The drifting Southern Ocean Wave Buoy is going round in circles deep in the Southern Ocean, temporarily slowing down its steady passage east across the southern margin of the Pacific.
The buoy is caught in an eddy, a circular movement of water created when a bend in a surface ocean current pinches off to make a loop, which separates from the main current.
The buoy, which has been drifting with the ocean currents since it left its moored location on 28 July, was deployed south of Campbell Island in February 2017. Part of a collaborative research project involving the Defence Technology Agency and MetOcean Solutions, the buoy has been transmitting wave spectra data via a satellite link, providing vital information which will help the New Zealand Defence Force to design patrol ships suited to the rough seas of the Southern Ocean.
In the two and a half months since its escape, the buoy has drifted some 450 nautical miles east-northeast. In late September, the buoy passed within 20 nautical miles of the remote uninhabited Antipodes Island group.
Senior Oceanographer Dr Peter McComb is happy that data is still being transmitted. "The buoy is solar powered, and we were expecting the batteries to run out during the subantarctic winter. However, it is still happily sending wave spectra data from its path drifting slowly eastwards along the southern margin of the Pacific Ocean. So far, it has encountered moderately rough seas, with significant wave heights of up to 9 m and maximum wave heights of 15 m.
"The prevailing winds and ocean currents in this region are towards the east, however, the buoy track meanders significantly as the drift is influenced by ocean eddies within the Antarctic Circumpolar Current. The average drift speed is about 1 km per hour, but the net eastward drift is about half that. The buoy has been trapped in an eddy for the last three weeks, resulting in almost no net drift. The eddy is unlikely to last long, and the buoy will soon be released and continue drifting east. From now on, there are very few islands in the way - if it continues due east at the current speed, it will get to the west coast of South America in about a year and a half. However, a strong southerly blow in the next few weeks could push it north toward the Chatham Islands, and if that happens we might launch a recovery mission.”
In May 2017 the buoy made headlines when it measured a monster 19.4 m wave from the moored location near Campbell Island.