Ocean variability contributing to basal melt rate near the ice front of Ross Ice Shelf, Antarctica

Abstract

Basal melting of ice shelves is an important, but poorly understood, cause of Antarctic ice sheet mass loss and freshwater production. We use data from two moorings deployed through Ross Ice Shelf, $6 and $16 km south of the ice front east of Ross Island, and numerical models to show how the basal melting rate near the ice front depends on sub-ice-shelf ocean variability. The moorings measured water velocity, conductivity, and temperature for $2 months starting in late November 2010. About half of the current velocity variance was due to tides, predominantly diurnal components, with the remainder due to subtidal oscillations with periods of a few days. Subtidal variability was dominated by barotropic currents that were large until mid-December and significantly reduced afterward. Subtidal currents were correlated between moorings but uncorrelated with local winds, suggesting the presence of waves or eddies that may be associated with the abrupt change in water column thickness and strong hydrographic gradients at the ice front. Estimated melt rate was $1.2 6 0.5 m a 21 at each site during the deployment period, consistent with measured trends in ice surface elevation from GPS time series. The models predicted similar annual-averaged melt rates with a strong annual cycle related to seasonal provision of warm water to the ice base. These results show that accurately modeling the high spatial and temporal ocean variability close to the ice-shelf front is critical to predicting time-dependent and mean values of meltwater production and ice-shelf thinning.

Modeling Ice Shelf/Ocean Interaction in Antarctica: A Review

“…Throughout most of the year, Mode 3 melting is controlled by the cold core of the AASW that, like SW, has a temperature near the surface freezing point. Melt rates are therefore similar to Mode 1, but Mode 3 is distinct in that the upper layer of AASW, which is warmed by interaction with the atmosphere in summer, can significantly increase melt rates in the outer cavity (e.g., Arzeno et al, 2014).…”

“…Most formulations of the exchange coefficients of salt and heat (γ S and γ T ) are dependent on the currents at the base of the ice shelf, and tides heavily influence these currents in many instances (e.g., Nicholls and Makinson, 1998;Arzeno et al, 2014). Including tides in regional models of some cold water ice shelves such as Amery (Galton-Fenzi et al, 2012), Filchner-Ronne (Makinson et al, 2011), Larsen C (Mueller et al, 2012), and Ross (Arzeno et al, 2014) increased the average melt rate by between 25% and 100%. The effect of tides is typically weaker for warm water ice shelves because the current under the ice shelf is more strongly controlled by meltwater-driven flows (e.g., Dutrieux et al, 2014a).…”

Ocean-Ice Shelf Interaction in East Antarctica

“…Fimbul Ice Shelves in the Weddell Sea (Makinson and Nicholls, 1999;Joughin and Padman, 2003;Hatterman et al, 2012) and the Ross and McMurdo Ice Shelves in the Ross Sea (Arzeno et al, 2014;Stern et al, 2013).…”

The Effect of Atmospheric Forcing Resolution on Delivery of Ocean Heat to the Antarctic Floating Ice Shelves*,+

“…Vertical mixing on the shelf, which changes CDW heat content, must also be properly represented. Nearshore surface processes that lead to warming of surface waters that can still penetrate below the ice shelf fronts (Hattermann et al 2012;Stern et al 2013;Arzeno et al 2014) need to be accurately modeled in order to account for mode 3 melting.…”