A phenomenon described as 'Dragon-skin' ice was observed on a research voyage in the Ross Sea in Antarctica. This rarely seen ice is produced as a result of hurricane strength winds, which remove ice from open water areas, allowing more and more new ice to be formed. Researchers are planning to study the phenomenon and the currents it causes below water in more detail
An autumn voyage to the heart of an Antarctic polynya has rewarded expeditioners on US icebreaker Nathaniel B Palmer with a glimpse of a rarely seen type of sea ice. The sighting of “Dragon-skin” ice was an early highlight of the PIPERS expedition voyage to the Ross Sea that began in early April, well after most Antarctic expeditioners have departed for warmer climes.
“Dragon-skin ice is very rare, bizarre, evidence of a darker chaos in the cryospheric realm, not seen in Antarctica since 2007,” said Dr Guy Williams researcher at the Institute for Marine and Antarctic Studies (IAMS) in Hobart, Tasmania. Dr Williams is one of 27 scientists from eight countries who are studying the winter behaviour of coastal polynyas - areas of open water around the Antarctic continent that are ‘ice –factories’, with 10 times the average amount of sea ice produced due to the strength of local ‘katabatic’ winds that flow from the interior of Antarctica. “Imagine your standard ice cube tray, filled once. After a week, you get one tray of ice cubes. But if you empty and re-fill the tray each night, you get so much more. That is what the katabatic winds are doing in the polynya, removing the ice, exposing the water and making more ice form.”
Dr Williams said enhanced sea ice growth has a vitally important effect on the local and global oceanography. Seawater largely freezes as freshwater ice. Salty brine is rejected during the formation of ice and makes the underlying water very cold and dense enough to ultimately sink to the abyssal layer of the major ocean basins and kick start the southern limb of the global overturning circulation.
“We are currently at ground zero of a hurricane-strength (65+ knots, 120 km/h) katabatic wind event in the Terra Nova Bay polynya, in the Ross Sea, West Antarctica. It’s quite incredible to experience such an epic demonstration of polar ocean-atmospheric interaction. “After a couple of weeks of work in the advancing sea ice pack to the north, we have found ourselves once again strapping everything down as the winds and waves buffet our progress.” “We will spend the next two weeks taking advantage of quiet periods when the katabatic winds drop off to observe the increase in salinity of the shelf waters below polynyas as brine-rejected during sea-ice formation rains down to depths below 1000 m in the Drygalski Trough.”
Source: University of Tasmania, Institute for Marine and Antarctic Studies (IAMS)