An unusual cooling trend with significant ecological impact in the Antarctic has been discovered by a team of 13 researchers from across the nation, including two ecologists from Colorado State University.
The study, published today in the online version of Nature, shows the Antarctic is the only continent of the earth’s landmasses to see a temperature decline over the past 35 years.
The research has been a multidisciplinary effort led by Peter Doran from the University of Chicago. Diana Wall and Andrew Parsons, ecologists with the Natural Resource Ecology Laboratory at Colorado State, were co-authors of the study. Wall, who also is interim dean of the College of Natural Resources, has been studying invertebrates in the Antarctic dry valleys for the past 11 years.
The research has focused on the McMurdo Dry Valleys in the Antarctic, the largest ice-free area on the continent, comprised of a cold desert with ice-covered lakes and streams, alpine glaciers and arid soil. The research team found that cooling over the past 14 years in the region, particularly in the summer, has caused a decrease in productivity from lakes and a significant decline in soil nematodes, the most dominant invertebrates in the dry valleys of the continent.
"The decline in invertebrates is alarming," said Wall. "There is very little diversity of invertebrates here, and although they can survive the stress of living in an extraordinarily extreme environment, these cooling repercussions may have a long-term effect."
Invertebrate numbers in the dry valleys have dropped by more than 10 percent per year between 1993 and 2000. The reduction indicates the ecosystem is stressed from the cooling temperatures. Nematodes are important in regulating the supply of soil nutrients to plants by helping break down carbon. Given the low diversity and the longevity of the invertebrates in decline, the study shows that an important shift in the ecology of the Antarctic dry valleys is occurring.
Contrary to earlier studies of a continental warming trend of the Antarctic, the research team found the Antarctic is not experiencing increased temperatures. The warming trend on the continent was shown only from 1958 to 1978. Earlier studies may have been impacted by measurements taken mostly on the Antarctic Peninsula, which extends toward South America.
The cooling trend in the dry valleys of the continent during past 14 years are associated with decreased winds and increased clear-sky conditions. Significant changes in the temperature show the strong influence the winds have in a dry valley climate. Summer temperatures have been dropping by 1.2 degrees Celsius per decade since 1986.
"I was not surprised that we found cooling," said Wall. "These results strengthen the global climate-change prediction that global warming will cause disparate local and regional conditions."
Availability of water in the area is dependent on small changes in summer temperatures and solar radiation, which melt glacier ice and provide water runoff to soils, streams and lakes.
Concentrations of phytoplankton, microscopic plants that live in lakes, also have shown a decrease in the region because of the cooler summer temperatures and consequently thicker ice coverage on lakes. Phytoplankton depend upon certain conditions for growth and are a good indicator of environmental change.
The research, sponsored by the National Science Foundation, is the first to emphasize the ecological response in the Antarctic because of decreased summer temperatures.