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Kobashi, T, Severinghaus JP, Barnola JM, Kawamura K, Carter T, Nakaegawa T.  2010.  Persistent multi-decadal Greenland temperature fluctuation through the last millennium. Climatic Change. 100:733-756.   10.1007/s10584-009-9689-9   AbstractWebsite

Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N(2) and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of similar to 20 years and 40-100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.

Aciego, SM, Cuffey KM, Kavanaugh JL, Morse DL, Severinghaus JP.  2007.  Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica. Quaternary Research. 68:303-313.   10.1016/j.yqres.2007.07.013   AbstractWebsite

Ice exposed in ablation zones of ice sheets can be a valuable source of samples for paleoclimate studies and information about long-term ice dynamics. We report a 28-km long stable isotope sampling transect along a flowline on lower Taylor Glacier, Antarctica, and show that ice from the last glacial period is exposed here over tens of kilometers. Gas isotope analyses on a small number of samples confirm our age hypothesis. These chronostratigraphic data contain information about past ice dynamics and in particular should be sensitive to the longitudinal strain rate on the north flank of Taylor Dome, averaged over millennia. The imprint of climatic changes on ice dynamics may be discernible in these data. (c) 2007 University of Washington. All rights reserved.

Fain, X, Ferrari CP, Dommergue A, Albert MR, Battle M, Severinghaus J, Arnaud L, Barnola JM, Cairns W, Barbante C, Boutron C.  2009.  Polar firn air reveals large-scale impact of anthropogenic mercury emissions during the 1970s. Proceedings of the National Academy of Sciences of the United States of America. 106:16114-16119.   10.1073/pnas.0905117106   AbstractWebsite

Mercury (Hg) is an extremely toxic pollutant, and its biogeochemical cycle has been perturbed by anthropogenic emissions during recent centuries. In the atmosphere, gaseous elemental mercury (GEM; Hg degrees) is the predominant form of mercury (up to 95%). Here we report the evolution of atmospheric levels of GEM in mid- to high-northern latitudes inferred from the interstitial air of firn (perennial snowpack) at Summit, Greenland. GEM concentrations increased rapidly after World War II from approximate to 1.5 ng m(-3) reaching a maximum of approximate to 3 ng m(-3) around 1970 and decreased until stabilizing at approximate to 1.7 ng m(-3) around 1995. This reconstruction reproduces real-time measurements available from the Arctic since 1995 and exhibits the same general trend observed in Europe since 1990. Anthropogenic emissions caused a two-fold rise in boreal atmospheric GEM concentrations before the 1970s, which likely contributed to higher deposition of mercury in both industrialized and remotes areas. Once deposited, this toxin becomes available for methylation and, subsequently, the contamination of ecosystems. Implementation of air pollution regulations, however, enabled a large-scale decline in atmospheric mercury levels during the 1980s. The results shown here suggest that potential increases in emissions in the coming decades could have a similar large-scale impact on atmospheric Hg levels.

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.

Buizert, C, Adrian B, Ahn J, Albert M, Alley RB, Baggenstos D, Bauska TK, Bay RC, Bencivengo BB, Bentley CR, Brook EJ, Chellman NJ, Clow GD, Cole-Dai J, Conway H, Cravens E, Cuffey KM, Dunbar NW, Edwards JS, Fegyveresi JM, Ferris DG, Fitzpatrick JJ, Fudge TJ, Gibson CJ, Gkinis V, Goetz JJ, Gregory S, Hargreaves GM, Iverson N, Johnson JA, Jones TR, Kalk ML, Kippenhan MJ, Koffman BG, Kreutz K, Kuhl TW, Lebar DA, Lee JE, Marcott SA, Markle BR, Maselli OJ, McConnell JR, McGwire KC, Mitchell LE, Mortensen NB, Neff PD, Nishiizumi K, Nunn RM, Orsi AJ, Pasteris DR, Pedro JB, Pettit EC, Price PB, Priscu JC, Rhodes RH, Rosen JL, Schauer AJ, Schoenemann SW, Sendelbach PJ, Severinghaus JP, Shturmakov AJ, Sigl M, Slawny KR, Souney JM, Sowers TA, Spencer MK, Steig EJ, Taylor KC, Twickler MS, Vaughn BH, Voigt DE, Waddington ED, Welten KC, Wendricks AW, White JWC, Winstrup M, Wong GJ, Woodruff TE, Members WDP.  2015.  Precise interpolar phasing of abrupt climate change during the last ice age. Nature. 520:661-U169.   10.1038/nature14401   AbstractWebsite

