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conditions: precipitation-minus-evaporation budget, plus any
continental contribution (runoff, iceberg discharge, etc.).
Because salinity is also sensitive to this hydrological budget,
a good correlation is observed between both tracers (Craig
and Gordon, 1965; Figure O36). For this reason, the local com-
ponent of d
18
O variation has been coined the “salinity effect,”
in addition to the global “ice volume” effect. The d
18
O distribu-
tion is also modified by changes in the ocean circulation, by
mixing the different water masses and altering their isotopic
fingerprint. Table O3 sums up the different interpretations of
a sediment d
18
O signal.
The “ice volume” effect is related to the decrease of the
global oceanic mass M
0
during the growth of ice sheets with
a mean isotopic composition d
18
O
i
. At steady state, the conser-
vation of the
18
O mass between the remaining oceanic mass M
and the additional mass dM of the ice sheets reads:
M d
18
O
s
þ dM d
18
O
i
¼ M
0
d
18
O
s0
; ð3Þ
where the subscripts
s
and
i
stand for sea and ice sheet, respec-
tively, and 0 for the time before the growth of ice sheets. dM
is expressed relative to ocean mass because it is then compar-
able to the eustatic sea level change. The global oceanic d
18
O
variation (“ice volume effect”) is then:
d
18
O
s
d
18
O
s0
¼ dM=M d
18
O
s0
d
18
O
i
: ð4Þ
Figure O35 Isotopic stack over the past 900,000 years (after Bassinot et al., 1994), representative of the global ocean variations. Note the usual
inverted y-axis, so that an upward excursion corresponds to a warming, and conversely. The d
18
O values have been scaled so that the
record has an average of 0 (centered) and a standard deviation of 1. The marine isotopic stages (MIS) are numbered in bold: odd numbers for
warm stages, even numbers for cold ones.
Figure O36 Relationships between surface salinity and water d
18
O for the Atlantic and Pacific Oceans, due to the common dependence on the
hydrological cycle. Note also the highest values in the tropical Atlantic, due to a net transfer of vapor to the Pacific (GEOSECS data from O
¨
stlund
et al., 1987).
670 OXYGEN ISOTOPES
For the Last Glacial Maximum, the variation d
18
O
s
– d
18
O
s0
is
estimated directly from benthic foraminifera records (Labeyrie
et al., 1987) and pore water analyses (Schrag et al., 1996), with
a current consensus value ranging between 1 and 1.3%. Ice
sheet growth dM is estimated from changes in coral terrace
levels, and from modeling the ice sheet distribution and iso-
static rebound. It is equivalent to approximately 120–140 m
of sea level (thus, dM/M 130/4,000). These values are con-
sistent with a mean ice composition d
18
O
i
between 30 and
50% (Mix et al., 2001). All these estimates are biased; for
instance, the benthic foraminifera record approximates the
d
18
O
s
–d
18
O
s0
difference because the temperature of their deep
environment has changed. Thus, only the combination of these
different approaches is able to reduce the uncertainties in each
term in Equation 4. Over the Cenozoic, the past 65 million
years, the marine d
18
O record shows a consistent increase of
about 5 per mil (Figure O37), an amplitude too large to be
interpreted by the waning and waxing of ice sheets. This long
positive trend is interpreted as a global ocean cooling by 7
C
over the Eocene. Increasing steps around 33 Ma and 15 Ma
ago are interpreted as corresponding to the building up of the
Antarctic ice sheet (for a total of about 1.2%) and the Northern
Hemisphere ice sheet around 3 Ma ago (Zachos et al., 2001).
On longer timescales, reliable marine oxygen records are
difficult to produce because of the scarcity of sediments, and
because the likelihood that the sediments have been altered
and re-equilibrated under different environmental conditions
increases dramatically. A case study is provided by reconstruc-
tions of climatic conditions during the Cretaceous and Early
Cenozoic periods. Different proxies, including marine d
18
O,
point to a globally warmer climate, consistent with a higher
atmospheric CO
2
level, except in the tropics where interpreta-
tion of marine d
18
O records points to temperatures as warm
as today or even cooler. This contradiction seems to be due to
an alteration of the isotopic signal during diagenesis (Pearson
et al., 2001). Over the Paleozoic (timescale of hundreds of mil-
lions of years), isotopic data display an increasing isotopic
trend of 8%, but its origin could be a long term cooling,
a diagenetic alteration, or even an
18
O enrichment of the
global ocean, among other possibilities (Veizer et al., 1999).
