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Mathematical algorithms relate satellite data of ocean color with the surface Chlorophyll-a concentration (Chl-a), a proxy of phytoplankton biomass. These mathematical tools work best when they are adapted to the unique bio-optical properties of a particular oceanic province. Ocean color algorithms should also consider that there are significant differences between datasets derived from different sensors. Common solutions are to provide different parameters for each sensor or use merged satellite data. In this paper, we use satellite data from the Copernicus merged product suite and in situ data from the southernmost part of the California Current System to test two widely used global algorithms, OCx and CI, and a regional algorithm, CalCOFI2. The OCx algorithm yielded the most favorable results. Consequently, we regionalized it and conducted further testing, leading to significant improvements, especially in eutrophic and oligotrophic waters. The database was then separated according to (a) dynamic boundaries in the area, (b) bio-optical properties, and (c) climatic conditions (El Niño/La Niña). Regional algorithms were obtained and tested for each partition. The Chl-a retrievals for each model were tested and compared. The best fit for the data was for the regional algorithms that considered the climatic conditions (El Niño/La Niña). These results will allow for the construction of consistent regionally adapted time series and, therefore, will demonstrate the importance of El Niño/La Niña events on the bio-optical properties of the area. [ABSTRACT FROM AUTHOR]

Depending on dimensions, orientation and topographic features, the circulation of semi-enclosed seas adjacent to regions of coastal upwelling are strongly influenced by their interaction with a shelf upwelling jet of adjacent waters. A special case are square bays, where opening is about the same size as length, and are bordered by headlands at the entrance. This study analyzed surface currents measured between 2009 and 2020 with high-frequency (HF) radar in Todos Santos Bay, a square bay located in northwestern México, to obtain mean and seasonal surface circulation patterns. HF radar measurements indicate that the average circulation pattern within the bay is cyclonic, with water of the California Current (CC) entering primarily as a coastal jet through the northern mouth of the bay. The similarity of monthly average maps with the long-term average suggests the cyclonic circulation persists year-round. Scale analysis demonstrates that given the size of the bay, only one eddy, primarily controlled by inertia, is dominantly formed inside. The mean cyclonic circulation defines the bay as an upwelling shadow. • Sea surface currents in Todos Santos Bay measured by HF radar. • Internal circulation pattern is cyclonic. • Seasonal variability is low, with cyclonic circulation year-round. • Main driver of circulation is the upwelling coastal jet entering the bay. [ABSTRACT FROM AUTHOR]

Phytoplankton photosynthetic parameters (maximum light utilization coefficient,α* ; maximum photosynthetic rate, P*m; maximum quantum yield, ϕmax) off Baja California were estimated from samples collected at the 50% light level during winter, spring, summer and autumn 1999. Chlorophyll concentration was also determined and in situ experiments were conducted using the 14C method to determine primary production (PP) in the euphotic zone. The highest α* and ϕmax values were found during the spring survey, mainly at the coastal areas, associated with diatom and dinoflagellate abundances and high chlorophyll concentrations. However, high P*m(z) values were measured during autumn in both inshore and offshore areas due to the presence of smaller phytoplankton cells. The average profiles of the photosynthetic parameters α(z)* and P*m(z) in the water column were estimated for 2 regions. These parameters were used to estimate PP with semi-analytical models. Modeled PP was contrasted with in situ PP to validate our calculated photosynthetic parameters in the euphotic zone. In general, modeled PP values were similar to in situ values (94 mg C·m-2·h-1), with a high correlation coefficient (r = 0.85). Modeled PP for coastal waters in the northern and central regions was 1.5-fold greater than in situ estimates during spring. In conclusion, when used with remotely sensed phytoplankton pigment and surface irradiance data, the average profiles ofα(z)* and P*m(z) could be a useful tool to calculate PP in our study area. [ABSTRACT FROM AUTHOR]

A succession of interannual warm events occurred in the Pacific during the 2013-2016 period, when positive thermal anomalies were detected. A broad region with abnormally warm waters in the northeastern Pacific Ocean was observed in 2013, which by 2015 had reached waters off Baja California (Mexico). In addition to the ongoing warming effect, early evidence of an El Niño event was detected in 2015. This paper analyzes hydrographic data measured at Todos Santos Bay and environs, as well as satellite-derived sea-level data, to characterize changes in the hydrographic conditions during the 2013-2016 period. The highest positive temperature anomalies (~5 °C) were observed in September 2015, with a steep decline to neutral conditions in spring 2016. Records for the bay showed slight variations in hydrographic conditions during spring, highlighting the importance of local over remote forcings during this time of year. In autumn, by contrast, interannual signals prevailed over local processes. Satellite-derived sea-level data revealed an alongshore propagation of remote signals, identified as shallow coastal poleward flows. [ABSTRACT FROM AUTHOR]

The ocean off the Baja California Peninsula (Mexico) has been affected by interannual processes. Some of these processes have produced changes in oceanic circulation and the atmosphere, which have been reflected in the structure of the water column. Stratification, defined as the amount of energy needed to mix water throughout the water column, determines nutrient availability in the euphotic zone for phytoplankton growth. The aim of this study is to describe and relate the interannual variations of phytoplankton production and biomass with changes in the structure of the water column. To this end we analyzed time series (1997-2016) for integrated Chlorophyll a, integrated primary production, pycnocline depth, mixed layer depth, and stratification indices along line 100 of the Investigaciones Mexicanas de la Corriente de California (IMECOCAL) program. The results showed 2 periods of high stratification and a decrease in phytoplankton production and biomass off Baja California, corresponding to the intrusion of subarctic water and El Niño 2015-2016. Finally, by using generalized additive models, we related 2 photosynthethic parameters-maximum photosynthetic rate and maximum light utilization coefficient-with water stratification. These relationships explained interannual variations in phytoplankton production in terms of water column stratification. The time series and the analysis reported here for IMECOCAL line 100 could be used to extrapolate the effects of interannual physical processes on phytoplankton in other zones off the Baja California peninsula. [ABSTRACT FROM AUTHOR]

