IMPACTS OF MELT RUNOFF FROM THE GREENLAND ICE SHEET ON SEAWATER 234U/238U COMPOSITION
In this study we have examine the Greenland Ice Sheet (GrIS) by sampling both subglacial drainage at the toe of outlet glaciers directly connected to the Southern GrIS, and proximal seawater at three depths ~20 km off of the GrIS coast at four unique locations: Narsarsuaq, Ilulissat, Nuuk and Kulusuk. All four outlet glaciers in this study are located on unique bedrock of varying ages which provide distinctive chemical compositions of subglacial water draining from these locations. Glaciers with the highest residence times (as inferred from high pH, cation concentrations) have the highest U concentration and 234U/238U activity ratios and have the largest impact on seawater chemistry (see Table below).
|Subglacial [U] (ppb)||1.010||0.046||0.006||0.005|
Chemical analysis of both subglacial drainage from GrIS outlet glaciers and adjacent seawater show that melt from Southern GrIS (Narsarsuaq) has a strong influence on the U composition of seawater. Our findings of notable variations of U in seawater related to changing subglacial melt contributions have substantial implications for paleoclimate studies that have relied on the assumption that seawater U compositions remain stable through time.