The analysis of a 28-year-long (1989-2016) series of monthly measurements of chlorophyll concentrations and primary production rates at a shelf station off A Coruña (NW Spain) provided evidence of changes at several time scales that were only partly related to upwelling intensity. Chlorophyll determinations were made in acetonic extracts and primary production rates by the measurement of 14 C-uptake by natural phytoplankton populations in simulated in situ conditions. Wavelet analysis revealed multiple modes of variation in both series, particularly at high frequencies, but some were only significant for part of the series. For instance, the seasonal cycle was not uniform through the series despite the annual repetition of maxima and minima. At multiannual time scales, both series were divided in three quasi-decadal periods characterized by significant increases in mean values. Fluctuations in chlorophyll and primary production covaried with changes in upwelling intensity at annual scales, but annual means showed low correlation. Changes in dissolved nutrient concentrations from continental sources were the likely drivers of the observed changes in productivity at large time scales. Increases in the decadal mean rates of production and concentrations of chlorophyll were driven by increased intensity of spring blooms associated to increased nutrients and low salinity water in the surface. In contrast, blooms caused by upwelling nutrients remained unchanged along the series. This study illustrates the complexity of interactions in coastal upwelling areas at large time scales, where changes in continental nutrient inputs may affect phytoplankton production more than variations in upwelling intensity.

A 29-year-long time series (1990–2018) of phyto- and zooplankton abundance and composition is analyzed to uncover regime shifts related to climate and local oceanography variability. At least two major shifts were identified: one between 1997 and 1998, affecting zooplankton group abundance, phytoplankton species assemblages and climatic series, and a second one between 2001 and 2002, affecting microzooplankton group abundance, mesozooplankton species assemblages and local hydrographic series. Upwelling variability was relatively less important than other climatic or local oceanographic variables for the definition of the regimes. Climate-related regimes were influenced by the dominance of cold and dry (1990–1997) vs. warm and wet (1998–2018) periods, and characterized by shifts from low to high life trait diversity in phytoplankton assemblages, and from low to high meroplankton dominance for mesozooplankton. Regimes related to local oceanography were defined by the shift from relatively low (1990–2001) to high (2002–2018) concentrations of nutrients provided by remineralization (or continental inputs) and biological production, and shifts from a low to high abundance of microzooplankton, and from a low to high trait diversity of mesozooplankton species assemblages. These results align with similar shifts described around the same time for most regions of the NE Atlantic. This study points out the different effects of large-scale vs. local environmental variations in shaping plankton assemblages at multiannual time scales.

The estimation of sea-air CO₂ fluxes are largely dependent on wind speed through the gas transfer velocity parameterization. In this paper, we quantify uncertainties in the estimation of the CO₂ uptake in the Bay of Biscay resulting from using different sources of wind speed such as three different global reanalysis meteorological models (NCEP/NCAR 1, NCEP/DOE 2 and ERA-Interim), one regional high-resolution forecast model (HIRLAM-AEMet) and QuikSCAT winds, in combination with some of the most widely used gas transfer velocity parameterizations. Results show that net CO₂ flux estimations during an entire seasonal cycle may differ up to 240% depending on the wind speed product and the gas exchange parameterization. The comparison of satellite and model derived winds with observations at buoys advises against the systematic overestimation of NCEP-2 and the underestimation of NCEP-1. In this region, QuikSCAT has the best performing, although ERA-Interim becomes the best choice in areas near the coastline or when the time resolution is the constraint

A coupled physical (Regional Ocean Modeling System, ROMS)-biogeochemical model (N2PZD2) at a horizontal resolution of 3.5 km was implemented for N and NW Iberia, an area of high productivity associated with upwelling. The physical model has been the object of previous studies and has proven its capability to perform well in reproducing the main oceanographic features in the area (upwelling, river plumes, slope currents, fronts, filaments), which is fundamental to properly representing the variability and distribution of the biogeochemical variables. The biogeochemical model was set up to account for the main nutrient inputs in the area: upwelling and rivers. Upwelling input required proper characterization of the nutrient content variability of the Eastern North Atlantic Central Water, which was achieved by using a temperature-nitrate relationship obtained from observations to impose nitrate at the open boundaries. The resulting biophysical model accurately reproduced the timing and interannual variability of the spring bloom compared with satellite chlorophyll (chl a) observations. A comparison with the Instituto Español de Oceanografía’s in situ spring-monitoring Pelacus cruises (which include plankton) revealed that the model was able to reproduce the variability at shorter scales (days) and demonstrated its ability to complement the observational data and reveal the variability in the area around the spring transition. In this respect, both the model and observations showed that productivity on this narrow shelf is affected by seasonal upwelling that results from the interplay of wind, river plumes and light intensity, all varying at interannual, seasonal and event scales.

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