Modelling the effect of submarine iceberg melting on glacier-adjacent water properties

Abstract

Abstract. The rate of ocean-driven retreat of Greenland’s tidewater glaciers remains highly uncertain in predictions of future sea level rise, in part due to poorly constrained glacier-adjacent water properties. Icebergs and their meltwater contributions are likely important modifiers of fjord water properties, yet their effect is poorly understood. Here, we use a 3-D ocean circulation model, coupled to a submarine iceberg melt module, to investigate the effect of submarine iceberg melting on glacier-adjacent water properties in a range of idealised settings. Submarine iceberg melting can modify glacier-adjacent water properties in three principle ways: (1) substantial cooling and modest freshening in the upper ~50 m of the water column; (2) warming of Polar Water at intermediate depths due to iceberg melt-induced upwelling of warm Atlantic Water, and; (3) warming of the deeper Atlantic Water layer when vertical temperature gradients through this layer are steep (due to vertical mixing of warm water at depth), but cooling of the Atlantic Water layer when vertical temperature gradients are shallow. The overall effect of iceberg melt is to make glacier-adjacent water properties more uniform with depth. When icebergs extend to, or below, the depth of a sill at the fjord mouth, they can cause cooling throughout the entire water column. All of these effects are more pronounced in fjords with higher iceberg concentrations and deeper iceberg keel depths. These iceberg melt-induced changes to glacier-adjacent water properties will reduce rates of glacier submarine melting near the surface, but increase them in the Polar Water layer, and cause typically modest impacts in the Atlantic Water layer. These results characterise the important role of submarine iceberg melting in modifying ice sheet-ocean interaction, and highlight the need to improve representations of fjord processes in ice sheet-scale models.

Impact of icebergs on the seasonal submarine melt of Sermeq Kujalleq

“…8). This matches well with the cooling and freshening of 5 • C and 0.7 PSU simulated for Sermilik Fjord in south-eastern Greenland by Davison et al (2020) with a similarly dense iceberg distribution, as well as with Davison et al (2022) studies in an idealised fjord. Comparison of IBP and NoIBP to observations in temperature-salinity (TS) space further highlights the contribution of iceberg melt (Fig.…”

“…Our results highlight the importance of including both icebergs and seasonal variations in subglacial discharge. Davison et al (2022) observe in a modelling study of an idealised steady-state fjord in summer conditions that when icebergs extend below sill depth, the deep basin is cooled, as it is in our model. On the other hand, without a sill the deep basin is warmed, due to increased up-fjord heat transport (Davison et al, 2020(Davison et al, , 2022.…”

“…However, they do not describe the processes causing this. Furthermore, Davison et al (2022) find that icebergs reduce the overall melt of the glacier front but find little impact of icebergs on a single point-source plume. We find that the dynamics and the interactions between icebergs and the plume merit further study due to the potential significance for the response of marine-terminating glaciers to changes in calving.…”

“…Recent advances in including icebergs in fjord-scale ocean circulation models (Davison et al, 2020(Davison et al, , 2022 show that buoyant meltwater from icebergs can drive circulation within the fjord and that iceberg melt can take up almost all available heat for melting and significantly freshen the upper layer of the fjord. Davison et al (2022) find that the response of a fjord basin to iceberg-induced modification is reversed from warming to cooling when the sill is shallower than the deepest iceberg keels. However, they do not describe the processes causing this.…”

Pathways, Form Drag, and Turbulence in Simulations of an Ocean Flowing Through an Ice Mélange

“…This, however, would introduce one or more new dimensions to the parameter space (cf. Davison et al., 2022; Sciascia et al., 2013); we leave this for future work.…”