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Records of the herring, Clupea harengus, fishery off the Swedish coast of Bohuslän, in the Skagerrak, date back to the 10th century. Nine periods, each lasting several decades, are known during which large quantities of herring were caught close to the shore. In the 1895–96 season, more than 200 000 tonnes were landed. During the `interim' periods, which stretched over 50 or more years, the herring fishery played little role in the economy of this region. Several other herring fisheries in European waters overlap with recent Bohuslän periods whereas the Norwegian spring‐spawning herring and some sardine, Sardina pilchardus, fisheries exhibit alternating periods. A study of the climatological/hydrographic scenario of all Bohuslän periods and those of herring in the English Channel and the Bay of Biscay showed that, on a decadal scale, they coincided with times when there was a strong ice cover off Iceland, severe winters in western Europe with extremely cold air and water temperatures, a reduction of westerly winds as indicated by negative anomalies in the North Atlantic Oscillation (NAO) index and a minimum of south‐westerly winds over England in response to meridional migrations of the belt of westerly winds. Periods of the Norwegian spring‐spawning herring and sardines in the English Channel coincided with inverse climatological/hydrographic situations. It is concluded that climate variation governed the alternating herring and sardine periods.

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Abstract. Very accurate thermodynamic potential functions are available for fluid water, ice, seawater and humid air covering wide ranges of temperature and pressure conditions. They permit the consistent computation of all equilibrium properties as, for example, required for coupled atmosphereocean models or the analysis of observational or experimental data. With the exception of humid air, these potential functions are already formulated as international standards released by the International Association for the Properties of Water and Steam (IAPWS), and have been adopted in 2009 for oceanography by IOC/UNESCO.In this paper, we derive a collection of formulas for important quantities expressed in terms of the thermodynamic potentials, valid for typical phase transitions and composite systems of humid air and water/ice/seawater. Particular attention is given to equilibria between seawater and humid air, referred to as "sea air" here. In a related initiative, these formulas will soon be implemented in a source-code library for easy practical use. The library is primarily aimed at oceanographic applications but will be relevant to air-sea interaction and meteorology as well.The formulas provided are valid for any consistent set of suitable thermodynamic potential functions. Here we adopt potential functions from previous publications in which they are constructed from theoretical laws and empirical data; they are briefly summarized in the appendix. The formulas make use of the full accuracy of these thermodynamic potentials, without additional approximations or empirical coefficients. They are expressed in the temperature scale ITS-90 and the 2008 Reference-Composition Salinity Scale.

Observations, hypotheses and derived scenarios are discussed for the Northwest-African coastal upwelling area. The process of coastal upwelling is considered to be composed of a climatic steady-state part and fluctuations acting on different spatial and temporal scales. Attention is focused on disturbances acting globally on the inter-annual timescale. El Niño-like changes occur in the system of trade winds and modify the equatorial regime of currents as well as the coastal upwelling regimes on both flanks of the Inter-tropical Convergence Zone. There is an opposite thermal response in near-surface layers along the zonal coast in the Gulf of Guinea and along the meridional coast off NW-Africa. Off the continental slope of Senegal and Mauritania, the poleward undercurrent is linked with the system of eastward flowing equatorial undercurrents via the transport of South Atlantic Central Water (SACW) around the eastern flank of the Guinea Dome. The upwelling undercurrent partly feeds its SACW properties into the belt of coastal upwelling and contributes significantly to the biological productivity during 'normal' and 'abnormal' upwelling years. Future investigations should focus on changes in the timescale of decades. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Résumé − Upwelling au nord-ouest de l'Afrique. La zone d'upwelling située au nord-ouest des côtes africaines est étudiée dans le cadre d'une discussion portant sur les observations, les hypothèses et les scénarios qui en dérivent. Le phénomène d'upwelling côtier est considéré comme formé d'une composante climatique permanente et de fluctuations à différentes échelles d'espace et de temps. L'accent est mis sur les perturbations globales inter-annuelles. Des variations de type El Niño se produisent dans les alizés et modifient les courants équatoriaux et les upwellings côtiers des deux côtés de la convergence intertropicale. La réponse thermique diffère dans les couches proches de la surface, en raison de l'orientation de la côte, zonale dans le golfe de Guinée et méridienne au nord-ouest de l'Afrique. Devant la pente continentale du Sénégal et de la Mauritanie, le sous-courant orienté vers le pôle se rattache au système des sous-courants équatoriaux dirigés vers l'est par l'intermédiaire de l'Eau centrale de l'Atlantique Sud (SACW) qui contourne le flanc est du dôme de Guinée. Le sous-courant transfère partiellement les propriétés de l'eau SACW à l'upwelling côtier et contribue de manière significative à la productivité biologique pendant les années d'upwelling 'normal' et 'anormal'. Les travaux à venir devraient, entre autres, porter sur les variations à l'échelle des décennies.

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Monthly maps of remotely sensed sea surface temperatures derived from NOAA/AVHRR thermal images are used to describe changes in 'Intense Benguela Upwelling' during 1982-1999. The coastal area under investigation lies between 9-34°S and 8-20°E and the total area of cold water between the coast and the course of the 13°C isotherm is considered to be an index of intense, active upwelling. It exhibits a decreasing trend over the study period of 18 years and some evidence for a quasi-cycle of about 27 months. Seasonal cycles are discussed for the total cold water area as well as for its mean alongshore and offshore extents. The main season of cold surface water was found to occur between July and September during the austral winter. It peaks in August with a mean area of about 30×10 3 km 2 and relaxes drastically during the rest of the year. The underlying process of intense coastal upwelling is regionally trapped in two coastal zones. These are centred around 26 and 29°S and reach a mean offshore extension of 210 and 130 km, respectively, to form giant upwelling filaments. The area of cold water drastically shrinks, roughly by a factor of two, during weak upwelling years but significantly expands by a factor of about 1.5 during strong years. Associated sea level changes along the southwest African coast were derived from measurements at four coastal stations between 23 and 34°S during 1982-1987. The first principal component describes about 63 % of the total sea level variance. The lowest sea levels were found in the prominent Lüderitz cell near 26°S. On both the annual and interannual time scale, decreasing cold water areas are accompanied by increasing sea levels and vice versa. Mean seasonal cycles reveal that variations in the total cold water area lag behind those in the sea level along the entire southwest African coast by about 1 month. © 2001 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS Résumé − Modifications saisonnières et interannuelles de l'upwelling intense de Benguela. Des cartes mensuelles de température de surface de la mer, obtenues par satellite à partir du capteur NOAA/AVHRR, sont utilisées pour décrire l'épisode intense de la remontée d'eau de Benguela entre 1982 et 1999. La région côtière étudiée s'étend de 9 à 34°S et de 8 à 20°E ; la totalité de la tâche d'eau froide entre la côte et l'isotherme 13°C est considérée comme le signe d'un upwelling intense. Cet indice décroît durant la période de 18 années et un cycle de 27 mois apparaît. Les cycles saisonniers sont discutés pour l'ensemble de la région « froide ». La saison principale de remontée se situe entre juillet et septembre, durant l'hiver austral. Elle atteint son maximum en août avec une aire moyenne concernée de 30×10 3 km 2 et l'upwelling est particulièrement faible tout le reste de l'année. Deux foyers de remontée existent le long de la côte. Ils sont centrés sur 26°et 29°S et s'étendent au large respectivement jusqu'à 210 et 130 km en formant des filaments géants. L'aire de remontée se réduit de moitié durant les...