Scientists have been working to gather more evidence from Antarctica pertaining to the long debate on whether a global rise in sea level is occurring due to global warming. While scientists hone in on the causes of mass glacial calving, NASA has also released a study on the rate at which the Antarctic ice shelf is increasingly losing mass which seems to indicate that the glacial calving and the melting of subterranean ice shelves by the warmer ocean are linked. The rapid increase in the rate of calving, or the breaking off of icebergs from the glacial shelf line, by some of Antarctica’s main glaciers seems to show a direct correlation to the melting of the ice shelves, and both, scientists say, are causing the accelerated rise in sea level observed over the last 100 years.
NASA was tapped in 2003 for a study to measure the rates of basal melt on the ice shelves which support Antarctica’s glaciers. NASA was able to acquire detailed data from its Moderate Resolution Imaging Spectroradiometer (MODIS) on one of its spacecrafts to determine just how much actual water mass was lost from the continent in the five years from 2003 to 2008. This data also helped scientists see where the largest melt areas were over the various glaciers which cover Antarctica, and to which calving glaciers they were linked. Scientists used the Antarctic basal melt data from NASA as well as regional climate models to determine snow accumulation which also contributes to the size and capacity of an ice shelf. They were able to determine that increasing basal melt, or the rate at which the ice shelf is being melted from the rising temperature of the ocean underneath it, counts for about 55 percent of ice mass lost over the course of the study.
This finding correlated with the results of another study done by a group of scientists in 2013, which also stated that about half of the ice shelf’s mass is lost in erosion from the ocean before reaching the front line of the ice shelf, or the line at which calving would begin. This study also goes on to state that the rate at which most glaciers are calving is around 1,321 metric gigatons per year, about 34 percent lower than the original estimate of 2,000 metric gigatons per year, and allowing for this new data to account for that loss.
Scientists’ original theory about the calving of Antarctic glaciers like Pine Island, the main glacier in the NASA study, was that it happened organically from the surface. They postulated that it was caused more by above-ground climate change such as lack of snowfall and the rate of change in weather patterns in certain regions in the Antarctic rather than any increase in subterranean melting of the ice shelf. With the new information in these studies, however, scientists are now hypothesizing that the rising temperature of the ocean bears much more responsibility for glacial mass loss and iceberg calving. The observable increase in the rate at which ice flows in the subterranean rivers housed by the ice shelves, measured over this five-year period also seems to support this data.
The new data suggests that the calving rate of a glacier comes from the flow rate and volume of water displacing sea water at the front line of the ice shelf. When enough of the fresh glacial water melts and meets a weak or eroded point in the glacier, a crack will occur and an iceberg will cleave away from the main glacial structure. As the temperature of the surrounding Antarctic Ocean has been observed to have increased, the ice flows feeding both the supporting ice shelf and its above-ground glacial mountain have also shown warming as well as faster flow speeds and volume of fresh water. This seems to support NASA’s above-ground observation that the glaciers and their ice shelves are indeed melting from underneath.
All of this data was put into the chart listed below to show the rate at which the sea level is rising due to these continental ice shifts. The new composite shows scientists’ projections originally determined in 1990 versus current ice shelf melting rates based on the studies in 2009 and 2013 respectively, and new projections into 2100 which include the new method of study and the curve created by current data. The difference in the rates is staggering, with the highest previous projection being around .47 meters increase by 2100, to the current projection of about 0.8 meters increase. This amounts to about a 40 percent difference with the new data.
While scientists are happy with the new more accurate data and their discovery of a new piece to the glacial calving puzzle, the new data shows an even dimmer view than originally projected. Scientists and NASA are keen to continue the study of the melting ice shelves: by the addition of this data to the already alarming glacial calving rate increase in Antarctica, scientists should be able to give even more weight to their already compelling case about the increase in global oceanic temperature and the causes of the ever-increasing danger of a rising sea level.
By Layla Klamt