Atlantic Water Influence on Glacier Retreat

The warming of Atlantic Water along Greenland’s southeast coast has been considered a potential driver of glacier retreat in recent decades. In particular, changes in Atlantic Water circulation may be related to periods of more rapid glacier retreat. Further investigation requires an understanding of the regional circulation. The nearshore East Greenland Coastal Current and the Irminger Current over the continental slope are relatively well studied, but their interactions with circulation further offshore are not clear, in part due to relatively sparse observations prior to establishing the OOI Irminger Sea Array and the Overturning in the Subpolar North Atlantic Program (OSNAP).

Satellite-derived sea surface temperature after adjustment for the Irminger Current (IC; green), Shelf Trough (ShTr; orange), and East Greenland Coastal Current (EGCC; purple). Monthly values (thin lines) are shown for 2000-2018 with 24-month low-passed records overlain. In situ observations from the fjord mouth (290 m: Black) and OOI flanking mooring FLMA (180 m; blue) are shown for comparison.

In a recent study (Snow et al., 2021) use in-situ mooring data to validate satellite SST records and then use the 19-year satellite record to investigate relationships between glacier melt and Atlantic Water variability. In order to use the satellite records for this purpose, several adjustments must be made, including accounting for cloud and sea ice contamination, eliminating seasonally-varying diurnal biases, and removing the influence of air temperature. This adjusted satellite SST can be compared to in-situ mooring data during a portion of the record. A coastal mooring near the Sermilik Fjord mouth and the OOI Irminger Sea Array provide useful records during 2009-2013 and 2014-2018, respectively (Figure 24). An interesting aspect is that the temperature record from OOI Flanking Mooring A (FLMA) is useful for this purpose even though the measurements are at 180 m depth. This is because the upper ocean is relatively homogeneous in this region, and the mixed layer is deeper than 180 m during much of the year. The authors find that the adjusted satellite SST is consistent with the in-situ records on monthly to interannual time scales (Figure above). This provided the motivation to investigate relationships between the 19 year satellite record and glacier discharge rates.

The study concludes that warmer upper ocean temperatures as far offshore as the OOI Irminger Sea Array were concurrent with increased glacier retreat in the early 2000s, in support of the idea that Atlantic Water circulation plays a role. However, they also note that this influence is not direct, because of substantial variation in how Atlantic Water is diluted as it flows across the shelf towards Sermilik Fjord. The idea that time-varying dilution of Atlantic Water governs the temperature of water reaching the glacier was not previously understood, and resolving such small-scale, time-varying processes is a challenge for models. The authors conclude that with appropriate adjustments, “[satellite] SSTs show promise in application to a wide range of polar oceanography and glaciology questions” and that the method can be generalized to other glacier outflow systems in southeast Greenland to complement relatively sparse in-situ records.

Snow, T., Straneo, F., Holte, J., Grigsby, S., Abdalati, W., & Scambos, T. (2021). More than skin deep: Sea surface temperature as a means of inferring Atlantic Water variability on the southeast Greenland continental shelf near Helheim Glacier. J. Geophys. Res: Oceans, 126, e2020JC016509.