PLASTIC CARDS USED TO STUDY OCEAN CURRENTS

Press, Volume XCIX, Issue 29232, 16 June 1960, Page 16

PLASTIC CARDS USED TO STUDY OCEAN CURRENTS

The chances are very poor of any material being cast ashore, after drifting more than 50 miles oft the east coast of New Zealand, or 100 miles off the west coast, according to a study of ocean currents by Mr J. W.

Brodie. Mr Brodie, who is director of the New Zealand Oceanographic Institute, studied the coastal surface currents by using some 12,000 floating plastic cards, which were dropped off the New Zealand and Australian coasts, and in the Tasman Sea, in 1953 and 1954. The results are published in the latest issue of the “New Zealand

Journal of Geology and Geophysics.” The cards were recovered through the co-operation of the public, who were asked to fill in details of the time, place, and circumstances of finding of the cards returned. Only 411 of the cards were returned, from many points on the New Zealand and Australian coasts. Five per cent of those released up to 160 miles offshore from New Zealand were recovered, and 2.3 per cent, of those released within the same distance of the Australian coast. Only one of the 2930 cards released beyond those limits was recovered, when a card dropped 170 miles east of Otago Harbour arrived in Te Whanga lagoon in the Chatham Islands, 400 miles further east.

An analysis of the results showed that the drifts recorded off any part of the coast, with the exception of the area from Cape Farewell to the Manukau Harbour, were all in the one direction. Six main currents were found: From North Cape down the Auckland east coast to the Bay of Plenty; from north and west of Cape Reinga down the Auckland west coast toward Kaipara; from the West Coast sounds region through Foveaux Strait and up the east coast of the South Island: from Banks Peninsula north past Cook Strait and the east coast of the North Island as far as Gisborne; from the West Coast of the South Island up to Cape Farewell, and less markedly north along the Cape Egmont coastline toward the Manukau Harbour; and from off the western entrances of Cook Strait through the strait. More than 50 merchant ships from 17 lines helped in the survey.