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The role of coastal lagoons and estuaries as sources or sinks of inorganic carbon in upwelling areas has not been fully understood. During the months of May–July, 2005, we studied the dissolved inorganic carbon system in a coastal lagoon of northwestern Mexico during the strongest period of upwelling events. Along the bay, different scenarios were observed for the distributions of pH, dissolved inorganic carbon (DIC) and apparent oxygen utilization (AOU) as a result of different combinations of upwelling intensity and tidal amplitude. DIC concentrations in the outer part of the bay were controlled by mixing processes. At the inner part of the bay DIC was as low as 1800 μmol kg −1 , most likely due to high water residence times and seagrass CO 2 uptake. It is estimated that 85% of San Quintin Bay, at the oceanic end, acted as a source of CO 2 to the atmosphere due to the inflow of CO 2 -rich upwelled waters from the neighboring ocean with high positive fluxes higher than 30 mmol C m −2 d −1 . In contrast, there was a net uptake of CO 2 and HCO 3 − by the seagrass bed Zostera marina in the inner part of the bay, so the p CO 2 in this zone was below the equilibrium value and slightly negative CO 2 fluxes of −6 mmol C m −2 d −1 . Our positive NEP and ΔDIC values indicate that Bahia San Quintin was a net autotrophic system during the upwelling season during 2005.

Using high-frequency radars, ocean surface currents were mapped every hour over an area of ≈5000 km2 in the inner Gulf of Tehuantepec (Mexico). The coastal circulation patterns (≈100 km offshore) were studied during spring, summer, and autumn 2006. The spring circulation was similar to the typical winter circulation, when the circulation is forced by outbursts of northerly winds (>8 m s–1) known locally as Tehuanos. Although Tehuano events are less common in spring than in winter, they are perfectly capable of modifying the sea surface by triggering cyclonic and anticyclonic eddies (≈50–200 km in diameter). Under moderate wind conditions, the ocean circulation showed a quasipermanent westward coastal current (≈50 cm s–1). Though the Tehuano winds were absent in summer, cyclonic eddies were observed and likely linked to the westward coastal current. Autumn was influenced by steady northerly winds with speeds of ≈12 m s–1 that remained over the region for almost 15 days. These conditions allowed us to study the competition between the wind-induced circulation and the more intense (≈100 cm s–1) westward coastal current during this period. The origin of this coastal current could be related to a warm coastal-trapped flow, composed of tropical low-salinity waters. The northwestward excursion of the observed coastal current is discussed, and the three-dimensional implications of surface current fields are studied by the Ekman theory and vorticity conservation. Se obtuvieron datos de corrientes superficiales mediante radares de alta frecuencia en un area de ≈5000 km2 dentro del golfo de Tehuantepec (Mexico). Los patrones de circulacion costera (≈100 km desde la costa) se estudiaron durante la primavera, el verano y el otono de 2006. La circulacion de primavera fue similar a la circulacion tipica de invierno, que esta influenciada por chorros de viento intenso del norte (>8 m s–1) conocidos localmente como tehuanos. Aunque menos comunes que en invierno, los tehuanos de primavera pueden modificar la superficie oceanica al generar grandes remolinos (≈50–200 km de diametro) ciclonicos y anticiclonicos. En ausencia de vientos tehuanos, la circulacion oceanica revelo una corriente costera (≈50 cm s–1) casi permanete con direccion al oeste. No se observaron eventos tehuanos en verano, aunque si remolinos ciclonicos que pudieran estar relacionados con la corriente costera que fluye hacia el oeste. Durante el otono se observo un evento de viento del norte que, aunque no supero los ≈12 m s–1 de magnitud, fue continuo y persistente durante casi 15 dias. Estas condiciones de otono permitieron observar una competencia continua entre la circulacion inducida por el viento y la corriente costera hacia el oeste en su etapa mas intensa (≈100 cm s–1). El origen de esta corriente costera podria estar relacionado con un flujo de agua calida y ligera, atrapado a la costa y compuesto por aguas tropicales. Se discute la excursion de la corriente costera hacia el noroeste del golfo, y se estudian las implicaciones tridimensionales de los campos de corriente superficial mediante los criterios clasicos de Ekman y conservacion de vorticidad.

The Gulf of Tehuantepec air–sea interaction experiment (intOA) took place from February to April 2005, under the Programme for the Study of the Gulf of Tehuantepec (PEGoT, Spanish acronym for Programa para el Estudio del Golfo de Tehuantepec). PEGoT is underway aiming for better knowledge of the effect of strong and persistent offshore winds on coastal waters and their natural resources, as well as performing advanced numerical modelling of the wave and surface current fields. One of the goals of the intOA experiment is to improve our knowledge on air–sea interaction processes with particular emphasis on the effect of surface waves on the momentum flux for the characteristic and unique conditions that occur when strong Tehuano winds blow offshore against the Pacific Ocean long period swell. For the field campaign, an air–sea interaction spar (ASIS) buoy was deployed in the Gulf of Tehuantepec to measure surface waves and the momentum flux between the ocean and the atmosphere. High frequency radar systems (phase array type) were in operation from two coastal sites and three acoustic Doppler current profilers were deployed near-shore. Synthetic aperture radar images were also acquired as part of the remote sensing component of the experiment. The present paper provides the main results on the wave and wind fields, addressing the direct calculation of the momentum flux and the drag coefficient, and gives an overview of the intOA experiment. Although the effect of swell has been described in recent studies, this is the first time for the very specific conditions encountered, such as swell persistently opposing offshore winds and locally generated waves, to show a clear evidence of the influence on the wind stress of the significant steepness of swell waves.

