Going with the current

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9 January 2012

After skirting the Panama coast to Mexico by way of Belize (and a cinematographic interlude with Yann Arthus Bertrand), Tara is now in the Gulf of Mexico. The pace is building up as we finally get down to scientific business. Our course takes us north, following the marine currents.

For Loïc, the captain, this leg is really split in two, “We were relatively calm before Belize, but now our schedule will get tighter. The scientific team is itching for more action. A single short station took place after exiting the Panama Canal, but then the rosette remained tethered on deck because we didn’t receive the authorisations for sampling. Now that we’re in American waters, things will change. We’ve scheduled 2 long sampling stations, one in the middle of the Gulf of Mexico, and the other along the Florida coast.

The main feature of this leg: Tara will be drifting the whole way thanks to ocean currents. After following the Caribbean current, which became the Yucatan current upon entering the Gulf, Tara will join the “Loop current”. This will bring us to the East Coast via the Florida current. Joined by other currents, it becomes the famous Gulf Stream. “This gives us a chance to follow the same water masses and the evolution of the organisms they carry,” says Emmanuel, the head scientist of the leg. “These organisms are all part of the same system, which lets us study changes in diversity, and the number of organisms in a connected system.”

To follow the currents as precisely as possible, the scientific team relies on satellite maps. Water temperature, sea level or phytoplankton concentrations – each chart shows the winding current as it makes its way to the East Coast.  This coincides perfectly with Tara’s route. But the question remains — are two stations enough? “All along the way, in addition to the stations, we’ve programmed at least 6 or 7 CTD profiles” replies Emmanuel.

Specifically, a CTD allows us to record a number of factors: not only Conductivity-Temperature-Depth, but also salinity, oxygen concentration and fluorescence. After immersing the rosette, the scientists then have a detailed profile of the actual water characteristics. “In addition, even without sampling, the camera shows us zooplankton distribution, and gives us an idea about the quantity and species present”, adds the French-Israeli scientist.

These multiple CTDs will let us correlate the water masses between the two long stations, while offering a global vision of these famous currents. But the positioning of these 2 stations is not motivated only by the study of currents. In the Gulf of Mexico, one station will take place not far from a sad ocean memory: the explosion of the Deepwater Horizon oil rig in April, 2010, which caused one of the worst oil spills in the United States. “Apparently, no traces of the catastrophe remain in the water, but some may be found in marine micro-organisms,” says Emmanuel. As often is the case, we’ll have to wait for the more complete laboratory analyses on land before we know for sure. For the scientists onboard, this leg offers many research directions.

For the sailors however, going north towards Savannah has a more symbolic aspect. “After Florida we’ll encounter a harsher climate, with a cold wind coming from the North,” says Loïc. “For Tara, this leg marks the end of summer!” A summer that lasted nearly a year.

Yann Chavance