Guest Post by Louis Hissink

The Glacier Girl Guide

One of the problems with ice core data is working out how quickly deposited snow becomes buried. Ice is peculiar in that, unlike silicate sediments such as clays and silts, it undergoes physical phase transformations that complicates subsequent stratigraphical analysis. Lacustrine varves can be shown to indicate distinct flooding events, most of which might be yearly, depending on the climate, and so the process of varve counting can be quite accurate since the layering, formed by distinct grain sizes of sediment, do not move vertically save for some compression at depth.

During WWII some American fighter planes were forced to land on the Greenland ice cap due to running out of fuel. The planes became quickly buried and disappeared from sight. These planes were discovered 46 years (in 1986) later at a depth of 260 feet, or 79.25 metres, which the New York Times reported in 1988. This suggests that an estimate of burial rate could be calculated as a first pass attempt.

From the reported depth of burial, 260 feet below surface, and the 46 year time span, we can obtain a burial rate of 1.72 metres per year; ([260×0.3048]/46).

We know from the Libby Cedar tree-ring data that a significant d18O event occurred at about 650CE and associated with the Comet of Justinian. We also know the Heinsohn Horizon is dated about 935CE.

I looked at the GISP2 ice data published by Stuiver etal and downloadable from
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/.

I plotted the d18O20y.txt data using depth and d18O columns only. The graph that results is shown in Figure 1 below.

GISP2 Bidecadal Oxygen Isotopes
There were 3 dud measurements which were corrected for by interpolation from the adjacent samples of d18O values, otherwise the data is ‘as is’. Zero depth was for year 1980.

There is a significant d18O anomaly at approx. 1700 metres depth. Using the burial rate calculated above, this depth corresponds to 988.37 years, 992 CE, which is near enough to the Heinsohn Horizon for this first pass interpretation. The final depth of 1844 metres represents a period of 1072.09 years, which could link to the 650 AD event, since the two d18O lows are separated by approx. 200 years and there are no more positive data points pointing to deeper ice, and thus older ice.

The d18O plot then becomes more or less constant from the depth of 1500 metres to the top. 1500 metres depth here calculates to a time period of approx. 872 years, or approx. 1108CE.

This suggests the Greenland ice cap started being formed about 250CE, or about the time of the Roman Termination Event.

Note: Retro-calculation here is based on the Gregorian system which was implemented in 1582CE. Before this year the Julian system was used, but as there were also hundreds of other lunar calendars in use, it will be anyone’s guess how accurate the arithmetic could be.

REFERENCES:

Stuiver, M., T.F. Braziunas, P.M. Grootes, and G.A. Zielinski. 1997. Is there evidence for solar forcing of climate in the GISP2 oxygen isotope record? Quaternary Research 48:259-266.

Stuiver, M., P.M. Grootes, and T.F. Braziunas. 1995. The GISP2 18O climate record of the past 16,500 years and the role of the sun, ocean and volcanoes. Quaternary Research 44:341-354.

Meese, D.A., R.B. Alley, R.J. Fiacco, M.S. Germani, A.J. Gow, P.M. Grootes, M. Illing, P.A. Mayewski, M.C. Morrison, M. Ram, K.C. Taylor, Q. Yang, and G.A. Zielinski. 1994. Preliminary depth-agescale of the GISP2 ice core. Special CRREL Report 94-1, US.

Steig, E.J., P.M. Grootes, and M. Stuiver. 1994. Seasonal precipitation timing and ice core records. Science 266:1885-1886.

DATA DESCRIPTION:

This file contains the GISP2 bidecadal delta 18O data set back to 16,510yr B.P., measured at the Quaternary Isotope Laboratory, University of Washington, as of February 1st, 1997. The timescale includes revisions by D. A. Meese as of September 1994. The GISP2 depths below 167 meters are those of the D core; above 167 meters the core depths are those of the B core + 1.09 meters. See the file gisp2age.dat for further information on the timescale.

Between 1650.29 and 1844.88 meters, the delta 18-O values of this time
series are based on high resolution data (0.2 meter). They differ slightly
from the 2-meter time series (file UW2md18O.dat).

The data columns represent:

(1) top depths of intervals (in meters)
(2) mean delta 18-O values (in per mil) over bidecadal intervals starting at top depths. Standard deviation in a single delta 18-O measurement is 0.14 per mil. Multiple measurements (such as for the ones below) reduce the standard deviation to the 0.05 to 0.1 per mil range.
(3) layer count ages at top depths (in yr BP) where 0 BP represents AD1950 SUMMER to AD 1949 SUMMER

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Gallery | This entry was posted in Catastrophism, Glaciology, Greenland, Gunnar Heinsohn, History, Radiocarbon Dating, Science. Bookmark the permalink.

One Response to Guest Post by Louis Hissink

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