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What These Images Show:

The gray area in the center of each image is the Antarctic continent; its coastline and major ice shelves are outlined in black. The multi-colored zone surrounding the continent shows the concentration and distribution of Antarctic sea ice, and the light blue area surrounding the sea ice represents open ocean. These six images were taken two months apart, and show a complete annual cycle of sea ice growth and decay.

In the December image, you can see two large areas of open water that are surrounded by ice. Known as polynyas, these areas of open water can range in size from tens to thousands of kilometers squared, and last from a few days to several weeks. Polynyas often occur in the same area each year. Their formation is influenced by a number of factors, including air temperature, surface winds, and the temperature, salinity, and currents of the ocean.

How The Images Were Produced

These views of Antarctica and the Southern Ocean were derived from data collected by the U.S. Defense Meteorological Satellite Program. The satellite's sensor, referred to to as the SSM/I (Special Sensor Microwave/ Imager), views the Earth as a grid of squares measuring 25 kilometers on a side, and records the amount of microwave energy being reflected from each square. These microwave values were then converted to brightness and temperature values. Brightness and temperature characteristics of sea ice are markedly different from those of open ocean, allowing scientists to calculate the percentage of sea ice present in each grid square. The percentage values (1-100) were then color-coded to produce the images you see here.

Why Monitor Sea Ice?

Sea ice forms at the interface between the ocean and the atmosphere, two major components of the global climate system. The interactions between ocean and atmosphere, primarily the exchange of heat and moisture, play a major role in driving global circulation patterns. Sea ice affects the amount of heat and moisture that is exchanged; it also reflects incoming solar radiation away from the ocean. Long-term monitoring of sea ice processes will allow us to detect changes that could potentially indicate global climate change.

Recent Research
Norwegian scientists have recently compared sea ice extent between 1978 and 1994 using data from the SSM/I and an earlier satellite microwave sensor. This study is the first that has calibrated and compared the two data sets, and it includes all satellite microwave data on sea ice concentrations collected through 1994. Results show a statistically significant decrease in Antarctic sea ice of 1.4 percent per decade; however, the record is not long enough to determine the exact cause. Continued monitoring is necessary to determine if global warming is responsible for the overall decrease in sea ice.

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