Time series of wind-stress data, AVHRR and SeaWiFS satellite images, and in situ data from seven cruises are used to assemble a coherent picture of the hydrographic variability of the seas off the Northwest Iberian Peninsula from the onset (September-October) to the cessation (February-May) of the Portugal coastal counter current (PCCC). During this period the chemistry and the biology of the shelf, slope and ocean waters between 40°and 43°N have previously been undersampled. Novel information extracted from these observations relate to:1. The most frequent modes of variability of the alongshore coastal winds, covering event, seasonal and long-term scales; 2. The conspicuous cycling between stratification and homogenisation observed in PCCC waters, which has key implications for the chemistry and biology of these waters; 3. The seasonal evolution of nitrite profiles in PCCC waters in relation to the stratification cycle; 4. The Redfield stoichiometry of the remineralisation of organic matter in Eastern North Atlantic Central Water (ENACW)-the water mass being transported by the PCCC; 5. The separation of coastal (mesotrophic) from PCCC (oligotrophic) planktonic populations by a downwelling front along the shelf, which oscillates to and fro across the shelf as a function of coastal wind intensity and continental runoff; and 6. The photosynthetic responses of the PCCC and coastal plankton populations to the changing stratification and light conditions from the onset to the cessation of the PCCC.
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An intensive study of pelagc primary production and microplankton community respiration was carried out during an entire upwehng season in the Ria de Vigo (NW Spain). From April to November measurements of oxygen production and respiration using the hght-dark bottle technique were made twice a week at the surface. l % Light depth ( l % LD, 12 r 4 m) and 40 m (8 m above sea floor) alongside routine physical, chemical and biological measurements. During the major part of the survey period intermittent intrusions of cold, nutrient-rich upwelled water were observed In the ria with a periodicity of about 2 wk. Rates of gross primary production (GPP) were high but variable averaging 37.3 + 30.7 pM O2 d-' and 3.6 + 4.8 pM O2 d-' at the surface and l % LD respectively over the period of survey (n = 50). Rates of dark community respiration (DCR) were also high and variable with maximum values being observed in the surface layer where the seasonal average was 12.2 * 9.8 pM O2 d-l. At the l % LD and 40 m, DCR averaged 5.3 + 4.4 and 2.8 * 3.0 I.IM O2 d-l respectively. Although seasonal average and maximal DCR (up to 46.5 pM 0, d-l) were among the highest reported for coastal areas, microplankton production over the period of survey was dominated by autotrophic processes. Respiration losses by the microplankton community in the euphotic zone represented on average 43 % of estimated mean seasonal water column GPP (2.1 to 2.7 g C m-' d-l). Net heterotrophy in the aphotic layer consumed the equivalent of a further 25% of estimated water column GPP. The degree of coup h g between primary production and respiration was primarily controlled by upwelling. Dunng upwelling events respiration was generally low in the water column but it increased as a linear function of chlorophyll a concentrat~on (R2 = 0.55. n = 13) and GPP (R2 = 0.47, n = 13) in the surface layer. Under such condition phytoplankton appears as the dominant component of community respiration consuming 14 % of GPP. During penods of upwelling relaxation respiration was high relative to GPP High water column respiration rates extending occasionally down to 40 m took place at the expense of organic matter trapped inside the bay. The seasonal breakdown of thermal stratification in autumn presented a relationship between surface respiration and chlorophyll a or GPP similar to that observed during upwelling events. The large excess primary production during this period was not remineralised inside the ria, suggesting that a large fraction may be exported towards the shelf.
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