Odekon M. Encyclopedia of paleoclimatology and ancient environments

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The present-day global thermohaline conveyor is driven by

deep convection associated with the formation of the North

Atlantic Deep Water (NADW). The North Atlantic Current

carries warm and salty surface water to the northern North

Atlantic and Norwegian Seas where it cools and sinks to the

deep sea. Continuity of the ocean currents requires that

the southward cross-equatorial deep-ocean outflow of NADW

(about 16  10

1

) must be compensated by an equal

amount of northward flowing water in the upper layers. The

combined effect of these two opposite flows leads to large

(up to 1 PW) northward cross-equatorial heat transport in the

Atlantic Ocean.

Since sea water density depends on both temperature and sali-

nity, freshwater balance at the sea surface may have a strong

effect on ocean circulation and its associated heat transport

(Bryan, 1986). Modeling studies have revealed that the ocean

meridional overturning has strong sensitivity to relatively small

inputs of freshwater, which are capable of capping the

convection at key sites. Paleoceanographic data support these

simulations and indicate that changes in ocean overturning inten-

sity and pattern might have happened many times through geolo-

gic history, especially during glacial-interglacial cycles of the

Pleistocene.

The NADW dominance is challenged by a powerful south-

ern deepwater source. In the Southern Ocean, chilled surface

water descends to the bottom and forms the ocean’s densest

water mass – the Antarctic Bottom Water (AABW). The com-

petition between NADW and AABW leads to unstable meri-

dional overturning characterized by rebounds on centennial to

millennial time scales. The idea of a bipolar seesaw has been

invoked to explain the oscillations of meridional overturning

by NADW-AABW wrestling (Broecker, 1998).

Numerical simulations offer an ocean seesaw scenario

explained in Figure H2. Present-day overturning is driven by

a relatively strong NADW formation instigating a strong north-

ward overturning pattern in the Atlantic Ocean, as shown

in Figure H2a. A glacial overturning pattern, e.g., during the

Last Glacial Maximum, is a reduced and shallowed version

of the present-day pattern, with NADW reduced yet still func-

tioning (not shown in Figure H2). After a glacial termination,

Figure H1 Simplified scheme of radiative balance and compensating heat transport in the ocean and atmosphere.

Figure H2 Schemes of water mass layering and overturning

structure; (a) present-day mode of overturning; (b) northern

meltwater event; (c) southern meltwater event. Direction of

cross-equatorial oceanic heat transport is shown by arrows above

each scheme (from Seidov et al., 2001).

408 HEAT TRANSPORT, OCEANIC AND ATMOSPHERIC

a post-glacial iceberg armada from a collapsing ice sheet

surged into the northern North Atlantic. Melting of the icebergs

created a freshwater layer that may have capped NADW forma-

tion in key convection areas, shown as the northern low surface

salinity impact in Figure H2b. Paleoclimate proxies, including

ice-rafted debris, suggest that such freshwater impacts, some

known as Heinrich events, have indeed happened and might

have caused great reductions in NADW formation. As NADW

subsided, stronger AABW allowed the southward cross-

equatorial heat transport in the Atlantic Ocean (Figure H2b).

The heat surplus in the Southern Ocean warmed surface water

in the Southern Ocean and sea ice there began to melt. Fresh-

water from melting ice (shown as a southern low salinity

impact in Figure H2c) then slowed AABW formation, with

the North Atlantic Ocean’s surface water concurrently be-

coming colder because of southward rather than northward

cross-equatorial heat transport.

The northern surface waters became colder and at some

point dense enough to restore or even overshoot NADW for-

mation (Figure H2c), followed by a seesaw-cycle repeat.

Oceanic heat transport is also thought to be a crucial ele-

ment for climate change on geological time scales of millions

of years and longer. Because of continental drift, the sea-land

distribution has been changing throughout geologic history.

The ocean circulation is sensitive to continental geometry and

position, especially to opening and closing of major oceanic

gateways, such as the Drake Passage, Indonesian Throughflow,

Bering Strait, etc. One of the explanations of past warm cli-

mates, e.g., during the Cretaceous, is that both polar areas were

open oceans.

Our knowledge of the ocean-atmosphere interactions is not

yet complete. Improving this knowledge is essential for under-

standing past, present, and anticipated future climate change.

For that reason, more research effort is still needed to observe

and model heat transport in the ocean and atmosphere.

Dan Seidov

Bibliography

Broecker, W., 1991. “The great ocean conveyor.” Oceanography, 1,79–89.

Broecker, W.S., 1998. “Paleocean circulation during the last deglaciation:

A bipolar seesaw?” Paleoceanography, 13,119–121.

Bryan, F., 1986. “High-latitude salinity effects and interhemispheric ther-

mohaline circulations.” Science, 323, 301–304.

Peixoto, J.P., and Oort, A.H., 1992. Physics of Climate. New York: Amer-

ican Institute of Physics.

Seidov, D., Haupt, B.J., Barron, E.J., and Maslin, M., 2001. “Ocean

bi-polar seesaw and climate: Southern versus northern meltwater

impacts”. In Seidov , D., Haupt, B.J., and Maslin, M. (eds.), The oceans

and rapid climate change: Past, present, and future. Washington, D.C.:

AGU, pp. 147–167.

Trenberth, K.E., and Caron, J.M., 2001. “Estimates of meridional atmo-

sphere and ocean heat transports.” J. Climate, 14, 3433–3443.

