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HB-1-9

The interplay between ocean circulation and Greenland Ice Sheet in theBaffin Bay since the last ice age

PhD student :Rebecca Jackson
Project supervisors :M. Kucera, R. Stein (Germany)
A. de Vernal, A. Rochon (Canada)
Key hypothesis
The inflow of North Atlantic water from the Labrador Sea into the Baffin Bay has been sensitive on millennial to centennial time scales to shifts in North Atlantic circulation. There has been a consistent phase relationship between inflow intensity, GIS melting and response of the marine ecosystem.
 
The Greenland Ice Sheet (GIS) has been sensitive to changes in external forcing on millennial time scales during both glacial and interglacial periods and currently shows a negative mass balance associated with meltwater discharge and acceleration of outlet glaciers. Recent observations and data from geological archives suggest a link between outlet glacier retreat and warming of subsurface waters advected into the Baffin Bay from the Labrador Sea. Data from marine sediment cores from settings proximal to the glacier outlets indicate that local ocean conditions have been highly variable on millennial to decadal time scales and that this variability was linked with the North Atlantic synoptic system. However, the exact nature of this link and the temporal scale at which it operates under interglacial and glacial boundary conditions remains unclear. High resolution Holocene records of ocean conditions in coastal settings off Greenland and in the Arctic Straits indicate the presence of millennial climate events, but their exact link with the North Atlantic event chronology, most likely reflecting shifts in ocean circulation, remains unclear. Baffin Bay is a key region for the understanding of the interaction between ocean circulation and the GIS. At present, the circulation in the basin reflects three processes: the extent of seasonal sea-ice, changes in surface water inflow from the Labrador Sea and freshwater transport from the Arctic and from the GIS. In line with the evidence from coastal settings off Greenland, oceanographic observations in the Baffin Bay proper show that the basin is currently undergoing a warming (from the North Atlantic) and freshening (from the Arctic) phase, which affects both surface and subsurface water masses. These observations indicate that the Baffin Bay proper could be an ideal target region to disentangle the link between Baffin Bay circulation and North Atlantic forcing. This region is less affected by local processes and provides an opportunity to extend existing Holocene coastal records into the glacial period. Sediments in the Baffin Bay contain calcareous planktonic and benthic foraminifera, allowing direct micropaleontological and geochemical characterization of surface ocean properties. Vernal et al. (1992) reported intermittent presence of temperate species of planktonic foraminifera, with a potential to act, together with the isotopic composition and shell morphology of the polar resident species, as independent proxies of the strength of Atlantic water advection across the Davis Strait. Studies of millennial scale variability in the open Baffin Bay sediments have been hampered by low sedimentation rates and poor carbonate preservation. In 2008, Michal Kucera led jointly with Anne de Vernal a “twin” cruise of the German research vessel Maria S. Merian (MSM09/2) and the Canadian icebreaker Hudson to the Baffin Bay, collecting a suite of sediment cores in the central Baffin Bay on both the Canadian and the Greenland side, which record a continuous, high resolution sequence of environmental change since MIS3. The cores are rich in glaciogenic material, leading to high sedimentation rates (>20cm/kyr), and contain abundant benthic and planktonic microfossils, allowing assessment of cryosphere processes, oceanography and biotic response on the same material.
The aim of this project is to take advantage of the newly available sediment material and generate high-resolution paleoceanographic records from bathyal sediments in the central Baffin Bay covering the time period since MIS3. Surface ocean conditions will be constrained using a combination of micropaleontological proxies (abundance of temperate taxa of planktonic foraminifera, shell morphology of N. pachyderma), including dinoflagellate cysts (to be carried out together with partners in Canada, CA-5) with stable isotope measurements of N. pachyderma, interpreted in the framework of the ecological model developed in HB-10. The dynamics of the ice sheets in the region will be assessed by analyzing sediment physical properties (XRF scan, granulometry, organic and inorganic carbon) combined with radiogenic isotopic tracers in HB-12. A high-resolution age model based on radiocarbon dating will allow the assessment of the link between millennial- and centennial-scale signals in the Baffin Bay proper and the North Atlantic system, as studied in CA-14. The resulting time series will be analysed for the occurrence of mode shifts and compared to model simulations generated in HB-4. The project will test the hypothesis that paleoceanographic signals from the central Baffin Bay record processes driven by North Atlantic climate variability on millennial to centennial time scales. Particular attention will be paid to major events such as Heinrich Event 1, the Bølling-Allerød, the Younger Dryas, and the millennial events of the Holocene.