Arctic sea-ice volume shows recovery
16 December 2013, by Tamera Jones
The latest satellite data suggests that a bounce back in Arctic sea-ice extent seen this summer compared with last summer is also mirrored in the volume of ice.
Data from the European Space Agency's Cryosat mission show there was more sea ice in the Arctic at the end of summer 2013 compared with summer 2012, say scientists.
In October 2012, the month after Arctic sea-ice extent and volume are at their lowest, data from the satellite show there were around 6000 cubic kilometres of sea ice. But fast forward to October 2013, and this volume had increased to 9000 cubic kilometres.
It seems about 90 per cent of this increase is down to growth of so-called multi-year ice – the sea ice that survives through more than one summer without melting.
'Multi-year ice is generally believed to be a good thing, as it means that the ice pack is older, thicker and more resilient. Growth of multi-year ice suggests that melting in this summer was relatively mild, or that snowfall or freezing last winter were harsh,' says Professor Andy Shepherd of the Centre for Polar Observation and Modelling (CPOM) at University College London (UCL).
'Although 2013 has seen a 50 per cent increase in volume over the 2012 minimum, this has to be considered against the backdrop of long-term change. 2013 still ranks among the lowest volumes in the past 30 years.'
Professor Andy Shepherd
Centre for Polar Observation and Modelling (CPOM) at University College London (UCL)
'One of the things we'd noticed in our data was that the volume of ice year-to-year was not varying anything like as much as the ice extent – at least for the years 2010, 2011 and 2012,' says Rachel Tilling, also from CPOM.
'This is why we're really surprised by what we've seen in 2013. We didn't expect the greater ice extent left at the end of the summer to be reflected in the volume. But it has been. And the reason is related to the amount of multi-year ice in the Arctic,' she adds.
Sea-ice extent is relatively simple to measure, but scientists think volume is a better indicator of the health of Arctic sea-ice.
However, Shepherd cautions against celebrating. 'Although 2013 has seen a 50 per cent increase in volume over the 2012 minimum, this has to be considered against the backdrop of long-term change. 2013 still ranks among the lowest volumes in the past 30 years.'
Indeed, past estimates of Arctic sea-ice volume by the respected Pan-Arctic Ice-Ocean Modelling & Assimilation System (PIOMAS) show this year's volume has decreased from around 20,000 cubic kilometres in the 1980s.
Cryosat allows scientists to measure volume using a high-resolution synthetic aperture radar altimeter, which fires pulses of microwave energy down towards the ice. The energy bounces off both the top of sections of ice and the water in the cracks in between. The difference in height between these two surfaces let scientists calculate the volume of the ice cover.
How CryoSat-2's radar will measure ice thickness from space.
This latest study was presented at the American Geophysical Union (AGU) Fall Meeting in San Francisco last week.
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