The role of tides in ocean--ice-shelf interactions in the southwestern Weddell Sea

Abstract

<p>A novel regional ocean-sea-ice model configuration is designed to investigate the mechanisms of ocean–ice-shelf-melt interactions in the Weddell Sea. It features explicit resolution of the cavities of eastern Weddell, Larsen and Filchner-Ronne ice-shelves (FRIS, at 1.5-2.5 km horizontal resolution), as well as of the adjacent continental shelves (~2.5 km) and deep open-ocean gyre (at 2.5-4 km), in presence of interannually-varying atmospheric and ocean boundary forcing as well as explicit ocean tides. Simulated circulation, water mass and ice-shelf melt properties compare overall well with available open-ocean and cavity observations, and simulated Weddell ice-shelf melting reveals large variability on tidal, seasonal and year-to-year timescales. The presence of ocean tides, investigated explicitly, is revealed to result in a systematic time-average enhancement of both the production of ice-shelf meltwater as well as its refreezing on ascending branches of especially the FRIS cavity circulation. This tide-driven enhancement of the melt-induced FRIS cavity circulation acts to increase net ice-shelf melting (by 50%, ~50 Gt/yr) and the meltwater export by the FRIS outflow, and modulates their seasonal and lower frequency variability. The tidal impact on ice-shelf melting is consistent with being primarily driven mechanically through enhanced kinetic energy of the time-varying flow in contact with the ice drafts. The dynamically-driven tide-induced melting is thereby to almost 90% compensated by cooling through meltwater produced, but not quickly exported from regions of melting in the Weddell cold-cavity regime. Ocean boundary layer thermal adjustment underneath ice drafts, minimizing departures from the in-situ freezing point, thus substantially dampens the impact of tides on Weddell ocean–ice-shelf interactions. Simulations furthermore suggest attendant changes on the open-ocean continental shelves, characterized by overall freshening and modest year-round sea-ice thickening, as well as a marked freshening of newly-formed bottom waters in the southwestern Weddell Sea.</p>

Observations of Modified Warm Deep Water Beneath Ronne Ice Shelf, Antarctica, From an Autonomous Underwater Vehicle

“…Observed diffusivity is up to two orders of magnitude higher than the standard values used in numerical models of ice shelf cavities (e.g. Hausmann et al, 2020;Jourdain et al, 2017), and these observations will provide a unique benchmark against which different numerical models can be compared and tuned.…”

“…MWDW inflow may recirculate close to the ice front in a gyre-type circulation (Hausmann et al, 2020;Makinson & Nicholls, 1999), although observations remain sparse. Furthermore, the different mechanisms by which the MWDW inflow navigates the ice front step in water column thickness throughout the year and different stratification environments requires further investigation.…”