Propagation of Gulf of Aden Intermediate Water (GAIW) in the Red Sea during autumn and its importance to biological production

Analysis of high-resolution CTD data acquired at closely spaced stations during two cruises in the Saudi Arabian waters of the Red Sea (17 to 27°N), supported by the multiple tracer analysis (Mackas et al., 1987), showed that the Gulf of Aden Intermediate Water (GAIW) is clearly detectable as far as north as 26°N in the Red Sea basin albeit at a fraction less than 10%. Continuity of core salinity minima of the GAIW layer also showed that the northward propagation of GAIW north of 20°N happens mainly along the Saudi Arabian coast. The discontinuity of core minima of GAIW properties in a section along the axis, coincidence of these with alternating directions of zonal currents, the good relationships between concentrations of nutrients and salinity in the GAIW layer, and the cores of high nutrient concentrations in this section led to the conclusions that the GAIW is entrained in eddy circulations across the basin and that it is a significant source of nutrients to the entire Red Sea basin. However, the addition of nutrients with GAIW could account for only a small fraction of the nutrients (as nitrogen) needed for primary production, suggesting that recycling within the Red Sea and input from other sources will have to be significant enough to sustain the current levels of primary production measured in Red Sea waters.