References

CPD

Climate of the Past Discussions

CPD

1814-9359

Copernicus GmbH

Göttingen, Germany

10.5194/cpd-8-1089-2012

On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

Parrenin

¹ ² Barker

³ Blunier

⁴ Chappellaz

² Jouzel

⁵ Landais

⁵ Masson-Delmotte

⁵ Schwander

⁶ Veres

² ⁷

Laboratoire Chrono-Environnement, Besançon, France

UJF Grenoble 1, UMR5183, CNRS – Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), Grenoble F38041, France

School of Earth and Ocean Sciences, Cardiff University, UK

Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark

Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France

Physics Institute, University of Bern, Bern, Switzerland

Institute of Speleology, Romanian Academy, Cluj-Napoca, Romania

03 04 2012

8 2 1089 1131

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This article is available from http://www.clim-past-discuss.net/8/1089/2012/cpd-8-1089-2012.html

The full text article is available as a PDF file from http://www.clim-past-discuss.net/8/1089/2012/cpd-8-1089-2012.pdf

We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. Observations allow direct and indirect estimate of Δdepth. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The bipolar seesaw antiphase relationship is generally supported by the ice-gas cross synchronisation between EDC and the GRIP, EDML and TALDICE ice cores, which provide support for method 4. Applying the bipolar seesaw hypothesis to the deeper section of the EDC core confirms that the ice flow is complex and can help improving our reconstruction of the thinning function and thus of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggested that it is due to an overestimation of the glacial Close Off Depth by the firn densification model. In contrast we find that the glaciological models probably underestimate the Δdepth during termination II. Finally, we show that method 2 based on 15N data produces for the last deglaciation a Δdepth estimate which is in good agreement with methods 3 and 4.

References 1

Arnaud, L., Barnola, J.-M., and Duval, P.: Physical modeling of the densification of snow/firn and ice in the upper part of polar ice sheets, in: Physics of Ice Core Records, edited by: Hondoh, T., Hokkaido University Press, Sapporo, Japan, 285–305, 2000.

Barker, S., Knorr, G., Edwards, R. L., Parrenin, F., Putnam, A. E., Skinner, L. C., Wolff, E., and Ziegler, M.: 800,000 Years of Abrupt Climate Variability, Science, 334, 347–351, 2011.

Bender, M. L., Floch, G., Chappellaz, J., Suwa, M., Barnola, J.-M., Blunier, T., Dreyfus, G., Jouzel, J., and Parrenin, F.: Gas age-ice age differences and the chronology of the Vostok ice core, 0–100 ka, J. Geophys. Res., 111, D21115, http://dx.doi.org/10.1029/2005JD006488doi:10.1029/2005JD006488, 2006.

Blunier, T. and Brook, E. J.: Timing of millennial-scale climate change in Antarctica and Greenland during the last glacial period, Science, 291, 109–112, 2001.

Blunier, T., Chappellaz, J., Schwander, J., Dällenbach, A., Stauffer, B., Stocker, T., Raynaud, D., Jouzel, J., Clausen, H., Hammer, C., and Johnsen, S.: Asynchrony of Antarctic and Greenland climate change during the last glacial period, Nature, 394, 739–743, 1998.

Blunier, T., Schwander, J., Chappellaz, J., Parrenin, F., and Barnola, J.-M.: What was the surface temperature in central Antarctica during the last glacial maximum?, Earth Planet. Sci. Lett., 218, 379–388, 2004.

Buiron, D., Chappellaz, J., Stenni, B., Frezzotti, M., Baumgartner, M., Capron, E., Landais, A., Lemieux-Dudon, B., Masson-Delmotte, V., Montagnat, M., Parrenin, F., and Schilt, A.: TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica, Clim. Past, 7, 1–16, http://dx.doi.org/10.5194/cp-7-1-2011doi:10.5194/cp-7-1-2011, 2011.

