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Graven, HD, Guilderson TP, Keeling RF.  2012.  Observations of radiocarbon in CO2 at seven global sampling sites in the Scripps flask network: Analysis of spatial gradients and seasonal cycles. Journal of Geophysical Research-Atmospheres. 117   10.1029/2011jd016535   AbstractWebsite

High precision measurements of Delta C-14 were conducted for monthly samples of CO2 from seven global stations over 2- to 16-year periods ending in 2007. Mean Delta C-14 over 2005-07 in the Northern Hemisphere was 5 parts per thousand lower than Delta C-14 in the Southern Hemisphere, similar to recent observations from I. Levin. This is a significant shift from 1988-89 when Delta C-14 in the Northern Hemisphere was slightly higher than the South. The influence of fossil fuel CO2 emission and transport was simulated for each of the observation sites by the TM3 atmospheric transport model and compared to other models that participated in the Transcom 3 Experiment. The simulated interhemispheric gradient caused by fossil fuel CO2 emissions was nearly the same in both 1988-89 and 2005-07, due to compensating effects from rising emissions and decreasing sensitivity of Delta C-14 to fossil fuel CO2. The observed 5 parts per thousand shift must therefore have been caused by non-fossil influences, most likely due to changes in the air-sea C-14 flux in the Southern Ocean. Seasonal cycles with higher Delta C-14 in summer or fall were evident at most stations, with largest amplitudes observed at Point Barrow (71 degrees N) and La Jolla (32 degrees N). Fossil fuel emissions do not account for the seasonal cycles of Delta C-14 in either hemisphere, indicating strong contributions from non-fossil influences, most likely from stratosphere-troposphere exchange.

Graven, HD, Guilderson TP, Keeling RF.  2012.  Observations of radiocarbon in CO2 at La Jolla, California, USA 1992-2007: Analysis of the long-term trend. Journal of Geophysical Research-Atmospheres. 117   10.1029/2011jd016533   AbstractWebsite

High precision measurements of Delta C-14 were performed on CO2 sampled at La Jolla, California, USA over 1992-2007. A decreasing trend in Delta C-14 was observed, which averaged -5.5 parts per thousand yr(-1) yet showed significant interannual variability. Contributions to the trend in global tropospheric Delta C-14 by exchanges with the ocean, terrestrial biosphere and stratosphere, by natural and anthropogenic C-14 production and by C-14-free fossil fuel CO2 emissions were estimated using simple models. Dilution by fossil fuel emissions made the strongest contribution to the Delta C-14 trend while oceanic C-14 uptake showed the most significant change between 1992 and 2007, weakening by 70%. Relatively steady positive influences from the stratosphere, terrestrial biosphere and C-14 production moderated the decreasing trend. The most prominent excursion from the average trend occurred when Delta C-14 decreased rapidly in 2000. The rapid decline in Delta C-14 was concurrent with a rapid decline in atmospheric O-2, suggesting a possible cause may be the anomalous ventilation of deep C-14-poor water in the North Pacific Ocean. We additionally find the presence of a 28-month period of oscillation in the Delta C-14 record at La Jolla.

Keeling, RF, Kortzinger A, Gruber N.  2010.  Ocean deoxygenation in a warming world. Annual Review of Marine Science. 2:199-229., Palo Alto: Annual Reviews   10.1146/annurev.marine.010908.163855   Abstract

Ocean warming and increased stratification of the upper ocean caused by global climate change will likely lead to declines in dissolved O(2) in the ocean interior (ocean deoxygenation) with implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitat. Ocean models predict declines of 1 to 7% in the global ocean O(2) inventory over the next century, with declines continuing for a thousand years or more into the future. An important consequence may be an expansion in the area and volume of so-called oxygen minimum zones, where O(2) levels are too low to support many macrofauna and profound changes in biogeochemical cycling occur. Significant deoxy enation has occurred over the past 50 years in the North Pacific and tropical oceans, suggesting larger changes are looming. The potential for larger O(2) declines in the future suggests the need for all improved observing system for tracking ocean O(2) changes.

