EGU2020-18743
https://doi.org/10.5194/egusphere-egu2020-18743
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Coupled ocean—ice shelf—ice sheet projections for the Weddell Sea Basin, Antarctica

Ralph Timmermann1 and Torsten Albrecht2
Ralph Timmermann and Torsten Albrecht
  • 1Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven, Germany (ralph.timmermann@awi.de)
  • 2Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany (albrecht@pik-potsdam.de)

To study Antarctica’s contribution to ongoing and future sea level rise, a coupled ice sheet – ice shelf – ocean model with an explicit representation of ice shelf cavities has been developed. The coupled model is based on a global implementation of the Finite Element Sea ice Ocean Model (FESOM) with a mesh that is substantially refined in the marginal seas of the Southern Ocean. The Antarctic Ice Sheet is represented by a regional setup of the Parallel Ice Sheet Model PISM, comprising the Filchner-Ronne Ice Shelf (FRIS) and the grounded ice in its catchment area up to the ice divides.  At the base of the FRIS, melt rates and ocean temperatures from FESOM are applied. PISM returns ice thickness and the position of the grounding line. Buildung on infrastructure developed for the Regional Antarctic and Global Ocean (RAnGO) model, we use a pre-computed FESOM mesh that is adopted to the varying cavity geometry in each coupling step, i.e. currently once per model year. Changes in water column thickness are easily accounted for by the terrain-following vertical coordinate system in the ice shelf cavity. The ice sheet model is run on a horizontal grid with 1 km resolution to ensure an appropriate representation of grounding line processes. Enhancement factors for the approximation of the stress balance, as often used in coarse-resolution ice sheet models, become obsolete at such high resolution. Ice stream flow is well captured by polythermal coupling of the ice flow and a Mohr-Coulomb yield stress criterion that accounts for properties of the till material and the effective pressure on the saturated till. We present results from model runs with a 20th-century climate forcing and projections until the end of the 22nd century. We will show that cavity hydrography, ice shelf basal melt rates and thickness evolution as well as the feedback on grounded ice  in the coupled model simulations are very sensitive to the atmospheric forcing scenario applied.

 

 

How to cite: Timmermann, R. and Albrecht, T.: Coupled ocean—ice shelf—ice sheet projections for the Weddell Sea Basin, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18743, https://doi.org/10.5194/egusphere-egu2020-18743, 2020

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  • CC1: Comment on EGU2020-18743, Stefano Ottolenghi, 08 May 2020

    Hey! Thanks for your presentation. I am particularly interested in the interface between ice and ocean. It looks like you have two separate computational models that interact with each other, is my understanding correct? Do you treat the ice-ocean interface in any way?

    • AC1: Reply to CC1, Ralph Timmermann, 08 May 2020

      Hi Stefano,

      that's right, the ice sheet/shelf model and the ocean model (including the sub-ice shelf cavities) are two seperate entities, which even run on different computers. The interface between them is a three-equation model that computes ice shelf basal melt (or freezing)  rates from the heat and freshwater balances for a thin (but finite) boundary layer along  the ice shelf base. That's the same as in standalone ocean cavity models; the difference here is that ice shelf and cavity geometries are variable. Variability of geometries is "slow" though compared to the typical time scale of processes in the ocean, which makes  a modeller's life a bit easier.

      Best reards,
      Ralph