Observation and Parameterization of Ablation at the Base of Ronne Ice Shelf, Antarctica

Abstract

Parameterizations of turbulent transfer through the oceanic boundary layer beneath an ice shelf are tested using direct measurements of basal ablation. Observations were made in the southwestern part of Ronne Ice Shelf, about 500 km from open water. The mean basal ablation rate was measured over a month-long and a year-long period using phase-sensitive radar to record the thinning of the ice shelf. Ocean temperatures were observed within about 25 m of the ice shelf base over the period of the radar observations, while the tidally dominated ocean currents were estimated from tidal analysis of collocated current observations from an earlier period. Ablation rates derived using these ocean data and a number of bulk parameterizations of turbulent transfer within the boundary layer are compared with the direct measurements. The ablation rates derived using a parameterization that explicitly includes the impact of ocean currents on the turbulent transfer of heat and salt match the observations to within 40%; with suitable tuning of the drag coefficient, the mismatch can be reduced below the level of the observational errors. Equally good agreement can be obtained with two slightly simpler, current-dependent parameterizations that use constant turbulent transfer coefficients, and the optimal values for the coefficients at this particular location on Ronne Ice Shelf are given.

Explicit representation and parametrised impacts of under ice shelf seas in the <i>z</i><sup>∗</sup> coordinate ocean model NEMO 3.6

“…) are based on the recommendation of Jenkins et al (2010). The drag coefficient is chosen to be 1.0 × 10 −3 .…”

Channelization of plumes beneath ice shelves

“…Following previous authors (eg. Jenkins et al 2010), we parameterize the turbulent heat transfer as proportional to the temperature difference and velocity of the plume,…”

“…Wells & Worster 2011;Jenkins 2011). If the salinity dependence of the melting point were included one would need, in addition to (2.4), to model the salinity at the interface; a number of parameterizations have been developed for this in the context of both ice shelves and sea ice (Jenkins et al 2010;McPhee et al 2008). …”

Dynamics of Greenland�s glacial fjords

“…Jenkins et al, 2010). Recent studies assume that both these things are governed by the glacier's freshwater inputs (Motyka et al, 2003;Rignot et al, 2010;Jenkins, 2011;Xu et al, 2012;Sciascia et al, 2013), and that other drivers, such as tides, air-sea fluxes and shelf-driven exchange, can be neglected.…”