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.