On the occasion of the UN Climate Week that takes place in New York from 23 to 29 September...
SOCLIM : Understanding the role of the Southern Ocean on our climate
“Without the oceans, the Earth would be about 18°C hotter than it actually is,” points out Sabrina Speich, a researcher at the Laboratory for Dynamic Meteorology attached to the Ecole Normale Supérieure in Paris. By absorbing around a quarter of our carbon dioxide emissions, the world’s oceans are rendering stout service. And there is one ocean which appears to be doing a particularly good job here: the Southern Ocean. This body of water alone is thought to absorb almost half of all the anthropic CO₂ which is captured by the oceans. However, this immense mass of water, which rotates around the Antarctic remains the least known of all our oceans.
Accordingly, the aim of the SOCLIM – an abbreviation of Southern Ocean and Climate – project is to collect lots of data from the glacial waters of the Southern Ocean in order to advance our understanding of its workings and anticipate the role it will play in climate change going forward.
The adventures of oceanic carbon
The Southern Ocean demands respect. To get there, you have to brave the Roaring Forties and then the Furious Fifties – the most violent winds on the planet, which sweep relentlessly across this broad and deep expanse of icy water. These extreme conditions explain why this ocean has been ignored by scientists for so long. Spinning around Antarctica, it connects and cools all the oceans of our planet and thus plays a major role in the earth’s climate mechanisms.
In addition to its cooling effects, it also absorbs a large proportion of atmospheric CO₂. In fact, wherever masses of water are less rich in CO₂ than the air, a transfer takes place. However, for this transfer process to become a real storage mechanism, the CO₂ dissolved at the surface has to sink to the depths of the ocean. This is precisely what happens when the cold waters of the Southern Ocean meet warmer –and therefore less dense – water from the temperate latitudes. They sink to the bottom, taking their CO₂ with them and keeping it locked up for several hundred years. This physical mechanism is not in fact the only means of storing atmospheric CO₂ in the oceans.
Certain marine organisms, such as phytoplankton, also help to sequester carbon, in a very simple manner: they eat it in order to grow. Through the workings of the food chain, this carbon subsequently finds itself inside other types of organism, which then excrete some of it and carry some of it away with them when they die and sink to the ocean floor.
This is “a particularly effective system, but it appears not to work very well in the Southern Ocean,” reveals Stéphane Blain, a researcher at the Microbial Oceanography Laboratory based at Banyuls-sur-Mer in southern France.
A fleet of floats
So what amount of CO₂ is actually sequestered in the Southern Ocean? And will changes in global temperature and ocean acidity alter the sequestration mechanisms? Those working on the SOCLIM project have found a way to answer these vital questions. Instead of sending out oceanographic vessels, the new approach is deploy dozens of individual floats, which can descend to a depth of 1,000 metres and carry out all kinds of measurements: temperature, salinity, pressure, the quantity of dissolved oxygen, light – by using optical sensors – plus also the quantity of phytoplankton and particulate carbon.
“These floats will be able to collect as much data as we could have obtained in 20 years of oceanographic expeditions,” stresses Hervé Claustre from the Oceanography Laboratory at Villefranche-sur-Mer in southern France, which is also a partner institute in the project. They can make up to 200 dives in their lifetime, and they carry an antenna so that dive frequency can be controlled remotely by satellite phone. Around twenty of these special floats are already in operation and there are plans to deploy a further fifteen by 2017.
Feeding into models and raising public awareness
This project is part of an international drive to learn more about the Southern Ocean. Forecasts of how these carbon sinks might evolve in a context of climate change will feed into existing climate models and enable scientists to refine them…and in turn obtain a clearer picture of what awaits us in future. And that’s not all. “We also want to use this project to help raise public awareness of the marine environment, the role played by the oceans and their vital importance for the human race,” stresses Stéphane Blain. An entire educational programme, under the heading Mon océan et moi (My ocean and me) has been created around the SOCLIM project. School classes are encouraged to ‘adopt a float, teachers can obtain training on the subject and a dedicated website has been set up for the purpose of sharing the research results with a wide variety of people.
“ The Southern Ocean plays a major role in our climate. As it’s really hard to carry out oceanographic expeditions there, we’re deploying a number of profiling floats in order to obtain as many measurements as possible over several years. ”
from the Microbial Oceanography Laboratory based at Banyuls-sur-Mer
Photos : ©Edouard Lemayrie, Stéphane Blain, Julien Boulanger
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