2023 |
Faïn, X., Etheridge, D., Fourteau, K., Martinerie, P., Trudinger, C., Rhodes, R., et al. (2023). Southern Hemisphere Atmospheric History Of Carbon Monoxide Over The Late Holocene Reconstructed From Multiple Antarctic Ice Archives. Climate Of The Past, 191(111), 2287–2311.
Abstract: Carbon Monoxide (Co) Is A Naturally Occurring Atmospheric Trace Gas, A Regulated Pollutant, And One Of The Main Components Determining The Oxidative Capacity Of The Atmosphere. Evaluating Climate-Chemistry Models Under Different Conditions Than Today And Constraining Past Co Sources Requires A Reliable Record Of Atmospheric Co Mixing Ratios ([Co]) That Includes Data Since Preindustrial Times. Here, We Report The First Continuous Record Of Atmospheric [Co] For Southern Hemisphere (Sh) High Latitudes Over The Past 3 Millennia. Our Continuous Record Is A Composite Of Three High-Resolution Antarctic Ice Core Gas Records And Firn Air Measurements From Seven Antarctic Locations. The Ice Core Gas [Co] Records Were Measured By Continuous Flow Analysis (Cfa), Using An Optical Feedback Cavity-Enhanced Absorption Spectrometer (Of-Ceas), Achieving Excellent External Precision (2.8-8.8 Ppb; 2 Sigma ) And Consistently Low Blanks (Ranging From 4.1 +/- 1.2 To 7.4 +/- 1.4 Ppb), Thus Enabling Paleo-Atmospheric Interpretations. Six New Firn Air [Co] Antarctic Datasets Collected Between 1993 And 2016 Ce At The De08-2, Dssw19K, Dssw20K, South Pole, Aurora Basin North (Abn), And Lock-In Sites (And One Previously Published Firn Co Dataset At Berkner) Were Used To Reconstruct The Atmospheric History Of Co From Similar To 1897 Ce, Using Inverse Modeling That Incorporates The Influence Of Gas Transport In Firn. Excellent Consistency Was Observed Between The Youngest Ice Core Gas [Co] And The [Co] From The Base Of The Firn And Between The Recent Firn [Co] And Atmospheric [Co] Measurements At Mawson Station (Eastern Antarctica), Yielding A Consistent And Contiguous Record Of Co Across These Different Archives. Our Antarctic [Co] Record Is Relatively Stable From – 835 To 1500 Ce, With Mixing Ratios Within A 30-45 Ppb Range (2 Sigma ). There Is A Similar To 5 Ppb Decrease In [Co] To A Minimum At Around 1700 Ce During The Little Ice Age. Co Mixing Ratios Then Increase Over Time To Reach A Maximum Of Similar To 54 Ppb By Similar To 1985 Ce. Most Of The Industrial Period [Co] Growth Occurred Between About 1940 To 1985 Ce, After Which There Was An Overall [Co] Decrease, As Observed In Greenland Firn Air And Later At Atmospheric Monitoring Sites And Attributed Partly To Reduced Co Emissions From Combustion Sources. Our Antarctic Ice Core Gas Co Observations Differ From Previously Published Records In Two Key Aspects. First, Our Mixing Ratios Are Significantly Lower Than Reported Previously, Suggesting That Previous Studies Underestimated Blank Contributions. Second, Our New Co Record Does Not Show A Maximum In The Late 1800S. The Absence Of A [Co] Peak Around The Turn Of The Century Argues Against There Being A Peak In Southern Hemisphere Biomass Burning At This Time, Which Is In Agreement With (I) Other Paleofire Proxies Such As Ethane Or Acetylene And (Ii) Conclusions Reached By Paleofire Modeling. The Combined Ice Core And Firn Air [Co] History, Spanning – 835 To 1992 Ce, Extended To The Present By The Mawson Atmospheric Record, Provides A Useful Benchmark For Future Atmospheric Chemistry Modeling Studies.
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2020 |
Nehrbass-Ahles, C., Shin, J., Schmitt, J., Bereiter, B., Joos, F., Schilt, A., et al. (2020). Abrupt CO2 release to the atmosphere under glacial and early interglacial climate conditions. Science, 369(6506), 1000–+.
