Publications

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2012
Nevison, CD, Keeling RF, Kahru M, Manizza M, Mitchell BG, Cassar N.  2012.  Estimating net community production in the Southern Ocean based on atmospheric potential oxygen and satellite ocean color data. Global Biogeochemical Cycles. 26   10.1029/2011gb004040   AbstractWebsite

The seasonal cycle of atmospheric potential oxygen (APO similar to O-2 + 1.1 CO2) reflects three seasonally varying ocean processes: 1) thermal in- and outgassing, 2) mixed layer net community production (NCP) and 3) deep water ventilation. Previous studies have isolated the net biological seasonal signal (i.e., the sum of NCP and ventilation), after using air-sea heat flux data to estimate the thermal signal. In this study, we resolve all three components of the APO seasonal cycle using a methodology in which the ventilation signal is estimated based on atmospheric N2O data, the thermal signal is estimated based on heat flux or atmospheric Ar/N-2 data, and the production signal is inferred as a residual. The isolation of the NCP signal in APO allows for direct comparison to estimates of NCP based on satellite ocean color data, after translating the latter into an atmospheric signal using an atmospheric transport model. When applied to ocean color data using algorithms specially adapted to the Southern Ocean and APO data at three southern monitoring sites, these two independent methods converge on a similar phase and amplitude of the seasonal NCP signal in APO and yield an estimate of annual mean NCP south of 50 degrees S of 0.8-1.2 Pg C/yr, with corresponding annual mean NPP of similar to 3 Pg C/yr and a mean growing season f ratio of similar to 0.33. These results are supported by ocean biogeochemistry model simulations, in which air-sea O-2 and N2O fluxes are resolved into component thermal, ventilation and (for O-2) NCP contributions.

2011
Keeling, CD, Piper SC, Whorf TP, Keeling RF.  2011.  Evolution of natural and anthropogenic fluxes of atmospheric CO2 from 1957 to 2003. Tellus Series B-Chemical and Physical Meteorology. 63:1-22.   10.1111/j.1600-0889.2010.00507.x   AbstractWebsite

An analysis is carried out of the longest available records of atmospheric CO(2) and its 13C/12C ratio from the Scripps Institution of Oceanography network of fixed stations, augmented by data in the 1950s and 1960s from ships and ice floes. Using regression analysis, we separate the interhemispheric gradients of CO(2) and 13C/12C into: (1) a stationary (possibly natural) component that is constant with time, and (2) a time-evolving component that increases in proportion to fossil fuel emissions. Inverse calculations using an atmospheric transport model are used to interpret the components of the gradients in terms of land and ocean sinks. The stationary gradients in CO(2) and 13C/12C are both satisfactorily explained by ocean processes, including an ocean carbon loop that transports 0.5 PgC yr-1 southwards in the ocean balanced by an atmospheric return flow. A stationary northern land sink appears to be ruled out unless its effect on the gradient has been offset by a strong rectifier effect, which seems doubtful. A growing northern land sink is not ruled out, but has an uncertain magnitude (0.3-1.7 PgC yr-1 centred on year 2003) dependent on the rate at which CO(2) from fossil fuel burning is dispersed vertically and between hemispheres.

2008
Rodenbeck, C, Le Quere C, Heimann M, Keeling RF.  2008.  Interannual variability in oceanic biogeochemical processes inferred by inversion of atmospheric O2/N2 and CO2 data. Tellus Series B-Chemical and Physical Meteorology. 60:685-705.   10.1111/j.1600-0889.2008.00375.x   AbstractWebsite

Atmospheric measurements of O(2)/N(2) and CO(2) at up to nine sites have been used to infer the interannual variations in oceanic O(2) exchange with an inverse method. The method distinguishes the regional contributions of three latitudinal bands, partly the individual contributions of the North Pacific and the North Atlantic also. The interannual variations of the inferred O(2) fluxes in the tropical band correlate significantly with the El Nino/Southern Oscillation. Tropical O(2) variations appear to be dominated by the ventilation of the O(2) minimum zone from variations in Pacific equatorial upwelling. The interannual variations of the northern and southern extratropical bands are of similar amplitude, though the attribution to mechanisms is less clear. The interannual variations estimated by the inverse method are larger than those estimated by the current generation of global ocean biogeochemistry models, especially in the North Atlantic, suggesting that the representation of biological processes plays a role. The comparison further suggests that O(2) variability is a more stringent test to validate models than CO(2) variability, because the processes driving O(2) variability combine in the same direction and amplify the underlying climatic signal.

2003
Stephens, BB, Keeling RF, Paplawsky WJ.  2003.  Shipboard measurements of atmospheric oxygen using a vacuum-ultraviolet absorption technique. Tellus Series B-Chemical and Physical Meteorology. 55:857-878.   10.1046/j.1435-6935.2003.00075.x   AbstractWebsite

We have developed an instrument for making continuous, field-based, part-per-million (ppm) level measurements of atmospheric oxygen concentration, and have implemented it on research cruises in the equatorial Pacific and Southern Oceans. The instrument detects changes in oxygen by the absorption of vacuum ultraviolet (VUV) radiation as it passes through a flowing gas stream, and has a precision comparable to existing laboratory techniques. Here we describe the VUV instrument and present atmospheric O-2 and CO2 data collected from the NOAA ship Ka' imimoana in the equatorial Pacific during April and May of 1998, and from the NSF ship Lawrence M. Gould in the Southern Ocean during October 1998. These data represent the first field-based measurements of atmospheric O-2, and significant additions to the O-2 datasets in these regions. Our boreal-springtime equatorial measurements reveal significant short-term variations in atmospheric O-2, resulting from variations in atmospheric mixing relative to the strong interhemispheric gradient. Our austral-springtime Southern Ocean observations confirm the low O-2 concentrations seen in flask samples from this region, allow the separate identification of oceanic and industrial influences on CO2, and provide evidence of a Southern Ocean source for CO2 at this time of year. These shipboard VUV observations do not provide any evidence to support coupled ocean-atmosphere model predictions of a large decreasing atmospheric O-2 gradient between equatorial and high-southern latitudes.