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2019
Eddebbar, YA, Rodgers KB, Long MC, Subramanian AC, Xie SP, Keeling RF.  2019.  El Nino-like physical and biogeochemical ocean response to tropical eruptions. Journal of Climate. 32:2627-2649.   10.1175/jcli-d-18-0458.1   AbstractWebsite

The oceanic response to recent tropical eruptions is examined in Large Ensemble (LE) experiments from two fully coupled global climate models, the Community Earth System Model (CESM) and the Geophysical Fluid Dynamics Laboratory Earth System Model (ESM2M), each forced by a distinct volcanic forcing dataset. Following the simulated eruptions of Agung, El Chichon, and Pinatubo, the ocean loses heat and gains oxygen and carbon, in general agreement with available observations. In both models, substantial global surface cooling is accompanied by El Nino-like equatorial Pacific surface warming a year after the volcanic forcing peaks. A mechanistic analysis of the CESM and ESM2M responses to Pinatubo identifies remote wind forcing from the western Pacific as a major driver of this El Nino-like response. Following eruption, faster cooling over the Maritime Continent than adjacent oceans suppresses convection and leads to persistent westerly wind anomalies over the western tropical Pacific. These wind anomalies excite equatorial downwelling Kelvin waves and the upwelling of warm subsurface anomalies in the eastern Pacific, promoting the development of El Nino conditions through Bjerknes feedbacks a year after eruption. This El Nino-like response drives further ocean heat loss through enhanced equatorial cloud albedo, and dominates global carbon uptake as upwelling of carbon-rich waters is suppressed in the tropical Pacific. Oxygen uptake occurs primarily at high latitudes, where surface cooling intensifies the ventilation of subtropical thermocline waters. These volcanically forced ocean responses are large enough to contribute to the observed decadal variability in oceanic heat, carbon, and oxygen.

2018
Le Quere, C, Andrew RM, Friedlingstein P, Sitch S, Hauck J, Pongratz J, Pickers PA, Korsbakken JI, Peters GP, Canadell JG, Arneth A, Arora VK, Barbero L, Bastos A, Bopp L, Chevallier F, Chini LP, Ciais P, Doney SC, Gkritzalis T, Goll DS, Harris I, Haverd V, Hoffman FM, Hoppema M, Houghton RA, Hurtt G, Ilyina T, Jain AK, Johannessen T, Jones CD, Kato E, Keeling RF, Goldewijk KK, Landschutzer P, Lefevre N, Lienert S, Liu Z, Lombardozzi D, Metzl N, Munro DR, Nabel J, Nakaoka S, Neill C, Olsen A, Ono T, Patra P, Peregon A, Peters W, Peylin P, Pfeil B, Pierrot D, Poulter B, Rehder G, Resplandy L, Robertson E, Rocher M, Rodenbeck C, Schuster U, Schwinger J, Seferian R, Skjelvan I, Steinhoff T, Sutton A, Tans PP, Tian HQ, Tilbrook B, Tubiello FN, van der Laan-Luijkx IT, van der Werf GR, Viovy N, Walker AP, Wiltshire AJ, Wright R, Zaehle S, Zheng B.  2018.  Global Carbon Budget 2018. Earth System Science Data. 10:2141-2194.   10.5194/essd-10-2141-2018   AbstractWebsite

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere - the "global carbon budget" - is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (E-FF) are based on energy statistics and cement production data, while emissions from land use and land-use change (E-LUC), mainly deforestation, are based on land use and land -use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly and its growth rate (G(ATM)) is computed from the annual changes in concentration. The ocean CO2 sink (S-OCEAN) and terrestrial CO2 sink (S-LAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (B-IM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as +/- 1 sigma. For the last decade available (2008-2017), E-FF was 9.4 +/- 0.5 GtC yr(-1), E-LUC 1.5 +/- 0.7 GtC yr(-1), G(ATM) 4.7 +/- 0.02 GtC yr(-1), S-OCEAN 2.4 +/- 0.5 GtC yr(-1), and S-LAND 3.2 +/- 0.8 GtC yr(-1), with a budget imbalance B-IM of 0.5 GtC yr(-1) indicating overestimated emissions and/or underestimated sinks. For the year 2017 alone, the growth in E-FF was about 1.6 % and emissions increased to 9.9 +/- 0.5 GtC yr(-1). Also for 2017, E-LUC was 1.4 +/- 0.7 GtC yr(-1), G(ATM) was 4.6 +/- 0.2 GtC yr(-1), S-OCEAN was 2.5 +/- 0.5 GtC yr(-1), and S-LAND was 3.8 +/- 0.8 GtC yr(-1), with a B-IM of 0.3 GtC. The global atmospheric CO2 concentration reached 405.0 +/- 0.1 ppm averaged over 2017. For 2018, preliminary data for the first 6-9 months indicate a renewed growth in E-FF of +2.7 % (range of 1.8 % to 3.7 %) based on national emission projections for China, the US, the EU, and India and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. The analysis presented here shows that the mean and trend in the five components of the global carbon budget are consistently estimated over the period of 1959-2017, but discrepancies of up to 1 GtC yr(-1) persist for the representation of semi-decadal variability in CO2 fluxes. A detailed comparison among individual estimates and the introduction of a broad range of observations show (1) no consensus in the mean and trend in land -use change emissions, (2) a persistent low agreement among the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) an apparent underestimation of the CO2 variability by ocean models, originating outside the tropics. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding the global carbon cycle compared with previous publications of this data set (Le Quere et al., 2018, 2016, 2015a, b, 2014, 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2018.

