Mesoscale eddies are characteristic of the eastern South Pacific (ESP), connecting coastal upwelling zones with oligotrophic oceanic waters, as well as meso- and epipelagic domains. Eddies create unique and relatively isolated environments where distinctive biological communities and chemical conditions can exist, depending on the nature of the water in the eddies, their characteristics and paths, and their interactions with winds and topography. Seamounts, ocean ridges and oceanic islands in the eastern South Pacific could also produce or strengthen mesoscale activity, thereby increasing surrounding biological production.

The IMO hypothesis is that mesoscale eddies in coastal areas create deficient O2/low pH conditions in the open sea (or the opposite in oxygen minimum zones), with corresponding changes in community structures and with biochemical cycles significantly different from those found in adjacent oceanic waters.  To test this theory, we will carry out a field experiment to study the characteristics and evolution of mesoscale eddies off central Chile (~36 ºS) flowing to the northwest and arriving near the Juan Fernández Archipelago. This field experiment will involve time-series observations by satellite tele-detection (e.g. altimetry and color scanner), an anchorage in the vicinity of the Juan Fernández Archipelago, as well as observations of certain sections using gliders and a research vessel. To study the evolution of the physical-chemical and biological conditions in one of these eddies we will visit it three times as it flows from the coast to the open ocean. On each occasion, we are going to assess changes in chemical characteristics (dissolved organic carbon, organic and inorganic dissolved particles, O2, pH/pCO2, and nutrients), community structures, gene expression and biogeochemical activity (e.g. primary production, nitrogen fixation, respiration, etc.) within and outside the eddies. We will also carry out on-board perturbation experiments, applying individual and multiple stress factors in contrasting waters. Additionally, through numerical experiments, we will analyze the structure of these eddies and the ways in which they are generated and move, particularly in the oxygen minimum zones (OMZs) around oceanic islands and seamounts associated with the Nazca and Juan Fernández ridges.

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