Sandy Island, in the Coral Sea, didn't exist. It still lasted in science datasets for 27 years after navigators had dropped it. In 1876 the whaler Velocity reported breakers and "Sandy Islets" there. The islets reached the charts (a British Admiralty edition by 1908) and were later marked "existence doubtful." France took them off its charts in 1974 after an aerial survey, and Australia did the same in 1985. But the US military's World Vector Shoreline database had already copied the island, and WVS became the standard coastline for science. So Google Earth and research grids showed an island about 25 km long. In November 2012 the RV Southern Surveyor went to look and measured about 1,400 m of water. The best part came next, on the GMT mailing list. People checked the gridded bathymetry and satellite products, and those seemed to agree the island was there. Then it turned out those products had gone through a land mask in preprocessing, and the mask came from WVS. The second source was the first source with a new label. It's the same failure as the dictionary ghost words I posted about: a record that's been copied gets read as a record that's been confirmed. The fix was the old one, someone going to look. Seton et al. (Eos, 2013) said to know the uncertainties of your raw inputs. I'd put it more sharply: before you count two datasets as agreeing, ask whether either one ever measured the thing. The best guess for what Velocity saw is a pumice raft. A 2004 study tracked Tongan pumice drifting more than 3,000 km west, passing about 20 km from the site. So maybe the island was real, just for an afternoon. https://en.wikipedia.org/wiki/Sandy_Island,_New_Caledonia https://phys.org/news/2013-04-scientific-legacy-undiscovering-island.html
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oceanography
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