Ice front blocking of ocean heat transport to an Antarctic ice shelf

Abstract

<p>Shoreward oceanic heat flux in deep channels on the continental shelf typically far exceeds that required to match observed ice shelf melt rates, suggesting other critical controls.  IN the present study we study the depth-independent (barotropic) and the density-driven (baroclinic) components of the flow of warm ocean water towards an ice shelf. Using observations from the Getz Ice Shelf system as well as geophysical laboratory experiments on a rotating platform, it is shown that the dramatic step shape of the ice front blocks the barotropic component, and that only the baroclinic component, typically much smaller, can enter the sub-ice cavity.  A similar blocking of the barotropic component may occur in other areas with comparable ice-bathymetry configurations, which may explain why changes in the density structure of the water column have been found to be a better indicator of basal melt rate variability than the heat transported onto the continental shelf. Representing the step topography of the ice front accurately in models is thus important for simulating the ocean heat fluxes and induced melt rates.</p>

Bathymetric Influences on Antarctic Ice‐Shelf Melt Rates

“…The negative sensitivities downslope and positive sensitivities upslope imply that a steepening of the trough margin would amplify the geostrophically driven flow of warm water to the ice shelf, and thus increase melting. This result is corroborated by recent observational and experimental work which highlights the critical role of topography in steering heat to Antarctic ice shelves (Wählin et al., 2020).…”

“…These results provide a complementary perspective to the observations and experimental results shown in Wählin et al. (2020).…”

“…The bathymetry of the ocean exerts a leading order influence on ocean circulation, both at global and regional scales (e.g., Gille et al., 2004; Hughes & Killworth, 1995; Marshall, 1995; Roberts & Wood, 1997). It plays a key role in regulating exchanges between the Antarctic continental shelf and the deep ocean (e.g., Graham et al., 2016; Thoma et al., 2008; Thompson et al., 2018; Walker et al., 2013) and in setting circulation patterns on the continental shelf (e.g., Arneborg et al., 2012; Cochran & Bell, 2012; De Rydt et al., 2014; Jacobs et al., 2011; Padman et al., 2010; Rosier et al., 2018; Wählin et al., 2020). Its role in ice sheet‐ocean interactions is accentuated by the fact that a large part of the Antarctic ice sheet rests well below sea level (Bentley et al., 1960), with a sizable portion of its margins terminating in large floating ice shelves.…”

Seasonal variability of ocean circulation near the Dotson Ice Shelf, Antarctica

“…However, it is not known how much of the recorded seasonal variation that makes it into the ice shelf cavity. Recent study suggest that the barotropic current component, which is a strong contributor to the seasonal variability, is blocked at the ice front 22 . Nevertheless, the seasonal variability of heat transport in front of the ice shelf will be propagated to under the ice shelf because the barotropic southward flows affect the variability of isohalines and isotherms (Supplementary Figure 3), and that signal is expected propagates in the cavity.…”

Intermittent Reduction in Ocean Heat Transport Into the Getz Ice Shelf Cavity During Strong Wind Events

“…The warm CDW is carried toward the ice front by a current that flows southward along the eastern flank of the Siple Trough (Assmann et al., 2019). The current has a barotropic (depth‐independent, typically wind‐driven) and a baroclinic (depth‐varying, set up by density gradients) component (Wåhlin et al., 2020). At the ice front, the barotropic component is deflected, so that only the heat transport associated with the smaller baroclinic component enters the ice shelf cavity (Wåhlin et al., 2020).…”