Award: OCE-0961207

The main objectives of this project were to measure the amount of organic carbon production that organisms carry out in the surface waters of the equatorial south Pacific. Several different approaches were used to assess the accuracy and complexity of each method. The isotopes of dissolved oxygen indicate the gross rate of oxygen production by plants. The amount of oxygen (relative to argon) in the surface ocean indicates the net excess of photosynthesis relative to respiration. Both of these techniques require estimation of the rate of exchange of oxygen across the air-water boundary, so knowing the rate of gas exchange is also key. We used naturally occurring radon gas as a tracer to help quantify this process and thus help in our interpretation of the oxygen data. Because we made so many oxygen/argon measurements, we saw a rich fabric of patterns in the surface ocean, with high oxygen production zones and lower oxygen production zones that have great heterogeneity in time and space. Stations along a cruise transect at 10° S had generally higher rates of productivity than stations along a transect at 20° S, between 80°W and 100°W. Our goal was to define how oxygen reflects production within this region of the ocean, but we teamed with other investigators to compare and contrast other methodologies. For example, satellites predict much higher rates of carbon production than those indicated by our oxygen production measurements. Traditional measurements of photosynthesis using 14C tracers also predict much larger growth rates than do our oxygen measurements. What this study indicates is that different types of measurements of ocean productivity, and thus estimates of marine carbon dioxide sequestration, may have significant differences. Much of these differences reflect variations of natural processes in space and time, responding to spatial variability of physical processes such as upwelling. Furthermore, each method detects responds slightly differently to organism physiology in carbon production in the ocean, both in time and location in the water column. Putting together a vast array of different measurement techniques has given us additional insight and teaches us about the spatial and temporal characteristics of plant production and decay in the upper ocean. Last Modified: 10/30/2013 Submitted by: William M Berelson