Cross-references

Antarctic Bottom Water and Climate Change

Climate Change, Causes

Heinrich Events

Ice-rafted Debris (IRD)

Last Glacial Termination

North Atlantic Deep Water and Climate Change

Paleocean Modeling

Paleoceanography

Sun-climate Connections

Thermohaline Circulation

HEINRICH EVENTS

Introduction

Heinrich (1988) first reported on the occurrence of six layers

with high ice-rafted detritus (IRD) concentrations within the

last glacial cycle, and they have been dubbed Heinrich layers

since correlative layers were discovered in marine core

DSDP609 and in the Labrador Sea in the North Atlantic Ocean

(Bond et al., 1992; Broecker et al., 1992; Andrews et al., 1994).

The six IRD layers can be correlated across the North Atlantic

(Figures H3 and H4). The high percentage of IRD in Heinrich

layers is due to a high IRD flux in four of the six Heinrich

layers over the last 60 kyr, namely H1, H2, H4 and H5

(Figure H5 ). These detrital carbonate-bearing Heinrich layers

(Bond et al., 1992; Andrews et al., 1994) appear to require a ser-

ies of repeated, anomalous, glaciological processes in or near the

Hudson Strait. They have razor-sharp bases, and thus must have

had extremely sharp onsets. Broecker et al. (1993) made a

detailed assessment of H1 and H2 from DSDP core 609. Their

results emphasize the decline in numbers of foraminifera during

the Heinrich events within the IRD belt and the change in the

slope of the

C age versus depth across these intervals. Although

overall foraminifera abundance is low, shells that are found are in

good condition, so that it is not a question of preservation. As

well as can be recorded in marine sediments, Heinrich layers

occur within the coldest parts of this record. These Heinrich

layers are rapidly followed by dramatic warm intervals.

Heinrich layers H3 and H6 are different from the other

Heinrich layers (Figure H5). For example, they show only a mod-

est increase in flux (McManus et al., 1998) and in the number of

lithic grains per gram (Bond et al., 1992, 1993) despite their

high %IRD. Gwiazda et al. (1996) concluded that H3 and

H6 were not really ice-rafting events, but instead were low

foraminifera intervals, which would account for the high %IRD.

Provenance

The provenance of Heinrich layers H1, H2, H4 and H5 within

the IRD belt is very distinctive and hence can be mapped by

any number of geochemical measurements, as well as magnetic

susceptibility (Grousset et al., 1993; see Figure H5 ) and detrital

carbonate content (Bond et al., 1992). The data that have been

collected reveal a remarkably complete story of the provenance

of the Heinrich layers (Hemming, 2004). Nd isotope com-

positions of bulk terrigenous detritus and Pb isotope composi-

tions of individual feldspar grains reveal an Archean source

area for the Heinrich layers. Furthermore, the Pb isotope com-

positions of individual feldspar grains and

Ar/

Ar ages of

individual hornblende grains indicate a profound Paleoprotero-

zoic metamorphic overprint on the Archean terrain. The pre-

sence of detrital carbonate grains, organic geochemistry, clay

mineralogy, and K/Ar and Rb/Sr ages of the fine fractions also

reveal a substantial sedimentary contribution to the layers. The

entire spectrum of provenance observations for the H1, H2, H4

and H5 layers is consistent with a derivation from near the

Hudson Strait.

In the eastern North Atlantic, events H3 and H6 have com-

positions that are distinct from those of H1, H2, H4, and H5.

Using Pb isotope compositions of composite feldspar samples,

Gwiazda et al. (1996) found that H3 and H6 resemble ambient

sediment in V28–82, suggesting a large European source

HEINRICH EVENTS 409

Figure H3 Ice rafted detritus data for North Atlantic sediment cores with Heinrich layers. Most of the data are % of lithic grains in

the >150 mm fraction; however the data from ME69-17 (Heinrich, 1988) is % of lithic grains in the 180–3,000 mm fraction. Also shown is the record

of number of lithic grains >150 mm per gram of dry sediment from core V28–82. Map shows the location of the cores. Data sources are: for

CH69-K09 (Labeyrie et al., 1999), V23-14 (Hemming and Hajdas, 2003), SU-9008 (Grousset et al., 1993), V28–82 (Gwiazda et al., 1996; Hemming et al.,

1998; McManus et al., 1998), DSDP609 (Bond et al., 1992; Broecker et al., 1992), ME69-17 (Heinrich, 1988).

410 HEINRICH EVENTS

contribution, which agrees with the conclusion of Grousset

et al. (1993). As mentioned above, H3 and H6 seem to be

low foraminifera intervals rather than major ice-rafting events.

These conclusions are consistent with other observations

around the North Atlantic. Although Heinrich layer H3 appears

to be a Hudson Strait event (Grousset et al., 1993; Bond and

Lotti, 1995; Rashid et al., 2003), it does not spread Hudson

Strait-derived IRD as far to the east as the other Heinrich

events (Grousset et al., 1993). The map pattern of Sr isotope

data from H3 shows a striking pattern of decrease in

Sr/

nearly perpendicular to the IRD belt (Hemming, 2004), consis-

tent with a mixture of sediments from the Labrador Sea ice-

bergs with those derived from icebergs from eastern

Greenland, Iceland and Europe.

Chronology and duration of the Heinrich layers

Constraining the chronology and duration of the Heinrich

layers is critical to understanding their origin as well as their

role in global abrupt climate change. The duration of Heinrich

layers has been estimated by the difference in

C ages across

Heinrich layers, particularly H1 and H2 (Bond et al., 1992,

1993), as well as by measurements of sediment flux by the

230

method (Francois and Bacon, 1994; Thomson et al.,

1995; McManus et al., 1998).

