Biogeochemical impact of tropical instability waves in the equatorial Pacific

Abstract

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.