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 (

Temperature and salinity anomalies derived from observations obtained in the period 1997–2008 are used to study the changes in physical properties off the Baja California west coast (24–31 N). Near surface anomalies were used to characterize four periods of distinctive variability: (1) a warm and saline phase of El Nino 1997–1998, (2) a saline period from 1999 to 2002, (3) fresh subarctic water in 2002–2006, and (4) a saline-fresh (El Nino-La Nina) phase in late 2006 to early 2008. Subsurface (200 m) salinity anomalies depicted a trend towards saltier conditions (ΔS ∼ 0.1) from 2001 onwards, and did not show the four periods discernible near surface. EOF analysis of sea surface wind stress and wind stress curl suggested that after the intense westerly winds in late 2001, freshening during late 2002–2006 was due to the weakening (strengthening) of the North Pacific Current (Aleutian Low), and to a decrease of wind stress curl produced upwelling. Data also showed differences in the timing and magnitude of anomalies observed between the north (poleward of 28 N) and the south (equatorward of 28 N). Subsurface geostrophic currents demonstrated the existence of two large scale cyclonic gyres, one associated with a subarctic domain in the northern region, and another having tropical characteristics. The likely role of subsurface cyclonic pairs in the definition of a provincial boundary, and the importance in influencing the CCS ecosystem, are discussed.

Observations of residual exchange flows at the entrance to four subtropical estuaries, two of them semiarid, indicate that these flows are mainly tidally driven, as they compare favorably with theoretical patterns of tidal residual flows. In every estuary examined, the tidal behavior was that of a standing or near-standing wave, i.e., tidal elevation and tidal currents were nearly in quadrature. The pattern of exchange flow that persisted at every estuary exhibited inflow in the channel and outflow over the shoals. Curiously, but also fortuitously, this pattern coincides with the exchange pattern driven by density gradients in other estuaries. The tidal stresses and the residual elevation slopes should be the dominant mechanisms that drive such tidal residual pattern because the Stokes transport mechanism is negligible for standing or near-standing waves. Time series measurements from the semiarid estuaries showed fortnightly modulation of the residual flow by tidal forcing in such a way that the strongest net exchange flows developed with the largest tidal distortions, i.e., during spring tides. This modulation is opposite to the modulation that typically results in temperate estuaries, where the strongest net exchange flows tend to develop during neap tides. The fortnightly modulation on tidal residual currents could be inferred from previous theoretical results because residual currents arise from tidal distortions but is made explicit in this study. The findings advanced herein should allow the drawing of generalities about exchange flow patterns in subtropical estuaries where residual flows are mainly driven by tides.

The hydrodynamics of a relatively small semi-enclosed bay influenced by the California Coastal Current were studied by means of sea surface current measurements obtained with two HF radars and by data recorded with sea surface drifters. Results showed that fine-scale tidal and subtidal circulation in the inner bay depends on two mesoscale processes, the California Coastal Current (CCC) and the synoptic variability of the wind field. On the one hand, a fringe or margin of convergence–divergence produced by the impinging CCC over the inner waters of the bay developed a barrier, which restrained surface particles, hence waters, inside the bay. On the other hand, the mountain chain around the bay apparently modifies the synoptic wind field, by means of developing a shadow-like zone inside the bay where the drifters tend to accumulate. This may be explained by slightly sea surface set up, hence, water convergence due to the fine-scale atmospheric pressure field.

Data from seven oceanographic cruises in the southern Gulf of California from 1997 to 2002 are used to describe the thermohaline variability and the geostrophic circulation. Baroclinic patterns exhibited spatial and temporal variability. A deepening of isotherms at the center of the section was evident in February 1999, suggesting anticyclonic flow. In May 1998 and November 1997, cyclonic flow was suggested by shoaling of isotherms at the center of the section. Other cruises showed alternating cores of flow into and out of the Gulf (August 1998, September 1997 and October 2002). Neither a seasonal nor a spatial pattern in geostrophic flows was apparent, suggesting that the exchange of waters between the cyclonic flow of Pescadero basin and the interior of the Gulf is complex. Relatively high salinities were recorded during most of the cruises indicating that Gulf of California Water (GCW) was present most of the year. Higher salinities were observed during winter and spring, although during summer, relatively high and low salinities were both observed as surface and subsurface cores. Temperature and salinity characteristics of California Current waters were observed only in August 1995 when they reached as far north as Cerralvo Island at ∼50 dbar. During El Nino conditions in November 1997, a mixed layer (∼70 dbar) and deepening of the thermocline (∼50 dbar) characterized anomalous conditions; during this cruise an asymmetric salinity pattern was observed with low salinities characteristic of Tropical Surface waters at the center and east of the section, while maximum salinities (34.9

The effect of Santa Ana winds on bio-optical properties (absorption coefficients of particles, detritus and phytoplankton) off Baja California (Mexico) was evaluated using data obtained during four cruises in January, April, August and October 1999. Meteorological data from a station at Todos Santos Bay and satellite-derived wind data indicated three Santa Ana events during October 1999, with low relative humidity, high air temperature and persistent ENE winds. The absorption coefficient of detritus (adT) in surface samples was ten-fold higher in October because of the inorganic material wind-driven by the Santa Ana events that occurred from 9 to 11 and from 17 to 20 October, 1999. The absorption coefficients of particles (ap) and phytoplankton (aɸ) in the euphotic zone were higher in the April survey as a result of higher phytoplankton abundance. The ap, a and Kd values in the euphotic zone were fitted to chlorophyll using a power function, with an explained variance of 37%, 72% and 16%, respectively. On excluding the October adT surface values, chlorophyll explained 82% of the changes in the absorption coefficients (ap and aɸ), and 87% of the Kd variability. Approximately 80% of the chlorophyll concentration can be explained by the water column spectral reflectance relationship: Rrs(443)/Rrs(555). According to our results, regional chlorophyll estimates from water column bio-optical information were not greatly affected by wind-borne dust transported during the October 1999 Santa Ana events.

