Submesoscale, tidally-induced biogeochemical patterns in the Strait of Gibraltar

Abstract

Tidal forcing and its fortnightly variation are known to be one of the main regulating agents of physical and biogeochemical signatures in the Strait of Gibraltar and surrounding areas. Samples obtained during spring and neap tides in the region were analyzed to determine the influence of this tidal variation on the submesoscale distribution of water masses and biological elements. During spring tides, strong and intermittent mixing processes between Mediterranean and Atlantic waters occur in the vicinity of the Camarinal Sill together with an eastward advection of those mixed waters into the Alboran Sea. Furthermore, the intense suction of surface coastal waters into the main channel of the strait was detected as chlorophyll patches in the Alboran Sea during spring tides. In contrast, the most characteristic phenomenon during neap tides was the arrival of pulses of relatively nutrient-rich North Atlantic Central Waters to the surface regions of the Alboran Sea. In addition, traces of the suction of coastal waters were observed for the first time during neap tides. Therefore, our results show that submesoscale processes are crucial in the dynamics of the Strait of Gibraltar, and they must be considered for the correct description of the biogeochemical features of Alboran Sea, especially during an inactive period of the coastal upwelling.