title: Water-air CO2fluxes in the Tagus estuary plume (Portugal) during two distinct winter episodes.
abstract: BACKGROUND
  Estuarine plumes are frequently under strong influence of land-derived inputs of organic matter. These plumes have characteristic physical and chemical conditions, and their morphology and extent in the coastal area depends strongly on physical conditions such as river discharge, tides and wind action. In this work we investigate the physical dynamics of the Tagus estuary plume and the CO2system response during two contrasting hydrological winter periods. A hydrodynamic model was used to simulate the circulation regime of the study area, thus providing relevant information on hydrodynamic processes controlling the plume.
  
  
  RESULTS
  Model simulations show that for the studied periods, the major cause of the plume variability (size and shape) was the interaction between Tagus River discharge and wind. The freshwater intrusion on Tagus shelf exerted considerable influence on biochemical dynamics, allowing identification of two regions: a high nutrient region enriched in CO2inside the estuarine plume and another warmer region rich in phytoplankton in the outer plume.
  
  
  CONCLUSIONS
  The Tagus estuarine plume behaved as a weak source of CO2to the atmosphere, with estimated fluxes of 3.5 ± 3.7 and 27.0 ± 3.8 mmol C m-2d-1for February 2004 and March 2001, respectively.
authors: Instituto Português do Mar e da Atmosfera (IPMA), I.P., Avenida de Brasília, 1449-006 Lisboa, Portugal.
authors: Ana P
authors: AP
authors: Oliveira
authors: MARETEC, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors: Marcos D
authors: MD
authors: Mateus
authors: Instituto Português do Mar e da Atmosfera (IPMA), I.P., Avenida de Brasília, 1449-006 Lisboa, Portugal.
authors: Graça
authors: G
authors: Cabeçadas
authors: MARETEC, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors: Ramiro
authors: R
authors: Neves