Oceanographic conditions in the Pacific waters off Baja California are described for the period 2002–2003. Anomalies in the temperature-salinity relationships were observed from October 2002 to April 2003, with a clear contribution of low salinity and low temperature subarctic water in the upper 100 m of the water column. Below 100 m, physical data suggested weak El Niño conditions. Weakened or poleward winds were not observed. The pelagic ecosystem during the intrusion of subarctic waters showed strong seasonal changes, with localized centers of high chlorophyll and zooplankton in July 2002, followed by a strong decrease in the following autumn and winter seasons. Both chlorophyll and zooplankton rebounded in April 2003, but zooplankton showed a stronger onshore-offshore gradient. There was no strong biological signal. The zooplankton taxa that showed an increase during El Niño 2002–2003 were salps and chaetognaths. The increase of salps did not appear to be related to this event, due to their seasonal occurrence limited to the northern region. In contrast the increase of chaetognaths presented a similar pattern to that observed in El Niño 1997–1998.

We present geostrophic velocities obtained using hydrographic-altimeter data and direct measurements of currents from 11 cruises offshore of Baja California from January 2000 to July 2002. The study area was dominated by meanders and eddies in geostrophic balance. Two mechanisms of eddy generation were observed; the first associated with the geometry of the coastline, and the second a product of the cooling of the California Current and the California Undercurrent from the South. There were two persistent eddies observed during the study. The first eddy was offshore of Bahia Vizcaino and had an anticyclonic circulation. Situated in the southern region, the rotation of the second eddy was dependant on which current was first to enter the transition zone along the coast. Spring was a transition period characterized by the formation of meanders. The summer brought a period of eddy generation along the coast. Autumn and winter were marked by a separation of eddies from the coast and their subsequent drift towards the west. The phase velocity of the mesoscale eddies was in accordance with the theory of the linear propagation of a Rossby wave.

Nine years of data (1992–2000) were used to study the evolution of the sea–surface temperature (SST) over the eastern south Pacific. Our analysis shows that the variability in the SST on the interannual scale is attributed mainly to the equatorial El Nino-La Nina events while cooling, associated with the wind-Ekman drift, is an important component of the annual cycle. The anomalies at the interannual scale show up as a front that parallels the coast. At the seasonal scale, anomalous warming and cooling of coastal waters is strongly altered by the local effect of the wind-driven Ekman transport. This latter effect is especially significant along the Peruvian and Northern Chilean coast where wind induced upwelling and cooling is out-of-phase with other important annual forcings (i.e radiation and annual Kelvin waves). These local wind effects show up in the time-latitude plots as a thinning of the warm-water bands along the Peruvian coast (∼10°S y 17°S) and a thickening of the bands further south (∼18°S y 22°S). Three anomalous events that stand out clearly at the interannual scale are El Nino 92–93, La Nina 96 and El Nino 97–98. Their individual evolutions over time and along the coast are very different. Though the least intense of the three, the 92–93 event had the longest duration. The 96 event was the shortest in duration and its strongest anomaly occurred around the Peruvian coast, similar to the warm event of 92–93. The strongest event for the period occurred in 97–98, its warm anomaly showing strongly along the whole latitudinal extent of the study area. Contrary to what occurs at the seasonal scale, the increase on east/west Ekman transport on the interannual scale seems to be in phase with other relevant cooling and warming mechanisms. The interannual Ekman anomalous transports are at their maximum near the Peruvian-northern Chilean coast; however, they do not seem to alter the SST in a significant way. A similar situation has been described for sea-level data in the California Current System, i.e. interannual variability being associated mostly with variability of equatorial origin while seasonal variability is associated to both wind-forced local variability and remotely forced variability (J. Geophys. Res. 94 (1989) 3159)

This paper examines the oceanic response off Baja California, Mexico, to the 1997–1998 El Nino and the transition to La Nina conditions. The data presented were gathered during seven cruises over a grid based on the CalCOFI station plan, from lines 100–130, out to station 80. T–S diagrams with data obtained during the peak phase of El Nino, demonstrate that warmer and saltier (spicier) than normal conditions prevailed in the upper 600 m over this region. Temperature and salinity anomalies calculated for CalCOFI line 120 revealed waters near the coast at 50 m depth to be up to 8.7 °C warmer and S=0.8 saltier than the climatology during October 1997. These large anomalies persisted through January 1998, with some slight diminution in the magnitudes near the surface. This study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest, identified as Subtropical Surface Water (StSW), and that low-salinity Tropical surface waters (TSW) were blocked to the southeast in the vicinity of the tip of the Peninsula. Subsurface waters associated with the California undercurrent (CU), fed from the Eastern Tropical Pacific (ETP), were also warmer and saltier than normal, and indicate a significant expansion in volume of the CU, presumably a result of intensification of poleward flow at depth. We postulate that the well defined near-surface and deep poleward flows in the study area reflect anomalous large-scale cyclonic circulation affecting the flow in the southeastern region of the North Pacific subtropical gyre east of 125°W. Following the El Nino event, warm and salty upper waters retreated to latitudes south of Punta Eugenia. With the return to normal and cooler conditions, equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity. Transition to La Nina conditions would have been associated with re-establishment of normal anticyclonic flow in the southeastern quadrant of the Pacific subtropical gyre.

