Professor searches for ancient land bridge to Asia

 campus geoscientist is part of a team of researchers sailing the Bering and Chukchi seas this summer, searching for clues about the sea floor history and the land bridge that once existed between what is now Alaska and Russia. The team will also explore how the disappearance of the land bridge may have affected that region's climate. Professor Julie Brigham-Grette and colleagues Lloyd Keigwin of Woods Hole Oceanographic Institute and Neal Driscoll of the Scripps Institution of Oceanography are conducting the research in two separate missions on the U.S. Coast Guard Cutter Healy, an ice-breaking vessel.

     The project is funded by the National Science Foundation's Office of Polar Programs and is the first coring program on the new ice breaker. The Healy is 420 feet long, or nearly 1.5 times the length of a football field and nearly eight stories high. This summer is the first official science cruise of the ice breaker in American waters.

     The five-month mission of the USCGC Healy to the Bering and Chukchi Seas, which includes two other research projects, will mark one of the most comprehensive scientific deployments ever conducted by a Coast Guard icebreaker, said Brigham-Grette. The team is doing a high-tech, seismic mapping of the area's ocean floor and its shallow sediments, then taking core samples of the sediments. The science team recently returned from the Bering Sea but will reoccupy the ship Aug. 26-Sept. 17 for work in the Chukchi Sea.

     "We want to know how quickly the land bridge formed or was flooded with changes in global sea level, cutting off the migration of people and a wide range of plants and animals," said Brigham-Grette. "And we're looking at the area's climate history to understand how the ocean and the atmosphere affected the land, and what happened to the watermasses in the region when the land bridge was submerged," she said. "It's scientifically exciting because it's interdisciplinary between the three of us as principal investigators. It's like putting a puzzle together; with each scientist contributing a different but important puzzle piece."

     Brigham-Grette's expertise is in culling ancient climate records from clues embedded in land, lake, and ocean sediment samples going back tens of thousands of years. Keigwin is an expert at interpreting changes in the temperature and water chemistry of ocean water masses and how these changes are related to past climate change using fossils and ocean sediments. Driscoll specializes in interpreting the layering and displacement of rock and sediments, especially in the distribution of sediments in basins and on continental shelves using geophysics.

     Brigham-Grette notes that the Bering Strait has actually been submerged dozens of times, as the glaciers approached and retreated. The submerged subcontinent is known as Beringia. The scientific team hopes to gain an understanding of the paleooceanographic history of the region since the last submergence of the strait, at the end of the last Ice Age, some 20,000 years ago.

     When the glaciers melted and the sea level rose, seawater drowned ancient rivers and tundra, creating salty estuaries, Brigham-Grette explained. The seismic exploration led by Driscoll and his students in the Chukchi Sea will locate channels where freshwater rivers once ran, and sediment cores drilled in those areas should offer clues to how quickly the sea level rose. Clues in the layers of deposited mud and silt include fossils and the remains of microscopic plants and animals, such as diatoms (made of silica) and foraminifera (made of carbonate). graduate student Zach Lundeen, and Woods Hole researchers working with Keigwin will be analyzing the sediments and fossil remains.

     "We know the climate was different here back then," said Keigwin. "We hope we can learn how different it was, and how the ocean and atmosphere responded to change. In addition to marine sediments, we hope to get samples of the soils and vegetation that existed on the land bridge. We should be able to learn a lot about how things changed here over time by examining the entire region as an environmental system."

      "We are thrilled with the performance of the Healy because this was the first cruise to seismically map the Bering Sea and obtain high resolution sediment cores through the Holocene," said Jane Dionne, program manager for the Arctic Natural Sciences, part of the Office of Polar Programs at the NSF. "This research should greatly advance our understanding of the region and should provide important answers to old questions about the role of the North Pacific in the world circulation system, especially during the past glacial periods."

     There is much to be learned about how the Earth works by studying climate change recorded in layers of sediment in the past, says Brigham-Grette. "It's as if the Earth and its oceans have already run a number of natural experiments in global change for us. It's our obligation now to read the results of these experiments in the sediments, so that we can use this information to predict the nature of climate change into the future."