The ages of Heinrich layers H1 and H2 are reasonably cer-

tain based on radiocarbon measurements, but estimations of

their duration are compromised by the events themselves

because they represent a large sediment flux increase (Manigh-

etti et al., 1995). Within the IRD belt, the estimated age at the

base of the layers is a maximum due to capping of the biotur-

bated layer by the Heinrich layer. The estimated age at the

top is a minimum due to bioturbation after the events. Addi-

tionally, the likelihood that Heinrich events are associated with

major deep-ocean circulation changes (Vidal et al., 1997; Kis-

sel et al., 1999; Elliot et al., 2001, 2002) and thus changes in

the atmospheric radiocarbon content (Yokoyama et al., 2000;

Waelbroeck et al., 2001) means that it is uncertain how to inter-

pret the value of the radiocarbon measurements near these

events. Data published by Bond et al. (1992, 1993) for core

V23–81 give the best greatest density of data, but reveal age

plateaus above both H2 and H1. Published estimates of Hein-

rich layer duration range from 208 to 2,280 years. Taking the

best estimates, the average duration is 495 years and the stan-

dard deviation in this duration is 255 years (Hemming, 2004).

Precursor events

Understanding the origin of Heinrich layers relies on constrain-

ing the provenance of the layers themselves, and also in recon-

structing the events leading up to their occurrence, the so-called

precursor intervals (Bond and Lotti, 1995). Percentages of fresh

basaltic glass and hematite-stained grains, counted at high reso-

lution in several North Atlantic cores, vary on a 1- to 2-kyr

interval, and the pacing of petrological changes in IRD appears

to be similar to that of d

O in Greenland ice (inferred to be

a proxy of air temperature changes) (Bond and Lotti, 1995;

Bond et al., 1997, 1999). Bond and Lotti (1995) showed that

peaks in Icelandic glass and hematite-stained grain abundances

fall within the broad lithic peaks that encompass Heinrich

layers, and that they precede detrital carbonate peaks for

Heinrich layers H1, H2, H3, and H4 in cores DSDP609 and

V23–81 (see also Bond et al., 1999). Grousset et al. (2001)

showed a series of provenance changes that are consistent with

Figure H4 Map showing locations of cores with identified Heinrich layers. Simplified geological provinces are shown for reference. Map

template and the 250 mg cm

2

kyr

1

flux lines from 25–13 kyr are from Ruddiman (1977); Ruddiman’s “IRD belt” is shown for reference.

HEINRICH EVENTS 411

these observations. They found that during Heinrich layers H1

and H2 there appear to be sequential increases in volcanic

grains, quartz grains, and carbonate grains at core SU9009 in

the south-central part of the IRD belt. This observation of a

precursor with greater lithic grains of non-Hudson Strait source

suggested that the Laurentide Ice Sheet was not always respond-

ing to the same climate forcing as the Dansgaard-Oeschger (D-O)

cycles, or was doing so later than other ice sheets. Furthermore,

Vance and Archer ( 2002) have found that the provenance of

precursory intervals to H4 and H2 are not similar based on radio-

genic isotope studies of DSDP609 sediments.

One view of these precursors is that they simply represent

the IRD signals of D-O cool phases in the North Atlantic (Bond

et al., 1999; G. Bond, personal communication in 2002), and

their appearance before the Hudson Strait-derived detritus

means that the sea surface cooled prior to the input of Heinrich

layers. Icelandic glass is an important component in Iceland

Sea (Voelker et al., 1998) and Irminger Basin sediments

(Elliot et al., 1998; van Kreveld et al., 2000), and East Green-

land may be a significant source of hematite-stained grains

(Bond et al., 1999; van Kreveld et al., 2000).

Although there is contention about whether Heinrich layers

have correlatives in the Nordic seas (Fronval et al., 1995 and

Elliot et al., 2002 vs. Dowdeswell et al., 1999), it is clear that

the pattern is different. In the IRD belt, Heinrich layers are out-

standing IRD events while events in between are modest

although apparently correlative with Greenland cooling events

(Bond et al., 1993, 1999; Bond and Lotti, 1995). In contrast,

there is apparently an IRD event of equal magnitude for each

of the Greenland cooling events, although there is a larger flux

in general during the Last Glacial Maximum.

The key precursory events to Heinrich events may be pre-

served in Labrador Sea sediments. The recognition that the

carbonate-rich intervals in the Labrador Sea marine sediment

cores are approximately synchronous with Heinrich events

(Bond et al., 1992; Andrews et al., 1994) helped to explain the

source of the Heinrich ice armadas. However, in contrast to the

case in the open ocean, where icebergs are the major sediment

contributors, a large fraction of the sediment deposited near the

Hudson Strait is brought by meltwater. Hesse and Khodabakhsh

(1998) showed that the carbonate-rich layers near the mouth

of Hudson Strait differ in sedimentological character from the

Heinrich layers in the open ocean, and in particular are much

finer-grained. They described a series of facies: nepheloid-layer

deposits (or type I Heinrich layers), mud-turbidites (or type II

Heinrich layers), laminae of IRD (or type III Heinrich layers),

and fine suspended sediment and dropstones supplied by ice raft-

ing (type IV Heinrich layers). These facies are generally arranged

proximal to distal from the Hudson Strait, with type IV being the

character of Heinrich layers in the IRD belt. Clarke et al. (1999)

suggest that at Orphan Knoll site HU91-045-094 Heinrich events

are separable into two distinct depositional processes. Turbidite

sedimentation with high fine-grained carbonate concentrations

is followed by a brief interval of increased IRD. The observations

from the Labrador Sea suggest an interval where sediments

were derived from subglacial meltwater prior to the launching

of iceberg armadas to the North Atlantic.

