Production and respiration rates estimated from in situ diel measurements of O2/Ar and particle concentrations and in vitro measurements of 14C and 18O across a trophic gradient in the North Pacific

Fernanda Henderikx Freitas1, Paul Quay2 and Angelicque E White1, (1)University of Hawaii at Manoa, Department of Oceanography, Honolulu, HI, United States, (2)Univ Washington, Seattle, WA, United States
Direct in situ estimates of gross production and community respiration rates based on diel changes in dissolved O2 gas, dissolved O2/Ar gas ratio, and beam attenuation coefficients were obtained across an ecologically diverse meridional gradient in the North Pacific Ocean spanning the high nutrient/low chlorophyll subarctic to the oligotrophic subtropical gyre. Diel rates were estimated simultaneously from diverse platforms, including continuous underway measurements, repeat CTD profiles, and autonomous profiling floats, allowing intercomparison of methods in relation to concurrent in vitro production rate estimates based on 18O and 14C tracer incubations. Oxygen and carbon-based production and respiration rates agreed well across platforms, highlighting the accuracy of in situ optical methods. Gross production and community respiration rates both varied by a factor of ~4 between subtropical and subpolar waters, despite a ~10 fold change in plankton biomass. While closely balanced, gross production slightly exceeded respiration, indicating net autotrophy across the entire latitudinal gradient. Phytoplankton biomass turnover times increased from 2 days in subtropics to 4 days in subpolar waters, with clear relationships between patterns of production, respiration, chlorophyll concentrations, and temperature. Comparisons among diel-, incubation-, and satellite-based estimates of production highlight the need for multiple measurements of production to identify potential outliers, particularly in areas where spatial heterogeneity or low signal to noise can bias observations, with important implications for development of food web and particle export models.