Strong CO2 outgassing from high nutrient low chlorophyll coastal waters off central Chile (30°S): The role of dissolved iron

Carbonate system parameters (pH and alkalinity) were used to estimate the coastal water CO2 fluxes off central Chile (30°S) during September 2007. Coastal waters rich in nitrate and silicate were strongly CO2 supersaturated and normally poor in chlorophyll a. MODIS satellite chlorophyll a data suggest that phytoplankton biomass remained particularly low during September 2007 although coastal waters were highly fertilized with nitrate and silicate. The phytoplankton gross primary productivity in macronutrient-rich waters was very low with the exception of shallow waters (e.g. within or near bays). Several iron-enrichment bottle experiments show that fCO2 rapidly decreases during iron-enrichment treatments compared to controls. This suggests that iron limitation of phytoplankton growth (mainly diatoms) plays a role in maintaining high-CO2 outgassing by preventing rapid interception of upwelled CO2.