Synoptic Antarctic Shelf-Slope Interactions Study: SASSI UK

The oceans contain salt that makes the water denser. Fresh water does not contain salt, and usually lies on top of the denser salty water.We now know that the amount of fresh water on the margins of Antarctica affects global climate, at least in the latest climate models. These climate models are still very crude, because we have to simplify them to make them run on our fastest computers in a reasonable time. Nevertheless we think that the large-scale behaviour of the models is probably similar to that in the real world. When we add additional fresh water around Antarctica in the model, the climate of Europe changes over a time scale as short as 5 years. This means that even places we think of as remote are in fact just as important to study as those close to us. We also believe that Antarctica is an important place to study because it is one of the places where the dense cold water sinks to the sea bed and flows towards the equator in what oceanographers call the thermohaline circulation. If this thermohaline circulation slows down then global climate is affected, as was dramatised in the film 'The Day After Tomorrow'. Because Antarctica is remote, and difficult and expensive to get to, we have very little information about the oceanographic characteristics, such as temperature or current velocity, and the amount of salt in the water, which we term salinity. It is especially difficult to obtain measurements close to Antarctica in winter, because most of the ocean is covered in a thick layer of frozen sea water, called sea ice. Observations suggest that changes in global climate are affecting the amounts of fresh water on the continental shelf of Antarctica. It seems that the ice sheets (on the Antarctic continent) and ice shelves (the floating parts of the ice sheet, where it meets the sea) may be melting more quickly than before, at least in some locations. Under normal climate conditions, water evaporates from the ocean, falls as snow onto Antarctica and is compacted into ice. This ice then flows slowly towards the sea, where it calves into icebergs, which then melt back into the ocean. This circle of water through the ocean, atmosphere and ice is called the hydrological cycle. What may be happening now as climate changes is that some parts of this cycle are going faster than they used to, knocking the cycle out of its normal equilibrium. This project will study what is happening to the fresh water on the Antarctic continental shelf and slope. We will deploy for one year some moored instruments on the shelf and slope, measuring ocean temperature, salinity, current speed and direction, and sea level. Two of these instruments are very novel - one of them collects a sample of water every week and stores it in a bag ready for collection when we return a year later. The other will sit on the sea bed, and every day sends a little pod up to the surface on a length of wire and down again, measuring temperature and salinity as it goes. Because it sits in the deep water, it shouldn't get mown down by icebergs as they go by! These instruments are going to sit just upstream of the largest Antarctic Ice Shelf. We're going to test the idea that the ocean water upstream influences the amount of very cold, dense water that descends to the deep ocean there. Although studying the conditions around Antarctica is an ambitious thing to do, we are not doing it alone. Countries around the world are coming together for the International Polar Year in 2007-2009. We have agreed to all make measurements of the current velocity at the same time in different places around Antarctica. This will be the first time that this has been done and ought to tell us much more about what is happening to the oceans, ice and atmosphere around Antarctica, and why. This in turn should help us to make better climate models to predict the future of our planet.