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2015
Rafelski, LE, Paplawsky B, Keeling RF.  2015.  Continuous measurements of dissolved O-2 and oxygen isotopes in the Southern California coastal ocean. Marine Chemistry. 174:94-102.   10.1016/j.marchem.2015.05.011   AbstractWebsite

Dissolved O-2/N-2, O-2/Ar, O-2 saturation and delta O-18 were measured continuously near the surface ocean at the Scripps Institution of Oceanography pier in La Jolla, California, for five weeks. The data showed diurnal cycles, in O-2 and delta O-18, with amplitudes of 19 mmol m(-3) and 1.1%., respectively. The diurnal cycles are well described by a box model that includes photosynthesis, respiration, air-sea gas exchange, and mixing. The timing of the cycles can be explained using a photosynthesis rate proportional to photosynthetically active radiation, and the shapes of the cycles can be explained by mixing with a subsurface layer of water that is supersaturated in O-2. Based on the diurnal cycles in O-2 and delta O-18, the average maximum daily photosynthesis rate was 3.7-4.7 mmol O-2 m(-3) h(-1), which is supported by the light-saturated photosynthesis rate estimated from the measured chlorophyll concentration. In the future, these continuous measurement techniques could be used at different locations and depths to improve the understanding of variability in oceanic primary production. (C) 2015 Elsevier B.V. All rights reserved.

2014
Rodgers, KB, Aumont O, Fletcher SEM, Plancherel Y, Bopp L, Montegut CD, Iudicone D, Keeling RF, Madec G, Wanninkhof R.  2014.  Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring. Biogeosciences. 11:4077-4098.   10.5194/bg-11-4077-2014   AbstractWebsite

Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model, where the objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000-2006, with a relative reduction with wind stirring on the order of 0.9 Pg C yr(-1) over the region south of 45 degrees S. This impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other ocean biogeochemical tracers. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong reduction on the order of 25-30% in the concentrations of NO3 exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry through its impact over the Southern Ocean.

1995
1993
Keeling, RF, Najjar RP, Bender ML, Tans PP.  1993.  What atmospheric oxygen measurements can tell us about the global carbon cycle. Global Biogeochemical Cycles. 7:37-67.   10.1029/92gb02733   AbstractWebsite

This paper explores the role that measurements of changes in atmospheric oxygen, detected through changes in the O2/N2 ratio of air, can play in improving our understanding of the global carbon cycle. Simple conceptual models are presented in order to clarify the biological and physical controls on the exchanges of O2, CO2, N2, and Ar across the air-sea interface and in order to clarify the relationships between biologically mediated fluxes of oxygen across the air-sea interface and the cycles of organic carbon in the ocean. Predictions of large-scale seasonal variations and gradients in atmospheric oxygen are presented. A two-dimensional model is used to relate changes in the O2/N2 ratio of air to the sources of oxygen from terrestrial and marine ecosystems, the thermal ingassing and outgassing of seawater, and the burning of fossil fuel. The analysis indicates that measurements of seasonal variations in atmospheric oxygen can place new constraints on the large-scale marine biological productivity. Measurements of the north-south gradient and depletion rate of atmospheric oxygen can help determine the rates and geographical distribution of the net storage of carbon in terrestrial ecosystems.

Tans, PP, Berry JA, Keeling RF.  1993.  Oceanic 13C/12C observations: A new window on ocean CO2 uptake. Global Biogeochemical Cycles. 7:353-368.   10.1029/93gb00053   AbstractWebsite

Equations are developed describing the rate of change of carbon isotopic ratios in the atmosphere and oceans in terms of deltaC-13 quantities. The equations enable one to perform calculations directly with delta and epsilon quantities commonly reported in the literature. The main cause of the change occurring today is the combustion of fossil fuel carbon with lower deltaC-13 values. The course of this isotopic anomaly in atmosphere and oceans can provide new constraints on the carbon budgets of these reservoirs. Recently published deltaC-13 isotopic data of total inorganic carbon in the oceans [Quay et al., 1992] appear to lead to incompatible results with respect to the uptake of fossil fuel CO2 by the oceans if two different approaches Lo the data are taken. Consideration of the air-sea isotopic disequilibrium leads to an uptake estimate of only a few tenths of a gigaton C (Gt, for 10(15) g) per year, whereas the apparent change in the ocean deltaC-13 inventory leads to an estimate of more than 2 Gt C yr-1. Both results are very uncertain with presently available data. The isotopic ratio has the advantage that the signal-to-noise ratio for the measurement of the uptake of the isotopic signal by the oceans is better than for the uptake of total carbon. The drawback is that isotopic exchange with carbon reservoirs that are difficult to characterize introduces uncertainty into the isotopic budget. The accuracy requirements for the measurements are high, demanding careful standardization at all stages.