Sediment cores reveal sea level seesaw

Initial results submitted by the IODP New Jersey Sea Level Expedition

The KAYD drilling platform used in New Jersey © E. Gillespie / IODP
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Scientists have drilled sediment cores as part of the Integrated Ocean Drilling Program (IODP) in the shallow waters off the coast of New Jersey, with surprising new results. After that, between 14 and 35 million years ago, the sea level fluctuated several times by up to a hundred meters.

"During the expedition, we explored an almost complete sequence of marine sediments covering the 14-35 million year period before today, " says Professor Gregory Mountain, geoscientist at Rutgers University New Jersey / USA and one of the two scientific expedition leaders. "All in all, we had 1, 311.4 meters of sediment cores at three drill locations 45 to 65 kilometers off the coast of New Jersey. The longest borehole reached more than 756 meters deep. "

Remains of former sandy beaches and continental soils

With the help of the excavated marine sediments, the international research team can find out when or how much and how quickly the sea level dropped and rose again - and this for a period in which the Antarctic ice sheet grew and faded again. The investigations in the core camp at the University of Bremen showed that the sediment cores also contain remnants of former sandy beaches and continental soils. From these and other indications, the researchers deduce that the sea level fluctuated by up to a hundred meters in the said period.

Overall, they were able to identify ten cycles between 14 and 35 million years ago today, with sea levels initially rising before dropping off again, with the result that New Jersey's shoreline shifted dramatically seaward.

Freshwater lenses 400 meters below the seafloor

"To our great surprise, we encountered freshwater lenses at all three drill points, which are up to 400 meters below the seafloor, " says expedition leader Jean-Noël Proust from the French University of Rennes. The fresh water collects in microscopic pores between the clay and sand particles. display

"We are already surprised that these lenses are more than 100 meters thick. We assume that the lenses that are now 50 kilometers off the coast were created during the last ice age more than 12, 000 years ago, when sea levels had dropped and the New Jersey coastline was at times seaward from our drilling locations, "the researcher continued,

More than 14, 000 samples taken

The coastal waters of the US state are particularly well-suited for the study of sea level fluctuations. Two major rivers in the earth's past made sure that much sediment was washed from land into the ocean. Today, these deposits can be used as excellent archives of Earth's history. In addition, the region is tectonically stable: the self-movements of the North American Earth Plate hardly affect the fluctuations of the sea level. After all, the expedition's drilling sites were in the center of the shallow K memen off New Jersey. Therefore, both rising and falling sea levels are well archived in the sediments.

The evaluation of the expedition in Bremen is expected to be completed on December 5, 2009. The more than 14, 000 samples taken so far from the sediment cores will be further investigated by participating scientists in their home laboratories over the coming months and years.

"New Jersey Shallow Shelf Expedition"

The New Jersey Shallow Shelf Expedition is a European contribution to the IODP. It is sponsored by ECORD, the European Consortium for Ocean Research Drilling. This consortium brings together 16 European nations and Canada. The expedition was also supported by the ICDP, the Intercontinental Drilling Program.

(idw - MARUM - Center for Marine Environmental Sciences at the University of Bremen, 30.11.2009 - DLO)