Hamme, RC, Keeling RF.  2008.  Ocean ventilation as a driver of interannual variability in atmospheric potential oxygen. Tellus Series B-Chemical and Physical Meteorology. 60:706-717.   10.1111/j.1600-0889.2008.00376.x   AbstractWebsite

We present observations of interannual variability on 2-5 yr timescales in atmospheric potential oxygen (APO approximate to O(2) + CO(2)) from the Scripps Institution of Oceanography global flask sampling network. Interannual variations in the tracer APO are expected to arise from air-sea fluxes alone, because APO is insensitive to exchanges with the terrestrial biosphere. These interannual variations are shown to be regionally coherent and robust to analytical artefacts. We focus on explaining a feature dominant in records from the Northern Hemisphere stations, marked by increasing APO in the late 1990s, followed by an abrupt drawdown in 2000-2001. The timing of the drawdown matches a renewal of deep convection in the North Atlantic, followed the next year by a severe winter in the western North Pacific that may have allowed ventilation of denser isopycnals than usual. We find a weak correlation between changes in the interhemispheric APO difference and El Nino indices, and the observations show no strong features of the 1997-98 El Nino. Comparisons with estimates of variations in ocean productivity and ocean heat content demonstrate that these processes are secondary influences at these timescales. We conclude that the evidence points to variability in ocean ventilation as the main driver of interannual variability in APO.

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.

Keeling, RF.  2002.  On the freshwater forcing of the thermohaline circulation in the limit of low diapycnal mixing. Journal of Geophysical Research-Oceans. 107   10.1029/2000jc000685   AbstractWebsite

[1] A conjecture is offered on the stability characteristics of the thermohaline circulation in the limit of very low diapycnal mixing. In this limit the action of the winds on the Antarctic Circumpolar Current (ACC) can sustain a deep overturning pattern known as the "reconfigured conveyor,'' consisting of upwelling around Antarctica and sinking in the North Atlantic, as shown by the work of Toggweiler and others. It is conjectured that in this limit, northern sinking should be stabilized in an "on'' state because of the penetration of freshwater into the ocean interior via isopycnal layers that outcrop to the surface within and south of the ACC. This conjecture is supported by qualitative arguments and by a hydraulic model for the reconfigured conveyor. The hydraulic model takes into account the freshwater budgets of the Atlantic basin, Antarctic surface waters, and the remaining oceans. It also takes into account, in simple terms, wind-driven Antarctic upwelling, eddy transports and mixing within the ACC, changes in pycnocline depth, the role of temperature forcing, and advective feedbacks on salinity. The hydraulic model suggests that multiple "on/off'' states of the reconfigured conveyor are possible but only if the deep waters that form in the Northern Hemisphere are fresher than the intermediate waters that form in the vicinity of the ACC in the Southern Hemisphere, a condition that is not satisfied in the modern ocean.

Garcia, HE, Keeling RF.  2001.  On the global oxygen anomaly and air-sea flux. Journal of Geophysical Research-Oceans. 106:31155-31166.   10.1029/1999jc000200   AbstractWebsite

We present a new climatology of monthly air-sea oxygen fluxes throughout the ice-free surface global ocean. The climatology is based on weighted linear least squares regressions using heat flux monthly anomalies for spatial and temporal interpolation of historical O-2 data. The seasonal oceanic variations show that the tropical belt (20degreesS-20degreesN) is characterized by relatively small air-sea fluxes when compared to the middle to high latitudes (40degrees-70degrees). The largest and lowest seasonal fluxes occur during summer and winter in both hemispheres. By means of an atmospheric transport model we show that our climatology is in better agreement with the observed amplitude and phasing of the variations in atmospheric O-2/N-2 ratios because of seasonal air-sea exchanges at baseline stations in the Pacific Ocean than with previous air-sea O-2 climatologies. Our study indicates that the component of the air-sea O-2 flux that correlates with heat flux dominates the large-scale air-sea O-2 exchange on seasonal timescales. The contribution of each major oceanic basin to the atmospheric observations is described. The seasonal net thermal (SNOT) and biological (SNOB) outgassing components of the flux are examined in relation to latitudinal bands, basin-wide, and hemispheric contributions. The Southern Hemisphere's SNOB (similar to0.26 Pmol) and SNOT (similar to0.29 Pmol) values are larger than the Northern Hemisphere's SNOB (similar to0.15 Pmol) and SNOT (similar to0.16 Pmol) values (1 Pmol = 10(15) mol). We estimate a global extratropical carbon new production during the outgassing season of 3.7 Pg C (1 Pg = 10(15) g), lower than previous estimates with air-sea O-2 climatologies.

