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Microparticles in “Byrd” station ice core: comments on the paper by L. G. Thompson, W. L. Hamilton and C. Bull

Published online by Cambridge University Press:  30 January 2017

S. J. Johnsen ,
C. U. Hammer ,
N. Reeh  and
W. Dansgaard
S. J. Johnsen
Affiliation:
Geophysical Isotope Laboratory, Københavns Universitet, Haraldsgade 6 DK 2200 København N, Denmark
C. U. Hammer
Affiliation:
Geophysical Isotope Laboratory, Københavns Universitet, Haraldsgade 6 DK 2200 København N, Denmark
N. Reeh
Affiliation:
Geophysical Isotope Laboratory, Københavns Universitet, Haraldsgade 6 DK 2200 København N, Denmark
W. Dansgaard
Affiliation:
Geophysical Isotope Laboratory, Københavns Universitet, Haraldsgade 6 DK 2200 København N, Denmark
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Information

Type
Correspondence
Information
Journal of Glaciology , Volume 17 , Issue 76 , 1976 , pp. 361
Copyright
Copyright © International Glaciological Society 1976

The Editor,

Journal of Glaciology

Sir,

In a recent paper in the Journal (Reference Thompson, Thompson, Hamilton and BullThompson and others, 1975) a new time scale along the "Byrd" station ice core is suggested. It is based on the interpretation of varying microparticle concentration in terms of seasonal variations, which leads to the conclusion that the age of the bottom ice is only 27 000 years.

We agree with several of the viewpoints put forward in the paper, for example that identification of annual layers by microparticle variations may push the limit for absolute dating of polar ice cores much farther back in time than that set by diffusive obliteration of seasonal stable-isotope cycles.

However, it is extremely difficult to accept the interpretation and the consequent conclusion of Reference Thompson, Thompson, Hamilton and BullThompson and others (1975), mainly for the following reasons:

  1. (1) Accepting the variations as seasonal implies a vertical strain-rate close to zero over the lower 90% of the ice core (cf. fig. 5 and the essentially linear relationships between depth and age claimed in fig. 6). This is hardly consistent with any realistic ice-flow model.

  2. (2) In principle, it is impossible to identify a short series of cycles of varying "wavelength" from less than two (in practice three or four) measuring points per cycle. In at least 11 out of the 13 core increments referred to by the authors the sample length was 2 cm or more (Reference ThompsonThompson, 1973). Therefore, the minimum layer thickness detectable by their technique is 6 cm, and the fact that no shorter cycles were found is no proof that they do not exist, neither does it disprove the time scale of Reference Johnsen, Johnsen, Dansgaard, Clausen and LangwayJohnsen and others (1972), according to which the layer thickness is smaller than 6 cm in the lower 50% of the core (smaller than 2 cm in the lower 14%). The variations in dust concentration measured at great depths are instead due to long-term changes, maybe connected to climatic variations.

The time scale suggested by Reference Johnsen, Johnsen, Dansgaard, Clausen and LangwayJohnsen and others (1972) may be shown to be wrong when better field data become available from the complicated "Byrd" station area, and indeed it is encumbered with considerable uncertainty, particularly at great depths. But so far it seems more realistic than that suggested by Reference Thompson, Thompson, Hamilton and BullThompson and others (1975).

6 January 1976

References

Johnsen, S.J. 1972 Oxygen isotope profites through the Antarctic and Greenland ice sheets[by] Johnsen, J.S., Dansgaard, W., Clausen, H.B., Langway, C.C. Nature, Vol. 335, No. 5339 p. 429–34.10.1038/235429a0CrossRefGoogle Scholar
Thompson, L.G. 1973 Analysis of the concentration of microparticles in an ice core from Byrd station, Antarctica. Ohio State University. Institute of Polar Studies. Report No. 46.Google Scholar
Thompson, L.G. 1975 Climatological implications of microparticle concentrations in the ice core from "Byrd" station, western Antarctica, by Thompson, L. G., Hamilton, W. L., Bull, C.[B.B.] . Journal of Glaciology, Vol. 14, No. 72, p. 433–44.10.1017/S0022143000021948CrossRefGoogle Scholar