The presence of thick sea ice at the base of melting glaciers can exert sufficient force to prevent icebergs breaking off (calving) into the water, according to an article published in Nature Communications. The findings show that as sea ice thins, the likelihood of iceberg calving and the contribution of glaciers to sea level rise increases.
The rate of iceberg calving, which has been increasing at many marine-terminating glaciers in Greenland and Antarctica, can have a strong effect on the rate at which sea level rises. This increase in calving rate has been associated with the rapid break up of iceberg melange - a dense patch of icebergs and sea ice floating in front of the glacier. However, while it is hypothesised that the presence of the melange suppresses iceberg calving, the mechanism remains unknown.
Alex Robel tests this theory using a novel numerical modelling approach where the motions and interactions of a large population of floating icebergs and their bonds with elastic plates of sea ice, which break and reform, are calculated. Robel’s computer simulations show that if the melange is packed with thick sea ice fastened to the coastline, the buttressing force applied is sufficient to prevent iceberg calving. However, the simulations also show that under thin sea ice conditions, calving is more likely and a wave of fast moving icebergs can break up the melange. If the melange fails to recover and refreeze before the next calving event, its buttressing effect may be removed entirely, which could potentially increase the rate of sea level rise.
Additional observations of melange material properties are needed to overcome model uncertainties and permit direct application of the processes modelled in this study to specific marine-terminating glaciers in Greenland and Antarctica.