2017
Keeling, RF, Graven HD, Welp LR, Resplandy L, Bi J, Piper SC, Sun Y, Bollenbacher A, Meijer HAJ.  2017.  Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis. Proceedings of the National Academy of Sciences of the United States of America. 114:10361-10366.   10.1073/pnas.1619240114   AbstractWebsite

A decrease in the C-13/C-12 ratio of atmospheric CO2 has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the C-13-Suess effect, is driven primarily by the input of fossil fuel-derived CO2 but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed C-13-Suess effect unless an increase has occurred in the C-13/C-12 isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C-3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements. We further show that the inferred discrimination increase of 0.014 +/- 0.007% ppm(-1) is largely explained by photorespiratory and mesophyll effects. This result implies that, at the global scale, land plants have regulated their stomatal conductance so as to allow the CO2 partial pressure within stomatal cavities and their intrinsic water use efficiency to increase in nearly constant proportion to the rise in atmospheric CO2 concentration.

2016
Nevison, CD, Manizza M, Keeling RF, Stephens BB, Bent JD, Dunne J, Ilyina T, Long M, Resplandy L, Tjiputra J, Yukimoto S.  2016.  Evaluating CMIP5 ocean biogeochemistry and Southern Ocean carbon uptake using atmospheric potential oxygen: Present-day performance and future projection. Geophysical Research Letters. 43:2077-2085.   10.1002/2015gl067584   AbstractWebsite

Observed seasonal cycles in atmospheric potential oxygen (APO similar to O-2+1.1 CO2) were used to evaluate eight ocean biogeochemistry models from the Coupled Model Intercomparison Project (CMIP5). Model APO seasonal cycles were computed from the CMIP5 air-sea O-2 and CO2 fluxes and compared to observations at three Southern Hemisphere monitoring sites. Four of the models captured either the observed APO seasonal amplitude or phasing relatively well, while the other four did not. Many models had an unrealistic seasonal phasing or amplitude of the CO2 flux, which in turn influenced APO. By 2100 under RCP8.5, the models projected little change in the O-2 component of APO but large changes in the seasonality of the CO2 component associated with ocean acidification. The models with poorer performance on present-day APO tended to project larger net carbon uptake in the Southern Ocean, both today and in 2100.

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.

2009
Keeling, RF.  2009.  Triage in the greenhouse. Nature Geoscience. 2:820-822.   10.1038/ngeo701   AbstractWebsite

The path towards mitigating global warming is going to be tortuous. capturing carbon dioxide and pumping it directly into the deep ocean to avoid atmospheric build-up is an option that has been dismissed prematurely.

2007
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.

2004
Keeling, RF, Blaine T, Paplawsky B, Katz L, Atwood C, Brockwell T.  2004.  Measurement of changes in atmospheric Ar/N2 ratio using a rapid-switching, single-capillary mass spectrometer system. Tellus Series B-Chemical and Physical Meteorology. 56:322-338.   10.1111/j.1600-0889.2004.00117.x   AbstractWebsite

The atmospheric Ar/N-2 ratio is expected to undergo very slight variations due to exchanges of Ar and N-2 across the air-sea interface, driven by ocean solubility changes. Observations of these variations may provide useful constraints on large-scale fluxes of heat across the air-sea interface. A mass spectrometer system is described that incorporates a magnet with a wide exit face, allowing a large mass spread, and incorporates an inlet with rapid (5 s) switching of sources gases through a single capillary, thus achieving high precision in the comparison of sample and reference gases. The system allows simultaneous measurement of Ar/N-2, O-2/N, and CO2/N-2 ratios. The system achieves a short-term precision in Ar/N-2 of 10 per meg for a 10 s integration, which can be averaged to achieve an internal precision of a few per meg in the comparison of reference gases. Results for Ar/N-2 are reported from flasks samples collected from nine stations in a north-to-south global network over about a 1 yr period. The imprecision on an individual flask, as estimated from replicate agreement, is 11 per meg. This imprecision is dominated by real variability between samples at the time of analysis. Seasonal cycles are marginally resolved at the extra-tropical stations with amplitudes of 5 to 15 per meg. Annual-mean values are constant between stations to within 5 per meg. The results are compared with a numerical simulation of the cycles and gradients in Ar/N-2 based on the TM2 tracer transport model in combination with air-sea Ar and N-2 fluxes derived from climatological air-sea heat fluxes. The possibility is suggested that Ar/N-2 ratios may be detectably enriched near the ground by gravimetric or thermal fractionation under conditions of strong surface inversions.

