Final Report Summary - MODISC (Modelling glacier response after Larsen B ice shelf collapse)
The general aim of this project is to use the unique opportunity provided by the collapse of Larsen B ice shelf, Antarctic Peninsula, in February 2002 to validate ice flow models, and to quantify their performance in reproducing the observed complex response of all Larsen B tributaries over the last 12 years. This work is a crucial step towards establishing confidence in the capability of current generation ice-flow models to forecast the impact of changing ice sheets on global sea levels.
The collapse of the Larsen B ice shelf in early 2002 was an exceptional event in the field of glaciology. Never before had the rapid disintegration of an ice shelf of this size been observed in real time. Observations soon showed that the tributaries of Larsen B all responded strongly to the disintegration of the ice shelf, and even now, 13 years later, this response still continues. In recent years, a wealth of new data has become available documenting the region before and after the collapse. Historical grounding line positions, ice thickness and velocity changes are all known in considerable detail. From a comprehensive analysis of grounding line positions and surface velocities, we have shown that the retreat has been complex in behavior and highly variable in time and space, with some tributaries reacting rapidly, others with delay, and some hardly at all [Wuite et al., 2015]. All publications are listed below.
Considerable effort was also spent collecting and processing available data from before the collapse of the ice shelf, including ice thickeness and bedrock elevations. This data was subsequently assimilated into an ice dynamics model to simulate the ice flow in the Larsen B area before the disintegration of the ice shelf [De Rydt et al., 2015a]. Several external collaborations were started to achieve this goal.
Despite the uniqueness of the ice shelf collapse and the direct insights it has provided into the mechanical coupling between ice shelves and grounded ice, and despite the stringent test it provides for ice flow models, no numerical ice-flow studies simulating the impact of the collapse on the grounded ice had been conducted. In the next stage of our work, we have partly filled this gap, and provided the first model tests of the interaction between floating and grounded ice masses that could be verified with observations. We modelled the instantaneous response of the tributary glaciers to the collapse of the Larsen B ice shelf, and the associated loss of buttressing which led to grounding line retreat and thinning. We found a good qualitative agreement between modelled changes in glacier flow and observations, providing improved confidence in
our numerical models and their ability to capture the complex mechanical coupling between floating ice
shelves and grounded ice
[De Rydt et al., 2015a]. We identified transient effects as being particularly important to quantify those changes, and highlighted this as a crucial future test for the models.
We stress that the relevance of this study is not confined to the particular area around the Larsen B. Loss of ice-shelf buttressing due to ocean-induced melting, and feedbacks associated with grounding-line retreat are considered to be the key processes currently responsible for mass loss from large areas of the West Antarctic Ice Sheet. We have further pursued the understanding of these processes through the development of a coupled ice-ocean model, which uses input from an ocean model to constrain the ice dynamics. Such a coupled approach, which is the first of its kind at the host institution, was shown to provide superior results in areas with a complex bathymetry, such as Pine Island Glacier, for two reasons. (i) Due to the physically based estimates of basal melt, higher confidence is obtained in the prediction of mass loss, and (ii) the incorporation of feedback mechanisms between ocean and ice dynamics provides new evidence for the importance of the bathymetry on glacier retreat and associated changes in ice shelf melt rate. This work was not part of the original project proposal, but led to important new insights into the recent retreat of Pine Island Glacier, and the associated estimates of sea level rise [De Rydt, 2015b].
Our work has been published in peer review journals, and has gained attention through the media, hence reaching a wider public audience. Besides its relevance for future specialist research on the complex interactions between ice shelves, the ocean and the grounded ice sheet, results from this project are also of direct relevance to policy makers, as they provide improved confidence in predictions on future sea level rise. Our results will be brought to the attention of the relevant authors of the next report of the Intergovernmental Panel on Climate Change (IPCC). The latter communicates to many potential beneficiaries in the academic and political world and broader society.
References:
------------------------
[Wuite et al., 2015] Wuite J., Rott H., Hetzenecker M., Floricioiu D., De Rydt J., Gudmundsson H., Nagler T., and Kern M., ‘Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013’, The Cryosphere 9.3 (2015): 957-969
[De Rydt et al., 2015a] G. H. Gudmundsson, H. Rott, and J. L. Bamber (2015), Modeling the instantaneous response of glaciers after the col- lapse of the Larsen B Ice Shelf, Geophys. Res. Lett., 42, 5355–5363, doi:10.1002/2015GL064355.