Buizert, C., Martinerie, P., Petrenko, V. V., Severinghaus, J. P., Trudinger, C. M., Witrant, E., Rosen, J. L., Orsi, A. J., Rubino, M., Etheridge, D. M., Steele, L. P., Hogan, C., Laube, J. C., Sturges, W. T., Levchenko, V. A., Smith, A. M., Levin, I., Conway, T. J., Dlugokencky, E. J., Lang, P. M., Kawamura, K., Jenk, T. M., White, J. W. C., Sowers, T., Schwander, J., and Blunier, T.: Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland, Atmos. Chem. Phys. Discuss., 11, 15975–16021, http://dx.doi.org/10.5194/acpd-11-15975-2011doi:10.5194/acpd-11-15975-2011, 2011.

Caillon, N., Severinghaus, J. P., Jouzel, J., Barnola, J.-M., Kang, J., and Lipenkov, V. Y.: Timing of Atmospheric CO2 and Antarctic Temperature Changes Across Termination III, Science, 299, 1728–1731, 2003.

Capron, E., Landais, A., Chappellaz, J., Schilt, A., Buiron, D., Dahl-Jensen, D., Johnsen, S. J., Jouzel, J., Lemieux-Dudon, B., Loulergue, L., Leuenberger, M., Masson-Delmotte, V., Meyer, H., Oerter, H., and Stenni, B.: Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period, Clim. Past, 6, 345–365, http://dx.doi.org/10.5194/cp-6-345-2010doi:10.5194/cp-6-345-2010, 2010.

Colbeck, S.: Air movement in snow due to windpumping, J. Glaciol., 35, 209–213, 1989.

Colbeck, S.: Model of wind pumping for layered snow, J. Glaciol., 43, 60–65, 1997.

Courville, Z. R., Albert, M. R., Fahnestock, M. A., Cathles, L. M., I., and Shuman, C. A.: Impacts of an accumulation hiatus on the physical properties of firn at a low-accumulation polar site, J. Geophys. Res., 112, F02030, http://dx.doi.org/10.1029/2005JF000429doi:10.1029/2005JF000429 2007.

Craig, H., Horibe, Y., and Sowers, T.: Gravitational Separation of Gases and Isotopes in Polar Ice Caps, Science, 242, 1675–1678, 1988.

Denton, G. H., Bockheim, J. G., Wilson, S. C., and Stuiver, M.: Late Wisconsin and early Holocene glacial history, inner Ross Embayment, Antarctica, Quaternary Res., 31, 151–182, 1989.

Dreyfus, G. B., Parrenin, F., Lemieux-Dudon, B., Durand, G., Masson-Delmotte, V., Jouzel, J., Barnola, J.-M., Panno, L., Spahni, R., Tisserand, A., Siegenthaler, U., and Leuenberger, M.: Anomalous flow below 2700 m in the EPICA Dome C ice core detected using $\Delta^18$O of atmospheric oxygen measurements, Clim. Past, 3, 341–353, http://dx.doi.org/10.5194/cp-3-341-2007doi:10.5194/cp-3-341-2007, 2007.

Dreyfus, G. B., Jouzel, J., Bender, M. L., Landais, A., Masson-Delmotte, V., and Leuenberger, M.: Firn processes and [delta]15N: potential for a gas-phase climate proxy, Quaternary Sci. Rev., 29, 28–42, 2010.

EPICA community members: One-to-one coupling of glacial climate variability in Greenland and Antarctica, Nature, 444, 195–198, 2006.

Fischer, H., Wahlen, M., Smith, J., Mastroianni, D., and Deck, B.: Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations, Science, 283, 1712–1714, 1999.

Flückiger, J., Blunier, T., Stauffer, B., Chappellaz, J., Spahni, R., Kawamura, K., Schwander, J., Stocker, T. F., and Dahl-Jensen, D.: N2O and CH4 variations during the last glacial epoch: Insight into global processes, Global Biogeochem. Cy., 18, GB1020, http://dx.doi.org/10.1029/2003GB002122doi:10.1029/2003GB002122, 2004.

Goujon, C., Barnola, J.-M., and Ritz, C.: Modeling the densification of polar firn including heat diffusion: application to close-off characteristics and gas isotopic fractionation for Antarctica and Greenland sites, J. Geophys. Res., 108, ACL10/1-10, http://dx.doi.org/10.1029/2002JD003319doi:10.1029/2002JD003319, 2003.

Guillou, H., Singer, B. S., Laj, C., Kissel, C., Scaillet, S., and Jicha, B. R.: On the age of the Laschamp geomagnetic excursion, Earth Planet. Sci. Lett., 227, 331–343, 2004.