Keeling, RF, Visbeck M.  2011.  On the linkage between Antarctic surface water stratification and global deep-water temperature. Journal of Climate. 24:3545-3557.   10.1175/2011jcli3642.1   AbstractWebsite

The suggestion is advanced that the remarkably low static stability of Antarctic surface waters may arise from a feedback loop involving global deep-water temperatures. If deep-water temperatures are too warm, this promotes Antarctic convection, thereby strengthening the inflow of Antarctic Bottom Water into the ocean interior and cooling the deep ocean. If deep waters are too cold, this promotes Antarctic stratification allowing the deep ocean to warm because of the input of North Atlantic Deep Water. A steady-state deep-water temperature is achieved such that the Antarctic surface can barely undergo convection. A two-box model is used to illustrate this feedback loop in its simplest expression and to develop basic concepts, such as the bounds on the operation of this loop. The model illustrates the possible dominating influence of Antarctic upwelling rate and Antarctic freshwater balance on global deep-water temperatures.

Keeling, RF, Manning AC, Paplawsky WJ, Cox AC.  2007.  On the long-term stability of reference gases for atmospheric O2/N2 and CO2 measurements. Tellus Series B-Chemical and Physical Meteorology. 59:3-14.   10.1111/j.1600-0889.2006.00228.x   AbstractWebsite

Measurements of changes in the atmospheric O-2/N-2 ratio have typically relied on compressed air derived from high-pressure tanks as the reference material against which atmospheric changes are assessed. The validity of this procedure is examined here in the context of the history of 18 O-2/N-2 reference tanks compared over a 12-yr time-frame. By considering differences in tank sizes, material types, and by performing additional tests, the long-term stability of the delivered gas is evaluated with respect to surface reactions, leakage, regulator effects, and thermal diffusion and gravimetric fractionation. Results are also reported for the stability of CO2 in these tanks. The results emphasize the importance of orienting tanks horizontally within a thermally insulated enclosure to reduce thermal and gravimetric fractionation of both O-2/N-2 and CO2 concentrations, and they emphasize the importance of avoiding elastomeric O-rings at the head-valve base. With the procedures documented here, the long-term drift in O-2/N-2 appears to be zero to within approximately +/- 0.4 per meg yr(-1), which projects to an uncertainty of +/- 0.16 Pg C yr(-1) (1 sigma) in O-2-based global carbon budgets.

Manizza, M, Keeling RF, Nevison CD.  2012.  On the processes controlling the seasonal cycles of the air-sea fluxes of O2 and N2O: A modelling study. Tellus Series B-Chemical and Physical Meteorology. 64   10.3402/tellusb.v64i0.18429   AbstractWebsite

The seasonal dynamics of the air-sea gas flux of oxygen (O-2) are controlled by multiple processes occurring simultaneously. Previous studies showed how to separate the thermal component from the total O-2 flux to quantify the residual oxygen flux due to biological processes. However, this biological signal includes the effect of both net euphotic zone production (NEZP) and subsurface water ventilation. To help understand and separate these two components, we use a large-scale ocean general circulation model (OGCM), globally configured, and coupled to a biogeochemical model. The combined model implements not only the oceanic cycle of O-2 but also the cycles of nitrous oxide (N2O), argon (Ar) and nitrogen (N-2). For this study, we apply a technique to distinguish the fluxes of O-2 driven separately by thermal forcing, NEZP, and address the role of ocean ventilation by carrying separate O-2 components in the model driven by solubility, NEZP and ventilation. Model results show that the ventilation component can be neglected in summer compared to the production and thermal components polewards but not equatorward of 30 degrees in each hemisphere. This also implies that neglecting the role of ventilation in the subtropical areas would lead to overestimation of the component of O-2 flux due to NEZP by 20-30%. Model results also show that the ventilation components of air-sea O-2 and N2O fluxes are strongly anti-correlated in a ratio that reflects the subsurface tracer/tracer relationships (similar to 0.1 mmol N2O/mol O-2) as derived from observations. The results support the use of simple scaling relationships linking together the thermally driven fluxes of Ar, N-2 and O-2. Furthermore, our study also shows that for latitudes polewards of 30 degrees of both hemispheres, the Garcia and Keeling (2001) climatology, when compared to our model results, has a phasing error with the fluxes being too early by similar to 2-3 weeks.

