Iron and Phytoplankton Growth in the Subarctic North Pacific

Abstract

Iron availability has been shown to have potential controls on phytoplankton growth, nutrient utilization, algal community composition, and the ecosystem structure in the subarctic North Pacific. Recent findings on the lateral iron transport from the surrounding marginal regions to the pelagic waters highlighted the importance of particulate iron in the subarctic North Pacific, but the transformation between dissolved and particulate phases and its interaction with organic ligands are still uncertain. In spite of active researches in the subarctic high-nitrate, low-chlorophyll (HNLC) waters, significant impacts of Asian dust on the phytoplankton productivity have not been detected, suggesting spatial and temporal mismatch between the dust inputs and biological activities. Satisfaction of algal demands for both light and iron is a key for phytoplankton blooming in the HNLC waters. Surprisingly, the community half-saturation constant for growth with respect to iron was found to be similar between the western and eastern gyres; however, differences in the iron supply process and its availability in these two gyres seem to have developed unique phytoplankton populations. It is essential to evaluate iron transport processes that work on a time-scale needed for phytoplankton blooms, and further studies are needed at the central regions of the subarctic North Pacific.