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The hydrographic structure and circulation of the Southern Mexican Pacific, from August 31 to September 24 2004, when tropical atmospheric activity was at its peak, was analyzed based on AVISO absolute dynamic topography and an array of 106 CTD profiles, within an area of about 500 km×500 km between Punta Maldonado and Puerto Chiapas. The surveyed area was occupied by mesoscale anticyclonic and cyclonic eddies that determined the path of water with temperature and salinity characteristic of the Costa Rica Coastal Current. The origin of each eddy was investigated with respect to QuikSCAT wind conditions. The sequence of AVISO images and wind data showed that the largest anticyclonic eddies originated outside the Gulf of Tehuantepec through mechanisms distinct from local wind forcing, although two northerly wind events in the Gulf of Tehuantepec possibly had an influence on the smallest anticyclonic and cyclonic eddies. The relative position of each eddy allowed the flow of relatively low temperature and salinity water (the Costa Rica Coastal Current) into and throughout the Gulf of Tehuantepec, converging at about Puerto Angel with relatively high temperature and salinity water moving from the west.

The southern region of the California Current (CC) off Baja California represents a transitional environment, with the influence of low temperature and less saline CC water during spring and summer, and warm and salty tropical and subtropical conditions through the end of summer and autumn. From 2002 to 2006, an anomalous subarctic water (SAW) intrusion generated changes in the epipelagic ecosystem dynamics, affecting phytoplankton biomass and primary production. The goal of the present work is to show the effects of the SAW intrusion off Baja California in the phytoplankton production during the two contrasting years 2002 and 2005. Our results show that the minimum water salinity was associated with density levels of 24.6–25.5 kg m −3 in 2002 and 24.3–25.2 kg m −3 in 2005, indicating that the anomalous SAW intrusion was more pronounced in 2005. In 2005, the mean chlorophyll concentration was low ( −3 ) and associated with negative salinity anomalies ( −3 in 2002 and 2005, although in the coastal zone they were >1.0 mg m −3 in some months. CHL values were significantly different between the north and south zone and among months ( p B ) and maximum photosynthesis rate (P B m )) were one order of magnitude higher in 2005 compared to 2002 ( p −2 d −1 respectively), but similar in 2005 (750 and 1006 mgC m −2 d −1 respectively). The differences between models may be due to the diverse chlorophyll data used in the singular models ( in situ vs. satellite-derived), and to the weight of the phytoplankton photosynthetic parameters in each algorithm. We conclude that for the present data set the Herman and Platt model is more suitable. To assess the relative importance of physical variables, as well as bio-optical and physiological parameters in primary production, we conducted a principal component analysis (PCA). There was an apparent separation between the two years, while each year experienced a special structuring due to different physical variables (mainly salinity, but also temperature and K PAR in 2002, and temperature and water stability in 2005). No clear structuring is discernible in 2005, suggesting that the anomalous SAW intrusion homogenized the pelagic ecosystem. The decrease in primary production suggests a change in phytoplankton biomass as a result of a phytoplankton physiological acclimatization.

The temporal variability of the physical and chemical conditions of coastal waters off Ensenada, Baja California (Mexico) was characterized. A historical analysis was made based on 11 years (1998–2008) of temperature and salinity data records measured quarterly by IMECOCAL, along a transect perpendicular to the coast (CalCOFI line 100). Moreover, the physical and chemical conditions at a coastal monitoring observatory called station ENSENADA were described using a 2-year data series (October 2006–November 2008) obtained with improved temporal resolution. The historical analysis of line 100 showed marked seasonal variability in the thermohaline conditions associated with fluctuations in the flow of the equatorward California Current and the poleward California Undercurrent, as well as with coastal upwelling events whose magnitude and frequency increase towards spring–summer. Interannual variability was also observed, related to warm and/or cold ENSO phases that modify the characteristics of the water column in this coastal region. The most striking characteristics of the interannual variability at station ENSENADA were La Nina conditions recorded from summer 2007 to mid 2008. During this cold ENSO phase, temperature, salinity, dissolved oxygen, density, and dissolved inorganic carbon data revealed the anomalous presence of subsurface water at the surface layers in spring 2008. Results suggest that the coastal observatory is sensitive to the temporal variability of hydrographic conditions on shelf coastal waters (

Nine free-drifting buoys were deployed for a period of 10 days in July 1990 in the western Irish Sea. High resolution buoy trajectories clearly revealed the existence of a cyclonic (anticlockwise) gyre with implied circulation velocities of 0.05 m s−1 and rotation time of about 10–15 days. Residual current vectors from ship-borne ADCP records extracted with the assistance of a numerical tidal model also showed cyclonic circulation in the region. The observed circulation pattern is consistent with geostrophic surface flow around a static, isolated dome of cold, dense, bottom water which is a repeatedly observed feature of the western Irish Sea summer density structure. It is suggested that the gyre may be important in promoting planktonic larval retention in the western Irish Sea.