Geology Reference
In-Depth Information
Marine Record of Isotopic Change
350 ka to present
800 ka to present
2000 ka to present
A
B
C
18
O ( ‰)
18
O (‰)
18
O ( ‰)
d
d
d
3
2
1
0
-
1
-2
-3
2
1
0
-1
-2
4.8
4.4
4
3.6
3.2
0
0
0
1
2
1
2
1
4
4
2
5a
5c
6
5
5
5d
7
3
100
8
5e
9
4
10
6
11
5a
7a
12
13
15
17
21
5b
500
200
7b
14
100
5c
7c
8
5d
16
9a
9b
B/M
18
5e
300
19
9c
20
6
10
2
26
30
3
36
25
1000
400
11
29
31
12
200
7a
35
13
500
37
7b
43
14
7c
46
52
58
62
70
47
8
15
600
1500
49
55
16
9a
17
9b
300
700
63
9c
Brunhes/
Matuyama
18
67
62
73
10
19
75
800
2000
X
X
X
Fig. 2.3
Isotopic composition of the oceans during the Pleistocene viewed at three different time scales.
Heavier oxygen isotopic compositions (increasing to the left) correlate with greater ice-sheet volumes and lower mean
sea level. Interglacial intervals correspond with high sea-level stands. A. 0-350 ka; B. 0-800 ka; and C. 0-2 Ma. Note the
prominent, 100 kyr periodicity during the past 800 kyr. Prior to that, periodicities are dominated by a 40 kyr cycle;
20 kyr cycles are superimposed on both 100 kyr and 40 kyr cycles. Labels next to the peaks and troughs refer to
isotopic stages. Stage 5e, for example, represents the last interglacial maximum. Modified after Porter (1989) and
Lisiecki and Raymo (2005).
glaciations. Thus, the pattern of isotopic fluctua-
tions derived from deep-sea cores provides a
proxy record for both climate and sea-level
variations (Fig. 2.3).
Unfortunately, a one-to-one correspondence
does not exist between seawater isotopic variations
and sea-level changes. This non-equivalence
occurs for several reasons. The world's oceans are
not simple bathtubs, meaning that an equal
volume of water does not translate into a uniform
increment in sea-level change because, as sea level
rises, the surface area of the ocean also increases.
In addition, withdrawal of water from the ocean
and sequestration on land rearranges the water
load on the Earth's crust and drives isostatic
rearrangements of deep crustal and mantle
materials, which differ from place to place (Clark
et al.
, 1978; Lambeck
et al.
, 2002). Therefore, the
best estimates for past sea-level variations require
calibration and have been largely derived from
studies of radiometrically dated coral terraces on
tectonically rising coasts. Some key calibration
studies have been conducted on the striking
successions of coral terraces preserved on the
Huon Peninsula of New Guinea (Bloom
et al.
,
1974; Chappell, 1974; Chappell
et al.
, 1996), a
coastline responding to rapid collision of an
island-arc terrain against the edge of the Australian
Plate. These terraces get older with increasing
elevation, and they record the
relative
sea-level
change through time. This relative change results
from the sum of the
real
changes in sea level and
the
apparent
changes in sea level (Fig. 2.4):
relative = real + apparent
Real sea-level changes are due to absolute ver-
tical changes of the ocean surface (due primarily
to changing volumes of water in the ocean as a
result of glaciation; also called
eustatic
) and
can be global in extent. Apparent sea-level