The last glacial period exhibited abrupt Dansgaard-Oeschger climatic oscillations, evidence of which is preserved in a variety of Northern Hemisphere palaeodimate archives'. Ice cores show that Antarctica cooled during the warm phases of the Greenland Dansgaard-Oeschger cycle and vice versa''', suggesting an interhemispheric redistribution of heat through a mechanism called the bipolar seesaw(4-6). Variations in the Atlantic meridional overturning circulation (AMOC) strength are thought to have been important, but much uncertainty remains regarding the dynamics and trigger of these abrupt events'. Key information is contained in the relative phasing of hemispheric climate variations, yet the large, poorly constrained difference between gas age and ice age and the relatively low resolution of methane records from Antarctic ice cores have so far precluded methane-based synchronization at the required sub-centennial precision''''". Here we use a recently drilled high-accumulation Antarctic ice core to show that, on average, abrupt Greenland warming leads the corresponding Antarctic cooling onset by 218 +/- 92 years (2 sigma a) for DansgaardOeschger events, including the Bolling event; Greenland cooling leads the corresponding onset of Antarctic warming by 208 +/- 96 years. Our results demonstrate a north-to-south directionality of the abrupt climatic signal, which is propagated to the Southern Hemisphere high latitudes by oceanic rather than atmospheric processes. The similar interpolar phasing of warming and cooling transitions suggests that the transfer time of the climatic signal is independent of the AMOC background state. Our findings confirm a central role for ocean circulation in the bipolar seesaw and provide clear criteria for assessing hypotheses and model simulations of Dansgaard-Oeschger dynamics.

Kobashi, T, Severinghaus JP, Brook EJ, Barnola JM, Grachev AM.  2007.  Precise timing and characterization of abrupt climate change 8200 years ago from air trapped in polar ice. Quaternary Science Reviews. 26:1212-1222.   10.1016/j.quascirev.2007.01.009   AbstractWebsite

How fast and how much climate can change has significant implications for concerns about future climate changes and their potential impacts on society. An abrupt climate change 8200 years ago (8.2 ka event) provides a test case to understand possible future climatic variability. Here, methane concentration (taken as an indicator for terrestrial hydrology) and nitrogen isotopes (Greenland temperature) in trapped air in a Greenland ice core (GISP2) are employed to scrutinize the evolution of the 8.2 ka event. The synchronous change in methane and nitrogen implies that the 8.2 ka event was a synchronous event (within +/- 4 years) at a hemispheric scale, as indicated by recent climate model results [Legrande, A. N., Schmidt, G. A., Shindell, D. T., Field, C. V., Miller, R. L., Koch, D. M., Faluvegi, G., Hoffmann, G., 2006. Consistent simulations of multiple proxy responses to an abrupt climate change event. Proceedings of the National Academy of Sciences 103, 837-842]. The event began with a large-scale general cooling and drying around similar to 8175 +/- 30 years BP (Before Present, where Present is 1950 AD). Greenland temperature cooled by 3.3 +/- 1.1 degrees C (decadal average) in less than similar to 20 years, and atmospheric methane concentration decreased by similar to 80 +/- 25 ppb over similar to 40 years, corresponding to a 15 +/- 5% emission reduction. Hemispheric scale cooling and drying.. inferred from many paleoclimate proxies, likely contributed to this emission reduction. In central Greenland, the coldest period lasted for similar to 60 years, interrupted by a milder interval of a few decades, and temperature subsequently warmed in several steps over similar to 70 years. The total duration of the 8.2 ka event was roughly 150 years. (c) 2007 Elsevier Ltd. All rights reserved.