Table O3 Basic interpretation of d
18
O signal recorded in biogenic sediments
Interpretation Main origin in variations of How to isolate it Original reference
Temperature Water temperature
(also: living depth, etc.)
Subtract the global ice signal,
assuming no local seawater change
Shackleton, 1967
Water d
18
O
Global component Ice sheet volume Assume no temperature change
(e.g., in benthic foraminifera)
Labeyrie et al., 1987
Local component Local hydrological balance
(“salinity effect”)
(also: water mass mixing)
Subtract the global ice signal plus
an independent estimate of
temperature change
Duplessy et al., 1991
Biological bias (“vital effect”) Non-equilibrium biogenic
fractionation (also: growth rate,
secondary calcification,
diagenetic exchange, etc.)
Isotopic measurements on living
organisms in known conditions
(collection with tows; culture)
Epstein et al., 1953
Figure O37 Trend of the deep ocean d
18
O over the Cenozoic (last 70 Myr), compiled from benthic records (Zachos et al., 2001). The close-up shows the
last 6 Myr. The measured d
18
O values have been adjusted to approximate the water value. The Deep Water Temperature (DWT) scale (right side) has
been calculated by considering a marine d
18
Oof1.2 before the appearance of ice sheets (before 35 Ma).
OXYGEN ISOTOPES 671
Still, positive excursions lasting tens of million years have been
contemporaneous with periods of cooling or large glaciations,
and seem to be of climatic origin.
Bias on the sediment d
18
O record
Comparisons have been performed between known environ-
mental conditions (temperature and water d
18
O) and the d
18
O
of living shells, from either tow fishing or aquarium cultures.
First, some species appear to calcify out of isotopic equilibrium
with water, possibly due to kinetic bias. Second, species live
at different depths and thus record different environmental
conditions. This is especially important for planktonic species
living in the mixed layer because of the strong vertical gradient
of temperature. In addition, organisms may migrate vertically
over several hundreds of meters, on a seasonal or daily basis.
Depending when the calcification happens, the exact depth
recorded by the d
18
O may be different to that of the usual living
habitat. Thus, interpreting a sediment d
18
O record requires a pre-
cise calibration on modern tests to know which conditions are
represented in terms of depth and season. Isotopic corrections
have been determined in order to estimate the correct environ-
ment; for instance, d
18
O measured from the foraminifera C.
wuellerstorffi is usually corrected by 0.64 per mil to be closer
to the value in equilibrium with deep water conditions. A good
review of these biases is provided by Wefer and Berger (1991).
Diagenesis may also alter the original isotopic signal. This
is especially true for aragonitic and high-magnesium calcitic
shells, because these minerals are not stable and recrystallize.
Low-magnesium calcitic shells, like those of foraminifera, are
not free of diagenetic alteration, which must be discarded by
a thorough examination and cleaning.
Other records: corals and speleothems
These carbonates, like sediments, record both the temperature
and the water d
18
O composition, with some possible offset to
the expected equilibrium value. In addition, they grow with
fine laminations that may be annual bands, as for corals, allow-
ing both a high-resolution sampling and a detailed chronology.
They can be well dated by counting the annual bands and
by
14
C and U/Th techniques. Subannual d
18
O measurements
on corals showed that oxygen isotopes record the seasonal tem-
perature, with some offset (Fairbanks and Dodge, 1979),
although changes in the isotopic composition of surface water
(linked to precipitation or river runoff) may explain part of
the variations. In the tropics, reef building species have
been shown to be especially useful for documenting ENSO
(El Niño-Southern Oscillation) variability in areas where either
temperature or precipitation change dominates the isotopic
signal (Cole et al., 1993). Because most reef-building corals
live in symbiosis with algae (zooxanthellae), they can only
grow within a restricted depth range, which makes them reli-
able records of sea level variations. Speleothems grow from
calcite precipitation when CO
2
-supersaturated water degasses.
