Ice Ages and Interglacials: Measurements, Interpretation, and Models

420 Pages·2012·9.46 MB·English

by  Donald Rapp (auth.)

Ice Ages and Interglacials
Measurements, Interpretation, and Models
(Second Edition)

Donald Rapp
Ice Ages and
Interglacials
Measurements, Interpretation, and Models
(Second Edition)
Published inassociationwith
PPrraaxxiiss PPuubblliisshhiinngg
Chichester, UK
Dr. Donald Rapp
South Pasadena
California
U.S.A.
SPRINGER–PRAXIS BOOKS IN ENVIRONMENTAL SCIENCES
ISBN 978-3-642-30028-8 ISBN 978-3-642-30029-5 (eBook)
DOI 10.1007/978-3-642-30029-5
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Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxi
List of abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii
1 Life and climate in an ice age . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Continental climates during the Ice Age. . . . . . . . . . . . . . . . . 1
1.2 The glacial world—according to Wally Broecker . . . . . . . . . . 8
1.3 Ice age forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.4 The Last Glacial Maximum (LGM) . . . . . . . . . . . . . . . . . . . 11
2 Variability of the Earth’s climate . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1 Factors that influence global climate . . . . . . . . . . . . . . . . . . 17
2.2 Stable extremes of the Earth’s climate . . . . . . . . . . . . . . . . . 21
2.3 The relation between ancient climates and CO concentration . . 26
2
2.3.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.3.2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.3.3 The transition from the Last Glacial Maximum (LGM) to
the pre-industrial era . . . . . . . . . . . . . . . . . . . . . . . 36
2.3.4 The Early Pliocene: 3 to 5 million years ago . . . . . . . . 49
2.3.5 The past 20 million years or so. . . . . . . . . . . . . . . . . 51
2.3.6 Initiation of Antarctic glaciation 34–33 million years ago 58
2.3.7 Peak warming around 40 million years ago . . . . . . . . . 60
2.3.8 60 to 40 million years ago . . . . . . . . . . . . . . . . . . . . 61
2.3.9 100 to 300 million years ago . . . . . . . . . . . . . . . . . . 66
v
vi Contents
2.3.10 Estimates of climate sensitivity based on CO and climate
2
in the Phanerozoic . . . . . . . . . . . . . . . . . . . . . . . . . 66
2.4 Continental drift and continental geometry as a factor in paleo-
climate change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2.4.1 Effects of continental geometry . . . . . . . . . . . . . . . . . 84
2.4.2 Evolution of glaciation near the South Pole (cid:2)34MYBP... 88
2.4.3 Effect of the Isthmus of Panama on NH glaciation in the
past 2,700,000 years . . . . . . . . . . . . . . . . . . . . . . . . 90
2.5 Ice ages in the recent geological past . . . . . . . . . . . . . . . . . . 95
2.6 Geological evidence of ice ages . . . . . . . . . . . . . . . . . . . . . . 97
3 Ice core methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.1 History of ice core research . . . . . . . . . . . . . . . . . . . . . . . . 105
3.2 Dating ice core data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
3.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
3.2.2 Age markers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
3.2.3 Counting layers visually . . . . . . . . . . . . . . . . . . . . . 113
3.2.4 Layers determined by measurement . . . . . . . . . . . . . . 116
3.2.5 Ice flow modeling . . . . . . . . . . . . . . . . . . . . . . . . . 120
3.2.6 Other dating methods . . . . . . . . . . . . . . . . . . . . . . . 122
3.2.7 Synchronizing the dating of ice cores from Greenland and
Antarctica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
3.2.8 GISP2 experience . . . . . . . . . . . . . . . . . . . . . . . . . . 123
3.2.9 Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
3.2.10 Flimsy logic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
3.3 Processing ice core data . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
3.3.1 Temperature estimates from ice cores . . . . . . . . . . . . . 127
3.3.2 Climate variations . . . . . . . . . . . . . . . . . . . . . . . . . 135
3.3.3 Trapped gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
4 Ice core data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
