In October 2022, Professor Marissa Tremblay of the Purdue University Department of Earth, Atmospheric, and Planetary Sciences (EAPS), led a four-woman team to conduct fieldwork in one of the most remote places on Earth: Antarctica.
Today, most of Antarctica is covered by ice sheets. These ice sheets are vulnerable to ongoing climate change. But just how vulnerable are they, and how much will they contribute to sea level rise as our planet continues to warm? To help answer these questions, scientists like Professor Tremblay look to Earth’s past climate, to time periods when the geologic record tells us that the planet was warmer and sea levels were higher.
One time period, known as the mid-Pliocene Warm Period, is of particular interest. During this time period 3 to 3.3 million years ago, carbon dioxide concentrations in the atmosphere were similar to today, and sea levels were 50 feet or more higher, about the height of a 5-story building! This required the entire Greenland ice sheet to have melted, as well as significant portion of the Antarctic ice sheets.
How warm was the Antarctic continent when this happened? This is a difficult question to answer, in part because we don’t have any local, land-based records of Antarctica’s past climate that extend this far back in time. Our oldest Antarctic ice cores extend back to 800,000 years, and we have some snapshots of what Antarctica’s climate was like 2.7 million years ago from unique, relatively new blue ice records. But nothing on the continent has taken us back to the mid-Pliocene Warm Period.
Until now.
Professor Tremblay and her team spent weeks traveling to different parts of the McMurdo Dry Valleys of Antarctica, collecting samples of rock and installing instruments to measure present- day temperatures, all in hopes of revealing just how warm Antarctica was during the mid-Pliocene Warm Period.
Professor Tremblay pioneered a technique that looks at rare chemical species in rocks that enables her to say what temperatures the rocks have experienced while they have been sitting at the Earth’s surface.
She’s applied this technique to study the past climate in places like the European Alps on relatively recent timescales of hundreds to a few tens of thousands of years.
"I am extremely grateful to the U.S. Antarctic Program and the National Science Foundation for providing the support that makes this remote field work possible," says Tremblay.
So how will Professor Tremblay and her team use this technique, called cosmogenic noble gas paleothermometry, to go back millions of years in Antarctica? The McMurdo Dry Valleys region is aptly named: this region of Antarctica is incredibly dry, and has also been ice free for many millions of years.
This means that rocks in the McMurdo Dry Valleys have been sitting at Earth’s surface, eroding at unfathomably slow rates: only a few centimeters per million years.
And throughout those millions of years, the rocks at the surface in the McMurdo Dry Valleys have been exposed to cosmic rays, high-energy particles ultimately originating from outer space.
These cosmic rays interact with the atoms in rocks to generate the rare chemical species that Professor Tremblay uses to study past temperatures.
Professor Tremblay’s field team included her co-principal investigator Dr. Jennifer Lamp of Lamont-Doherty Earth Observatory, Dr. Marie Bergelin of the Berkeley Geochronology Center, and boilermaker graduate student Emily Apel. Emily’s Ph.D. research centers around reconstructing mid-Pliocene temperatures in Antarctica, and she will lead the charge to prepare the rock samples the team collected after the samples make their long journey back to the United States by ship this spring.
The field team often also included a field coordinator from the Berg Field Center at McMurdo Station, a bustling research station on the tip of Ross Island operated by the United States Antarctic Program.
For much of the field season, the team was based out of McMurdo Station. They reached their most remote and exposed field sites by helicopter, with just a few hours on the ground to identify and collect samples, as well as install their instruments, which will be retrieved in early 2023.
"In many ways, our research on the past climate of Antarctica is only just beginning! Once the rocks we collected to make their way back to Purdue this spring, we will spend many months to years studying their chemistry to unlock their climate secrets," says Tremblay.
A photo gallery of the stunning Antarctic landscape and the research team in action
#boilerup
Credits:
Photos by Dr. Marissa Tremblay, Assistant Professor at Purdue Earth, Atmospheric, and Planetary Sciences