Hydrographic data collected along the West Coast of North America between January 1997 and January 1999 have been compiled into a web-based Atlas of the 1997–8 El Nino event. This paper discusses the organization of the Atlas, describes the data that were incorporated into the Atlas and explains how vertical and horizontal distributions for the different properties were constructed. Examples of figures from the Atlas are shown.

Spatial and temporal size-fractionated phytoplankton chlorophyll-a (Chl-a) variability as pico-nanoplankton (PN, 0.4- 8.0 μm) and nano-microplankton (NM, 8.0 μm) off Baja California is shown. Chl-a samples from the upper 200 m were obtained from nearshore, offshore, and intermediate locations during winter, spring, and summer 2008. PN-Chl-a contribution to phytoplankton biomass was ~4 times higher than NM fraction. Chl-a PN/NM ratio increased toward offshore, while total Chl-a (PN + NM) decreased. Seasonally, offshore phytoplankton cells abundance had a comparable contribution for both size-fractions, without an apparent change by the integrated water-column total Chl-a (60 mg m2). Vertical Chl-a profiles were similar for winter and summer seasons. The highest Chl-a concentration and phytoplankton- cells abundance arose in spring, predominantly for NM at nearshore locations, reaching from 2.7-fold (nearshore: middle) to 4.2-fold (middle: offshore) ratios. Phytoplankton Chl-a increased from winter to spring (5.4 times), with maximum contribution of NM (6.6 times) at nearshore zones. Water-column integrated phytoplankton abundance was 5-fold higher in spring than winter, and 2-fold over summer. Using optical microscopy, dinoflagellate cells were the most abundant and variable phytoplankton recognizable group at intermediate zone. Smaller phytoplankton cells sustained approximately continuous biomass off Baja California. The spatial and temporal phytoplankton biomass variability was mainly influenced by an increase of larger cells as result of spring coastal upwelling events.

Seasonal variability at the entrance to the Gulf of California is described using high resolution CTD data from a section across the entrance to the gulf that was occupied eight times between 1992 and 1998. Variability decreased rapidly below 100 dbar, so that standard deviations exceeding 0.5ºC and 0.05 for temperature and salinity, respectively, were confined to the upper 150 dbar. The mean salinity field wasasymmetric, with fresher waters (S < 34.6) between 25 and 75 dbar next to Sinaloa and saltier waters (S > 34.8) above 50 dbar and between 100 and 150 dbar near Baja California. A seasonal thermocline developed in the upper 50 dbar, increasing from 21ºC in February surface temperatures to 31ºC in August. Below 100 dbar, temperature at a given pressure was typically colder in the center of the section, indicating cyclonic flow (flow into the gulf next to Sinaloa and out of the gulf next to Baja California). The subsurface mid-gulf cooling (cyclonic flow) was strongest during winter and spring when the exchange of heat between the gulf and the Pacific Ocean is large. Subsurface mid-gulf heating (corresponding to anticyclonic flow) was not observed. Temporal and spatial distribution of saline water masses suggests that heat exchanges take place by alternating the inflow and outflow of warm (surface) and cold (subsurface) water masses. The 1997–1998 El Niño resulted in a 50 dbar deepening of the thermocline in November 1997, as well as a freshening of 0.1 to 0.2 of waters above the thermocline.

Seabird counts were carried out along six transects across a tidal mixing front in the western Irish Sea using, for the first time, a combination of conventional visual bird observation techniques and very high-resolution mapping of frontal structure using an undulating CTD. Four seabird species were clearly aggregated at a precisely defined frontal boundary. Flocks of seabirds were found to change location over short time periods (hours), maintaining their position relative to the surface physical parameters and the subsurface thermocline. Results confirmed considerable anecdotal and limited documentary evidence that suggest fronts are important feeding areas for seabirds.

ARGOS drifters deployed in the Northern Gulf of California in September 1995 showed the presence of a cyclonic gyre, while a second deployment in March 1996 revealed an anticyclonic gyre. A circulation pattern consisting of a seasonally reversing gyre had been proposed before on the basis of satellite images, geostrophic calculations, and numerical models, but so far no direct observations have been made to test its existence. In September the gyre was cyclonic, baroclinic, very well defined, stable, and strong; its mean speed and rotation time were 0.3 m s−1 and ∼7 days. In March the gyre had the same mean speed, but it was anticyclonic and displaced to the northwest of the summer position. The March gyre has barotopic and baroclinic characteristics, but the observed speeds are stronger than in numerical simulations. These data and a data bank analysis suggest that the summer gyre is a persistent summer feature, but the winter–spring situation remains ill-defined and requires further research.

