Increased production of smelly sulfur compound in Southern Ocean tied to climate change

Anne M Stark, LLNL, (925) 422-9799, stark8@llnl.gov

  The cold and windy Southern Ocean favors the exchange of CO2 with the atmosphere. At high latitudes (photo), a recent and persistent increase in winds has produced a saturation of the Southern Ocean sink for CO2. Photo courtesy of N.Metzl, August 2000, oceanographic cruise OISO-5.

LIVERMORE, Calif. -- An organic compound that smells like cabbage and has been called the "smell of the sea" could be more sensitive to global climate change than commonly believed.

In a recent report, a Livermore researcher, along with colleagues from Los Alamos and Oak Ridge national laboratories and the New Mexico Institute of Mining and Technology, found through computer modeling that dimethyl sulfide (DMS) will increase significantly in certain parts of the ocean and decrease in others if the world continues with a business-as-usual fossil fuel dependency.

DMS, a sulfur-containing compound that affects the heat balance of the Earth, is one of the major precursors for aerosols and cloud condensation in the marine boundary layer over much of the remote ocean. DMS is produced by marine plankton and represents the largest source of natural sulfur emissions. Upon reaching the atmosphere, DMS is converted into sulfate aerosols, which reflect sunlight and can stimulate cloud formation.

"We found that DMS is locally much more sensitive to climate change than in previous modeling studies," said LLNL's Philip Cameron-Smith. "The shift in emissions will change the heating patterns."

The Southern Ocean is a locale where the effects of global climate change are noticeable. In this region, there is substantial biological production, carbon drawdown and convective return of nutrients.

Using climate simulations with a global ocean biogeochemical model, scientists looked at the impact of present-day (355 parts per million) and future (970 parts per million) concentrations of carbon dioxide in the atmosphere on DMS levels and emissions in the Southern Hemisphere.

What they found was quite a surprise: In the future scenario, the average DMS emission to the atmosphere was 150 percent more than current levels in the Southern Ocean. Team members found that sea ice changes and ocean ecosystem composition shifts caused by changes in temperature, mixing, nutrient and light regimes caused the increase in DMS in their simulation.

"DMS emissions in the Southern Ocean are significantly more sensitive to climate change than previously thought," Cameron-Smith said. "The melting of the southern sea-ice has a large impact on DMS flux in the model, because it opens up a lot of cold open water in which the DMS-producing plankton thrive (particularly a species called Phaeocystis). This compensates for the warming of the ocean in other areas where Phaeocystis stops growing so well."

In the future, scientists may have to consider how ocean acidification, which is tied directly to climate warming, could affect the plankton community, and therefore DMS production.

The research appears in a recent issue of the journal, Geophysical Research Letters.

Oceans Are at Dire Risk, Team of Scientists Warns

By David Jolly

The state of the oceans is declining far more rapidly than most pessimists had expected, an international team of experts has concluded increasing the risk that many marine species — including those that make coral reefs — could be extinct within a generation.

 

The scientists, who gathered in April at the University of Oxford, cited the cumulative impact of the stresses on the oceans, which include ocean acidification related to growing carbon dioxide emissions, a global warming trend that is reducing the polar ice caps, pollution and overfishing. 

‘‘This examination of synergistic threats leads to the conclusion that we have underestimated the overall risks and that the whole of marine degradation is greater than the sum of its parts, and that degradation is now happening at a faster rate than predicted,’’ they wrote in the report, released on Monday.

The April workshop, organized by the International Program on the State of the Ocean in concert with the International Union for Conservation of Nature, brought scientists from a broad range of disciplines together to talk about the problems in the marine environment and what steps can be taken to arrest the collapse of ocean ecosystems.

Chris Reid, a professor of oceanography at the Marine Institute of Plymouth University who took part in the workshop, described the report as ‘‘a synthesis of existing work.’’ ‘‘When we added it all up, it was clear that we are in a situation that could lead to major extinctions of organisms in the oceans,’’ he said by telephone. 

The scientists said that studies of the earth’s past have indicated that global warming, ocean acidification and hypoxia, or reduced oxygen content in the seas, are three symptoms of a disturbance in the carbon dioxide cycle that have been ‘‘associated with each of the previous five mass extinctions on Earth.’’ 