Keeling, RF.  1993.  On the role of large bubbles in air-sea gas exchange and supersaturation in the ocean. Journal of Marine Research. 51:237-271.   10.1357/0022240933223800   AbstractWebsite

A parameterization of bubble-induced gas exchange is presented in which the bubble contribution to gas exchange is expressed in terms of separate transfer velocities for ingassing (K(b)in) and outgassing (K(b)out). The difference between the ingassing and outgassing velocities (K(b)in - K(b)out) is further separated into two components, the first caused by the injection of small bubbles into the water, the second caused by gas exchange across the surface of hydrostatically compressed larger bubbles. It is argued that both K(b)out and the exchange contribution to the difference K(b)in - K(b)out should be largely independent of the dissolved concentrations of the major gases N2 and O2. A simple model is presented which allows K(b)out and the exchange contribution to the difference K(b)in - K(b)out to be estimated. The model incorporates data from laboratory simulation experiments on the bubble production spectrum. The results indicate that bubbles larger than 0.05 cm in radius, which have often been assumed to play a negligible role, contribute significantly to bubble-induced gas exchange and supersaturation in the ocean. The model is used to explore the sensitivity of bubble-induced gas exchange to the overall air entrainment rate, size and depth distributions of the bubbles, and to the gas exchange rates across the surface of individual bubbles. The model suggests that bubbles may make an important contribution to overall gas exchange at windspeeds above 10 m sec-1. In this regime gas transfer velocities should depend, not just on diffusivity, but also on the solubility of the gases. It is suggested that K(b)(out) should scale roughly as alpha-0.3D0.35 where a is the solubility and D is the diffusivity. The model results, in combination with measurements on inert gas supersaturations, suggest that the global-mean supersaturation of CO2 induced by bubbles is not larger than 0.3% and most probably is around 0.08%. A major uncertainty results from a lack of information on production rates and distributions of large bubbles. Several possible experiments are proposed for improving estimates of bubble-induced gas exchange and supersaturation.

Lueker, TJ, Keeling RF, Dubey MK.  2001.  The oxygen to carbon dioxide ratios observed in emissions from a wildfire in Northern California. Geophysical Research Letters. 28:2413-2416.   10.1029/2000gl011860   AbstractWebsite

At Trinidad, California we observed elevated CO2 concentrations and concomitant lowered O-2 levels coincident with forest fires 70 kin distant (from 10/8/99 to 10/21/99). The precision of our O-2 data, 1 mu mol O-2 /mol dry air, revealed the reduction of atmospheric oxygen resulting from the combustion of biomass, and the stoichiometric ratios (-O-2/CO2) of the wildfire emissions. Estimates of daily -O-2/CO2 ratios were obtained by regression of CO2 against corresponding O-2 data (R-2, 0.86 to 0.96). Daily -O-2/CO2 ratios changed from 1.15 to 1.41 on a particularly smoky day that coincided with elevated levels of CH4 and increased CH4/CO2 ratios. The change to a higher ratio during smoky conditions illustrates the association between changing emissions and -O-2/CO2 ratios, possibly due to changing wildfire dynamics.

