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Climate variations during 3Ma BP, revealed by the
oxygen isotope ratio of a deep ocean sediment core, include the
geological boundaries between the Pliocene Epoch of Tertiary Period and
the Pleistocene Epoch of Quaternary Period (1,5Ma BP), between the
Pleistocene Epoch and the Recent or Holocene Epoch, and the beginning of
glacial and interglacial cycles (last one is the Holocene Epoch),
started around 0.7Ma BP, when the positive feedback mechanism began
operating to a stronger degree. Climates depend not only on increases in
greenhouse gas concentrations (internal components) and earth orbital
changes (external ones), but also depend heavily on changes in global
ocean circulation and sea surface temperature (both components).
The spectra of climatic variations are more
complicated and universal than they would appear to advocates of the
single cycle (41 ka) of the Earth’s changing orbital inclination or
the single cycle (90 ka)of the orbital eccentricity. Table indicates the
Pleistocene harmonics based on oxygen-isotope and on astronomical data.
These cycles of the Sun system and
periods
(TK ) have
coincided well with each other and have been fixed in sedimentary rocks
of different geological periods in the glacial and mild climatic epoch,
not only in strata of the Pliocene and the Pleistocene Epochs.
Table. Model (TK), Climatic (TC)
and Astronomical (TA) cycles of the range 104 - 106
years:
|
N
|
K
|
Oct.
|
TK(ka)
|
TC (ka)
|
TA (ka)
|
Original sources
|
|
1
|
320
|
20
|
78.43
|
79
|
|
Berry, 1993
|
|
2
|
305
|
19
|
40.95
|
40
|
40,9
|
Raymo, 1992, Monin, 1982,
|
|
3
|
290
|
18
|
21.38
|
21
|
|
Raymo, 1992
|
|
3
|
306
|
19
|
42.76
|
43
|
|
Berry, 1993
|
|
4
|
291
|
18
|
22.33
|
22
|
22.4
|
Raymo, 1992, Monin, 1982
|
|
4
|
323
|
20
|
89.32
|
90
|
|
Raymo, 1992
|
|
5
|
276
|
17
|
11.66
|
11.5
|
|
Hays et al., 1976
|
|
5
|
292
|
18
|
23.32
|
23
|
23.7
|
Hays et al., 1976, Monin,
1982
|
|
5
|
|
|
|
23
|
|
Raymo, 1992
|
|
5
|
308
|
19
|
46.6
|
|
47
|
Brouwer, Woerkom, 1950
|
|
5
|
324
|
20
|
93.27
|
93
|
94.6
|
Berry, 1993, Br., Woerk., 1950
|
|
6
|
293
|
18
|
24.35
|
24
|
|
Hays et al., 1976
|
|
6
|
325
|
20
|
97.4
|
96
|
99.4
|
Raymo, 1992, Monin, 1982
|
|
6
|
341
|
21
|
194.8
|
191
|
|
Berry, 1993
|
|
7
|
294
|
18
|
25.43
|
|
25.73
|
Kulikov, Sidorenkov, 1977
|
|
7
|
310
|
19
|
50.86
|
|
50
|
Brouwer, Woerkom, 1950
|
|
7
|
326
|
20
|
101.7
|
100
|
|
Hays et al., 1976
|
|
8
|
311
|
19
|
53.11
|
|
52.5
|
Monin, 1982
|
|
8
|
359
|
22
|
424.9
|
425
|
|
Subakov, 1990
|
|
9
|
280
|
17
|
13.86
|
14
|
|
Berry, 1993
|
|
9
|
312
|
19
|
55.46
|
56
|
|
Berry, 1993
|
|
9
|
344
|
21
|
221.8
|
|
220
|
Brouwer, Woerkom, 1950
|
|
9
|
360
|
22
|
443.7
|
|
450
|
Brouwer, Woerkom, 1950
|
|
10
|
297
|
18
|
28.96
|
|
28.6
|
Monin, 1982
|
|
11
|
266
|
16
|
7.560
|
7.5
|
|
Hays et al., 1976
|
|
11
|
330
|
20
|
121.0
|
121
|
121.6
|
Berry, 1993, Monin, 1982
|
|
11
|
394
|
24
|
1935
|
|
1923
|
Monin, 1982
|
|
12
|
347
|
21
|
252.6
|
|
250
|
Brouwer, Woerkom, 1950
|
|
12
|
395
|
24
|
2021
|
|
2000
|
Brouwer, Woerkom, 1950
|
|
13
|
300
|
18
|
32.98
|
33
|
|
Berry, 1993
|
|
13
|
332
|
20
|
131.9
|
|
129.8
|
Monin, 1982
|
|
14
|
317
|
19
|
68.87
|
70
|
|
Berry, 1993
|
|
14
|
|
|
|
68
|
|
Raymo, 1992
|
|
15
|
270
|
16
|
8.990
|
9
|
|
Hays et al., 1976
|
|
15
|
318
|
19
|
71.92
|
|
72
|
Brouwer, Woerkom, 1950
|
|
16
|
287
|
17
|
18.780
|
19
|
18.9
|
Hays et al., 1976, Monin, 1982
