Geoscience Reference
In-Depth Information
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Periodic variation
%
Impulsive change
of central tendency
Quasi-periodic variation
&
Downward trend
of central tendency
Stable central tendencies
(stationary)
'
Increasing variability
Time
Mean temperature
in July (°C)
lake shorelines may be used to indicate former moisture
conditions. At the same time, sea level fell by up to about
136 m because so much water was locked up in the form
of ice in ice caps, ice sheets and glaciers. Surface oceanic
currents almost certainly changed and the strength of
North Atlantic deep water (NADW) formation varied
(see box, p. 242). New shapes of coastlines would have
modified the pre-existing surface currents to generate
further changes. For short periods of time warmer phases
or
interstadials
developed, allowing some vegetation
growth. Pollen and other evidence for these have been
preserved in some sediments.
In Britain sediments dated to about 60,000
BP
contain
signs of birch, pine and spruce trees growing in the area,
together with a beetle assemblage that suggests a cool,
continental climate rather like northern Finland today.
Somewhat, later about 42,000
BP
to 38,000
BP
, sediments
at Upton Warren near Droitwich in the English Midlands
have been found to contain much grass pollen, beetles,
indicating relatively warm conditions, and plenty of bones
of grazing animals such as bison, reindeer and woolly
palaeo-
magnetism
marine
influence
Ma
0
20
Interglacial
,9
Noordbergum
Glacial C
Interglacial
,,,
Rosmalen
Glacial B
MIDDLE
PLEISTOCENE
Cromerian
Interglacial
,,
Westerhoven
Glacial A
Interglacial
,
Waardenburg
Dorst Glacial
Leerdam Interglacial
Linge Glacial
Bavel Interglacial
0.7
Bavelian
0.9
Menapian
C
B
A
Waalian
EARLY
PLEISTOCENE
Eburonian
C5
C4c
1.8
Tiglian
C3
B
A
Praetiglian
middle Pleistocene period, showing the oscillations of glacial
and interglacial conditions.
Source: After Jones and Keen (1993)
2.4
LATE
PLIOCENE
Reuverian
