A large-ensemble, data-constrained study of Antarctic deglaciation
Abstract
Ice sheet modelling is an effective tool to generate glaciologically self-consistent reconstructions that can be used to provide input to GIA models. Like any numerical model, ice sheet models implicitly and explicitly depend on parametrisations to capture uncertainties and simplifications in the physics (e.g. missing or sub-grid processes) and the boundary conditions (basal interactions, climate forcing, ice-ocean interactions etc.). Hand-tuning of these parameters restricts models from exploring the potential phase-space of such a highly non-linear and complex system. Applying methods from similar work for the Eurasian and North American ice-sheets, we present results from a large-ensemble, data-constrained analysis of Antarctic deglaciation. The ice sheet model we use has a 3-D thermo-mechanically coupled dynamical core that models sheet stream/shelf flow regimes and includes a sub-grid grounding-line flux parametrisation, visco-elastic bedrock response, multi-method climate field generation (removing dependence on a single forcing technique), separate shelf and tidewater calving treatment, and a physically-motivated, empirically derived sub-shelf melt component. It has 31 ensemble parameters to capture uncertainties in the paleo-climate, the mass-balance processes, and in the ice dynamics. The large ensemble method samples from these parameters to generate thousands of reconstructions. Using a suite of observations (including relative sea level and paleo-ice thickness indicators, grounding line retreat data, and the present-day ice sheet configuration) and a misfit-to-observation based evaluation methodology, each reconstruction is attributed a misfit score. The evaluation method accounts for the measurement uncertainties and addresses the challenges in using heterogeneous spatial and temporal observations as constraint data. Using the scores as weights in effect defines a probability distribution of the past evolution of the ice sheet. Weighted mean values and uncertainty estimates of key metrics (e.g. grounded ice volume) are computed. Our results predict that the Last Glacial Maximum in Antarctica occurred at approximately 24 ka BP, with an associated eustatic contribution from 24 ka BP until present day of between 5.8 to 12.2 m sea level equivalent (SLE) and a mean of 8.9 m SLE. There is little change in the grounded ice volume from 24 ka BP until 16-17 ka BP at which time widespread deglaciation commences. The Ross and Weddell sea sectors are the predominant sources of the ice mass loss. The maximum contribution to melt water pulse 1a is predicted to be 1.7 m SLE (subject to uncertainties from potentially insufficient grounding line advancement at LGM). The major period of grounding line retreat in the Weddell Sea sector, resulting in the present day Ronne-Filchner shelf system, occurs after 12 ka BP; the grounding line of the Ross Sea sector starts its major retreat phase after 10 ka BP.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.G23C..04B
- Keywords:
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- 0726 CRYOSPHERE / Ice sheets;
- 0798 CRYOSPHERE / Modeling;
- 1223 GEODESY AND GRAVITY / Ocean/Earth/atmosphere/hydrosphere/cryosphere interactions