Fernández-Barajas et al. (1994) reportan los resultados de mediciones hidrográficas realizadas en la entrada del Golfo de California en agosto de 1992. Durante ese crucero, el CTD se encontraba calibrado inadecuadamente, teniendo como resultado mediciones anómalas de altas temperaturas y bajas salinidades. Fernández-Barajas et al. (1994) incorrectamente atribuyeron estas condiciones anómalas al fenómeno El Niño de 1991- 1993 y a la tormenta tropical Lester. Fernández-Barajas et al. (1994) report results of hydrographic measurements at the entrance to the Gulf of California in August 1992. During this cruise, the CTD was improperly calibrated, and this resulted in anomalously high (low) near-surface temperatures (salinities) being reported. Fernández-Barajas et al. (1994) incorrectly attribute these anomalous surface conditions to the 1991-1993 El Niño and tropical storm Lester.

In this chapter we present some of the features of the wind forced mesoscale current in the Gulf of Tehuantepec, Mexico. We use a three-dimensional numerical model with topography and a realistic wind as the only forcing. We find that starting with “at rest” conditions and horizontally uniform vertical stratification, in a few days (\(\sim \)20) the main features observed in regional coastal circulation are developed, which establishes the importance of local wind on coastal dynamics. Our results show that the model produces an asymmetrical ocean response on both sides of the wind jet, forming only an anticyclonic eddy on the western side of the Gulf of Tehuantepec. This response is explained by the balance of momentum in terms of external mode equations (vertically average). It was observed that the geostrophic balance dominates and is asymmetrical with respect to the axis of high wind. On the west side, the balance is part of a nearly geostrophic anticyclonic eddy. In the east, the presence of a wide platform and the shore-line, results in an altered geostrophic balance, making other terms important. The terms of lower order of magnitude also showed this asymmetry, notably on the west side where the anticyclonic eddy is formed and along the coast, influenced by the decrease in depth. This adds alternative information to the descriptions given (stationary and uniform offshore wind) of the ocean response to northerly winds and complements the explanation of the asymmetrical results. The wind used to force the model contains much of the temporal variability, therefore allowing the observation of differences in length, intensity and frequency between wind events.

B vitamins are some of the most commonly required biochemical cofactors in living systems. Therefore, cellular metabolism of marine vitamin-requiring (auxotrophic) phytoplankton and bacteria would likely be significantly compromised if B vitamins (thiamin B 1 , riboflavin B 2 , pyridoxine B 6 , biotin B 7 , and cobalamin B 12 ) were unavailable. However, the factors controlling the synthesis, ambient concentrations, and uptake of these key organic compounds in the marine environment are still not well understood. Here, we report vertical distributions of five B vitamins (and the amino acid methionine) measured simultaneously along a latitudinal gradient through the contrasting oceanographic regimes of the southern California-Baja California coast in the Northeast Pacific margin. Although vitamin concentrations ranged from below the detection limits of our technique to 30 pM for B 2 and B 12 and to ∼500 pM for B 1 , B 6 , and B 7 , each vitamin showed a different geographical and depth distribution. Vitamin concentrations were independent of each other and of inorganic nutrient levels, enriched primarily in the upper mesopelagic zone (depth of 100–300 m), and associated with water mass origin. Moreover, vitamin levels were below our detection limits (ranging from ≤0.18 pM for B 12 to ≤0.81 pM for B 1 ) in extensive areas (100s of kilometers) of the coastal ocean, and thus may exert important constraints on the taxonomic composition of phytoplankton communities, and potentially also on rates of primary production and carbon sequestration.

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.

Sea surface current measurements and wind stress and sea surface temperature satellite data were used to study the effect of northerly wind events (Tehuanos) on coastal dynamics in the Gulf of Tehuantepec, Mexico. The winter 2005 observations show a significant change in the intensity and direction of surface currents during wind events, which is reflected in an increase in kinetic energy and negative relative vorticity. The analysis revealed that kinetic energy of the coastal current decreases (increases) in periods when there is absence (presence) of Tehuano wind events, and that the relative vorticity has a tendency to positive values under low wind conditions and a tendency to negative values during high wind events. An asymmetric ocean response was observed due to wind stress forcing and the interaction between a persistent coastal current and offshore wind stress. Con base en mediciones de corrientes superficiales del océano e información satelital de vientos y temperatura superficial del océano, se estudió el efecto de los eventos de viento del norte (tehuanos) sobre la dinámica costera en el golfo de Tehuantepec, México. Las observaciones realizadas durante el invierno de 2005 mostraron un cambio significativo en la intensidad y dirección de las corrientes superficiales durante los eventos de viento, que se vio reflejado en un aumento de la energía cinética y de la vorticidad relativa negativa. El análisis mostró que la energía cinética de la corriente costera decrece (incrementa) en los periodos cuando hay ausencia (presencia) de eventos de viento tehuano, y que la vorticidad relativa presenta una tendencia a valores positivos bajo condiciones de viento débil y una notoria tendencia a valores negativos durante los eventos de viento intenso. Se observó una asimetría en la respuesta del océano por el forzamiento del esfuerzo del viento y la interacción entre una corriente costera persistente y el viento normal a la costa.

Twenty years since the discovery of tidal mixing fronts there are still few convincing observations of the velocity field associated with these structures. Simple models of shelf sea fronts predict strong along-front jets, weaker convergent circulations and instabilities. During the North Sea Project a series of studies of the Flamborough frontal system has used a new approach based upon novel combinations of modern instrumentation (HF radar, acoustic Doppler current profiler, Decca-Argos drifting buoys and towed undulating CTD) and have provided one of the first directly observed pictures of shelf sea frontal circulation. Observational confirmation of jetlike along-front flow has been found together with evidence of cross-frontal convergence. A new generation of eddy-resolving models will help to focus the next phase of frontal circulation studies in relation to questions concerning baroclinic instability and eddy generation.