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Buizert, C, Baggenstos D, Jiang W, Purtschert R, Petrenko VV, Lu ZT, Muller P, Kuhl T, Lee J, Severinghaus JP, Brook EJ.  2014.  Radiometric Kr-81 dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica. Proceedings of the National Academy of Sciences of the United States of America. 111:6876-6881.   10.1073/pnas.1320329111   AbstractWebsite

We present successful Kr-81-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four similar to 350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The Kr-81 radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 +/- 2.5 ka. Our experimental methods and sampling strategy are validated by (i) Kr-85 and Ar-39 analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the Kr-81 ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA Kr-81 analysis requires a 40-80-kg ice sample; as sample requirements continue to decrease, Kr-81 dating of ice cores is a future possibility.

Goodge, JW, Severinghaus JP.  2016.  Rapid Access Ice Drill: a new tool for exploration of the deep Antarctic ice sheets and subglacial geology. Journal of Glaciology. 62:1049-1064.   10.1017/jog.2016.97   AbstractWebsite

A new Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to create borehole observatories and take cores in deep ice, the glacial bed and bedrock below. RAID is a mobile drilling system to make multiple long, narrow boreholes in a single field season in Antarctica. RAID is based on a mineral exploration-type rotary rock-coring system using threaded drill pipe to cut through ice using reverse circulation of a non-freezing fluid for pressure-compensation, maintenance of temperature and removal of ice cuttings. Near the bottom of the ice sheet, a wireline latching assembly will enable rapid coring of ice, the glacial bed and bedrock below. Once complete, boreholes will be kept open with fluid, capped and available for future down-hole measurement of temperature gradient, heat flow, ice chronology and ice deformation. RAID is designed to penetrate up to 3300 m of ice and take cores in <200 hours, allowing completion of a borehole and coring in similar to 10 d at each site. Together, the rapid drilling capability and mobility of the system, along with ice-penetrating imaging methods, will provide a unique 3-D picture of interior and subglacial features of the Antarctic ice sheets.

Orsi, AJ, Kawamura K, Masson-Delmotte V, Fettweis X, Box JE, Dahl-Jensen D, Clow GD, Landais A, Severinghaus JP.  2017.  The recent warming trend in North Greenland. Geophysical Research Letters. 44:6235-6243.   10.1002/2016gl072212   AbstractWebsite

The Arctic is among the fastest warming regions on Earth, but it is also one with limited spatial coverage of multidecadal instrumental surface air temperature measurements. Consequently, atmospheric reanalyses are relatively unconstrained in this region, resulting in a large spread of estimated 30 year recent warming trends, which limits their use to investigate the mechanisms responsible for this trend. Here we present a surface temperature reconstruction over 1982-2011 at NEEM (North Greenland Eemian Ice Drilling Project, 51 degrees W, 77 degrees N), in North Greenland, based on the inversion of borehole temperature and inert gas isotope data. We find that NEEM has warmed by 2.7 +/- 0.33 degrees C over the past 30 years, from the long-term 1900-1970 average of -28.55 +/- 0.29 degrees C. The warming trend is principally caused by an increase in downward longwave heat flux. Atmospheric reanalyses underestimate this trend by 17%, underlining the need for more in situ observations to validate reanalyses.

Butler, JH, Battle M, Bender ML, Montzka SA, Clarke AD, Saltzman ES, Sucher CM, Severinghaus JP, Elkins JW.  1999.  A record of atmospheric halocarbons during the twentieth century from polar firn air. Nature. 399:749-755.   10.1038/21586   AbstractWebsite

Measurements of trace gases in air trapped in polar firn (unconsolidated snow) demonstrate that natural sources of chlorofluorocarbons, halons, persistent chlorocarbon solvents and sulphur hexafluoride to the atmosphere are minimal or non-existent. Atmospheric concentrations of these gases, reconstructed back to the late nineteenth century, are consistent with atmospheric histories derived from anthropogenic emission rates and known atmospheric lifetimes. The measurements confirm the predominance of human activity in the atmospheric budget of organic chlorine, and allow the estimation of atmospheric histories of halogenated gases of combined anthropogenic and natural origin. The pre-twentieth-century burden of methyl chloride was close to that at present, while the burden of methyl bromide was probably over half of today's value.

