Data from an autonomous ARGO float launched on December 26, 2016, south of the entrance of the Gulf of California, reveal variations in the distribution of water masses in the tropical-subtropical convergence off Mexico. The float trajectory drifted through three areas of distinct characteristics: i) the southern Gulf of California in January 2017, ii) south of Cabo San Lucas from February 2017 to January 2018, when the float crossed an eddy, and iii) off Cabo Corrientes from February 2018 to April 2021. During the sampling, the vertical distribution of the water masses showed for the first time with “in situ” data a semiannual variability mainly in the salinity as response to poleward propagating semiannual Kelvin wave. The surface water masses had potential densities <26 kg m−3. A shallow salinity minimum (<34.6 g kg−1) observed at ∼ 70 m depth south of Cabo San Lucas provided a proxy for the California Current Water distribution, which had its maximum southern extension during winter. The Tropical Surface Water was observed off Cabo Corrientes mainly above 50 m depth and had maximum northern extension during summer. The Gulf of California Water was scarcely evident in the float trajectory in the southern Gulf. The Transitional Water was located above ∼ 50 m depth and was dominant southwest of Cabo San Lucas during winter and spring, when the California Current Water extended furthest south. The Subtropical Subsurface Water, in spite of its high density (>25 kg m−3) at times extended up to only 20 m below surface in the three areas around the summer as part of a semiannual cycle. The intermittent presence of this oxygen-deficient water close to the surface (∼ 20 m depth) is consistent with the on-going expansion of the shallow oxygen minimum zone. Wavelet analysis highlighted a bimonthly spectral frequency in the StSsW lower limit when the float crossed the eddy in the south of Cabo San Lucas, showing the influence of the mesoscale features of the area, and therefore a possible interchange of properties between deep waters.

La Paz Bay (LPB) considered one of the most highly productive bays in the southwestern Gulf of California, Mexico, recently established as Priority Marine Region, supports many species of ecological importance. In this context, daily composites of surface chlorophyll a (Chl-aSAT), sea surface temperature (SST) satellite images derived from the MODIS-Aqua sensor, and a wind intensity index (WI) calculated with data recorded simulta-neously at four points along the coast, were used to describe the strong 2015-2016 El Nin & SIM;o impact over the surface chlorophyll pigments in LPB, relative to its average for 2003-2013. Significant relationships between SST, WI (used as environmental factors) and Chl-aSAT (RSST =-0.74, RWI =-0.40, P < 0.01) were found using exponential models for the entire study period, with moderate correlation during El Nin & SIM;o winter condition (December 2015 to March 2016) between SST and Chl-aSAT (RSST = 0.45, P < 0.02). The Chl-aSAT showed un-expectedly low values (-0.5-1.2 mg m-3) with one month-lag of the winter bloom period jointly with the presence of warmer-than-usual water (-1.0 C) and episodes of strong northwesterly winds (speed 8.0-10.0 m s- 1) that began in autumn that drove a-2 month-lag in its winter peak. The Chl-aSAT and SST winter spatial patterns, showed low Chl-aSAT values (--0.5 to-1.0 mg m-3) along the bay and higher-than-usual SST by -0.5-1.0 C relative to a year under the La Nin & SIM;a winter condition (2017-2018). This triggered the possible thermocline deepening and the lowest levels of nutrient supply to the photic layer during the El Nin & SIM;o winter episode. Hovmoller diagrams of Chl-aSAT and SST anomalies along the coast revealed a sharp drop to negative anomaly values (--0.7 to-1.2 mg m-3), in-phase but negatively correlated with the SST coastal anomalies (R = -0.88, P < 0.01). This biophysical coupling played a crucial role in the exceptional drop to the lowest winter Chl-aSAT levels seen in LPB since the MODIS satellite sensor began taking measurements in 2002 (Chl-aSAT values were lower than usual by -0.9-1.2 mg m-3). Besides the lowest winter levels observed, this research reflected the El Nin & SIM;o signal-driven changes over the basic seasonal average of the LPB climate system The non-significant negative trend observed in the winter average Chl-aSAT values, indicates that LPB may be less resilient to future environmental disturbances.

