Although the Arctic Ocean is warming at an unprecedented rate, the local and global consequences of its rapid evolution remain uncertain. In particular, the ‘last ice zone’ north of Canada and Greenland is home to unique endemic ecosystems whose survival is closely dependent on the perennial presence of sea ice. As part of a thesis funded by the Priority Research Programme on Ocean & Climate, Corentin Gouzien is conducting an in-depth study of the microbial biodiversity of this remote region, in order to monitor in detail the ecosystem changes caused by climate change.
By Carole Saout-Grit
The Arctic Ocean plays a crucial role in the global climate by absorbing around 10% of atmospheric CO2 thanks to its cold waters and productive continental shelves. However, it is bearing the full brunt of the effects of climate change, which threaten many of its ecosystems, which are rich in unique endemic species.
Unique ecosystems at risk from the accelerated melting of sea ice
In the Arctic, the air temperature is increasing more than twice as fast as in the rest of the world, sea ice is retreating every year and the input of fresh water from melting coastal glaciers is gradually increasing. Over the last 40 years, scientists estimate that the extent of first-year ice has decreased by 10 to 15% per decade, and multi-year ice by 70%, directly threatening ecosystems dependent on sea ice.
The ‘Last Ice Area’ (LIA), which is the last sanctuary of multi-year sea ice in the Arctic Ocean, is located north of Canada and Greenland. The LIA includes the Lincoln Sea, which is home to unique endemic ecosystems. At the base of the food web, marine microbial communities are widely recognised as key players in the functioning of global ecosystems, playing crucial ecological and biogeochemical roles. While microorganisms form the basis of the marine food web and play an essential role in regulating the climate through their consumption and production of greenhouse gases, their biodiversity needs to be better understood and protected.
The Last Ice Area (LIA) © WWF / Ketill Berger
The marine microbiome*, a natural bioindicator of the health of the Arctic Ocean
After studying cellular and molecular biology applied to agronomy and human health, Corentin Gouzien wanted to put his skills in bioinformatics and genetics to use in the marine environment and in monitoring the health of the oceans in the face of global warming.
In this region far from the LIA, the research he has been conducting during his three-year PhD at the University of Nantes in partnership with the Sorbonne University and the CNRS, aims specifically to quantify the impact of changes in environmental parameters on the Arctic marine microbiome.
Corentin Gouzien in action on the Arctic ice floe- photo : Emmanuelle Jaouen
The research is based primarily on new holistic and standardised sampling in this region far from the Lincoln Sea. In October 2024, the expedition Refuge-Arctic** took place to collect more data in the Arctic, focusing in particular on the last area of multi-year ice. Once these field measurements have been taken, the work continues behind a computer to analyse the data collected.
Given the central role of the marine microbiome of the Arctic Ocean in maintaining and regulating biodiversity and associated ecosystem services, it has the potential to be used as a natural bioindicator to diagnose the health of the oceans. During his thesis, Corentin is therefore developing bioindicators targeting bacterial plankton and based on metagenomics (which brings together a set of technologies making it possible to understand complex and dynamic biological systems in their entirety, editor’s note).
To study the overall response of plankton to environmental changes in the Arctic Ocean, it analyses the relationship between the growth rate of the bacterial community inferred from genetic metrics and a set of environmental variables including water temperature. Data from ocean ecosystems and sea ice collected during large-scale campaigns in the Arctic (notably Refuge-Arctic**) are integrated for this purpose in order to decipher the spatio-temporal distribution of these relationships.
Deployment plan for the 4th set of measures taken during the Refuge-Arctique campaign in August 2024, in which Corentin Gouzien took part © Corentin Gouzien
In parallel, a second method based on graph theory is used to identify bioindicators. The idea is to predict the biological interactions that exist between bacteria to get a better idea of the potential interactions between bacteria in the Arctic, using genetic information. The objective is to highlight the characteristic properties of bacterial networks in the Arctic, properties that would be sensitive to the effects of climate change.