Lee, JY, Marti K, Severinghaus JP, Kawamura K, Yoo HS, Lee JB, Kim JS.  2006.  A redetermination of the isotopic abundances of atmospheric Ar. Geochimica Et Cosmochimica Acta. 70:4507-4512.   10.1016/j.gca.2006.06.1563   AbstractWebsite

Atmospheric argon measured on a dynamically operated mass spectrometer with an ion source magnet, indicated systematically larger Ar-40/Ar-16 ratios compared to the generally accepted value of Nier [Nier A.O., 1950. A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon, and potassium. Phys. Rev. 77, 789-793], 295.5 +/- 0.5, which has served as the standard for all isotopic measurements in geochemistry and cosmochemistry. Gravimetrically prepared mixtures of highly enriched Ar-36 and Ar-40 were utilized to redetermine the isotopic abundances of atmospheric Ar, using a dynamically operated isotope ratio mass spectrometer with minor modifications and special gas handling techniques to avoid fractionation. A new ratio Ar-40/Ar-36 = 298.56 +/- 0.31 was obtained with a precision of 0.1%, approximately 1% higher than the previously accepted value. Combined with the Ar-38/Ar-36 (0.1885 +/- 0.0003) measured with a VG5400 noble gas mass spectrometer in static operation, the percent abundances of Ar-36, Ar-38, and Ar-40 were determined to be 0.3336 +/- 0.0004, 0.0629 +/- 0.0001, and 99.6035 +/- 0.0004, respectively. We calculate an atomic mass of Ar of 39.9478 +/- 0.0002. Accurate Ar isotopic abundances are relevant in numerous applications, as the calibration of the mass spectrometer discrimination. (c) 2006 Elsevier Inc. All rights reserved.

Grachev, AM, Brook EJ, Severinghaus JP, Pisias NG.  2009.  Relative timing and variability of atmospheric methane and GISP2 oxygen isotopes between 68 and 86 ka. Global Biogeochemical Cycles. 23   10.1029/2008gb003330   AbstractWebsite

The global biogeochemical cycle of methane has received wide attention because of methane's role as a greenhouse gas. Measurements of methane in air trapped in Greenland ice cores provide a high-resolution record of methane levels in the atmosphere over the past similar to 100 ka, providing clues about what controls the methane cycle on geologic timescales. Remarkable similarity between local temperature recorded in Greenland ice cores and changes in global methane concentrations has been noted in previous studies, with the inference that the local temperature variations have global significance, but the resolution of sampling and measurement precision limited fine-scale comparison of these variables. In this work a higher-precision (similar to 2 ppb) methane data set was obtained from the Greenland Ice Sheet Project 2 (GISP2) ice core for the time interval between 86 and 68 ka, encompassing three large abrupt warming events early in the last glacial period: Dansgaard-Oeschger (D-O) events 19, 20, and 21. The new data set consists of duplicate measurements at 158 depths, with average time resolution of 120 years. Such detailed measurements over D-O 21, the longest in Greenland records, have not yet been reported for other ice cores. The new data set documents short-term variability (similar to 20 ppb typical amplitude), which is remarkably persistent, and in many cases similar features are observed in the most detailed published delta(18)O(ice) record. High-precision GISP2 delta(15)N data show that changes in Greenland temperature are synchronous with the methane variations at the onset of D-O events 19, 20, and 21, supporting previous results from the Greenland Ice Core Project ice core for D-O 19 and 20. Cross-spectral analysis quantifies the extremely close similarity between the new methane record and the delta(18)O(ice) record. Because methane sources are widely distributed over the globe, this work further validates delta(18)O(ice) at Greenland summit as a geographically broad climate indicator on millennial to multicentennial timescales.

