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SUMMARY:Assessment of oscillation feature in sub-shelf melting from ideali
 zed coupled ice sheet ocean models - Chen Zhao\, University of Tasmania
DTSTART:20211201T100000Z
DTEND:20211201T110000Z
UID:TALK163357@talks.cam.ac.uk
CONTACT:Dr. Shenjie Zhou
DESCRIPTION:Changes in ocean-driven melting have a key influence on the st
 ability of ice shelves\, the mass loss from the ice sheet\, ocean circulat
 ion and global sea level rise. Coupled ice sheet - ocean models have a cri
 tical role in examining the processes governing basal melting and understa
 nding future ice sheet evolution. However\, as a new approach\, coupled ic
 e-sheet/ocean systems comes with new challenges\, and the impacts of solut
 ions implemented to date have not been quantified. Here  we  use  a  recen
 tly  developed  coupling  framework\, FISOC\,  between  the  ocean  model 
  ROMS  and  ice-sheet model Elmer/Ice to investigate the impact of coupled
  modelling strategies on the simulated basal melt in an idealised ice shel
 f cavity\, based on the Marine Ice Sheet–Ocean Model Intercomparison Pro
 ject (MISOMIP) setup. An  emergent  feature  was  that  the  spatial-avera
 ged  basal melt rates (3.56 m yr−1) oscillated with an amplitude∼0.7 m
  yr−1 and approximate period of ∼6 years between year 30 and 100\, dep
 ending on the experimental design. The oscillation of the spatial-averaged
  basal melt rates emerged as a  feature  in  the  coupled  system  and  th
 e  stand-alone  ocean model  using  a  prescribed  change  of  cavity  geo
 metry.  This feature was also observed in several other models under the M
 ISOMIP design experiments. It was found that the oscillation feature is cl
 osely related to the discretised row-by-row ungrounding of the ice sheet\,
  exposing new ocean\, and is likely strengthened by a combination of melt-
 plume feedback and/or melt-geometry feedback near the grounding line\, and
  the frequent coupling of ice geometry and ocean evolution in a couple sys
 tem. Sensitivity tests were done to determine the origin of the feature an
 d show that the oscillation behaviour is insensitive to the choice of coup
 ling interval\, vertical resolution in the ocean model\, tracer properties
  of immediately ungrounded cells by the retreating ice sheet\, or the depe
 ndency of friction velocities to the vertical resolution. We locally conse
 rve absolute tracer values when adjusting the ice draft to obtain a physic
 ally plausible tracer evolution. Furthermore\, a conservative\, parabolic 
 splines reconstruction of vertical derivatives was chosen to defeat the nu
 merical overshoot introduced by large vertical gradients near the groundin
 g line\, which may be instructive for future model configurations.
LOCATION:https://ukri.zoom.us/j/96463295770\; BAS seminar room 2
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