The Greenland melt

Eric Steig

Last July (2012), I heard from a colleagues working at the edge of the Greenland ice sheet, and from another colleague working up at the Summit. Both were independently writing to report the exceptional conditions they were witnessing. The first was that the bridge over the Watson river by the town of Kangerlussuaq, on the west coast of Greenland, was being breached by the high volumes of meltwater coming down from the ice sheet. The second was that there was a new melt layer forming at the highest point of the ice sheet, where it very rarely melts.

A front loader being swept off a bridge into the Watson River, Kangerlussuaq, Greenland, in July 2012. Fortunately, nobody was in it at the time. Photo: K. Choquette

I’ve been remiss in not writing about these observations until now. I’m prompted to do so by the publication in Nature today (January 23, 2013) of another new finding about Greenland melt. This paper isn’t about the modern climate, but about the climate of the last interglacial period. It has relevance to the modern situation though, a point to which I’ll return at the end of this post.

The new paper in Nature, Eemian interglacial reconstructed from a Greenland folded ice core (NEEM Community Members, (2013)) is the culmination of many years of work in Greenland led by Dorethe Dahl-Jensen and her team from the Centre for Ice and Climate at the Niels Bohr institute in Copenhagen, with substantial involvement of scientists from around Europe, the U.S., China, Japan, and Canada.*

The big news is that this group has managed to obtain and use the information in ice from the Eemian — the peak of the last interglacial period, about 125,000 years ago — in Greenland. Getting usable Eemian ice from Greenland has been a Holy Grail of ice core research for the better part of two decades. We thought, back in the early 1990s, that we had obtained Eemian ice in the GISP2 and GRIP ice cores drilled near the ice sheet summit. It turned out that the lowermost part — anything older than 100,000 years — was messed up by ice flow, making it impossible to learn anything much about climate from it. The Danish group then led a project further to the north at “North GRIP” that, based on radar-echo-sounding data, should have had an intact Eemian period. But the temperature at the base at NGRIP was higher than expected, and the Eemian ice had melted away.

The latest attempt was the “North Eemian” (NEEM) site in northeast Greenland. Here too, the initial results were disappointing. As at GISP2 and GRIP, there are folds in the ice, and some of the layers containing the ice of Eemian age are repeated several times. However, in this case the folds are very large, and there are continuous sections that are not scrambled; they are just a bit out of order. It took significant work, but the group has unfolded the data from the folded layers and it is now evident that the goal of the NEEM project– having an interpretable section of Eemian ice — has succeeded after all.

The findings are spectacular. In the Eemian ice, there is clear evidence of significant melting of what would then have been snow at the surface. The amount of air trapped in the ice undergoes rapid fluctuations, resulting from the fact that ice that melts and then refreezes generally winds up with fewer air bubbles in it than the original porous snow. There are also strong fluctuations observed in soluble gases such as N2O whereas variations in the oxygen isotope concentration — both in the molecular oxygen (O2) in the air and in the ice (H2O) itself — are small. The isotope concentration of the O2 can be matched to that in undisturbed ice from the same time period in ice cores from Antarctica, providing a way to date the ice, showing unambiguously that non-disturbed layers are preserved from the peak of the Eemian period, about 125,000 years ago.

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  1. D. Dahl-Jensen, M.R. Albert, A. Aldahan, N. Azuma, D. Balslev-Clausen, M. Baumgartner, A. Berggren, M. Bigler, T. Binder, T. Blunier, J.C. Bourgeois, E.J. Brook, S.L. Buchardt, C. Buizert, E. Capron, J. Chappellaz, J. Chung, H.B. Clausen, I. Cvijanovic, S.M. Davies, P. Ditlevsen, O. Eicher, H. Fischer, D.A. Fisher, L.G. Fleet, G. Gfeller, V. Gkinis, S. Gogineni, K. Goto-Azuma, A. Grinsted, H. Gudlaugsdottir, M. Guillevic, S.B. Hansen, M. Hansson, M. Hirabayashi, S. Hong, S.D. Hur, P. Huybrechts, C.S. Hvidberg, Y. Iizuka, T. Jenk, S.J. Johnsen, T.R. Jones, J. Jouzel, N.B. Karlsson, K. Kawamura, K. Keegan, E. Kettner, S. Kipfstuhl, H.A. Kjær, M. Koutnik, T. Kuramoto, P. Köhler, T. Laepple, A. Landais, P.L. Langen, L.B. Larsen, D. Leuenberger, M. Leuenberger, C. Leuschen, J. Li, V. Lipenkov, P. Martinerie, O.J. Maselli, V. Masson-Delmotte, J.R. McConnell, H. Miller, O. Mini, A. Miyamoto, M. Montagnat-Rentier, R. Mulvaney, R. Muscheler, A.J. Orsi, J. Paden, C. Panton, F. Pattyn, J. Petit, K. Pol, T. Popp, G. Possnert, F. Prié, M. Prokopiou, A. Quiquet, S.O. Rasmussen, D. Raynaud, J. Ren, C. Reutenauer, C. Ritz, T. Röckmann, J.L. Rosen, M. Rubino, O. Rybak, D. Samyn, C.J. Sapart, A. Schilt, A.M.Z. Schmidt, J. Schwander, S. Schüpbach, I. Seierstad, J.P. Severinghaus, S. Sheldon, S.B. Simonsen, J. Sjolte, A.M. Solgaard, T. Sowers, P. Sperlich, H.C. Steen-Larsen, K. Steffen, J.P. Steffensen, D. Steinhage, T.F. Stocker, C. Stowasser, A.S. Sturevik, W.T. Sturges, A. Sveinbjörnsdottir, A. Svensson, J. Tison, J. Uetake, P. Vallelonga, R.S.W. van de Wal, G. van der Wel, B.H. Vaughn, B. Vinther, E. Waddington, A. Wegner, I. Weikusat, J.W.C. White, F. Wilhelms, M. Winstrup, E. Witrant, E.W. Wolff, C. Xiao, and J. Zheng, "Eemian interglacial reconstructed from a Greenland folded ice core", Nature, vol. 493, pp. 489-494, 2013.