We estimated the net flux of inorganic phosphorus (kg P d–1) due to geostrophic transport in the upper 100 m of a control volume (CV) off Baja California (Mexico) during 2003 and 2004. The influence of this flux on integrated primary production (IPP) in the photic zone (less than 100 m depth) was estimated comparing the net P flux into the CV against the P requirements for IPP. The greatest P fluxes occurred during spring and summer 2004; the northern side of the CV was the main recipient of P. The most persistent P outflow occurred along the southern side of the CV, except in winter 2003, when there was an input of P fluxes related to cyclonic and anticyclonic eddies off Ensenada. The net geostrophic transport during 2003 and 2004 contributed enough P to support the IPP requirements during winter and spring, indicating that P was not limiting for phytoplankton organic carbon production during these seasons. Se calculo el flujo de fosforo inorganico (kg P d–1) debido al transporte geostrofico en los primeros 100 m de profundidad de una caja de estudio (CE) frente a Baja California durante 2003 y 2004, y su influencia en la produccion primaria a partir de la relacion entre los aportes de fosforo (P) por geostrofia y los requerimientos de P para la produccion primaria integrada (PPI) estimada en la zona eufotica (menor a 100 m de profundidad). Los flujos mayores de P se presentaron en primavera y verano de 2004, con los aportes mas altos por la frontera norte de la CE. El flujo de salida de P mas persistente se obtuvo por la frontera sur de la CE, a excepcion del invierno de 2003 cuando hubo un ingreso relacionado con la presencia de remolinos ciclonicos y anticiclonicos frente a Ensenada. Durante invierno y primavera de 2003 y 2004 el flujo geostrofico aporto en forma neta el P necesario para cubrir los requerimientos de este nutriente en la PPI, por lo que en estos periodos el P no fue limitante para la sintesis de carbono organico por el fitoplancton.

Seasonal anomalies of salinity, phytoplankton chlorophyll a, and zooplankton volume off Baja California were examined from data obtained during 2001–2007. The analyses helped to identify a strong effect of physical processes on the pelagic ecosystem, diminishing near surface salinity and water column integrated phytoplankton biomass, and enhancing zooplankton volume. These changes are associated with an increase of the Pacific Decadal Oscillation (PDO) index, characterizing a warm phase of the index from summer 2002 to at least summer 2006. Negative chlorophyll a anomalies appear to respond to zooplankton grazing activity, with a possible top down effect during this period. Empirical orthogonal functions (EOFs) of Ekman drift reveal the seasonal and interannual patterns that describe the influence of upwelling zones, and there was a strong response to changes in the equatorward wind forcing from 2002 to 2006. The relationship between negative salinity anomalies and the two temporal EOF modes of Ekman drift was evident as a result of relaxation of coastal upwelling during this period. After 2006, the PDO index showed more neutral or negative values, defining the beginning of a cool phase, with positive nearsurface salinity anomalies off Baja California. Se estudiaron las anomalias estacionales de salinidad, clorofila-a y del volumen del zooplancton obtenidas de datos recolectados frente a Baja California de 2001–2007. A partir de su analisis se identifico el efecto de procesos fisicos en el ecosistema pelagico, al disminuir la salinidad cercana a la superficie y la biomasa del fitoplancton integrada en la columna de agua, con un aumento en el volumen del zooplancton. Estos cambios se asociaron con un incremento en el indice de la Oscilacion Decadal del Pacifico (ODP), que caracteriza a un periodo calido del indice a partir del verano de 2002 y al menos hasta el verano de 2006. Las anomalias negativas de clorofila-a parecen responder al pastoreo por el zooplancton, con un posible efecto de arriba hacia abajo durante este periodo. Las funciones empiricas ortogonales (FEOs) de la deriva de Ekman describieron el patron estacional e interanual producido en las zonas de afloramientos costeros de 2002 a 2006, como una respuesta a los cambios en el forzamiento del viento hacia el ecuador. Las semejanzas entre las anomalias negativas de salinidad y la variabilidad en los dos modos temporales de las FEOs fueron evidentes en la serie de tiempo, como resultado del relajamiento en los afloramientos costeros durante el periodo calido. Despues de 2006, el indice de la ODP tuvo mayormente valores neutros o negativos, lo que parece delimitar el inicio de un periodo frio con anomalias positivas de salinidad frente a Baja California.

A partir de las propiedades bio-ópticas, los coeficientes de absorción por partículas, detritos y fitoplancton (ap, adT, a #966;) se evaluó el efecto de los vientos Santa Ana en el océano frente a Baja California ocurridos durante octubre de 1999. Los vientos medidos en la estación meteorológica frente a la Bahía de Todos Santos y los determinados a partir de información de satélite indicaron tres eventos Santa Ana, caracterizados por baja humedad relativa, alta temperatura del aire y vientos con dirección predominante del este-noreste. Los valores del coeficiente de absorción de detritos (adT) fueron hasta diez veces mayores en las muestras superficiales de octubre, con relación a las de enero, abril y agosto de 1999. Los altos valores de adT se debieron al material inorgánico aero-transportado por los vientos tierra-mar ocurridos del 9 al 11 y del 17 al 20 de octubre. Los coeficientes de absorción de las particulas (ap) y el fitoplancton (a #966;) en la zona eufótica fueron mayores en abril, como resultado de la abundancia del fitoplancton. Los valores de ap, a #966; y Kd para la zona eufótica fueron ajustados a una función de potencia con la clorofila como variable independiente, con una variancia explicada de 37%, 72% y 16%, respectivamente. Cuando se excluyeron del ajuste los valores de adT medidos en la superficie durante octubre, la clorofila explicó 82% de la variabilidad en los coeficientes de absorción (ap y a #966;) y 87% en Kd. A partir de la ecuación que relaciona la reflectancia de la radiancia espectral ascendente (Rrs) con la clorofila, se determinó que ~80% de la variabilidad en la clorofila superficial es explicada por la razón de reflectancia Rrs(443)/Rrs(555) medida en la zona de estudio. Las estimaciones regionales de clorofila a partir de información bioóptica obtenida en la columna de agua no fueron afectadas fuertemente por el polvo aero-transportado durante los vientos Santa Ana ocurridos en octubre de 1999.