Corentin is conducting his thesis at the Digital Sciences Laboratory of Nantes University (LS2N), co-supervised by Samuel Chaffron (CNRS, LS2N), Mathieu Ardyna (CNRS, Takuvik) and Fabien Joux (SU) of the Microbial Oceanography Laboratory (LOMIC) of the Oceanological Observatory of Banyuls-sur-Mer. This research programme is funded by the Priority Research Programme PPR Ocean & Climate as part of its support for training through research.
Overall, this research is crucial to understanding the various local responses to climate change in the Arctic Ocean and the LIA in particular. Identifying microbial indicators of ocean health, such as genes and metabolic pathways, is a key research objective for monitoring ocean health. These bioindicators based on the ocean microbiome, using taxa and genes as specific signatures, could thus enrich oceanic indicators and offer an innovative approach, specifically adapted to Arctic ecosystems.
*microbiome: a microbial community that evolves within a well-defined habitat, the term referring both to the microorganisms and to this habitat.
** The Refuge-Arctic project was conducted with the help of the Canadian research icebreaker CCGS Amundsen with the support of the Amundsen Science programme funded by the Major Science Initiatives Fund (MSIF) of the Canada Foundation for Innovation (CFI). We would like to thank the officers and crew of the CCGS Amundsen as well as Aurélie François, Bastian Raulier, Claudine Ouellet, Flavienne Bruyant, Guislain Bécu, Audrey Limoges, Juliette Provencher, Marcel Babin, Marie-Hélène Forget, Mathieu Ardyna, Matthieu Huot, Sébastien Guérin and the entire TAKUVIK laboratory team for planning the fieldwork, as well as all the other scientists and technicians involved in the Refuge-Arctic campaigns for their contribution to the fieldwork and data collection. The project was carried out under the scientific coordination of the Takuvik International Research Laboratory (IRL3376, CNRS/Sorbonne University/Laval University). We would also like to thank Québec-Océan and the Polar Continental Shelf Program for their in-kind contribution in terms of polar logistics and scientific equipment. The Refuge-Arctic project is funded by the following French and Canadian programmes and agencies: Amundsen Science, ArcticNet, BNP Paribas Foundation, Centre national d’études spatiales (CNES), Centre national de la recherche scientifique (CNRS), Crown-Indigenous Relations and Northern Affairs Canada (CIRNAC), European Research Council (ERC), French Oceanographic Fleet (FOF), Institut Nordique du Québec (INQ), Institut français de recherche pour l’ exploitation de la mer (IFREMER), Institut Polaire français Paul-Émile Victor (IPEV), Les Enveloppes Fluides et l’Environnement (LEFE), Mission for Interdisciplinary and Transverse Initiatives (MITI), Natural Sciences and Engineering Research Council of Canada (NSERC), Fisheries and Oceans Canada (DFO), Sentinelle Nord and Université Laval.
Reference : Corentin Gouzien, « The planktonic microbiome of the Arctic Ocean as a bioindicator of biodiversity and its resilience to climate change », thesis 2023-2026
Contact : gouzien@obs-banyuls.fr
3 Questions to Corentin Gouzien
Why did you want to do a thesis in marine sciences?
A thesis is an opportunity to continue learning and ask questions about subjects that fascinate us. I think it’s great that, in a way, society gives us time to reflect, perhaps in the hope that it will benefit them in the long term.
The marine environment echoes deeper instincts. Perhaps it is the fact of working on a daily basis in an environment whose vastness awakens serenity in me.
What made you want to apply for this thesis topic? What were your motivations?
During my studies, I mainly studied the cellular and molecular scale through examples in agronomy or human health. I wanted to acquire the tools specific to this scale, but keeping in mind the desire to return to the marine environment. When I saw this thesis offer, combining bioinformatics, genetics and the marine environment with fieldwork, I didn’t hesitate.
How do you imagine your future after this thesis?
I don’t have a clear idea of my professional future. I hope to continue working on subjects that are meaningful and that I believe are useful to society.