Processes that may produce Heinrich layers

The timing of Heinrich events is in striking coincidence with

the pattern of climate fluctuations documented from ice cores

(Bond et al., 1993; Broecker, 1994). There is also good evidence

for a global, or at least Northern Hemisphere wide, footprint

(Broecker and Hemming, 2001; Hemming, 2004). Although

the mechanism that drives the events remains a matter of debate,

there is no doubt that they are spectacular examples of interac-

tions among Earth’s atmosphere, oceans and cryosphere. Most

of the individual studies of sites outside the North Atlantic ice-

rafting zone conclude that the Heinrich-correlated events are

caused by changes in winds; stronger trade winds in the tropics,

stronger winter monsoon winds in China (Porter and An, 1995;

Wang et al., 2001) and the Arabian Sea, stronger northerly winds

in the western Mediterranean. When compared to the ambient

glacial conditions, there appears to be a general pattern of ten-

dency for wetter (milder?) conditions along the western North

Atlantic margin during Heinrich events, and perhaps along

the eastern South Atlantic margin. In contrast, more extreme

cold/dry glacial conditions prevailed during Heinrich intervals

on the eastern North Atlantic margin and western Mediterranean.

The pattern of differences between Heinrich events and ambient

glacials, as well as the geographic distribution of sites that are

sensitive to Heinrich events versus D-O events, may provide

important clues as to the driving forces of these abrupt climate

Figure H5 Different measures of IRD in core V28–82. Note that the

Heinrich intervals defined by number of grains per gram do not appear

to be precisely correlated with those defined by %IRD. Additionally,

the intervals of high flux measured by

230

Th excess are smaller than

those defined by counts. The intervals of high magnetic susceptibility

are also smaller and appear to be offset from the flux peaks. These

records reflect at least four independent samplings of the core, so

partly the apparent offsets could be related to that. However, they are

too large to be entirely explained in this way. Data sources are: %IRD

and number of lithic grains per gram (Gwiazda et al., 1996; McManus

et al., 1998; Hemming et al., 1998), flux (McManus et al., 1998),

magnetic susceptibility (Greg Downing, unpublished data).

412 HEINRICH EVENTS

changes. The coincidence in timing with the D-O pattern and the

broad pattern of Northern Hemisphere correlations imply an

important climate connection to Heinrich events. The layers

themselves, however, reflect anomalous glaciological processes,

and proposed mechanisms for their origin are discussed below.

Three broad categories of proposed mechanisms for Heinrich

layers are reviewed by Hemming (2004): (a) catastrophic pur-

ging of the Laurentide Ice Sheet (MacAyeal, 1993) or episodic

activity of an ice stream in the Hudson Strait (Marshall and

Clarke, 1997), (b) jökulhlaups (Johnson and Lauritzen, 1995),

and (c) ice shelf breakup (Hulbe, 1997; Hulbe et al., 2004). All

appear to be capable of producing the first order features of the

Heinrich layers, including the large injection of fresh water into

the North Atlantic Current (with volume depending on duration)

and the large volume of sediment deposited rapidly in these

events.

Hemming (2004) concluded that glaciological instability

(episodic purging) is the most likely explanation for the

Heinrich layers unless it can be demonstrated that these events

are much shorter than the estimated 500 year duration (essen-

tially instantaneous). Although it is conceivable that the

Heinrich layers represent instantaneous deposition as required

by the ice shelf and jökulhlaup scenarios, the data appear to

be more consistent with at least hundreds of year duration for

the layers. Further examination of hydrographic changes in

the North Atlantic may provide additional constraints on the

ice-derived water volume by documenting the mixed layer

thickness. Additionally, further examination of detailed sedi-

mentology and hydrography proxies in the Labrador Sea pro-

vides constructive ways to decide among the proposed

possibilities.

Summary

Heinrich layers are spectacular IRD deposits in the North Atlantic

that resulted from massive discharges of icebergs from the Lauren-

tide Ice Sheet through the Hudson Strait. They are clearly linked to

dramatic climate shifts in the Northern Hemisphere. Detailed stu-

dies of the interval containing H1 through H4 in the IRD belt have

demonstrated a strong connection between the timing of Heinrich

layers and the pace of climate variability in the North Atlantic.

More work is needed in the Southern Hemisphere in order to eval-

uate whether or not an inter-hemispheric correlation truly exists at

the times of Heinrich events.

Much effort has gone into characterizing the Heinrich events

in the North Atlantic and in identifying potentially correlative

climate events globally, and from this effort a picture is emer-

ging about the causes and effects related to them. They

occurred during extreme cold periods in the North Atlantic,

followed abruptly by dramatic warming trends. A large influx

of ice-derived water into the North Atlantic accompanied these

events, and it appears that a major reorganization of deep ocean

circulation was produced. What remains to be better under-

stood is whether the correlations were global or only Northern

Hemisphere-wide, and what was the ultimate driver of these

dramatic events.