Since this water comes, more or less directly, from precipita-
tion, the calcite d
18
O is strongly influenced by the factors
affecting the d
18
O of precipitation (see above), including the
local temperature. At mid-to-high latitudes, the positive corre-
lation between the d
18
O of precipitation and temperature
(Figure O33) is balanced by the negative effect of the tempera-
ture on the isotopic fractionation (Emiliani, 1971, note 23). At
low latitudes, if the precipitation d
18
O is under greater control
of the quantity of precipitation (Figure O33), the influence of
temperature may be amplified (Neff et al., 2001). Changes in
the marine d
18
O add to this complexity, making a quantitative
interpretation of a speleothem record not that straightforward.
Several records, d
18
O, d
13
C, growth rate, trace elements, etc., are
usually combined in order to decipher the origin of the signals.
One of the longest d
18
O records, from Devils Hole, Nevada,
covers more than half a million years (Winograd et al., 1992).
Global biogenic productivity estimated from oxygen
isotopes
Measurements of the isotopic composition of atmospheric oxygen,
O
2
, have shown an enrichment as compared to the ocean (Dole,
1935), by 23.5 per mil versus V-SMOW. This enrichment, called
the “Dole effect” (see Dole effect), is mainly determined by gross
biospheric fluxes, respiration and photosynthesis. Estimation of
Dole effect variations from measurements in air bubbles trapped
in glacial ice allows one to infer past changes in these fluxes. More
recently, Luz et al. (1999) exploited a mass-independent frac-
tionation of oxygen isotopes in the stratosphere to infer the global
biospheric productivity (i.e., gross production of O
2
by photo-
synthesis). Most chemical processes fractionate oxygen isotopes
according to their mass, in which case the fractionation of
17
O
to
16
O is around half that of
18
Oto
16
O (0.521, precisely). In
contrast, in the stratosphere, a series of reactions involving O
2
,
O
3
and CO
2
does not fractionate
18
Oversus
17
O, and thus modifies
their proportion in atmospheric CO
2
and O
2
. The extent of this
atmospheric anomaly depends on the relative intensities of mass-
dependent and mass-independent processes. It is expressed as
the deviation towards the mass-dependent relationship between
18
Oand
17
O:
D
17
Oð10
6
per megÞðd
17
O 0:521 d
18
OÞð5Þ
where d
17
O and d
18
O are isotopic compositions with respect
to air.
Measurements of oxygen D
17
O in air bubbles trapped in
Greenland ice core allowed Luz et al. (1999) to infer that the
global biospheric productivity did not differ significantly over
the last 80,000 years, although it was slightly lower than
at present.
Gilles Delaygue
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Cross-references
Cenozoic Climate Change
Coral and Coral Reefs
Deuterium, Deuterium Excess
Dole Effect
Ice Cores, Antarctica and Greenland
Ice Cores, Mountain Glaciers
Isotope Fractionation
Ocean Paleotemperatures
Paleohydrology
Paleotemperatures and Proxy Reconstructions
Quaternary Climate Transitions and Cycles
Sea Level Change, Quaternary
SPECMAP
Speleothems
Stable Isotope Analysis
OXYGEN ISOTOPES 673
P
PAGES
The PAGES mission
PAGES (Past Global Changes) is the IGBP (International
Geosphere Biosphere Programme) project charged with providing
a quantitative understanding of the Earth’s past climate and envir-
onment. Reliable predictions of global climate change and its
environmental impacts in the future require an understanding of
processes operating on timescales longer than the short instrumen-
tal record. The study of natural archives of past climatic and envir-
onmental variability can provide this information.
Why PAGES?
PAGES operates on the principle of subsidiarity, a term borrowed
from the European Union. This means that projects within the
PAGES umbrella are those that clearly benefit from value added
through participation in a coordinated, international, cooperative
framework. Although research funding for paleoenvironmen-
tal science is almost entirely national, the global nature of the
questions involved, the global distribution of proxy archives,
and the fact that the community of paleoresearchers is global,
requires a globally integrated research strategy. PAGES provides
interdisciplinary and international linkages between nationally
funded research projects in order to ensure that the combined
effort adds to more than the sum of the parts. PAGES synergies
lead to community building and the development of integrated
research objectives. Tangible products include the website
(www.pages-igbp.org), newsletter (PAGES News), and numer-
ous books (Markgraf, 2001; Alverson et al., 2002), special
issues (Alverson et al., 2000; Clark and Mix, 2002), synthesis
papers (Alverson and Kull, 2002), outreach publications
(Alverson et al., 2001a), and brochures (Alverson et al., 2001b).
