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Interaction between the ocean, atmosphere and ice sheet dynamics along the Greenland margin
A research project of the Department of Geography.
A better understanding of the interactions between the Earth’s polar ice sheets and climate is key to understanding the possible impacts of future global warming, including ice sheet contribution to global sea-level rise and ocean circulation. This is especially so since recent observations suggest that ice sheets respond to climate change much more quickly than originally suggested in IPCC2001. However, a key uncertainty in our understanding of ice sheet behaviour is the role of atmospheric versus oceanic forcing in influencing ice sheet dynamics. On the one hand, it is argued that ice sheets respond rapidly to changes in air temperature, with rapid instabilities caused by enhanced ice sheet melt. Conversely, warmer ocean currents can enhance basal melting of the marine based portions of an ice sheet and hence induce rapid ice stream retreat. A powerful way to test these competing hypotheses is to investigate ice sheet response to previous periods of climate change.
Despite being the second largest ice sheet on Earth, we know remarkably little about the response of the Greenland Ice Sheet (GIS) to past climate change. Observations over the last 10-15 years have identified significant instability in some of the major ice stream draining the GIS. For example, Jakobshavns Isbrae has experienced a doubling of ice stream velocity and associated increase in flux of meltwater and icebergs to the marine environment. These rapid changes have raised concern that the GIS is responding faster than previously thought to global warming. However, it is unclear whether such instabilities are part of the natural cycle of ice sheet change or indeed whether they are driven by atmospheric or ocean warming.
This collaborative research programme investigates the evidence for past instabilities in the GIS. Our particular focus is on testing the hypothesis that ocean forcing has had a significant impact on ice sheet stability in Greenland since the LGM. This provides improved constraints on the timing and nature of deglaciation of the Greenland Ice Sheet from the LGM. We also focus on the more recent past investigating possible oceanic forcing during climate fluctuations such as the Neoglacial cooling, Medieval Warm Period and the Little Ice Age (LIA) cooling through a period of warming during the mid 20th Century and into the potentially anthropogenically induced warming of the last few decades. Much of the focus of this research has been in the Disko Bay and Ummannaq area of central west Greenland but also includes research from Kejser Franz Joseph Fjord and adjacent shelf of north east Greenland.
To address the research questions a series of cruises have been undertaken collecting geophysical data, CTD, surface grab samples and 6 - 12 m long piston cores. A wide range of techniques have been used in analysis of material including; microfossil analysis (foraminifera, diatoms, dinoflagellates); sedimentology (particle size and IRD analysis); inorganic and organic geochemistry (oxygen isotopes, organic carbon, IP25, TEX86); mineral magnetic analysis; chronological analysis (Pb210, 14C dating).
This research has produced the first offshore dates on deglaciation of the shelf west of Disko Bay, through Disko Bay to the current coastline. This data suggests rather late but rapid deglaciation of the shelf from c. 11 ka cal BP reaching central Disko Bay by c. 10.4 ka cal BP and the mouth of Jakobshavn Isbrae by c. 8.4 ka cal BP. We have also identified the initiation and evolution of the relatively warm and saline West Greenland Current (WGC) along the central west Greenland margin associated with deglaciation and the Holocene evolution of area. High resolution foraminiferal data from the last 2000 years also shows a clear link between ocean circulation (relative strength/warmth of the WGC) and ice stream dynamics - relatively warm bottom water temperatures during the Medieval Warm Period associate with retreat of the Jakosbhsavn Isbrae ice stream followed by advance during the Little Ice Age associated with colder bottom water temperatures.
Lloyd, J.M., Kuijpers, A., Long, A., Moros, M., Park, L.A. 2007. Foraminiferal
reconstruction of mid to late Holocene ocean circulation and climate variability
in Disko Bugt, West Greenland. The Holocene 17
Lloyd, J. 2006. Modern distribution of benthic foraminifera from Disko Bugt, west Greenland. Journal of Foraminiferal Research 36, 315-331
Lloyd, J. 2006. Late Holocene environmental change in Disko Bugt, west Greenland: interaction between climate, ocean circulation and Jakobshavn Isbrae. Boreas 35, 36-49
Lloyd, J., Park, L.A., Kuijpers, A., Moros, M. 2005. Early Holocene palaeoceanography and deglacial chronology of Disko Bugt, West Greenland. Quaternary Science Reviews 24, 1741-1755
- Dr Matthias Moros (Baltic Sea Research Institute, Germany)
- Dr Antoon Kuijpers (Geological Survey of Denmark and Greenland)
- Professor Andrzej Witkowski (University of Szczecin, Poland)
- Dr Ian Snowball, Professor Per Sandgren (University of Lund)
- Dr Erin McClymont (University of Newcastle)