Ocean metabolism observed with oxygen sensors on profiling floats in the South Pacific

Abstract

We estimated rates of production and export in the South Pacific (80°W to 180°W in a zonal band between 35°S and 50°S) using 1.5 yr of oxygen measurements from profiling floats. Export production, calculated from oxygen utilization rates below the compensation depth from December to April, was 10.7 ± 2 mmol C m−2 d−1 (n = 36, 95% CI). The corresponding satellite net primary production was 46 ± 4 mmol C m−2 d−1, yielding a regional e‐ratio of 0.23 ± 0.05. Averaging oxygen utilization rates resulted in a net cancellation of most water mass changes related to advection and float migration. The composite vertical profile of remineralization rates, obtained by binning 36 rate profiles, agreed with published measurements based on oxygen utilization rates in hydrographic surveys and fits the classic form of a particulate organic carbon (POC) attenuation function. However, the disagreement between oxygen‐based remineralization rates and those obtained by sediment traps suggests fundamental differences between these two methods. Using float data to constrain a one‐dimensional mixed‐layer model, the annual net community production at 45°S, 144°W was ~2.5 mol C m−2 d−1. Spatial trends in export production coinciding with the New Zealand shelf and Subtropical Front are identified.