Abstract
AbstractThe injection at depth of ice sheet runoff into fjords may be an important control on the frontal melt rate of tidewater glaciers. Here we develop a new parameterization for ice marginal plumes within the Massachusetts Institute of Technology General Circulation Model (MITgcm), allowing three‐dimensional simulation of large (500 km2) glacial fjords on annual (or longer) time scales. We find that for an idealized fjord (without shelf‐driven circulation), subglacial runoff produces a thin, strong, and warm down‐fjord current in the upper part of the water column, balanced by a thick and slow up‐fjord current at greater depth. Although submarine melt rates increase with runoff due to higher melt rates where the plume is in contact with the ice front, we find that annual submarine melt rate across the ice front is relatively insensitive to variability in annual runoff. Better knowledge of the spatial distribution of runoff, controls on melt rate in those areas not directly in contact with plumes, and feedback mechanisms linking submarine melting and iceberg calving are necessary to more fully understand the sensitivity of glacier mass balance to runoff‐driven fjord circulation.
Highlights
The melting of Greenland’s marine terminating glaciers by warm oceanic waters may be a significant cause of dynamic mass loss from the Greenland ice sheet [Holland et al, 2008; Straneo and Heimbach, 2013]
The convection of glacial plumes was modeled by Jenkins [2011], providing a theoretical relationship between meltwater discharge and submarine melt rate, but this approach cannot provide information on the impact of such plumes on the wider fjord circulation
If only the central 200 m of the ice front are considered, plume melting dominates and we find a similar power law relation between melt and discharge to that identified in previous studies [Jenkins, 2011; Sciascia et al, 2013; Xu et al, 2012], with m_ / Q2=5 (Figure 6c)
Summary
The melting of Greenland’s marine terminating glaciers by warm oceanic waters may be a significant cause of dynamic mass loss from the Greenland ice sheet [Holland et al, 2008; Straneo and Heimbach, 2013]. Numerical ocean models have been used to examine the impact of glacial runoff on fjord circulation [Salcedo-Castro et al, 2011; Sciascia et al, 2013; Xu et al, 2013, 2012] Such studies have been limited by the computational expense of both resolving the fine-scale, highly nonhydrostatic dynamics of the turbulent glacial outflow plume and incorporating the wider circulation of fjords that may be hundreds of square kilometers in area. This constraint has resulted in simulations being limited to two-dimensional fjords [Sciascia et al, 2013; Xu et al, 2012] or small (
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