Tracking submarine meltwater pathways

We proudly present our latest GROCE publication by Huhn et al., (2021) in the Journal of Geophysical Research - Oceans: 'Submarine Meltwater from Nioghalvfjerdsbræ (79 North Glacier), Northeast Greenland'! 

What did our colleagues from subproject 4 study on?
Ans what conclusions did they draw?

Insights from Oliver Huhn (08. July 2021)

Figure 1: He and Ne observations near (red) and off (blue and black) the 79NG. The offset from submarine meltwater (SMW-line, thick magenta) towards higher He indicate radiogenic He; the offset towards higher Ne stems from fractionation during sea ice formation.

Figure 2: Spatial distribution of submarine meltwater (SMW) on the Northeast Greenland Shelf. Up to 1.8% (dark red) directly at the calving front, diluting by ambient water (orange, yellow, white) to nonsignificant in Fram Strait (black dots).

Background

Melting at the 79 North Glacier occurs at the surface and, moreover, by warm Atlantic Water at the underside of its 80 km long floating ice tongue. However, freshwater from submarine melting is hardly distinguishable in the ocean. Therefore, to identify and to quantify the distribution of submarine meltwater on the Northeast Greenland Shelf, we use helium (He) and neon (Ne) observations. These tracers uniquely identify submarine meltwater and allow quantifying its fraction in ambient ocean water (Figure 1).

What are our new findings?

  • Submarine meltwater from the 79NG is present on the entire Northeast Greenland Shelf but dilutes from 1.8% at the calving front to nonsignificant in Fram Strait (Figure 2).
  • The formation rate of submarine meltwater at the 79NG was estimated to be 14.5 ± 2.3 Gt per year (equivalent to a melt rate of 8.6 ± 1.4 m per year). 
  • A surplus of He compared to Ne in the SMW indicates a substantial addition of radiogenic He from the bedrock, the 79NG is resting on before it slides into the ocean. 
  • A surplus of Ne compared to He in the upper 100 meters observed on most of the shelf region is attributed to noble gas fractionation during sea ice formation. Combining this 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.

Why is that relevant & what’s next?

Our He and Ne data illustrate the active glacier-ocean interaction at the 79NG. These tracer observations allow to quantify the formation and to elucidate the fate of submarine meltwater, its circulation and further mixing with ambient water masses. Furthermore, we can validate modeled distributions of submarine meltwater with our observations.

As a next step, we will analyse He, Ne, and oxygen isotope data from a revisit of the 79NG and Northeast Greenland Shelf from 2017, as well as seven He and Ne sections across the East Greenland Shelf downstream of the 79NG towards the southern tip of Greenland from 2019 (more details can be found here).