Measurements from ESA's CryoSat satellite show that the volume of Arctic sea ice has significantly increased this autumn. The volume of ice measured this autumn is about 50% higher compared to last year. In October 2013, CryoSat measured about 9000 cubic km of sea ice - a notable increase compared to 6000 cubic km in October 2012.

Over the last few decades, satellites have shown a downward trend in the area of Arctic Ocean covered by ice. However, the actual volume of sea ice has proven difficult to determine because it moves around and so its thickness can change.

CryoSat was designed to measure sea-ice thickness across the entire Arctic Ocean, and has allowed scientists, for the first time, to monitor the overall change in volume accurately.

About 90% of the increase is due to growth of multiyear ice - which survives through more than one summer without melting - with only 10% growth of first year ice. Thick, multiyear ice indicates healthy Arctic sea-ice cover.

This year's multiyear ice is now on average about 20%, or around 30 cm, thicker than last year.

"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 in 2010, 2011 and 2012," said Rachel Tilling from the UK's Centre for Polar Observation and Modelling, who led the study.

"We didn't expect the greater ice extent left at the end of this summer's melt to be reflected in the volume. But it has been, and the reason is related to the amount of multiyear ice in the Arctic."

While this increase in ice volume is welcome news, it does not indicate a reversal in the long-term trend.

"It's estimated that there was around 20 000 cubic kilometres of Arctic sea ice each October in the early 1980s, and so today's minimum still ranks among the lowest of the past 30 years," said Professor Andrew Shepherd from University College London, a co-author of the study.

The findings from a team of UK researchers at the Centre for Polar Observation and Modelling were presented last week at the American Geophysical Union's autumn meeting in San Francisco, California.

"We are very pleased that we were able to present these results in time for the conference despite some technical problems we had with the satellite in October, which are now completely solved," said Tommaso Parrinello, ESA's CryoSat Mission Manager.

In October, CryoSat's difficulties with its power system threatened the continuous supply of data, but normal operations resumed just over a week later.

With the seasonal freeze-up now underway, CryoSat will continue its routine measurement of sea ice. Over the coming months, the data will reveal just how much this summer's increase has affected winter ice volumes.