Ice core methodology - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 126

Figure 3.14. Dansgaard's correlation of d 18 O with temperature. The circles apply to south
Greenland and the squares to north Greenland.

and its counterpart d (D) are indicators of past temperatures that prevailed when
snow was deposited at the site, which eventually agglomerated into an ice sheet. In
the early days of ice core exploration, Dansgaard (2005) prepared a correlation
between current surface temperature at various Greenland sites and the current
values of d 18 O at these sites (see Figure 3.14 ). Dansgaard also measured d 18 O,
and d (D) as well, for recently deposited ice at a large number of NH sites span-
ning a range of latitudes from 60 to 85 and found that, when they were plotted
vs. current average temperature, the data were grouped around a straight line. If
the same relationship between temperature and d 18 O, or d (D), held during the past
few hundred thousand years (a rather large extrapolation), these straight line
correlations between d 18 O, or d (D), and temperature can be used to infer past
temperatures from measurements of d 18 O, or d (D), in the core. A number of such
correlations evolved, and one of the recent ones was:
T ð C Þ¼ 1 45 d 18 O þ 19

: : 7

T ð C Þ¼ 0

: 18 d D þ 18

in which the d are measured in units of (parts per thousand). This was the

method of choice for converting isotope measurements to temperature for several
decades. For example, according to Kotlyakov (1996):

%

''The main method of paleotemperature estimation involves analysis of
the stable isotopes ratios H/D and 16 O/ 18 O in ice. The isotopic composition
of deposited snow depends on its formation temperature. It has been found