Publications

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2000
Najjar, RG, Keeling RF.  2000.  Mean annual cycle of the air-sea oxygen flux: A global view. Global Biogeochemical Cycles. 14:573-584.   10.1029/1999gb900086   AbstractWebsite

A global monthly-mean climatology of the air-sea oxygen flux is presented and discussed. The climatology is based on the ocean oxygen climatology of Najjar and Keeling [1997] and wind speeds derived from a meteorological analysis center. Seasonal variations are characterized by outgassing of oxygen during spring and summer and ingassing of oxygen during fall and winter, a pattern consistent with thermal and biological forcing of the air-sea oxygen flux. The annual mean flux pattern is characterized by ingassing at high latitudes and the tropics and outgassing in middle latitudes. The air-sea oxygen flux is shown to exhibit patterns that agree well with patterns seen in a marine primary productivity climatology, in model generated air-sea O-2 fluxes, in estimates of remineralization in the shallow aphotic zone based on seasonal oxygen variations, in observed seasonal nutrient-temperature relationships, and in independent estimates of meridional oxygen transport in the Atlantic ocean. We also find that extratropical mixed layer new production during the spring-summer period, computed from biological seasonal net outgassing of oxygen, is equivalent to the production of 4.5-5.6 Gt C, much lower than previous estimates based on atmospheric O-2/N-2 measurements.

1998
Stephens, BB, Keeling RF, Heimann M, Six KD, Murnane R, Caldeira K.  1998.  Testing global ocean carbon cycle models using measurements of atmospheric O2 and CO2 concentration. Global Biogeochemical Cycles. 12:213-230.   10.1029/97gb03500   AbstractWebsite

We present a method for testing the performance of global ocean carbon cycle models using measurements of atmospheric O-2 and CO2 concentration. We combine these measurements to define a tracer, atmospheric potential oxygen (APO approximate to O-2 + CO2), which is conservative with respect to terrestrial photosynthesis and respiration. We then compare observations of APO to the simulations of an atmospheric transport model which uses ocean-model air-sea fluxes and fossil fuel combustion estimates as lower boundary conditions. We present observations of the annual-average concentrations of CO2, O-2, and APO at 10 stations in a north-south transect. The observations of APO show a significant interhemispheric gradient decreasing towards the north. We use air-sea CO2, O-2, and N-2 fluxes from the Princeton ocean biogeochemistry model, the Hamburg model of the ocean carbon cycle, and the Lawrence Livermore ocean biogeochemistry model to drive the TM2 atmospheric transport model. The latitudinal variations in annual-average APO predicted by the combined models are distinctly different from the observations. All three models significantly underestimate the interhemispheric difference in APO, suggesting that they underestimate the net southward transport of the sum of O-2 and CO2 in the oceans. Uncertainties in the model-observation comparisons include uncertainties associated with the atmospheric measurements, the atmospheric transport model, and the physical and biological components of the ocean models. Potential deficiencies in the physical components of the ocean models, which have previously been suggested as causes for anomalously large heat fluxes out of the Southern Ocean, may contribute to the discrepancies with the APO observations. These deficiencies include the inadequate parameterization of subgrid-scale isopycnal eddy mixing, a lack of subgrid-scale vertical convection, too much Antarctic sea-ice formation, and an overestimation of vertical diffusivities in the main thermocline.