Drivers of phytoplankton community heterogeneity in the Eastern Tropical North Pacific
MetadataShow full item record
We must understand the drivers of primary producer community composition in the open ocean in order to model accurately carbon and nutrient cycling for our planet. I collected samples along a transect in the Eastern Tropical North Pacific, one of the three oxygen deficient zones (ODZ) on the planet. Here, the shoaling of anoxic waters creates a unique secondary chlorophyll maximum, previously recorded to be dominated by picocyanobacteria. I sampled four depths at each station along the transect and performed size-fractionation of chlorophyll to characterize phytoplankton community composition as well as collected surface net tows to identify phytoplankton. As the ODZ shoaled, the proportion of picoplankton decreased at depth. Station 10, a station geographically located where the ODZ shoals into the euphotic zone, lacked a secondary chlorophyll maximum because of a slight oxygen intrusion, possibly caused by an eddy. This slight difference eliminated an entire deep ocean community. Surface phytoplankton community composition was most strongly influenced by the environmental variables of the depth at which the oxygen concentration fell below 20 μM, sea surface temperature, salinity, phosphate, >10μm chlorophyll concentration, and nitrate. Therefore, the shoaling of the oxygen minimum zone, variations in sea surface temperature and salinity, and patchiness of nutrients played major roles in community structure. Understanding the environmental factors that influence community composition is essential when modeling carbon and nutrient cycling, because different genera can perform different ecological roles, which affect rates and cycling.