The cause of bright waters in the Bering Sea in winter

In the last few years, a new sea-viewing satellite has revealed surprising bright expanses of water in the eastern Bering Sea in the middle of winter. Similar bright waters occur in summer, and have been identified as blooms of the coccolithophore phytoplankton Emiliania huxleyi. However, E. huxleyi blooms are an unlikely cause of the bright waters in winter because hostile conditions should prevent any phytoplankton from blooming then. We report the results of in situ sampling that was carried out with the aim of determining the cause of the curious bright winter waters. Samples of water and surface sediment were taken and analysed later using light and electron microscopy and geochemical techniques. The results appear to rule out E. huxleyi coccoliths as the cause of the bright waters, and implicate instead material resuspended from the shallow shelf sediments. In particular, empty and broken-up diatom frustules were seen in abundance and are estimated to be the main light-scattering constituents. The results indicate that resuspension of diatom debris (minus the living cells and their pigments) can produce water colour mimicking the appearance of E. huxleyi blooms.