If you haven't heard about it - there is a very interesting research project called Argo which consists of a global array of 3,000+ free-drifting floats that measure the temperature and salinity of the upper 6,000 ft of the oceans. Argo deployments started in 2000 and were completed in November of 2007.
Each autonomous probe is programmed to sink to a depth of more than a mile, then drift in total darkness for nine days — much deeper than submarines typically go. Every 10th day, the probes ascend, collecting temperature and salinity measurements as they go. At the surface, they transmit their data, then descend to start the cycle anew.
So why the research? The data collected represents the first time we have been able to continuously monitor of the temperature, salinity, and currents of the upper ocean, with all data being relayed and made publicly available within hours after collection. This information will be invaluable in learning how the earth's climate works and in the creation of long-term climatic models.
Check out the following link for more information.
Worldwide Argo Float Positions