Herron, M. M. and Langway, C. C.: Firn densification: an empirical model, J. Glaciol., 25, 373–385, 1980.

Huber, C., Leuenberger, M., Spahni, R., Flückiger, J., Schwander, J., Stocker, T. F., Johnsen, S., Landais, A., and Jouzel, J.: Isotope calibrated Greenland temperature record over Marine Isotope Stage 3 and its relation to CH4, Earth Planet. Sci. Lett., 243, 504–519, 2006.

Huybrechts, P., Rybak, O., Pattyn, F., Ruth, U., and Steinhage, D.: Ice thinning, upstream advection, and non-climatic biases for the upper 89 % of the EDML ice core from a nested model of the Antarctic ice sheet, Clim. Past, 3, 577–589, http://dx.doi.org/10.5194/cp-3-577-2007doi:10.5194/cp-3-577-2007, 2007.

Hörhold, M., Laepple, T., Freitag, J., Bigler, M., Fischer, H., and Kipfstuhl, S.: On the impact of impurities on the densification of polar firn, Earth Planet. Sci. Lett., 325–326, 93–99, 2012.

Jouzel, J., Masson-Delmotte, V., Cattani, O., Dreyfus, G., Falourd, S., Hoffmann, G., Minster, B., Nouet, J., Barnola, J. M., Chappellaz, J., Fischer, H., Gallet, J. C., Johnsen, S., Leuenberger, M., Loulergue, L., Luethi, D., Oerter, H., Parrenin, F., Raisbeck, G., Raynaud, D., Schilt, A., Schwander, J., Selmo, E., Souchez, R., Spahni, R., Stauffer, B., Steffensen, J. P., Stenni, B., Stocker, T. F., Tison, J. L., Werner, M., and Wolff, E. W.: Orbital and Millennial Antarctic Climate Variability over the Past 800,000 Years, Science, 317, 793–796, 2007.

Köhler, P.: Rapid changes in ice core gas records – Part 1: On the accuracy of methane synchronisation of ice cores, Clim. Past Discuss., 6, 1453–1471, http://dx.doi.org/10.5194/cpd-6-1453-2010doi:10.5194/cpd-6-1453-2010, 2010.

Kawamura, K.: Variations of atmospheric components over the past 340 000 years from Dome Fuji deep ice core, Antarctica, Ph.D. thesis, Tohoku University, 2000.

Krinner, G., Raynaud, D., Doutriaux, C., and Dang, H.: Simulations of the Last Glacial Maximum ice sheet surface climate: Implications for the interpretation of ice core air content, J. Geophys. Res., 105, 2059–2070, 2000.

Landais, A., Barnola, J., Kawamura, K., Caillon, N., Delmotte, M., Ommen, T. V., Dreyfus, G., Jouzel, J., Masson-Delmotte, V., Minster, B., Freitag, J., Leuenberger, M., Schwander, J., Huber, C., Etheridge, D., and Morgan, V.: Firn-air $\delta^15$N in modern polar sites and glacial-interglacial ice: a model-data mismatch during glacial periods in Antarctica?, Quaternary Sci. Rev., 25, 49–62, 2006.

Landais, A., Dreyfus, G., Capron, E., Pol, K., Loutre, M. F., Raynaud, D., Lipenkov, V. Y., Arnaud, L., Masson-Delmotte, V., Paillard, D., Jouzel, J., and Leuenberger, M.: Towards orbital dating of the EPICA Dome C ice core using ΔO2/N2, Clim. Past, 8, 191–203, http://dx.doi.org/10.5194/cp-8-191-2012doi:10.5194/cp-8-191-2012, 2012.

Lliboutry, L.: A critical review of analytical approximate solutions for steady state velocities and temperature in cold ice sheets, Z. Gletscherkd. Glacialgeol., 15, 135–148, 1979.

Loulergue, L., Parrenin, F., Blunier, T., Barnola, J.-M., Spahni, R., Schilt, A., Raisbeck, G., and Chappellaz, J.: New constraints on the gas age-ice age difference along the EPICA ice cores, 0–50 kyr, Clim. Past, 3, 527–540, http://dx.doi.org/10.5194/cp-3-527-2007doi:10.5194/cp-3-527-2007, 2007.

