Feedback on Silicate
This stabilising feedback is part of wider pattern whereby phytoplankton removal keeps certain elements at anomalously low concentrations in seawater (click here for further explanation).
Refrences:
Yool, A. & Tyrrell, T. (2003). Role of diatoms in regulating the ocean's silicon cycle. Global Biogeochemical Cycles 17, 1103, doi:10.1029/2002GB002018.