Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 136

Table 4.2. Characteristics of major ice core sites in Greenland (adapted from Oard, 2005).

Ice core Latitude Date Surface Ice Core Average Accumu-

drilled elevation thickness depth tempera- lation

ture

( C) (m) (m) (m) (cm/yr)

Camp Century 77 1963-1966 1,885 1,390 1,390 24 38

Milcent 70 1973 2,450 2,350 398 23 50

Crete 71 1974 3,172 3,200 405 30 32

Dye 3 65 1981 2,486 2,037 2,037 20 56

Renland 72 1988 2,340 324 324 18 50

GRIP 72 1990-1992 3,230 3,029 3,029 32 23

GISP2 72 1989-1993 3,208 3,053 3,053 31 24

NorthGRIP 75 1999-2003 2,921 3,080 3,080 32 20

The Internet site http://www.ncdc.noaa.gov/paleo/icecore/current.html provides
links to a multitude of ice core data at Greenland, Antarctica, and elsewhere.
Data from the various Greenland ice cores are plotted in Figures 4.2 through 4.7 .
Figure 4.2 shows the GISP2 data for the past two centuries. There is good
evidence for the Medieval Warm Period around 1000 ad and the Little Ice Age
from about 1400 to 1850 ad . As Figure 4.3 shows, temperatures were remarkably
stable over the past 10,000 years as the Earth emerged from the last ice age, but
were sharply lower prior to that. Note the sudden sharp drop in temperature
around 8,200 ybp . This event has also been observed in:

a variety of other palaeoclimatic archives including lake sediments,
ocean cores, speleothems, tree rings, and glacier oscillations from most of the
Northern Hemisphere

'' ...

. Today there is a general consensus that the
primary cause of the cooling event was the final collapse of the Laurentide ice
sheet near Hudson Bay and the associated sudden drainage of the proglacial
Lake Agassiz into the North Atlantic Ocean around 8,400 ybp '' (Rasmussen et
al., 2007).

...

Figure 4.4 shows temperature change over a 20,000-year period. The Dryas
events are widely believed to have been associated with major calving of large ice
sheet segments. It is possible, however, that a comet impact about 12,900 ybp may
have contributed to the Younger Dryas (Kennett et al., 2009). The 8,200 ybp event
is shown with an arrow. Figure 4.5 extends the data to 40,000 years. Two things