Sidney Hemming

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Cross-references

Dansgaard-Oeschger Cycles

Deep Sea Drilling Project (DSDP)

Ice-Rafted Debris (IRD)

Millennial Climate Variability

Quaternary Climate Transitions and Cycles

HISTORY OF PALEOCLIMATOLOGY

The roots of paleoclimatology

This narrative will treat sequentially (i) the discovery phase

of the evidence (which still continues to this day) and (ii) the

causative and experimental phase. Short biographies of major

paleoclimatologists are presented in a companion piece.

Earliest observations

The elemental concept of climate change probably evolved in

documentary form in ancient Egypt (Nile Valley), Mesopotamia,

the Indus Valley and in China, where exceptional river floods or

extended droughts were experienced. Decadal to century-long

variations in the amplitudes of the Nile floods were more or

less paralleled by the fortunes of successive dynasties. Times

of drought and famine were socially more serious than episodic

experiences of excessive (summer) floods. Early chapters of the

Judeo-Christian Bible, notably Genesis, recounted the tale of

the forty-day rain, resulting in the “flood of Noah,” and the

subsequent recovery. Other oriental cultures contained compar-

able traditional sagas. It can therefore be a reasonable specula-

tion that the concept or idea of periodic climate change was not

only firmly established in human folklore, but also justified by

periodic reinforcement provided by anomalous climatic events

(as discussed below); see especially Ryan and Pitman (1999).

During the last 10,000 years or so, climatic events have

affected human history on various scales, evidence for which

is now being uncovered with increasing frequency. The role

of external events, large or small, as causative factors in human

history, thus became a central feature in Aristotelian thinking,

and this approach tended to dominate “natural history” for the

next two millennia (Schramm, 1963). For example, the devel-

opment of huge pro-glacial lakes across North America during

the retreat of the Laurentian Ice Sheet was accompanied by iso-

static crustal rebound that eventually tilted the lakes seawards,

resulting in great floods of freshwater that spread out and even-

tually diluted adjacent ocean surfaces, causing paleoclimatic

crises with global repercussions. This may have contributed

to universal flood mythology.

Another single-event phenomenon was the drowning

of the Euxinic freshwater lakes in the Black Sea region when

the postglacial sea-level rise surpassed the threshold sill

of the Bosporus (Zenkovitch in Fairbridge, 1966, p.146). Recent

414 HISTORY OF PALEOCLIMATOLOGY

oceanographic exploration here has disclosed abundant evidence

of the former littoral, its fauna and human inhabitants (Ryan and

Pitman, 1999).

From a historical point of view, the rejection of catastrophic

hypotheses illustrates the innate conservatism of geologists

raised on a philosophy of Lyellian uniformitarianism (see

discussion, below). The eventual acceptance of such “outra-

geous” hypotheses has gradually led to a modified philosophy

of neocatastrophism.

Dawn of reason

Even prior to the time of Lyell (1797–1875), gradual build-up

of an anti-catastrophic and anti-miracle camp had begun. By

the eighteenth century, observations could often be supplemen-

ted by chemistry and geological fieldwork, and the latter pre-

sented the endless paradoxes of paleoclimatology (although

this term did not emerge until the twentieth century). At first,

the observers were like the hunter-gatherers of anthropology.

They simply explored. They started recording their observa-

tions on maps. Specialized concepts like petrology, stratigra-

phy, structure, mineralogy and paleontology emerged only in

the early nineteenth century. The observers of the eighteenth

to early nineteenth centuries were in two categories: (i) the

gentlemen-traveler, i.e., personages with “private funds” who

explored the world out of curiosity; and (ii) the commercially

funded people who were “mission-oriented,” searching specifi-

cally for resources such as coal or metallic minerals such as

gold, silver, iron, copper, zinc and lead; or engineer-trained,

who were planning canals or water-supplies. Those observers

who asked questions about the climatic conditions indicated

by this or that proxy at the time of its formation had both

leisure and literacy. An early discussion of scientific questions

was by Emanuel Swedenborg (1688–1772), the Swedish

scientist and theologian, who attributed elevated shorelines to

progressive desiccation of the world ocean following the Bibli-

cal flood (see further, below).

Oddly enough, the people asking questions were frequently

members of the clergy, who were not only literate but whose

duties called for considerable traveling. Thus, Nicolaus Steno

(Stensius; 1638–1686), the “father of stratigraphy,” although

trained in the flat terrain of Denmark, spent most of his (theo-

logical) career in northern Italy, where he found time to accu-

rately observe and record the stratification and structures of

rock formations.

The scientific approach

The earth-science historian Schwarzbach (1963, 1974) recog-

nized Robert Hooke (1635–1703), the English physicist, as

the first scientist in paleoclimatology. He observed giant turtles

and oversized ammonites in the Portlandian (uppermost

Jurassic) of Dorset in England and concluded that they indi-

cated a once warmer climate. This he believed could only be

explained by a shift in the Earth’s axis.

Another i maginativ e pioneer was George L. Lecl erc,

Conte de Buffon (1707–1788 ), a celebr ated French natural

scientist. In his book “Epoques de la Nature” (1778),

Buffon described the gradu al cooli ng of a once-molten

Earth, a cooling that began at the poles. Formerly warm

temperatures at high latitudes were demonstrated by discov-

eries of large mammal remains, such as elephants and rhino-

ceroses, in these regions; such creatures are o nly f ound in

warm climate s today.