We conducted a study from January 2002 to February 2008 on silicoflagellate fluxes in Alfonso Basin at the entrance to the Gulf of California. Thirteen taxa were identified in sediment trap samples, with Octactis pulchra as the dominant species. Total flux climatology reached a maximum value of 5×106 skeletons m-2 day-1 in December and then sharply decreased to a minimum value in February (2.3×103 skeletons m-2 day-1) concurrently with the climatological sea surface temperature (SST) minimum. Subsequently, there was a positive trend with a second relative maximum of 1.6×106 skeletons m-2 day-1 in September coincident with a maximum in climatological SST. During this period, there was a similar increase to 1.4×106 skeletons m-2 day-1 in May. Factor analysis identified three patterns of variation: 'subtropical oceanic,' 'subarctic,' and 'equatorial El Niño.' Factors had reasonable correlations with the Pacific decadal oscillation (PDO), North Pacific Gyre oscillation (NPGO), and El Niño Modoki indices (r=0.53, 0.67, and 0.63, respectively). The first and second modes were apparently linked to decadal climatic conditions correlated to PDO and NPGO, as suggested by the silicoflagellate species Dictyocha messanensis forma messanensis and the assemblage of D. epiodon and Distephanus speculum, respectively; the third mode was related to the presence of warm equatorial-oceanic waters identified by D. messanensis forma spinosa, which defines El Niño influence. These results demonstrate the importance of the region where there is a confluence of the low-frequency, high-latitude PDO, NPGO, and high-frequency El Niño signals. [ABSTRACT FROM AUTHOR]

Abstract: 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 (24–31N). Near surface anomalies were used to characterize four periods of distinctive variability: (1) a warm and saline phase of El Niño 1997–1998, (2) a saline period from 1999 to 2002, (3) fresh subarctic water in 2002–2006, and (4) a saline-fresh (El Niño-La Niña) phase in late 2006 to early 2008. Subsurface (200m) 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 28N) and the south (equatorward of 28N). 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Experiments were carried out at a coastal upwelling site (ENSENADA station) off northern Baja California (México) during autumn 2015 (OCT-15) and spring 2016 (APR-16) to estimate phytoplankton daily growth (μo) and mortality (m) rates and to assess microzooplankton grazing impact (m:μo) on the phytoplankton community and specific autotrophic groups. In accordance with regional seasonality and under an environmental warming scenario due to the El Niño 2015-2016 event, significant differences in both hydrographic conditions and the growth--mortality dynamics of the phytoplankton community were observed between the 2 study periods. The μo and m estimates were, respectively, 0.120 ± 0.012 d-1 and 1.145 ± 0.049 d-1 for OCT-15 and 1.186 ± 0.002 d-1 and 0.409 ± 0.086 d-1 for APR-16. The results of this study suggest that the effects of the anomalous warming on the phytoplankton community were more evident in OCT-15. During that period, growth of the larger autotrophic components (diatoms) was severely controlled by the environmental limitation of nutrients caused by the sinking of the thermocline that resulted from the entrance of warm water to the region. Furthermore, microzooplankton exerted active grazing pressure on phytoplankton biomass (72% of chlorophyll a [Chla]) and primary production (PP = 0.20 μg Chla·L-1 d-1), with grazing impact >100% of PP. In APR-16, when the ecosystem apparently started returning to the spring conditions, a high value for PP (3.73 μg Chla L-1 ·d-1) was estimated, with only one third of it being consumed by microzooplankton (34% of PP). The results of this research evidence the high dynamism of multivorous food webs coupled to the seasonal and interannual variability of coastal upwelling systems. [ABSTRACT FROM AUTHOR]

Fetch-limited wave growth was analyzed using high spatial and temporal resolution measurements obtained with high-frequency (HF) radars. To calculate the wave spectrum, the second-order echo (S2N) was extracted from the Doppler spectrum and mapped to the wave frequency domain. The conversion of S2N to the wave frequency spectrum was carried out using a linear parametric model dependent on wind speed. Wave growth, represented by the dimensionless energy and peak frequency as a function of dimensionless fetch, was determined from the spectra calculated for 25 cells (~400 km²) in the vicinity of a moored Air-Sea Interaction Spar buoy. The buoy data were used as reference and to provide the wind information required for the wave growth analysis. The simultaneous data from the buoy and HF radars showed a suitable agreement with the wave growth curves. The analysis of the 25 cells showed an adequate agreement and certain dispersion around the growth curves. Possible causes of this dispersion are related to errors in the estimation of the frequency spectrum and fetch, and the assumption of homogeneous wind conditions. From the limited data set used, it was not possible to prove any impact of swell on wave growth; however, it is possible that analysis over a wider range of swell heights may provide this evidence. Nevertheless, the results suggest that the linear parametric model is able to reproduce fetch-limited wave growth. This work represents the first effort focused on fetch-limited wave growth using HF radars. [ABSTRACT FROM AUTHOR]

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 Bahía Vizcaíno 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. [Copyright &y& Elsevier]