), and low values in summer (7.1 ± 1.0 M NO 3 , 1.22 ± 0.06 M PO 4 , and 16.0 ± 2.1 M Si(OH) 4 ), related to vertically stratified water column conditions ( = 150-223 J m -3 ). In contrast, below 200 m the seasonal variability of the three nutrient concentrations was reduced. The hydrographic analysis indicated that the wintertime surface nutrient enrichment was due to an intensification of the water column mixing, which vertically transported Subtropical Subsurface Water (SSW, cold and nutrient-enriched) to the surface of BC. In contrast, nutrient impoverishment in summertime was due to biological consumption combined with the stratification of the water column, which reduced the vertical flow of SSW and, consequently, the supply of nutrients to the surface of this system. The N:P and Si:N ratios and an excess of PO 4 > 0.65 M in surface waters indicated that NO 3 was the potential limiting nutrient for primary production in this oceanographic province of the Gulf of California.Key words: nutrients, enrichment, vertical mixing, Ballenas Channel. RESUMEN.Se realizaron tres cruceros oceanográficos en la región del canal de Ballenas (CB) durante el invierno de 2002, la primavera de 2003 y el verano de 2004, con el objetivo de estudiar el impacto de la mezcla vertical de la columna de agua () sobre la concentración superficial de los nutrientes inorgánicos disueltos (NO 3 , PO 4 y Si(OH) 4 ). Las concentraciones promedio de nutrientes integrados en los primeros 100 m del CB mostraron una clara variación estacional, con valores altos en el invierno (18.2 ± 1.1 M de NO 3 , 2.36 ± 0.08 M de PO 4 y 35.4 ± 3.2 M de Si(OH) 4 ), asociados a condiciones de mezcla intensa de la columna de agua ( = 0.7-16 J m -3 ), y valores bajos en el verano (7.1  1.0 M de NO 3, 1.22 ± 0.06 M de PO 4 y 16.0 ± 2.1 M de Si(OH) 4 ), asociados a condiciones de estratificación de la columna de agua ( = 150-223 J m -3 ). En contraste, por debajo de los 200 m la variabilidad estacional de la concentración de los tres nutrientes fue muy pequeña. El análisis hidrográfico indicó que el enriquecimiento superficial de nutrientes en invierno se debió a la intensificación de la mezcla de la columna de agua, la cual transportó verticalmente el Agua Subsuperficial Subtropical (ASS, fría y rica en nutrientes) hacia la superficie del CB. En contraste, el empobrecimiento de nutrientes durante el verano se debió a que el consumo por la actividad biológica se combinó con la estratificación de la columna de agua, la cual redujo el flujo vertical del ASS y, en consecuencia, el aporte de nutrientes hacia la superficie de este sistema. Las razones N:P, Si:N y un exceso de PO 4 > 0.65 M en las aguas superficiales indicaron que el NO 3 fue el nutriente potencialmente limitante para la producción primaria de esta provincia oceanográfica del golfo de California.Palabras clave: nutrientes, enriquecimiento, mezcla vertical, canal de Ballenas.

Eolian transport of mineral dust is one of the main inputs of iron (Fe) to the global ocean; however, the magnitude and biogeochemical impact of this supply depends on the solubility of the deposited dust. In particular, the effect of temperature on Fe‐bearing dust solubility has been scarcely investigated even though a seasonal gradient of sea surface temperature (SST) is a common feature in coastal zones adjacent to the major dust source regions of the world. In this work, the effect of temperature on the fractional solubility of Fe (FFeS) was evaluated experimentally using sieved soils (as a dust proxy) from the Baja California Peninsula and surface seawater from the Gulf of California (GC). Two incubations were performed at 17°C (winter) and 29°C (summer) considering the seasonal variability of SST in the GC. Differences in FFeS up to 3 orders of magnitude (0.003–4.49%) were linked to incubation temperature, dust load, and contact time between seawater and dust. After 72 hr of incubation, the effect of temperature was statistically significant (p < 0.05) for all dust treatments, with FFeS higher (4–24 times) at 29°C. High FFeS in warmer waters are a result of increased Fe‐bearing dust dissolution and decreased scavenging of Fe by dust particles. Since temperature appears to control the magnitude of FFeS in the GC, we suggest that this factor could have an effect on the atmospheric inputs of soluble Fe in marginal seas with similar seasonal SST contrasts; including the global ocean, where well‐defined latitudinal temperature gradients exist.

