Between 2 Hemispheres

Papeete in the Tahitian Islands, Honolulu in the Hawaiian Islands. 2 tropical destinations in different hemispheres. Between the 2 archipelagos, 2 equatorial currents and 2 counter-currents.

Twice as much work to do, because we’ll have to sample each one of these huge currents that transport -- either towards Indonesia or towards South America -- water, nutrients, microscopic and macroscopic organisms. Surprisingly, our sampling plan is extremely simple.  Taking into account the position of the currents and the amount of time we have, we will do a sampling station every 3° latitude between 15°S and 15°N.
Sailing northward, we follow a chain of deserted islands with unlikely names: Millenium, Vostok, Starbuck. Once the newly embarked scientific team has learned the sampling procedures, we start the series of stations that will lead us to the equator.

There, we will encounter very particular conditons: the shearing motion between the equatorial counter-current (running between 80 and 200 meters deep) and the surface current is so violent that we have trouble getting our instruments to descend below this interface. At this depth, certain nets are drawn out horizontally, no matter what cable length is unwound.

Still following the line of islands, with the help of trade-winds we continue our progression into the northern hemisphere to complete our study of the great ocean currents, but also to sample the deeper, less oxygenated layer.

Xavier De Madron Durrieu
Head scientist on the Tahiti/Hawaii leg
Researcher at CEFREM (Centre de Formation et de Recherche sur les Environnements Méditerranéens) in Perpignan,  CNRS research director.