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Esta obra ofrece una síntesis de la información recogida en las series temporales de observaciones oceánicas del IEO en la región atlántica del norte de España iniciadas en 1943 con el registro mareográfico; muestra evidencias de cambios interanuales en la física, la química y la biología del océano en relación con los factores climáticos, y estima los impactos más probables del clima en el océano futuro. Este volumen continúa la serie de estudios de la influencia del cambio climático en el mar iniciada con el Cambio climático en el Mediterráneo español (Vargas Yánez et al., 2010). En este caso, el enfoque es multidisciplinar, empleando, por primera vez, series de observaciones recogidas de forma coordinada y simultánea. A lo largo de sus ochos capítulos, se analiza la variabilidad climática atmosférica reciente y su influencia sobre las condiciones oceanográficas de la región, especialmente en relación con la intensidad y frecuencia del afloramiento de aguas profundas que determina, en gran medida, el aporte estacional de nutrientes a la superficie y, por tanto, la producción biológica. Se describen las tendencias en el nivel del mar a partir de las medidas de los mareógrafos de la zona con una estimación de los niveles extremos esperados a largo plazo. Se realiza un análisis comparativo –entre Galicia y el Cantábrico– de la variabilidad en los nutrientes inorgánicos y se determinan los elementos limitantes de la producción primaria en cada zona. Finalmente, se analizan las variaciones en las comunidades de fitoplancton, picoplancton y zooplancton como indicadoras de cambios en el ecosistema pelágico, destacando las fluctuaciones en la biomasa y producción primaria, base de la red trófica pelágica de la región, y la presencia de medusas y salpas y su relación con el clima., This book presents a synthesis of the oceanic time-series observations of IEO in the Atlantic region of northern Spain. These series, starting in 1943 with tide-gauges, reveal evidence of interanual changes in physical, chemical and biological properties of the ocean that were related to climatic factors, allowing to estimate future impacts of climate on the ocean. The volume continues the series started with “Climate Change in the Spanish Mediterranean” (Vargas Yánez et al., 2010). In this case the study is multidisciplinary, including for the first time series obtained in coordinated and simultaneous observational programs. The eight chapters first analyse recent climatic variability and its influence on the regional oceanography, particularly in relation to the intensity and frequency of the deep-water upwelling that largely determines the seasonal inputs of nutrients and primary production in this region. Next, the main trends in sea level revealed by tidal gauges along with the estimates of expected extreme levels are described. The variability in inorganic nutrients and the identification of limiting elements for primary production were presented as a comparative analysis between Galicia (in the West) and the Mar Cantábrico (in the east). Finally, the variability in the composition of the plankton communities, including phytoplankton, picoplankton and zooplankton, is analysed as indicative of changes in the pelagic ecosystem. Particular attention is given to the fluctuations in primary biomass and production and to the presence of salps and jellyfish in relation to climate.

The available information on phytoplankton biomass and species composition in Galician waters was studied to find out their spatial variability as well as the annual trends. The areas covered included the oceanic zone, the shelf and the inner part of the Rías. In general a significant drop in diatoms was observed. The series also indicated an increase in dinoflagellates, although it was not statistically significant. The diatom species related to blooms in the area declined, whereas those indicative of weak upwelling or stratificacion showed an increase. Even though not all trends were significant, the available data are consistent with the decrease in upwelling intensity over the last 40 years. The results also suggest that effects of climate changes on phytoplankton may be delayed for several years. In any case, the large oceanographic variability of the region, along with the lack of continuity of some of the series, makes it difficult to find clear relationships between environmental changes and phytoplankton.

The southern Bay of Biscay (NW Spain) shows a very active hydrography due to the different origins of its Central Waters, the local modifications exerted on them by continental effects and the recurrence of mesoscale processes such as slope currents, upwellings and eddies. In order to assess the role of the different sources of variability we conducted a monthly series of CTD sampling in the central Cantabrian Sea along a coastal-oceanic transect, from 1993 to 2003. We analyzed the spatial variability of the hydrographic processes over different timescales. The thermohaline properties of Central Waters varied between those typical of the subpolar mode of the Eastern North Atlantic Central Water (ENACWsp) and a local mode, the Bay of Biscay Central Water (BBCW), though there has been a clear shift toward the BBCW prevalence in the last years. The Iberian Poleward Current (IPC) conveyed subtropical Central Waters (ENACWst) into the region almost every winter. This slope current may display a double-core structure during some extreme events. The upper layers of the ocean showed a long-term trend toward increasing temperature and decreasing salinity, and accordingly density was on the decrease. These patterns suggest an enhancement of the water column stratification. Coastal upwellings are an important source of inshore variability and counteract these long-term changes on the coast. However, their intensity seems to be decreasing and their seasonal pattern changing toward a general advancement of the upwelling-favorable season.

Chlorophyll, primary production, zooplankton biomass and the species composition of phytoplankton and zooplankton were studied in 2003, after the Prestige shipwreck. The information obtained was compared to previous data series available for the area affected by the spill. A large data series on plankton variables for the N–NW Spanish coast existed, and therefore a realistic evaluation of the effects by comparison with the range of natural variability could be carried out. We emphasized the evaluation of impact during the spring bloom, the first important biological event after the spill. Some minor changes were observed occasionally, but they did not show any clear pattern and were more related to the natural variability of the ecosystem than to effect of the spill. Plankton community structure did not undergo any changes. Only a few species were more abundant during spring 2003 than in previous years. No significant changes were detected in the planktonic community during productive periods, such as the spring bloom and the summer blooms related to intrusions of East North Atlantic Central Waters. The lack of evidence of the effects of the spill on planktonic communities is discussed in terms of the characteristics of the fuel, the high dynamics of the water masses, the biological mechanisms through which the fuel from the surface waters is transferred to the sea floor and, particularly, the influence of the natural variability by means of large and meso-scale hydrographic processes in the area under study. At the present time it is not possible to determine any minor effects the spill may have had on the plankton owing to the great variability of the planktonic cycles and the short-term impact of the oil from the Prestige on the pelagic system.