River plumes formed in the Cantabrian coast of the Bay of Biscay constitute the main source of nutrients for this coastal area. They are able to sustain high levels of phytoplankton and primary productivity which, in turn, affect the associated ecosystems. Moreover, these plumes also influence other processes as stratification, flow circulation, transport of pollutants or erosion-sedimentation patterns, affecting the morphodynamical and biogeochemical characteristics of the area, which makes their study of high importance. The general small extension of these plumes makes necessary the use of high spatial and temporal resolution data to characterize their fine-spatial structure and to identify their evolution that happens at a short time scale. For that, the response of the Cantabrian plumes to the main forcing was analyzed by means of data provided by the Moderate Resolution Imaging Spectroradiometer sensor onboard Aqua and Terra satellites, which provides daily high resolution of up to 250 m. Composite images of Nalon, Pas-Besaya, Nervion and Adour plumes were created to analyze the effect of each forcing, including river discharge, wind and tides. Adour is the only Cantabrian plume formed even under low discharges due to the greater basin and river discharge. The rest of Cantabrian plumes are only well developed under high river discharges, which shows this forcing as the most important. Nalon, Pas-Besaya and Nervion plumes mainly influence eastward locations whereas Adour plume mainly affects areas located north of river mouth, due to the predominant currents in each area. Wind has a remarkable impact when plumes are well developed, being especially important in Nalon, Pas-Besaya and Nervion plumes. Plume material is dispersed to the ocean (under upwelling and seaward winds) or retained near coast (under downwelling and landward winds) attending to the main wind direction, conditioning the characteristics of the plume area. The semidiurnal tidal cycle is also important when plumes are developed, being all of them greater under low tidal conditions, although the impact is less important in the Adour plume. The higher stability of Adour plume to the forcing could be related to the much greater extension, which makes necessary stronger forcing to cause similar effects. On the other hand, this greater extension favors its impact on thermohaline properties of seawater. The Adour River is able to provoke winter stratification in the plume area, as well as thermal inversions, which condition the thermohaline properties respect to oceanic area not affected by the plume. By last, the influence of Cantabrian plumes on the annual cycle of chlorophyll was evaluated for each plume area and the adjacent ocean also by means of MODIS data. A chlorophyll peak was detected in both areas for early spring and high values of chlorophyll were also detected during autumn and winter but only in plume areas, associated to the input of nutrients and the haline stratification promoted by the high rivers discharges during these months.
Fernández-Nóvoa, D., Costoya, X., M. deCastro, & Gómez-Gesteira, M. (2019). Dynamic characterization of the main Cantabrian river plumes by means of MODIS. Continental Shelf Research, 183, 14–27. https://doi.org/10.1016/j.csr.2019.06.005