Mother-of-Pearl Holds the Key to Historical Ocean Temperatures

Studying this iridescent material in mollusk shells may give scientist a more accurate way to track historical ocean temps
Photo by Tony RinaldoPhoto by Tony Rinaldo
Scientific American
December 22, 2016
By Kavya Balaraman

A group of researchers think they’ve found a simpler, more accurate way to track historical ocean temperatures: studying nacre, or mother-of-pearl, under a microscope.

Mother-of-pearl is an iridescent material that’s found in mollusk shells. It forms in layers, which allows it to reflect light and shimmer. But these layers could be useful in another way, according to Pupa Gilbert, a professor with the University of Wisconsin, Madison: They provide a good estimation of the temperatures they grow in.

“The thickness of the layers becomes larger as the temperature increases, and then goes back down when the temperature decreases — so you can track the seasons based on it,” she explained.

The researchers documented their findings in a study funded by the Department of Energy, National Science Foundation and Radcliffe Institute for Advanced Study Fellowship Program, and published it in scientific journal Earth and Planetary Science Letters.

The structure of mother-of-pearl comprises small polygonal tablets. The rate at which these grow is based on the temperature of the water around them, explained Kristin Bergmann, with the Massachusetts Institute of Technology’s Department of Earth, Atmospheric and Planetary Sciences, and one of the study’s authors.

The team collected fossil samples of a species of saltwater clam — some of which were 200 million years old — and studied them to understand what influences the formation of the layers. While there are other factors that could contribute to their thickness, the researchers found a strong linear relationship between water temperature and the width of the tablets.

This finding could change the way scientists seek out data on ocean temperature. Current methods include studying the chemical composition of fossil shells, but as Gilbert pointed out, this can often be inaccurate. After a mollusk dies, the shells sometimes dissolve and then recrystallize — the new crystals will then capture water temperatures of a later period.

“You have one part of the shell that recrystallized a million years after [the mollusk] died, and another that did so 20 million years later — so when you measure the entire shell, you have a mess,” explained Gilbert.

Physically measuring elements of the shell, however, can help scientists avoid this problem. While there are certain drawbacks to this method, as well — for instance, the fluids inside the shell can sometimes start to eat away at it after death, altering its physical state — this is a much slower process than changes in chemical components.

Moreover, this methodology is also a lot simpler, less expensive and less equipment-intensive than trying to track the chemical composition of deep-sea sediments.

“It basically makes it possible for anybody to measure ancient temperature. The potential impact is huge, because any undergrad who knows how to do this can acquire the data and simply convert that into temperature,” said Gilbert.

“Of course, this all becomes relevant only once we have a ton of data from lots of people around the world. But because it’s so easy, I expect it to reach a lot of people,” she added.

Reprinted from ClimateWire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.

Search Year: 
2016