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Validation of standard and alternative satellite ocean-color chlorophyll products off Western Iberia

Publication . Sá, Carolina; D'Alimonte, Davide; Brito, A.; Kajiyama, T.; Mendes, C. R.; Vitorino, J.; Oliveira, P. B.; da Silva, J. C. B.; Brotas, V.

Chlorophyll a concentration (Chl) product validation off theWestern Iberian coast is here undertaken by directly comparing remote sensing data with in situ surface reference values. Both standard and recently developed alternative algorithms are considered for match-up data analysis. The investigated standard products are those produced by the MERIS (algal 1 and algal 2) and MODIS (OC3M) algorithms. The alternative data products include those generatedwithin the CoastColour Project and Ocean Color Climate Change Initiative (OC-CCI) funded by ESA, as well as a neural net model trained with field measurements collected in the Atlantic off Portugal (MLPATLP). Statistical analyses showed that satellite Chl estimates tend to be larger than in situ reference values. The study also revealed that a non-uniform Chl distribution in the water column can be a concurring factor to the documented overestimation tendency when considering larger optical depth match-up stations. Among standard remote sensing products, MODIS OC3M and MERIS algal 2 yield the best agreement with in situ data. The performance of MLPATLP highlights the capability of regional solutions to further improve Chl retrieval by accounting for environmental specificities. Results also demonstrate the relevance of oceanographic regions such as the Nazaré area to evaluate how complex hydrodynamic conditions can influence the quality of Chl products.

2015Journal article

Open access

Phytoplankton distribution and physical processes off NW Iberia during two consecutive upwelling seasons

Publication . Oliveira, P. B.; Amorim, F. N.; Dubert, J.; Nolasco, R.; Moita, Teresa

This work presents the results of two oceanographic surveys conducted off NW Iberia during successive summer upwelling seasons, aiming at the identification of the physical processes underlying the phytoplankton distribution in the area. Mooring (ADCP and thermistors) and ship-based CTD-F observations corroborate previous results that wind-driven upwelling circulation, (sub)mesoscale eddies and the stratification induced by the Western Iberia Buoyant Plume (WIBP) are the main processes affecting the chlorophyll distribution, but also provide new insights on key oceanographic structures governing the shelf circulation and phytoplankton structuring, namely (i) the link between frontal activity along the shelf break south of similar to 41 degrees N, the flow bifurcation at that latitude and the establishment of a cyclonic area with low frontal activity over the mid-shelf; (ii) the measurement of a previously unreported, remarkably persistent (> 1 month), near bottom poleward flow at the 30 m isobath, interpreted as the response to the alongshore pressure gradient driven by the stronger upwelling intensity north of 41 degrees N; (iii) the impact of low salinity buoyant plumes expressed on the shallowing of the Ekman layer, with the consequent frictional (Ekman) currents intensity increase, their low chlorophyll content contrary to previous winter/spring observations, and the lack of a direct relationship between plume salinities and river runoff; and (iv) the strong coupling between the chlorophyll distribution and the small-scale (O(1 - 10)km) oceanographic features providing further evidence that the phytoplankton distribution off NW Iberia in the summer upwelling season is strongly coupled to submesoscale processes.

2019-11Journal article

Restricted access

Toward predicting Dinophysis blooms off NW Iberia: a decade of events

Publication . Moita, Maria Teresa; Pazos, Yolanda; Rocha, Carlos; Nolasco, Rita; Oliveira, Paulo B.

Dinophysis acuminata and Dinophysis acuta are recurrent species off NW Iberia but their outbreaks occur under different conditions. A decade (2004-2013) of weekly data for each species at two sentinel stations located at the entrance of Rias de Aveiro-AV (NW Portugal, 40 degrees 38.6' N) and Pontevedra-PO (Galicia, Spain, 42 degrees 21.5' N), were used to investigate the regional synchronism and mesoscale differences related to species detection, bloom (>200 cells L-1) initiation and development. Results highlight the high interannual variability of bloom events and summarize the associated meteorological/oceanographic conditions. D. acuta blooms were observed in 2004-2008 and 2013, and the species highest maxima at AV occurred after the highest maxima of its prey Mesodinium, with a time-lag of 2-3 weeks. D. acuminate blooms were observed every year at both stations. The cell concentration time series shows that the blooms generally present a sequence starting in March with D. acuminata in PO and three weeks later in AV, followed by D. acuta that starts at AV and three months later in PO. Exceptionally, D. acuminate blooms occurred earlier at AV than PO, namely in high spring upwelling (2007) or river runoff (2010) years. A four-year gap (2009-2012) of D. acuta blooms occurred after an anomalous 2008 autumn with intense upwelling which is interpreted as the result of an equatorward displacement of the population core. Numerical model solutions are used to analyze monthly alongshore current anomalies and test transport hypotheses for selected events. The results show a strong interannual variability in the poleward/equatorward currents associated with changes in upwelling forcing winds, the advection of D. acute blooms from AV to PO and the possibility that D. acuminata blooms at AV might result from inocula advected southward from PO. However, the sensitivity of the results to vertical position of the lagrangian tracers call for more studies on species distribution at the various bloom stages. (C) 2015 Elsevier B.V. All rights reserved.

2016-07Journal article

Open access