|
|
16
|
303
|
18
|
37.55
|
38
|
|
Raymo, 1992
|
|
16
|
351
|
21
|
300.4
|
294
|
300
|
Berry, 1993, Br., Woerk., 1950
|
Below, using physical-empirical models and factual
material, we show the main causes and consequences of changes in ocean
circulation, land cover and climate variations during 3Ma BP. The
reconstructions for the last glacial period, approximation and extrapolation of
the last homogeneous part (from 0.7Ma BP) of the row allow enhancement of the
interpretation of the isotope series (Figure).
Figure. Three million years of the oxygen-isotope
series
d18O(%o)
(Raymo, 1992) and environmental reconstruction and prediction (Berry, 1993).
tE
-
surface ocean temperature in the Equatorial belt in Celsius degrees, tNH
-
surface land temperature in the Northern Hemisphere in Celsius degrees, l(m) - level of Oceans,
V(Mkm3) - volume of Ice sheets, A(Mkm2) - area of Ice
sheets, H(m) - thickness of loess in Tajikistan (1),
SLT=
0.129m/y1/2 , in Western Siberia (2),
SLWS
= 0.110m/y1/2
, in Hungary (3),
SLH
= 0.0767m/y1/2
, in Poland (4),
SLP
= 0.025m/y1/2
.
During the Pliocene Epoch the climate was cooling
because the surface of the continents had increased and the common circulation
of the ocean had been broken up. There are many reconstructions for the last
glacier period. They allow the creation of new scales for the diagram which
enhance the picture. When the global ocean circulation developed (3.1-2.7Ma),
the solar system’s oscillations changed the temperature of the ocean surface
slightly (~0.5C) because of the active circulation and the negative feedback.
Later the circulation in the oceans has had
limitation. About 2.6Ma BP North American ice sheet rose at first, subsequently
disappearing and coming into view again many times. The formation of durable
snow-ice covers on the northern parts of the continent has activated positive
feedback. This feedback has reduced the temperatures and increased their
amplitudes (2.6-1.5Ma). The average temperature has continued to decrease and
the amplitudes to grow in the period of the relative equilibrium between warm
and cold climates (1.5-0.7Ma).
It was the turning point when the Arctic Ocean was covered by pack-ice
(0.7Ma). After that time, the long glacier (~90Ma), with ice sheets (60-75Mkm3,
27-33Mkm2) on all northern continents, and short interglacial (~10Ma)
periods have determined changes in the vegetation, land cover, amplitudes of the
level (120m) and temperature (~2
Celsius
degrees) of the
surface of the oceans. Periodical fluxes of heat have destroyed the ice-sheets
only for short periods of time.
The curve contains the solar system’s rhythms;
therefore, we can approximate and extrapolate the homogeneous part of this
oxygen-isotope series using harmonic components. Humanity must be ready for some
cooling-after 4ka and the next heavy cooling after a further 20ka. Global
warming will be able to reduce the amplitudes of the forced oscillations of the
climate by blocking the positive feedback in the next cycle of global cooling.
References:
Berry,
B. L. 1992. Basic systems of geosphere -
biospheric cycles and the prediction of natural conditions. Biophysics, Vol.37,
N3, 414-428, (in Russian), Pergamon Press Ltd. Printed in Great Britain, 1993,
328-341 (in English).
Berry,
B. L., 1998. Regularities of natural cycles, prediction of climate and surface
conditions. Hydrol. Process. 12, 2267-2278.
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