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Ocean Research


May 2011 Issue

Measurements of Arctic Sea Ice Show Ongoing Loss, Study Finds
The 2011 Arctic sea ice extent maximum appears to be tied for the lowest ever measured by satellites.

A research team at the University of Colorado Boulder's (CU-Boulder) National Snow and Ice Data Center said it believes the lowest annual maximum ice extent of 5.65 million square miles occurred on March 7. The maximum ice extent was 463,000 square miles below the 1979 to 2000 average. The 2011 measurements were tied with those from 2006 as the lowest maximum sea ice extents measured since satellite record keeping began in 1979.

The majority of climate scientists believe shrinking Arctic sea ice is tied to warming temperatures in the region caused by an increase in human-produced greenhouse gases being pumped into Earth's atmosphere. Because of the downward trend of Arctic sea ice extent in the last decade, some CU-Boulder scientists predict the Arctic Ocean may be ice-free in the summers within the next several decades.

The seven lowest maximum Arctic sea ice extents measured by satellites all have occurred in the past seven years, said CU-Boulder research scientist Walt Meier of the National Snow and Ice Data Center, who participated the latest study.

"I think one of the reasons the Arctic sea ice maximum extent is declining is that the autumn ice growth is delayed by warmer temperatures and the ice extent is not able to 'catch up' through the winter," Meier said. "In addition, the clock runs out on the annual ice growth season as temperatures start to rise along with the sun during the spring months."

For more information, visit www.sciencedaily.com.

Ancient 'Hyperthermals' Leave Clues to Anticipated Climate Changes
Bursts of intense global warming that have lasted tens of thousands of years have taken place more frequently throughout history than previously believed, according to evidence gathered by researchers.

Richard Norris, a professor of geology at led by Scripps Institution of Oceanography at the University of California, San Diego (UCSD), who co-authored the report, said releases of carbon dioxide sequestered in the deep oceans were the most likely trigger of these ancient "hyperthermal" events.

Most of the events raised average global temperatures between 2° and 3° C, an amount comparable to current conservative estimates of how much temperatures are expected to rise in coming decades as a consequence of anthropogenic global warming. Most hyperthermals lasted about 40,000 years before temperatures returned to normal. The study, conducted by a team led by Scripps Institution of Oceanography, appeared in March in Nature.

The hyperthermals took place roughly every 400,000 years during a warm period some 50 million years ago. The events stopped taking place around 40 million years ago, when the planet entered a cooling phase. No warming events of the magnitude of these hyperthermals have been detected since then.

The authors concluded a release of carbon dioxide from the deep oceans was a more likely cause of the hyperthermals than other triggering events that have been hypothesized. The regularity of the hyperthermals and relatively warm ocean temperatures of the period make them less likely to have been caused by events such as large melt-offs of methane hydrates, terrestrial burning of peat or cometary impacts. The hyperthermals could have been prompted by a buildup of carbon dioxide in the deep oceans caused by slowing or stopping of circulation in ocean basins that prevented carbon dioxide release, the scientists said. For more information, visit http://scrippsnews.ucsd.edu.

Deep-Sea Volcanoes Don't Just Produce Lava Flows—They Erupt
Between 75 to 80 percent of all volcanic activity takes place at deep-sea, mid-ocean ridges. Most of these volcanoes produce effusive lava flows rather than explosive eruptions.

Over the past 10 years, however, geologists have speculated, based on the presence of volcanic ash in certain sites, that explosive eruptions can also occur in deep-sea volcanoes. But no one has been able to prove it until now. By using an ion microprobe, Christoph Helo, a Ph.D. student in McGill University's Department of Earth and Planetary Sciences, has discovered very high concentrations of carbon dioxide (CO2) in droplets of magma trapped within crystals recovered from volcanic ash deposits on Axial Volcano on the Juan de Fuca Ridge off the coast of Oregon.

These entrapped droplets represent the state of the magma prior to eruption. As a result, Helo and researchers from McGill, the Monterey Bay Aquarium Research Institute and the Woods Hole Oceanographic Institution have been able to prove explosive eruptions can occur in deep-sea volcanoes.

Their work also shows the release of CO2 from the deeper mantle to Earth's atmosphere, at least in certain parts of mid-ocean ridges, is much higher than previously thought.

Given that mid-ocean ridges constitute the largest volcanic system on Earth, scientists said, this discovery has implications for the global carbon cycle that have yet to be explored. For more information, visit www.sciencedaily.com.

Study Shows Ocean's Role in Transporting Heat to Glaciers
Warmer air is only part of the story when it comes to Greenland's rapidly melting ice sheet. Research released in March by scientists at Woods Hole Oceanographic Institution (WHOI) highlights the role ocean circulation plays in transporting heat to glaciers.

Greenland's ice sheet has lost mass at an accelerated rate over the past decade, dumping more ice and freshwater into the ocean. Scientists have found that between 2001 and 2005, Helheim Glacier, a large glacier on Greenland's southeast coast, retreated eight kilometers, and its flow speed nearly doubled.

A research team led by WHOI physical oceanographer Fiamma Straneo discovered warm, subtropical waters deep inside Sermilik Fjord at the base of Helheim Glacier in 2009.

"We knew that these warm waters were reaching the fjords, but we did not know if they were reaching the glaciers or how the melting was occurring," said Straneo, lead author of the study, which was published in Nature Geoscience's online edition.

For more information, visit www.whoi.edu.


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