Variability in Basal Melting Beneath Pine Island Ice Shelf on Weekly to Monthly Timescales

Abstract

Ocean‐driven basal melting of Amundsen Sea ice shelves has triggered acceleration, thinning, and grounding line retreat on many West Antarctic outlet glaciers. Here we present the first year‐long (2014) record of basal melt rate at sub‐weekly resolution from a location on the outer Pine Island Ice Shelf. Adjustment of the upper thermocline to local wind forced variability in the vertical Ekman velocity is the dominant control on basal melting at weekly to monthly timescales. Atmosphere‐ice‐ocean surface heat fluxes or changes in advection of modified Circumpolar Deep Water play no discernible role at these timescales. We propose that during other years, a deepening of the thermocline in Pine Island Bay driven by longer timescale processes may have suppressed the impact of local wind forcing on high‐frequency upper thermocline height variability and basal melting. This highlights the complex interplay between the different processes and their timescales that set the basal melt rate beneath Pine Island Ice Shelf.

Wind-Driven Processes Controlling Oceanic Heat Delivery to the Amundsen Sea, Antarctica

“…Melting of the ice shelves at the Amundsen Sea's southern rim is primarily regulated by changes in the thermocline depth in front of the ice shelves and in the heat content on the continental shelf farther offshore (Dutrieux et al 2014;Webber et al 2017;Davis et al 2018). Thus, our identification of the processes by which CDW accesses the Amundsen Sea troughs is an important step in understanding the preconditioning, that is, the heat source, for ice shelf melting downstream.…”

“…Finally, we acknowledge several caveats of our study. The relatively coarse temporal resolution of the model output impeded assessment of the fast response of water masses in the troughs to winds or other forcings (e.g., Wåhlin et al 2012Wåhlin et al , 2013Davis et al 2018). Further, although the model's spatial resolution is sufficient to reproduce CDW inflows onto the continental shelf (Nakayama et al 2014), it may not capture all the important processes implicated in the interaction of the flow with topography (e.g., St-Laurent et al 2013), as FIG.…”

Acceleration and Overturning of the Antarctic Slope Current by Winds, Eddies, and Tides

“…As emphasized in section 2d, our ''eddy'' and ''tidal'' components only approximately correspond to their representative flow phenomena, and include other flows that evolve on comparable time scales. For example, the effect of tides could be more accurately isolated via tidal harmonic analysis (Foreman and Henry 1989) and the ''eddy'' component may also include phenomena such as lowfrequency coastal-trapped waves (Kusahara and Ohshima 2014;Spence et al 2017) and the oceanic response to synoptic wind variability (e.g., Davis et al 2018). Our analysis options were strongly constrained by the computational cost of performing operations on the very large volume of model output (see Stewart et al 2018), a problem that might be ameliorated in future by improved computational infrastructure and tools for working with large datasets.…”

Topographic Shelf Waves Control Seasonal Melting Near Antarctic Ice Shelf Grounding Lines

“…The observations give an insight into ice‐ocean interaction mechanisms that mediate subshelf melting along the Dronning Maud Land coast. ApRES has been implemented in the other regions to derive time series of subshelf melt rates (Davis et al, ). This is the first occasion that time series of subshelf melt rates with such high temporal resolution have been obtained for this ice shelf.…”