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Observations of anthropogenic global warming

Papers of Willi Dansgaard

Posted by Ari Jokimäki on February 2, 2011

Professor emer. Dr. Phil. Willi Dansgaard passed away Saturday, January 8, 2011 at the age of 88 years. Read the full article in Niels Bohr Institute.

Here are some papers written by Willi Dansgaard. The emphasis is on the papers that have full text freely available:

Validity of the temperature reconstruction from water isotopes in ice cores – Jouzel & Dansgaard et al. (1997) “Well-documented present-day distributions of stable water isotopes (HDO and H2 18O) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (δD and δ18O) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMs) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes.” Jouzel, J., et al. (1997), J. Geophys. Res., 102(C12), 26,471–26,487, doi:10.1029/97JC01283. [full text]

Evidence for general instability of past climate from a 250-kyr ice-core record – Dansgaard et al. (1993) “RECENT results from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades. Here we present a detailed stable-isotope record for the full length of the Greenland Ice-core Project Summit ice core, extending over the past 250 kyr according to a calculated timescale. We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial (as explored more fully in a companion paper) and during the previous Saale–Holstein glacial cycle. This is in contrast with the extreme stability of the Holocene, suggesting that recent climate stability may be the exception rather than the rule. The last interglacial seems to have lasted longer than is implied by the deep-sea SPECMAP record4, in agreement with other land-based observations. We suggest that climate instability in the early part of the last interglacial may have delayed the melting of the Saalean ice sheets in America and Eurasia, perhaps accounting for this discrepancy.” W. Dansgaard, S. J. Johnsen, H. B. Clausen, D. Dahl-Jensen, N. S. Gundestrup, C. U. Hammer, C. S. Hvidberg, J. P. Steffensen, A. E. Sveinbjörnsdottir, J. Jouzel & G. Bond, Nature 364, 218 – 220 (15 July 1993); doi:10.1038/364218a0. [full text]

Irregular glacial interstadials recorded in a new Greenland ice core – Johnsen & Dansgaard et al. (1992) “THE Greenland ice sheet offers the most favourable conditions in the Northern Hemisphere for obtaining high-resolution continuous time series of climate-related parameters. Profiles of 18O/<16O ratio along three previous deep Greenland ice cores seemed to reveal irregular but well-defined episodes of relatively mild climate conditions (interstadials) during the mid and late parts of the last glaciation, but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate, rather than artefacts due to disturbed stratification. Here we present results from a new deep ice core drilled at the summit of the Greenland ice sheet, where the depositional environ-ment and the flow pattern of the ice are close to ideal for core recovery and analysis. The results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt. According to a preliminary timescale based on stratigraphic studies, the interstadials lasted from 500 to 2,000 years, and their irregular occurrence suggests complexity in the behaviour of the North Atlantic ocean circulation.” S. J. Johnsen, H. B. Clausen, W. Dansgaard, K. Fuhrer, N. Gundestrup, C. U. Hammer, P. Iversen, J. Jouzel, B. Stauffer & J. P. steffensen, Nature 359, 311 – 313 (24 September 1992); doi:10.1038/359311a0. [full text]

Secular trends of accumulation rates at three Greenland stations – Reeh & Dansgaard et al. (1978) “The annual layer thickness profiles along three 400 m ice cores are transferred into accumulation-rate records. A linear decrease of 3±2% per millenium is found in mid-Greenland. Intermediate-term (periods longer than 120 years) deviations from the linear trend lines are less than 5% in midGreenland, but reach 11% at Dye 3 around A.D. 1700 and 1400. Short-term (periods between 120 and 30 years) oscillations are generally in phase at Milcent and Crete.” Reeh, N.; Clausen, H. B.; Dansgaard, W.; Gundestrup, N.; Hammer, C. U.; Johnsen, S. J., Journal of Glaciology, vol.20, Issue 82, pp.27-30. [full text]

Less surface accumulation on the Ross Ice Shelf than hitherto assumed – Clausen & Dansgaard (1977) “Total β-activity profiles along 36 hand-augered firn cores from the southeastern part of the Ross Ice Shelf indicate accumulation rates of only half the previous estimates determined from stratigraphie pit studies.” H. B. Clausen and W. Dansgaard, Isotopes and impurities in snow and ice, 1977. [full text]

Stable isotope profile through the Ross Ice Shelf at Little America V, Antarctica – Dansgaard et al. (1977) “The δ(18O)-proflle along the Little America V ice core ranges from — 20‰ near the surface to — 35‰ at the bottom, i.e. lower than at any surface value hitherto measured in West Antarctica.” W. Dansgaard, S. J. Johnsen, H. B. Clausen, C. U. Hammer and C. C. Langway Jr, Isotopes and impurities in snow and ice, 1977. [full text]

