Interview: "I use a global ocean biogeochemical model to understand the impact of ice sheet nutrient delivery on ecosystems and carbon dynamics"

In this interview, postdoctoral researcher Onur Karakus discusses his research on Antarctic iceberg-derived iron and silicic-acid fluxes, ocean modelling, his vision of science, and his life beyond science.

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

My name is Onur, I’m a postdoc at iC3 working on iron and silicic acid fluxes from icebergs and meltwater discharge from the Antarctic Ice Sheet. I use a global ocean biogeochemical model that resolves nutrient and carbon cycling as well as phytoplankton–zooplankton ecosystem dynamics to study how these fluxes affect the Southern Ocean.

Credit: Aman Akeerath Mundanatt (Alfred Wegner Institute).

Why is it important to research this now?

Climate change is rapidly reshaping the cryosphere-ice sheets, sea ice, and iceberg discharge-and, in turn, the ocean’s physics and chemistry. To anticipate what comes next, we must quantify these impacts with observations and lab experiments, and complement them with models that test mechanisms, sensitivities, and future scenarios.

The cryosphere modulates freshwater and nutrient delivery - notably iron in the Southern Ocean - and alters stratification and upwelling. It thus influences the ocean’s capacity to absorb CO2 and sustain life.

At the heart are phytoplankton, the base of the marine food web. Using light and nutrients, they fix dissolved inorganic carbon into organic matter, shape air–sea CO2 exchange, and feed higher trophic levels. When phytoplankton die, they export particulate organic carbon via the biological pump. 

How does your previous work inform this research?

During my PhD at the Alfred Wegner Institute (AWI, Germany), I examined the biological carbon pump and how multiple zooplankton size classes shape vertical carbon flux and bloom timing using the model FESOM-REcoM. During my postdoc at the Woods Hole Oceanographic Institution (USA), I used a high-resolution regional model to study riverine nutrient impacts on the U.S. East Coast shelf. Conceptually, both address interactions between nutrients and lower trophic ecosystems in the ocean.

You are a modeller. Have you also done any fieldwork?

Yes-several research cruises in the Mediterranean, Irish Sea, U.S. East Coast, and the North Sea. I helped teams run the CTD, collect zooplankton and phytoplankton samples, and measure oxygen.

What new technologies or methods are you most excited about in your research?

High-resolution global models that better resolve mesoscale and submesoscale processes like eddies, which strongly influence nutrient supply and plankton dynamics. Also, accelerating models on GPUs rather than CPUs to shorten run times and enable more detailed or larger ensembles.

If you had an unlimited budget for your research, how would you use it?

I’d build a strong, synergistic team—PhD students and postdocs working together. Yes, compute time matters, but people matter more. Topics could include model development and parameterizations—like temperature dependence of growth tailored to specific phytoplankton functional types—grounded in experiments and observations.

Credit: Judith Hauck (Alfred Wegner Institute).

Can you share a memorable moment or breakthrough in your career?

Early on, I remember the satisfaction of tracing equations from the model documentation into the Fortran code and back to observations—really “seeing” the system and how to use it to answer questions. Also, every research cruise stands out; even as a modeler, being at sea is a highlight.

On a day off, how do you like to spend your time?

Outdoors—running, cycling, hiking—and I’d like to learn kayaking. I also enjoy cooking, often vegetarian. A favorite is Turkish-style chickpeas: onion and garlic sautéed with tomato paste, simple spices like black pepper and salt, then slow-cooked chickpeas, served with rice or bread.

Is there a book or film that has influenced you?

Rachel Carson’s The Sea Around Us. It’s beautifully written, weaving connections from planetary dynamics to ocean currents to phytoplankton. It’s an inspiring, accessible entry point for anyone interested in the ocean.

If you could travel anywhere right now, where would you go and why?

Antarctica—the continent. I’m drawn to unexplored, harsh environments. I’d love to go there to do research and experience those conditions firsthand.

If you are interested in joining the friendly iC3 team as a postdoc, please keep an eye out for 2026 MSCA grant opportunities. We expect to announce them on this website in late February. 

Onur Karakus is a postdoc working at the iC3 Polar Research Hub in Tromsø, the capital of the Arctic. To find out more about his work, please check out her list of publications, or contact him by LinkedIn or by email.