Mesoscale Variability in the Boundaries of the Oxygen Minimum Zone in the Eastern South Pacific: Influence of Intrathermocline Eddies

The vertical variability in the oxygen minimum zone (OMZ) in the eastern South Pacific (ESP; 0–40°S) is characterized by the influence of anticyclonic intrathermocline eddies (ITEs), which are subsurface-intensified mesoscale features that are frequently generated in the coastal upwelling zone off Peru and Chile. The unique lens-shaped signatures that ITEs leave on temperature, salinity, and dissolved oxygen vertical distributions are used as proxies to assess their influences on vertical OMZ boundaries and thickness. Data from in situ profiles in the region (World Ocean Database and Argo databases) are used in correlation analyses between anomalous depths (and vertical displacements) of oxyclines and isopycnals/isotherms, together with an objective eddy detection method based on satellite altimetry to identify the location of such profiles (i.e., outside or inside cyclonic and anticyclonic eddies). The results indicate that most of the vertical fluctuations in the climatological OMZ have a lens-shaped signature and that those at the mesoscale are largely due to ITEs. ITEs are a main driver of the upper oxycline variability in the coastal band, the coastal transition zone (CTZ, 3–10° from the coast) and beyond at mid-latitudes (12–26°S). The influence of ITEs on the upper and lower oxycline variability is mostly observed within the horizontal (offshore) climatological boundary of the OMZ, suggesting that ITEs play a role in the OMZ offshore extension in the ESP. ITEs may produce mesoscale variations in the thickness of the surface-oxygenated layer, resulting in potential changes in prey-predator interactions and in food web functioning.