Research program
The PAGES research program is structured to bring researchers
from a variety of disciplines and countries together. Thus,
no explicit disciplinary or national structures exist within the
program. Rather, the program elements are designed to reduce
constraints imposed by geography and artificial disciplinary
boundaries such as those that commonly separate physical
oceanography from continental paleoecology from archaeol-
ogy. Although the five foci that make up the core of the
PAGES program have been created to group types of research
together, they are by no means restrictive, and collabora-
tion between foci is strongly encouraged. The activities of
each focus are guided by a chair and a small steering group.
PAGES activities are driven by rapidly evolving scientific
understanding and are designed to shift focus accordingly.
The most recent structure and activities are always readily
available on the website; www.pages-issp.org.
Focus 1 – PANASH
The goal of the Paleoclimate and Environments of the Northern
and Southern Hemispheres (PANASH) focus is to reconstruct
paleoenvironments and paleoclimate along three Pole-Equator-
Pole (PEP) terrestrial transects using a multiproxy data and model-
ing approach. One of the major roles of the PEP transects is
to facilitate the development of north-south research partner-
ships and foster a unified sense of purpose within the diverse
international and interdisciplinary community that addresses
questions of past global change. The PEP transects have been
extremely successful in achieving these goals, as evidenced
by the strong community interest in PEP meetings, as well as the
peer reviewed synthesis publications that have arisen from each
transect (Dodson and Guo, 1998; Markgraf, 2001; Battarbee et al.,
2004;Dodsonetal.,2004).
In addition to supporting the PEP transects, PANASH as a
whole stimulates global exchange of information among marine,
atmospheric, and terrestrial scientists, historical ecologists, and
environmental archaeologists. Its primary tasks are to:
– document the amplitude, phase, and geographic extent of
past climate change in the two hemispheres,
– determine the history of potentially important forcing
factors,
– identify the feedbacks that amplify or reduce the influence
or the effect of these forcings,
– identify the mechanisms of climatic coupling between the
two hemispheres.
The basis of all PANASH activities is a hypothesis-driven
approach to understanding modes of climatic and environmental
variability through the use of global, multi-proxy based climate
and environmental reconstruction. As an example of the wealth
of information that must be integrated within PANASH,
Figure P1 shows a highly condensed impression of the variety
of proxy records of environmental variability available over a
range of timescales from around the world.
Focus 2 – The PAGES/CLIVAR interse ction
The PAGES/CLIVAR Intersection focus aims to improve the
understanding of decadal to century scale climate variability, espe-
cially when relevant to improving predictability, through the use of
high resolution paleoclimatic data. The activities within this focus
are overseen by a joint working group shared between PAGES and
the World Climate Research Program (WCRP) Climate Variability
and Predictability Program (CLIVAR). The four principal areas of
focus, as outlined at the first international CLIVAR conference
(Alverson et al., 1999), are:
1. extending the instrumental climate record back in time with
quantitative proxy data that can be accurately calibrated
against instrumental records,
2. documenting and understanding rapid climate change,
3. documenting and understanding natural climate variability
during the Holocene and other interglacial periods with
background climatic states similar to those of today,
4. testing the ability of climate models to capture known past
climate variability.
Focus 3 – IMAGES
The International Marine Past Global Changes Study (IMAGES)
is the marine program shared between PAGES and the Scientific
Committee for Ocean Research (SCOR). The principal aim of
this program is to understand the mechanisms and consequences
of past climate changes involving ocean circulation, salinity,
and ventilation as well as the past history of marine ecosystems
and carbon cycle dynamics, using oceanic sedimentary records.
