Primary Production Rates in the N. Pacific from Oxygen Isotope Measurements

University Of Washington, Seattle WA

Investigators

Abstract

ABSTRACT OCE-0095534 In this study, researchers at the University of Washington will determine the in-situ rates of gross and net primary productivity in the North Pacific Ocean using measurements of the isotopic composition and saturation level of dissolved oxygen. Marine productivity affects a wide range of fundamental properties of the earth from, for example, the concentration of CO2 and O2 in the atmosphere to the magnitude of potential fisheries harvests. Within the near future, potential climate change-induced alterations of ocean productivity could feedback into changes in the rate of anthropogenic CO2 build up in the atmosphere. All in all our ability to quantify rates of marine productivity is critical to our understanding of how earth's carbon cycle has changed in the past and will change in the future. Primary production (PP) rates in the ocean have historically been determined from rate measurements made in bottles. However, bottle measurements of PP suffer to an unknown extent from the inequality between in vitro and in situ conditions. Furthermore 14C uptake derived estimates of PP, by far the most common in vitro method, suffers an additional uncertainty about whether the rates represent gross or net PP. In a classic comparison, estimates of carbon export rates derived indirectly from subsurface estimates of oxygen utilization rates were twice the 14C-based measurements of primary production rates (Jenkins and Goldman, 1985). These uncertainties emphasize the need for PP rate determinations using methods that do not rely on bottle incubations. Recently a new technique has been developed to estimate both gross and net PP in the ocean (Luz and Barkan, 2000). It depends on extremely precise measurements of the isotopic composition of dissolved O2. The advantage of this method is that it does not require bottle incubations. In this study, the principal investigator will use this oxygen isotope method to determine in situ rates of gross and net PP in the N. Pacific and compare these rates to bottle measurements of PP made using 14C and 18O labeling techniques. The research team will make these measurements at two JGOFS time series sites in the subtropical (Station ALOHA) and subpolar (Ocean Station Papa) North Pacific. Both these sites have 10 or more years of 14C-based productivity data with which to compare in situ PP estimates determined by this new method. The time history of PP rate measurements at these two sites, the several estimates of carbon export made at these sites over the years (e.g., sediment traps, O2 budgets, DIC budgets, 234 Th budgets, etc.), and the contrast in biogeochemical regimes of these two sites (high vs. low nutrient) make the North Pacific an excellent choice for extending the application of the oxygen isotope method.