We present measurements of the stable carbon isotope ratio in air extracted from Antarctic ice core and firn samples. The same samples were previously used by Etheridge and co-workers to construct a high precision 1000-year record of atmospheric CO 2 concentration, featuring a close link between the ice and modern records and high-time resolution. Here, we start by confirming the trend in the Cape Grim in situ d13C record from 1982 to 1996, and extend it back to 1978 using the Cape Grim Air Archive. The firn air d13C agrees with the Cape Grim record, but only after correction for gravitational separation at depth, for diffusion effects associated with disequilibrium between the atmosphere and firm, and allowance for a latidudinal gradient in d13C between Cape Grim and the Antarctic coast. Complex calibration strategies are required to cope with several additional systematic influences on the ice core d13C record. Errors are assigned to each ice core value to reflect statistical and systematic biases (between ±0.025‰ and ±0.07‰); uncertainties (of up to ±0.05‰) between core-versus-core, ice-versus-firn and firn-versus-troposphere are described separately. An almost continuous atmospheric history of d13C over 1000 years results, exhibiting significant decadal-to-century scale variability unlike that from earlier proxy records. The decrease in d13C from 1860 to 1960 involves a series of steps confirming enhanced sensitivity of d13C to decadal timescale-forcing, compared to the CO 2 record. Synchronous with a ''Little Ice Age'' CO 2 decrease, an enhancement of d13C implies a terrestrial response to cooler temperatures. Between 1200 AD and 1600 AD, the atmospheric d13C appear stable.

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We present measurements of the stable carbon isotope ratio in air extracted from Antarctic ice core and firn samples. The same samples were previously used by Etheridge and co‐workers to construct a high precision 1000‐year record of atmospheric CO2 concentration, featuring a close link between the ice and modern records and high‐time resolution. Here, we start by confirming the trend in the Cape Grim in situ δ13C record from 1982 to 1996, and extend it back to 1978 using the Cape Grim Air Archive. The firn air δ13C agrees with the Cape Grim record, but only after correction for gravitational separation at depth, for diffusion effects associated with disequilibrium between the atmosphere and firm, and allowance for a latidudinal gradient in δ13C between Cape Grim and the Antarctic coast. Complex calibration strategies are required to cope with several additional systematic influences on the ice core δ13C record. Errors are assigned to each ice core value to reflect statistical and systematic biases (between ± 0.025‰ and ± 0.07‰); uncertainties (of up to ± 0.05‰) between core‐versus‐core, ice‐versus‐firn and firn‐versus‐troposphere are described separately. An almost continuous atmospheric history of δ13C over 1000 years results, exhibiting significant decadal‐to‐century scale variability unlike that from earlier proxy records. The decrease in δ13C from 1860 to 1960 involves a series of steps confirming enhanced sensitivity of δ13C to decadal timescale‐forcing, compared to the CO2 record. Synchronous with a ‘‘Little Ice Age’′ CO2 decrease, an enhancement of δ13C implies a terrestrial response to cooler temperatures. Between 1200 AD and 1600 AD, the atmospheric δ13C appear stable.

[1] High-precision, multispecies measurements of flask air samples since 1992 from CSIRO's global sampling network reveal strong correlation among interannual growth rate variations of CO 2 and its d 13 C, H 2 , CH 4 , and CO. We show that a major fraction of the variability is consistent with two emission pulses coinciding with large biomass burning events in 1994/1995 and 1997/1998 in tropical and boreal regions, and observations of unusually high levels of combustion products in the overlying troposphere at these times. Implied pulse strengths and multispecies emission ratios are not consistent with any other single process, but do not exclude possible contributions from covarying processes that are linked through climatic forcing. Comparison of CO 2 with its d 13 C indicates that most of the CO 2 variation is from terrestrial exchange, but does not distinguish forcing by biomass burning from imbalance in photosynthesis/respiration of terrestrial ecosystems. Partitioning of terrestrial CO 2 fluxes is constrained by H 2 , CH 4 , and CO, all of which are products of biomass burning but which have no direct link to net respiration of CO 2 . While CO is a strong indicator of biomass burning, its short lifetime prevents it from usefully constraining the magnitude of CO 2 emissions. If the H 2 and CH 4 variations were dominated by biomass burning, they would imply associated carbon emissions in excess of mean annual levels of other years, of 0.6-3.5 and 0. 8-3.7 Pg C for 19948-3.7 Pg C for /19958-3.7 Pg C for and 19978-3.7 Pg C for /1998. The large range in emission estimates mainly reflects uncertainty in H 2 /CO 2 and CH 4 /CO 2 emission ratios of fires in these years.