Loulergue, L., Schilt, A., Spahni, R., Masson-Delmotte, V., Blunier, T., Lemieux, B., Barnola, J. M., Raynaud, D., Stocker, T. F., and Chappellaz, J.: Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years, Nature, 453, 383–386, 2008.

Lüthi, D., Floch, M. L., Bereiter, B., Blunier, T., Barnola, J.-M., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H., Kawamura, K., and Stocker, T. F.: High-resolution carbon dioxide concentration record 650,000–800,000 years before present, Nature, 453, 379–382, 2008.

Martinerie, P., Raynaud, D., Etheridge, D. M., Barnola, J.-M., and Mazaudier, D.: Physical and climatic parameters which influence the air content in polar ice, Earth Planet. Sci. Lett., 112, 1–13, 1992.

Martinerie, P., Lipenkov, V. Y., Raynaud, D., Chappellaz, J., Barkov, N. I., and Lorius, C.: Air content paleo record in the Vostok ice core Antarctica: A mixed record of climatic and glaciological parameters, J. Geophys. Res., 99, 10565–10576, 1994.

Masson-Delmotte, V., Hou, S., Ekaykin, A., Jouzel, J., Aristarain, A., Bernardo, R. T., Bromwich, D., Cattani, O., Delmotte, M., Falourd, S., Frezzotti, M., Gallée, H., Genoni, L., Isaksson, E., Landais, A., Helsen, M. M., Hoffmann, G., Lopez, J., Morgan, V., Motoyama, H., Noone, D., Oerter, H., Petit, J. R., Royer, A., Uemura, R., Schmidt, G. A., Schlosser, E., Simões, J. C., Steig, E. J., Stenni, B., Stievenard, M., van den Broeke, M. R., van de Wal, R. S. W., van de Berg, W. J., Vimeux, F., and White, J. W. C.: A Review of Antarctic Surface Snow Isotopic Composition: Observations, Atmospheric Circulation, and Isotopic Modeling*, J. Climate, 21, 3359–3387, 2008.

Monnin, E., Indermuhle, A., Dallenbach, A., Fluckiger, J., Stauffer, B., Stocker, T. F., Raynaud, D., and Barnola, J.-M.: Atmospheric CO2 concentrations over the last glacial termination, Science, 291, 112–114, 2001.

Parrenin, F. and Hindmarsh, R.: Influence of a non-uniform velocity field on isochrone geometry along a steady flowline of an ice sheet, J. Glaciol., 53, 612–622, 2007.

Parrenin, F., Remy, F., Ritz, C., Siegert, M., and Jouzel, J.: New modelling of the Vostok ice flow line and implication for the glaciological chronology of the Vostok ice core, J. Geophys. Res., 109, D20102, http://dx.doi.org/10.1029/2004JD004561doi:10.1029/2004JD004561, 2004.

Parrenin, F., Dreyfus, G., Durand, G., Fujita, S., Gagliardini, O., Gillet, F., Jouzel, J., Kawamura, K., Lhomme, N., Masson-Delmotte, V., Ritz, C., Schwander, J., Shoji, H., Uemura, R., Watanabe, O., and Yoshida, N.: 1-D-ice flow modelling at EPICA Dome C and Dome Fuji, East Antarctica, Clim. Past, 3, 243–259, http://dx.doi.org/10.5194/cp-3-243-2007doi:10.5194/cp-3-243-2007, 2007a.

Parrenin, F., Barnola, J.-M., Beer, J., Blunier, T., Castellano, E., Chappellaz, J., Dreyfus, G., Fischer, H., Fujita, S., Jouzel, J., Kawamura, K., Lemieux-Dudon, B., Loulergue, L., Masson-Delmotte, V., Narcisi, B., Petit, J.-R., Raisbeck, G., Raynaud, D., Ruth, U., Schwander, J., Severi, M., Spahni, R., Steffensen, J. P., Svensson, A., Udisti, R., Waelbroeck, C., and Wolff, E.: The EDC3 chronology for the EPICA Dome C ice core, Clim. Past, 3, 485–497, http://dx.doi.org/10.5194/cp-3-485-2007doi:10.5194/cp-3-485-2007, 2007b.

