ACE CRC scientists have made a major contribution to research in the sea-ice zone. ACE CRC authors are represented in 13 of the 20 peer-reviewed papers in a special volume of the international journal Deep Sea Research II published in May. This special volume is dedicated to research conducted during the International Polar Year (2007 - 2009) in the Antarctic sea ice zone.  The work from the ACE CRC authors comes from their participation in the Sea Ice Physics and Ecosystem eXperiment (SIPEX) of Spring 2007. Australia is one of few countries to have conducted research in the Antarctic sea ice zone, an area which experiences a huge variation in extent from about 20 million square kilometres (nearly three times the area of Australia) in September to 3 to 4 million square kilometres in February. The SIPEX voyage aboard the Aurora Australis was a major Australian contribution to the International Polar Year and involved more than 50 scientists from 13 countries. Scientists weathered three blizzards and a four-day white-out and had to navigate through sea ice which, at 10 metres thick in some locations, was some of the thickest reported in the East Antarctic region. The overarching goal of the project was to understand the links between the physical, chemical and biological parameters of sea ice, and the importance of these links for productivity in the sea-ice zone in Australian Antarctic Territory off East Antarctica. The chief scientist on the SIPEX project, Dr Tony Worby, said the work published in Deep Sea Research II would help to build understanding of the complexity of life in the sea ice zone. Research being published in the journal reports major differences in growth, diet and condition of larval and post-larval krill sampled from open water and from under the ice, indicating that different wintering strategies are used in different life-cycle stages. "From this research we know more about the role of sea ice organisms as a food source for Antarctic krill, and the links between krill distribution and sea ice extent in the Southern ocean," Dr Worby said. One of the really interesting aspects of the project was the range of novel instruments and techniques used, including, for the first time, laser altimetry from a helicopter to measure ice freeboard (which can be used to calculate ice thickness). "A Remotely Operated Vehicle recorded observations under the ice, a custom-build trawl caught krill under the ice, and trace-metal-clean sampling equipment was developed to determine the concentration and distribution of iron in sea ice," Dr Worby said. The trace metal team investigated the relationships at work when sea ice, acting as a giant sponge, concentrates iron and other essential micronutrients in the colder months before releasing them during the spring melt, creating suitable conditions for a phytoplankton bloom. Iron is vital to phytoplankton growth, and therefore critical to the ocean's ability to biologically fix carbon dioxide, but is in short supply in the Southern Ocean. The ice conditions were particularly difficult at times, not only for navigation but for setting up stations for scientific work on the ice. A range of direct measurements, including drilling to measure sea ice and snow cover thickness, were conducted at 15 ice stations, in addition to sampling while the ship was underway and the observations from helicopters. Depending on their purpose, the duration of ice stations, which require teams of scientists to leave the ship via a walkway to conduct operations on the ice, varied from a few hours to two days, with the longer stations allowing measurements to be collected over a full diurnal cycle. A similar ship-based sea ice project run by the US Antarctic program took place on the other side of Antarctica at approximately the same time.  Both programs contributed to a calibration/validation program for ICESat, NASA's Ice Cloud and Land Elevation Satellite. Data collected on the voyage enabled aircraft measurements to be validated over drilled thickness lines on the ice, while at the same time improving knowledge of the issues surrounding long-base-line GPS positioning. "Field studies such as this, that measure and monitor critical sea ice processes and provide ground validation data for hemispheric to global-scale satellite monitoring, are critical to understanding changes in sea ice thickness and the impacts of this on the Southern Ocean environment,'' Dr Worby said. Read the special volume of Deep Sea Research II

---