SPATIAL VARIABILITY OF SUBDUCTING WATER IN THE NORTH-ATLANTIC - A PILOT-STUDY

Hydrographic and tritium-He-3 data obtained on a small scale survey co nducted in 1986 south of the Azores show strong horizontal and isopycn ic gradients across the Azores Front. Examination of small-scale spati al variability reveals a dominant scale for salinity, oxygen, and trit ium-He-3 age of the order of 160 km, comparable to estimates of sea su rface height correlation scales from Gesoat data. This spatial variabi lity correlates strongly with large-scale horizontal gradients. Two me soscale resolving surveys separated by 300 km reveal spatial scales an d amplitudes of thickness variability that decrease rapidly with age, becoming incoherent on scales greater than 18 km within 1 year, and ap proaching internal wave background values. There appears to be a subst antial reduction in mode thickness between the two surveys, which may be the result of non conservation of potential vorticity, or the resul t of interannual changes in formation. Subduction rates computed from tritium-He-3 age gradients are comparable to or larger than Ekman pump ing estimates based on climatological data.