IMAGES supports a number of working groups, some of which
are oriented around cruise planning and others around more gen-
eral research questions. One major task of IMAGES is to organize
international pooling of financial resources and research expertise
in order to enable cruises to be carried out throughout the world
oceans. All IMAGES activities are carried out with strong input
Figure P1 A highly condensed view of the variety of proxy records of Quaternary environmental variability available over a range of timescales
from around the world. Yellow dots indicate the location of these records on the underlying global map. The records are: 1. A three hundred year
record of snow accumulation, related to the Pacific Decadal Oscillation, from an ice core on Mt. Logan, Canada (Moore et al., 2002). 2. A two
thousand year record of runoff intensity, related to the North Atlantic Oscillation, from a Finish laminated lake sediment core (Ojala, 2001).
3. An oxygen isotope record, as indicator of moisture source and hence monsoon penetration, covering the last glacial period through
the Holocene from a speleothem in Eastern China (Wang et al., 2001). 4. A lake level reconstruction from Naivasha, Kenya as an indicator of
regional hydrological balance (Verschuren et al., 2000). 5. Isotopically inferred temperature changes over four glacial cycles from the Vostok ice
core in Antarctica (Petit et al., 1999).
676 PAGES
and interaction from climate modelers, continental scientists, and
ice core researchers.
Focus 4 – Polar programs
The focus of the Polar programs is bi-polar. Examples of research
within the scope of this focus include the European and US N
GRIP ice core programs, EPICA, and the International Trans-
Atlantic Scientific Expedition (ITASE), which seeks to map the
spatial variability of Antarctic climate over the last millennium.
This initiative is shared with the Scientific Committee on Antarctic
Research (SCAR). In addition to ice core work, a wealth of other
archives in polar regions are employed to provide a robust picture
of high latitude environmental change. For example, the ESF-
funded Quaternary Environment of the Eurasian North project
(QUEEN) concentrates on mapping the extent of the last glacia-
tion, and the CircumArctic Paleo-Environments program (CAPE)
facilitates integration of paleoenvironmental research on terrestrial
and adjacent margins covering the last few glacial cycles.
Focus 5 – Past ecosystem processes and human
environment interact ions
The Past Ecosystems and Human-Environment Interactions focus
highlights PAGES concern with ecological responses to climate
change and past human activities. The research within Focus 5
integrates past human-environment interactions at sub-continental
scale with research and modeling based on present-day ecosys-
tems and watersheds. The focus is divided into three main activ-
ities: Human Impacts on Terrestrial Ecosystems (HITE), Land
Use and Climate Impacts on Fluvial Systems during the Period
of Agriculture (LUCIFS), and Human Impact on Lake Ecosys-
tems (LIMPACS). These activities are case-study based and
focus on ecosystems made vulnerable to global change through
any combination of natural and human-induced stresses. They
also explore the basis for the durability of long-sustained ecosys-
tems, and questions of sensitivity, thresholds, and non-linear
responses.
Initiatives
In addition to its standing foci, PAGES supports initiatives driven
by scientific questions arising within the community. The PAGES
Steering committee serves to critically ascertain if proposed initia-
tives should qualify for PAGES endorsement and support. Suc-
cessful initiatives develop a clear research and workshop agenda
over a 3–5 year period leading to a tangible goal. PAGES support
for theseinitiativesis flexible but can include enhancing the profile
of the initiative, advertising it to the international community, and
providing partial funding for workshops. One example of a suc-
cessful initiative is the Environmental Processes of the Ice Age:
Land, Oceans, Glaciers (EPILOG) program, which arose in 1999
as a multi-national working group of the PAGES marine program
IMAGES. EPILOG received PAGES support, including co-fund-
ing for several workshops, and recently published an extensive
special issue on ice sheets and sea level of the last glacial maxi-
mum (Clark and Mix, 2002). The required qualifications for a
PAGES initiative are:
1. A question that seems likely, within a 3–5 year timeframe,
to be tractable in the sense of leading to a peer-reviewed
product that advances the field.
2. A clear reason why PAGES should be involved, for example
to facilitate new international or interdisciplinary bridges
and community building.
