Phytoplankton Bloom in the Gulf of Elat/Aqaba: Physical Versus Ecological Forcing

Phytoplankton bloom in the Gulf of Elat/Aqaba (the Gulf) was studied before, mainly using one-dimensional models and observations from the northern Gulf. Thus, the spatial variability within the Gulf and the contribution of physical processes such as horizontal advection to the bloom have not yet been studied. Moreover, various factors such as the effect of light limitation on phytoplankton growth in the Gulf are still debated. Here, we used a three-dimensional coupled physical-ecological model for the Gulf to study the mechanisms for phytoplankton bloom throughout the Gulf. We found the southern surface bloom to be higher than the northern surface bloom. In contrast, southern integrated bloom is lower than the northern integrated bloom. These differences result from spatial variations in the mixed layer depth, which is much deeper in the northern Gulf compared with the south. Moreover, horizontal advection controls phytoplankton integrated biomass during the northern bloom, a process often neglected when dealing with phytoplankton blooms. Finally, we found that light limits growth in the northern integrated bloom. The results from the northern Gulf are compared to the North Atlantic bloom, while those from the southern Gulf are compared to the bloom in subtropical oceans due to similarities in mixing depth and consequently in nutrient versus light limitation on phytoplankton growth.