4.1 Greenland ice core historical temperatures . . . . . . . . . . . . . . . 137
4.2 Antarctica ice core historical temperatures . . . . . . . . . . . . . . . 142
4.2.1 Vostok and EPICA data . . . . . . . . . . . . . . . . . . . . . 142
4.2.2 Homogeneity of Antarctic ice cores . . . . . . . . . . . . . . 144
4.3 North–south synchrony . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
4.3.1 Direct comparison of Greenland and Antarctica ice core
records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
4.3.2 Interpretation in terms of ocean circulation . . . . . . . . . 150
4.3.3 Seasonal variability of precipitation . . . . . . . . . . . . . . 151
4.3.4 Worldwide effects of changes originating in the NH . . . 152
4.4 Interglacials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
4.5 Data from high-elevation ice cores . . . . . . . . . . . . . . . . . . . . 157
4.6 Carbon dioxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
4.7 Sudden climate changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Contents vii
5 Ocean sediment data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
5.2 Chronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
5.3 Universality of ocean sediment data . . . . . . . . . . . . . . . . . . . 181
5.4 Summary of ocean sediment ice volume data . . . . . . . . . . . . . 182
5.5 Ocean sediment data and polar ice core data compared . . . . . . 184
5.6 Historical sea surface temperatures . . . . . . . . . . . . . . . . . . . 187
5.7 Ice-rafted debris . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
6 Other data sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
6.1 Devil’s Hole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
6.1.1 Devil’s Hole data . . . . . . . . . . . . . . . . . . . . . . . . . . 191
6.1.2 Devil’s Hole data and ocean sediment data compared . . 192
6.1.3 Devil’s Hole: Global or regional data? . . . . . . . . . . . . 194
6.1.4 Devil’s Hole data and Vostok data compared . . . . . . . 195
6.2 Speleothems in caves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
6.3 Magnetism in rocks and loess . . . . . . . . . . . . . . . . . . . . . . . 199
6.3.1 Magnetism in loess . . . . . . . . . . . . . . . . . . . . . . . . 199
6.3.2 Rock magnetism in lake sediments . . . . . . . . . . . . . . 200
6.4 Pollen records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
6.5 Physical indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
6.5.1 Ice sheet moraines . . . . . . . . . . . . . . . . . . . . . . . . . 202
6.5.2 Coral terraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
6.5.3 Mountain glaciers . . . . . . . . . . . . . . . . . . . . . . . . . 205
6.6 Red Sea sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
6.7 Influence of dust and iron . . . . . . . . . . . . . . . . . . . . . . . . . 207
7 Summary of climate variations . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
8 Overview of the various models for ice ages in the recent past (3MYBP to
present). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
8.2 Variability of the Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
8.3 The astronomical theory. . . . . . . . . . . . . . . . . . . . . . . . . . . 218
8.4 Volcanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
8.5 Greenhouse gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
8.6 Role of the oceans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
8.6.1 Glacial–interglacial cycles: the consensus view . . . . . . . 224
8.6.2 Sudden climate change: the consensus view . . . . . . . . . 228
8.6.3 Wunsch’s objections . . . . . . . . . . . . . . . . . . . . . . . . 231
8.7 Models based on clouds . . . . . . . . . . . . . . . . . . . . . . . . . . 236
8.7.1 Extraterrestrial dust accretion . . . . . . . . . . . . . . . . . . 238
8.7.2 Clouds induced by cosmic rays . . . . . . . . . . . . . . . . . 239
8.7.3 Ocean–atmosphere model . . . . . . . . . . . . . . . . . . . . 242
8.8 Models based on the Southern Hemisphere . . . . . . . . . . . . . . 244
viii Contents
9 Variability of the Earth’s orbit: The astronomical theory . . . . . . . . . . 247
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
