Uranium-dating Through Deep Sea Corals Deposits a Useful Reference on Northern Glacial Retreat

Oct 11, 2016 09:11 AM EDT

Ancient preserved deep-sea corals were found to be useful by experts in reconstructing uranium traces that can provide information on the northern glacial activities thousands of years ago. The new possible approach explored has paved another opportunity in understanding past climatic scenarios and its effect on the marine ecosystem.

A research team composed of experts from universities of Bristol, Leeds, Cardiff, Woods Hole Oceanographic Institution and Colgate University were able to publish their paper in Science regarding the examination of uranium levels linking it to ice sheet retreats. According to a press release from the University of Bristol, the researchers tried to track down and measure uranium and its isotopes, namely uranium-238 (238U) and uranium-234 (234U) that have varying atomic masses and radioactive decaying rates, as these may help in providing temporal information.

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The element uranium, aside from being known as a component of nuclear weapons and explosives, is also naturally present in many rocks. Following the concept of plate movements, continental rocks are vulnerable to erosion, thus providing traces of uranium to be available in the oceans.

"Subtle changes in the ratio in seawater have the potential to tell us about past changes in weathering. This is important because it is the input of material from the land to sea that provides the nutrients needed to support life in the ocean. However measuring these ratios is not easy because the changes are small, and the record is not easily preserved. It turned out that reliable reconstruction of past seawater 234U/238U was quite challenging," said Dr. Tianyu Chen of the School of Earth Sciences, University of Bristol, the lead author of the study.

The team's findings as featured on Science Daily showed that the deep-sea corals from the Pacific Galapagos area and equatorial North Atlantic have excellently provided a good overview of the glacial retreats which happened within the last 50,000 years. It was noted as well with their generated data that around 11,000 to 18,000 years ago, the latest deglaciation happened.

According to the authors, the uranium isotopes traced in the study were hypothesized to be released in the oceans due to the meltdown of ice sheets underlying the rocks that moved from time to time. The "melting" of the frozen ground rocks during the warmer periods significantly increased the release of uranium isotopes in the ocean.

There was also a clear variation between the isotopes of Atlantic and the Pacific around 17,000 years ago (during the glacial event) but since an overturning happened in the waters of Atlantic region, both areas' 234U and 238U levels were normalized, with similar measurements until present.

"Previous interest in the excess uranium-234 in the ocean has stemmed from its importance in determine [sic] the age of fossil corals," Dr. Chen added. "Fossil corals from reef areas have been used to establish the timing of major sea level change in the past. Our study puts new constraints on how these ages are calculated and verified."

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