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Ocean Research


November 2011 Issue

6 Percent of Sea-Level Rise Came From Groundwater, Study Finds
Groundwater depletion between 2000 and 2008 was responsible for raising global sea level at a rate of 0.4 millimeters per year, an eighth of the observed sea-level rise over the same period, according to a study by U.S. Geological Survey scientist Leonard Konikow.

Published in September in Geophysical Research Letters, the study found that global groundwater depletion from 1900 to 2008 totals approximately 4,500 cubic kilometers (nearly the volume of Lake Michigan), equivalent to a sealevel rise of 12.6 millimeters, or six percent of the total. Groundwater depletion has increased over the years: Nearly a quarter of this volume, 1,100 cubic kilometers, was pumped out from 2000 to 2008 alone.

"If the removal of groundwater from storage in the continental subsurface is sufficiently large and persistent, it can represent a substantial transfer of water mass from the land to the oceans, and thereby represent a measureable contributor to long-term sea-level rise," Konikow wrote.

To find these values, Konikow combined the results from a number of previous studies that estimated groundwater storage using measurements of groundwater levels, satellite observations of aquifer water volumes and models that track long-term changes in groundwater storage. These updated values fall near the middle of the range of previous estimates.

U.S. groundwater depletion was calculated from 41 aquifer systems and subareas, and plotted for eight major systems. Because five groundwater systems outside the U.S. have unreliable data, Konikow calculated global depletion using the relative magnitudes of U.S. and global withdrawals, and the fraction of total withdrawals represented by depletion. More assessments are needed for these systems, Konikow said, which have substantial known depletion. For more information, visit www.usgs.gov.

NOC Team Conducts Expedition via Satellite
National Oceanography Centre (NOC) scientists have been exploring the depths of the Cayman Trough without setting foot on a ship, thanks to a telepresence link from a U.S. ship that was operating in the Caribbean, the center announced in October.

Last year, a U.K. research cruise led by the NOC's Doug Connelly found and sampled hydrothermal vent fields on the Mid-Cayman Spreading Center for the first time. In August, the RV Okeanos Explorer returned to explore the area as part of NOAA's Ocean Exploration program.

Unusual for a research cruise, the RV Okeanos Explorer only had two scientists aboard: professor Paul Tyler from the University of Southampton and Chris German from Woods Hole Oceanographic Institution. But the ship was linked via satellite to a shoreside command center in Rhode Island, where a full science team kept watch and assisted in directing operations.

In addition, the program broadcast three high-definition video feeds, real-time audio and oceanographic data via the Internet, allowing scientists at the NOC to watch ROV dives live and interact with the team aboard ship.

The expedition's highlights have included the discovery of live tubeworms on an undersea mountain in the Cayman Trough, near the vent field discovered by the U.K. team last year. The NOC said bringing together scientists around the world to explore the Cayman Trough together has proved useful in refining targets for future investigation. A second U.K. research cruise is being planned for the area. For more information, visit www.noc.soton.ac.uk.

Scientists Probe Indian Ocean for Clues to Weather Patterns
An international team of researchers began in October a six-month field campaign in the Indian Ocean to improve long-range weather forecasts and seasonal outlooks.

The goal of the DYNAMO (Dynamics of the Madden-Julian Oscillation) field campaign is to better understand Madden-Julian Oscillation (MJO), a disturbance of the tropics that originates in the equatorial Indian Ocean roughly every 30 to 90 days. MJO is part of the Asian and Australian monsoons and can enhance hurricane activity in the northeast Pacific and Gulf of Mexico, trigger torrential rainfall along the West Coast of North America and affect the onset of El Niño. Scientists believe that the MJO is the world's greatest source of atmospheric variability over one- to three-month time frames.

"The MJO drives weather in both hemispheres even though it sits along the equator," said Jim Moore of the National Center for Atmospheric Research and director of DYNAMO's project office. "Its origins have never been measured in such a systematic fashion before."

DYNAMO will use aircraft, ships, moorings, radars, numerical models and other tools to study how tropical weather brews in the region and moves eastward along the equator, enabling scientists to further refine computer models of global climate. For more information, visit www.eol.ucar.edu.

Researchers Find Comet with Earth-Like Water
Taking measurements of a comet with technology from the European Space Agency's space observatory Herschel, scientists have found water in a comet with almost the same composition as Earth's oceans, meaning that not only asteroids may have brought water to Earth.

Approximately one year ago, the comet 103P/Hartley 2 passed Earth at a distance of 18 million kilometers, allowing for highly sensitive measurements of its coma, the sheath of gas and dust that surrounds the comet. The data showed the comet's water had one deuterium atom to every 6,200 hydrogen atoms, which is close to Earth's 1:6,400 ratio.

The key to why Hartley 2's makeup is different from other comets may be because of where it was born: far beyond Pluto, in a frigid region known as the Kuiper Belt. Other comets previously studied are all thought to have formed near to Jupiter and Saturn.

Thus, these new observations suggest that perhaps Earth's oceans came from comets after all—but only a specific family of them, born in the outer solar system, the space agency said. Scientists have speculated that in the deep cold, the deuterium-to-hydrogen ratio imprinted into water-ice might have been quite different from that which arose in the warmer inner solar system. For more information, visit http://sci.esa.int.


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