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Con el propósito de determinar la biomasa y la composición del fitoplancton (picofitoplancton, nanodiatomeas y microdiatomeas) bajo condiciones oligotróficas, se realizó un estudio en la capa superficial de la cuenca de Guaymas, golfo de California, durante el verano tardío de 2016. El estudio contempló la medición de variables hidrográficas, químicas y biológicas en la capa superficial del área de estudio. Nuestros resultados mostraron una columna de agua cálida, fuertemente estratificada, empobrecida en nutrientes y con biomasas fitoplanctónicas reducidas (<1 mg Cla·m–3). Los cocientes promedio de N:P (0.55 ± 1.34), N:Si (0.13 ± 0.18) y Fe:N (52.70 ± 29.70) indicaron condiciones de limitación por N. La contribución de los grupos fitoplanctónicos a la biomasa fluctuó ampliamente por nivel de profundidad, y se observó  el predominio del picofitoplancton (85.0 ± 2.7%) en superficie (5 m) y de las nano-microdiatomeas (91.5 ± 5.9%) en el nivel más profundo (35-40 m), adyacente a la termoclina. Las diatomeas dominaron la biomasa integrada entre la superficie y 50 m de profundidad, con una contribución promedio ~6 veces mayor que la del picofitoplancton. A pesar de que se registraron condiciones ideales para la proliferación de cianobacterias diazótrofas, la presencia de Trichodesmium spp. y Richelia intracellularis fue muy irregular y en abundancias relativamente bajas (2,220 ± 1,575 célula·L–1). Nuestros resultados son especialmente relevantes, ya que sugieren que, bajo condiciones de limitación por N, el paradigma de la alta biomasa y dominancia de células grandes en el golfo de California puede verse desafiado durante la temporada de verano.

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The Gulf of Mexico (GoM) is one of the most dynamic marginal seas in the world owing to the intrusion of the Loop Current and the shedding of anticyclonic eddies (LCE) that travel westward across the Gulf. However, the impacts of these mesoscale dynamics on the supply and removal of bioessential trace metals in surface waters remain unclear. We study the impact of mesoscale eddies on the distribution of dissolved nickel (Ni), a biologically active element scarcely studied in the region. The vertical distribution of Ni was determined in the deep-water region of the GoM during summer of 2017, when two anticyclonic LCE (Quantum and Poseidon) were present. Nutrient-like profiles of Ni in the GoM resemble those from the Atlantic Ocean, but they showed high spatial variability within the first 1000 m, which was associated with the impact of mesoscale eddies. Similarly to subtropical gyres, macronutrients were almost depleted in surface waters, while Ni never fell below 1.51 nmol kg-1, suggesting low Ni lability or alternatively, slow biological uptake compared to that of macronutrients. In particular, lowest levels of Ni and macronutrients (PO4 and NO3) were recorded in surface waters of the anticyclonic eddies and the Loop Current area. Anticyclonic LCEs deepened these Ni-poor waters pushing the Ni-rich core of Tropical Atlantic Central Water up to 600 m, whereas its shallowest position (up to 200 m) was recorded under cyclonic conditions in Campeche Bay. This eddy-induced vertical displacement of water masses also affected the integrated Ni and macronutrient concentrations in the upper 350 m but without modifying their stoichiometries. We suggest that a significant decrease in surface inventories of Ni and macronutrient in areas impacted by LCEs is a consequence of the trapping of the water within eddies, the biological uptake of Ni and macronutrients combined with their limited replenishment from below, which likely affects autotrophic groups. In conclusion, the mesoscale dynamic permanently present in the GoM play an important role in modifying the vertical distribution of Ni and macronutrients as well as their availability in the upper water column of this marginal sea.

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