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Keeling, RF, Visbeck M.  2001.  Palaeoceanography - Antarctic stratification and glacial CO2. Nature. 412:605-606.   10.1038/35088129   AbstractWebsite

One way of accounting for lowered atmospheric carbon dioxide concentrations during Pleistocene glacial periods is by invoking the Antarctic stratification hypothesis, which links the reduction in CO2 to greater stratification of ocean surface waters around Antarctica1, 2. As discussed by Sigman and Boyle3, this hypothesis assumes that increased stratification in the Antarctic zone (Fig. 1) was associated with reduced upwelling of deep waters around Antarctica, thereby allowing CO2 outgassing to be suppressed by biological production while also allowing biological production to decline, which is consistent with Antarctic sediment records4. We point out here, however, that the response of ocean eddies to increased Antarctic stratification can be expected to increase, rather than reduce, the upwelling rate of deep waters around Antarctica. The stratification hypothesis may have difficulty in accommodating eddy feedbacks on upwelling within the constraints imposed by reconstructions of winds and Antarctic-zone productivity in glacial periods.

Langenfelds, RL, Francey RJ, Steele LP, Battle M, Keeling RF, Budd WF.  1999.  Partitioning of the global fossil CO2 sink using a 19-year trend in atmospheric O2. Geophysical Research Letters. 26:1897-1900.   10.1029/1999gl900446   AbstractWebsite

O-2/N-2 is measured in the Cape Grim Air Archive (CGAA), a suite of tanks filled with background air at Cape Grim, Tasmania (40.7 degrees S, 144.8 degrees E) between April 1978 and January 1997. Derived trends are compared with published O-2/N-2 records and assessed against limits on interannual variability of net terrestrial exchanges imposed by trends of delta(13)C in CO2. Two old samples from 1978 and 1987 and eight from 1996/97 survive critical selection criteria and give a mean 19-year trend in delta(O-2/N-2) of -16.7 +/- 0.5 per meg y(-1), implying net storage of +2.3 +/- 0.7 GtC (10(15) g carbon) yr(-1) of fossil fuel CO2 in the oceans and +0.2 +/- 0.9 GtC yr(-1) in the terrestrial biosphere. The uptake terms are consistent for both O-2/N-2 and delta(13)C tracers if the mean C-13 isotopic disequilibrium flux, combining terrestrial and oceanic contributions, is 93 +/- 15 GtC parts per thousand yr(-1).

Perks, HM, Charles CD, Keeling RF.  2002.  Precessionally forced productivity variations across the equatorial Pacific. Paleoceanography. 17   10.1029/2000pa000603   AbstractWebsite

[1] Measurements of combustion oxygen demand (COD) in two sediment cores provide a record of paleoproductivity driven by surface-ocean dynamics in the equatorial eastern and western Pacific for the past 400,000 years. The COD time series are well correlated with each other over this time span and show pronounced precessionally forced peaks of higher productivity during globally colder periods. The phase of this signal in the two cores is identical, to within chronological uncertainties, suggesting a common insolation forcing mechanism for the upper ocean across the equatorial Pacific. COD is also in phase with the precessionally forced component of global ice volume, as indicated by oxygen isotopes, and with atmospheric methane in the Vostok ice core. These relationships imply that the COD relative paleoproductivity index provides an important diagnostic measure of the mechanisms of tropical ocean dynamics and climate change.

Manning, AC, Keeling RF, Severinghaus JP.  1999.  Precise atmospheric oxygen measurements with a paramagnetic oxygen analyzer. Global Biogeochemical Cycles. 13:1107-1115.   10.1029/1999gb900054   AbstractWebsite

A methodology has been developed for making continuous, high-precision measurements of atmospheric oxygen concentrations by modifying a commercially available paramagnetic oxygen analyzer. Incorporating several design improvements, an effective precision of 0.2 ppm O-2 from repeated measurements over a 1-hour interval was achieved. This is sufficient to detect background changes in atmospheric O-2 to a level that constrains various aspects of the global carbon cycle. The analyzer was used to measure atmospheric O-2 in a semicontinuous fashion from air sampled from the end of Scripps Pier, La Jolla, California, and data from a 1-week period in August 1996 are shown. The data exhibit strongly anticorrelated changes in O-2 and CO2 caused by local or regional combustion of fossil fuels. During periods of steady background CO2 concentrations, however, we see additional variability in O-2 concentrations, clearly not due to local combustion and presumably due to oceanic sources or sinks of O-2. This variability suggests that in contrast to CO2, higher O-2 sampling rates, such as those provided by continuous measurement programs, may be necessary to define an atmospheric O-2 background and thus aid in validating and interpreting other O-2 data from flask sampling programs. Our results have also demonstrated that this paramagnetic analyzer and gas handling design is well suited for making continuous measurements of atmospheric O-2 and is suitable for placement at remote background air monitoring sites.