Then came Thomas Jefferson (1743–1826), third president

of the United States, who had also served as ambassador to

France and had become acquainted with Buffon. In his book

“Notes on the State of Virginia” (1785), Jefferson discussed

the discovery of fossil mammoth bones in what he regarded

as anomalistically high latitudes. He believed this could possi-

bly be explained by a change in the angle of the Earth’s eclip-

tic, and thus the tilt of the spin axis that controls the annual

distribution of the seasons. At present, the Southern Hemi-

sphere summer coincides with the Earth’s closest approach to

the Sun and the Northern Hemisphere summer comes when

they are farthest apart. About 9,000 years ago, the northern

summer came when the Earth’s orbit was closest to the sun,

so that mid-latitude mean summer temperatures were 2–3



warmer than today. The question of the mammoths in North

America could alternatively be explained by a change in the

creatures’ preferred habitat, a choice also considered (and

favored) by Jefferson.

The classic “gentleman-scientist-traveler” was Alexander

von Humboldt (1769–1859), who became the most famous

German earth scientist of the nineteenth century, notably for

his work in South America. He also lived for nearly 20 years

in Paris and thus had the good fortune to gain access to its

scientific libraries and to contemporary naturalists and thinkers

like Buffon. To begin with, in 1799, however, he succumbed to

A. G. Werner’s “Neptunian” concept of water-laid granites and

basalts, a false idea, albeit contributing to a once warmer Earth.

Later, after observing active volcanoes, he was probably the

first to recognize the potential influence of ash and dust clouds

on cooling of the climate (1823).

Idea of climate cycles

The classic concept of climatic cycles is probably that attribu-

ted to Joseph who was a member of the Israelite community

in the Egypt of the New Kingdom, perhaps around the four-

teenth century

BC. Joseph (in the scriptures) warned of 7 years

of bounty followed by 7 years of lean conditions. The message

was clear: climates fluctuate, so, take care and plan ahead!

Egyptological data include evidence of high-water marks (car-

bonate crusts) on temple columns, alternating with signs of

erosional dissection in Nile terraces, which point to times

when the flow was sluggish. Papyrus descriptions can now be

confirmed by geological surveys (Fairbridge, 1962).

Systematic measurement of Nile flood cycles was initiated dur-

ing the Moslem era (

AD. 610), with many centuries of accurate

data. Both short and long cycles have been identified (Hassan,

1981), which reflect monsoonal rainfall, mainly in the Ethiopian

headwaters of the Blue Nile. Spectrum analysis (Currie, 1995)dis-

closes both solar (11 years) and lunar (18.6 years) periodicities.

The first discussion of elevated shorelines (around the Baltic)

appears to have been by Emanuel Swedenborg (1688–1772),

mentioned above, who attributed them to traces of former levels

accumulated or eroded during the progressive desiccation of the

world ocean after the Biblical flood. An experimental approach

was that of Carl Linneus (1707–1778), a Swedish professor from

Uppsala, jointly with Anders Celsius, the professor of physics.

Linneus was best known for his systematic biologic classifica-

tion (having introduced the structured nomenclature of biology

with species, genus, and so on). Together they made a remarkable

contribution to climatic history when they disproved the “Desic-

cation Theory,” which had been widespread in the eighteenth

century. The theory was formulated by the Bishop of Åbo (now

Turku, in Finland) and based on the gradual emergence of the

HISTORY OF PALEOCLIMATOLOGY 415

coasts of Scandinavia, which he and fellow-theologians inter-

preted as conclusive evidence for the Bible story of the Noachian

Flood and its subsequent recession. Linneus and Celsius devised

a practical experiment to test the Biblical Desiccation Theory.

Having heard that southern Sweden was emerging more slowly

than the northern part of the country, they decided on a summer

vacation on horseback and chiseled a series of water-level marks

along the coast. Each site was revisited annually for 10 years,

after which they announced their results. In the north around

the Gulf of Bothnia, the coast appeared to be rising at 6–8mm

a year, while in the south, the Baltic shore was progressively

sinking; in places it was even negative (the water marks were

submerged). A desiccation of the world ocean would be uni-

form, but relative motion must reflect motion of the Earth’s

crust. This was probably the first practical experiment in both

crustal change and paleoclimatology. (However, they did not

perceive the connection to isostatic rebound due to removal

of the former ice load [Ed]).

Anders Celsius (1701–1744), the Swedish physicist and

astronomer at Uppsala at the same time as Linneus, was distin-

guished for his early observations of the aurora borealis (1716–

1732). Besides helping to measure the arc of the meridian in

Lapland (with colleagues from the French Academy of

Science, in 1736), he became known for developing the centi-

grade scale, later known as the “Celsius scale” for thermo-

meters. Accurately calibrated instruments were distributed to

the physics departments of all major universities. For the first

time, temperatures could be measured quantitatively.

In connection with the Linneus-Celsius experiments should

be mentioned the experience of Baron Christian Leopold von

Buch (1774–1853), a famous German geologist who had been

a fellow student with von Humboldt at the Freiberg Mining

Academy in Saxony. He made extensive trips by boat around

northern Norway, as well as in the Baltic. Von Buch confirmed

that the coast was indeed rising at Åbo, as was most of Scandi-

navia. Northern Norway, exposed to severe storm waves of the

North Atlantic, is subject to spectacular coast erosion. The

crustal uplift in northern Norway, however, created a succes-

sion of emerged benches in the form of a staircase. These dra-

matic landforms are repeated along the coast for more than

1,000 km. In 1810, Von Buch attributed the uplifting not to

cyclical climate factors but to pulsatory magmatic causes, such

as he had seen operating in the Canary Islands and other volca-

nic regions. (The glacioisostatic explanation for the uplift had

to wait for over one hundred years: see below.)

