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

Ute Hausmann1, Jean-baptiste Sallee2, Nicolas Jourdain3, Pierre Mathiot4, Clement Rousset5, Gurvan Madec2, Julie Deshayes6 and Tore Hattermann7, (1)Sorbonne Université, LOCEAN-IPSL, Paris, France, (2)LOCEAN-IPSL, CNRS/IRD/MNHN/Sorbonne Université, Paris, France, (3)CNRS - Université Grenoble Alpes - Institut des Géosciences de l'Environnement, Saint-Martin d’Hères, France, (4)Met Office, Exeter, United Kingdom, (5)LOCEAN-CNRS, Universite Pierre et Marie Curie, Paris, France, (6)Universite Pierre et Marie Curie, LOCEAN, Paris, France, (7)Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
Abstract:
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 dynamic tide-driven anomalies in 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.