UC Santa Cruz Tip Sheet December 5, 1995
Research news and feature ideas, issued periodically by the UCSC Public Information Office
For more information, contact Robert Irion at (408) 459-2495 or irion@ua.ucsc.edu
*Marine toxicology* DDT contamination in California sea lions plummets
Amid concerns about the lingering effects of DDT along California's coast comes this bit of good news: Sea lions carried about one hundred times less of the toxic substance in their fat a few years ago than they did two decades earlier.
The average level of DDT and its major breakdown product, DDE, was 5.2 parts per million in sea-lion blubber collected between 1988 and 1992. In contrast, blubber analyzed in 1970 contained an average of 760 parts per million--an incredible quarter-pound of DDT in each animal's body. Although DDT and DDE levels have dropped in other animal populations over the same period, the decline in California sea lions is the most precipitous yet seen.
The scientists say there is a direct link between this dramatic change and the cessation of DDT dumping off southern California. The Montrose Chemical Corporation, at the time the world's largest manufacturer of DDT, flushed thousands of tons of DDT waste into the ocean between 1949 and 1970. The waste polluted a gyre of water near the Channel Islands, tainting much of the breeding area for California sea lions. Since then, the population of the species has more than doubled, although factors other than lower DDT levels may have helped them thrive. Even with this heartening progress, researchers warn that the remaining amounts of DDT-related chemicals still may inflict subtle harm on sea lions and other marine mammals.
"The waste from just one industrial plant was enough to have a severe effect on an entire population of animals, because it was dumped directly into their habitat," says study coauthor Walter Jarman of UCSC's Institute of Marine Sciences. "But the DDT levels we found are not 'low,' they're just 'lower'--and they're still higher than in marine mammals in many other parts of the world." The team published its findings in the November issue of Marine Pollution Bulletin.
Contact: Jarman--(408) 459-3769 or wmjarman@cats.ucsc.edu
*Astronomy* Hubble peers deep into the heart of the densest known star cluster
By pinpointing individual suns in the glare of the most tightly packed cluster of stars in our galaxy, the Hubble Space Telescope has unveiled hints of either a massive black hole or another remarkable phenomenon: a "core collapse" driven by the intense gravitational pull of so many stars in such a small volume of space.
A team of astronomers used the telescope's sharp images to count an extraordinary number of stars in the ancient globular cluster M15, about 37,000 light-years away. Hubble spied hundreds of stars in a tiny area at the center of M15, whereas earthbound telescopes see a single blur of light. Careful analysis of the distribution of these and thousands of neighboring stars suggest that at some point in the distant past, the stars converged on M15's core, like bees swarming to their hive. This runaway collapse, long theorized by researchers but never seen in such detail, may have lasted a few million years-- a flash in the 12-billion-year life of the cluster.
Thanks to the laws of physics, the core probably stopped collapsing before many of the stars collided. Rather, stars near the center would have settled into an uneasy cosmic waltz, both attracted to each other by gravity and repelled by close encounters that slingshot them through space. An alternate scenario also could explain the pileup of stars at M15's core: a black hole that may have formed early in the cluster's history. The black hole would have gradually gained mass as more stars spiraled inward. If it exists, it would now be several thousand times more massive than our sun.
A precise reading of the speeds at which stars move near M15's core would reveal whether the stars are packed so tightly because of the influence of a single massive object, or simply by their own mutual attraction. The study, led by Puragra Guhathakurta of UCO/Lick Observatory at UCSC, is set for the January 1996 issue of Astronomical Journal.
Contact: Guhathakurta--(408) 459-5169 or raja@ucolick.org
*Seismology I* A way to probe fault zones for seismic hazard before a quake strikes
A new technique may let seismologists estimate which parts of a fault are likely to rupture most severely during an earthquake, even if the fault hasn't broken for a century or more.
