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

Hydrographic and tritium-He-3 data obtained on a small scale survey conducted in 1986 south of the Azores show strong horizontal and isopycnic gradients across the Azores Front. Examination of small-scale spatial variability reveals a dominant scale for salinity, oxygen, and tritium-He-3 age of the order of 160 km, comparable to estimates of sea surface height correlation scales from Gesoat data. This spatial variability correlates strongly with large-scale horizontal gradients. Two mesoscale resolving surveys separated by 300 km reveal spatial scales and amplitudes of thickness variability that decrease rapidly with age, becoming incoherent on scales greater than 18 km within 1 year, and approaching internal wave background values. There appears to be a substantial reduction in mode thickness between the two surveys, which may be the result of non conservation of potential vorticity, or the result of interannual changes in formation. Subduction rates computed from tritium-He-3 age gradients are comparable to or larger than Ekman pumping estimates based on climatological data.