Surface salinity prediction for today from the Met Office Forecast Ocean Assimilation Model (FOAM). The Bay of Bengal has some of the strongest horizontal salinity gradients in the world, and is unique in the tropics. Very salty water enters the Bay from the Arabian Sea (bottom left of image), while rivers and rain input huge amounts of freshwater in the far north and east. The colour scale on this figure cannot show just how fresh these waters are – they reach as low as 18 g/kg. Most of the worlds oceans are close to 35 g/kg. The white crosses mark the location of Seagliders deployed during the BoBBLE project, with ships and moorings also taking measurements at either end of the section.