9.2 Variability of the Earth’s orbit . . . . . . . . . . . . . . . . . . . . . . 250
9.2.1 Variability within the orbital plane . . . . . . . . . . . . . . 250
9.2.2 Variability of the orbital plane . . . . . . . . . . . . . . . . . 253
9.3 Calculation of solar intensities . . . . . . . . . . . . . . . . . . . . . . 254
9.4 Importance of each orbital parameter . . . . . . . . . . . . . . . . . . 255
9.5 Historical solar irradiance at higher latitudes . . . . . . . . . . . . . 259
9.6 Connection between solar variability and glaciation–deglaciation
cycles according to the astronomical theory . . . . . . . . . . . . . . 261
9.6.1 Models for ice volume . . . . . . . . . . . . . . . . . . . . . . 263
9.6.2 Review of the Imbrie model . . . . . . . . . . . . . . . . . . . 271
9.6.3 Memory model . . . . . . . . . . . . . . . . . . . . . . . . . . . 274
9.7 Models based on eccentricity or obliquity . . . . . . . . . . . . . . . 274
9.7.1 A model based on eccentricity . . . . . . . . . . . . . . . . . 274
9.7.2 The Mid-Pleistocene Transition . . . . . . . . . . . . . . . . . 276
9.8 North or south? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
10 The astronomical theory and data compared . . . . . . . . . . . . . . . . . . 281
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
10.2 Data and the astronomical theory compared. . . . . . . . . . . . . . 282
10.2.1 Direct comparison of the variability of peak solar inten-
sity with ice core data . . . . . . . . . . . . . . . . . . . . . . 284
10.2.2 The Imbrie ice volume model and ocean sediment data
compared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
10.2.3 Change in ice sheet volume and peak solar intensity
compared . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
10.2.4 Terminations of ice ages and origins of interglacials. . . . 296
10.3 Spectral analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
10.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
10.3.2 Spectral analysis of solar and paleoclimate data . . . . . . 315
10.4 Status of our understanding . . . . . . . . . . . . . . . . . . . . . . . . 320
11 Future prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
11.1 The next ice age (or lack thereof) . . . . . . . . . . . . . . . . . . . . 327
11.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
11.1.2 Orthodoxy in climatology . . . . . . . . . . . . . . . . . . . . 328
11.1.3 Effect of CO growth on global temperature . . . . . . . . 333
2
11.1.4 Other evidence on the role of CO . . . . . . . . . . . . . . 348
2
11.2 Ways of improving our understanding . . . . . . . . . . . . . . . . . 370
11.2.1 The need to depoliticize climate change . . . . . . . . . . . 370
11.2.2 Technical progress. . . . . . . . . . . . . . . . . . . . . . . . . . 372
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
Preface
The typical description of the past million years would be that the Earth has
experienced about 10 major periods of glaciation (ice ages) spaced at roughly
100,000-year intervals. This presupposes that ice ages are unusual departures from
normalcy.Actually,it appears asif the natural stateof theEarth during this period
was an ice age, but there were about 10 interruptions during which the climate
resembled something like today’s climate for perhaps 10,000 years or so. Each ice
age required several tens of thousands of years to develop to its maximum state of
glaciation.
During the Last Glacial Maximum, some 20,000 years ago, Canada and the
northern U. S. were blanketed by huge ice sheets up to 4km thick. In addition,
there was a large ice sheet covering Scandinavia that reached down into Northern
Europe. The Antarctic ice sheet was somewhat more full than today. Local glacia-
tions existed in mountainous regions of North America, Europe, South America,
andAfricadrivingthetreelinedownbyasmuchas700m(800minsomecases).The
temperature of Greenland dropped by as much as 20(cid:3)C, but the climate was prob-
ably only a few degrees colder than normal in the tropics. Conditions were very
harsh20,000yearsagoattheLastGlacialMaximum(LGM)whenanicesheetmore
than 2 miles thick pushed down from Canada into the northern U. S.
