Fluxes of particulate carbon, nitrogen, and phosphorus in the upper water column of the northeast Pacific

Abstract

Concentrations of carbon, nitrogen and phosphorus were determined in particles that passively sank into multi-replicate collectors set at 50, 250, and 700 m in coastal waters, and 75, 575, and 1050 m in the open ocean. Fluxes as high as 36, 4.1, and 0.19 mmoles of C, N, and P m −2 day −1 were observed at 50 m under coastal upwelling conditions; at 700 m, upwelling period fluxes (9.6, 0.9, and, 0.053 mmoles of C, N and P m −2 day −1) exceeded those measured at 50 and 75 m when samplers were set under low productivity surface waters. 210Pb flux estimates were made on coastal trap particulates. The resulting values were close to the expected and suggest that overall flux estimates are representative of those occuring in the environment. Atomic ratios of C:N:P under upwelling conditions were similar to values reported for living plankton (∼180:18:1), while in the open ocean, atomic ratios of C and N in relation to P were markedly higher (400 to 900:30:1). Fecal pellet fluxes were two orders of magnitude higher under upwelling conditions (∼1 to 3 × 10 5m −2 day −1) than those in the open ocean (∼1000 m −2 day −1). Quantities of passively sinking particulate C, N, and P appeared to be equal to or in excess of the amounts required to meet the nutritional needs of the mid-water zooplankton. Rates of change for C, N, and P and inferred rates of oxygen change varied widely in relation to surface productivity. For example, oxygen utilization rates were as high as 790 μll −1 yr −1 in near-surface waters under upwelling conditions and as low as 4.4 μll −1 yr −1 at mid-depth in the open ocean. Our rates of change, determined by direct measurement, generally agree with previously published estimates from mathematical models.