The stable isotope ratios of atmospheric CO(2) ((18)O/(16)O and (13)C/(12)C) have been monitored since 1977 to improve our understanding of the global carbon cycle, because biosphere-atmosphere exchange fluxes affect the different atomic masses in a measurable way. Interpreting the (18)O/(16)O variability has proved difficult, however, because oxygen isotopes in CO(2) are influenced by both the carbon cycle and the water cycle. Previous attention focused on the decreasing (18)O/(16)O ratio in the 1990s, observed by the global Cooperative Air Sampling Network of the US National Oceanic and Atmospheric Administration Earth System Research Laboratory. This decrease was attributed variously to a number of processes including an increase in Northern Hemisphere soil respiration; a global increase in C(4) crops at the expense of C(3) forests; and environmental conditions, such as atmospheric turbulence and solar radiation, that affect CO(2) exchange between leaves and the atmosphere. Here we present 30 years' worth of data on (18)O/(16)O in CO(2) from the Scripps Institution of Oceanography global flask network and show that the interannual variability is strongly related to the El Niño/Southern Oscillation. We suggest that the redistribution of moisture and rainfall in the tropics during an El Niño increases the (18)O/(16)O ratio of precipitation and plant water, and that this signal is then passed on to atmospheric CO(2) by biosphere-atmosphere gas exchange. We show how the decay time of the El Niño anomaly in this data set can be useful in constraining global gross primary production. Our analysis shows a rapid recovery from El Niño events, implying a shorter cycling time of CO(2) with respect to the terrestrial biosphere and oceans than previously estimated. Our analysis suggests that current estimates of global gross primary production, of 120 petagrams of carbon per year, may be too low, and that a best guess of 150-175 petagrams of carbon per year better reflects the observed rapid cycling of CO(2). Although still tentative, such a revision would present a new benchmark by which to evaluate global biospheric carbon cycling models.

[1] We present new measurements of ı 13 C of CO 2 extracted from a high-resolution ice core from Law Dome (East Antarctica), together with firn measurements performed at Law Dome and South Pole, covering the last 150 years. Our analysis is motivated by the need to better understand the role and feedback of the carbon (C) cycle in climate change, by advances in measurement methods, and by apparent anomalies when comparing ice core and firn air ı 13 C records from Law Dome and South Pole. We demonstrate improved consistency between Law Dome ice, South Pole firn, and the Cape Grim (Tasmania) atmospheric ı 13 C data, providing evidence that our new record reliably extends direct atmospheric measurements back in time. We also show a revised version of early ı 13 C measurements covering the last 1000 years, with a mean preindustrial level of -6.50 . Finally, we use a Kalman Filter Double Deconvolution to infer net natural CO 2 fluxes between atmosphere, ocean, and land, which cause small ı 13 C deviations from the predominant anthropogenically induced ı 13 C decrease. The main features found from the previous ı 13 C record are confirmed, including the ocean as the dominant cause for the 1940 A.D. CO 2 leveling. Our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric CO 2 concentration. Those causes are of potential significance for predicting future CO 2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through Coupled Climate Carbon Cycle Models.

[1] We present estimates of the surface sources and sinks of CO 2 for 1992-2005 deduced from atmospheric inversions. We use atmospheric CO 2 records from 67 sites and 10 d 13 CO 2 records. We use two atmospheric models to increase the robustness of the results. The results suggest that interannual variability is dominated by the tropical land. Statistically significant variability in the tropical Pacific supports recent ocean modeling studies in that region. The northern land also shows significant variability. In particular, there is a large positive anomaly in 2003 in north Asia, which we associate with anomalous biomass burning. Results using d 13 CO 2 and CO 2 are statistically consistent with those using only CO 2 , suggesting that it is valid to use both types of data together. An objective analysis of residuals suggests that our treatment of uncertainties in CO 2 is conservative, while those for d 13 CO 2 are optimistic, highlighting problems in our simple isotope model. Finally, d 13 CO 2 measurements offer a good constraint to nearby land regions, suggesting an ongoing value in these measurements for studies of interannual variability.

Abstract. The isotopic composition of carbon ( 14 C and δ 13 C) in atmospheric CO 2 and in oceanic and terrestrial carbon reservoirs is influenced by anthropogenic emissions and by natural carbon exchanges, which can respond to and drive changes in climate. Simulations of 14 C and 13 C in the ocean and terrestrial components of Earth system models (ESMs) present opportunities for model evaluation and for investigation of carbon cycling, including anthropogenic CO 2 emissions and uptake. The use of carbon isotopes in novel evaluation of the ESMs' component ocean and terrestrial biosphere models and in new analyses of historical changes may improve predictions of future changes in the carbon cycle and climate system. We compile existing data to produce records of 14 C and δ 13 C in atmospheric CO 2 for the historical period 1850-2015. The primary motivation for this compilation is to provide the atmospheric boundary condition for historical simulations in the Coupled Model Intercomparison Project 6 (CMIP6) for models simulating carbon isotopes in the ocean or terrestrial biosphere. The data may also be useful for other carbon cycle modelling activities.