Seasonal variability of submarine melt rate and circulation in an East Greenland fjord

Abstract

[1] The circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front. The model configuration and water properties are based on data collected in Sermilik Fjord near Helheim Glacier, a major Greenland outlet glacier. The approximately two-layer stratification of the fjord's ambient waters causes the meltwater plume at the glacier front to drive a "double cell" circulation with two distinct outflows, one at the free surface and one at the layers' interface. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) causes the circulation to be much more vigorous and associated with a larger melt rate than in winter. The simulated "double cell" circulation is consistent, in both seasons, with observations from Sermilik Fjord. Seasonal differences are also present in the vertical structure of the melt rate, which is maximum at the base of the glacier in summer and at the layers' interface in winter. Simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge, to changes in water temperature, and to the height of the layers. They are also consistent with those inferred from simplified one-dimensional models based on the theory of buoyant plumes. Our results also indicate that to correctly represent the dynamics of the meltwater plume, care must be taken in the choice of viscosity and diffusivity values in the model. Citation: Sciascia, R., F. Straneo, C. Cenedese, and P. Heimbach (2013), Seasonal variability of submarine melt rate and circulation in an East Greenland fjord,

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

“…Indeed, when the SgFW discharge increases at Store, the PluW outflow becomes shallower and evolves from state 2 to state 3 (Fig. 6), an observation which resonates with recent modelling (Sciascia et al, 2013;Xu et al, 2013).…”

“…Furthermore, it is emerging that circulation in Greenland's deep fjords is more complex than the single convective cell (estuarine-like) circulation model that has been assumed previously in energymass balance calculations (Motyka et al, 2003;Rignot et al, 2010). For instance, a vertical superposition of convective cells was observed (Straneo et al, 2011;Sutherland and Straneo, 2012) and more recently modelled (Sciascia et al, 2013;Sole et al, 2012) within fjords in east Greenland.…”

“…To date, several processes of interaction between fjord water and tidewater calving fronts have been observed, modelled and/or speculated upon including forced convection caused by buoyant subglacial fresh water (SgFW) discharged at depth and entraining AW as it rises (Jenkins, 2011;Mugford and Dowdeswell, 2011;Salcedo-Castro et al, 2011;Sciascia et al, 2013;Sole et al, 2012;Xu et al, 2012Xu et al, , 2013 as well as wind stress and tide-driven fjord circulation Sole et al, 2012;Straneo et al, 2010;Sutherland and Straneo, 2012). Furthermore, it is emerging that circulation in Greenland's deep fjords is more complex than the single convective cell (estuarine-like) circulation model that has been assumed previously in energymass balance calculations (Motyka et al, 2003;Rignot et al, 2010).…”

Channelization of plumes beneath ice shelves

“…General circulation models have also been used to study the effect of patterned ice shelf topography or subglacial discharge on the melt rate (e.g. Millgate et al 2013;Sciascia et al 2013). Until recently, these models have assumed a fixed ice shelf geometry.…”

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.…”