Do Seasonal Nutrient Fluctuations Induce Blooms of Diatom-Diazotroph Associations in the Oligotrophic Pacific Ocean?

The biology of the oligotrophic Pacific Ocean is dominated by micron sized phytoplankton, consistent with resource limitation theory and the low nutrient inputs to the surface ocean in this region. Despite this, large diatoms containing nitrogen fixing symbionts (DDAs) persist and can reach bloom conditions during the summer months. These associations generate a yearly summertime export pulse (SEP) at station ALOHA off of the Hawaiian Islands which is a significant portion of the yearly export. We use a size structured model to explore the relative fitness of DDAs at Hawaii by taking advantage of the relatively large size of DDAs relative to smaller diatoms. When given the environmental conditions at station ALOHA, model DDAs have higher growth rates than model unicellular diazotrophs during the summer months when the mixed layer decreases in depth and are less competitive during the winter when the mixed layer deepens. We will frame these results in the context of data on the diurnal fluctuations in the stoichiometry (C,N,P) of the DDA size class at station ALOHA.