Do some South Pacific, Caribbean and Indian Ocean Islands really have to be worried about their future? Will your favourite natural island be gone below the oceans in a few years? This is much discussed by cruising sailors in cockpit sundowners, sometimes with hot divisions. According to a new paper in the British Antarctic Survey website, it is not a matter of if, but when, and scientists have been having a hard time working this out.
Satellite image of a gigantic iceberg broken from Pine Island Glacier
Recently, an iceberg the size of Singapore broke from the Pine Island Glacier and, last reported on, was heading north - not a good thing for a Southern Ocean sailor to meet.
By thinning and speeding up, West Antarctic ice streams contribute to about 10% of the observed global sea-level rise. A significant amount of this ice loss is from Pine Island Glacier, which has thinned over past decades, driven by changes in ocean heat transport beneath its ice shelf and retreat of the grounding line.
Details of the processes driving this change, however, remain largely elusive, hampering our ability to predict the future behaviour of this and similar systems.
In a new paper, a novel methodology is developed to measure oceanic melting of such rapidly advecting ice. High-resolution satellite and airborne observations of ice surface velocity and elevation are used to quantify patterns of basal melt under the Pine Island Glacier ice shelf and the associated adjustments to ice flow.
At the broad scale, melt rates of up to 100m/yr occur near the grounding line, reducing to 30m/yr just 20km downstream.
At smaller scales, a network of basal channels typically 500m to 3km wide is sculpted by concentrated melt, with kilometre-scale anomalies reaching 50% of the broad-scale basal melt.
Pine Island Glacier
Basal melting enlarges the channels close to the grounding line, but farther downstream melting tends to diminish them.
Kilometre-scale variations in melt are a key component of the complex ice-ocean interaction beneath the ice shelf, implying that greater understanding of their effect, or very-high-resolution models, are required to predict the sea-level contribution of the region.
One step at a time, our ocean scientists are gaining new insights.
Click here for the full paper in the NERC Open Research Archive.
British Antarctic Survey website