The tritium:krypton‐85 age of Denmark Strait Overflow Water and Gibbs Fracture Zone Water just south of Denmark Strait

Abstract

The opposite time trends of the input of tritium and 85Kr to the surface ocean produce a tritium:85Kr ratio for surface water that is a strong function of time and this ratio was used to determine the age of Denmark Strait Overflow Water (DSOW) and Gibbs Fracture Zone Water (GFZW) just south of Denmark Strait. DSOW and GFZW were identified by their temperature, salinity, oxygen, and silica characteristics in a section of stations 460 km south of Denmark Strait taken during the Transient Tracers in the Ocean/North Atlantic Study expedition in 1981. DSOW was the densest water observed in the section and there were two types, a low salinity type and a slightly higher salinity, more dense type. Both types originated from Arctic Intermediate Water (AIW) behind the Greenland‐Iceland ridge. The tritium and 85Kr data reveal that the low salinity type resided behind the Greenland‐Iceland ridge for about 1 year before flowing into the Irminger Sea, compared to about 15 years for the higher salinity type. The volume transport of the low salinity type of DSOW was estimated to have a lower limit of 0.8 Sv. GFZW forms in the northeastern Atlantic from a mixture of water flowing out of the Norwegian Sea at about 900 m depth and the northeastern Atlantic water into which it flows. About 70% of the tritium and 85Kr burden of GFZW comes from northeastern Atlantic water and 30% from Norwegian Sea water. The age of GFZW just south of Denmark Strait relative to its formation in the northeastern Atlantic is 7.5+4/−6.5 years which corresponds to a mean current speed of 1.6+10.1/−0.6 cm/s.