The Gulf of California and adjacent Pacific have passed through a prolonged warming period that affects the Humboldt squid D. gigas life cycle, which was the third largest fishery in Mexico until its total collapse after 2010. The aims of the present study were (i) to characterize the nursery habitat of paralarvae of the complex Sthenoteuthis oualaniensis-Dosidicus gigas (SD complex) on the basis of 1112 paralarvae collected from zooplankton trawls carried out during ten oceanographic cruises off northwestern Mexico between 2010 and 2017; and (ii) to model the seasonal and interannual variability of the nursery habitat, applying a generalized additive model (GAM) using a regional long-term (1922-2017) hydrographic database. The GAM showed significant relationships of paralarvae abundance with the seasonal average of thermocline depth, absolute salinity, and conservative temperature. The potential nursery habitat of the SD complex paralarvae showed its maximum expected abundance in the entrance of the Gulf of California during spring, when the thermocline depth was shallowest (< 30 m). During summer the nursery habitat moved northward along the Pacific west coast of the peninsula. Autumn and winter were less suitable seasons for paralarvae nursery because the thermocline was deep throughout the area of study. Potential nursery habitat did not change interannually in location during La Nina conditions, but did increase the expected abundance in its southern extension. El Nino events contracted the nursery habitat near Cabo San Lucas, and caused the habitat to move northwards over both coasts of the Baja California peninsula. Despite seasonal and interannual climatic variability, two regions remained suitable habitats almost throughout the year. One was associated with coastal upwelling regions (Cabo Corrientes) and the second comprised the oceanic region of high mesoscale kinetic energy located south of Cabo San Lucas. We conclude that the potential nursery habitat of the SD complex is more coastal than oceanic, and is associated with a shallow thermocline in the tropical-subtropical convergence off Mexico. The recent anomalous warming period in this region could drive the changes in the morphology of D. gigas in the Gulf of California, given the effects of environmental variability over early stages of development throughout the adult ontogenesis.

In early summer (June 2010), we used zooplankton and hydrographic sampling to analyze relationships between larval fish habitats and converging water masses in the Pacific tropical-subtropical region off Mexico. Results showed an equatorward jet parallel to the Baja California Peninsula (the Tropical Branch of California Current) which was located northward of 25oC surface isotherm. In this area, a larval fish habitat indicated by Triphoturus mexicanus larvae was identified. The habitat had low larval abundance (17 larvae per 10 m2) with major larval concentration below the thermocline (∼ 20 Co and oligotrophic conditions, < 0.3 mg m-3). Two larval fish habitats were defined south of the 25oC surface isotherm. One larval fish habitat was located in a coastal jet and cyclonic field immersed in the Transitional Waters, with the highest larval fish abundance (49 larvae 10 per m2). The indicator species were Vinciguerria lucetia and Diogenichthys laternatus. Both species had the greatest abundance in the warm (∼25 oC) and mesotrophic (>1 mg m-3) waters of the shallow thermocline (∼30 m depth). The other larval fish habitat occupied an area of anticyclonic circulation in the offshore California Current Water, where the thermocline was depressed ∼ 70 m depth. Oligotrophic conditions (0.3 mg m-3) corresponded with the lowest mean larval abundance (14 larvae per 10 m2) of the study. The distribution of the larval fish habitats and their indicator species correspond with the water masses distributions in the Tropical-Subtropical convergence, which are modulated by mesoscale structures affecting the thermocline depth and the larval life-history.