[1] The divergence of the surface heat flux in the Gulf of California is driven by the exchange of waters with the Pacific Ocean [Castro et al., 1994]. To estimate these exchanges, geostrophic velocities and heat fluxes were computed from nine sections of closely spaced conductivity-temperature-depth stations across the entrance to the Gulf of California between 1992 and 1999. The mean geostrophic velocity was composed of two alternating cores of inflow and outflow. The two cores that were adjacent to either coast were broader and contained the highest inflow (0.40 m/s) and outflow (−0.25 m/s) velocities, supporting the general idea of inflow along Sinaloa and outflow along Baja California (BC). During winter and spring the baroclinic outflow usually occurred near BC, and the baroclinic inflow occurred either through the center of the section and/or along the Sinaloa coast. Both inflow and outflow cores were ∼45 km wide and extended deeper than 700 dbar. Summer and fall showed a more complex pattern, with alternating cores of inflow and outflow but with inflow along Sinaloa on all cruises. During May the inflow was mainly in the center of the section, while outflow was concentrated along BC. The heat transport associated with the geostrophic flow was calculated and compared with estimates derived from surface heat budgets for the gulf [Castro et al., 1994]. Both the geostrophic flow and heat transport exhibited (for the first empirical orthagonal function mode) a strong seasonal signal with the maximum amplitude in May and the minimum amplitude in late October. A seasonal fit to the net heat transport had an amplitude of 50 × 1012 W and phase of 133 days, in good agreement with other authors, further validating the geostrophic velocity estimates. The heat added to (subtracted from) the Pacific Ocean accelerates (decelerates) alongshore currents and appears to propagate ∼10° westward as a Rossby wave.

Fernández-Barajas et al. (1994) report results of hydrographic measurements at the entrance to the Gulf of California m August 1992. During this cruise, the CTD was improperly calibrated, and this resulted in anomalously high (low) near-surface temperatures (salinities) being reported. Fernández- Bara,jas et al. (1994) incorrectly attribute these anomalous surface conditions to the 1991-1993 El Niño and tropical storm Lester.

The freshwater discharge of the Colorado River into the Gulf of California has been reduced to negligible quantities since the construction of the Hoover Dam in 1935. These radical anthropogenic changes in the hydrography of the Colorado River Delta had striking repercussions on both physical and biological processes. Using historical river discharge data, the changes in the flow dynamics and hydrographic patterns before and after the drastic freshwater reduction are studied numerically, using a three-dimensional nonlinear shelf model. The results are applied to assess the environmental impact of the reduction of river discharge on the area. Satellite imagery is also used to compare our results with observed fronts.

BACKGROUND: Highly productive hotspots in the ocean often occur where complex physical forcing mechanisms lead to aggregation of primary and secondary producers. Understanding how hotspots persist, however, requires combining knowledge of the spatio-temporal linkages between geomorphology, physical forcing, and biological responses with the physiological requirements and movement of top predators. METHODOLOGY/PRINCIPAL FINDINGS: Here we integrate remotely sensed oceanography, ship surveys, and satellite telemetry to show how local geomorphology interacts with physical forcing to create a region with locally enhanced upwelling and an adjacent upwelling shadow that promotes retentive circulation, enhanced year-round primary production, and prey aggregation. These conditions provide an area within the upwelling shadow where physiologically optimal water temperatures can be found adjacent to a region of enhanced prey availability, resulting in a foraging hotspot for loggerhead sea turtles (Caretta caretta) off the Baja California peninsula, Mexico. SIGNIFICANCE/CONCLUSIONS: We have identified the set of conditions that lead to a persistent top predator hotspot, which increases our understanding of how highly migratory species exploit productive regions of the ocean. These results will aid in the development of spatially and environmentally explicit management strategies for marine species of conservation concern.

Se describen las características y la estructura de frentes térmicos presentes durante el verano en el Alto Golfo de California, y que separan un régimen costero verticalmente mezclado de uno estratificado en la zona profunda. La posición de estos frentes se determina de la distribución de energía potencial observada con datos hidrográficos de septiembre de 1986, y se relaciona con un modelo unidimensional de mezcla vertical que predice la posición mediante el parámetro SH = log₁₀ h/u³ (h es la profundidad y u es una medida de la corriente de marea en el fondo). La posición de la zona de transición concuerda de manera general con valores críticos de SH de 3.0 a 3.6. La distribución espacial de u se obtuvo mediante la aplicación de un modelo numérico barotrópico bidimensional de alta resolución (paso de malla = 3.3 km). El modelo reproduce adecuadamente la propagación de la onda de marea M₂ en la cuenca y define zonas de intensificación de corrientes (hasta 70 cm s⁻¹) en el interior de las bahías costeras. Las discrepancias entre la posición observada del frente y la predicha se explican principalmente en función de la advección por la corriente de deriva normal al frente. Se encontró que la franja frontal se orienta en la dirección de la corriente de deriva, la cual sigue los contornos de batimetría. Se propone para el verano del Alto Golfo una estructura frontal típica: el frente climático-desértico. Este tipo de frente se caracteriza porque presenta aguas someras verticalmente mezcladas cerca de la costa, de temperatura promedio mayor que la región profunda estratificada. La capa de mezcla superficial se distribuye en toda la cuenca, y la termoclina intersecta el fondo sobre el margen costero. N/E