Program structure
PAGES activities are overseen by an international scientific
steering committee (SSC) appointed by the Steering Committee
of the IGBP. The sixteen members, who each serve for at most
two consecutive three-year terms, are chosen to provide a bal-
ance of scientific expertise and national representation. This
committee meets once a year to provide guidance for and over-
sight of the program as a whole. A subset of five commit-
tee members serves as an executive committee. As a general
guideline, the five member executive committee includes an
American and a Swiss by virtue of the fact that these two coun-
tries currently provide the bulk of PAGES funding, and at least
one member from a less developed country. Under direction of
the SSC, the staff of the small International Project Office
(IPO) carries out the day to day running of the PAGES program
as a whole. These activities include maintaining the PAGES
website and database, organizing meetings and workshops,
editing and writing PAGES publications, and serving as a liai-
son with other global change programs. In addition, the office
regularly hosts both short-and long-term (sabbatical) visits
from paleoscientists around the world.
Links with other international programs
PAGES continues to be primarily concerned with understanding
the past operation of the Earth system. The PAGES domain
includes the physical climate system, biogeochemical cycles, eco-
system processes and, human dimensions. Thus, PAGES activities
are not restricted to IGBP, but overlap substantially with IGBP’s
sister programs within the “earth system science partnership,”
the WCRP, the International Human Dimensions Program on Glo-
bal Environmental Change (IHDP) and Diversitas. Facilitating
publicly accessible paleodata access, engaging with the climate
modeling community, and strengthening the role of developing
countries in PAGES research are the stable tripod upon which
the wider PAGES scientific program rests.
PAGES has built bridges with many other international scienti-
fic programs. Although only two of the foci are officially shared
(Focus 2 with WCRP-CLIVAR and Focus 3 with SCOR), all of
them have substantial interactions with other programs. PAGES
has launched joint initiatives with all of the other components of
the IGBP, including both the core projects of IGBP phase 1. In
the newly developing IGBP phase 2, which runs from 2003 to
2013, PAGES is expected to serve in a central synthesizing role,
and thereby interact strongly with all of the new IGBP programs
(Figure P2). A full listing of PAGES science partnerships is avail-
able on the PAGES website; some examples include the Global
Network for Isotopes in Precipitation (GNIP), shared with the
WCRP and the International Atomic Energy Agency (IAEA),
and the International Mountain Research Initiative, co-sponsored
by three other IGBP core projects, IHDP, GTOS (Global Terre-
strial Observing System), and UNESCO. Through these inter-
section activities, PAGES provides the historical context for
global change programs.
Outreach, communication, and publications
One major task for PAGES is to provide easy access to paleoen-
vironmental information to active researchers in paleosciences,
researchers in other aspects of global change research, and the
public. One of the most important communication platforms is
the website, www.pages-igbp.org. This site is modified regularly
and includes lists of new products, links to paleoenvironmental
databases, science highlights, a calendar of upcoming events,
and information on how to become involved in PAGES activities.
PAGES 677
Another important element in the PAGES communication
strategy is the newsletter. PAGES NEWS is produced three
times a year and sent free of charge to more than 3,000 sub-
scribing scientists in more than 70 countries. All issues are
made available as pdf files on the PAGES website. Such wide
distribution, coupled with a high degree of proactive submission
by the research community, has made the newsletter an impor-
tant vehicle for the dissemination of research results, workshop
reports, and program news, especially in countries with limited
access to western journals. Most issues are developed around a
specific theme, which might be a PAGES program or a particu-
lar paleoarchive. In addition to its newsletter and website,
PAGES strongly encourages publications in the peer-reviewed
literature as one outcome of all of its scientific activities.
Data archives
Internationally accessible data archives are one of the primary
foundations for paleoclimatic research that seeks to go beyond
reporting results on a site by site basis. PAGES is committed to
ensuring the preservation of all data needed for long-term, global
change research and making them openly available. PAGES
endorses a number of such data repositories, including the World
Data Center for paleoclimatology, Boulder (www.ngdc.noaa.
gov/paleo/, appendix B) and PANGAEA (http://www.pangaea.
de). PAGES supports a data board with a primary responsibility
for assuring compatibility and accessibility of available existing
paleo-databases. The PAGES data board is open to all interested
participants and includes members from most major database
centers and focus leaders.
