Meltwater injections and their impact on Atlantic meridional overturning circulation and climate during the time period of Heinrich Event 1 and the last deglaciation

• Main Author: Stanford, Jennifer D.
• Format: Thesis
• Language: English
• Published: 2008
• Subjects: Greenland; Greenland ice core; GRIP; ice core; NADW; Nordic Seas; North Atlantic Deep Water; North Atlantic
• Online Access: https://eprints.soton.ac.uk/66346/; https://eprints.soton.ac.uk/66346/1/Stanford_2008_PhD.pdf

The temporal relationship between meltwater pulse 1a (mwp-1a) and the climate history of the last deglaciation remains a subject of debate. By combining the GRIP ?18O ice core record on the new Greenland Ice Core Chronology 2005 (GICC05) timescale with the U/Th-dated Barbados coral record, it is conclusively derived that mwp-1a did not coincide with the sharp Bølling warming, but with the abrupt cooling of the Older Dryas. To evaluate whether there is a relationship between meltwater injections, North Atlantic Deep Water (NADW) formation and climate change (i.e., the long term change in the average weather), a high-resolution magnetic (?ARM/?) proxy record of NADW flow intensity from Eirik Drift, south of Greenland, is presented. A record of mean sortable silt grain sizes (an established proxy for near bottom current flow speed), obtained from the same samples on which the ?ARM/? was measured, shows remarkable similarity to the magnetic record and validates ?ARM/? as a proxy for NADW flow intensity. The record of ?ARM/? indicates only a relatively minor 200-yr weakening of NADW flow, coincident with mwp-1a. This compilation of records also indicates that during Heinrich event 1 (H1) and the Younger Dryas there were no discernible sea-level rises, and yet these periods were characterised by intense NADW slowdowns. Records of planktonic foraminiferal ?18O, as well as lithic and foraminiferal counts from Eirik Drift are combined with previous studies from the Nordic seas and the ‘Ice Rafted Debris (IRD) belt’, and portray a sequence of events through the interval of H1. These events progressed from an onset of meltwater release around 19 ka BP, through the ‘conventional’ H1 phase from ~17.5 ka BP, to a final phase between 16.5 and 14.6 ka BP, characterised by a pooling of fresh waters in the Nordic Seas, which were injected hyperpycnally. This build up of fresh waters was purged from the Nordic Seas, preconditioning the Nordic Seas for convective deep-water formation. This allowed the abrupt re-start of NADW ...