The hydrography and circulation of the Northwestern Iberian Margin (NWIM) was studied over an annual cycle from November 2008 to December 2009. The study was focused on the Cape Silleiro border region that separates the rugged northern coastline of the Rias Baixas embayments and the smoother southern coastline, a source of major fresh water outflows. Monthly across-shelf transects off Cape Silleiro monitored hydrography and currents, while an upward-looking ADCP registered currents in 72 m depth on the shelf over the period. To provide greater detail of the variability both spatial and temporal, during the annual cycle, a ROMS-AGRIF configuration of the region was built. Validation of the model against the observations produced robust results that reproduced many aspects of the observed variability. It was therefore possible to examine features of the NWIM, such as the seasonal cycle, wind-induced upwelling and downwelling and their associated horizontal circulations, as well as nearshore countercurrents related to freshwater plumes, in unprecedented detail. Five different scenarios were investigated in the study year through examination of characteristic physical processes: (1) late autumn up welling, (2) high energy winter conditions, (3) spring upwelling-downwelling cycles, (4) summer upwelling, and (5) autumn transition to high energy conditions. The demonstration of the robust capacity of this model configuration, to reproduce in detail the phenomena observed in this region, suggests that the physical model could be reliably extended to other years in order to provide the basis for multidisciplinary studies in relation to biogeochemical cycles and harmful blooms. Other applications could include transport of sediments, larvae, microplastics and other contaminants as well as operational application for general ocean forecasting.

Data from an acoustic Doppler current profiler (ADCP), a wave-gauge, a met-ocean buoy and model results provide new insights into the wave regime in a partially sheltered upwelling-driven bay, the Ria de Vigo (NW Iberia), and the adjacent continental shelf from June 2013 to August 2014. Swell on the NW-Iberian shelf comes mainly from NW directions, while wind sea comes from the NW under upwelling conditions, and from the SW under downwelling conditions. As the ria is protected from the NW and exposed to the SW, swell is almost always attenuated when entering the bay, and wave height inside the ria depends mostly on shelf wind sea variability. During the upwelling season, swell and wind sea barely enter the ria and wave heights inside the ria are small (0.21 m). During the downwelling season, shelf wind sea directly enters the ria, contributing more to the total wave height which achieves its maximum values (0.46 m). There is a cumulative action of wave and currents (wave current coupling, WCC) that is stronger during the downwelling season. The WCC entails an increase in the seabed energy which could reinforce bottom remineralization. The inter-annual variability (2009-2016) of winter wave height and WCC in the ria is associated with the combined role played by the North Atlantic Oscillation (NAO) and West Europe Pressure Anomaly (WEPA) indices. The highest waves and strongest WCC occur during the coincidence of negative NAO and positive WEPA phases and can have potentially relevant repercussions on the ecosystem services of the ria.

The changes in temperature and dissolved oxygen concentration in the Pacific Ocean in the northern region of the shallow oxygen minimum zone (OMZ) off Mexico were analyzed on the basis of the Word Ocean Database and a series of oceanographic cruises (LEGOZ-Mex). In order to test the changes in both parameters between two similar oceanographic scenarios according to the Pacific Decadal Oscillation (PDO), a comparison was made between the last two cool PDO phases of 1962-1974 and 2002-2012 when conditions might be expected to be relatively similar. Results show that the surface layer (upper layer of 50 m depth) has been warming significantly in two of the three areas included in this study: 1) the southern end of the California Current (0.8 degrees C; p < 0.001), 2) the southern Gulf of California (0.49 degrees C; p < 0.001), and 3) the Tropical Transitional Pacific (0.4 degrees C). Simultaneously, the water column has been deoxygenating significantly (p < 0.001), not only in the subsurface shallow OMZ layer (similar to 100 to 300 m depth) in the Tropical Transitional area (- 45%), as has been recorded previously, but from 300 to 1000 m depth (by between -38% and - 57%). The exception was the California Current area at the northern limit of the shallow OMZ, where the deoxygenation was only significant (p < 0.001) from 300 to 1000 m depth (similar to - 20%). We conclude that the significant warming of the surface layer in the Pacific OMZ off Mexico has increased the stratification of the water column and contributed to the deoxygenation of the interior ocean, at least between the last two cool phases of the PDO. These changes may be significantly affecting the marine biota that inhabit the shallow OMZs.

