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The RV Kaharoa motored out of Wellington, New Zealand on Saturday, loaded with more than 100 scientific instruments, each eventually destined for a watery grave. Crewmembers will spend the next two months dropping the 50-pound devices, called Argo floats, into the seas between New Zealand and Mauritius, off the coast of Madagascar. There, the instruments will sink and drift, then measure temperature, salinity and pressure as they resurface to beam the data to a satellite. The battery-powered floats will repeat that process every 10 days – until they conk out, after four years or more, and become ocean junk.

Under an international program begun in 2000, and that started producing useful global data in 2005, the world’s warming and acidifying seas have been invisibly filled with thousands of these bobbing instruments. They are gathering and transmitting data that’s providing scientists with the clearest-ever pictures of the hitherto-unfathomed extent of ocean warming. About 90 percent of global warming is ending up not on land, but in the oceans.


An Argo float. Credit: Alicia Navidad/CSIRO. 

Research published Sunday concluded that the upper 2,300 feet of the Southern Hemisphere’s oceans may have warmed twice as quickly after 1970 than had previously been thought. Gathering reliable ocean data in the Southern Hemisphere has historically been a challenge, given its remoteness and its relative paucity of commercial shipping, which helps gather ocean data. Argo floats and satellites are now helping to plug Austral ocean data gaps, and improving the accuracy of Northern Hemisphere measurements and estimates.

“The Argo data is really critical,” said Paul Durack, a Lawrence Livermore National Laboratory researcher who led the new study, which was published in Climate Nature Change. “The estimates that we had up until now have been pretty systematically underestimating the likely changes.”

Durack and Lawrence Livermore colleagues worked with a Jet Propulsion Laboratory scientist to compare ocean observations with ocean models. They concluded that the upper levels of the planet’s oceans – those of the northern and southern hemispheres combined – had been warming during several decades prior to 2005 at rates that were 24 to 58 percent faster than had previously been realized.