On the influence of the Norwegian-Greenland and Weddell seas upon the bottom waters of the Indian and Pacific oceans

Abstract

The bottom waters of the North Pacific and North Indian oceans have temperature and salinity distributions that suggest origins from the extreme waters of the Norwegian-Greenland and Weddell seas. We attempt to trace these waters from their sources to the abyssal Pacific and Indian oceans by examining distributions of temperature and salinity along a stratum defined by density parameters. We assume that the major flow and mixing will take place along such surfaces, though the results make plain that vertical mixing is also important. The density stratum we have chosen to examine extends from the sea surface in the Norwegian-Greenland Sea and from near the surface in the Weddell Sea to depth of about 3500 m in the central oceans and below 4000 m in the North Pacific. The cold and saline water of the Norwegian-Greenland Sea is traced along the density stratum through the Denmark Strait, where vertical mixing raises both temperature and salinity to their maximum values in the central North Atlantic. From there the temperature and salinity decrease monotonically southward toward the Weddell Sea, partly by lateral mixing with the cold, low-salinity waters on this stratum where it lies near the sea surface in the Weddell Sea, and partly by vertical mixing with the underlying Antarctic Bottom Water. From the southern South Atlantic the high values of temperature and salinity (the stratum now lies close to the vertical maximum in salinity) extend eastward with the Antarctic Circumpolar Current into the Indian and Pacific oceans, with monotonically decreasing temperature and salinity as further vertical mixing erodes the maximum in salinity, until the salinity maximum is found at the bottom in the North Pacific Ocean. The stratum we have defined terminates at abyssal depths in the northern Indian and Pacific oceans; since water must rise somewhere to balance the sinking in regions of bottom-water formation, there must be upward flow across the stratum elsewhere. The tremendous areal extent of the salinity maximum, however, suggests that the upward flow through the stratum must be minimal except in the North Indian and North Pacific oceans, where stability is shown to be very low at the depth of the stratum.