Reusch, in 1894, coined the term “strandflat,” for the wide

shore platforms. However, storm waves were not responsible

because shore erosion is also found on the inner sides of fjords.

To explain them, Nansen (1922) proposed a two-stage process:

(i) frost action at or above sea level, followed by (ii) freezing

and transport of the debris by floating ice. First observations

in Quebec by Lyell helped his drift theory (see below). Traces

of “fossil” strandflats and ice-transported boulders are seen on

the Channel coasts of England and France, and as far south

as northwest Spain (Fairbridge, 1977).

Could cyclical processes be triggered extraterrestrially? The

idea that the Sun might have something to do with climatic

events was to tread on delicate ground. When Galileo Galilei

(1564–1642) first observed sunspots, it implied to some theolo-

gians an imperfection in the face of God’s creation, the Sun,

and that was anathema. Astronomy led nevertheless to the idea

of predictable cycles. When Sir Edmond Halley (1656–1742)

successfully anticipated the return of his eponymous comet in

1758 (from earlier orbits in 1531, 1607, and 1682), the case

was established. The comet returned again in 1835, 1910 and

1986. He also laid the foundations for the new science of geo-

magnetism, which eventually helped to link endogenetic forces

with paleo-climatology. Later, Sir William Herschel (1738–

1822), when astronomer-royal of England, hinted that not only

did the sunspots fluctuate in a cyclical manner, but that they

might also relate to some climatic fluctuations that could affect

the price of wheat.

Systematic observations of sunspots were begun in 1826 by

an amateur astronomer, S. H. Schwabe, of Dessau, Germany,

who announced a roughly 10-year cycle in 1843. At that time,

Sir Edward Sabine had been monitoring geomagnetic fluctua-

tions in Canada and found a similar variation, even hinting at

“a common cause.” This was also suggested independently in

1852, by R. Wolf and A. Gautier, in Switzerland and France,

respectively, and by R. C. Carrington in 1860, in England.

A century of controversy about Sun-climate relations has

followed. An abundant literature accumulated over the decades,

summarized in “Sunspot Cycles” (Schove, 1983). Today, the

concept of a solar forcing cycle is beginning to be recognized,

but the “how” and “why” are still elusive (e.g., Bond et al.,

2001; Shindell et al., 2001; Rind, 2002). Systematic measure-

ment of temperature opened the door (very gradually) to the

idea of climatic cycles. This practical step was made possible

by Celsius in the early eighteenth century, and two centuries

later came the first analysis of an instrumental temperature time

series (which had been assembled by the Dutch meteorologist

Labrijn during World War II) that clearly displayed climate

cycles (Fairbridge, 1968, p.210).

Labrijn’s time series disclosed temperature cycles corre-

sponding to the 22-year solar magnetic reversals and radiation

fluctuations. These observations applied only to the North

Atlantic-European area covered by the temperature recordings

initiated by Celsius, but they opened the way to some twentieth

century thinking.

The existence of that 22-year cycle was later confirmed by

Schuurmans (in Flohn and Fantechi, 1984). The cycle was

further strengthened when small errors caused by the urban

heating effect were skillfully removed in a 250-year study of

Stockholm temperatures by Anders Moberg (1995). The statis-

tical procedure that made Labrijn’s study so impressive used

the mean summer months (June, July, August) minus the mean

winter months (December, January, February) (3-month values)

to create an oceanicity/continentality record.

One clue to solar-climatic relationships lies in the Moon. The

role of the Moon in weather cycles has long been established in

folklore, for better or worse. In science, George Schübler a pro-

fessor of physics at the University of Tübingen, Germany, pre-

sented a paper in 1836 containing statistical analysis of his

60 years of systematic measurements of rainfall, which disclosed

the 18.6 years lunar nodal cycle (see: “Earth-Moon system –

dynamics” in Shirley and Fairbridge, 1997). Also worth men-

tioning is a fifteenth century agronomy text published in Italy

that pointed out the advantage in seeding time because of the

rainfall indications of the 18.6 years cycle. Sir Arthur Schuster

of Manchester (U.K.), known for his invention of the time-series

periodogram, published on the lunar and solar periodicities in

earthquakes (1897) and on the influence of planets on sunspot

formation (1911). In the late twentieth century, R. G. Currie dis-

closed lunar cycles in practically all geophysical and climatic

time series, not least the nearly 1,400 years’ record of the Nile

floods (Currie, 1995).

416 HISTORY OF PALEOCLIMATOLOGY

William Gilbert’s (1544–1603) pioneering discoveries in

geomagnetism eventually led to an understanding of the aurora

borealis and later the aurora australis as expressions of the

Earth’s magnetic field in the face of an initially mysterious

solar force. A comprehensive review of the history of this sub-

ject was done by Siscoe (1980), establishing their correlations

with sunspot cycles, but he set aside specific linkage with the

solar wind and the geomagnetic field.

Scientific observations of the aurora and the geomagnetic

field were begun in Scandinavia in the ninteenth century.

Because of the high latitude, the common folk of Norway

and Sweden had been observing these phenomena for many cen-

turies. Country pastors recorded many sightings and these were

analyzed by two distinguished scientists Nils Ekholm and Svante

Arrhenius (a meteorologist and a geochemist) in a publication of

the Royal Swedish Academy of Science. They identified both

the 11-year solar cycle and the 18.6-year lunar cycle, as well

as their climatic associations (Ekholm and Arrhenius, 1898).