[De Rydt et al., 2015b] Coupled ice-ocean modeling and complex grounding line retreat for Pine Island Glacier, submitted to Journal of Geophysical Research: Earth Surface
The collapse of the Larsen B ice shelf in early 2002 was an exceptional event in the field of glaciology. Never before had the rapid disintegration of an ice shelf of this size been observed in real time. Observations soon showed that the tributaries of Larsen B all responded strongly to the disintegration of the ice shelf, and even now, 13 years later, this response still continues. In recent years, a wealth of new data has become available documenting the region before and after the collapse. Historical grounding line positions, ice thickness and velocity changes are all known in considerable detail. From a comprehensive analysis of grounding line positions and surface velocities, we have shown that the retreat has been complex in behavior and highly variable in time and space, with some tributaries reacting rapidly, others with delay, and some hardly at all [Wuite et al., 2015]. All publications are listed below.
Considerable effort was also spent collecting and processing available data from before the collapse of the ice shelf, including ice thickeness and bedrock elevations. This data was subsequently assimilated into an ice dynamics model to simulate the ice flow in the Larsen B area before the disintegration of the ice shelf [De Rydt et al., 2015a]. Several external collaborations were started to achieve this goal.
Despite the uniqueness of the ice shelf collapse and the direct insights it has provided into the mechanical coupling between ice shelves and grounded ice, and despite the stringent test it provides for ice flow models, no numerical ice-flow studies simulating the impact of the collapse on the grounded ice had been conducted. In the next stage of our work, we have partly filled this gap, and provided the first model tests of the interaction between floating and grounded ice masses that could be verified with observations. We modelled the instantaneous response of the tributary glaciers to the collapse of the Larsen B ice shelf, and the associated loss of buttressing which led to grounding line retreat and thinning. We found a good qualitative agreement between modelled changes in glacier flow and observations, providing improved confidence in
our numerical models and their ability to capture the complex mechanical coupling between floating ice
shelves and grounded ice
[De Rydt et al., 2015a]. We identified transient effects as being particularly important to quantify those changes, and highlighted this as a crucial future test for the models.
We stress that the relevance of this study is not confined to the particular area around the Larsen B. Loss of ice-shelf buttressing due to ocean-induced melting, and feedbacks associated with grounding-line retreat are considered to be the key processes currently responsible for mass loss from large areas of the West Antarctic Ice Sheet. We have further pursued the understanding of these processes through the development of a coupled ice-ocean model, which uses input from an ocean model to constrain the ice dynamics. Such a coupled approach, which is the first of its kind at the host institution, was shown to provide superior results in areas with a complex bathymetry, such as Pine Island Glacier, for two reasons. (i) Due to the physically based estimates of basal melt, higher confidence is obtained in the prediction of mass loss, and (ii) the incorporation of feedback mechanisms between ocean and ice dynamics provides new evidence for the importance of the bathymetry on glacier retreat and associated changes in ice shelf melt rate. This work was not part of the original project proposal, but led to important new insights into the recent retreat of Pine Island Glacier, and the associated estimates of sea level rise [De Rydt, 2015b].
Our work has been published in peer review journals, and has gained attention through the media, hence reaching a wider public audience. Besides its relevance for future specialist research on the complex interactions between ice shelves, the ocean and the grounded ice sheet, results from this project are also of direct relevance to policy makers, as they provide improved confidence in predictions on future sea level rise. Our results will be brought to the attention of the relevant authors of the next report of the Intergovernmental Panel on Climate Change (IPCC). The latter communicates to many potential beneficiaries in the academic and political world and broader society.
References:
------------------------
[Wuite et al., 2015] Wuite J., Rott H., Hetzenecker M., Floricioiu D., De Rydt J., Gudmundsson H., Nagler T., and Kern M., ‘Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013’, The Cryosphere 9.3 (2015): 957-969
[De Rydt et al., 2015a] G. H. Gudmundsson, H. Rott, and J. L. Bamber (2015), Modeling the instantaneous response of glaciers after the col- lapse of the Larsen B Ice Shelf, Geophys. Res. Lett., 42, 5355–5363, doi:10.1002/2015GL064355.
[De Rydt et al., 2015b] Coupled ice-ocean modeling and complex grounding line retreat for Pine Island Glacier, submitted to Journal of Geophysical Research: Earth Surface