Heat sources for glacial melt in a sub-Arctic fjord (Godthåbsfjord) in contact with the Greenland Ice Sheet

Abstract

Recent warming of Subpolar Mode Water off Greenland has been suggested to accelerate the mass loss from tidal outlet glaciers of the Greenland Ice Sheet. We present a comprehensive analysis of water masses, dynamics, and interannual hydrographic variability in Godthåbsfjord, a sill fjord in contact with tidal outlet glaciers on the west coast of Greenland. Through seasonal observations we recognize an intermediate baroclinic circulation mode driven by tidal currents and an associated important local heat source for the fjord. During summer this results in significant warming and freshening of the intermediate layer of the main fjord, and the increase in heat content is equivalent to melting of ∼2.1 km3 of glacial ice. This is comparable to ∼8 km3 glacial ice discharge estimated from the Kangiata Nunâta Sermia calving front per year. During winter the external heat source in the West Greenland Current enters the fjord as intermittent inflows of either cold (<2°C) or warm (>2°C) dense water in pulses of 1 to 3 months duration. Four distinct circulation modes are observed in the fjord, of which all can contribute to glacial ice melt. An important aspect of the ice distribution in the fjord is that only a minor fraction is exported out of the fjord.

Oceanic Boundary Conditions for Jakobshavn Glacier. Part I: Variability and Renewal of Ilulissat Icefjord Waters, 2001–14

“…However, the interval between renewal episodes (for instance, in certain Scottish lochs) could be much longer than 1 yr (Gade and Edwards 1980). Mortensen et al (2011) studied Godthåbsfjord, south of JG along the coast of Greenland, and described four modes of circulation that can transport heat to the head of the fjord and also bring about fjord-shelf exchange. First is the estuarine mode of circulation present in all fjords in which freshwater runoff enters the fjord at the surface.…”

“…These data include annual surveys, moorings, and instrumented seals and Greenland halibut. Similar efforts have been undertaken at several major Greenland outlet glaciers (Rignot et al 2010;Mortensen et al 2011;Straneo et al 2010;Murray et al 2010;Christoffersen et al 2011;Rignot and Steffen 2008;Johnson et al 2011). Summer water properties in DB have been routinely monitored since the mid-twentieth century (Andersen 1981) and more intensively in recent decades (Hansen et al 2012;Ribergaard 2013).…”

Rapid last-deglacial thinning and retreat of the marine-terminating southwestern Greenland ice sheet

“…The outer sill at Nuuk is ~170 m below modern sea level (Mortensen et al, 2011), 476 and with a coastal marine limit of ~90 m asl (Kelly, 1985), this restricted deglacial 477 seawater deeper than ~260 m from entering the fjord (Fig. 2B).…”

Ice–ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers

“…The west Greenland current advects deep (> 400 m), warm (> 3 • C) and saline (> 34.8 PSU -practical salinity units) Atlantic water around the south coast of Greenland, transferring large fluxes of thermal energy of a subtropical origin into this sensitive polar environment Holland et al, 2008;Kjaer et al, 2012;Mortensen et al, 2011;Ribergaard, 2007;Sutherland et al, 2013). The frontal dynamics of tidewater outlet glaciers draining the Greenland Ice Sheet (GrIS) can be profoundly influenced by Atlantic water (AW), which has the potential to directly access their…”