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Resplandy, L, Keeling RF, Eddebbar Y, Brooks MK, Wang R, Bopp L, Long MC, Dunne JP, Koeve W, Oschlies A.  2018.  Quantification of ocean heat uptake from changes in atmospheric O2 and CO2 composition. Nature. 563:105-108.   10.1038/s41586-018-0651-8   Abstract

The ocean is the main source of thermal inertia in the climate system1. During recent decades, ocean heat uptake has been quantified by using hydrographic temperature measurements and data from the Argo float program, which expanded its coverage after 20072,3. However, these estimates all use the same imperfect ocean dataset and share additional uncertainties resulting from sparse coverage, especially before 20074,5. Here we provide an independent estimate by using measurements of atmospheric oxygen (O2) and carbon dioxide (CO2)—levels of which increase as the ocean warms and releases gases—as a whole-ocean thermometer. We show that the ocean gained 1.33 ± 0.20  × 1022 joules of heat per year between 1991 and 2016, equivalent to a planetary energy imbalance of 0.83 ± 0.11 watts per square metre of Earth’s surface. We also find that the ocean-warming effect that led to the outgassing of O2 and CO2 can be isolated from the direct effects of anthropogenic emissions and CO2 sinks. Our result—which relies on high-precision O2 measurements dating back to 19916—suggests that ocean warming is at the high end of previous estimates, with implications for policy-relevant measurements of the Earth response to climate change, such as climate sensitivity to greenhouse gases7 and the thermal component of sea-level rise8.

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Rahmstorf, S, Cazenave A, Church JA, Hansen JE, Keeling RF, Parker DE, Somerville RCJ.  2007.  Recent climate observations compared to projections. Science. 316:709-709.   10.1126/science.1136843   AbstractWebsite

We present recent observed climate trends for carbon dioxide concentration, global mean air temperature, and global sea level, and we compare these trends to previous model projections as summarized in the 2001 assessment report of the Intergovernmental Panel on Climate Change (IPCC). The IPCC scenarios and projections start in the year 1990, which is also the base year of the Kyoto protocol, in which almost all industrialized nations accepted a binding commitment to reduce their greenhouse gas emissions. The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates.

Resplandy, L, Keeling RF, Rodenbeck C, Stephens BB, Khatiwala S, Rodgers KB, Long MC, Bopp L, Tans PP.  2018.  Revision of global carbon fluxes based on a reassessment of oceanic and riverine carbon transport. Nature Geoscience. 11:504-+.   10.1038/s41561-018-0151-3   AbstractWebsite

Measurements of atmospheric CO2 concentration provide a tight constraint on the sum of the land and ocean sinks. This constraint has been combined with estimates of ocean carbon flux and riverine transport of carbon from land to oceans to isolate the land sink. Uncertainties in the ocean and river fluxes therefore translate into uncertainties in the land sink. Here, we introduce a heat-based constraint on the latitudinal distribution of ocean and river carbon fluxes, and reassess the partition between ocean, river and land in the tropics, and in the southern and northern extra-tropics. We show that the ocean overturning circulation and biological pump tightly link the ocean transports of heat and carbon between hemispheres. Using this coupling between heat and carbon, we derive ocean and river carbon fluxes compatible with observational constraints on heat transport. This heat-based constraint requires a 20-100% stronger ocean and river carbon transport from the Northern Hemisphere to the Southern Hemisphere than existing estimates, and supports an upward revision of the global riverine carbon flux from 0.45 to 0.78 PgC yr(-1). These systematic biases in existing ocean/river carbon fluxes redistribute up to 40% of the carbon sink between northern, tropical and southern land ecosystems. As a consequence, the magnitude of both the southern land source and the northern land sink may have to be substantially reduced.