Poster presented at the Ocean Sciences Meeting 2020, 16-21 February 2020, San Diego, Calif. USA

The distribution and transport of paralarvae of the complex Sthenoteuthis oualaniensis - Dosidicus gigas (SD complex, Cephalopoda: Ommastrephidae) in the tropical-subtropical convergence off Mexico were analyzed under contrasting interannual environmental conditions. Two El Niño years were sampled (2010 and 2016), in which the SST were up to 3 °C above the average throughout the study area, while during La Niña year (2012) the SST anomalies were up to 2 °C below the average. During El Niño years, a relative shallow thermocline (<60 m depth) was detected around Cabo Corrientes, where the paralarvae were found with mean abundance of 2 org 1000 m−3. During La Niña condition, a shallower thermocline was detected in the entrance of the Gulf of California (~20 m depth) and the paralarvae abundance rose to 84 org 1000 m−3 with high frequency of occurrence. In both El Niño and La Niña conditions the paralarvae were mainly found in the strongly stratified waters (>80 cycles h−1). In addition, a simple dispersion Lagrangian model based on observed satellite geostrophic currents, suggested association of the SD complex paralarvae with mesoscale structures, in which the eggs and hatched paralarvae had an appropriate habitat for a nursery, retaining the paralarvae until their recruitment in a ~100 km radius. But during warm extreme events, with less mesoscale activity, the paralarvae could be transported as far as 500 km southeast of the spawning zone. Even though the interannual ENSO conditions modulate the magnitude of the paralarvae abundance, the shallow and well developed thermocline could help paralarvae to increase their survival chances, while mesoscale activity retains them near the productive coastal waters.

We present results from a 2 month deployment of an ocean glider over the Northwestern Iberian Margin. Glider observations during the exceptionally strong 2010 summer upwelling season resolved the evolution of physical and biogeochemical variables during two upwelling events. Upwelling brought low oxygen Eastern North Atlantic Central Water from 190 m depth onto the shelf up to a depth of 50 m. During the two observed periods of upwelling, equatorward transport over the shelf increased from 0.13 (± 0.04) Sv to 0.18 (± 0.08) Sv and a poleward jet developed over the shelf-break. The persistent upwelling favourable winds maintained equatorward flow on the outer shelf for two months with no reversals during relaxation periods, a phenomenon not previously observed. During upwelling, near surface chlorophyll a concentration increased by more than 6 mg m-3 . Dissolved oxygen concentration in the near surface increased by more than 40 μmol kg-1 , 6 days after the chlorophyll a maximum. This was the first and, to date, only deployment of a glider over the North West Iberian Margin. A single glider was able to occupy a cross shelf section for two months, without the need for a costly ship based campaign. This presentation highlights some of the challenges of using gliders to study shelf break regions.

The dynamics of the bottom boundary layer and their effects on the development of nepheloid layers (NLs) on a high-energy and upwelling-affected margin, the NW Iberian continental shelf, were studied by means of ADP currents, wave time series, and across-shelf hydrographic surveys covering an entire annual cycle. The bottom boundary layer hydrodynamics showed that high levels of bottom shear stress over the inner shelf occurred mainly during downwelling seasons, when there was a coupling between storm waves and intense currents. This wave-current coupling promotes strong resuspension events that favored the generation of bottom NLs (BNLs). BNLs were well developed on the inner continental shelf inshore of a thermohaline front generated by the interaction of the Iberian Poleward Current and the West Iberian Buoyant Plume. The existence of this front limited the extent of offshore export of resuspended particles during the downwelling season. In contrast, during the upwelling season, only thin BNLs were developed, and surface NLs, principally composed by biogenic particulate material, were advected offshore in the Ekman layer, often as part of the development of upwelling filaments. Our study confirmed that wave orbital velocity under stormy conditions, in combination with the hydrography, could explain the shoreward boundary of the Galician mud depocenter.

