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Science Highlights: Core Science 15

NGRIP reveals detailed climatic history 123 kyrs back in time

DORTHE DAHL-JENSEN Niels Bohr Institute, University of Copenhagen, ; [email protected] Introduction In 2003, for the fi rst time, an undis- turbed ice core record reaching further back than the gla- cial period was completed. The 3090 m long ice core from NGRIP, on the northern part of the Greenland Ice Sheet, contains layers of snowfall from the last 123,000 years. The annual layers close to the surface are 0.19 m thick, corresponding to the present accumulation rate (in ice equivalent) and the annual lay- Fig. 1: The δ18O record from NGRIP (black) (NGRIP members, 2004) on the GICC05 timescale down to 2128.28 m (age 41,760 yr b2k) and below on a timescale based on a fl ow model that ers at the base are all around 1 cm has been tuned to the GICC05 timescale. The synchronized δ18O record from GRIP (gray) is thick. The basal annual layer thick- shown down to 105,000 yr b2k so the two records can be compared. Some of the Dansgaard- ness is so well preserved due to a Oeschger warm stages (DO) are shown, and the Younger Dryas (YD), and climatic periods are marked. basal melt of 7 mm/yr, reducing the thinning near the bed (Dahl-Jensen extent of the , to resolve these layers to gain un- et al., 2003). This very high-resolu- sea ice and the extensive North At- derstanding of the system tion record contains 1490 m of ice lantic ice shelves, NorthGRIP shows and to produce a timescale based from the present period a more continental climate regime on counted annual layers. Chemical (0-11,703 yr b2k (before AD 2000)), and may have seen a higher fraction measurements using Continuous 1600 m of ice from the of air coming over the northern side Flow Analysis (CFA), including dust (11,703-115,000 yr b2k) and 90 m of of the Laurentide ice sheet, bringing and ECM on the melt water, visual ice from the last interglacial period, with it colder and more isotopically stratigraphy (VS) and ECM on the the Eemian climatic period (NGRIP depleted moisture than GRIP might frozen ice cores make it possible to members, 2004) have seen. Taken as a whole, the resolve the annual layers down to 60 fi ndings here suggest that the atmo- kyr b2k and perhaps further (Fischer The NGRIP isotope record spheric water cycle over Greenland is et al., 2006; Rasmussen et al., 2005). The stable isotope record from the substantially different between mod- The highly resolved records reveal NGRIP ice core is measured in 5 cm ern and glacial worlds. The bottom that the abrupt climate changes like resolution. Down to a depth of 2900 90 m of the NGRIP ice core contains the warmings into DO events, the m (105 kyr b2k), the record shows ice from the last interglacial period. transition into the Bølling/Allerød the same general climatic features The isotopic value of this ice is high and from the Younger Dryas into the as observed in other Greenland ice and corresponds to temperatures 5K Holocene happened over very short cores, including the Younger Dryas, higher than the present. The part of periods, sometimes only a few years. the Bølling Allerød and the 24 abrupt the Eemian period from 123-115 kyr The highest resolution record is the and climatic warm Dansgaard/Oe- b2k found in the NGRIP ice core re- visual stratigraphy with a resolution schger (DO) events during the gla- veals that the period was warm and of 0.1 mm (Svenson et al., 2005). The cial period (NGRIP members, 2004). stable. The decline to glacial condi- annual layers can be seen here down Whereas NorthGRIP and GRIP have tions happened slowly over 5000 to 100 kyr b2k. The visual record also very similar δ18O levels during the years. It is interesting to note how clearly demonstrates that the stratig- Holocene, glacial isotopic levels in soon the DO events begin to infl u- raphy is preserved through the full the NorthGRIP record are systemati- ence the climatic pattern. The fi rst to NGRIP ice core. cally depleted by 1-2‰. The magni- be found at a depth of 3040 m (age A new Greenland Ice Core Chro- tude of the difference appears to be 114 kyr b2k) might have happened nology (GICC05) covering the last related to the before the full build up of the big gla- 41 kyr has been constructed from climate curve, as represented by a cial ice sheets was reached. stratigraphic annual layer counting smoothed version of the NorthGRIP of high-resolution records from the record, such that colder conditions Stratigraphic dating of the NGRIP ice core and from GRIP and have larger differences. A spatial pat- NGRIP ice core Dye3 (Rasmussen, in press). Dating tern of glacial climate over Greenland The very high resolution of the of the Holocene period back to the begins to unfold. Our best theory is NGRIP ice core allows identifi cation 8.2 kyr event is based partly on exist- that the air masses reaching the two of the single annual layers down ing and partly on new stable isotope sites during the glacial were from through large parts of the ice core. measurements of the Dye-3 (GISP1) different sources. In response to the One of the goals of NGRIP has been ice core. For the interval 8.2-10 kyr

