The Relationship between Photosynthesis and Irradiance for Gulf of California Phytoplankton

During June 17-28, 1982, we carried on experiments to generate photosynthesis-irradiance curves for phytoplankton from five locations of the central and northern Gulf of California. Using natural sunlight, on board 14C incubations were done with samples collected from five different depths within the euphotic zone. In general there were great vertical changes of variables controlling primary productivity, even in cases where weak vertical TOC gradients indicated high instability and mixing of the euphotic zone. The assimilation number (PBm) had a two fold variation within the mixed layer. In general PBm decreased monotonically with depth due to phytoplankton conditioning to lower irradiances. Surface PBm values had a range of 8 to 15mg C. mg Chl a- 1. h-1. When a thermocline was present, PBm for the bottom of the euphotic zone was about 4 to 10% of that for surface waters. But, without a thermocline, P~ for the bottom of the euphotic zone was ~ 60% of that for surface waters, due to turbulence moving phytoplankton up and down the water column. Diatoms were abundant in three stations near Angel de la Guarda and Tiburon islands. For the station at the central gulf and the one at the very northern gulf, very few nano and microplankton were found with the inverted scope technique, but high chlorophyll concentrations and primary productivity indicated a high abundance of picoplankton. This difference in plankton size composition was not reflected in PBm values. Nutrient concentrations were high and did not limit PBm values. Our PBm values are higher than those reported for the gulf's winter phytoplankton; and they are about two times higher than those for winter phytoplankton of the oceanic region between San Diego and Acapulco. Our Gulf of California integrated primary productivity values had a range of 1.3 to 4.4gC. m-2. d-1

Chlorophyll profiles and the water column structure in the Gulf of California

Remote sensors provide information on the photosynthetic pigment concentration for the upper 22% of the euphotic zone. To model primary production in the water column from satellite-derived photosynthetic pigments, estimates of the vertical distribution of pigment concentration are required. A Gaussian distribution function is used to represent the pigment vertical profile with four parameters. We used 268 chlorophyll concentration profiles from 1973 through 1993, to estimate these parameters. Cluster analysis of surface temperature was used to define the cool season as the period end of November-end of June, and the rest of the year is considered the warm season. Cluster analysis of surface temperature acid chlorophyll data grouped the stations into four regions for the cool season and into two regions for the warm season. Regression models were developed for each region and season to estimate the depth of the deep chlorophyll maximum as a function of the mixed layer depth or an index of stratification. We were not able to generate useful regression models to predict the other three Gaussian parameters. Thus, their representative means were calculated for each region and season. Assuming a homogeneous biomass profile resulted in underestimation of integrated primary production by as much as 60% with respect to the values derived from the non-homogeneous profiles.La télédétection donne accès à la concentration de pigments photosynthétiques dans les 22% supérieurs de la couche euphotique. La modélisation de la production primaire dans la colonne d’eau à partir des pigments photosynthétiques dérivés de cette estimation implique des mesures de la distribution verticale de la concentration en pigments. Une fonction de distribution gaussienne a été utilisée pour représenter le profil vertical des pigments avec quatre paramètres. Nous avons utilisé 268 profils de concentrations de chlorophylles, obtenus de 1973 à 1993. L’analyse de nuages de la température superficielle est utilisée pour définir la saison froide (fin novembre – fin juin). Le reste de l’année a été considéré comme la saison chaude. Cette analyse des données de température superficielle et de teneur en chlorophylle met en évidence quatre régions pour la saison froide et deux pour la saison chaude. Les modèles de régression sont développés pour chaque région et pour chaque saison afin d’estimer le maximum profond de chlorophylle en fonction de la profondeur de la couche mélangée ou un indice de stratification. Nous n’avons pas développé de modèle de régression pour la prédiction des trois autres paramètres gaussiens. Aussi, leurs moyennes représentatives ont été calculées pour chaque région et saison. En supposant un profil de biomasse homogène, l’estimation peut conduire une sous-estimation de la production primaire intégrée au plus à 60%, en relation avec des valeurs dérivées de profils non homogènes

Atmosphere-ocean CO2 flux in the Gulf of California

The CO2 fluxes were obtained in three cruises in RV Mexican Navy Altair in September 2016 in Navachiste, Sinaloa and Guaymas, Sonora in the Gulf of California