Abstract
AbstractI explore the tidewater glacier cycle with a 1-D, depth- and width-integrated flow model that includes a mass-flux calving parameterization. The parameterization is developed from mass continuity arguments and relates the calving rate to the terminus velocity and the terminus balance velocity. The model demonstrates variable sensitivity to climate. From an advanced, stable configuration, a small warming of the climate triggers a rapid retreat that causes large-scale drawdown and is enhanced by positive glacier-dynamic feedbacks. Eventually, the terminus retreats out of deep water and the terminus velocity decreases, resulting in reduced drawdown and the potential for restabilization. Terminus readvance can be initiated by cooling the climate. Terminus advance into deep water is difficult to sustain, however, due to negative feedbacks between glacier dynamics and surface mass balance. Despite uncertainty in the precise form of the parameterization, the model provides a simple explanation of the tidewater glacier cycle and can be used to evaluate the response of tidewater glaciers to climate variability. It also highlights the importance of improving parameterizations of calving rates and of incorporating sediment dynamics into tidewater glacier models.
Highlights
Tidewater glaciers, i.e. those that terminate in the ocean, respond nonlinearly to climate and ocean variability due to complex relationships between glacier geometry and ice flow (Post and others, 2011)
As described above, for tidewater glaciers terminus retreat is associated with surface lowering and flow acceleration while terminus advance is associated with thickening and slow glacier flow
Once the terminus retreated into deep water, the rate of retreat abruptly increased and was governed by glacier-dynamic feedbacks that resulted in the terminus velocity and calving rate increasing by more than a factor of 4
Summary
I.e. those that terminate in the ocean, respond nonlinearly to climate and ocean variability due to complex relationships between glacier geometry and ice flow (Post and others, 2011). The complexity of these relationships is illustrated in regional studies of tidewater glaciers in Alaska (McNabb and Hock, 2014) and Greenland (Moon and Joughin, 2008), which document asynchronous fluctuations in terminus position of adjacent glaciers that are subjected to similar forcings. The response of tidewater glaciers to climate and ocean variability is poorly constrained due to deficiences in our understanding of iceberg calving and submarine melting. There remains much uncertainty regarding the physics of the glacier–ocean interface despite the important insights provided by these previous studies
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