These ice sheets tied up so much of the Earth’s water that the oceans were as
much as 120m shallower. As a result, the shorelines of continents extended much
fartheroutthantoday.TheBeringialandbridgefromSiberiatoAlaskawascreated,
allowinganimalsandhumanstocrossfromonecontinenttotheother.Intheupper-
to mid-latitudes the climate was semi-Arctic and the flora shifted to tundra.
Humidity was reduced and much of the land dried out. The sharp temperature
discontinuity at the edges of the ice sheets generated violent winds that swept up
dust and dirt from dry regions, filling the atmosphere. This ice age began to wane
around 15,000 years ago and dissipated through a series of gyrating climate
ix
x Preface
oscillations, ending in the comparatively benign period that has lasted for the past
(cid:2)10,000 years called the Holocene.
A few geologists in the 19th century were perceptive enough to notice signs of
glaciation in rocks and geological formations and concluded that the Earth must
haveonce(atleast)beenheavilyglaciatedwithmassiveicesheetsthatgeneratedthe
markings and rock depositions that they observed. They eventually overcame the
initial resistance to this new (and shocking) concept in the geological community.
But, it was not until the 1970s that extensive studies of marine sediments (followed
by polar ice core studies in the 1980s and 1990s) demonstrated the existence,
amplitude, and recurrent chronology of multiple ice ages.
During the 19th century several scientists proposed that ice ages could have
resulted from the quasi-periodic variability of the Earth’s orbital parameters that
affect relative solar energy input to higher latitudes. As the theory goes, when
summersolarenergyinputtohighernorthernlatitudesdropsbelowacriticalthresh-
old, ice and snow can better survive the summer. Data acquired in the 20th century
suggestthaticesheetsslowlybegintoformovermanymillenniaatlatitudesroughly
in the range 60(cid:3)N to 70(cid:3)N. As the ice cover spreads, the albedo (reflectivity) of the
region increases, further adding to the cooling effect. Water increasingly leaves the
oceans and gets deposited in the process of building ice sheets, lowering the oceans
and extending shorelines. Since land has a higher albedo than the ocean, this pro-
vides further cooling. In regions adjacent to the ice sheets vegetation is inhibited,
adding still further to increased Earth albedo. As northerly regions cool, the con-
centrations of key greenhouse gases such as water vapor, CO , and CH decrease,
2 4
creating a worldwide cooling effect that converts the budding ice age into a global
phenomenon.Othereffectssuchaswidespreadduststormsandtheexpansionofsea
iceandmountainglaciersalsocontribute.Thus,therunawayexpansionoficesheets
developsovermanymillennia.JamesCrollformulatedtheconceptoftheSunacting
as a trigger for ice ages based on variations of the Earth’s orbit in 1875. In the first
several decades of the 20th century, M. Milankovitch quantified this theory by
carrying out extensive calculations by hand (no mean feat in the pre-computer
age). Nevertheless, in the absence of long-term data over many ice ages, the astro-
nomical theory remained an abstract concept. Furthermore, there were no credible
mechanistic models to describe how changing solar energy input to higher latitudes
could lead to alternating ice ages and deglaciations.
With the advent of marine sediment data in the 1970s, it became possible to
compare the astronomical theory with data over many glacial cycles. John Imbrie
was a pioneer in this regard. He built up a stack of ocean sediment data—which he
dubbed the ‘‘SPECMAP’’ stack—from several sites with the objective of reducing
noise and devised models to compare ice sheet volume (V) with solar variations. In
doingthis,hetunedthechronologyoftheSPECMAPstackusingsolarvariabilityas
aguide.Healsousedspectralanalysistoshowthatsomeoftheprominentfrequency
componentsinSPECMAPvariabilitywereinconsonancewithknownfrequenciesof
solar variation. From this, he concluded that the astronomical model explained
much of the ice age record—at least for the past (cid:2)650,000 years. However, there
seems to be some circular reasoning involved and one could construe his procedure