Grachev, AM, Severinghaus JP.  2005.  A revised +10 +/- 4 degrees C magnitude of the abrupt change in Greenland temperature at the Younger Dryas termination using published GISP2 gas isotope data and air thermal diffusion constants. Quaternary Science Reviews. 24:513-519.   10.1016/j.quascirev.2004.10.016   AbstractWebsite

We revisit the portion of (Nature 391 (1998) 141) devoted to the abrupt temperature increase reconstruction at the Younger Dryas/Preboreal transition. The original estimate of + 5 to + 10 degrees C abrupt warming is revised to + 10 +/- 4 degrees C. The gas isotope data from the original work were employed, combined with recently measured precise air thermal diffusion constants (Geochim. Cosmochim. Acta 67 (2003a) 345; J. Phys. Chem. 23A (2003b) 4636). The new constants allow a robust interpretation of the gas isotope signal in terms of temperature change. This was not possible at the time of the original work, when no air constants were available. Three quasi-independent approaches employed in this work all give the same result of a + 10 degrees C warming in several decades or less. The new result provides a firm target for climate models that attempt to predict future climates. (c) 2005 Elsevier Ltd. All rights reserved.

Bertler, NAN, Conway H, Dahl-Jensen D, Emanuelsson DB, Winstrup M, Vallelonga PT, Lee JE, Brook EJ, Severinghaus JP, Fudge TJ, Keller ED, Baisden WT, Hindmarsh RCA, Neff PD, Blunier T, Edwards R, Mayewski PA, Kipfstuhl S, Buizert C, Canessa S, Dadic R, Kjaer HA, Kurbatov A, Zhang DQ, Waddington ED, Baccolo G, Beers T, Brightley HJ, Carter L, Clemens-Sewall D, Ciobanu VG, Delmonte B, Eling L, Ellis A, Ganesh S, Golledge NR, Haines S, Handley M, Hawley RL, Hogan CM, Johnson KM, Korotkikh E, Lowry DP, Mandeno D, McKay RM, Menking JA, Naish TR, Noerling C, Ollive A, Orsi A, Proemse BC, Pyne AR, Pyne RL, Renwick J, Scherer RP, Semper S, Simonsen M, Sneed SB, Steig EJ, Tuohy A, Venugopal AU, Valero-Delgado F, Venkatesh J, Wang FT, Wang SM, Winski DA, Winton VHL, Whiteford A, Xiao CD, Yang J, Zhang X.  2018.  The Ross Sea Dipole - temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years. Climate of the Past. 14:193-214.   10.5194/cp-14-193-2018   AbstractWebsite

High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually dated ice core record from the eastern Ross Sea, named the Roosevelt Island Climate Evolution (RICE) ice core. Comparison of this record with climate reanalysis data for the 1979-2012 interval shows that RICE reliably captures temperature and snow precipitation variability in the region. Trends over the past 2700 years in RICE are shown to be distinct from those in West Antarctica and the western Ross Sea captured by other ice cores. For most of this interval, the eastern Ross Sea was warming (or showing isotopic enrichment for other reasons), with increased snow accumulation and perhaps decreased sea ice concentration. However, West Antarctica cooled and the western Ross Sea showed no significant isotope temperature trend. This pattern here is referred to as the Ross Sea Dipole. Notably, during the Little Ice Age, West Antarctica and the western Ross Sea experienced colder than average temperatures, while the eastern Ross Sea underwent a period of warming or increased isotopic enrichment. From the 17th century onwards, this dipole relationship changed. All three regions show current warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea but increasing in the western Ross Sea. We interpret this pattern as reflecting an increase in sea ice in the eastern Ross Sea with perhaps the establishment of a modern Roosevelt Island polynya as a local moisture source for RICE.

