The depth of the tropical Pacific Ocean's warm surface layer shrank during the last three decades of the twentieth century — an effect of climate change that has been predicted by climate models.
Branwen Williams, now at the University of Toronto in Canada, and Andréa Grottoli at Ohio State University in Columbus collected soft and black corals from three different depths in the top 105 metres of the western tropical Pacific Ocean, off an island in Palau. They analysed the ratio of nitrogen and carbon isotopes in the coral skeletons, which indicate nutrient levels in the water. Nutrients do not mix much between warm shallow waters and colder, deeper layers, so water temperature at a given point can be inferred from nutrient levels. And by measuring from the corals' outer surfaces inwards, the researchers reconstructed the ocean's temperature profile stretching back over more than a century.
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Oceanography: Cold water rising in the Pacific. Nature 467, 886 (2010). https://doi.org/10.1038/467886a
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DOI: https://doi.org/10.1038/467886a
