Centennial‐scale evolution of Dansgaard‐Oeschger events in the northeast Atlantic Ocean between 39.5 and 56.5 ka B.P.

Abstract

[1] There is much uncertainty surrounding the mechanisms that forced the abrupt climate fluctuations found in many palaeoclimate records during Marine Isotope Stage (MIS)-3. One of the processes thought to be involved in these events is the Atlantic Meridional Overturning Circulation (MOC), which exhibited large changes in its dominant mode throughout the last glacial period. Giant piston core MD95-2006 from the northeast Atlantic Ocean records a suite of palaeoceanographic proxies related to the activity of both surface and deep water masses through a period of MIS-3 when abrupt climate fluctuations were extremely pronounced. A two-stage progression of surface water warming during interstadial warm events is proposed, with initial warming related to the northward advection of a thin warm surface layer within the North Atlantic Current, which only extended into deeper surface layers as the interstadial progressed. Benthic foraminifera isotope data also show millennialscale oscillations but of a different structure to the abrupt surface water changes. These changes are argued to partly be related to the influence of low-salinity deepwater brines. The influence of deepwater brines over the site of MD95-2006 reached a maximum at times of rapid warming of surface waters. This observation supports the suggestion that brine formation may have helped to destabilize the accumulation of warm, saline surface waters at low latitudes, helping to force the MOC into a warm mode of operation. The contribution of deepwater brines relative to other mechanisms proposed to alter the state of the MOC needs to be examined further in future studies.

British Ice Sheet dynamics inferred from North Atlantic ice‐rafted debris records spanning the last 175 000 years

“…At intermediate water depths in the northeast Atlantic, an important influence on benthic d 18 O is the formation of deep-water brines, whereby sea-ice-derived brines and their d 18 O signature are transferred to the deep ocean. Dickson et al (2008) postulate for MD95-2006 a core located approximately 83 km away from MD04-2822 at a similar water depth, that millennial-scale changes in benthic d 18 O through MIS 3 are related at least in part to the formation of low salinity, deep-water brines. Indeed these changes in the benthic d 18 O possess not only a component of local brine formation (i.e.…”

Fine scale sediment structure and geochemical signature between eastern and western North Atlantic during Heinrich events 1 and 2

“…Freshwater released from the Hudson Strait and St. Lawrence ice-streams (Shaw et al, 2006), in addition to freshwater emanating from iceberg-rafting, are presumed to form a freshwater cap in the North Atlantic. This freshwater cap may have prevented the North Atlantic Current, the northern extension of the Gulf Stream, from reaching the Greenland-Iceland-Norwegian seas, which in turn may have weakened the Atlantic meridional ocean circulation (AMOC) (Rahmstorf, 1994;Stouffer et al, 2006;Dickson et al, 2008;Renold et al, 2010;Cheng et al, 2011;Guihou et al, in press). After the ice sheet had thinned sufficiently at the end of an H-event, rapid iceberg calving stopped and the previous ocean circulation mode resumed, causing the climate to warm rapidly (Seidov and Haupt, 2003;Kageyama et al, 2009).…”

Non‐synchronous deposition of North Atlantic Ash Zone II in Greenland ice cores, and North Atlantic and Norwegian Sea sediments: an example of complex glacial‐stage tephra transport

“…Electron microprobe analysis on single tephra shards were performed on an ARL–SEMQ microprobe by wavelength dispersal spectrometry following the methodology described in Brendryen et al (2010). The methods applied when generating data from cores SO82‐05 and MD95‐2006 are described in the original publications: from core SO82‐05 (Haflidason et al , 2000; van Kreveld et al , 2000) and from core MD95‐2006 (Austin et al , 2004; Dickson et al , 2008).…”