Physical mechanisms affecting phytoplankton variability along the Chilean coast

Chile has high phytoplankton production due to being a classic example of an Eastern Boundary Upwelling System. Monthly averaged chlorophyll-α (Chl) and physical parameters (sea surface temperature, precipitation rate, southerly and westerly winds) were studied off the Chilean coast from 2002 to 2018, in order to understand the primary production along this important ocean margin. The coastal margin was split into three zones and ten sub-sections. The Northern Zone had a low phytoplankton production with small seasonal variability, except in its north. This pattern is due to a narrow shelf, weak winds, lack of precipitation and relatively stable weather conditions driven by the Southeast Pacific Subtropical Anticyclone (SPSA). The Central Zone presented a seasonally varying production, with a high Chl concentration in summer and early spring. This is linked to the SPSA movement and sunlight reduction during the winter. A high Chl activity is seen in the Southern Zone despite this Zone being at the limits of the SPSA effect, leading to weak longshore winds only during the warm season. Overall, this study has demonstrated the importance of shelf width and the upwelling driven by the presence or absence of the SPSA for ocean primary production. Thus, the most productive region is from 35°S to 45°S owing to both variables being present.