Constraint on North Atlantic Circulation Change During the 8.2 ka Event Using High Resolution Sediment Cores, and its Comparison to Industrial Era Circulation Changes.
Abstract
The 8.2 ka event is often cited as a canonical example of how freshwater input to the North Atlantic can disrupt the Atlantic meridional overturning circulation (AMOC) and lead to abrupt cooling in the Northern Hemisphere. However there are few records that provide direct evidence of changes in the deep circulation of the Atlantic across the 8.2 ka event. Two prominent, high resolution studies present geochemical (Kleiven et al., 2008, Science) and paleo-flow speed (Ellison et al., 2008, Science) proxy evidence for changes in components of the AMOC, however, the interpretation of these proxy studies has been questioned: the geochemical data may be adversely affected by local productivity whereas the flow speed reconstruction may be responding to changes in overlying water properties rather than recording an increase in deep water formation and transport. Here we provide new high resolution data ( 6 yr spacing) from an exceptional sediment core located at 2.3km depth, south of Iceland. We report benthic foraminiferal d13C (a proxy for incursions of southern-source water into the North Atlantic), sortable silt grain size analysis (a proxy for the flow speed of Iceland Scotland Overflow Water - a major constituent of the AMOC), planktic foraminiferal assemblage and bulk sediment d15N (proxies for surface ocean conditions and nutrient utilization) data. We reveal abrupt changes in deep circulation during the 8.2 ka event, suggesting a marked shoaling and weakening of the AMOC. The high resolution of our records enables a detailed analysis of the onset and recovery of the event and its links to surface ocean circulation. Moreover, we place the events of the 8.2 ka in the context of Holocene variability at this site, and specifically compare it to the reported recent weakening of the AMOC (Thornalley et al., 2018, Nature). By also drawing on several sets of new, unpublished data from cores throughout the North Atlantic, our ongoing comparison work suggests recent events likely had a greater impact on the AMOC than the 8.2 ka event, and the AMOC responded in markedly different ways during the two events. These new constraints on the nature of the 8.2 ka event and comparison to other AMOC weakening events enables advancement of our understanding of the mechanistic linkages between the AMOC response to the 8.2 ka event and its climate impacts.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP43E1970M
- Keywords:
-
- 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHYDE: 4914 Continental climate records;
- PALEOCEANOGRAPHYDE: 4928 Global climate models;
- PALEOCEANOGRAPHYDE: 4962 Thermohaline;
- PALEOCEANOGRAPHY