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 δ18O 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 (κARM/κ) 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 κARM/κ was measured, shows remarkable similarity to the magnetic record and validates κARM/κ as a proxy for NADW flow intensity. The record of κARM/κ 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 δ18O, 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 formation in the Nordic Seas at the Bølling warming. In contrast to previous estimates for the duration of H1 (i.e., 1000 years to only a century or two), the total, combined composite signal of H1 presented here had a duration of nearly 4000 yrs (~19–14.6 ka BP), now spanning the established period of NADW shutdown. Clearly, deep-water formation and climate are not simply controlled by the magnitude or rate of meltwater addition. Instead, the results presented here emphasise that the location of meltwater pulses may be more important, with NADW formation being particularly sensitive to surface freshening in the Arctic/Nordic Seas.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:500750 |
| Date | January 2008 |
| Creators | Stanford, Jennifer D. |
| Publisher | University of Southampton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://eprints.soton.ac.uk/66346/ |
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