This item is made of 2 files, of which 1 is the dataset in matlab format and the other (Readme .txt) include a small description of the computed variables. Dataset contributed to the Projects CAIBEX and RAIA.-- Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0). The authors appreciate that users of these data: 1) Contact Des Barton (e.d.barton@iim.csic.es; barton.des@gmail.com ) to follow the uses of the data, and 2) Include the requested acknowledgment (cite using the DOI of this dataset) in any presentations or publications

This contribution has been funding by the Spanish Ministry of Education project “CAIBEX Shelf–ocean exchanges in the Canaries–Iberian Large Marine Ecosystem” (CTM2007–66408–C02–01/MAR), by the European Union FEDER project MarRISK: Adaptacion costera ante el Cambio Climatico: conocer los riesgos y aumentar la resiliencia (0262_MarRISK_1_E) and by the Spanish Ministry of Science and Innovation project “i-SMALL: Importancia de lo pequeno en un oceano en cambio: desentranando la variabilidad de corta escala y el papel del plancton pequeno”. (CTM2014-56119-R

The tropical Oxygen Minimum Zones (OMZ) are known to shelter a chlorophyll-a maximum (CM) within suboxic waters (<20 μmol kg−1), below other chlorophyll-a maxima and with an unknown temporal variability in the Pacific OMZ off Mexico. Here, 1161 chlorophyll-a fluorescence and oxygen profiles collected between 2003 and 2016 were used to describe statistically the physical situation in which the suboxic-CM was found. Results indicate that the suboxic-CM was a persistent feature at seasonal scale at depths between 40 and 190 m at an average density potential anomaly of 26 ± 0.2 kg m−3, related to the Subtropical Subsurface Water, which is nearly unaffected by mixing with other water masses. The suboxic-CM south of 21°N was generally associated with the upper limit of the suboxic waters of the OMZ. In this region, the distance between the suboxic waters and the euphotic zone (1% of surface irradiance) was > - 25 m year-round, which suggests that persistent low-light levels allow development of the suboxic-CM. The persistence of the suboxic-CM is consistent with its association with a stable microbial community. The effects on the ecosystem and biogeochemical cycles remain to be investigated.

The distribution of calanoid copepods was investigated in the convergence zone between the California Current Water and Transitional Tropical Water in June 2010 to understand how this zooplankton community responds to mesoscale environmental structure. Hydrographic conditions and zooplankton profiles were measured along two transects which crossed a mesoscale front and adjacent structures, visible in sea surface temperature and ocean color satellite images. The hydrographic structure showed strong temperature (similar to 2 degrees C) and oxygen (50 mu mol kg(-1)) gradients in the frontal zone (similar to 90 km) associated with a sinking of the thermocline and oxycline, from similar to 30 m depth in the Transitional Tropical Water, to similar to 90 m depth in the California Current Water. The front was marked by a salinity minimum (<34.3 g kg(-1)) that sank along the sloping thermocline. High chlorophyll-a concentrations associated with the thermocline were detected in the Transitional Tropical Water, where a cyclonic eddy was defined. These concentrations decreased as the thermocline depth increased. Multivariate analysis defined three calanoid copepod habitats related to the hydrographic structure. A habitat with the highest copepod concentration (24,704 copepods 1000 m(-3)) was found on the tropical water side associated with a cyclonic eddy. Subeucalanus subtenuis and Centropages furcatus, indicator species, were concentrated between the thermocline (similar to 30 m depth) and the sea surface. On the subtropical water side, where the thermocline was deeper, a habitat with the lowest copepod concentration (3304 copepods 1000 m(-3), an order of magnitude smaller), characterized by Euchaeta indica and Centropages elongates, was observed. As an unexpected result, the habitat located in the frontal zone, characterized by Scolecithrix bradyi and Heterorhabdus papilliger had low copepod concentration (4453 copepods.1000 m(-3)). This low concetration could be due to the steep thermocline slope in the frontal zone, which could cause the thermocline depth to rapidly exceed the photic zone depth, and therefore affect the availability of food for calanoid copepods. It is concluded that the definition of the calanoid copepod habitats, was not only caused by the front itself, but by its interaction with other fine-scale mechanisms that generate oceanographic conditions leading to development of different food webs depending on the structure of water column.

