Due to the global reliance on coastal groundwater for drinking water, and its vulnerability to
saltwater intrusion, there is increased scientific interest in offshore freshened groundwater
(OFG). During the drilling carried by IODP Expedition #400 off the West Greenland Margin
(WGM), a previously undiscovered unit of freshened water was discovered at a depth of 600
- 800 m, about 20 m below the sea floor, which was up to 200 m thick at some sites. There
are several candidate sources for this freshened water, including hydrate destabilization and
basal melting of glaciers during previous glacial maxima. In contrast to many previously
described groundwater systems, the freshwater in West Greenland is not connected to the
land mass, and thus is actively being displaced by modern seawater from above. This system
therefore offers unique insights into the potential fate of modern coastal freshwater aquifers
in regions threatened by sea level rise. Therefore, it is important to characterize the origins
of this freshwater, and to study the past variability of groundwater and benthic water in this
region.
The aim of this project is to isotopically characterize the WGM groundwater in order to
constrain potential end-member sources. In addition, the history of groundwater and
benthic water temperatures and salinities will be reconstructed using (dual) clumped
isotope measurements on bivlaves, glendonites and carbonate concretions. Isotopic analysis
of bivalve geochemistry will unlock an archive of benthic temperature and salinity, both
important factors governing ice sheet stability. Glendonites (calcite replacing ikaite)
potentially record past events where freshwater and seawater were mixing, as modern ikaite
is oUen precipitated from freshwater-seawater mixtures. The presence of glendonites from
the Pliocene and Miocene could indicate that fresh groundwater was already present in
these periods - a hypothesis that we aim to test using clumped isotope analysis. Carbonate
concretions, on the other hand, provide an archive for reconstructing changes in the
composition of groundwater over time, as these cemented nodules form during the burial of
sediments, and their isotopic composition will reflect the groundwater that was present at
that time.
This project directly supports the objectives of IODP Expedition 400 by reconstructing
temporal variations in the temperature of ocean currents in the WGM from the Miocene to
present, which are an important variable governing the stability of its ice sheet. We further
contribute by constraining the extent of glacial melting during previous glacial maxima. In
addition, our results will be relevant for the upcoming IODP3 Expedition 501, which aims to
characterize a freshwater aquifer and its surrounding sediments.