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Keeling, RF, Shertz SR.  1992.  Seasonal and interannual variations in atmospheric oxygen and implications for the global carbon cycle. Nature. 358:723-727.   10.1038/358723a0   AbstractWebsite

Measurements of changes in atmospheric molecular oxygen using a new interferometric technique show that the O2 content of air varies seasonally in both the Northern and Southern Hemispheres and is decreasing from year to year. The seasonal variations provide a new basis for estimating global rates of biological organic carbon production in the ocean, and the interannual decrease constrains estimates of the rate of anthropogenic CO2 uptake by the oceans.

Keeling, RF, Stephens BB, Najjar RG, Doney SC, Archer D, Heimann M.  1998.  Seasonal variations in the atmospheric O2/N2 ratio in relation to the kinetics of air-sea gas exchange. Global Biogeochemical Cycles. 12:141-163.   10.1029/97gb02339   AbstractWebsite

Observations of seasonal variations in the atmospheric O-2/N-2 ratio are reported at nine baseline sites in the northern and southern hemispheres. Concurrent CO2 measurements are used to correct for the effects of land biotic exchanges of O-2 on the O-2/N-2 cycles thus allowing the residual component of the cycles due to oceanic exchanges of O-2 and N-2 to be calculated. The residual oceanic cycles in the northern hemisphere are nearly diametrically out of phase with the cycles in the southern hemisphere. The maxima in both hemispheres occur in summer. In both hemispheres, the middle-latitude sea level stations show the cycles with largest amplitudes and earliest phasing. Somewhat smaller amplitudes are observed at the high-latitude stations, and much smaller amplitudes are observed at the tropical stations. A model for simulating the oceanic component of the atmospheric O-2/N-2 cycles is presented consisting of the TM2 atmospheric tracer transport model [Heimann, 1995] driven at the lower boundary by O-2 fluxes derived from observed O-2 saturation anomalies in surface waters and by N-2 fluxes derived from the net air-sea heat flux. The model is optimized to fit the observed atmospheric O-2/N-2 cycles by adjusting the air-sea gas-exchange velocity, which relates O-2 anomaly to O-2 flux. The optimum fit corresponds to spatially and temporally averaged exchange velocities of 24+/-6 cm/hr for the oceans north of 31 degrees N and 29+/-12 cm/hr for the oceans south of 31 degrees S. These velocities agree to within the uncertainties with the gas-exchange velocities expected from the Wanninkhof [1992] formulation of the air-sea gas-exchange velocity combined with European Centre for Medium-Range Weather Forecasts winds [Gibson et al., 1997] but are larger than the exchange velocities expected from the Liss and Merlivat [1986] relation using the same winds. The results imply that the gas-exchange velocity for O-2, like that of CO2, may be enhanced in the open ocean by processes that were not systematically accounted for in the experiments used to derive the Liss and Merlivat relation.

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.

Fischer, ML, Parazoo N, Brophy K, Cui XG, Jeong S, Liu JJ, Keeling R, Taylor TE, Gurney K, Oda T, Graven H.  2017.  Simulating estimation of California fossil fuel and biosphere carbon dioxide exchanges combining in situ tower and satellite column observations. Journal of Geophysical Research-Atmospheres. 122:3653-3671.   10.1002/2016jd025617   AbstractWebsite

We report simulation experiments estimating the uncertainties in California regional fossil fuel and biosphere CO2 exchanges that might be obtained by using an atmospheric inverse modeling system driven by the combination of ground-based observations of radiocarbon and total CO2, together with column-mean CO2 observations from NASA's Orbiting Carbon Observatory (OCO-2). The work includes an initial examination of statistical uncertainties in prior models for CO2 exchange, in radiocarbon-based fossil fuel CO2 measurements, in OCO-2 measurements, and in a regional atmospheric transport modeling system. Using these nominal assumptions for measurement and model uncertainties, we find that flask measurements of radiocarbon and total CO2 at 10 towers can be used to distinguish between different fossil fuel emission data products for major urban regions of California. We then show that the combination of flask and OCO-2 observations yields posterior uncertainties in monthly-mean fossil fuel emissions of similar to 5-10%, levels likely useful for policy relevant evaluation of bottom-up fossil fuel emission estimates. Similarly, we find that inversions yield uncertainties in monthly biosphere CO2 exchange of similar to 6%-12%, depending on season, providing useful information on net carbon uptake in California's forests and agricultural lands. Finally, initial sensitivity analysis suggests that obtaining the above results requires control of systematic biases below approximately 0.5ppm, placing requirements on accuracy of the atmospheric measurements, background subtraction, and atmospheric transport modeling.

