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 activity. Using a coupled dynamical–biogeochemical model, we show that contrary to this suggestion, TIWs induce a decrease of iron concentration by 20% at the equator and by about 3% over the “TIW box” [90°W180, 5°N-5°S]. Chlorophyll decreases by 10% at the equator and 1% over the “TIW box”. This leads to a decrease of new production up to 10% at the equator (4% over the “TIW box”). TIW-induced horizontal advection brings more iron-depleted water to the equator than it exports iron-rich equatorial water to the north. 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 weaker phytoplankton concentration, and to a lesser extend by TIWinduced iron vertical advection.