Marie-Noëlle Houssais is CNRS research director at the Laboratory of Oceanography and Climate: Experimentation and Numerical Approaches (LOCEAN). This physical oceanographer, who specialises in the polar regions, is interested in the link between the cryosphere, the atmosphere and the ocean.
“Women oceanographers (8/12). 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
On this cold January morning, we meet an oceanographer who has set her sights on the Earth’s smallest and most mysterious ocean: theArctic Ocean. Marie-Noëlle Houssais has been studying the dynamics of the polar oceans for 40 years, trying to understand how they interact with the pack ice, the frozen layer on the surface.
The polar regions have always fascinated Marie-Noëlle Houssais, more attracted by the desert side than by the icy wind. Yet the sub-zero temperatures have never repelled the oceanographer-physicist, who has taken part in more than twenty missions to reach the poles. The first to the Arctic was in 1980. “I embarked on a Norwegian ship, and there were only men on board, top oceanographers. I was still a student and very intimidated. A local newspaper, present for the departure, wanted to interview me to find out what it was like to be a woman on a ship’, she recalls. The crossing lasted weeks, the sailing conditions were harsh and the work difficult: “We were launching a probe in a place totally exposed to the wind and snow. It was a difficult first experience because I was ill, but a very rewarding one from a scientific point of view.
Today, the journey is less trying but still complicated. For a two-week mission in the Antarctic waters off the coast of Terre Adélie, another object of his research, she has to face the crossing of the Howling 50th from Tasmania.
French researchers are forced to set up European or international partnerships to reach these remote regions because France does not have an icebreaker dedicated to research, a vessel designed to navigate in ice-covered waters. ‘Polar researchers are to some extent the hitchhikers of oceanography’, laments the CNRS research director at the Laboratoire d’Océanographie et du Climat : expérimentation et approches numériques(LOCEAN), a joint research unit under the auspices of four supervisory bodies: Sorbonne University, the National Centre national for Scientific Research (CNRS), the French National Institute for Sustainable Development (IRD) and the Muséum national d’histoire naturelle.
The supply ship L’Astrolabe sailing in the pack ice among the icebergs off Adelie Land (© Claudie Marec)
The Arctic, a vulnerable region
The poles may be among the least accessible parts of the globe, but what happens there is no less important. ‘The Arctic regions are undoubtedly among the most vulnerable to climate change,’ says Marie-Noëlle Houssais. The Arctic Ocean is bearing the full brunt of the consequences of climate upheaval: air temperatures are rising twice as fast as in the rest of the world, sea ice is melting and biodiversity is being lost.
These phenomena are well known, but the interactions between the atmosphere, the ocean and the sea ice remain uncertain. “I’m trying to understand how these environments interact: how the pack ice filters the effects of the atmosphere on the ocean and how the ocean can influence the pack ice.
For several years, the physicist and her team have been installing moorings equipped with sensors that measure the temperature, salinity and currents in the water column at the entrance to the Arctic Ocean, north of Svalbard. “This is where the Atlantic waters, which are relatively warm and salty, enter the Arctic, a cold ocean with a low surface salinity.The aim is to understand how these contrasting waters interact with the pack ice and create episodes of melting, including in winter.
The data collected by these French moorings, coupled with that collected at other sites maintained by European colleagues and spread out along the Arctic, provide a time series for studying the variability of this polar ocean. “What we see in winter is that the water under the ice warms up during very short events, not a continuous diffusion of heat towards the ice but very brief episodes. There is also a great deal of inter-annual variability, probably linked to the variability of the ice’.
Real-time monitoring of CTD profile acquisition in Commonwealth Bay, Antarctica, during the ALBION 2008 oceanographic campaign(© Mickael Beauverger)
This information is invaluable, as the Arctic remains an under-sampled region. Monitoring the polar oceans is more difficult because the thick layer of ice on the surface makes it impossible to observe from space. Satellite remote sensing offers large-scale observations in almost real time, but it is more difficult to use them for the polar oceans. “We can observe the pack ice from space, but to study the water column in the poles, we need to use other autonomous means: moorings, which are still very heavy and very expensive, or drifting floats, but these autonomous systems, under the ice, need to be able to be positioned and transmit their data.
To collect more data in situ, we need to consider a multi-instrument system comprising buoys spread out over the ice pack, underwater platforms equipped with different sensors and acoustic sources and receivers spread out over the ocean.
“We don’t know who will take over”
At the start of her career, Marie-Noëlle Houssais did a lot of coding. ‘When I started, we were at the very beginning of ocean modelling, coding the first French ocean model, which became the Nemo model, coupled with pack ice’. At the dawn of the 2000s, and after 10 years of numerical modelling, the native of Brittany turned to observation and took part in six scientific campaigns in the Greenland Sea before leading a project on the formation of deep waters on the Antarctic shelf off the coast of Terre Adélie.
In a year’s time, her long career as a physical oceanographer will come to an end. But there’s no question of hanging it up: the physicist wants to continue research as a professor emeritus. ‘A generation of researchers is about to leave and we don’t know who will take over from them. In polar oceanography, especially in physical oceanography, recruitment is becoming a real problem. It’s very worrying. The physical oceanographer at the poles is disappearing ‘.
She believes that the lack of resources is to blame for the lack of applicants: “France prides itself on being a great polar nation, but we are cruelly lacking in resources. We’ve been warning for years that if we’re not given the resources, we won’t be able to train the new polar oceanographers, because if they can’t go to sea, they’ll move on to other disciplines.The fewer resources we make available, the less interest we generate in these regions!
Marie-Noëlle Houssais © Marion Durand
A tipping point
And yet, the poles need to be preserved more than ever. The extent of the Antarctic ice pack has never been so low for a month of January, according to the Copernicus climate change observatory. In 44 years of satellite observations, the Arctic ice pack has shrunk dramatically, with more global implications: ‘Studies suggest that changes in the Arctic may influence the climate in Europe’, warns Marie-Noëlle Houssais.
The melting of the Earth’s cryosphere, in which the ocean seems to be playing an increasingly obvious role, is inevitably leading to a rise in sea levels: “If the Antarctic ice cap destabilises, several metres of water will be released!
According to recent studies, the currents in the Atlantic Ocean may be slowing down as the climate warms, which could have consequences for global weather conditions. “The Atlantic meridional overturning circulation redistributes heat around the planet, transporting warm water from the tropics to the poles. It is fed by the cold, salty water, which is denser and dives deep into the polar regions before feeding the return circulation at depth’.
A slowdown in this overturning circulation would constitute a tipping point, a critical threshold beyond which the system could change irreversibly, as it would upset the current climate. Given these worrying prospects, ‘polar research is essential if we are to anticipate future upheavals in these regions and, beyond that, on a global scale’, concludes the oceanographer.
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