Nevison, CD, Keeling RF, Weiss RF, Popp BN, Jin X, Fraser PJ, Porter LW, Hess PG.  2005.  Southern Ocean ventilation inferred from seasonal cycles of atmospheric N2O and O2/N2 at Cape Grim, Tasmania. Tellus Series B-Chemical and Physical Meteorology. 57:218-229.   10.1111/j.1600-0889.2005.00143.x   AbstractWebsite

The seasonal cycle of atmospheric N(2)O is derived from a 10-yr observational record at Cape Grim, Tasmania (41 degrees S, 145 degrees E). After correcting for thermal and stratospheric influences, the observed atmospheric seasonal cycle is consistent with the seasonal outgassing of microbially produced N(2)O from the Southern Ocean, as predicted by an ocean biogeochemistry model coupled to an atmospheric transport model (ATM). The model-observation comparison suggests a Southern Ocean N(2)O source of similar to 0.9 Tg N yr(-1) and is the first study to reproduce observed atmospheric seasonal cycles in N(2)O using specified surface sources in forward ATM runs. However, these results are sensitive to the thermal and stratospheric corrections applied to the atmospheric N(2)O data. The correlation in subsurface waters between apparent oxygen utilization (AOU) and N(2)O production (approximated as the concentration in excess of atmospheric equilibrium Delta N(2)O) is exploited to infer the atmospheric seasonal cycle in O(2)/N(2) due to ventilation of O(2)-depleted subsurface waters. Subtracting this cycle from the observed, thermally corrected seasonal cycle in atmospheric O(2)/N(2) allows the residual O(2)/N(2) signal from surface net community production to be inferred. Because N(2)O is only produced in subsurface ocean waters, where it is correlated to O(2) consumption, atmospheric N(2)O observations provide a methodology for distinguishing the surface production and subsurface ventilation signals in atmospheric O(2)/N(2), which have previously been inseparable.

Yadav, V, Duren R, Mueller K, Verhulst KR, Nehrkorn T, Kim J, Weiss RF, Keeling R, Sander S, Fischer ML, Newman S, Falk M, Kuwayama T, Hopkins F, Rafiq T, Whetstone J, Miller C.  2019.  Spatio-temporally resolved methane fluxes from the Los Angeles megacity. Journal of Geophysical Research-Atmospheres. 124:5131-5148.   10.1029/2018jd030062   AbstractWebsite

We combine sustained observations from a network of atmospheric monitoring stations with inverse modeling to uniquely obtain spatiotemporal (3-km, 4-day) estimates of methane emissions from the Los Angeles megacity and the broader South Coast Air Basin for 2015-2016. Our inversions use customized and validated high-fidelity meteorological output from Weather Research Forecasting and Stochastic Time-Inverted Lagrangian model for South Coast Air Basin and innovatively employ a model resolution matrix-based metric to disentangle the spatiotemporal information content of observations as manifested through estimated fluxes. We partially track and constrain fluxes from the Aliso Canyon natural gas leak and detect closure of the Puente Hills landfill, with no prior information. Our annually aggregated fluxes and their uncertainty excluding the Aliso Canyon leak period lie within the uncertainty bounds of the fluxes reported by the previous studies. Spatially, major sources of CH4 emissions in the basin were correlated with CH4-emitting infrastructure. Temporally, our findings show large seasonal variations in CH4 fluxes with significantly higher fluxes in winter in comparison to summer months, which is consistent with natural gas demand and anticorrelated with air temperature. Overall, this is the first study that utilizes inversions to detect both enhancement (Aliso Canyon leak) and reduction (Puente Hills) in CH4 fluxes due to the unintended events and policy decisions and thereby demonstrates the utility of inverse modeling for identifying variations in fluxes at fine spatiotemporal resolution.