Publications

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.

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.

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.