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Fricker, HA, Powell R, Priscu J, Tulaczyk S, Anandakrishnan S, Christner B, Fisher AT, Holland D, Horgan H, Jacobel R, Mikucki J, Mitchell A, Scherer R, Severinghaus J.  2011.  Siple Coast subglacial aquatic environments; the Whillans ice stream subglacial access research drilling project. Geophysical Monograph. 192:199-219.   10.1029/2010gm000932   AbstractWebsite

The Whillians Ice Stream Subglacial Access Research Drilling (WISSARD) project is a 6-year (2009-2015) integrative study of ice sheet stability and subglacial geobiology in West Antarctica, funded by the Antarctic Integrated System Science Program of National Science Foundation's Office of Polar Programs, Antarctic Division. The overarching scientific objective of WISSARD is to assess the role of water beneath a West Antarctic Ice Stream in interlinked glaciological, geological, microbiological, geochemical, hydrological, and oceanographic systems. The WISSARD's important science questions relate to (1) the role that subglacial and ice shelf cavity waters and wet sediments play in ice stream dynamics and mass balance, with an eye on the possible future of the West Antarctic Ice Sheet and (2) the microbial metabolic and phylogenetic diversity in these subglacial environments. The study area is the downstream part of the Whillans Ice Stream on the Siple Coast, specifically Subglacial Lake Whillans and the part of the grounding zone across which it drains. In this chapter, we provide background on the motivation for the WISSARD project, detail the key scientific goals, and describe the new measurement tools and strategies under development that will provide the framework for conducting an unprecedented range of scientific observations.

Severinghaus, JP.  2009.  Southern see-saw seen. Nature. 457:1093-1094.   10.1038/4571093a   AbstractWebsite

The bipolar see-saw hypothesis provides an explanation for why temperature shifts in the two hemispheres were out of phase at certain times. The hypothesis has now passed a test of one of its predictions.

Seltzer, AM, Severinghaus JP, Andraski BJ, Stonestrom DA.  2017.  Steady state fractionation of heavy noble gas isotopes in a deep unsaturated zone. Water Resources Research. 53:2716-2732.   10.1002/2016WR019655   AbstractWebsite

To explore steady state fractionation processes in the unsaturated zone (UZ), we measured argon, krypton, and xenon isotope ratios throughout a ∼110 m deep UZ at the United States Geological Survey (USGS) Amargosa Desert Research Site (ADRS) in Nevada, USA. Prior work has suggested that gravitational settling should create a nearly linear increase in heavy-to-light isotope ratios toward the bottom of stagnant air columns in porous media. Our high-precision measurements revealed a binary mixture between (1) expected steady state isotopic compositions and (2) unfractionated atmospheric air. We hypothesize that the presence of an unsealed pipe connecting the surface to the water table allowed for direct inflow of surface air in response to extensive UZ gas sampling prior to our first (2015) measurements. Observed isotopic resettling in deep UZ samples collected a year later, after sealing the pipe, supports this interpretation. Data and modeling each suggest that the strong influence of gravitational settling and weaker influences of thermal diffusion and fluxes of CO2 and water vapor accurately describe steady state isotopic fractionation of argon, krypton, and xenon within the UZ. The data confirm that heavy noble gas isotopes are sensitive indicators of UZ depth. Based on this finding, we outline a potential inverse approach to quantify past water table depths from noble gas isotope measurements in paleogroundwater, after accounting for fractionation during dissolution of UZ air and bubbles.

McConnell, JR, Burke A, Dunbar NW, Kohler P, Thomas JL, Arienzo MM, Chellman NJ, Maselli OJ, Sigl M, Adkins JF, Baggenstos D, Burkhart JF, Brook EJ, Buizert C, Cole-Dai J, Fudge TJ, Knorr G, Graf HF, Grieman MM, Iverson N, McGwire KC, Mulvaney R, Paris G, Rhodes RH, Saltzman ES, Severinghaus JP, Steffensen JP, Taylor KC, Winckler G.  2017.  Synchronous volcanic eruptions and abrupt climate change similar to 17.7 ka plausibly linked by stratospheric ozone depletion. Proceedings of the National Academy of Sciences of the United States of America. 114:10035-10040.   10.1073/pnas.1705595114   AbstractWebsite

Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until similar to 17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, similar to 192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics-similar to those associated with modern stratospheric ozone depletion over Antarctica-plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation similar to 17.7 ka.

