|A Comparison of Tracer-Based Primary Production Methods: Is There a Redfield Paradox?
Dr. William Jenkins (WHOI)
Dr. Scott Doney (WHOI)
Dempsey E Lott, III (WHOI)
A time-series of Helium-3, tritium, oxygen, and noble gases collected in the Sargasso Sea is being used to quantify new production, export production, and net community production. By using these three methods concurrently to quantify different aspects of production, we are able to address a number of apparent inconsistencies in the elemental budgets of carbon, oxygen, and nitrogen.
From the initial fourteen months of data (July 2004 to Sept 2005), the flux of Helium-3 from the mixed layer is used to estimate a new production rate of 0.9 +- 0.3 mol N m-2 y-1, which is equivalent to 10 +- 3 mol O2 m-2 y-1. Apparent oxygen utilization rates calculated from tritium/helium dating of thermocline waters lead to estimates of export production of 3.7 to 5.0 mol O2 m-2 y-1. Euphotic zone seasonal cycles of O2 and Ar, combined with an upper ocean one-dimensional vertical model, result in estimates of net community production of 3.0 to 5.2 mol O2 m-2 y-1. The discrepancy between the new production estimate vs. the estimates of export and net community production may reflect a larger than expected contribution of biological production in the winter or may be a result of uncertainties and differences in the temporal and spatial scales inherent in the methods. The helium-3 flux gauge and apparent oxygen utilization rates yield a regional scale estimate of new production whereas the euphotic zone O2 and Ar cycles give a local, immediate estimate of net community production.