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The Easter Island Province (EIP) encompasses Easter Island (EI) and Salas y Gómez Island (SGI), which are located in the eastern boundary of the south Pacific subtropical gyre. This province is one of the most oligotrophic region in the world ocean with a high degree of endemism and distinguished by having the clearest waters in the world. Issues related to the biophysical coupling that sustains biological production in this region are still poorly understood. Satellite data compiled over a ten year period was used to characterize the spatial and temporal chlorophyll-α (Chl-α) variability around the EIP and determine the relationship between Chl-α and several physical forcing. Results shows a clear Chl-α annual cycle around the EIP, with maximum concentration during the austral winter. Chl-α spatial distribution shows a strong zonal dipole over EI that divides the island into two zones: southeast and northwest. Due to its small size and low elevation of SGI, it does not generate a significant local effect in Chl-α concentration, but a Chl-α increase is observed southeast of this island (~2 km) associated to a seamount. The mean geostrophic current in the EIP flows eastward, associated with the southeastern boundary of the subtropical gyre. However, recurrent mesoscale eddies traveling northwestward and produce large surface current variability with periods of high velocities in opposite direction. In the spring, wakes of high Chl-α concentration can be observed over EI, associated with the generation and detachment of submesoscale eddies from EI, which could have important biological implications during periods of low regional biological production.

Se utilizan dieciocho anos de datos satelitales de nivel del mar y esfuerzo del viento, en la región del Pacifico suroriental, para mostrar las cualidades del Multitaper Method - Singular Value Decomposition (MTM-SVD) como método de análisis de múltiples series de tiempo distribuidas en extensas áreas del océano. Se realiza una exhaustiva revisión del MTM-SVD, propuesto inicialmente por Mann & Park (1999), y se implementan los algoritmos computacionales en MATLAB, para aprovechar las capacidades de despliegue gráfico de los resultados y facilitar su interpretación y análisis. El MTM-SVD permitió obtener una visión general de las principales frecuencias de variabilidad del nivel del mar, determinar la fracción de la varianza explicada para cada una de estas frecuencias en las distintas regiones de la zona de estudio y determinar sus patrones de oscilación, tanto estacionarios como de propagación. Dentro de las principales frecuencias de variabilidad se encuentra que la senal anual e interanual domina en forma significativa gran parte del registro del nivel del mar en el Pacifico suroriental. La senal anual está asociada a las fluctuaciones del esfuerzo del viento y a la propagación de ondas de Rossby. La senal interanual se encuentra fuertemente asociada a las fluctuaciones de El Niño y la Oscilación del Sur, que se extiende en la región mediante perturbaciones generadas en la costa, que posteriormente viajan hacia el oeste a una velocidad cercana a la velocidad teórica de propagación del primer modo baroclino de una onda de Rossby.Eighteen years of satellite data on sea level and wind stress in the southeastern Pacific region, were used to show the capabilities of Multitaper Method - Singular Value Decomposition (MTM-SVD) as a valuable method to analyze multiple time series distributed over a large area on the ocean. Here we performed a comprehensive review of the MTM-SVD method,that was first proposed by Mann & Park (1999), and also we done an implementation of the MTM-SVD algorithms in MATLAB (MAtrix LABoratory), in order to take advantage of the graphical capabilities that brings this computational language and make easier the result interpretation. The MTM-SVD allowed to obtain a regional view of the main frequencies of sea level variability, and showed the explained variance along the study area for each frequency. Besides, the method also shown the spatial oscillation patterns on each frequency, both stationary or propagation patterns. A significant annual and interannual variability appear dominate much of the sea level fluctuations in the southeastern Pacific. The annual signal was found associated with the wind stress and the propagation of a Rossby wave. The interannual signal was strongly observed associated with the El Niño and the Southern Oscillation. On these frequencies the sea level perturbations were generated on the coast, and then traveling westward at a speed close to the theoretical propagation of the first baroclinic mode of a Rossby wave.

An approach that improves the spectral-based PHYSAT method for identifying phytoplankton functional types (PFT) in satellite ocean-color imagery is developed and applied to one study case. This new approach, called PHYSTWO, relies on the assumption that the dominant effect of chlorophyll-a (Chl-a) in the normalized water-leaving radiance (nLw) spectrum can be effectively isolated from the signal of accessory pigment biomarkers of different PFT by using Empirical Orthogonal Function (EOF) decomposition. PHYSTWO operates in the dimensionless plane composed by the first two EOF modes generated through the decomposition of a space–nLw matrix at seven wavelengths (412, 443, 469, 488, 531, 547, and 555 nm). PFT determination is performed using orthogonal models derived from the acceptable ranges of anomalies proposed by PHYSAT but adjusted with the available regional and global data. In applying PHYSTWO to study phytoplankton community structures in the coastal upwelling system off central Chile, we find that this method increases the accuracy of PFT identification, extends the application of this tool to waters with high Chl-a concentration, and significantly decreases (~60%) the undetermined retrievals when compared with PHYSAT. The improved accuracy of PHYSTWO and its applicability for the identification of new PFT are discussed.