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Atwater, T, Severinghaus J.  1989.  Tectonic maps of the northeast Pacific. The Eastern Pacific Ocean and Hawaii. ( Winterer EL, Hussong DM, Decker RW, Eds.).:15-20., Boulder, Colo.: Geological Society of America Abstract
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Severinghaus, JP, Grachev A, Battle M.  2001.  Thermal fractionation of air in polar firn by seasonal temperature gradients. Geochemistry Geophysics Geosystems. 2   10.1029/2000GC000146   AbstractWebsite

Air withdrawn from the top 5-15 m of the polar snowpack (fim) shows anomalous enrichment of heavy gases during summer, including inert gases. Following earlier work, we ascribe this to thermal diffusion, the tendency of a gas mixture to separate in a temperature gradient, with heavier molecules migrating toward colder regions. Summer warmth creates a temperature gradient in the top few meters of the firn due to the thermal inertia of the underlying firn and causes gas fractionation by thermal diffusion. Here we explore and quantify this process further in order to (1) correct for bias caused by thermal diffusion in firn air and ice core air isotope records, (2) help calibrate a new technique for measuring temperature change in ice core gas records based on thermal diffusion [Severinghaus et al., 1998], and (3) address whether air in polar snow convects during winter and, if so, whether it creates a rectification of seasonality that could bias the ice core record. We sampled air at 2-m-depth intervals from the top 15 m of the firn at two Antarctic sites, Siple Dome and South Pole, including a winter sampling at the pole. We analyzed (15)N/(14)N, (40)Ar/(36)Ar, (40)Ar/(38)Ar, (18)O/(16)O of O(2), O(2)/N(2), (84)Kr/(36)Ar, and (132)Xe/(36)Ar. The results show the expected pattern of fractionation and match a gas diffusion model based on first principles to within 30%. Although absolute values of thermal diffusion sensitivities cannot be determined from the data with precision, relative values of different gas pairs may. At Siple Dome, delta (40)Ar/4 is 66 +/- 2% as sensitive to thermal diffusion as delta (15)N, in agreement with laboratory calibration; delta (18)O/2 is 83 +/- 3%, and delta (84)Kr/48 is 33 +/- 3% as sensitive as delta (15)N. The corresponding figures for summer South Pole are 64 +/- 2%, 81 +/- 3%, and 34 +/- 3%. Accounting for atmospheric change, the figure for deltaO(2)/N(2)/4 is 90 +/- 3% at Siple Dome. Winter South Pole shows a strong depletion of heavy gases as expected. However, the data do not fit the model well in the deeper part of the profile and yield a systematic drift with depth in relative thermal diffusion sensitivities (except for Kr, constant at 34 +/- 4%), suggesting the action of some other process that is not currently understood. No evidence for wintertime convection or a rectifier effect is seen.

Severinghaus, JP, Sowers T, Brook EJ, Alley RB, Bender ML.  1998.  Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice. Nature. 391:141-146.   10.1038/34346   AbstractWebsite

Rapid temperature change fractionates gas Isotopes in unconsolidated snow, producing a signal that is preserved in trapped air bubbles as the snow forms ice, The fractionation of nitrogen and argon isotopes at the end of the Younger Dryas cold interval, recorded in Greenland ice, demonstrates that warming at this time was abrupt. This warming coincides with the onset of a prominent rise in atmospheric methane concentration, indicating that the climate change was synchronous (within a few decades) over a region of at least hemispheric extent, and providing constraints on previously proposed mechanisms of climate change at this time, The depth of the nitrogen-isotope signal relative to the depth of the climate change recorded in the Ice matrix indicates that, during the Younger Dryas, the summit of Greenland was 15 +/- 3 degrees C colder than today.

