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Ocean Research


January 2011 Issue

Sea-Level Models Predict Massive Loss of Coastal Wetlands
Many coastal wetlands worldwide, including several on the U.S. Atlantic coast, may be more sensitive than previously thought to projected changes in climate and sea level, according to research published in December.

Scientists engaged in an international research modeling effort have come to this conclusion in a paper published in Geophysical Research Letters. The researchers identified conditions under which coastal wetlands could survive rising sea level.

Using a rapid sea-level rise scenario, most coastal wetlands worldwide will disappear near the end of the 21st century, the research team found. Using the contrasting slow sea-level rise projection, wetlands with low sediment availability and low tidal ranges are vulnerable and may drown; wetlands with higher sediment availability would be more likely to survive.

"Accurate information about the adaptability of coastal wetlands to accelerations in sea-level rise, such as that reported in this study, helps narrow the uncertainties associated with their disappearance," said Glenn Guntenspergen, a U.S. Geological Survey (USGS) scientist and one of the authors of the study. "This research is essential for allowing decision makers to best manage local tradeoffs between economic and conservation concerns."

Several coastal marshes along the east coast of the United States, for example, have limited sediment supplies and are likely to disappear this century. Vulnerable East Coast marshes include the Plum Island Estuary (the largest estuary in New England) and coastal wetlands in North Carolina's Albemarle-Pamlico Sound (the second largest U.S. estuary).

"Previous assessments of coastal wetland responses to sea-level rise have been constrained because they did not consider the ability of wetlands to naturally modify their physical environment for adaptation," said USGS scientist Matt Kirwan, another report author. "Failure to incorporate the interactions of inundation, vegetation and sedimentation in wetlands limits the usefulness of past assessments."

The research team specifically identified the sediment levels and tidal ranges necessary for marshes to survive sea-level rise. As water floods a wetland and flows through its vegetation, sediment is carried from upstream and deposited on the wetland's surface. High tidal ranges allow for better sediment delivery, and the higher sediment concentrations in the water allow wetlands to build more elevation.

Coastal wetlands provide critical services such as absorbing energy from coastal storms, preserving shorelines, protecting human populations and infrastructure, supporting commercial seafood harvests, absorbing pollutants and serving as habitat. For more information, visit www.agu.org.

Changing Winds Could Influence Ocean Carbon Dioxide Storage
The Southern Hemisphere Westerlies, the prevailing winds in the Southern Hemisphere, can strongly influence ocean circulation, scientists report in a new study published in Geophysical Research Letters.

Using a climate model, scientists with the Climate Change Research Centre at the University of New South Wales studied how changes in the Southern Hemisphere Westerlies affected atmospheric carbon dioxide through their influence on ocean carbon storage.

The researchers confirmed earlier assumptions that an increase in the wind amplitude would have the effect of accelerating the deep overturning circulation, decreasing ocean carbon storage and releasing carbon dioxide into the atmosphere. In this research, however, the scientists found that a latitudinal shift of the Southern Hemisphere Westerlies would affect carbon storage in the upper and deep ocean oppositely, resulting in little effect on atmospheric carbon dioxide. For more information, visit www.agu.org.

Global Warming Could Cause Cooler Winters in the North
The overall warming of Earth's northern half could result in colder winters, new research shows. The shrinking of sea ice in the eastern Arctic causes some regional heating of the lower levels of air, which may lead to strong anomalies in atmospheric airstreams, triggering an overall cooling of the northern continents, according to a study published in November in the Journal of Geophysical Research.

"These anomalies could triple the probability of cold winter extremes in Europe and northern Asia," said Vladimir Petoukhov, lead author and a climate scientist at the Potsdam Institute for Climate Impact Research. "Recent severe winters like last year's or the one of 2005-06 do not conflict with the global warming picture, but rather supplement it."

The researchers base their assumptions on simulations with an elaborate computer model of general circulation, ECHAM5, with a focus on the Barents-Kara Sea north of Norway and Russia, where a drastic reduction of ice was observed in the cold European winter of 2005 to 2006. Those surfaces of the sea lacking ice cover lose a lot of warmth to the normally cold and windy Arctic atmosphere.

Researchers with the study fed the computer model with data, gradually reducing the sea ice cover in the eastern Arctic from 100 percent to one percent in order to analyze the relative sensitivity of wintertime atmospheric circulation.

"Our simulations reveal a rather pronounced nonlinear response of air temperatures and winds to the changes of sea-ice cover," Petoukhov said. "It ranges from warming to cooling to warming again as sea ice decreases."

An abrupt transition between different regimes of the atmospheric circulation in the subpolar and polar regions may be very likely. Warming of the air over the Barents-Kara Sea seems to bring cold winter winds to Europe.

"This is not what one would expect," Petoukhov said. "Whoever thinks that the shrinking of some faraway sea ice won't bother him could be wrong."

The connection between cold winters and global warming is not a new idea, but Petoukhov said the research about the impact of reduced sun activity or, most recently, the Gulf Stream "tend to exaggerate the effects," Petoukhov said. He said the correlation between these phenomena and cold winters is relatively weak compared to the new findings.

While the study is not about weather but rather overall climate, Petoukhov said, "I suppose nobody knows how harsh this year's winter will be." For more information, visit www.agu.org.


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