On January 10, 1992, on a voyage from Hong Kong to Tacoma, Washington, the cargo vessel Ever Laurel encountered rough seas and a container was washed off the ship. The container broke open and released its contents: 28,800 yellow rubber duckies and other floating bath toys. Since then, the duckies have been floating around, moved by wind and wave, and washed up on coasts around the world. By tracking the date and location of washed-up duckies, oceanographers can get a sense for the speed and direction of surface circulation at an oceanic scale. It’s like having 28,800 messages in bottles dumped from the same known location at the same known time.
Oceanographers sometimes want to be more precise in their measurements. The duckies probably floated very high in the water (at least at first), so that the wind could easily affect their direction and speed. Additionally, the rubber duckies are hard to track while they are at sea because they are small, few, and far between.
When more precise measurements are required, oceanographers turn to specially-designed drift buoys. These maintain a lower profile above water, and have a large “holey sock” sea anchor tethered to them in order to more accurately measure the ocean surface currents and not the wind. The buoys also have a thermometer—and sometimes additional sensors for salinity or barometric pressure—and a radio transmitter to establish the buoy’s position (by Doppler shift from 401.65 MHz, not GPS) and relay data via satellite back to the operations center.
Different floats can be used to measure temperature and salinity profiles, rather than surface currents. Argo floats are autonomous diving instruments, which can maintain neutral buoyancy and perform controlled ascent/descent to 2000 m. These floats make their temperature, pressure, and salinity measurements during a 6–12 hour ascent. Upon reaching the surface, they transmit their GPS location and the recorded data back to the operations center via satellite. Argo floats are not cheap, with each carrying a price tag of around $15k.
On the Heard Island Expedition, our team will be deploying both of these types of instruments. These measurements will improve understanding of ocean circulation, heat content, and salinity, as well as providing ground-truth sea surface temperature measurements for use in weather forecasting models. No rubber duckies will be deployed, but we’ll document any we find washed up on the beaches.
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