Geoscience Reference
In-Depth Information
Figure 10.4.
Reconstructions from several data sources illustrating climate changes
since 93 ka. The top two panels give the abundance of
N. Pachyderma
from two
North Atlantic ocean cores (DSDP 609, approximately 50
o
N, 45
o
W, Vema 23-81,
approximately 54
o
N, 18
o
W), and the bottom panel is the δ
18
O record from the GRIP
Summit ice core. The dotted lines on the bottom panel illustrate long-term cooling
trends. H1-H6 indicate Heinrich Events, and YD indicates the Younger Dryas event.
The age scale is approximate (courtesy of G. Bond, Lamont-Doherty Earth Observatory,
Palisades, New York).
that the most extensive glaciation there may have been during the so-called Middle
Valdai, prior to 40 ka, contrasting with the maximum in global ice volume 25-18
ka, as discussed later.
There were large fluctuations in sea level (marine transgressions and regressions)
associated with ice sheet growth and decay. These represent the direct influence of
changes in terrestrial ice volume on eustatic sea level, as well as the response of
the earth through glacio-hydro-isostatic effects. The latter involve vertical move-
ments of the land induced by varying loads of ice and water and the redistribution
of mass. These processes are still occurring today. During the marine regressions
and transgressions, zones of frozen ground in the coastal and continental shelf areas
of the Arctic, especially Eurasia, underwent successive north-south displacements
(Rozenbaum and Shpolyanskaya,
2000
).
Figure 10.4
, based on the original work of G. Bond et al. (
1993
), gives a closer
focus on climate changes from about 93 ka through the early Holocene on the basis
of the relative abundance of left-coiling (sinistral)
N. Pachyderma
in two ocean
cores in the North Atlantic and in the δ
18
O record at the GRIP Summit ice core.
These records go back to Stage 5b (5.2). Recall that a more negative (i.e., lighter)
