ZOOPLANKTON PHOSPHORUS CONCENTRATIONS AND REDFIELD STOICHIOMETRY IN THE CENTRAL TROPICAL NORTH PACIFIC

Zooplankton play a critical role in nutrient and carbon biogeochemistry and the export of material from the surface ocean to depth. However, there have been few studies that have focused specifically on phosphorus (P) concentrations and how they vary with zooplankton size class and depth in the ocean. Here we present P concentrations from day plankton tow samples collected in February 2014 across 5 different size fractions (0.2 mm to 5 mm) from 25 to 1250 m at Station ALOHA located in the Central North Pacific. When analyzed across all size fractions and depths, P concentrations remain surprisingly invariant, averaging 270 ± 55 umol P/gram dry weight). Molar carbon (C) to P ratios also remain relatively constant and close to canonical Redfield ratios, averaging 122 ± 33. Closer inspection of the data, however, show that P concentrations increase across size classes, with highest P concentrations in the larger, > 5 um, zooplankton (from 220 to >250 umol P/gram dry weight. At the same time, molar C/P ratios significantly decrease with increasing size class, from ~145 to 110. Combined, our results suggest that larger zooplankton are more efficient at retaining P relative to C and that this is likely related to a combination of zooplankton composition and nutrient status.