In this study, we explored the changes in the vertical distribution and abundance of copepod nauplii and ichthyoplankton every hour in three different depth strata during a period of strong internal tides, which have been shown to accumulate and transport plankters. In the deeper stratum, the abundance of copepod nauplii was significantly greater, significantly increased during the cold phase of the internal tide, and was significantly correlated with both total and baroclinic current flows in the direction of internal tide propagation. On the other hand, ichthyoplankton abundance was generally low, with no stratification in vertical distribution, no significant changes across the two phases of the internal tide, and no correlation at any depth with any current flows. The cold phases of the internal tide were characterized by a shallow thermocline, a cooler water column, and a significant increase in the abundance of copepod nauplii in the bottom stratum. On the other hand, the warm phases of the internal tide were characterized by abrupt warming in surface waters, a depression of the thermocline, and a significant decrease of copepod nauplii in the bottom stratum. The depth distribution and buoyancy of the different groups of larvae may be responsible for the differences found.

The Canary and Portugal Currents form the eastern limb of the North Atlantic Subtropical Gyre. Detailed knowledge of the currents is still surprisingly sparse in some respects and is largely based on indirect methods of estimating the Sow. The entire eastern boundary of the gyre is affected by the process of coastal upwelling, driven by the seasonally varying Trade Winds. Upwelling is intimately related to the currents on the continental shelf, and varies on timescales from several days upwards. This phenomenon has been studied intensively at different places and times and long-term sampling has only begun in recent years.

Dataset associated with the submitted publication - "LARVAL FISH HABITATS AND DEOXYGENATION IN THE NORTHERN LIMIT OF THE OXYGEN MINIMUM ZONE OFF MEXICO" Created: 10/10/2019 by Victor M. Godínez (CICESE). Ver. 1.0 Authors: Laura Sánchez-Velasco, Victor M. Godínez, Erick D. Ruvalcaba-Aroche, Amaru Márquez-Artavia, Emilio Beier, Eric D. Barton and S. Patricia A. Jiménez-Rosenberg. Project_info: This data base has been obtained during the project funded by the financial support of SEP-CONACyT (contracts 2014-236864, L. Sanchez-Velasco) and Fronteras de la Ciencia-CONACyT (contracts 2015-2-280, L. Sanchez-Velasco). License: The authors appreciate that users of these data: 1) Contact Laura Sánchez-Velasco (lsvelasc@gmail.com) to follow the uses of the data, and 2) Include the requested acknowledgment (cite using the DOI of this dataset) in any presentations or publications. Variables: five structures for the four surveys (Survey_Feb2010, Survey_Apr2012, Survey_Jun2015, Survey_Mar2016, Survey_Oct2017) with the following variables: Name Units ___________ ________ 'Latitude' 'degrees' 'Longitude' 'degrees' 'XX' 'Distance (km)' 'YY' 'Distance (m)' 'Pressure' 'decibars' 'Temperature' 'conservative temperature (oC)' 'Salinity' 'Absolute Salinity (g/Kg)' 'Oxigen' 'dissolved oxygen (mL/L)' 'Fluorescence' '(mg/m^3)' 'xlar' 'Distance (km)' 'ylar' 'Distance (m)' 'Bb' 'Bregmaceros bathymaster (Larvae/10m^2)' 'Bp' 'Benthosema panamense (Larvae/10m^2)' 'Dl' 'Diogenichthys laternatus (Larvae/10m^2)' 'Asp' 'Auxis spp (Larvae/10m^2)' One structures for the oldest data with the following variables: Name Units ___________ ________ 'Latitude' 'degrees' 'Longitude' 'degrees' 'Time' 'absolute julian day' 'Pressure' 'decibars' 'Temperature' 'conservative temperature (oC)' 'Salinity' 'Absolute Salinity (g/Kg)' 'Oxigen' 'dissolved oxygen (mL/L)

[This corrects the article DOI: 10.1371/journal.pone.0197627.].