The workshop members agreed on the following recommendations as points of action to pursue in addressing the process-based questions mentioned above.
1) An extensive effort must be put into site surveying prior to drilling any of the below mentioned sites around Greenland, including shallow and deep seismic profiles and swath bathymetry mapping. Some of the discussed drilling sites are, however, more “shovel ready” whereas others will need a more targeted surveying effort.
2) A higher resolution preglacial topographic map of Greenland is needed for the selection of drilling sites that will record its late Neogene evolution. Some constraint on the Greenland topographic changes during the late Neogene would also aid in assessing the ice-sheet’s long-term sensitivity to climate change.
3) The questions to be addressed by continental slope drilling should focus on large-scale Greenland Ice-Sheet changes, which can better inform ice-sheet models.
4) Small-scale instability related processes might, however, be addressable through localized investigation at the individual fjord outlet glacier scale on the continental shelf.
5) Surface and subsurface ocean temperatures should be reconstructed in concert with the past history of the Greenland Ice Sheet because ocean warming may play an important role in triggering ice-sheet instability and driving marine ice-margin retreat. This will require both reconstructing near-field sea surface temperatures and looking further afield to reconstruct subsurface ocean temperatures with depth transects.
6) Improvements in sea-ice and ice-shelf proxies are needed, because the Greenland Ice Sheet is sensitive to albedo/heat flux changes associated with sea-ice extent and the buttressing affect of potential ice shelves.
7) Ultimately, ocean drilling is required around all of Greenland to document its late Neogene evolution, the sensitivity of different sectors to climate change, and the related spatial pattern in ocean temperature change.
8) Ocean-drilling projects should develop in close collaboration with the climate-ice sheet modeling community so that data driven models can be constructed, hypotheses can be readily tested, and ice sheet-climate targets provided to the modeling community.
Climate Targets: The following climate periods were discussed and chosen as periods of interest to address the process-oriented questions raised at the workshop.
1) Establish the climate state during the Miocene before a Greenland Ice Sheet existed (there may have been small valley glaciers on Greenland as early as the Eocene).
2) Establish when and to what aerial extent valley glaciers coalesced to form the Greenland Ice Sheet in the late Neogene.
3) Document the volatility of the Greenland Ice Sheet (if in existence) during the Pliocene when atmospheric CO2 concentrations were close to present concentrations.
4) Record the advance and retreat of the Greenland Ice Sheet during the Quaternary and any potential change during the transition from a 40 to 100 kyr glacial-interglacial world, noting glacial periods when the Greenland Ice Sheet reached its maximum extent at the continental shelf break.
5) Estimate the minimum extent of the Greenland Ice Sheet during interglaciations, particularly during MIS 1, 5e, 7, 11, 19 and 31.
Drilling Targets: The workshop participants discussed and decided on the following locations as critical drilling targets for assessing the paleo history of the Greenland Ice Sheet.
Please join the DEGREE Wiki for discussion of targets
1) Eirik Drift: Revisit sites not drilled during Expedition 306 on northwest side of the drift to recover Pliocene to Miocene sediment, which will address climate targets 1-3. Re-drill ODP site 646 for better recovery back to the Pliocene and thus provide a complete Miocene to present record from Eirik Drift, addressing climate targets 1-5 for this portion of Greenland.
2) South of Davis Strait: These sites will document southwest Greenland ice retreat as well as record water mass and ice rafting changes into and out of Baffin Bay, addressing climate targets 2-5 (unlikely to retrieve Miocene age sediment).
3) Baffin Bay: These sites would provide information on the late Neogene evolution of the surrounding cyrosphere and the existence of a potential ice shelf during glaciations, addressing climate targets 1-4.
