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Was Antarctica an important Cretaceous link between South America and India-Madagascar?

Marine geophysical data on the Antarctic-African tectonic plate boundary reveal an undersea wonder

Science notebook--News from Antarctica and beyond

Marine geology/geophysical cruises use new techniques to chart antarctic climate history

Participants in the internationally supported Ocean Drilling Program (ODP) returned to antarctic waters for the first time in 10 years in December 1997. Working aboard the drilling ship JOIDES Resolution, researchers will conduct two 56-day investigations. The first cruise (Leg 177), which began on 15 December 1997 and ended on 9 February 1998, focused on the southern Atlantic region of the southern oceans, and the second (Leg 178), scheduled to begin in mid-February 1998, focuses on the Pacific margin of the Antarctic Peninsula. Funded principally by the National Science Foundation with substantial contributions from international partners, ODP supports basic research into the history of the ocean basins and the nature of the crust beneath the ocean floor.

During Leg 177, 25 investigators from nine nations collected sediment cores, hoping to unearth 40- to 50-million-year-old material from the ocean bottom and, with it, to unlock the key to the region's paleoclimate. The cruise, which left from Capetown, focused on six sites across the southern oceans, the deepest of which was expected to be 700 meters below the seafloor. The southernmost drill site was near Bouvet Island, a Norwegian possession and the world's most remote island. The cruise ended on 9 February 1998 in Punta Arenas, Chile.

The team's goal is to reconstruct the climate history of the high-latitude region of the Southern Hemisphere using recently developed techniques and modern drilling methods not available to researchers who participated during the last ODP investigation a decade ago. Aboard the JOIDES Resolution, the world's largest research ship, the team will study the history of the antarctic ice build up. This research will help scientists better understand when the massive antarctic ice sheet--the largest accumulation of ice on Earth--formed and how stable it has been.

According to David A. Hodell of the University of Florida, co-chief scientist of Leg 177, "The build up of the antarctic ice sheet around 40 million years ago led to dramatic changes in the Earth's climate system and biosphere. Earth's climate changed from a relatively warm 'hothouse' world to a cold 'icehouse' world." Scientists know that the southern oceans have a major role in defining the Earth's climate system, but many questions remain about the history of climate and ocean changes in the southern high-latitudes.

"The ability to resolve short-term climate change depends on how fast the sediments accumulate on the seafloor," Hodell explains. "We will drill in zones of high sediment accumulation rates in order to resolve climatic changes that lasted for centuries to millennia. Recovery of sediment cores deposited at high rates will permit a direct comparison of marine and ice-core records to understand how the ocean-atmosphere system behaved during the last four cycles of glacial-to-interglacial climate change."

Leg 178, which begins in mid-February in Punta Arenas, Chile, is designed to provide a high-resolution record of antarctic continental climate over the past 6 to 10 million years (the Cenozoic) and to directly check the relationship between the global sea-level changes and the waxing and waning of the antarctic ice sheet. The research to be conducted during this cruise is part of a larger effort to better understanding of antarctic glacial history, particularly the stability of the antarctic ice sheet.

Was Antarctica an important Cretaceous link between South America and India-Madagascar?

Small, ratlike creatures that once roamed with the dinosaurs are providing clues to ancient continent migration, suggesting that in Earth's distant past, Antarctica may have been a bridge that enabled animals to migrate from South America to Indo-Madagascar.

The 65- to 70-million-year-old mammals called gondwanatheres had distinctive high-crowned teeth. Until recently, scientists had found these teeth only in South America. In the 4 December issue of Nature, however, paleontologist David Krause of the State University of New York at Stony Brook announced that he and his National Science Foundation-funded team of researchers have found gondwanathere teeth in 80-million-year-old rocks in Madagascar and slightly younger rocks in India.

"Finding representatives of gondwanatheres on these now widely separated land masses suggests to us that the land masses were connected in the Late Cretaceous," said Krause of the discovery. "A recently proposed geophysical model shows that India and Madagascar were attached to eastern Antarctica well into the Cretaceous while South America was attached to the western end of Antarctica. This discovery supports that hypothesis with totally independent evidence derived from the fossil record."

Christopher Maples, program director for the National Science Foundation's Division of Earth Sciences, which funded Krause's research, commented on the far-reaching implications of the find. "These are major discoveries that go far beyond their obvious significance to paleontologists," Maples said. "Krause and have provided an excellent example of the contributions that paleontology can make to many areas of geoscience, including tectonic plate positions in Earth's past."

Marine geophysical data on the Antarctic-African tectonic plate boundary reveal an undersea wonder

In the waters between Africa's Cape of Good Hope and the Antarctic, a multinational marine geophysical team--called InterRidge--mapping the Southwest Indian Ridge, the boundary between the Antarctic and African tectonic plates, has found the steepest underwater cliff ever recorded. InterRidge used remote sensing devices to map a 2,000-kilometer section of the ridge, focusing on a 650-kilometer-long segment between 15E and 25E, a previously uncharted region.

John Madsen, a University of Delaware geologist, reported InterRidge's findings at the 1997 Fall Meeting of the American Geophysical Union, held in December in San Francisco. The ridge drop discovered by the InterRidge team plummets from 150 meters to 6,000 meters in only 16 kilometers. "It's the steepest change in elevation along the mid-ocean ridge that's been mapped any place on the globe," Madsen reports. The mid-ocean ridge encircles the entire Earth.

The maps produced by the InterRidge team will help scientists understand the physical characteristics of the sea and the ocean floor. The early work of this team suggests that unusual geologic activity and volcanic processes are at work along the Southwest Indian Ridge.

"Some biologists believe life may have originated at hydrothermal vents beginning at 10,000 feet [3,000 meters] below the surface," Madsen notes. At that depth, the temperature of the ocean water is close to freezing, and when the 340C flow from seafloor vents hits the near-freezing ocean water, sulfide deposits are formed. Some scientists believe these deposits may hold the key to the beginnings of life on Earth. "We'll be making maps of the seafloor for people interested in finding these vents," says Madsen, whose work is supported in part by a National Science Foundation grant.