One of the oldest methods for studying ocean circulation is to drop something into the water and let the ocean carry it wherever it may go. And in the early years of physical oceanography, that is pretty much what scientists didalbeit with a bit of forethought.
Making the scientific equivalent of the “message in a bottle,” researchers such as famed WHOI oceanographer Dean Bumpus dropped waterproof bottles and other labeled objects into strategic spots in the ocean, let the currents carry them away, and waited for someone to find and return them. Postcards or other markings told beachcombers to send a note back to WHOI with the location and date of the discovery, sometimes in exchange for a small reward. During the 1960s alone, more than 165,000 bottles were released by ships and planes along the U.S. East Coast, with an estimated ten percent return.
The science and construction has grown more sophisticated, but the core principles of “drifters” remain the same. Researchers now outfit their drifters with radio or satellite beacons and Global Positioning System receivers, and the shapes of drifters can vary from cylinders to hardened, floating kites.
In the past 30 years, the development of floats has taken this “drifting” idea one step further. Like drifters, floats are built in various shapes and sizes, and they move horizontally with ocean currents, traveling long distances without the need of a ship, person, or propeller. But floats are also built to rise and fall vertically through the water. Simple mechanical pumps, bladders, and other devices are used to change the buoyancy of the float relative to the water, allowing it to bob between various depths. Modern floats are usually programmed to rise to the surface periodically in order to send data via satellite antenna to scientists on shore.
For all of the high-tech gadgetry and satellite views of the ocean, floats and drifters still have a critical role to play in measuring the fine details of ocean dynamicsfrom the direction and speed of currents and eddies to the physical characteristics (particularly temperature and salinity) of parcels of water within the wider ocean.