Capacity building – encouraging north-south research
partnerships
PAGES has a strong interest in capacity building. The majority
of paleo-environmental data are extracted in less developed
countries. Recent high profile examples include ice cores from
Kilimanjaro, tree rings and lake sediments from Siberia, loess
records in China, tropical tree rings in SE Asia, and spe-
leothems in Oman. Bringing these records together into a
synthesis view of past environmental change requires that a
global community of independent working scientists matching
the diversity of these records also exists. PAGES therefore allo-
cates approximately 20% of its budget directly to activities
geared towards building the capacity of scientists residing in
developing countries to carry out active participation in
paleoenvironmental research. In addition, most PAGES work-
shop and summer school support is earmarked for participants
from developing countries. In addition to finances, PAGES
seeks to follow up one-time support wherever possible, by
enhancing the number of young scientists from developing
countries in the database, nominating outstanding individuals
for various awards, and entraining them directly in PAGES
major scientific initiatives. PAGES occasionally hosts visits at
the PAGES office, usually when tied to academic visits at a
department at the nearby University of Bern or the Swiss Cli-
mate summer school.
The PAGES Regional, Educational and Infrastructure
Efforts (REDIE) project seeks to:
1. enlist scientists and technicians in developing countries in
international paleoenvironmental research activities, and
2. promote the development of paleoscience research within
developing countries.
Within the REDIE program, a number of approaches are used.
Financial support is made available for the attendance of active
young scientists at key conferences and summer schools.
PAGES publications are made available free of charge to
libraries and university laboratories in less-developed countries.
Scientists from Asia, Africa, and South America sit on the
PAGES Science Committee and act as liaisons with their regio-
nal communities. PAGES scientific meetings are regularly
organized in developing countries, with ample support and
presentation time provided for the attendance of scientists from
the region.
Keith Alverson and Christoph Kull
Bibliography
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Using Paleorecords. In Rodó X., and Comín F.A. (eds.), Global
Climate: Current research and uncertainties in the climate system.
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Figure P2 Schematic diagram of the core projects expected to be
active in phase 2 of the International Geosphere Biosphere Programme
(IGBP), which runs from 2003 to 2013. These new projects are based
around the three Earth system components, land, atmosphere, and
ocean, and the three interfaces between them. Two further projects,
GAIM (AIMES) and PAGES will serve as integrating projects, providing
past and future time dimensions to the program. PAGES will play a
central, integrating role in the new IGBP structure.
678 PAGES
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Cross-references
Climate Variability and Change, Last 1,000 Years
Holocene Climates
Ice Cores, Antarctica and Greenland
Millennial Climate Variability
Paleotemperatures and Proxy Reconstructions
Pleistocene Climates
Quaternary Climate Transitions and Cycles
PALEOBOTANY
Introduction
Plants are ideally suited as records of, or proxies for, terrestrial
climate because they are sessile organisms. As climate changes
around them, they must adapt or perish. Over evolutionary
time, many aspects of plant growth have been constrained by
adaptation to specific climate regimes (e.g., Parkhurst and
Loucks, 1972; Chaloner and Creber, 1990; Uhl and Mosbrug-
ger, 1999). The sessile nature of plants combined with the ten-
dency for most plant parts to be preserved relatively close to
the site at which they grew means that plant fossils can be used
as a record of local paleoclimate (Spicer, 1989; Greenwood and
Wing, 1995).
Three main techniques are often used to determine paleocli-
mate from fossil plants. The first is referred to as the nearest-
living-relative technique. The nearest-living-relative technique
compares fossil plants to the modern plants to which they are
most closely related and assumes that the climatic tolerances
for both have remained similar through geologic time. The
second technique uses plant structures as vegetation proxies
for climate. These methods use various aspects of leaves and
wood, such as leaf morphology, tree rings or stomatal index,
as proxies to determine the climate in which these plant
organs grew. The final technique involves measuring isotopic
ratios of plant tissue to determine the climatic surroundings
of the plant.
Nearest-living-relative technique
The nearest-living-relative technique is widely used in paleocli-
mate reconstructions. This technique is taxon based and com-
pares fossil plants to their most closely related modern plants,
which are usually determined by finding similar morphological
characters in a fossil and in a living taxon. The main assump-
tions are that the climatic tolerances for both fossil and modern
plants are similar and the identifications and relationships pro-
posed between the fossil and living taxa are reliable. Dilcher
(1974, 2000) suggests that upwards of 60–75% of taxa identified
for Paleogene and Cretaceous fossil angiosperms are incorrect.
