Home > Boats, planes, trains, and automobiles: A global journey to understand sea-surface temperatures during the Pliocene and Pleistocene eras

Boats, planes, trains, and automobiles: A global journey to understand sea-surface temperatures during the Pliocene and Pleistocene eras

Written by: Allison Preston

Three continents, five countries, and countless hours spent traveling by boat, plane, train, and car. To say Alejandra Cartageña-Sierra's research is her passion project is an understatement. The past year has been a wild ride for the Ph.D. candidate as she studies sea-surface temperatures (SSTs) during the Pliocene and Pleistocene epochs around southern Africa, a region that has rarely been explored due to plenty of roadblocks and red tape. 

Cartageña-Sierra's journey began in 2016 with a two-month voyage at sea accompanied by her advisor, Professor Melissa Berke, and a crew of 27 other Ph.D. students, professors, and researchers.

“It was a big honor to be on the expedition,” said Cartageña-Sierra. “I was the youngest one there, the one with the least experience, and therefore, thirsty for knowledge.”

The boat set sail from the island of Mauritius near Madagascar. From there the crew would make their way to South Africa, ending in Cape Town. There were several obstacles in place that made the research process long and arduous. The location was ideal for the lack of data from that area, yet research off the coast of southern Africa was limited for several reasons.

“It is hard to get there, the ocean is not always your best friend in that area, and piracy is still an issue in that region,” said Cartageña-Sierra. “Plus, it is really hard to get the licenses and permits to drill and work, we had to wait almost 10 days on sea just to get permission.”

Days were filled with sample collection of mud from the ocean floor, description, and analyses of those samples, and weekends were not a time for relaxing. Considering this was just the beginning of her long academic odyssey, there was no time to give in to exhaustion. 

Texas and Utah

Following the ocean voyage, Cartageña-Sierra and the other researchers gathered in Texas to join the “Sample Party” where more than 36,000 were taken from the cores that were recovered during the expedition at sea. The samples she was most interested in contained the climatic history of the last five-million years along with potential links to changes in the global climate during that period of time. Using the samples, Cartageña-Sierra would be able to reconstruct the past sea surface temperature and salinity to understand how the variability of these parameters could affect or could be affected by major global climate transitions within the past five million years.

“This is important to us right now because one of the periods I am reconstructing is the mid-Pliocene warm-period, and that was the last time the planet experienced global mean temperatures higher than today’s,” said Cartageña-Sierra. “The average temperature was two-to-three degrees higher than what we have right now and the carbon dioxide levels in the atmosphere was close to what it is today, so we believe that even though we did not have the same players, it is in our best interest to try to understand how this planet behaves under these conditions, at least locally.”

But before she could analyze her samples, Cartageña-Sierra traveled to Utah for a two-week summer camp where she learned how to use the equipment and instruments necessary to test the samples she collected in Texas.

“It was interesting because I was able to talk to oceanographers about the correct terminology.”

It also gave her the opportunity to hear feedback on her research, the good and the bad.

“One of them was like, why would you think that? Why would you want to try that?” said Cartageña-Sierra. “Then I asked these two researchers who are well known and they said to try it!”

Equipped with new techniques and knowledge, Cartageña-Sierra returned to Notre Dame and was finally able to start working with her samples. The first time period she focused on was the Plio-Pleistocene transition, covering from 3.0 to 1.8 million years ago.

Italy and the Netherlands

After countless hours in the lab, Cartageña-Sierra packed her bags for Italy in September 2017 to present her research at the International Meeting of Organic Geochemists. She was awarded the Geological Society of America Graduate Student Research Grant to support her project, Temperature Reconstructions of the Agulhas Corridor during the Plio-Pleistocene Transition. She also received the 2017 European Association of Organic Geochemists Travel Scholarship Award to continue her work at the Royal Netherlands Institute for Sea Research.

The opportunity to work in the Netherlands was invaluable and the facility had an awe-inspiring amount of instruments for analysis.

“The dream,” said Cartageña-Sierra. “We only have one of these instruments at Notre Dame. They have many instruments dedicated to analyzing specific molecules at the Royal Institute.”

It was no easy feat traveling from Italy to the Royal Netherlands Institute for Sea Research.

“You had to first fly to Amsterdam, then take a train to a little town nearby, then take a bus to the ferry, and then take a ferry to the island,” said Cartageña-Sierra. “I tried every kind of transportation there was!”

Upon arrival, Cartageña-Sierra had the opportunity to work with renowned researcher Dr. Marcel T.J. van der Meer who showed her how to use the instrument, perform analyses, and served as a sounding board and mentor for her research.

“He told me he was really interested in my work, his favorite word to use was, intriguing!” said Cartageña-Sierra. “It was so exciting to see someone else excited about my research.” 

Cartageña-Sierra's priority was trying to reconstruct sea surface temperature and salinity variability through the utilization of molecular fossils, alkenones, from sediments. In order to get the relative salinity from the molecules, she needed to analyze the hydrogen isotopic composition of alkenones. 

"We have the instrument needed to measure these molecules at Notre Dame but the problem is nobody here has done it before,” said Cartageña-Sierra. "The instrument needs to be set a certain way and the results need to be manually integrated.”

Dr. van der Meer's expertise was especially helpful for Cartageña-Sierra to be able to learn how to use the necessary tools for her research. He also provided plenty of feedback and guidance for what her next steps should be. 

After three weeks it was time to pack her bags and return back to Notre Dame. Cartageña-Sierra will now be focusing on another time period and will work with younger samples to analyze the climate transitions between different periods of time. Her suitcase will barely have time to collect dust before she is back on the road again, this time to work with a professor in Massachusetts.