Tag Archives: Buoys

Argo Buoy Update

Argo buoy tracks from buoys deployed on the Heard Island Expedition.  Red dots indicate most recent position.  The first set of buoys were deployed between Cape Town, South Africa, and Heard Island (center).  The color scheme has been reused for the second set of buoys, deployed between Heard Island and Fremantle, Western Australia.  Image credit: Bill Mitchell (CC-BY).
Argo buoy tracks from buoys deployed on the Heard Island Expedition. Red dots indicate most recent position. The first set of buoys were deployed between Cape Town, South Africa, and Heard Island (center). The color scheme has been reused for the second set of buoys, deployed between Heard Island and Fremantle, Western Australia. Image credit: Bill Mitchell, using OpenStreetMap continents (CC-BY).

About ten months ago, the Heard Island Expedition team launched the first of our eleven Argo buoys into the Indian Ocean. The buoys are equipped with conductivity-temperature-depth (CTD) instruments, and spend most of their time drifting about 1 km beneath the ocean surface. Every ten days, they dive to 2 km, then record CTD data as they ascend to the surface. At the surface, they relay the data via satellite over the course of a day before returning to 1 km depth. With a large network of these buoys, scientists can gather important data on currents under the ocean, as well as changes in temperature and salinity profiles.

Over time, ocean currents move the buoys. None of our eleven buoys are where they started, and some have moved far away from where they entered the ocean. We deployed two batches of buoys: six before reaching Heard Island from Cape Town, and five more on our voyage on to Fremantle/Perth.

I have obtained the latest position data (as of Jan 14, 2017) for the eleven buoys. Their tracks are shown in the figure at the top of this post. Tracks are colored by buoy, reusing the colors for the first and second batch. Some of the buoys have moved more than 1500 km as the albatross flies, with path lengths approaching 3000 km!

The CTD data are also interesting. For instance, here are the temperature/depth and salinity/depth profiles measured by buoy 5902454 (dark blue path on second leg of map above).

Temperature/depth profiles over time for buoy 5902454.  Image credit: Coriolis Data Centre.
Temperature/depth profiles over time for buoy 5902454. Image credit: Coriolis Data Centre.
Salinity/depth profiles over time for buoy 5902454.  Image credit: Coriolis Data Centre.
Salinity/depth profiles over time for buoy 5902454. Image credit: Coriolis Data Centre.

Around December 1, buoy 5902454 encountered a different water mass with colder, saltier water throughout much of the 2 km water column.

Generally for these buoys, the surface water temperatures reflect the seasonal variations (warmer in Austral summer, colder in winter), while the deep water shows less variation—but sometimes there are shifts between different water masses.

Interested in keeping up with the latest from these buoys, or checking out their CTD data? Use these links (buoy number, in order by our deployment date):
1901910
1901812
1901811
1901813
1901809
1901838

5902451
5902452
5902453
5902454
5902455

Correction An earlier version of this article referred in several places to deploying ten buoys. The correct number is eleven.

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Rubber Duckies and Other Oceanographic Equipment

Rubber ducks in the 2009 Ken-Ducky Derby, floating along an inland stream.  Image credit: Tony Crescibene (CC-BY)
Rubber ducks in the 2009 Ken-Ducky Derby, floating along an inland stream. Image credit: Tony Crescibene (CC-BY)

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.

Surface Velocity Program buoys around the world.  All instruments have sea surface temperature (SST), blue instruments have sea-level pressure (SLP).  Several red points near Heard Island and between Heard Island and Perth, Australia are from the recent R/V Investigator voyage the Heard Island area.  Image credit: NOAA (public domain).
Surface Velocity Program buoys around the world. All instruments have sea surface temperature (SST), blue instruments have sea-level pressure (SLP). Several red points near Heard Island and between Heard Island and Perth, Australia are from the recent R/V Investigator voyage the Heard Island area. Image credit: NOAA (public domain).

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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