While speaking in the measured language of science, the report calls for a complete rethinking of humans’ relationship with the oceans. ‘‘It is clear that the traditional economic and consumer values that formerly served society well, when coupled with current rates of population increase, are not sustainable,’’ it said. 

“Deferring action will increase costs in the future leading to even greater losses of benefits,” the scientists added. 

They warned that in addition to steep declines in the populations of many commercially important commercial species, the oceans are at risk for ‘‘an unparalleled rate of regional extinctions of habitat types,’’ including mangroves and seagrass meadows. ‘‘We now face losing marine species and entire marine ecosystems, such as coral reefs, within a single generation,’’ the report said.

Mr. Reid said corals were particularly at risk because they were suffering both from the bleaching effect caused by rising sea temperatures and from acidification, which deprive the tiny organisms of the calcium carbonate they need to build their homes.

The authors call for immediate action to take the pressure off ocean ecosystems, including measures to reduce carbon dioxide emissions and ‘‘coordinated and concerted action’’ by governments in national waters and on the high seas to enact sustainable fisheries polices and reduce pollution. 

They also called on the United Nations Security Council and General Assembly to create a global body that would have the power to ensure compliance with the United Nations Convention on the Law of the Sea and other statutes and treaties and to establish new rules and procedures for acting in “a precautionary manner.’’ Mr. Reid said that action by the United Nations was vital because there was effectively no protection at all for most of the ocean.

‘‘Once you’re outside the 200-mile limits of the nation states, it’s an open field,’’ he said. ‘‘So we’re calling for the U.N. and national governments to come up with some kind of agreement to protect the open oceans. At the moment, we’re not doing anything in the oceans sustainably.’’

 Fastest Sea-Level Rise in Two Millennia Linked to Increasing Global Temperatures

Rate is greater now than at any time during past 2,100 years

The rate of sea level rise along the U.S. Atlantic coast is greater now than at any time in the past 2,000 years--and has shown a consistent link between changes in global mean surface temperature and sea level. The findings are published this week in the journal Proceedings of the National Academy of Sciences (PNAS).

The research, funded by the National Science Foundation (NSF), was conducted by Andrew Kemp, Yale University; Benjamin Horton, University of Pennsylvania; Jeffrey Donnelly, Woods Hole Oceanographic Institution; Michael Mann, Pennsylvania State University; Martin Vermeer, Aalto University School of Engineering, Finland; and Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany.

"Having a detailed picture of rates of sea level change over the past two millennia provides an important context for understanding current and potential future changes," says Paul Cutler, program director in NSF's Division of Earth Sciences.

"It's especially valuable for anticipating the evolution of coastal systems," he says, "in which more than half the world's population now lives."

Adds Kemp, "Scenarios of future rise are dependent on understanding the response of sea level to climate changes. Accurate estimates of past sea-level variability provide a context for such projections."

Kemp and colleagues developed the first continuous sea-level reconstruction for the past 2,000 years, and compared variations in global temperature to changes in sea level over that time period.

The team found that sea level was relatively stable from 200 BC to 1,000 AD. Then in the 11th century, sea level rose by about half a millimeter each year for 400 years, linked with a warm climate period known as the Medieval Climate Anomaly.

Then there was a second period of stable sea level during a cooler period called the Little Ice Age. It persisted until the late 19th century. Since the late 19th century, sea level has risen by more than 2 millimeters per year on average, the steepest rate for more than 2,100 years.

"Sea-level rise is a potentially disastrous outcome of climate change," says Horton, "as rising temperatures melt land-based ice, and warm ocean waters."

To reconstruct sea level, the scientists used microfossils called foraminifera preserved in sediment cores extracted from coastal salt marshes in North Carolina. The age of the cores was estimated using radiocarbon dating and other techniques.

To test the validity of their approach, the team compared its reconstructions with tide-gauge measurements from North Carolina for the past 80 years, and global tide-gauge records for the past 300 years.

A second reconstruction from Massachusetts confirmed their findings.

The records were corrected for contributions to sea-level rise made by vertical land movements.

