Ice sheets caused massive sea level change during late Cretaceous

02/27/04

Period was previously thought to be ice-free

Arlington, Va.-Scientists using cores drilled from the New Jersey coastal plain have found that ice sheets likely caused massive sea level change during the Late Cretaceous Period -an interval previously thought to be ice-free. The scientists, who will publish their results in the March-April issue of the Geological Society of America (GSA) Bulletin, assert that either ice sheets grew and decayed in that greenhouse world or our understanding of sea level mechanisms is fundamentally flawed.

Led by Kenneth Miller of Rutgers University, the scientists examined cores from Ocean Drilling Program Leg 174AX, an onshore extension of an offshore expedition. They found indications that sea level changes were large (more than 25 meters) and rapid (occurring on scales ranging from thousands to less than a million years) during the Late Cretaceous greenhouse world (99- 65 million years ago).

"The onshore-offshore drilling forms a important, coordinated link to study the history of sedimentation along this area of the U.S. continental margin," said Leonard Johnson, director of the National Science Foundation (NSF)'s continental dynamics program, which co-funded the research with NSF's ocean drilling program.

Analyses indicate minimal tectonic effects on the New Jersey Coastal Plain at this time, the scientists say. The other explanation for such large, rapid changes is the waxing and waning of large continental ice sheets, they maintain. What is perplexing, however, is that such large and rapid sea-level changes occurred during an interval thought to be ice free.

"Our studies of cores in New Jersey provide one of the best- dated estimates of how fast and how much sea level changed during the greenhouse world of the Late Cretaceous," said Miller. "The Earth was certainly much warmer at that time, probably due to high carbon dioxide levels in the atmosphere. At the same time, our estimates require that ice sheets grew and decayed on Antarctica during this period of peak warmth, which has been a previously heretical view."

The scientists propose that the ice sheets were restricted in area to Antarctica and were ephemeral. The ice sheets would not have reached the Antarctic coast, explaining the relative warmth in Antarctica, but still could significantly alter global sea level.

Source: Eurekalert & others

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