Evolution of Pacific Meridional and Zonal Sea Surface Temperature Gradients Over the Past Five Million Years

Katherine Huska ’15, Environmental Studies

Laura Peterson, Associate Professor of Environmental Studies/Chemistry

About the Project

“Our goal was to understand climate dynamics during an interval of geologic time called the Pliocene (~3-5 million years ago),” Peterson says. “It’s the most recent time in Earth's history when climate conditions were warmer than today and comparable to projected climate conditions for the next century as a result of anthropogenic global warming.”

Huska says that the project focused on two points. “Our first goal was to generate a sea surface record for a southern hemisphere site in the Pacific Ocean for the last 5 million years,” she says. “The second is to use the data to look at ocean temperature gradients to better understand how the oceans and climate evolved over this time period.”

The Biggest Challenges

Both agree that the most difficult part of the project was working with such large data sets.

“The sea surface temperature records we generated are 5 million years long, with data points every 2-3 thousand years,” Peterson says. “That means we analyzed over 2,000 samples! It’s time-consuming work, but the reward is that we get a high-resolution record that allows us to make a more detailed assessment of sea surface temperature change at our site, and to better understand how changes at our site are related to patterns of climate change observed elsewhere.”

Huska agrees it was challenging work. “We were unable to explain some of what we observed, which led to some frustrating days,” she says. “However, our site is the first southern hemisphere record that showed symmetrical evolution with the northern hemisphere oceans. This is surprising since the northern hemisphere oceans were subject to major glaciation changes over this time period, while the southern hemisphere oceans were not.”

What’s Been the Most Fascinating Discovery?

“It looks like temperature changes at our southern hemisphere site very closely mirrored those from sites in comparable locations in the northern hemisphere,” Peterson says. “This symmetry is surprising because most of the climate change from the warmer Pliocene to the more recent, colder Pleistocene time period involved major changes in northern hemisphere climate associated with the growth of northern hemisphere ice sheets. It also looks as if southern hemisphere climate has been closely coupled with tropical climate dynamics, which may help us better understand the factors that sustained the permanent El Nino-like state of the Pliocene.”

Why This Research Is Important

“Studying warm climate intervals helps give us a better understanding of how we might expect the climate system to function in the future,” Peterson says. “We’re ultimately interested in connecting our results to hypotheses about what caused the warmth of the Pliocene. If the warmth is explained strictly by a change in atmospheric carbon dioxide, then it's reasonable to assume that our climate future will look a lot like the Pliocene, which may then lead us back to the permanent El Nino-like state that was believed to exist during the Pliocene. If instead, additional factors beyond a change in carbon dioxide helped maintained Pliocene warmth, there may be different implications for the future.”

How Will the Results Be Shared?

Katherine presented her research results at the North Central Section Meeting of the Geological Society of America in Madison, Wisconsin. The study was recently published in Nature Geoscience.