The reconstructed changes in sea level over the past millennium are consistent with past global temperatures, the researchers say, and can be determined using a model relating the rate of sea level rise to global temperature.

"Data from the past helped calibrate our model, and will improve sea level rise projections under scenarios of future temperature increases," says Rahmstorf.

Support for the research also was provided by the National Oceanic and Atmospheric Administration, United States Geological Survey, the Academy of Finland, the European Science Foundation through European Cooperation in Science and Technology and the University of Pennsylvania.

New Map Reveals Giant Fjords Beneath East Antarctic Ice Sheet

 

ScienceDaily (June 1, 2011) — Scientists from the U.S., U.K. and Australia have used ice-penetrating radar to create the first high- resolution topographic map of one of the last uncharted regions of Earth, the Aurora Subglacial Basin, an immense ice-buried lowland in East Antarctica larger than Texas.

The map reveals some of the largest fjords or ice cut channels on Earth, providing important insights into the history of ice in Antarctica. The data will also help computer modelers improve their simulations of the past and future Antarctic ice sheet and its potential impact on global sea level.

"We knew almost nothing about what was going on, or could go on, under this part of the ice sheet and now we've opened it up and made it real," said Duncan Young, research scientist at The University of Texas at Austin's Institute for Geophysics and lead author on the study, which appears in the journal Nature.

"We chose to focus on the Aurora Subglacial Basin because it may represent the weak underbelly of the East Antarctic Ice Sheet, the largest remaining body of ice and potential source of sea-level rise on Earth," said Donald Blankenship, principal investigator for the ICECAP project, a multinational collaboration using airborne geophysical instruments to study the ice sheet.

Because the basin lies kilometers below sea level, seawater could penetrate beneath the ice, causing portions of the ice sheet to collapse and float off to sea. Indeed, this work shows that the ice sheet has been significantly smaller in the past.

Previous work based on ocean sediments and computer models indicates the East Antarctic Ice Sheet grew and shrank widely and frequently, from about 34 to 14 million years ago, causing sea level to fluctuate by 200 feet . Since then, it has been comparatively stable, causing sea-level fluctuations of less that 50 feet. The new map reveals vast channels cut through mountain ranges by ancient glaciers that mark the edge of the ice sheet at different times in the past, sometimes hundreds of kilometers from its current edge.

"We're seeing what the ice sheet looked like at a time when Earth was much warmer than today," said Young. "Back then it was very dynamic, with significant surface melting. Recently, the ice sheet has been better behaved."

However, recent lowering of major glaciers near the edge detected by satellites has raised concerns about this sector of Antarctica.

Young said past configurations of the ice sheet give a sense of how it might look in the future, although he doesn't foresee it shrinking as dramatically in the next 100 years. Still, even a small change in this massive ice sheet could have a significant effect on sea level. Scientists at The University of Texas at Austin's Institute for Computational Engineering and Sciences, and at Australia's Antarctic Climate and Ecosystems CRC are developing models that will use the new map to forecast how the ice sheet will evolve in the future and how it might affect sea level.

This research is part of ICECAP (Investigating the Cryospheric Evolution of the Central Antarctic Plate), a joint project of The University of Texas at Austin's Jackson School of Geosciences, the University of Edinburgh and the Australian Antarctic Division. For three field seasons, the team flew an upgraded World War II-era DC-3 aircraft with a suite of geophysical instruments to study the ice and underlying rock in East Antarctica.

Funding for this research is provided by the National Science Foundation (U.S.), the National Aeronautics and Space Administration (U.S.), the Natural Environment Research Council (U.K.), the Australian Antarctic Division, the G. Unger Vetlesen Foundation (U.S.), the Antarctic Climate and Ecosystems CRC (Aus.), and the University of Texas at Austin's Jackson School of Geosciences (U.S.).

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Journal Reference:

1. Duncan A. Young, Andrew P. Wright, Jason L. Roberts, Roland C. Warner, Neal W. Young, Jamin S. Greenbaum, Dustin M. Schroeder, John W. Holt, David E. Sugden, Donald D. Blankenship, Tas D. van Ommen, Martin J. Siegert. A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes. Nature, 2011; 474 (7349): 72 DOI: 10.1038/nature10114