PAGES NEWS, VOL.14, N°1, APRIL 2006 16 Science Highlights: Ice Core Science

b2k, the timescale has been obtained from Electrical Conductivity Mea- surements (ECM) of the solid ice and multiparameter chemical CFA of the GRIP ice core. Beyond 10 kyr b2k, the timescale is based on records from the NGRIP ice core: An extended spectrum of chemical paramaters using CFA, ECM, and the light inten- sity curve of the recorded VS. At any depth, the dating is based on the ice core with the best available high-res- olution data, and the three ice cores are tied together using unambiguous reference horizons, such as volcanic Fig. 2: As an example of the high-resolution data along the NGRIP ice core, data from the ash layers or major acidity spikes. visual stratigraphy using the line scan instrument (a) is shown. A 50 cm long section of the The maximum counting error at 41 record is shown in (b). TThehe record is from 2358.0-2358.5 m where the age is 57 kyrkyr b2k and kyr b2k is 1600 years. The new times- the mean annual thickness is 1.2 cm. cale places the Holocene/ the ice sheet formation. Many ad- outstanding results and will soon be transition at 11,703 yr b2k, the onset ditional parameters like the gases, published. of Greenland Interstadial 3 (GIS3) at deuterium, deuterium excess, dust, 27.8 kyr b2k, and the onset of GIS8 at as well as detailed comparisons with REFERENCES Dahl-Jensen, D., Gundestrup, N., Gogineni, P. and 38.3 kyr b2k. the Antarctic ice cores, are revealing Miller, H., 2003: Basal melt at NorthGRIP modeled from borehole, ice-core and radio-echo sounder Outlook Project facts observations. Annals of Glaciology, 37: 207-212. Fischer, H., Siggard-Andersen, M.L. and Ruth U., At the base of the 3090 m thick ice Project: North Greenland Ice Core Project submitted: Glacial/interglacial changes in mineral sheet, the ice is melting and when (NGRIP) dust and sea salt records in polar ice cores: sources, bedrock was reached in 2003, basal Contact: Dorthe Dahl Jensen, [email protected] transport, and deposition. Reviews of Geophysics. water fl ooded the lowest 45 m of the Participants: Numerous scientists from labo- North Greenland Ice-Core Project (NorthGRIP) Mem- ratories in 8 European nations and the USA. bers, 2004: High resolution Climate Record of the borehole (Dahl-Jensen et al., 2003). Northern Hemisphere reaching into the last Glacial The reddish refrozen basal water Funding: Funding agencies in Denmark Interglacial Period. Nature, 431: 147-151. (SNF), Belgium (FNRS-CFB), France (IPEV from the sub-glacial water system Rasmussen, S. O., Andersen, K. K., Svensson, A. M., and INSU/CNRS), (AWI), Iceland Steffensen, J. P., Vinther, B. M., Clausen, H. B., in the lowest 45 m of the borehole (RannIs), Japan (MEXT), (SPRS), Andersen, M. -L., Johnsen, S. J., Larsen, L. B., Bigler, was recovered by drilling in 2004 Switzerland (SNF) and the USA (NSF, Offi ce M., Röthlisberger, R., Fischer, H., Goto-Azuma, K., and two macroscopic plant remains of Polar Programs) Hansson, M. E. and Ruth, U., 2005: A new Greenland Where: Northern Greenland ice core chronology for the last glacial termination, were recovered from the NGRIP core. Journal of geophysical research. in press. When: drilling 1996-2003, analysis ongoing. One is a wood fragment of willow Svensson, A., Wedel Nielsen, S., Kipfstuhl, S., John- What: 3090 m ice core from surface to bed- (Salix) and the other is a fragment son, S.J., Peder Steffensden, J.P., Bigler, M., Ruth, rock, multiparameter analysis U. and Röthlisberger, R., 2005: Visual stratigraphy of a bud scale, probably also from Web page: www.glaciology.gfy.ku.dk/ngrip/ of the North Greenland Ice Core Project (NorthGRIP) willow. Also, a few tiny fragments index_eng.htm ice core during the . Journal of of or larch (Picea/Larix) werewere Database: www.glaciology.gfy.ku.dk/ngrip/ Geophysical Research 110, D02108, doi:10.1029/ found, potentially representing an- index_eng.htm 2004JD005134. cient vegetation from the time of

Paleoenvironmental reconstruction from Alpine ice cores

MARGIT SCHWIKOWSKI Paul Scherrer Institute, Villigen, Switzerland; [email protected] Introduction Austria, into Slovenia. The total potential ice core sites are limited The European Alps, located in number of is 5422, cover- to a few high-elevation areas, such South-Central Europe, extend 800 ing an area of 3010 km2 (Paul et al., as the Bernese Alps, and the Monte km in the west-east and 150-200 2004). Glaciers with suffi ciently cold Rosa and Mont Blanc areas. km in the north-south direction (44- fi rn temperatures, where melt-water The Alps are especially interest- 48°N, 5.5-16°E). They form a great percolation is negligible and which ing for ice core studies because arc from the Riviera coast on the are therefore suitable for ice core a dense network of instrumental Mediterranean Sea, along the bor- studies, can be found above 4000 m meteorological measurements ders of northern Italy and adjacent asl in the northern part and above is available there and in the sur- regions of southeast France, Swit- 4300 m asl in the southern part of rounding countries. The existence zerland, southwest Germany and the Alps (Suter et al., 2001). Thus, of such exclusive data sets is a ma-

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