Between the normal water and the brine is a short (1.5 metres) boundary zone called a halocline. The salt content rises sharply there, and oxygen reduces towards zero. This halocline between the seawater above and the brine below has many bacterial and archaeal cells: they are chemoautotrophs, which feed on ammonia from the brine but cannot function without some oxygen. Certain methane oxidizers and haloarchaea are found only in the halocline.