Oceanographer Sophie Bonnet, a specialist in ocean deserts, is studying the role of phytoplankton in ocean carbon sequestration. Her research project, Hope, is opening up new perspectives, tinged with hope.
“Women oceanographers (3/12). They have made the ocean their object of study, sometimes even their main concern.Physicists, chemists, geologists or biologists, they all contribute to improving our knowledge of the marine environment. Océans connectés sets out to meet them across France.
By Marion Durand.
Cover photo © Marion Durand
Changing the game. Sophie Bonnet remains modest and measured but, it has to be said, her research work makes you smile. She has already been working for six months on the ‘Hope’ project, which is studying the capacity of our tropical oceans to sequester CO2, in other words, to trap the carbon present in the atmosphere.
The ocean’s role in the carbon cycle is unequivocal: it captures 30% of the CO2 emitted by humans. But could marine micro-organisms absorb even more? This question is at the heart of the work being carried out by Sophie Bonnet, Director of Research at theMediterranean Institute of Oceanology (MIO) in Marseilles. Her project, funded by a European ERC Consolidator grant, is studying the role of ocean deserts in the biological sequestration of carbon. “I’m cautious about the hopes pinned on the Hope project. I want to remain measured, it’s not going to change everything. But today’s pessimistic scenarios could be a little less so.
A new field of research
Various phenomena are involved in the sequestration of CO2 by the ocean. Among these, phytoplankton absorb carbon through photosynthesis, so that it is transferred along the food chain and, when the organisms die, this carbonaceous material sediments to the ocean floor. Tropical and subtropical zones are considered to be inefficient in this process because they are low in nitrogen, an essential nutrient for plankton. Yet they account for 50% of the global ocean.
Sophie Bonnet’s research has shown that these ocean deserts are not excluded from this ‘biological carbon pump’ phenomenon because they are home to another type of plankton: diazotrophs. “These micro-organisms fix CO2 like traditional phytoplankton and are also capable of transforming dissolved nitrogen gas to make it available to themselves and other organisms. In this way, they fertilise the marine environment like a natural fertiliser,’ explainsthe oceanographer from Marseilles. Until now, we thought that this area of the ocean played only a minor role, or even none at all, but these new processes are proving to be very effective’, enthuses the researcher from the French National Research Institute for Sustainable Development (IRD).
Sophie Bonnet ©Anne Desnues, IRD
Sophie Bonnet has already highlighted the role of diazotrophs, but it remains to be seen to what extent these micro-organisms are involved in the carbon cycle. The answers provided by the ‘Hope’ project could ‘modify climate change forecasts’, she says, because ‘these processes are not yet integrated into climate models, which probably distorts future predictions’.
An autonomous buoy off the coast of Noumea
While the first phase of this project took place in the south of France, in the laboratory in Marseille, the next phase will take place on the other side of the world. Starting next year, Sophie Bonnet will be heading for the Pacific for the next two years. The project includes the deployment of an autonomous platform in the open sea, carrying innovative technologies and high-tech sensors. This multi-instrumented buoy, measuring five metres in diameter, will be launched off the coast of Nouméa, New Caledonia, in March 2024. It will explore the ocean surface and at depth ‘to an unprecedented biological degree’ and will sample the ocean every four hours for three years.
An instrumented buoy © Jean-Michel Grisoni, CNRS
‘When a new field of research is discovered, a new door opens’,Sophie Bonnet reminds us, even if her previous expeditions have already confirmed certain hypotheses about the role of diazotrophs. Back in 2020, she embarked on the Atalante, a French oceanographic vessel, in search of shallow submarine volcanoes off the Tonga Islands. The Tonga expedition identified a carbon sink that extends over an area of around 400,000 km in the middle of the South Pacific marine desert.
‘At night, the captain would take us to sleep ‘in the garage’, an expression which means that the boat is moved to the middle of the ocean, away from the volcanic arc, to avoid the gas bubbles emanating from the volcano disturbing the buoyancy of the ship’, she remembers.
400 days at sea
The oceanographer has coordinated a number of major expeditions in the Pacific Ocean and taken part in many other missions around the world. At the age of 45, this mother of two little girls has already spent 400 days at sea. Fifteen months plus a year sailing between West Africa and Madagascar. At the age of 19, Sophie Bonnet wanted to experience ‘personal adventures and get involved in causes close to her heart’ before embarking on her years of study. She set sail with navigator Michel Huchet. In one year, they crossed the Atlantic. Keen to ‘travel in a useful way’, they set up the Voiles sans frontières association to bring aid to isolated populations that are only accessible by sea or river. ‘A lot of sailors are looking for meaning when they set out to sea, so we enabled them to add a humanitarian dimension to their journey’. The association, of which she was president for ten years, is still active.
Sophie Bonnet © Armelle Renaud, IRD
On her return, she enrolled on a course at Sorbonne University to pursue the career she had dreamed of since childhood. “It all started in Corsica. That’s where my fascination for the sea began. I used to spend hours underwater with a mask over my face. I was in awe of that column of water,” she laughs. One day, a friend told me she wanted to be an oceanographer. I must have been 11. I didn’t know the word, but I learnt that you could make a living studying the sea.She never became an oceanographer, but I did.
Considering the attractiveness of the profession
Does reality live up to his childhood dreams? It certainly has. ‘It’s a great honour to be trusted with the Hope project, but it’s also a bit of pressure and a lot of work,” she sums up, adding that she is one of the few oceanographers who doesn’t work at weekends or in the evenings.
“It’s a job that demands a lot of time and commitment. Many students don’t want to continue in research because the workload is too heavy and it takes too long to get a permanent position, which is a barrier, especially for young women.
She continued: “We have a personal responsibility and we need to set limits. We also need to think collectively within the laboratories to make the job of researcher more pleasant and more attractive! The oceanographer is concerned about the consequences of this lack of interest on the part of young people, ‘they refuse to put their job before their life’.
Sophie Bonnet © Hugo Berthelot, Ifremer
For Sophie Bonnet, making the profession more attractive also means showing ‘what goes on behind the scenes’. With the Hope project, the research director wants to launch a series, ‘we hope’, of videos and sound clips to shed light on the day-to-day lives of researchers : ‘I want to talk about their lives and their work, their day-to-day feelings. I want to give everyone a voice: women, research students, PhD students’. Above all, she wants to “show that there is room for everyone. Depending on your talents, the marine sciences offer a wide range of fields of research’.
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