PNNL

Scientists have improved our ability to interpret one of the most common measures of the temperature of Earth's oceans in the distant past.

The measurement is based on the ancient remains of tiny marine organisms called foraminifera, a type of plankton that lives and feeds in water.

The organisms use calcium and magnesium from seawater to help form their shells — more magnesium when ocean temperatures are warmer and less when the temperatures are cooler. But magnesium levels can vary significantly within individual shells, and scientists have been exploring why.

In a paper published recently in Nature Communications, scientists explain that changes in light levels from daytime to nighttime can cause the organisms to vary how they build their shells, which plays a direct role in determining the levels of magnesium in the shells. The information gives scientists a better understanding of the biological processes involved when using this plankton-based temperature gauge to assess past ocean conditions.

The project was led by Jennifer Fehrenbacher of Oregon State University and also included scientists from UC Davis, the University of Washington, and EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science User Facility at the Pacific Northwest National Laboratory. The team included John B. Cliff III and Zihua Zhu from EMSL and PNNL.

For more information, see the reports from UC Davis, Oregon State University, or EMSL.