Parrenin, F., Petit, J.-R., Masson-Delmotte, V., Basile-Doelsch, I., Jouzel, J., Lipenkov, V., Rasmussen, S., Schwander, J., Severi, M., Udisti, R., Veres, D., Vinther, B., and Wolff, E.: Volcanic synchronisation between the EPICA Dome C and Vostok ice cores (Antarctica) 0–145 kyr BP, Clim. Past Discuss., 7, 4105–4147, http://dx.doi.org/10.5194/cpd-7-4105-2011doi:10.5194/cpd-7-4105-2011, 2011.

Pol, K., Debret, M., Masson-Delmotte, V., Capron, E., Cattani, O., Dreyfus, G., Falourd, S., Johnsen, S., Jouzel, J., Landais, A., Minster, B., and Stenni, B.: Sub-millennial climate variability during MIS 11 revealed by high resolution EPICA Dome C isotopic data – a comparison with the Holocene, Clim. Past Discuss., 6, 1777–1810, http://dx.doi.org/10.5194/cpd-6-1777-2010doi:10.5194/cpd-6-1777-2010, 2010.

Raisbeck, G. M., Yiou, F., Jouzel, J., and Stocker, T. F.: Direct north-south synchronization of abrupt climate change record in ice cores using Beryllium 10, Clim. Past, 3, 541–547, http://dx.doi.org/10.5194/cp-3-541-2007doi:10.5194/cp-3-541-2007, 2007.

Raynaud, D., Lipenkov, V., Lemieux-Dudon, B., Duval, P., Loutre, M.-F., and Lhomme, N.: The local insolation signature of air content in Antarctic ice. A new step toward an absolute dating of ice records, Earth Planet. Sci. Lett., 261, 337–349, 2007.

Reeh, N.: Dating by ice flow modeling : a useful tool or an exercice in applied mathematics?, in: The environmental record in glaciers and ice sheets, edited by: Oeschger, H. C. and Langway, John Wiley and Sons, New York, 1989.

Ritz, C., Rommelaere, V., and Dumas, C.: Modeling the evolution of Antarctic ice sheet over the last 420,000 years: implications for altitude changes in the Vostok region, J. Geophys. Res., 106, 31943–31964, 2001.

Röthlisberger, R., Mudelsee, M., Bigler, M., de Angelis, M., Fischer, H., Hansson, M., Lambert, F., Masson-Delmotte, V., Sime, L., Udisti, R., and Wolff, E. W.: The Southern Hemisphere at glacial terminations: insights from the Dome C ice core, Clim. Past, 4, 345–356, http://dx.doi.org/10.5194/cp-4-345-2008doi:10.5194/cp-4-345-2008, 2008.

Ruddiman, W. F. and McIntyre, A.: The mode and mechanism of the last deglaciation: Oceanic evidence, Quaternary Res., 16, 125–134, 1981.

Ruth, U., Barnola, J.-M., Beer, J., Bigler, M., Blunier, T., Castellano, E., Fischer, H., Fundel, F., Huybrechts, P., Kaufmann, P., Kipfstuhl, S., Lambrecht, A., Morganti, A., Oerter, H., Parrenin, F., Rybak, O., Severi, M., Udisti, R., Wilhelms, F., and Wolff, E.: "EDML1": a chronology for the EPICA deep ice core from Dronning Maud Land, Antarctica, over the last 150 000 years, Clim. Past, 3, 475–484, http://dx.doi.org/10.5194/cp-3-475-2007doi:10.5194/cp-3-475-2007, 2007.

Salamatin, A. N., Tsyganova, E. A., Popov, S. V., and Lipenkov, V. Y.: Ice flow line modeling in ice core data interpretation: Vostok Station East Antarctica, in: Physics of Ice Core Records 2, edited by: Hondoh, T., Hokkaido University Press, Sapporo, 2009a.

Salamatin, A. N., Lipenkov, V. Y., Barnola, J. M., Hori, A., Duval, P., and Hondoh, T.: Snow-firn densification in polar ice sheets, in : Physics of Ice Core Records-2, edited by: Hondoh, T., Hokkaido University Press, Sapporo, 2009b.

