Temporal Variability of Oceanic Mesoscale Events in the Gulf of California

Edgardo Basilio Farach-Espinoza,Sofia Ortega-García,Ricardo García-Morales,Manuel Otilio Nevárez-Martínez,Daniel Bernardo Lluch-Cota,Juana López-Martínez

doi:10.3390/rs13091774

Edgardo Basilio Farach-Espinoza, Sofia Ortega-García + Show 4 more

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https://doi.org/10.3390/rs13091774

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Abstract

Oceanic mesoscale events such as eddies, coastal upwelling, filaments and fronts created by water mass intrusion present properties allowing them to concentrate, transport and disperse salt, nutrients and plankton, among other important constituents in the ocean. The use of satellite images enables the continuous monitoring of the ocean dynamics at different temporal and spatial scales, aiding the study of its variability. This study focuses on the identification of these mesoscale events in the Gulf of California (GC) by means of sea surface temperature (SST) and chlorophyll a (Chl a) fronts (edge) detection by processing 5-day satellite images from the 1998–2019 period. The annual occurrence or frequency and duration of each event was identified; the interannual variability was evaluated and underlying correlations with the Multivariate El Niño Index (MEI) and the Pacific Decadal Index (PDOI) were assessed via Principal Component Analysis. Most events showed a seasonal variability due to the seasonal behavior of forcing agents (i.e., Pacific Ocean and winds) that stimulate their formation or presence in the GC; seasonality was more evident in the northern region than in the southern region. The interannual variability of their frequency or duration was associated with strong and intense El Niño and La Niña conditions (positive or negative MEI values) together with positive or negative phases of the PDOI. The use of SST and Chl a satellite images with a 5-day temporal resolution allowed to better identify and quantify the annual frequency and duration of each mesoscale event. It allowed to detect a seasonal behavior of these events in the northern region, followed by the central region. The southern region, due to the interaction of different water masses with unique characteristics, exhibited a less evident seasonality in the frequency of eddies, and no apparent association between their interannual frequency and duration with the MEI and PDOI. Constantly monitoring these oceanic events and their variability will help in the understanding of how the different regions of this large marine ecosystem respond to these variations in the long term.

Highlights

IntroductionGradients in extensive oceanic regions of the world
Physical events in the marine environment may generate structures at various spatial and temporal scales so they are important in delimiting sea surface temperature (SST)gradients in extensive oceanic regions of the world
Applying a Wilcoxon–Mann–Whitney test (p < 0.05) for comparing the annual frequency of eddies showed that the Gulf of California can be divided into three regions: the Northern Gulf of California (NGC) comprises the area north of the Midriff Islands including the Tiburón Basin; the Central Gulf of California (CGC) encompasses the area just south of the Midriff Islands down to the 25◦ N latitude; while the Southern Gulf of California (SGC) includes the area from the 25◦ N to the 22◦ N latitude

Summary

Introduction

Gradients in extensive oceanic regions of the world These structures include mesoscale events exhibiting dimensions raging from tens to a few hundred kilometers and a life span from several weeks to a few months [1,2]. 2021, 13, 1774 often referred to as the ocean “weather”, include vortices distinguished by temperature and salinity anomalies; they possess distinctive properties allowing them to transport heat, salt, carbon and nutrients [3]. They can be generated by barotropic or baroclinic instabilities, by atmospheric forcing, and by the interaction between water mass movements with irregular continental shelves, with islands or capes [4,5].

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