The technique relies upon an apparent connection between the pre-earthquake geology of a fault zone and the amount of motion that a quake triggers along different segments of the fault. A similar relationship exists between fault-zone geology and the pattern of aftershocks that strike after the main earthquake.
UCSC seismologist Justin Revenaugh, who devised the method, says it cannot predict when an earthquake will happen or how large it will be. However, the method may help researchers refine their maps of seismic hazard by hinting in advance which fault segments will pack the biggest wallop. That information could prove especially useful for the many mysteriously "locked" segments in southern California and elsewhere.
"It's difficult to figure out how much slip might occur on locked faults," says Revenaugh. "This scheme begins to give us a rational way of looking at each fault and dividing it into segments. Those segments are the building blocks that could break in one large earthquake or several smaller ones." Revenaugh based his work on an analysis of the magnitude 7.3 Landers temblor and two other sizable quakes that ripped across California's Mojave Desert region in 1992. His study appeared in the November 24 issue of Science.
Contact: Revenaugh--(408) 459-3055 or jsr@earthsci.ucsc.edu
*Seismology II* Oil companies need seismological tools that are anything but crude
Billions of barrels of oil lurk beneath the floor of the Gulf of Mexico, shrouded by twisted layers of rock and domes of salt. If Ru-Shan Wu's group does its job well, the oil industry soon will have far better tools to find that black gold.
Wu and his colleagues at UCSC's Institute of Tectonics are developing a new way to make 3-D images of geologic structures that hide deposits of oil and natural gas. Their method promises to work hundreds or even thousands of times faster than existing 3-D mapping techniques, which require too much computer memory and expensive processing time to make them feasible for widespread use. The Department of Energy will fund the work during the next three years with a grant of $697,000.
The grant is part of a program known as the Advanced Computational Technology Initiative (ACTI), which invites collaborations among national labs, petroleum and computing industries, and universities. ACTI projects are intended to help gas and oil companies tap into U.S. petroleum fields to the fullest possible extent--thereby lowering the nation's dependence on foreign oil.
In essence, the technique developed by Wu's team compresses subterranean structures into a series of 2-D sheets, rather than analyzing the whole 3-D medium, which is far more complex. The method also neglects the multiple echoes among various layers that can make the imaging process prohibitively time-consuming.
"This is a good opportunity for us to apply the theoretical techniques we have developed in recent years to a crucially important technology," says Wu, a research geophysicist. "There are risks involved--it may not work in very complex geologic environments. But if it does, it would represent a breakthrough for 3-D imaging in complex media."
Contact: Wu--(408) 459-5135 or wrs@earthsci.ucsc.edu
*Biochemistry* Acronyms abound: Mapping a protein-RNA complex in BIV, with NMR
Biochemists have published the first detailed view of the molecular tango between two critical units in the life cycle of a retrovirus--a virus that uses RNA, not DNA, to direct its genetic infiltration of a host cell.
The research reveals a precise fit between the viral RNA and a section of a protein that triggers the virus to make copies of itself. The protein segment lies snugly within a curved groove in the RNA, like a sausage resting in its bun. In an infected cell, this protein- RNA complex acts as a "switch" that turns on the assembly line for further virus production.
The scientists derived this structure by studying the bovine immunodeficiency virus, or BIV, which infects cows and is genetically related to HIV. The work may set the stage for a better grasp of a crucial step in the life cycle of HIV, which causes AIDS in humans. However, the researchers caution, there are significant differences in the ways that proteins bind to RNA in the two viruses, so an immediate application to HIV research is unlikely.
"The interactions between RNA and protein are of paramount importance to the life cycles of retroviruses," says UCSC biochemist Joseph Puglisi, who led the study. "This is only the fifth or sixth example of a detailed structure of a protein-RNA complex, and it's the first time anyone has solved a protein-RNA structure in a retrovirus." The research was published in the November 17 Science.
Contact: Puglisi--(408) 459-3961 or puglisi@chemistry.ucsc.edu
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