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.

Lueker, TJ, Walker SJ, Vollmer MK, Keeling RF, Nevison CD, Weiss RF, Garcia HE.  2003.  Coastal upwelling air-sea fluxes revealed in atmospheric observations of O2/N2, CO2 and N2O. Geophysical Research Letters. 30   10.1029/2002gl016615   AbstractWebsite

[1] We capture water column ventilation resulting from coastal upwelling in continuous records of O-2/N-2, CO2, and N2O at Trinidad, California. Our records reveal the gas exchange response time of the ocean to the upwelling and ensuing biological production. Satellite and buoy wind data allow extrapolation of our records to assess coastal upwelling air-sea fluxes of O-2 and N2O. We improve on previous regional estimates of N2O flux in coastal and continental shelf region of the western U. S. We characterize the source of N2O as being predominately from nitrification based on the O-2/N2O emissions ratio observed in our atmospheric records.

2002
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.

1998
Perks, HM, Keeling RF.  1998.  A 400 kyr record of combustion oxygen demand in the western equatorial Pacific: Evidence for a precessionally forced climate response. Paleoceanography. 13:63-69.   10.1029/97pa02892   AbstractWebsite

We have developed a combustion analysis technique for sediments which measures the amount of O-2 consumed by the reduced species. We have measured this quantity, which we call "combustion oxygen demand (COD)," on a carbonate-rich sediment core from the Ontong-Java Plateau in the western equatorial Pacific back to marine oxygen isotope stage 11. The precision of the COD technique is +/-6.3 mu mol O-2 g(-1), which corresponds to similar to+/-0.0076% wt C-org, assuming oxidation of organic carbon dominates the signal. The COD time series is characterized by values which are about twice as high during glacials as during interglacials, the largest shift occurring from 401 mu mol O-2 g(-1) in midstage 6 to 144 mu mol O-2 g(-1) at 5e, and is coherent with the oxygen isotope curve of Globigerinoides sacculifer in the same core at the Milankovitch frequencies of 100 and 41 kyr, Pronounced variations in the 19-23 kyr band suggest that the climate of the western equatorial Pacific is sensitive to precessional forcing, a response not apparent from other records obtained in this region.

Bender, ML, Battle M, Keeling RF.  1998.  The O2 balance of the atmosphere: A tool for studying the fate of fossil-fuel CO2. Annual Review of Energy and the Environment. 23:207-223.   10.1146/annurev.energy.23.1.207   AbstractWebsite

Carbon dioxide is a radiatively active gas whose atmospheric concentration increase is likely to affect Earth's climate. CO2 is added to the atmosphere by biomass burning and the combustion of fossil fuels. Some added CO2 remains in the atmosphere. However, substantial amounts are taken up by the oceans and land biosphere, attenuating the atmospheric increase. Atmospheric O-2 measurements provide one constraint for partitioning uptake rates between the ocean and the land biosphere. Here we review studies of atmospheric O-2 concentration variations and discuss their implications for CO2 uptake by the ocean and the land biosphere. We compare estimates of anthropogenic carbon fluxes from O-2 studies with estimates from other approaches and examine the contribution of natural ocean carbon fluxes to atmospheric O-2 variations.

1996
Keeling, RF, Piper SC, Heimann M.  1996.  Global and hemispheric CO2 sinks deduced from changes in atmospheric O2 concentration. Nature. 381:218-221.   10.1038/381218a0   AbstractWebsite

THE global budget for sources and sinks of anthropogenic CO2 has been found to be out of balance unless the oceanic sink is supplemented by an additional 'missing sink', plausibly associated with land biota(1,25). A similar budgeting problem has been found for the Northern Hemisphere alone(2,3), suggesting that northern land biota may be the sought-after sink, although this interpretation is not unique(2-5); to distinguish oceanic and land carbon uptake, the budgets rely variously, and controversially, on ocean models(2,6,7), (CO2)-C-13/(CO2)-C-12 data(2,4,5), sparse oceanic observations of p(CO2) (ref. 3) or C-13/C-12 ratios of dissolved inorganic carbon, (4,5,8) or single-latitude trends in atmospheric O-2 as detected from changes in O-2/N-2 ratio.(9,10). Here we present an extensive O-2/N-2 data set which shows simultaneous trends in O-2/N-2 in both northern and southern hemispheres and allows the O-2/N-2 gradient between the two hemispheres to be quantified. The data are consistent with a budget in which, for the 1991-94 period, the global oceans and the northern land biota each removed the equivalent of approximately 30% of fossil-fuel CO2 emissions, while the tropical land biota as a whole were not a strong source or sink.

1992
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.