Summer diatom and dinoﬂagellate blooms in Lisbon Bay from 2002 to 2005: Pre-conditions inferred from wind and satellite data Paulo B. Oliveira a, * , Teresa Moita a , Alexandra Silva a , Isabel T. Monteiro b , A. Soﬁa Palma a a INRB-IPIMAR, Av. Brasilia, 1449-006 Lisboa, Portugal b Instituto de Meteorologia, Rua C do Aeroporto, 1749-077 Lisboa, Portugal article info Article history: Received 31 July 2008 Received in revised form 27 February 2009 Accepted 16 July 2009 Available online 26 July 2009 abstract Sea surface temperature (SST) and chlorophyll (Chl) maps derived from satellite data, together with wind and phytoplankton cell concentration time-series, are used to characterize the wind forcing and the spa- tio-temporal SST/Chl variability for periods preceding the summer (June–September) diatom and dinoﬂa- gellate blooms. The blooms (concentrations of cells higher than 200  10 3 cells l 1 ) were identiﬁed in the weekly samples collected at the long-term phytoplankton study site in Lisbon Bay, from 2002 to 2005. It is shown that bloom detection at the site occurs either during upwelling events, i.e. when offshore north- erly wind speed is greater than 5 m s 1 for more than 5 days, or up to 4 days after wind relaxation. How- ever, no direct relationship was found between the blooms and either the intensity or duration of the wind pulses. The satellite image sequences show that the Chl patterns in Lisbon Bay are strongly linked to the orientation and branching of the upwelling ﬁlament rooted at Cape Roca and the westward pro- gression of the warm-core cyclones shed from the slope off Setúbal Bay. High Chl values are typically maintained throughout the upwelling cycle along the inshore boundary of the Roca ﬁlament, covering the whole bay during the intense wind phase. During the relaxation phase, there is a Chl increase concur- rent with the contraction of the high Chl area to the northern part of the bay, associated with an inshore poleward current. It is proposed that the earlier setup of the offshore stratiﬁcation conditions and the shedding of a slope eddy favored the bloom of dinoﬂagellates in July 2004, while the stable position of the main circulation features in July 2002 favored a diatom bloom. The results add further evidence that, in summer, the ocean circulation in the embayments south Cape Roca is dominated by the upwelling dynamics and plays a key role in the development of phytoplankton blooms off central Portugal. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Recent studies on coastal upwelling ecosystems productivity and the underlying physical forcing have highlighted that the spa- tial and temporal structure of the upwelling is a key factor in pro- viding the necessary conditions for plankton growth (Largier et al., 2006). The temporal structure of the upwelling and relaxation cy- cles and the associated alternation in the advective conditions, combined with time-scales of plankton production, have been shown to strongly modulate the plankton concentration on the shelf (Botsford et al., 2006). Among the different phytoplankton groups observed in coastal upwelling ecosystems, diatoms and dinoﬂagellates are known to take advantage of different oceanographic conditions. While chain-forming diatoms dominate spring and summer upwelling events in coastal waters, dinoﬂagellates are abundant during sum- mer in stratiﬁed conditions (Margalef, 1978). However, this sea- sonal pattern shows considerable temporal and spatial heterogeneity, related to episodic wind-forcing cycles and different hydrographic structures (Kudela et al., 2005). From the analysis of the spatial distribution of phytoplankton cells and satellite-derived SST off central Portugal in summer, Moita et al. (2003) proposed that the warmer waters found in Lis- bon Bay, inshore of the upwelling ﬁlament rooted at Cape Roca (in the northern shore of the embayment), would favour the accumu- lation/growth of the dinoﬂagellates. These results motivated the detailed study of the time evolution of SST, Chl (satellite-derived chlorophyll) and ocean circulation during one summer upwelling event using satellite data and numerical model results (Oliveira et al., 2009). These authors showed that the Chl distributions are strongly linked to the shelf circulation and mixed layer depth resulting from the upwelling dynamics in the region. Here we use 4 years of weekly cell counts, wind, SST and Chl data, to generalize previous results for single upwelling events and characterize the conditions preceding the summer diatom and dinoﬂagellate blooms at the monitoring site in Lisbon Bay (Cascais). The large scale wind forcing from June to September is ﬁrst described, focusing on the upwelling favourable wind events, their temporal relationship with the occurrence of very high cell 0079-6611/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.pocean.2009.07.030 * Corresponding author. Tel.: +351 213 027 068; fax: +351 213 015 948. E-mail address: pbo@ipimar.pt (P.B. Oliveira). Progress in Oceanography 83 (2009) 270–277 Contents lists available at ScienceDirect Progress in Oceanography journal homepage: www.elsevier.com/locate/pocean