Geotimes
Untitled Document

Geophenomena

A far-off new ocean
Longer to patch the ozone hole

A far-off new ocean

A new ocean basin opened up in an African desert last fall, or at least, made its first cracks. The ruptures, researchers say, could mark the beginning of an inland sea in Ethiopia’s East African rift zone.

This 6-meter-wide fissure in Ethiopia’s East African rift zone spouted ash after earthquakes shook the region, in what may be the first visible events leading to ocean spreading in the rift. Image courtesy of Cynthia Ebinger.

In September, a large earthquake followed by a series of tremors shook the region, and about a week later, a segment of the rift spewed ash in a volcanic eruption and tore several cracks amounting to an opening of more than 6 meters at the surface, according to Cynthia Ebinger, a geologist at Royal Holloway University of London. “It appears that we’ve seen the birth of an ocean basin,” she told the BBC Dec. 8.

The new opening is part of the Afar triple junction (also sometimes called the Gulf of Aden triple junction), where the Arabian and African plates come together at a point where Africa is also splitting. The newly active portion of the basin, about 20 kilometers wide and 60 kilometers long, is fractured by a series of 1.8-million-year-old faults, with the new fissures splitting it further. Researchers hailing from a variety of institutions, including Royal Holloway University of London, University of Oxford and Addis Ababa University in Ethiopia, have tracked strain and movement in the region with seismic arrays as well as by satellite. Taken together with eyewitness accounts, the data, presented by the researchers at the American Geophysical Union annual meeting in San Francisco in December, suggest that the system is transitioning between continental rifting to oceanic spreading, accompanied by changes in the rocks beneath.

Hot magma from the mantle welling up under the southern part of the zone may be facilitating the rifting, members of the research group suggested, in a region where tectonic forces are too small to explain the rifting occurring now. Although this may be the first time human eyes have observed such speedy and perceptible rifting, it will take millions of years for a true ocean to develop here: Researchers predicted that the rift will continue to pull apart very slowly, at around 6 millimeters per year.

Naomi Lubick

Back to top


Longer to patch the ozone hole

Scientists predicted in 2002 that the atmosphere’s ozone “holes” would recover to 1980 levels by 2050. But new research shows the ozone layer will take 15 years longer to heal than previously thought.

Not quite a “hole,” ozone depletion in the Antarctic reaches its maximum from August to October every year. Last year, the peak occurred Sept. 11, shown here in blue, slightly larger than the maximum depletion in 2004 — but almost 2 million square kilometers smaller than the largest ever measured in 1998, which averaged about 26 million square kilometers. Scientists announced revised recovery dates for the ozone holes at both poles in December. Image courtesy of NASA/GSFC.

After the discovery of an ozone hole in the Antarctic in 1985, researchers determined that chlorofluorocarbons (CFCs) and halon gases had destroyed ozone in a layer that protects Earth from ultraviolet rays, over both the Arctic and Antarctic. International efforts taken in 1996 to stop the manufacture and use of CFCs had dramatically reduced the amount of the substances, which travel into the lower atmosphere. There, strong ultraviolet light breaks up the molecules, freeing chlorine, which can destroy ozone.

Despite the ban on CFCs, new research shows that emissions of the molecules in 2003 from the United States and Canada still ranged from 10 to 45 percent of the global total, according to Dale Hurst of the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Division in Boulder, Colo., and his co-workers. Hurst hypothesizes that in addition to continued manufacture and use in developing countries, remaining pools of CFCs in old appliances and even car air conditioners are enough to extend the damaging effects of the chemical by a decade and a half more than modelers previously thought. More CFCs may also come from sources squirreled away after manufacturing officially ended, he said in a Dec. 6 presentation at the American Geophysical Union (AGU) meeting in San Francisco.

The ozone hole in the Antarctic reached its maximum last year on Sept. 11, when temperature conditions and chemical concentrations hit their prime during the Antarctic spring, according to Michelle Santee of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Using NASA’s Aura satellite, which has been tracking global ozone levels and other ozone-depleting chemicals since its launch in 2004, Santee and co-workers have determined that seasonal changes in ozone levels vary at the north and south poles.

Monitoring so far, she said at the AGU meeting, shows that the Arctic gets warm enough so that chlorine-containing molecules have less of a destructive effect than in Antarctica, where it is cold enough to maintain the chemical reactions that destroy ozone year-round. But wind patterns in the Arctic also disperse chemicals and ozone, enough so that the status of ozone at the northern pole remains unclear, Santee said.

The condition of the Arctic, where the ozone hole may mend by 2030 or 2040, still seems likely to improve more rapidly than at the southern pole, according to John Austin of NOAA’s Geophysical Fluid Dynamics Laboratory at Princeton University in New Jersey. The Antarctic hole most likely will not recover until 2065, but even that prediction remains subject to the variability in chemistry and the two polar environments.

Naomi Lubick

Back to top

Untitled Document


Geotimes Home | AGI Home | Information Services | Geoscience Education | Public Policy | Programs | Publications | Careers

© 2014 American Geological Institute. All rights reserved. Any copying, redistribution or retransmission of any of the contents of this service without the express written consent of the American Geological Institute is expressly prohibited. For all electronic copyright requests, visit: http://www.copyright.com/ccc/do/showConfigurator?WT.mc_id=PubLink