Sea ice breakup and marine melt of a retreating tidewater outlet glacier in northeast Greenland (81°N)

Abstract

Rising temperatures in the Arctic cause accelerated mass loss from the Greenland Ice Sheet and reduced sea ice cover. Tidewater outlet glaciers represent direct connections between glaciers and the ocean where melt rates at the ice-ocean interface are influenced by ocean temperature and circulation. However, few measurements exist near outlet glaciers from the northern coast towards the Arctic Ocean that has remained nearly permanently ice covered. Here we present hydrographic measurements along the terminus of a major retreating tidewater outlet glacier from Flade Isblink Ice Cap. We show that the region is characterized by a relatively large change of the seasonal freshwater content, corresponding to ~2 m of freshwater, and that solar heating during the short open water period results in surface layer temperatures above 1 °C. Observations of temperature and salinity supported that the outlet glacier is a floating ice shelf with near-glacial subsurface temperatures at the freezing point. Melting from the surface layer significantly influenced the ice foot morphology of the glacier terminus. Hence, melting of the tidewater outlet glacier was found to be critically dependent on the retreat of sea ice adjacent to the terminus and the duration of open water.

Storm-induced water dynamics and thermohaline structure at the tidewater Flade Isblink Glacier outlet to the Wandel Sea (NE Greenland)

“…The PcW and ArAW layers were separated by warm halocline water at 70-100 m, while the cold and extraordinarily low salinity waters in the uppermost 15-20 m layer were diluted by local freshwater sources . Bendtsen et al (2017) reported on a similar vertical thermohaline structure west of FIIC glacier observed during the short ice-free period in August 2016. The only changes occurred in the surface layer, where considerable freshening (S < 10) and warming (θ > +2 • ) were observed in relation to snow/ice melting and solar radiative heating.…”

“…These data showed the absence of warm halocline water in the vicinity of the glacier, and Bendtsen et al (2017) argued that bottom water from the shelf can intrude below the tidewater glacier and cool to the freezing temperature through heat loss to the glacial ice. This cooling is not accompanied by basal melting, and hence the salinities of underlying water below the glacier are not changed.…”

“…1a; also referred to as McKinley Sea) occupies the shelf area between Cape Nordøstrundingen (81 • 22 N, 11 • 40 W) and Herluf Trolle Land (NE Greenland). It can be a significant source of freshwater that originates from the summer snow/sea ice meltwater Bendtsen et al, 2017) and glacial runoff (Willis et al, 2015). The latter source might be of importance since numerous outlets of the Greenland Ice Sheet (in Independence and Hagen fjords) and Flade Isblink Ice Cap (FIIC) drain meltwater into the Wandel Sea via three marine-terminating glaciers (Palmer et al, 2010).…”

The Inferred Formation of a Subice Platelet Layer Below the Multiyear Landfast Sea Ice in the Wandel Sea (NE Greenland) Induced by Meltwater Drainage

“…Furthermore, due to a strong underlying density interface, this freshwater remains within the surface where it accumulates a large amount of solar radiation and becomes warmer. In August 2015, surface salinities within the ice‐free areas were below 10 while surface temperatures rose above 4°C at place and decreased toward 1.3°C at the MYI edge (Bendtsen et al, ). The warm freshwater layer predominantly occupied the uppermost 10 m of the water column (Bendtsen et al, ), and its persistence implies that the strong stratification suppressed vertical mixing.…”

“… SAR‐C satellite images showing the position of multiyear ice edge on (left) 17 August and (right) 19 August and positions of CTD casts carried out in 15–21 August 2015 (Bendtsen et al, ). The shape of symbols indicates the date of the CTD cast, and water temperature at 2 m depth is indicated by color shading.…”