Net community production in the deep euphotic zone of the subtropical North Pacific gyre from glider surveys

Nicholson, David, Steven Emerson, Charles C. Eriksen

Limnol. Oceanogr., 53(5_part_2), 2008, 2226-2236 | DOI: 10.4319/lo.2008.53.5_part_2.2226

ABSTRACT: Seagliders, deployed through most of 2005 in the subtropical North Pacific gyre, made measurements of temperature, salinity, and dissolved oxygen to quantify net community production (NCP) at Station A Long- Term Oligotrophic Habitat Assessment (ALOHA) of the Hawaii Ocean Time-series (HOT) using an oxygen mass balance approach. A ‘bowtie’-shaped pattern, 50 km by 50 km in size was repeatedly traversed at two week intervals with the goal of observing the influence of Rossby waves and eddies on the productivity of the study region. Rossby waves and eddies in the region cause a vertical displacement of isopycnal depth of ~±50 m at the base of the euphotic zone. Shoaling of isopycnals is demonstrated to drive productivity in the deep euphotic zone. Four mesoscale shoaling events were observed between February and November in 2005. During each event when isopycnals shoaled, oxygen concentrations on isopycnals increased, fluorescence in the deep euphotic zone was higher, and net community production was elevated. Productivity in the deep euphotic zone was strongly influenced by Rossby waves and eddies, but this influence was not observed to extend into the mixed layer.

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