Mezcla diapicna en la Zona de Mínimo Oxígeno frente a Chile Central: el rol de los dedos de sal.
Loading...
Date
2023
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Universidad de Concepción
Abstract
La Zona de Mínimo Oxígeno (ZMO) de Perú-Chile es una de las ZMO más amplias, deficientes en oxígeno, y someras del océano mundial. Frente al sur de Perú y Chile, esta ZMO está estrechamente asociada a un máximo de salinidad que define el núcleo del Agua Ecuatorial Subsuperficial. Esta masa de agua está limitada por otras dos masas de agua provenientes del sur, que están bien ventiladas, de relativamente baja salinidad y frías. Nuestra hipótesis es que la estructura de estas masas de agua influye en la mezcla diapicna y, por tanto, en la ventilación de la ZMO. En esta investigación, utilizamos observaciones directas de microestructura, junto con mediciones de corriente y oxígeno, para analizar el impacto de la mezcla diapicna en los flujos de oxígeno disuelto dentro de las oxiclinas que delimitan la ZMO frente a Chile Central. Nuestros resultados muestran que el contraste termohalino en la oxiclina inferior favorece las condiciones para el desarrollo de inestabilidades de dedos de sal, que aumentan la difusividad diapicna hasta 2 órdenes de magnitud con respecto a la oxiclina superior, en donde predomina la turbulencia mecánica. Así, los dedos de sal contribuyen significativamente al transporte diapicno de oxígeno, favoreciendo la ventilación de la ZMO desde abajo. A lo largo de la mayor parte del oxiclina inferior en el Pacífico Sur Oriental, se observan condiciones para la formación de dedos de sal. Los sistemas de surgencia de Canarias y Benguela también se caracterizan por presentar ZMOs fuertes a moderadas, nuestros resultados indican que allí, también existen condiciones favorables para dedos de sal, sugiriendo que este proceso juega un papel clave en la dinámica de estas ZMOs.
The Peru-Chile Oxygen Minimum Zone (OMZ) is one of the most oxygen-depleted, wide, and shallowest OMZs in the world ocean. Off southern Perú and Chile, this OMZ is closely associated with a salinity maximum that defines the core of the Equatorial Subsurface Water. This water mass is bounded by other two water masses of southern origin that are well-ventilated, relatively fresh, and cold. We hypothesize that this water mass structure impact on diapycnal mixing and, thus, on the OMZ ventilation. In this investigation, we use direct microstructure observations, along with current and oxygen measurements, to analyze the impact of diapycnal mixing on dissolved oxygen fluxes within the oxyclines that delimit the OMZ off Central Chile. Our results show that the thermohaline contrast in the lower oxycline favors conditions for salt-finger instabilities, which increase diapycnal diffusivities up to 2 orders of magnitude with respect to a regime that only considers mechanical turbulence. Thus, salt fingers significantly contribute to diapycnal oxygen transport and thus favoring ventilation of the OMZ from below. Along most of the lower oxycline in the Eastern South Pacific, conditions for salt-fingers are observed. Canarias, and Benguela upwelling systems are also characterized for presenting strong to moderated OMZs, and our results indicate that conditions favorable for salt fingers along these systems are also present, suggesting that this process plays a key role in the OMZs dynamics.
The Peru-Chile Oxygen Minimum Zone (OMZ) is one of the most oxygen-depleted, wide, and shallowest OMZs in the world ocean. Off southern Perú and Chile, this OMZ is closely associated with a salinity maximum that defines the core of the Equatorial Subsurface Water. This water mass is bounded by other two water masses of southern origin that are well-ventilated, relatively fresh, and cold. We hypothesize that this water mass structure impact on diapycnal mixing and, thus, on the OMZ ventilation. In this investigation, we use direct microstructure observations, along with current and oxygen measurements, to analyze the impact of diapycnal mixing on dissolved oxygen fluxes within the oxyclines that delimit the OMZ off Central Chile. Our results show that the thermohaline contrast in the lower oxycline favors conditions for salt-finger instabilities, which increase diapycnal diffusivities up to 2 orders of magnitude with respect to a regime that only considers mechanical turbulence. Thus, salt fingers significantly contribute to diapycnal oxygen transport and thus favoring ventilation of the OMZ from below. Along most of the lower oxycline in the Eastern South Pacific, conditions for salt-fingers are observed. Canarias, and Benguela upwelling systems are also characterized for presenting strong to moderated OMZs, and our results indicate that conditions favorable for salt fingers along these systems are also present, suggesting that this process plays a key role in the OMZs dynamics.
Description
Tesis presentada para optar al grado de Magíster en Ciencias con mención en Oceanografía.
Keywords
Ecosistemas marinos, Masas de agua, Zonas de Mínimo Oxígeno, Mezcla diapicna