Caillon, N, Severinghaus JP, Jouzel J, Barnola JM, Kang JC, Lipenkov VY.  2003.  Timing of atmospheric CO2 and Antarctic temperature changes across termination III. Science. 299:1728-1731.   10.1126/science.1078758   AbstractWebsite

The analysis of air bubbles from ice cores has yielded a precise record of atmospheric greenhouse gas concentrations, but the timing of changes in these gases with respect to temperature is not accurately known because of uncertainty in the gas age-ice age difference. We have measured the isotopic composition of argon in air bubbles in the Vostok core during Termination III (similar to240,000 years before the present). This record most likely reflects the temperature and accumulation change, although the mechanism remains unclear. The sequence of events during Termination III suggests that the CO2 increase tagged Antarctic deglacial warming by 800 +/- 200 years and preceded the Northern Hemisphere deglaciation.

Brook, EJ, White JWC, Schilla ASM, Bender ML, Barnett B, Severinghaus JP, Taylor KC, Alley RB, Steig EJ.  2005.  Timing of millennial-scale climate change at Siple Dome, West Antarctica, during the last glacial period. Quaternary Science Reviews. 24:1333-1343.   10.1016/j.quascirev.2005.02.002   AbstractWebsite

Using atmospheric methane and the isotopic composition of O-2 as correlation tools, we place the 6D record of ice from the Siple Dome (West Antarctica) ice core on a precise common chronology with the GISP2 (Greenland) ice core for the period from 9 to 57 ka. The onset of major millennial warming events in Siple Dome preceded major abrupt warmings in Greenland, and the pattern of millennial change at Siple Dome was broadly similar, though not identical, to that previously observed for the Byrd ice core (also in West Antarctica). The addition of Siple Dome to the database of well-dated Antarctic paleoclimate records supports the case for a coherent regional pattern of millennial-scale climate change in Antarctica during much of the last ice age and glacial-interglacial transition.

Hamme, RC, Severinghaus JP.  2007.  Trace gas disequilibria during deep-water formation. Deep-Sea Research Part I-Oceanographic Research Papers. 54:939-950.   10.1016/j.dsr.2007.03.008   AbstractWebsite

We present high-precision measurements by a new isotope dilution technique of a suite of inert gases in the North Pacific. Remarkably smooth gradients in Ar, Kr and Xe from near equilibrium in intermediate waters to several percent undersaturated in deep waters were observed. The general pattern in the deepest waters was that Ar, Kr and Xe were undersaturated (Ar least and Xe most), while N-2 was close to equilibrium, and Ne was supersaturated. We propose that this pattern was produced by the interaction between the different physical properties of the gases (solubility and the temperature dependence of solubility) with the rapid cooling and high wind speeds that characterize deep-water formation regions. In a simple model of deep-water formation by convection, the saturations of the more temperature-sensitive gases were quickly driven down by rapid cooling and could not reequilibrate with the atmosphere before the end of the winter. In contrast, the gas exchange rate of the more bubble-sensitive gases (Ne and N-2) was able to meet or exceed the drawdown by cooling. Our simple convection model demonstrates that the heavier noble gases (Ar, Kr and Xe) are sensitive on seasonal timescales to the competing effects of cooling and air-sea gas exchange that are also important to setting the concentration Of CO2 in newly formed waters. (c) 2007 Elsevier Ltd. All rights reserved.

Severinghaus, JP, Broecker WS, Peng TH, Bonani G.  1996.  Transect along 24 degrees N latitude of C-14 in dissolved inorganic carbon in the subtropical North Atlantic Ocean. Radiocarbon. 38:407-414. AbstractWebsite

The distribution of bomb-produced C-14 in the ocean provides a powerful constraint for circulation models of upper ocean mixing. We report C-14 measurements from an east-west section of the main thermocline at 24 degrees N latitude in the subtropical North Atlantic Ocean in summer 1992, and one profile from the Gulf of Mexico in 1993. Observed gradients reflect the transient invasion of bomb C-14 into the thermocline via mixing along isopycnals from the poleward outcrop, with progressively more sluggish mixing at greater depths. A slight deepening of the profile is observed over the 20-yr period since the GEOSECS survey at one location where the comparison is possible.