Modeling SST and chlorophyll patterns in a coupled estuary-coastal system of Portugal: the Tagus case study

Abstract

This work studies the influence of the Tagus estuary, Portugal, on the near coastal systemusing amodel application to describe the main physical and biogeochemical processes in the Region of Freshwater Influence (ROFI). It was used as nested modeling approach, downscaling the solution for the general circulation from a larger domain model (the Portuguese coast), to the local Tagus estuary domain. The model is evaluated during a very dynamic and biologic productive period of the year, corresponding to the winter and early summer (January–May 2007). Also during this period, there is a strong freshwater inflow into the Tagus estuary, which in turn modulates the estuarine outflow to the Tagus ROFI. The results focus on water temperature and chlorophyll and a skill assessment was made, given the lack of data required to perform a thorough validation. Simulation results reveal an adequate reproduction of the vertical thermal structure and chlorophyll concentrations. While a fairly reasonable agreement is seen for water temperature, showing no significant thermal stratification at the study area (average surface-to-bottom difference ranging from 1.3 °C to 1.6 °C), chlorophyll vertical profiles show some differences between the model results and the measurements. Maximum model bias for surface temperature is 1.4 °C and ranges from1 to 2 mgm−3 for chlorophyll, revealing an underestimation of the predicted chlorophyll and surface temperature for the area in the vicinity of the Tagus mouth. The general trends of surface chlorophyll and surface water temperature are satisfactorily reproduced by themodel.