Biogeochemical impact of tropical instability waves in the equatorial Pacific

Tropical Instability Waves (TIW) have been suggested to fertilize the equatorial Pacific in iron leading to enhanced ecosystem productivity. Using a coupled dynamical–biogeochemical model, we show that contrary to this suggestion, TIWs induce a decrease of iron concentration by 10% at the equator and by about 3% over the Wyrtki box [90°W–180, 5°N–5°S]. Chlorophyll decreases by 10% at the equator and 1% over the Wyrtki box. This leads to a decrease of new production up to 10% at the equator (4% over the Wyrtki box). TIW‐induced horizontal advection exports iron‐rich equatorial water to the north, but also brings iron‐depleted water to the equator leading to a net decrease in iron. Additional iron decrease is caused by TIW‐induced iron vertical diffusion. These two mechanisms are partly counter balanced by a decrease of iron biological uptake, driven by lower phytoplankton concentrations, and to a lesser extent by TIW‐induced iron vertical advection.