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Ocean Research


August 2011 Issue

Warming Ocean May Undermine Ice Sheets, Climate Models Show
Warming of the ocean's subsurface layers will melt underwater portions of the Greenland and Antarctic ice sheets faster than previously thought, according to research led by the University of Arizona. The research, based on 19 climate models, proposes a new mechanism by which global warming will accelerate the melting of the great ice sheets this century and the next. It appeared in Nature Geoscience in July.

In addition to being exposed to warming air, underwater portions of the polar ice sheets and glaciers will be bathed in warming seawater, the scientists found, with the subsurface ocean along the Greenland coast increasing as much as 2° C by 2100.

"To my knowledge, this study is the first to quantify and compare future ocean warming around the Greenland and the Antarctic ice sheets using an ensemble of models," said lead author Jianjun Yin, an assistant professor of geosciences at the University of Arizona. Most previous research has focused on how increases in atmospheric temperatures would affect ice sheets, he said.

Given a mid-level increase in greenhouse gases, the researchers found the ocean layer about 200 to 500 meters below the surface would warm, on average, about 1° C by 2100. Along Greenland, that layer would warm twice as much, but along Antarctica would warm less, only 0.5° C.

Part of the warming in the north comes from the Gulf Stream carrying warm subtropical waters north. By contrast, the Antarctic Circumpolar Current blocks some of the subtropical warmth from entering the Antarctic's coastal waters.

NASA Sets Sail for Arctic Ocean on Final Campaign of ICESCAPE
NASA scientists embarked June 25 from Alaska on the second and final mission of a five-week NASA field campaign to study how changing conditions in the Arctic affect the ocean's chemistry and ecosystems.

The mission, named ICESCAPE, resumed its shipborne investigation of the impacts of climate change in the Chukchi and Beaufort seas along Alaska's western and northern coasts. Research teams departed aboard the U.S. Coast Guard Cutter Healy.

The field campaign is taking 47 scientists to the Arctic Ocean, where a variety of instruments will be used on the Healy and deployed into the ocean and on sea ice. Following the mission's first campaign in summer 2010, the second year of sampling seeks to find year-to-year differences and provide data for new lines of investigation.

NASA said combined observations from the field and from its satellites are critical to understanding the Arctic, where the signals of climate change are amplified. The accelerated decline of Arctic sea ice extent and thickness exemplifies this trend, and scientists want to know how this change affects other ocean processes and marine life.

Last year, researchers saw some indication that nutrients were moving between deep and shallow water. Wind unexpectedly blew thick, multiyear sea ice south to the edge of the shelf, at some places up to 20 feet thick, and the ice proved too thick for the icebreaker to penetrate. The Healy, the newest and most technologically advanced U.S. polar icebreaker, is designed to break 4.5 feet of ice continuously at three knots.

This year, the field campaign began two weeks later, which means the Healy is expected to encounter thinner summer ice and thus have a better chance of exploring the ecosystems. For more information, visit www.nature.com.

Stiff Ocean Sediment Contributed to Severity of 2004 Tsunami
An international team of geoscientists has discovered an unusual geological formation that helps explain how an undersea earthquake off the coast of Sumatra in December 2004 spawned the deadliest tsunami in recorded history, killing more than 230,000.

Instead of the usual weak, loose sediments typically found above the type of geologic fault that caused the earthquake, scientists found a thick plateau of hard, compacted sediments.

Once the fault snapped, the rupture was able to spread from tens of kilometers below the seafloor to just a few kilometers below the seafloor, much farther than weak sediments would have permitted. The extra distance allowed it to move a larger column of seawater above it, unleashing a larger tsunami.

"The results suggest we should be concerned about locations with large thicknesses of sediments in the trench, especially those which have built marginal plateaus," said Sean Gulick, lead author and a research scientist at the University of Texas.

The team's results appeared in June in Nature Geoscience. For more information, visit www.nature.com.

IEO Embarks on a Study of Large Submarine Valleys of Catalonia
The deepwater UUV Liropus 2000, operated by the Spanish Institute of Oceanography (IEO), will be used for the first time in a study of seafloor relief and the dynamic processes that take place along the continental margin of Spain's Catalan coast, in particular in the submarine canyons of Cap de Creus, Palamós and Blanes.

The research will be carried out as part of Promares-Oasis del Mar, an oceanographic campaign directed by Miquel Canals, head of the Marine Geosciences Research Group at the University of Barcelona. The mission is led from Sarmiento de Gamboa, a research vessel owned by the Spanish National Research Council.

The scientific campaign, which was to run June 30 to July 14, will focus on reconnaissance to map and analyze the seafloor in the areas in question and to study the sedimentary structures, benthic communities and the impact of human activity in the submarine canyons and slopes of the continental margin along Catalan's coast.

A team of experts will study the dynamic processes that take place in submarine canyons and neighboring slopes, in particular the phenomena linked to extreme storms and dense water cascading along the northeastern Mediterranean platform, at depths of up to 2,000 meters. For more information, visit www.ub.edu.


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