Diel Measurements of Oxygen- and Carbon-Based Ocean Metabolism Across a Trophic Gradient in the North Pacific

Abstract

Daily in situ rates of gross production and community respiration estimated from high-frequency diel cycles in oxygen (O2) and optically derived particulate carbon from several platforms (both ship based and via profiling floats) were made across an ecological gradient in the North Pacific spanning the high-nutrient/low-chlorophyll sub-Arctic to the oligotrophic subtropical gyre. Both oxygen and carbon-based gross primary production and respiration rates indicated a ~3× increase between subtropical and subpolar stations. We consistently found that gross production and community respiration rates were in approximate balance at all stations across the full ecological gradient, implying that community respiration is fueled by recently produced organic matter and that recycling efficiency (~90%) is similar along the gradient. We determined that phytoplankton turnover time doubles (from 2 to 4 days) between subtropical and subpolar regimes, whereas biomass increases by approximately tenfold. We found a consistent photosynthetic quotient (1.4 ± 0.2 mol O2 mol C−1), respiratory quotient (1.0 ± 0.2 mol O2 mol C−1), and gross to net production ratio (2.0 ± 0.3) at all stations which underscores the similarity of fundamental ecological characteristics despite the transition from nutrient deplete to replete conditions. That the float- and ship-based estimates of in situ production and respiration generally agreed well suggests that float-based diel O2 and particulate organic carbon measurements have the potential to greatly expand our knowledge of spatial and temporal variability of productivity and respiration in the ocean.