Role of internal waves on mixing, nutrient supply and phytoplankton composition during spring and neap tides in the Ría de Vigo (NW Iberian Peninsula)

Aquatic Sciences Meeting, Aquatic Sciences: Global And Regional Perspectives - North Meets South, 22-27 February 2015, Granada, SpainThe effect of internal wave activity on nutrient supply to the euphotic layer and its potential impact on phytoplankton composition and size-structure remain unexplored in the shelf edge off NW Iberian Peninsula. In August 2013, continuous measurements (yo-yo) of dissipation rates of turbulent kinetic energy, obtained with a microstructure profiler, were carried out during spring and neap tides, covering a complete tidal cycle (25 hours). Every hour the yo-yo was interrupted to collect samples for inorganic nutrient concentration. Microturbulence and nutrient concentration data were combined to compute the nutrient input into the euphotic zone driven by vertical diffusivity. Size-fractionated chlorophyll-a and pigment composition samples were taken for the determination of phytoplankton community structure. As a result of increased mixing levels, nitrate transport to the euphotic layer during spring tides was approximately 4-fold higher (34.6 mmol m-2 d-1) than during neap tides (9.4 mmol m-2 d-1). However, the phytoplankton community was always dominated by large (>20 µm) chain-forming diatoms and seemed to be mainly controlled by the upwelling conditions predominating in late AugustPeer Reviewe