From EMSL: “Improved understanding of a widely used ‘thermometer’ for Earth’s ancient oceans”

EMSL

EMSL

June 16, 2017
Tom Rickey
tom.rickey@pnnl.gov
(509) 375-3732

1
Foraminifera – a key to understanding ancient Earth. Credit: Jennifer Fehrenbacher/Oregon State University

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.

Earlier from EMSL:

Daily Light/Dark Cycle Controls Patterns within Marine Protist Shells

The trace element composition of the calcite shells of foraminifera, sand grain-sized marine protists, is commonly used to reconstruct the history of ocean conditions in Earth’s past. A recent study explored environmental and biological factors that control the compositional variability of the element magnesium (Mg), which is used to reconstruct past ocean temperature.

The Impact

These findings suggest the same light-triggered mechanism is responsible for Mg banding in two species that occupy different ecological niches in the ocean, and that Mg variability is an integral component of shell-building processes in planktic foraminifera. The experimental results will be used to update a 70-year-old model of foraminifera shell development and could be used to develop more accurate methods for assessing past ocean conditions.

Summary

The relationship between seawater temperature and the average Mg/Calcium (Ca) ratios in planktic foraminifera is well established, providing an essential tool for reconstructing past ocean temperatures. However, the mechanism responsible for variability in the trace element composition within individual shells is poorly understood. In particular, many species display alternating high and low Mg bands within their shell walls that cannot be explained by temperature alone. Recent experiments demonstrate intrashell Mg variability in Orbulina universa, which forms a spherical terminal shell, is paced by the daily light and dark cycle. Whether Mg heterogeneity is also controlled by the light and dark cycle in species with more complex shell structures was previously unknown. To address this knowledge gap, a team of researchers from Oregon State University; University of California, Davis; University of Washington; and EMSL, the Environmental Molecular Sciences Laboratory, a DOE Office of Science User Facility, combined culture techniques and high-resolution NanoSIMS imaging to show high Mg/Ca-calcite forms at night (in dark conditions) in cultured specimens of the multi-chambered species Neogloboquadrina dutertrei. The results also demonstrate N. dutertrei adds a significant amount of calcite, as well as nearly all Mg bands, after the final chamber forms. These results have implications for interpreting patterns of calcification in N. dutertrei, and suggest daily Mg banding is an intrinsic component of biomineralization in planktic foraminifera, likely modified by growth conditions. Moreover, the findings suggest the overall Mg content of the shell is primarily controlled by temperature, while the amplitude of the intrashell banding, which is triggered by a light response, is modulated by pH. By shedding light on mechanisms that control Mg variability in the shells of diverse planktic foraminifera, the findings could lead to improved methods for reconstructing past ocean conditions.

PI Contact

Jennifer S. Fehrenbacher
Oregon State University
fehrenje@coas.oregonstate.edu

EMSL Contacts

Zihua Zhu
EMSL
zihua.zhu@pnnl.gov

John Cliff
EMSL
john.cliff@pnnl.gov

Funding

This work was supported by the U.S. Department of Energy’s Office of Science (Office of Biological and Environmental Research), including support of the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility; and the U.S. National Science Foundation.

See the full article here .

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