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Bonus-Goodhope

Science at Large

It’s with a mixture of excitement and apprehension that Sabrina Speich, from LPO,1 and Marie Boyé, from LEMAR,2 are looking forward to the expedition’s departure. For nearly six weeks, together with around 50 colleagues from South Africa, Russia, the US, and Brazil, they will be crammed into a space not much larger than a few dozen square meters. Not only is the space limited on board the Marion Dufresne–the French Polar Institute’s famous oceanographic research vessel–but in addition, they’re likely to be shaken around quite a bit given the wind conditions that rage in the Southern Ocean off the Cape of Good Hope. On the day of departure, these two experts from the European Institute for Marine Studies,3 in Plouzané near Brest, will at last see the project they’ve led for the past two years take on its concrete shape: the Bonus-Goodhope project. On behalf of the International Polar Year, the objective of the mission is to measure a host of parameters to better understand conditions in the Southern and Atlantic Oceans to the south of the African continent. The importance of this region and its role in global ocean circulation is no longer in doubt. The oceans have huge thermal inertia–the ability to accumulate and then distribute heat over the whole planet–thanks in part to the thermohaline circulation. Its principle is simple: The water that forms at high latitudes is dense, because it is cold and particularly salty. As a result, it sinks to great depths in the ocean, re-emerging at other latitudes and in regions that may be at a significant distance (sometimes at the antipodes). Due to its ring-shaped geometry, the Southern Ocean is the only route by which water can flow between the different world oceans. Because its waters are exposed to extreme climate conditions, the Southern Ocean very strongly affects fluxes of mass, heat, fresh-water, and many biogeochemical elements. Any anomaly in flow rate or water mass properties could affect the world ocean climate. But how do you go about studying this ocean, which completely surrounds Antarctica? “It has three bottlenecks: the Drake Passage, which separates the tip of South America from Antarctica, the area south of Tasmania, and the area south of the African continent,” Speich explains. The first two passageways, which are narrower, have been studied in detail, while the one to the south of Africa–which is the widest–has been neglected until now. In fact, recent research describes it as being the most “sensitive” passage for today’s climate and for the transport of heat towards the North Atlantic. Any slowdown in ocean circulation might therefore cool the climate in that region of the planet.

bateau

© DR

In early february, the Marion Dufresne will take off from the port of Cap Town. It will be the first to measure a host of biochemical and physical parameeters south of the African continent.




Everything will get under way on the evening of February 8th, 2008, when the Marion Dufresne sails off from Cape Town, South Africa. “Less than six hours later, we’ll be at the first measuring station,” says Boyé. Scientists interested in physical parameters, like Speich, will already have collected some data. “Apart from the standard measurements of temperature, salinity, pressure, and fluorescence, we’re going to quantify the oxygen content, which tells us if the water has been in recent contact with the atmosphere. We’re also going to determine the speed of the entire water column, as well as many other geochemical parameters... a step toward understanding the Southern Ocean circulation and its changes.”  
As for the geochemists and biogeochemists, “as soon as the sampling bottles that collect deep waters are brought back to the surface, everyone will get enough for their measurements,” explains Boyé. They will look at a large number of parameters: (1) trace elements and isotopes (atoms of the same element with different atomic masses), which are used to understand the key processes in the ocean, such as the mixing of waters, or whether the water-masses have been in contact with the continental shelf; (2) fundamental nutritive chemical species such as the micronutrients–
iron, cobalt, zinc, manganese, and carbon–which microorganisms feed on; (3) and finally particles in suspension in the water column, as well as
atmospheric and sedimentary geochemical conditions. Quantifying them will help scientists gain insights into one of the distinctive features of the Southern Ocean: Its waters trap less carbon resulting from biological activity than waters at most other latitudes. This is because, surprisingly, the microorganisms that proliferate elsewhere by fixing carbon from the atmosphere (and which then accumulate on the ocean floor after they die), are not very active in the Southern Ocean, though the macronutrients that are essential for their growth are present there. These researchers already seem to have their “17-hour days” fully booked.
Azar Khalatbari


Notes :

1. Laboratoire de physique des océans (CNRS / IFREMER / Université de Brest).
2. Laboratoire des sciences de l'environnement marin (CNRS / Université de Brest).
3. www.univ-brest.fr/IUEM/

Contacts :

Sabrina Speich,
LPO, Brest.
speich@univ-brest.fr

Marie Boyé
LEMAR, Brest.
marie.boye@univ-brest.fr


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