Impact of an atmospheric-oceanic disturbance on phytoplankton community dynamics in the North Pacific Central Gyre

Abstract

During the ADIOS I (Asian Dust Input to the Oceanic System) expedition to 26°N, 155°W in the North Pacific Central Gyre (NPCG) atmospheric-oceanic disturbances caused significant changes in phytoplankton community dynamics. A low pressure disturbance and several major dust deposition events resulted in a 37 and 25% increase in autotrophic carbon and nitrogen assimilation rates, respectively, relative to the pre-storm rates. The integrated submicron autotrophic N-assimilation rate increased by 72%. This submicron autotrophic community was responsible for 63 ± 7% of total autotrophic N-assimilation. New production increased by up to a factor of 4 as a result of the disturbances. The areal Chl a concentration doubled with the most significant increase observed near the base of the photic zone. Chemotaxonomic identification by HPLC pigment analyses indicated that the characteristic pigment concentrations of all major phytoplankton classes (except prokaryotic algae) increased as a result of the disturbances. Water column stability estimates and NO 3 − gradient measurements indicated that turbulent vertical transport of NO 3 − across the pycnocline could not explain the observed increases in photosynthetic parameters. Near surface NO 3 − concentrations increased following a dust deposition event. In addition, a positive temporal correlation was observed between the atmospheric Al concentration and the near-surface Chl a concentration. The data suggested that atmospheric deposition of NO 3 − and Fe stimulated autotrophic growth. Atmospheric deposition of NO 3 − and Fe may significantly enhance new production rates in the NPCG, especially during episodic dust events.