Abstract: Pulse-like carbon dioxide release to the atmosphere on centennial time scales has only been identified for the most recent glacial and deglacial periods and is thought to be absent during warmer climate conditions. Here, we present a high-resolution carbon dioxide record from 330,000 to 450,000 years before present, revealing pronounced carbon dioxide jumps (CDJ) under cold and warm climate conditions. CDJ come in two varieties that we attribute to invigoration or weakening of the Atlantic meridional overturning circulation (AMOC) and associated northward and southward shifts of the intertropical convergence zone, respectively. We find that CDJ are pervasive features of the carbon cycle that can occur during interglacial climate conditions if land ice masses are sufficiently extended to be able to disturb the AMOC by freshwater input.
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Shin, J., Nehrbass-Ahles, C., Grilli, R., Beeman, J., Parrenin, F., Teste, G., et al. (2020). Millennial-scale atmospheric CO2 variations during the Marine Isotope Stage 6 period (190-135 ka). Climate Of The Past, 16(6), 2203–2219.
Abstract: Using new and previously published CO2 data from the EPICA Dome C ice core (EDC), we reconstruct a new high-resolution record of atmospheric CO2 during Marine Isotope Stage (MIS) 6 (190 to 135 ka) the penultimate glacial period. Similar to the last glacial cycle, where high-resolution data already exists, our record shows that during longer North Atlantic (NA) stadials, millennial CO2 variations during MIS 6 are clearly coincident with the bipolar seesaw signal in the Antarctic temperature record. However, during one short stadial in the NA, atmospheric CO2 variation is small (similar to 5 ppm) and the relationship between temperature variations in EDC and atmospheric CO2 is unclear. The magnitude of CO2 increase during Carbon Dioxide Maxima (CDM) is closely related to the NA stadial duration in both MIS 6 and MIS 3 (60-27 ka). This observation implies that during the last two glacials the overall bipolar seesaw coupling of climate and atmospheric CO2 operated similarly. In addition, similar to the last glacial period, CDM during the earliest MIS 6 show different lags with respect to the corresponding abrupt CH4 rises, the latter reflecting rapid warming in the Northern Hemisphere (NH). During MIS 6i at around 181.5 +/- 0.3 ka, CDM 6i lags the abrupt warming in the NH by only 240 +/- 320 years. However, during CDM 6iv (171.1 +/- 0.2 ka) and CDM 6iii (175.4 +/- 0.4 ka) the lag is much longer: 1290 +/- 540 years on average. We speculate that the size of this lag may be related to a larger expansion of carbonrich, southern-sourced waters into the Northern Hemisphere in MIS 6, providing a larger carbon reservoir that requires more time to be depleted.
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2016 |
Touzeau, A., Landais, A., Stenni, B., Uemura, R., Fukui, K., Fujita, S., et al. (2016). Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters. Cryosphere, 10(2), 837–852.
Abstract: The isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second-order parameters (d-excess and O-17-excess) are related to delta O-18 and how they are controlled. d-excess increases in the interior of the continent (i.e., when delta O-18 decreases), due to the distillation process, whereas O-17-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the delta O-18 vs. temperature (T) relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation in terms of source climatic parameters is strongly complicated by local temperature effects in East Antarctica. Finally we check if the same relationships between delta O-18 and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to delta O-18 in most snow pits, the O-17-excess is no longer positively correlated to delta O-18 and even shows anti-correlation to delta O-18 at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes.
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2013 |
Landais, A., Dreyfus, G., Capron, E., Jouzel, J., Masson-Delmotte, V., Roche, D. M., et al. (2013). Two-phase change in CO2, Antarctic temperature and global climate during Termination II. Nature Geoscience, 6(12), 1062–1065.
Abstract: The end of the Last Glacial Maximum (Termination I), roughly 20 thousand years ago (ka), was marked by cooling in the Northern Hemisphere, a weakening of the Asian monsoon, a rise in atmospheric CO2 concentrations and warming over Antarctica. The sequence of events associated with the previous glacial-interglacial transition (Termination II), roughly 136 ka, is less well constrained. Here we present high-resolution records of atmospheric CO2 concentrations and isotopic composition of N2-an atmospheric temperature proxy-from air bubbles in the EPICA Dome C ice core that span Termination II. We find that atmospheric CO2 concentrations and Antarctic temperature started increasing in phase around 136 ka, but in a second phase of Termination II, from 130.5 to 129 ka, the rise in atmospheric CO2 concentrations lagged that of Antarctic temperature unequivocally. We suggest that during this second phase, the intensification of the low-latitude hydrological cycle resulted in the development of a CO2 sink, which counteracted the CO2 outgassing from the Southern Hemisphere oceans over this period.
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