Today, a century later, this seminal paper is never cited and these

relationships are still very little understood.

Popularization of paleoclimatology

Popularization of scientific thought became the fashion in early

nineteenth century Europe and North America. Hugh Miller

(1802–1856) made fossil discoveries that became a basis for

paleogeographic and paleoclimatic reconstructions in his writ-

ings. They proved to be immensely exciting for his non-technical

audiences.

A Swiss naturalist and professor of botany in Zürich,

Oswald Heer (1809–1883) was the first to discover evidence

(fossil leaves and fruit) of a warm climate during an interglacial

interval in the Alps. Heer’s epoch-making book “The Primeval

World of Switzerland” (2 vols., 1865, transl. 1876) was very

widely read and helped establish him as one of the founders

of paleoclimatology and of paleogeography. By assuming that

fossilized plants could be used as analogues for modern ones,

the present-day habitats (in terms of temperature and precipita-

tion) could be used for calculating proxy temperatures and rain-

fall. Bearing in mind that during the early Cenozoic the Tethys

seaway was open to the Indian Ocean and Pacific, Heer’s cal-

culation of a mean warming of 7



F (3.5



C) at that time was

“probably the best approximation” (Brooks, 1949). Intervals

of the warm paleoclimates in the Cenozoic would appear to

have been achieved by three synergetic global paleogeographic

factors: (i) open Tethyan seaway worldwide; (ii) limited oro-

graphic blocking; (iii) restricted Antarctic mountain glaciers

(Fairbridge, 1961).

Uniformitarianism and actualism

The Scottish “gentleman-farmer” James Hutton (1726–1797)

was the first to examine climate as a global phenomenon,

although this work was largely eclipsed by his revolutionary

role in geology as a whole. His original “Theory of the Earth”

(a paper to the Royal Society of Edinburgh, 1785) endeavored

to set out the natural laws by which the dynamics of Earth his-

tory could be explained. To explain erosion of the Earth’s sur-

face, he introduced the idea of climate and the atmosphere, and

the year before (1784) he outlined his “Theory of Rain.” This

included a global review of climate, recognizing that atmo-

spheric humidity was the key to rainfall, and that precipitation

must occur when a warm air mass encounters a cooler one.

An invaluable summary of his ideas was published by John

Playfair in 1803 (see also below). Hutton contributed funda-

mentally to the eighteenth century concept that eventually came

to be called “uniformitarianism.” Lyell (1830) reasoned that

the “laws of nature” were immutable and permanent, which

permits one “to reason by analogy.” The standard aphorism

is: “the Present is the Key to the Past.” Whereas Nicolaus

Steno (1631–1687) discovered the idea of sequence, or time-

ordering, it was Hutton, after his famous discovery of a strati-

graphic unconformity, who realized that geological processes

should not be seen as a continuum but as subject to periodic

upsets or revolutions. Thus, the concept of a cycle of events or

processes emerged, to be further consolidated by Lyell in his stra-

tigraphic sequences. It was not, however, until the late twentieth

and early twenty first centuries that those sequences became

locked into a paleoclimatologic framework, when Milutin

Milankovitch (1879–1958) and Frederick Zeuner (1905–1963)

developed, respectively, astronomic forcing potentials, with their

stratigraphic representation.

A slightly different concept of uniformitarianism and terminol-

ogy had already emerged in Russia and eastern Europe, the word

“actualism” being coined by M. V. Lomonosov (1711–1765),

Russia’s “Father of Science.” As generally conceived, actualism

was practical methodology. It was therefore an investigative tool

based on laws derived from quantitative models and would justify

predictions as well as past events. In contrast, uniformitarianism

was more a philosophy of “geohistory,” subject to many potential

dangers of interpretation (Albritton, 1975). Today, the actualistic

approach is preferred.

In northern Germany the late eighteenth century was marked

by frequent observations of exotic boulders (mainly granite or

ancient limestones), called “Findlinge” (foundlings). Both

country people and geologists recognized they did not belong

in the local suite of outcrops. In folklore, they were generally

attributed to relics of the Biblical Flood. In 1802, John Playfair

(1748–1819), the Scottish geologist and follower of James

Hutton, appreciated that these blocks or boulders were similar

to others in the peripheral valleys of the Alps, where local

scientists attributed them to glaciers that were formerly more

extensive.

The glacial theory

The “glacial theory” was to become one of the scientific world’s

preoccupations during the first half of the nineteenth century.

Good summaries are to be found in Flint (1971), Schwarzbach

(1963, 1974) and Imbrie and Imbrie (1979, 1986).

The glacial theory received a significant spurt when, in

1817, the Swiss Natural Science Society announced a competi-

tion for members to demonstrate the former extension of the

Alpine glaciers. This was rewarded in 1822 by a key lecture

delivered by the Swiss engineer, Ignatz Venetz (although it

was not published until 1833). The theme was taken up enthu-

siastically by geologist Louis Agassiz (1805–1873) who even-

tually came to teach at Harvard University.

Scandinavia was also a potential source of erratic blocks,

but the glaciers there were smaller and less known than those

of Switzerland. Nevertheless, in 1824 Jens Esmark of Denmark

(1762–1829) proposed a former glacial source for northern

Europe’s widespread erratics.

At this point in history, the “establishment” struck back,

through the powerful and colorful pen of the Reverend Dean

William Buckland (1784–1856), first professor of geology at

Oxford, and president of the Geological Society of London in

HISTORY OF PALEOCLIMATOLOGY 417