Abstract
Abstract. Two hundred marine-terminating Greenland outlet glaciers deliver more than half of the annually accumulated ice into the ocean and have played an important role in the Greenland ice sheet mass loss observed since the mid-1990s. Submarine melt may play a crucial role in the mass balance and position of the grounding line of these outlet glaciers. As the ocean warms, it is expected that submarine melt will increase, potentially driving outlet glaciers retreat and contributing to sea level rise. Projections of the future contribution of outlet glaciers to sea level rise are hampered by the necessity to use models with extremely high resolution of the order of a few hundred meters. That requirement in not only demanded when modeling outlet glaciers as a stand alone model but also when coupling them with high-resolution 3-D ocean models. In addition, fjord bathymetry data are mostly missing or inaccurate (errors of several hundreds of meters), which questions the benefit of using computationally expensive 3-D models for future predictions. Here we propose an alternative approach built on the use of a computationally efficient simple model of submarine melt based on turbulent plume theory. We show that such a simple model is in reasonable agreement with several available modeling studies. We performed a suite of experiments to analyze sensitivity of these simple models to model parameters and climate characteristics. We found that the computationally cheap plume model demonstrates qualitatively similar behavior as 3-D general circulation models. To match results of the 3-D models in a quantitative manner, a scaling factor of the order of 1 is needed for the plume models. We applied this approach to model submarine melt for six representative Greenland glaciers and found that the application of a line plume can produce submarine melt compatible with observational data. Our results show that the line plume model is more appropriate than the cone plume model for simulating the average submarine melting of real glaciers in Greenland.
Highlights
Since the 1990s the decadal loss of ice mass by the Greenland ice sheet (GrIS) has quadrupled (Straneo and Heimbach, 2013), with an average 1993–2010 contribution of 0.33 ± 0.08 mm yr−1, which is about 10 % of the observed sea level rise during this period (Church and White, 2011; Church et al, 2013)
We do not use this approximation in our calculation, but this is helpful to interpret some of the results presented in our paper, in particular in quantifying the amount of melt rate and simplifying the melt rate dependence on temperature and subglacial discharge (Appendix A)
For a wide glacier, the LP model gives much higher cumulative melt rate compared to the CP model, when assuming the existence of a single subglacial channel
Summary
Since the 1990s the decadal loss of ice mass by the Greenland ice sheet (GrIS) has quadrupled (Straneo and Heimbach, 2013), with an average 1993–2010 contribution of 0.33 ± 0.08 mm yr−1, which is about 10 % of the observed sea level rise during this period (Church and White, 2011; Church et al, 2013) This acceleration of the GrIS mass loss is attributed to increase of surface melt due to atmospheric warming (Khan et al, 2014) and speedup of the marine-terminating outlet glaciers (Rignot and Kanagaratnam, 2006). As an alternative to costly three-dimensional models, one-dimensional flow line models were convincingly applied to several major outlet glaciers
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