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Using coupled biological-physical model based on NPZD-type biological model and 3D coastal ocean model (ROMS) we studied dissolved oxygen (DO) dynamics and hypoxia development on Oregon shelf during April-August of 2002, 2006, and 2008. We found that shelf hypoxia existed during summer months of all three years. It was characterized by variable severity, horizontal and vertical extent, duration and timing, and it was more pronounced in 2002 and 2006. By the means of numerical sensitivity analysis we found out that: inadequate initial DO and NO3 conditions in late-spring 2002 prevented or delayed hypoxia development; offshore and especially northern DO and NO3 boundary conditions are important to simulating hypoxia on the Oregon shelf, this was especially critical for early bottom hypoxia on the shelf north of 45N in 2006; hypoxia occurred earlier in the north in 2006 and in the south (Heceta Bank) in 2002, perhaps, due to different northern boundary conditions for these years; the DO and NO3 conditions at western open boundary located some 400 km offshore are unimportant for DO dynamics in spring-summer. Although DO production due to biological processes is large, physical processes, mostly horizontal advection and diffusion, are responsible for net DO reduction in spring-summer and hypoxia onset in summer on the Oregon shelf. The physical mechanism most responsible for Oregon shelf hypoxia is the coastal upwelling. Diffusive fluxes of NO3 and DO are negligible at northern and southern boundaries of the Oregon shelf and appreciable at the western boundary. In 2006, about two thirds of total April-August DO loss happened in April-May as a result of strong and long-lasting upwelling event., Comment: 31 pages; 4 tables; 10 figures. 2013 EGU General Assembly

Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) Modelling Workshop Galway, Ireland, June 2009.-- 1 page, Alfacs Bay is an estuarine bay located in NW Spain, as part of the Ebro river Delta. It has great interest due to the importance of its fishery and aquaculture industries. However, during the last decades, episodes of Harmful Algal Blooms have been repeatedly observed. Analyses of 14 year-long time series have shown a clear seasonal behavior of the two main functional groups of phytoplankton in the bay. Diatoms present a population peak in autumn while dinoflagellates are more abundant in winter and spring. Factors affecting the variability of the different phytoplankton assemblages include inputs of freshwater into Alfacs Bay, which occur from April to October and influence the amount of nutrients and the stability of the water column. We used a zerodimensional N-PP-Z D model with two phytoplankton functional groups to explore the relationships between physico-chemical variability and the behavior of the two main phytoplankton groups in the Bay, with the aim of defining scenarios that can explain the alternation between these groups

18 pages, 9 figures, 7 tables, The effect of Dissolved Organic Phosphorus (DOP) availability and nutrient limitation of phytoplankton growth in an estuarine bay (Alfacs Bay, NW Mediterranean) have been studied by means of a zero-dimensional ecological model including nitrogen, phosphorus (organic and inorganic), two groups of phytoplankton (diatoms and flagellates), one group of zooplankton, and detritus. Simulations with and without DOP as an extra source of phosphorus for phytoplankton growth suggest that DOP plays an important role in the dynamics of the Alfacs Bay ecosystem. DOP is indeed necessary to simulate the observed draw-down of nitrate and build up of phytoplankton biomass. Two non-exclusive mechanisms allowing DOP availability for phytoplankton are possible: direct uptake, or remineralization to Dissolved Inorganic Phosphorus. Including both gives a better agreement with the observations. Inclusion of DOP in the model leads to predominance of phosphorus limitation of phytoplankton growth in fall and winter, and of nitrogen limitation in late spring and summer. Simulations with and without sediment resuspension suggest that this process does not significantly affect the nutrient budget in the bay, This work was funded by projects TURECOTOX (CTM2006-13884-CO2-00/MAR9, Ministerio de Ciencia e Innovacion, Spain) and CANESP (a joint project between the National Research Council of Canada and the Ministerio de Asuntos Exteriores of Spain), and by the CSIC. CL was supported by a fellowship of the Spanish National Research Council, CSIC (Beca CSIC Predoctoral I3P-BPD2005), and during the last months for a postgraduate grant of La Fundación Caja Madrid. The modeling was performed during CL's internship in the College of Oceanic and Atmospheric Sciences at Oregon State. We thank Tim Cowles for hosting CL during her first stay in the US and for his help and support during the first stages of the model development. JS was funded by Proyecto Intramural Especial del CSIC, “Desarrollo de algoritmos y validación de productos en el Centro Experto SMOS en Barcelona” (200430E530). We are grateful to Maximinio Delgado for kindly providing phytoplankton data, to Elisa Berdalet, Esther Garcés and Mariona Segura for valuable advice and information, and Francisco Rueda for his help during the process of implementation of the physical model Si3D to Alfacs. IRTA (Institut de Recerca i Tecnologia Agroalimentàries, Generalitat de Catalunya) sponsored the collection of time series of environmental data in Alfacs Bay. The Servei Meteorològic de Catalunya and the Instituto Nacional de Meteorología provided meteorological data. We also acknowledge the valuable comments of Annie Chapelle and an anonymous reviewer