Submarine Meltwater From Nioghalvfjerdsbræ (79 North Glacier), Northeast Greenland

Abstract

AbstractThe Greenland Ice Sheet (GrIS) faces accelerated melting under a warming climate. This also affects the largest marine‐terminating outlet glacier of the Northeast Greenland Ice Stream (NEGIS), the Nioghalvfjerdsbræ (79 North Glacier, 79NG). In the cavity below its floating ice tongue, the heat of inflowing warm and saline Atlantic Water melts the ice at the base, and colder and fresher outflow is exported toward the shelf break and presumably south with the East Greenland Current (EGC). However, freshwater from submarine melting is hardly distinguishable from other freshwater sources by salinity alone. To identify and to quantify the distribution of submarine meltwater on the Northeast Greenland Shelf, we use helium (He) and neon (Ne) observations obtained directly at the calving front of the 79NG, on the Northeast Greenland Shelf, and in Fram Strait during an expedition aboard R/V POLARSTERN in summer 2016. These tracers uniquely identify submarine meltwater (SMW) and allow quantifying its fraction. SMW is present on the shelf but dilutes from 1.8% at the 79NG calving front to nonsignificant in Fram Strait. The SMW formation rate of the 79NG was estimated to be 14.5 ± 2.3 Gt per year. A surplus of Ne compared to He in the upper 100 dbar observed on most of the shelf region is attributed to noble gas fractionation during sea ice formation. Combining the Ne excess with the ventilation time on the shelf of 1.5 years yields a mean sea ice formation rate of 4 m per year.