Interview: "Phytoplankton makes the Southern Ocean a significant carbon sink"

In this interview, iC3 researcher Sebastien Moreau talks about his work on biogeochemical cycles in the Southern Ocean and the importance of phytoplankton in the carbon cycle.

Could you briefly introduce yourself and explain the focus of your research at iC3?

My name is Sebastien Moreau. I am a biological oceanographer working at the Norwegian Polar Institute, focusing on marine biology and biogeochemical cycles in the Southern Ocean. My work involves field expeditions to collect water and sea ice samples, which I then analyze in the laboratory.

I am particularly interested in the carbon and nutrient cycles in the Southern Ocean. In addition to field samples, I use sensors and devices like gliders, BGC Argo floats, and sediment traps to gather data over seasonal or multi-year periods. These tools help measure processes like the biological carbon pump. I also incorporate satellite data and models in my research.

Credit: Marius Bratrein (Norwegian Polar Institute)

Why is this important to study?

My research is important because the Southern Ocean is a significant carbon sink, capturing a large portion of atmospheric CO2. Marine organisms, especially phytoplankton, play a crucial role in this process through the biological carbon pump. Understanding these mechanisms is vital for assessing the Southern Ocean's role in global climate regulation.

Do you have a specific region of focus in the Southern Ocean?

My primary focus is the eastern part of the Weddell Gyre, specifically the King Haakon VII Sea, where we conduct annual sampling and maintain moorings. I also study other regions of the Southern Ocean, including the sub-Antarctic island of Bouvet, which features unique marine systems influenced by the Antarctic Circumpolar Current.

Could you give an example of a concrete application of your research?

During a recent cruise to the King Haakon VII Sea, we observed the effects of sea ice melting on the upper ocean. During this expedition, we documented a significant phytoplankton bloom triggered by the melting sea ice, which releases iron and stratifies the upper ocean, creating favorable conditions for phytoplankton growth.

Credit: Delphine Lannuzel (University of Tasmania, Australia)

How did you come to work at the Norwegian Polar Institute?

I joined the Norwegian Polar Institute because of its prestigious reputation and its alignment with my research interests in Southern Ocean marine biology. The institute's focus on fieldwork and long-term ecosystem monitoring is invaluable for understanding climate change impacts.

How has your research focus evolved since the beginning of your career?

While my research has remained focused on Southern Ocean marine biology, I have expanded to study various regions, including coastal areas, polynyas, and sub-Antarctic zones. I’ve also incorporated sea ice research and modeling into my work, which has broadened my perspective on cryosphere-ocean interactions.

What qualities and skills do you look for in a postdoc or collaborator?

I value strong computational skills, expertise in biogeochemical cycles, and an interest in fieldwork. Working with data from BGC Argo floats or conducting incubation experiments on board are examples of potential research avenues. Candidates with experience in modeling or marine biology would also be a great fit.

What technologies or methodologies are you most excited about in your field?

One of the most exciting advancements in my field is the use of BGC Argo floats, which provide extensive data on ocean physics, biology, and biogeochemistry across the Southern Ocean. These instruments have revolutionized our understanding of marine systems, offering unprecedented insights into seasonal and regional variations.

Can you describe a particularly memorable moment or breakthrough in your research?

A memorable moment in my career was a cruise to Antarctic polynyas, where I learned about glacier melting and its interactions with the ocean. This experience sparked my interest in cryosphere-ocean interactions, and ultimately led me to iC3.

Credit: Sebastien Moreau

What big question would you like to answer in the future?

I aim to find out how Southern Ocean ecosystems and biogeochemical cycles will respond to climate change. Observing and understanding these changes is critical for predicting the Southern Ocean's future role in Earth's climate.

How would you allocate an unlimited budget for your research?

With an unlimited budget, I would deploy more instruments, conduct year-round cruises, and support PhD students and postdocs to analyze data and advance Southern Ocean research.

What does an ideal day off look like for you?

An ideal day off would be a sunny day in April in Tromsø, going for a top tour with friends, climbing up a nice mountain, and then skiing down with a splitboard. I’d end the day playing with my kids, maybe going to an ice rink to skate and play ice hockey.

Could you share a book or a movie that has significantly influenced you?

One of my favorite books is Samarkand or Léon l’Africain by Amin Maalouf. These books are about adventures, which I find inspiring. Recently, I also enjoyed Les Naufragés du Wager, which tells the story of a British army ship that sank near Cape Horn during a colonial war with Spain. The survivors ended up on an island and tried to survive—it’s a fascinating tale of adventure and resilience.

What’s one thing you’re looking forward to in the next year, either personally or professionally?

I’m looking forward to a large campaign next year with the Norwegian icebreaker heading to Antarctica. This is something we’ve been waiting for six or seven years, especially since we launched iC3.

The cruise will allow us to conduct critical measurements, particularly in terms of trace metals, which we currently lack the capacity to analyze at the Norwegian Polar Institute. It’s going to be a major highlight for me and for iC3.

If you are interested in applying for an MSCA postdoctoral fellowship with Sebastien, please read this first and then send him an email briefly outlining your proposed research project and enclose your CV. 

Sebastien Moreau is a researcher at the Norwegian Polar Institute and at the Department of Geosciences at UiT The Arctic University of Norway. His research focuses on phytoplankton and the biogeochemistry of polar oceans.