Spatial and temporal variability of the sea surface temperature in the Ballenas‐Salsipuedes Channel (central Gulf of California)

Abstract

[1] The Ballenas-Salsipuedes Channel (BSC) is considered an oceanographic province on its own within the Gulf of California. In this region, tidal mixing is modulated by quarterdiurnal, semidiurnal, diurnal, and fortnightly frequencies, producing a strong outcropping of cold and nutrient-rich waters. In this work we analyze the temporal and spatial variability of sea surface temperature (SST) data recorded simultaneously over a period of 1 year in six bays along the BSC. Minimum mean SST differences (< 0.5°C) among bays were observed in December, while maximum differences (> 2.5°C) were recorded in June. The monthly SST anomaly showed that from late October to late January, the channel behaved as a very well mixed region. In contrast, SST anomalies of up to 2.2°C among bays were observed from May to September, indicating intense heat gain in summer and highlighting spatial heterogeneity in the intensity of vertical mixing. Besides the seasonal temperature cycle, influenced by solar irradiation, four main periods (0.25, 0.5, 1, and 15 days) were identified, corresponding to the main timescales of variability induced by the tides. This work demonstrates that the main source of temporal SST variability in BSC is the tide-induced fortnightly modulation, suggesting the possibility of a pulsation mechanism in the outcropping of nutrient-rich waters reaching the surface layer throughout the channel; this could play a crucial role in explaining the exceptionally high biological production of this region.Citation: Martínez-Díaz-de-León, A., I.

Wintertime enrichment of inorganic nutrients in the Ballenas Channel, Gulf of California

“…This heat loss to the atmosphere in the BC region may cause convection in the water column, which would facilitate vertical water transport and, in turn, explain the wintertime enrichment of nutrients in the surface layer of BC. Preliminary evidence supporting this hypothesis has been provided by Martínez-Díaz-de-León et al (2006, who installed thermographs in six bays along BC to study the seasonal variation of surface temperature over a one-year period. Their data showed a considerable decrease in water temperature in autumn that was attributed to heat lost to the atmosphere.…”

“…Sin embargo, en la primavera el  osciló entre 42 y 108 J m -3 debido a la ganancia de calor del agua desde la atmosfera en esta época de transición (Martínez-Díaz-de-León et al 2013), lo que favoreció la formación de una termoclina más estable (Castro et al 1994). Durante el verano, a pesar de que la mezcla asociada a las mareas varía con una frecuencia quincenal y se presenta en la región del CB a lo largo de todo el año (Marinone y Lavín 2003, Martínez-Díaz-de-León et al 2006, la turbulencia del agua disminuyó sustancialmente y se obtuvieron los valores máximos (150-223 J m -3 ) del , lo cual se reflejó en una columna de agua muy estable (fig. 4).…”

“…Este proceso de pérdida de calor del agua hacia la atmósfera en la zona del CB podría provocar un proceso de convección de la columna de agua, lo que facilitaría el transporte vertical de agua y explicaría, a su vez, el enriquecimiento invernal de nutrientes en la capa superficial del CB. Evidencia preliminar para la zona del CB que apoya esta hipótesis ha sido dada por Martínez-Díaz-de- León et al (2006León et al ( , 2013, quienes instalaron termógrafos en seis bahías localizadas a lo largo del CB y estudiaron la variación estacional de la temperatura superficial por un periodo de un año. Los datos de estos autores indican que durante el otoño ocurre una intensa disminución de la temperatura del agua, la cual fue atribuida a la pérdida de calor hacia la atmosfera.…”

“…We present evidence that the temporal variability of nutrient concentrations in the surface layer of BC, on an annual scale, is the result of seasonal variations in water column mixing, variations in the vertical flow of Subtropical Subsurface Water, and the biological activity that occurs in this layer. se ha registrado el agua superficial más fría (Soto-Mardones et al 1999, Martínez-Díaz-de-León et al 2006) y menos salina (Roden 1964, Beron-Vera y Ripa 2000) del GC. Además, en la capa profunda del CB el agua es más cálida y más salina que a la misma profundidad en la región central del GC (Roden 1964, Álvarez-Borrego et al 1978.…”

“…Por ejemplo, en el CB 1999, Martínez-Díaz-de- León et al 2006) and less saline (Roden 1964, Beron-Vera andRipa 2000) in BC than in the GC, whereas deep waters are warmer and more saline in BC than at the same depth in the central gulf (Roden 1964, Álvarez-Borrego et al 1978. These unique characteristics of BC have been attributed to the intense water column mixing related to the interaction of vigorous tidal currents with the complex bathymetry of the area (Badan-Dangon et al 1991).…”