Schilt, A., Baumgartner, M., Schwander, J., Buiron, D., Capron, E., Chappellaz, J., Loulergue, L., Schüpbach, S., Spahni, R., Fischer, H., and Stocker, T. F.: Atmospheric nitrous oxide during the last 140,000 years, Earth Planet. Sci. Lett., 300, 33–43, 2010.

Schwander, J. and Stauffer, B.: Age difference between polar ice and the air trapped in its bubbles, Nature, 311, 45–47, 1984.

Severi, M., Becagli, S., Castellano, E., Morganti, A., Traversi, R., Udisti, R., Ruth, U., Fischer, H., Huybrechts, P., Wolff, E., Parrenin, F., Kaufmann, P., Lambert, F., and Steffensen, J. P.: Synchronisation of the EDML and EDC ice cores for the last 52 kyr by volcanic signature matching, Clim. Past, 3, 367–374, http://dx.doi.org/10.5194/cp-3-367-2007doi:10.5194/cp-3-367-2007, 2007.

Severi, M., Udisti, R., Becagli, S., Stenni, B., and Traversi, R.: Volcanic synchronisation of the EPICA-DC and TALDICE ice cores for the last 42 kyr BP, Clim. Past, 8, 509–517, http://dx.doi.org/10.5194/cp-8-509-2012doi:10.5194/cp-8-509-2012, 2012.

Severinghaus, J. P., Albert, M. R., Courville, Z. R., Fahnestock, M. A., Kawamura, K., Montzka, S. A., Mühle, J., Scambos, T. A., Shields, E., Shuman, C. A., Suwa, M., Tans, P., and Weiss, R. F.: Deep air convection in the firn at a zero-accumulation site, central Antarctica, Earth Planet. Sci. Lett., 293, 359–367, 2010.

Sime, L. C., Wolff, E. W., Oliver, K. I. C., and Tindall, J. C.: Evidence for warmer interglacials in East Antarctic ice cores, Nature, 462, 342–345, 2009.

Sowers, T., Bender, M. and Raynaud, D.: Elemental and isotopic composition of occluded O2 and N2 in polar ice, J. Geophys. Res., 94, 5137–5150, 1989.

Sowers, T. A., Bender, M., Raynaud, D., and Korotkevich, Y. L.: The $\delta^15$N of N2 in air trapped in polar ice : a tracer of gas transport in the firn and a possible constraint on ice age-gas age differences, J. Geophys. Res., 97, 15683–15697, 1992.

Stenni, B., Buiron, D., Frezzotti, M., Albani, S., Barbante, C., Bard, E., Barnola, J. M., Baroni, M., Baumgartner, M., Bonazza, M., Capron, E., Castellano, E., Chappellaz, J., Delmonte, B., Falourd, S., Genoni, L., Iacumin, P., Jouzel, J., Kipfstuhl, S., Landais, A., Lemieux-Dudon, B., Maggi, V., Masson-Delmotte, V., Mazzola, C., Minster, B., Montagnat, M., Mulvaney, R., Narcisi, B., Oerter, H., Parrenin, F., Petit, J. R., Ritz, C., Scarchilli, C., Schilt, A., Schupbach, S., Schwander, J., Selmo, E., Severi, M., Stocker, T. F., and Udisti, R.: Expression of the bipolar see-saw in Antarctic climate records during the last deglaciation, Nat. Geosci., 4, 46–49, 2011.

Stocker, T. F. and Johnsen, S. J.: A minimum thermodynamic model for the bipolar seesaw, Paleoceanography, 18, 1–9, 2003.

Stommel, H.: Thermohaline convection with two stable regimes of flow, Tellus, 13, 224–230, 1961.

Witrant, E., Martinerie, P., Hogan, C., Laube, J. C., Kawamura, K., Capron, E., Montzka, S. A., Dlugokencky, E. J., Etheridge, D., Blunier, T., and Sturges, W. T.: A new multi-gas constrained model of trace gas non-homogeneous transport in firn: evaluation and behavior at eleven polar sites, Atmos. Chem. Phys. Discuss., 11, 23029–23080, http://dx.doi.org/10.5194/acpd-11-23029-2011doi:10.5194/acpd-11-23029-2011, 2011.