The subtropical cell controls large-scale transport of heat, freshwater, carbon, nutrients and dissolved O2 in the eastern South Pacific Basin. These processes contribute to the modulation of chemical and biological conditions, as well as of the regional component of climate variability.
Models and field observations have shown that, in the context of global warming, the subtropical cell in the South Pacific could be reinforced as a response to changes in large-scale surface winds over the Tropical Pacific. Additionally, global warming is expected to directly affect the South Pacific by strengthening the productivity gradient. As temperature in the upper layers increases, ocean water stratification is reinforced, affecting the mixing of water masses and vertical diffusivity in subtropical regions, whereas stronger coastal winds could increase vertical mixing and eastern coastal upwelling.
It has been argued that transport in the Humboldt Current and coastal upwelling have increased in recent decades and that they will continue to get stronger on a decadal timescale. This will, in turn, modify the properties of subtropical cell waters and cause an increase in the physical, biochemical and ecological gradients between coastal and oceanic environments. The low O2 concentrations typical in warmer ocean waters, along with the sharper gradients between upwelling and stratified oceanic waters, will contribute to expanding waters low in O2/pH and high in pCO2, affecting biological communities and biogeochemical cycles.
To address this issue, IMO will perform new analyses combined with advanced regional numeric models in expeditions and regular transects between the Chilean coast and the Juan Fernández Archipelago using gliders. The collected data will include temperature, salinity, O2 and other biogeochemical variables (e.g. pH, pCO2, nutrients, gases, and organic and inorganic carbon, including their isotopes: 12C, 13C, 14C, and 15N). We will also perform a high-resolution analysis of the microstructure and turbulent mixing rates, allowing us to calculate vertical salt flows, heat and relevant biogeochemical properties. This high-resolution information, together with historical data, will allow us to assess inter-annual frequency changes, as well as minor frequency changes in meridional transport and the physical and chemical properties in the thermocline and intermediate waters. This data will be used for refining models and validating their outcomes. Different simulations will produce outcomes that will be used in regional models to assess the mechanisms affecting coastal upwelling, generation of mesoscale eddies, regional circulation and modification of water masses.