Surface distribution of chlorophyll, particles and gelbstoff in the Atlantic jet of the Alboran Sea: from submesoscale to subinertial scales of variability

J. Ruiz et al., Surface distribution of chlorophyll, particles and gelbstoff in the Atlantic jet of the Alboran Sea: from submesoscale to subinertial scales of variability, J MAR SYST, 29(1-4), 2001, pp. 277-292
Citations number
Categorie Soggetti
Aquatic Sciences","Earth Sciences
Journal title
ISSN journal
0924-7963 → ACNP
Year of publication
277 - 292
SICI code
The surface distribution of light attenuation due to particles (c) as well as chlorophyll-a and gelbstoff fluorescence (F-ch and F-cd, respectively) w ere recorded during an OMEGA (EU funded. MAST III project) cruise in the no rthwestern Alboran Sea through a high spatial (zonally separated by 10 km a nd virtually meridionally continuous) and temporal (about 3 days between ea ch of the three repeated surveys made in the zone) resolution sampling desi gn. The distributions obtained for these variables were tightly linked to t he physical forcing at the different scales that the sampling design was ab le to resolve. Low values dominate the quasi permanent anticyclonic gyre oc cupying the western Alboran Sea, whereas the frontal zone directly affected by the entrance of the Atlantic jet depicts much higher records for c, F-c h and F-cd. High geostrophic Froude numbers in the jet, and the subsequent increase in turbulence diffusion of nutrients towards the surface, cannot alone justify this spatial distribution. Instead, high phytoplankton concentration at th e jet could also result from the entrainment and advection of water from th e upwelling zone at the Spanish coast. However. T-S characteristics suggest that this is neither the most important process for the biological enrichm ent of the jet, so that other mechanisms such as vertical ageostrophic velo cities at the edge of the gyre must also be considered. Due to the time nee ded for phytoplankton growth, the intense horizontal velocities associated to the jet can decouple the sectors where deep nutrient-rich waters reach t he surface from sectors where high values of the recorded variables are obs erved. The decoupling hinders a differentiation of this fertilization mecha nism from other possible alternatives as mixing at the sills in the Strait of Gibraltar. In the third survey, the spatial structure of surface warm waters in the gy re and cold waters in the front became less apparent. ADCP data show a sout hward migration of the jet in a fluctuation probably related to transient s tares in the Atlantic jet and western Alboran gyre system. The qualitative response of c, F-ch and F-cd to these scales of variability was very simila r and close to the changes observed in temperature. However, the values of F-ch varied in a much narrower range than c or F-cd (a factor of 2 and 10. respectively), which indicates a distinct control for the abundance of Gelb stoff. This control dumps the range of variability in the western Alboran a nd its origin is discussed in the context of photobleaching or bacterial de gradation of these substances. (C) 2001 Elsevier Science B.V. All rights re served.