Convection-Driven Melting near the Grounding Lines of Ice Shelves and Tidewater Glaciers

Abstract

Subglacial meltwater draining along the bed of fast-flowing, marine-terminating glaciers emerges at the grounding line, where the ice either goes afloat to form an ice shelf or terminates in a calving face. The input of freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice-ocean interface. This process is modeled using the theory of buoyant plumes that has previously been applied to the study of the larger-scale circulation beneath ice shelves. The plume grows through entrainment of ocean waters, and the heat brought into the plume as a result drives melting at the ice-ocean interface. The equations are nondimensionalized by using scales appropriate for the region where the subglacial drainage, rather than the subsequent addition of meltwater, supplies the majority of the buoyancy forcing. It is found that the melt rate within this region can be approximated reasonably well by a function that is linear in ocean temperature, has a cube root dependence on the flux of subglacial meltwater, and has a complex dependency on the slope of the ice-ocean interface. The model is used to investigate variability in melting induced by changes in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelves and tidewater glaciers. The results show how warming ocean waters and increasing subglacial drainage both generate increases in melting near the grounding line.

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

“…The direct effect of changes in temperature and salinity on the melt equations are well tested. Past studies using uniform ambient temperature and salinity conditions have found a linear relationship between increases in ambient fjord temperatures and melt rates, with the slope of the relationship dependent upon the discharge volume (P. R. Jenkins, 2011;Xu et al, 2013). Salinity, on the other hand, has been shown to have a negligible effect on melt rates (D. M. .…”

“…A model based upon one-dimensional plume theory (e.g. Jenkins, 2011;Carroll et al, 2015;Slater et al, 2016) would be less computationally expensive and may allow some of these limitations to be addressed. However, such a model would not capture the strong surface currents driven by the plume which are important for the terminus morphology studied here.…”

“…Straneo and Heimbach (2013) proposed two mechanisms responsible for the increase of submarine melt rates at the ice-ocean interface in Greenland: a warmer and thicker layer of Atlantic water in the fjords and an increase in subglacial discharge mainly during summer and autumn. Buoyant meltwater plumes entrain warm ocean water (Jenkins, 2011) and are thought to enhance melt undercutting (Slater et al, 2015) at the ice cliff triggering collapse of the ice above. Luckman et al (2015) investigated controls on seasonal variations in calving rates and showed that calving variations at Kronebreen, the glacier this study focuses on, are strongly correlated with sub-surface ocean temperature changes linked to melt undercutting of the calving front.…”

Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

“…Both have been widely applied to simulate plumes adjacent to glaciers and have been described in detail elsewhere (Jenkins, 2011;Carroll and others, 2015;Slater and others, 2016). …”

Entrainment in two coalescing axisymmetric turbulent plumes

“…Ocean outfall design is governed by the dynamics regulating the interaction of multiple buoyant jets (Lai & Lee 2012;Lee 2012) and their ability to dilute the waste waters. Finally, the dynamics of buoyant vertical plumes has recently been shown to have an important role in the melting of some vertical glacier faces (Jenkins 2011;Xu et al 2012;Sciascia et al 2013). At the front of marine terminating glaciers, freshwater plumes are generated by subglacial discharge and submarine melting.…”