Meet Aja

Aja Trebec is a PhD candidate at the Biological Oceanography Group (GOB). Her thesis is framed within one of the priority objectives of the OceanICU research project. She discussed the aim of her thesis and the work she is doing onboard.

What is your role in the OceanICU project?

My objective is to study the effects of atmospheric deposition in marine plankton communities. My PhD is part of the OceanICU project, it is in particular conducted within the scientific work package 3 (WP3). Within it, we want to study the impacts of climatic multistressors: atmospheric aerosol deposition, temperature increase and the biological carbon pump.

We aim to vary the types of atmospheric deposition, studying not only desert dust deposition but also ash from volcanic eruptions and biomass burning.

What is the main goal of the dust fertilization experiment within OceanICU?

During this expedition, as part of the OceanICU project, we want to study the desert dust deposition. In particular, we are using Namibian dust from ephemeral rivers and Mauritanian dust from Sahara desert. The research vessel departs from Namibia and arrives to Palmas de Gran Canaria. Our target is to add Namibian or Sahara dust in the different regions we sail through, which have different temperatures, chlorophyll and oxygen concentrations. We will study how the initial populations present in seawater respond to these conditions in experiments.

How do you conduct these experiments?

These experiments involve collecting water as far away from the ship as possible, using trace metal clean techniques.  For this, we sample from an inflatable boat (Zodiac) and come back to the main research vessel.

The water is then distributed in different bags that are kept in containers used for incubation experiments. Desert dust is added to these bags and the experiment begins.

We are trying to see what the response is to dry deposition and wet deposition. In the first case, we simply add dry dust to the seawater collected. In the second case, the dust is dissolved in a solution that has the same pH as rain; leaving it for one day allows the dust to dissolve as much as possible. The rain solution is then incubated as well. The idea is to collect the water and follow the evolution in these treatments for 3 days.

On the second and third day, we subsample water for different objectives; among them, trace metals. Others include photosynthetic efficiency, microbial community structure (virus, heterotrophic bacteria and phytoplankton), environmental DNA, inorganic nutrients and dissolved organic matter (in particular carbon and nitrogen).

Onboard, we have the chance to look at the preliminary results from the experiments by analyzing the community structure with CytoSense, a flow cytometer, and photosynthetic efficiency with LabSTAF, a Single Turnover Active Fluorometry system. Based on these measurements, we have a first insight into what’s happening below the sea surface; however, we will know more once we get back on land and start analyzing all the other parameters.

Have you faced any unexpected challenges during your research?

Back on land, I was studying the nutrient limitation in the offshore waters of the Canary Islands. While doing so, I faced many challenges, from how to properly collect water using trace metal free techniques to how to coordinate people that helped me in these experiments. With all the experience acquired I came to the ship with the idea of taking my work to another level and adding dust to the seawater. But science is never what you expect, especially onboard, where you need a plan A, B and C; sometimes, even a plan D. You expect that everything will go well, but then you find yourself working in the tropical zone within a trace metal clean container with scarce air conditioning for hours. At the end of the day, you are just glad you did your best.  The high temperatures were surely one of the main challenges for me and Catarina, the colleague that helps me with these experiments.

What are the next steps in your research?

The first thing to do when I get back on land would be to get all the analysis from the onboard experiments done. The next step would be to try to experiment with ashes from wildfires to see whether there is any difference between desert dust aerosol and wildfire aerosol.

Are there any collaborations with other institutions that you’re excited about?

No, we don’t have surgeons onboard! Aja and Catarina finished their work for the day inside the container and pose with the clothing necessary to avoid metal contamination.

I am excited to collaborate with Catarina Guerreiro from the Lisbon University. I met her around five months ago through Zoom meetings to discuss how to conduct these onboard experiments. I am thankful that I have the possibility to work in close contact with a scientist that knows so much about desert dust deposition and marine plankton response and dynamics. This collaboration has truly transformed my day-to-day life. It is good to talk with external collaborators and immerse yourself in another type of environment, getting introduced to different perspectives and work styles. I really appreciate that I can see how Catarina works and learn a lot from her, but at the same time teach her some things that she has never done before in her line of work.

I am also really grateful for the collaboration with Jan-Berend Stuut from NIOZ (Royal Netherlands Institute for Sea Research), who kindly provided the dust samples for the experiments.