Abstract Highly productive summer phytoplankton blooms in the central North Pacific Subtropical Gyre (NPSG) are an annual occurrence that leads to the export of considerable amounts of surface particulate carbon to depth. The mechanisms that control the formation of these blooms remain unresolved, but iron (Fe) availability may be an important factor. From July to October 2022, a large, persistent phytoplankton bloom was detected near 23.3°N, 154.6°W in satellite imagery and in situ measurements. Elevated Fe concentrations and nitrogen (N 2 ) fixation activity measured within the bloom suggest that high Fe may have supported enhanced diazotrophic activity. To evaluate whether aerosol deposition created favorable conditions for bloom formation, we reconstructed the Fe deposition history of the bloom's source waters by integrating surface water back trajectory analyses with aerosol Fe flux simulations. Our results show that waters that hosted the diatom‐diazotroph assemblage bloom received up to 20% more soluble Fe through aerosol deposition than its surrounding waters, primarily from a strong wet deposition event that occurred approximately 1 month before the bloom. The observed lag between deposition and bloom suggests a delayed biological response to atmospheric Fe inputs. Although this moderate increase does not represent incontrovertible evidence that the bloom was stimulated by aerosol Fe deposition, our findings establish the potential for episodic delivery of atmospheric Fe to stimulate diazotrophic activity and phytoplankton growth over month‐long timescales in the NPSG.
Kong et al. (Thu,) studied this question.