Interaction Between the Warm Subsurface Atlantic Water in the Sermilik Fjord and Helheim Glacier in Southeast Greenland

Abstract

Recent observations of ocean temperature in several Greenland fjords suggest that ocean warming can cause large changes in the outlet glaciers in these fjords. We have observed the Helheim outlet-glacier front in the Sermilik Fjord over the last three decades using satellite images, and the vertical fjord temperature and salinity during three summer expeditions, 2008-2010. We show that the subsurface water below 250 m depth is the warm saline Atlantic Water from the Irminger Sea penetrating into the fjord and exposing the lower part of the Helheim glacier to warm water up to 4°C. Lagged correlation analysis spanning the 30-year time series, using the subsurface Atlantic Water temperature off the coast as a proxy for the variability of the subsurface warm Atlantic Water in the fjord, indicates that 24% of the Helheim ice-front movement can be accounted for by ocean temperature. A strong correlation (-0.75) between the ice-front position and the surface air temperature from a nearby meteorological station suggests that the higher air temperature causes melting and subsequent downward percolation of meltwater through crevasses leading to basal lubrication; the correlation accounts for 56% of the ice-front movement. The precise contribution of air temperature versus ocean temperature however, remains an open question, as more oceanographic and meteorological measurements are needed close to the glacier terminus.

Multi-decadal marine- and land-terminating glacier recession in the Ammassalik region, southeast Greenland

“…3 and Table 1). The observed meteorological data, air temperature and precipitation were obtained from the Danish Meteorological Institute (DMI) station in Tasiilaq for 1972-2011, located less than 10 km from the Sermilik Fjord outlet, and reconstructed ocean subsurface water temperatures at 400 m depth in the Irminger Sea were used as a proxy for the variability of the subsurface warm Atlantic water in the Sermilik Fjord (Johannessen et al, 2011).…”

“…Howat and Eddy (2011), for the GrIS outlet glaciers, noted a transition from stable and Table 2. Frontal position change rate statistics for the period 1972-2011 for the GrIS marine-terminating glaciers in the Ammassalik region, mean annual air temperature and precipitation anomaly from the DMI meteorological station in Tasiilaq, and mean annual reconstructed ocean water temperature anomaly at 400 m depth in the Irminger Sea (Johannessen et al, 2011). -periods 1972-1986 (green), 1986-1999 (blue), and 1999-2011 (yellow).…”

“…The underlying mechanisms of GrIS marine-terminating glacier dynamics remain somehow unclear (Straneo et al, 2010;Johannessen et al, 2011). The frontal recessions at the calving front are highly due to changes in the force balance due to thinning, reduced resistive force, and speed-up based on warming of oceanic subsurface waters and warming of the atmosphere, where warm subsurface waters are suggested by Luthcke et al (2006), Velicogna and Wahr (2006), Holland et al (2008), Howat et al (2008), Thomas et al (2009), van den Broeke et al (2009), Velicogna (2009, Murray et al (2010), Rignot et al (2010), Straneo et al (2010), and Andresen et al (2011) to play a significant role.…”

“…The frontal recessions at the calving front are highly due to changes in the force balance due to thinning, reduced resistive force, and speed-up based on warming of oceanic subsurface waters and warming of the atmosphere, where warm subsurface waters are suggested by Luthcke et al (2006), Velicogna and Wahr (2006), Holland et al (2008), Howat et al (2008), Thomas et al (2009), van den Broeke et al (2009), Velicogna (2009, Murray et al (2010), Rignot et al (2010), Straneo et al (2010), and Andresen et al (2011) to play a significant role. However, Johannessen et al (2011) stated, based on statistical correlations, that penetration of snow and ice melt water to the glacier bed might play an important role, influencing the GrIS sliding and dynamic processes. The mechanisms suggested for land-terminating GIC recession are less complex.…”

“…The imagery gives us the possibility to map "snapshots" and the averaged behaviour of glacier changes for the past four decades for the identified marine-terminating glaciers, the GrIS landterminating margin, and the GIC during a period of climate warming. The average multi-decadal glacier recession in the Ammassalik region (65 • N, 37 • W) was examined, rather than the annual range of variability, even though recent observations suggest that major changes in the dynamics of Greenland marine-terminating glaciers take place over timescales of 3-10 yr (Howat et al, 2007;Nick et al, 2009;Andresen et al, 2011;Johannessen et al, 2011), rather than over several decades or centuries as previously believed (Truffer and Fahnestock, 2007). Here, on approximately decadal scale we examine net frontal position and area fluctuations using multispectral Landsat satellite data, observing 21 marine-terminating glaciers from 1972-2011, land-terminating glacier frontal positions for parts of the GrIS, and of 35 GIC from 1986-2011 for the Ammassalik region -a region including the thermodynamic transition zone from the North Atlantic Ocean into the Arctic Ocean through the Denmark Strait.…”