Holocene dynamics of North Atlantic Deep Water masses

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Author(s): Hoogakker, B.; Chapman, M.; McCave, I. N.; Hillaire-Marcel, C.
Author Affiliation(s): Primary:
University of Oxford, Earth Sciences, Oxford, United Kingdom
University of East Anglia, United Kingdom
University of Cambridge, United Kingdom
Université du Québec à Montréal, Canada
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The Atlantic Meridional Overturning Circulation (AMOC) is a key component in latitudinal heat and salt transport, comprising northward flow of salty warm near-surface waters in the North Atlantic Current, and its compensating cool return flow at depth. During the early Holocene high summer insolation and strong inflow of North Atlantic surface waters into the Nordic Seas and the Arctic Ocean may have contributed to increased deep-water formation. To assess the effect of increased deep-water formation in the Nordic Seas and the Arctic Ocean on AMOC we reconstructed and assessed bottom flow vigor (using the mean grain size of the sortable silt) and hydrographic properties (using benthic foraminiferal isotopes) at key locations in the deep North Atlantic. The core sites of MD99-2251 and ODP 980 are currently influenced by North East Atlantic Deep Water (NEADW-origin Iceland Scotland Overflow Water), whilst that of MD95-2024 is under the influence of North West Atlantic Bottom Water (NWABW-currently densest North Atlantic Deep Water mass, origin Denmark Strait Overflow). When exiting the Labrador Sea, NEADW and NWABW mix to make up Lower North Atlantic Deep Water. Our results show that NEADW at Gardar Drift in the northeast Atlantic was considerably enhanced and denser (comparable to NWABW) during the early Holocene, until ∼6.5 ka. The density increase is attributed to NEADW mainly consisting of Iceland Scotland Overflow Water, lacking significant contributions of Labrador Sea Water or Lower Deep Water (LDW-origin Antarctic Bottom Water) that it contains at present. This implies there was no density gradient between these two deep-water masses during the early Holocene, contrary to today. A subsequent weakening of NEADW accompanied with a reduction in its density after 6.5 ka allowed a shoaling of LDW and deeper eastward advection of Labrador Sea Water into the northeast Atlantic Basin. The density gradient observed between current NEADW and NWABW might have been acquired progressively between the early and mid Holocene, possibly coincident with enhanced NWABW production and inception of active modern-like LSW formation. References: Oppo et al., 2003. Nature 422, 277-400. Hoogakker et al., 2011. Paleoceanography 26, PA4214.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Atlantic Ocean; Cenozoic; Holocene; Leg 162; Marine sediments; North Atlantic; North Atlantic Deep Water; ODP Site 980; Ocean Drilling Program; Ocean circulation; Quaternary; Rockall Bank; Sea surface water; Sea water; Sea-surface salinity; Sea-surface temperature; Sediments
Coordinates: N552906 N552906 W0144208 W0144208
Record ID: 2015005596
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