Oxygen Isotope Profiles through the Antarctic and Greenland Ice Sheets – Johnsen & Dansgaard et al. (1972) “The Camp Century, Greenland, deep ice core reveals seasonal variations in the isotopic composition of the ice back to 8,300 years BP. This is not the case for the Byrd Station, Antarctica, deep ice core. Both cores show long-term perturbations in isotopic composition reflecting climatic changes from before the beginning of the last glaciation. But the complexity of the glaciological regime at Byrd Station precludes a rational choice of a time scale. Pole-to-pole correlations of the palaeoclimatic data therefore become speculative except for the more pronounced features and general trends.” S. J. Johnsen, W. Dansgaard, H. B. Clausen & C. C. Langway jun, Nature 235, 429 – 434 (25 February 1972); doi:10.1038/235429a0.

Climatic Oscillations 1200−2000 AD – Johnsen & Dansgaard et al. (1970) “THE idea of using the isotopic composition of glacier ice as a climatic indicator was proposed in 1954. The method is based on the fact that the concentration of heavy stable isotopes (deuterium and oxygen-18) in high polar snow increases with the temperature of formation of the snow. This causes seasonal variations in the isotopic composition of accumulated snow and ice4, as well as long-term variations due to climatic changes5. A unique possibility for studying palaeoclimates was offered when the US Army Cold Region Research and Engineering Laboratory succeeded in recovering a 1,400 metre long surface-to-bottom ice core from Camp Century on the North Greenland ice sheet. No physical dating method can be applied on the relatively small amounts of ice available, so the age of the various increments of the core had to be calculated by considering a simple ice flow model. This procedure turned out to be successful, in so far as the climate record that resulted from plotting the δ(18O) data (δ is defined as the relative deviation of the 18O/16O ratio of a sample from that of standard mean ocean water) against the calculated ages depicted known climatic events dated by other methods. In addition, unlike other methods, the stable isotope technique applied on the deep ice core gave an unbroken and detailed climatic record spanning probably 100,000 years.” S. J. Johnsen, W. Dansgaard, H. B. Clausen & C. C. Langway, Nature 227, 482 – 483 (01 August 1970); doi:10.1038/227482a0.

One Thousand Centuries of Climatic Record from Camp Century on the Greenland Ice Sheet – Dansgaard et al. (1969) “A correlation of time with depth has been evaluated for the Camp Century, Greenland, 1390 meter deep ice core. Oxygen isotopes in approximately 1600 samples throughout the core have been analyzed. Long-term variations in the isotopic composition of the ice reflect the climatic changes during the past nearly 100,000 years. Climatic oscillations with periods of 120, 940, and 13,000 years are observed.” W. Dansgaard, S. J. Johnsen, J. Møller and C. C. Langway, Jr., Science 17 October 1969, Vol. 166 no. 3903 pp. 377-380, DOI: 10.1126/science.166.3903.377.

Isotopic Distribution in a Greenland Iceberg – Dansgaard et al. (1960) “THE heavy-oxygen content in the ice of the Greenland ice cap is extremely low. This is part of a common feature showing decreasing H2 18O content in fresh water when going towards a colder climate.” W. Dansgaard, G. Nief & E. Roth, Nature 185, 232 (23 January 1960); doi:10.1038/185232a0.

The O18-abundance in fresh water – Dansgaard (1954) “Fresh water of various origins as distinct from ocean water shows great variations in O18-abundance. Proceeding from the temperate towards the colder climates a considerable decrease is noticeable. It is demonstrated that the O18-abundance in atmospheric water vapour is dependent on (a) the precipitation temperature, (b) the origin of the vapour and (c) the average cooling of the vapour during the circulation of the water in nature, whereas the O18-abundance in a certain precipitation, further, depends on (d) the condensation temperature, (e) the cooling since the beginning of the condensation of the vapour in question and (f) the evaporation during the fall of the precipitation from cloud to ground. Furthermore, the O18-abundance in ground water from a certain locality depends on (g) the evaporation from the precipitation since its reaching the ground and (h) the possible exchange of O18 between the water and oxygenic substances in the ground. Computations on this basis and on measurements of the O18-abundance of ocean water are in agreement with measurements of fresh water of various origins.” Willi Dansgaard, Geochimica et Cosmochimica Acta, Volume 6, Issues 5-6, December 1954, Pages 241-260, doi:10.1016/0016-7037(54)90003-4.

Additional documents

Frozen Annals Willi Dansgaard’s book about Greenland ice sheet research (freely available).


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