4) Southwest of Denmark Strait: Sites from this area would record intervals of southeast Greenland maximum ice extent and retreat, and when Greenland valley glaciers coalesced into a full ice sheet, addressing climate targets 2-5. These sites may also provide more local pollen records due to the blocking of the westerlies by the island of Greenland. Areas to target would be to revisit ODP leg 153 sites that were not drilled during Expedition 303 and sites closer to Denmark Strait
5) Scoresby Sund, Jakobshavn and Umiak Ice Stream Fans: These sites will provide information on when the Greenalnd Ice Sheet reached its maximum glacial extents and will require the use of down hole logging tools. They will address climate targets 2-4.
6) More distal sites from Greenland: These will record the evolution of subsurface water mass properties, in particular temperature, which may impact the Greenland Ice Sheet directly or indirectly through melting ice shelves. Coring sites should allow for collection of depth transects in the northern North Atlantic.
7) Outlet glaciers (Jakobshavn, Helheim, Kangerdlussuaq, Humboldt, Petermann, 79 North): Using a mission specific platform, these sites would provide information on local-scale instability to test the existence of bifurcation points. Records would be discontinuous but with extensive seismic surveying, coring of trough mouth fans and in fjords could potentially document the existence of instabilities in these different glacier systems as well as ice-sheet response time to a climate perturbation. Down hole logging tools would be necessary.
8) Northeast to north Greenland shelf and slope: These sites could potentially contain a long record of Greenland history obtainable by coring oceanward-dipping strata. The records may be discontinuous and down hole logging tools will be necessary, but climate targets 1-4 may be addressable.
9) Nares and Fram Straits: Records from these straits would document the flow of water from the Arctic around Greenland, which plays an important role in governing ocean temperatures around the island. Down hole logging tools would be necessary, particularly for Nares Strait where records may be discontinuous.
Site Survey Plan:
Before any drilling expeditions are taken with the exception of previously surveyed sites (i.e., drilling sites 1 & 4, above), extensive site surveying missions are needed with the collection of the following information. This extensive seismic surveying and bathymetric mapping plan will allow the collection of the best cores in a given location, and for the linkage of discontinuous continental shelf and fan records to the continuous continental slope records, key for reconstructing the full behavior of the Greenland Ice Sheet.
1) For high-resolution surface and shallow subsurface imaging, swath bathymetry and CHIRP.
2) Mid-resolution imaging should be conducted with either a deep-tow and autonomous underwater vehicle Huntec boomer profiler.
3) Deep penetrating seismic and bathymetric-profiling should be conducted with a generated injection air gun.
Strategies for Addressing Process-Oriented Questions:
The workshop participants decided upon the following research strategies for addressing the process-oriented questions raised during the workshop.
1) What controls the rate of ice mass change on Greenland and the respective roles of atmospheric and oceanic forcings? These questions will be addressed by targeting outlet glacier fjord and shelf records, and through the longer records from the continental slope where glacial-interglacial Greenland Ice Sheet fluctuations and ocean temperature records can be reconstructed. Although long atmospheric temperature records are lacking beyond ~130 ka, a first order forcing can be approximated from boreal summer insolation, and further improved by regional climate modeling.
2) Is subsurface oceanic temperature important in predicting the behavior of the Greenland Ice Sheet? The drilling of more distal sites to Greenland will document when and to what degree the subsurface ocean warmed before penetrating around Greenland. Through improved paleomagnetic stratigraphies, the relative timing between Greenland Ice Sheet (and ice shelves if they existed) retreat and subsurface warming might be resolvable. High-resolution ocean and ice-sheet modeling will allow testing of hypotheses arising from these records.
3) What is the role of ice shelves and sea ice? Records from the Labrador and Greenland Seas and Baffin Bay as well as fjord outlet glaciers will potentially document the existence of ice shelves or extensive sea ice, which can be compared to the Greenland Ice Sheet records from the same cores to address their roles in modulating this ice sheet’s behavior.
4) How does Greenland freshwater influence global ocean circulation? Records from Nares and Fram Straits will track the influence of Arctic freshwater discharge to the North Atlantic whereas the records from central to south Greenland will also include the influence of Greenland Ice Sheet runoff, which could be linked to more distal records of North Atlantic circulation as well as proximal records of bottom water circulation from winnowing records.