate change has focused on the northern North Atlantic as a key component of global ocean circulation. The production of cold, deep waters in the Southern Ocean is an important factor in the Earth's heat budget, but the involvement of deep Southern Sourced Water (SSW) in deglacial climate change has yet to be fully established. Here we use terrigenous silt grain size data from two ocean sediment cores retrieved from the western subtropical North Atlantic to reconstruct past changes in the speed of deepwater flow. The first core site is located under the influence of Lower North Atlantic Deep Water (LNADW), and is representative of changes in the MOC. The second core site is close to the modern boundary between LNADW/SSW and is therefore ideally positioned to detect changes in SSW delivery to the North Atlantic. We find evidence for a broad-scale difference in flow speed changes at the two sites, with the presence of a vigorous, but poorly ventilated SSW mass at similar to 4200 m water depth during the cold episodes of the last deglaciation when shallower (2975 m water depth) grain size and geochemical data suggest that Northern Sourced Water (NSW) was suppressed. (C) 2010 Elsevier B.V. All rights reserved.