Se establecen patrones de circulación superficial en la región costera de la zona fronteriza México-Estados Unidos, con base en mediciones de corrientes inferidas utilizando radares de alta frecuencia. Se utiliza un conjunto de cuatro sistemas de radares de alta frecuencia, con los cuales se obtuvieron 171 series horarias de las corrientes superficiales de la región, en el período de septiembre de 2002 a noviembre de 2003. El flujo medio muestra una estructura paralela a la costa con dirección sur. El análisis armónico de los datos de corrientes superficiales reveló que la marea representa hasta un 35% de la variabilidad del flujo. Los residuales fueron examinados con la técnica de funciones empíricas ortogonales conjuntas. El modo más energético explica el 43% de la varianza del residual y establece variaciones meridionales de la corriente superficial en periodos de 9 y 18 días. La región de estudio también se caracteriza por la presencia de eventos Santa Ana. Se analizaron dos eventos que se desarrollaron en marzo y octubre de 2003. Las corrientes superficiales, en general, respondieron al forzamiento por viento lo que se manifestó como afloramientos en la costa. Sin embargo, durante marzo, la influencia del Santa Ana fue debilitada en mar abierto por efecto del campo medio. Por el contrario, en octubre, el campo medio de corrientes no fue tan importante como el efecto del Santa Ana, por lo cual se presentaron corrientes con dirección oeste y norte. Surface current data has been acquired using four HF radar sites to establish surfacecurrent patterns around the Mexican-USA coastal water. The data has been acquiredfrom September 2002 to November 2003. The mean flow was parallel to the coast, inSouthward direction. The tidal analysis explained 35 % of the variability on the surfacecurrent. The residual was study using Empirical Orthogonal Functions. The first moderepresents the mean flown variations and explain 43 % of the residual variance, and itestablish meridian variations in periods of 9 and 18 days.The region also presents Santa Ana winds events. We analyses two of these events,one recorded during March and the other during October of 2003. The influences ofthe Santa Ana wind events from March were notorious near the coast. However theOctober events were well observed on the currents and also there was a notoriousNorthward flown.

Datos de ADCP´s (Acoustic Doppler Current Profilers) anclados por 60 días se usan para estudiar el patrón de circulación residual en Bahía San Quintín, Baja California México. El patrón de circulación residual es complementado con datos de un ADCP adaptado a una embarcación, que realizó pases sobre un transecto cercano a la boca de conexión, lo que permitió estimar los flujos netos de intercambio entre la bahía y el océano adyacente. Los datos muestran una circulación de dos capas originada por el esfuerzo del viento en la superficie, mismo que da lugar a un apilamiento de agua hacia el sur-este, del orden de 8 cm. Durante periodos de vientos débiles el nivel del mar disminuye y da lugar a corrientes del orden de 1 cm s⁻¹ en dirección contraria al viento. La marea juega un papel secundario en la circulación de la capa superficial, en contraste, es el agente dominante en la capa de fondo. Durante vientos débiles se inhibe la circulación de dos capas, dando lugar a una circulación homogénea en toda la columna de agua y modulada por la marea. En la boca de conexión la circulación es homogénea en la vertical, dominada por la marea y sin presentar ningún indicio de la influencia del viento. Aquí los flujos netos de entrada se restringen al canal profundo (lado oeste de la boca), mientras que los flujos de salida se ubican en el canal somero (lado este de la boca). Este patrón de circulación es similar al esperado por la teoría, en el que el hecho de que los flujos netos de entrada sean restringidos al canal profundo en este tipo de sistemas, se debe a que los efectos de fricción son más importantes que los efectos de la rotación de la tierra (número de Ekman ≈ 1). Current data from 60 days moored ADCP’s (Acoustic Doppler Current Profilers)are used to study the residual circulation of the San Quintín Bay in Baja California,México. The residual circulation pattern was completed with data from a towed ADCP,that made cross transects near the inlet bay, this allowed the estimation of the meanflow between the bay and the adjacent ocean. Data showed a two layers circulation dueto wind stress forcing over the surface, this caused a rising of surface level around 8 cm.During low wind periods the sea level diminish and give place to weak currents (≈ 1cm s⁻¹ ) against wind direction. Tide has a secondary roll in the surface layer, whereasin the bottom layer it dominates the circulation. In the low wind periods, the twolayer circulation is inhibited and a vertically homogeneous tide modulated circulationits developed. In the inlet bay the circulation is vertically homogeneous, dominated bythe tide and without influence of the wind. Here the inflows are restricted to the deepchannel (western side of the inlet), while the outflows are located over the shallow channel(eastern side of the inlet). This pattern of circulation is similar to expected by thetheory, in which the net inflows are restricted to the deep channel due to large frictionalinfluences or less important effects of the earth’s rotation (Ekman number ≈ 1).