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What’s Behind the ‘Freshening’ of the Arctic?

Researchers at the Marine Biological Laboratory in Woods Hole, Mass., who are lookng at links between Arctic seawater and climate change say that a significant increase of freshwater flow to the Arctic Ocean could slow or halt the "conveyor belt" current responsible for redistributing salt and thermal energy around the globe.

WOODS HOLE, MA-Over the last few years, much attention has been given to the observed freshening of Arctic Ocean and the potential impacts it may have on the earth’s climate. Scientists contend that a significant increase of freshwater flow to the Arctic Ocean could slow or halt the Atlantic Deep Water formation, a driving factor behind the great “conveyor belt” current that is responsible for redistributing salt and thermal energy around the globe, influencing the planet’s climate. One of the potential effects of altered global ocean circulation could be a cooling of Northern Europe within the 21st century.

Bruce Peterson, James McClelland, and Robert (Max) Holmes, scientists in the Marine Biological Laboratory’s (MBL) Ecosystems Center, have been studying the arctic hydrologic cycle.  In 2002 they made the significant observation that flow of freshwater from rivers into the Arctic Ocean has increased significantly over recent decades. Since that time, the team has focused their efforts on figuring out where all the extra water is coming from and how the increasing discharge may be influencing productivity in the Arctic’s coastal waters.

In a recent paper published in the Journal of Geophysical Research, the MBL team used a combination of data evaluation and computer modeling to examine three mechanisms often suggested as possible driving forces behind the increase in river discharge to the Arctic-permafrost thaw, dam construction and operation, which changes the seasonality of freshwater discharge to the Arctic; and increasing forest fires, which result in burned land masses with less vegetation to capture and retain freshwater.  Their evaluation showed that while these mechanisms are contributors, they are probably not the major drivers of increased freshwater to arctic rivers.  The team’s observations, and those of other scientists, suggest that an acceleration of the global hydrologic cycle, in particular global warming-driven moisture transport from lower to higher latitudes, is the most plausible explanation for the increase in freshwater. Identifying what’s behind the freshening of the Arctic Ocean is critically important, they maintain, for projecting future changes and impacts to the Earth’s climate.

The team is also examining how increasing river discharge may be influencing productivity in the Arctic’s coastal waters. Nutrient inputs from land to these waters are increasing along with river discharge.  At the same time, the extra freshwater from rivers may increase stratification-the separation of surface waters from deeper waters due to salinity differences-and thus work against upwelling of nutrients to the coastal zone from deeper ocean reservoirs.  According to the team’s calculations, the combined effect of increased water and nutrient inputs from rivers is a decrease in production of organisms such as phytoplankton and zooplankton in coastal waters.

The Marine Biological Laboratory is an independent scientific institution, founded in 1888, dedicated to improving the human condition through basic research and education in biology, biomedicine, and environmental science. The MBL is the oldest private marine laboratory in the western hemisphere. The research of the MBL’s Ecosystems Center, which was established at the MBL in 1975, is focused on the study of natural ecosystems.  Among the key environmental issues being addressed are: the ecological consequences of global climate change; tropical deforestation and its effects on greenhouse gas fluxes; nitrogen saturation of mid-latitude forests; effects of acid rain on North American lakes; and pollution and habitat destruction in coastal ecosystems of the United States.

[Read more at Marine Biological Laboratory]

| Posted 12.10.04 at 4:39 pm

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