One advantage to this technique is that it can be used with many
different plant organs, including leaves, pollen, wood, fruits and
seeds. For some plant assemblages, a combination of different
plant organs can be used to establish a more robust determina-
tion of paleoclimate. In general, assemblages with fruits and
seeds or combinations of plant organs give more accurate results
than those that preserve only leaves, as taxonomic affinity is
often difficult to determine with leaf material. The best results
are obtained when a large number of taxa are used, the taxo-
nomic identifications are correct and the taxonomic identifica-
tions are at the species level. Use of this technique assumes
that the ecological tolerances of the fossil and extant relatives
are similar, and have not changed through time. The more recent
the fossil, the more likely it is that the ecological tolerances are
similar. Thus Holocene and Neogene climate reconstructions
are more likely to be accurate than Paleogene and Mesozoic
comparisons. Paleozoic plants are too dissimilar to recent plants
to use this technique (Chaloner and Creber, 1990).
Species level comparisons are the most robust, because eco-
logical tolerances of species are often better defined than those
of higher taxonomic groups. However, in many instances deter-
mination of the fossil can be made only to the genus or family
level, especially when using pollen or wood. Some genera and
families have similar tolerances throughout the group. For
example, palms and gingers have been said to live only in sub-
tropical and tropical areas (Wing and Greenwood, 1993),
although palms often grow and reproduce in warm temperate
areas of southeastern North America and South America. How-
ever, some genera have broad ecological tolerances, (e.g.,
Quercus and Acer), and most plant families have an extremely
broad ecological range (e.g., Fabaceae). This problem is some-
what circumvented by using large numbers of taxa to recon-
struct paleoclimate, which reduces the likelihood that one
broad-ranging taxon will influence the results.
The nearest-living-relative technique is used both to estimate
paleoclimate with absolute values and to determine vegetation or
climatic zones. The former method requires knowledge of the
climatic tolerances of many different modern species, while the
latter relies on determining which combinations of taxa are com-
monly found together in modern vegetation or climate zones.
Absolute climate values can be determined from individual
modern taxonomic relatives of fossil taxa, and a range of tem-
peratures or precipitation values may result. However, combining
many modern climate ranges should result in a more precise esti-
mate for the fossil assemblage, with the resulting climatic estimate
being the range where all of the modern taxa align (Figure P3).
Combining many taxonomic ranges decreases the likelihood that
a single problem taxon will skew the resulting climate range.
One application of this method has been termed the coexistence
approach (Mosbrugger and Utescher, 1997) and uses a database
of modern ecological tolerances of leaves, fruits and seeds from
PALEOBOTANY 679
Europe to apply the nearest-living-relative technique to fossil
assemblages. This approach works for Tertiary and younger-aged
fossil assemblages and has resulted in temperature estimates with
ranges as small as 1–4
C.
Using the nearest-living-relative technique to determine
vegetation and climatic zones is more common than finding
absolute climate values, as it is the method preferred by palynol-
ogists. This application of the method relies on finding similar
taxonomic combinations in both modern and fossil assemblages.
As with the coexistence approach, using many taxa is preferable
in determining a paleovegetation or paleoclimatic zone. This is
especially true when using pollen grains, which are often only
determined on the genus level and thus may have large indivi-
dual ecological tolerances, but a smaller tolerance as an assem-
blage. However, on occasion, the presence of a small number
of extremely indicative taxa can constrain the paleovegetation
or paleoclimatic zone regardless of the other taxa involved (Mar-
tin, 1997). Sinka and Atkinson (1999) have used factor analysis
to determine the overlapping climate zones of modern plant
assemblages, and then map the unknown fossil ranges onto a
“climate space.” This technique is a more objective method of
determining climatic zones of fossil assemblages, and eliminates
the bias that one taxon may have in the overall zonation.
Plant structure proxies
Similar combinations of wood or leaf characters tend to be
common in floras that live in similar climates (Dilcher, 1973;
Givnish, 1987; Woodcock and Ignas, 1994), even those that
are widely separated spatially and compositionally (Halloy
and Mark, 1996). Thus, specific plant characters are emergent
properties of a flora living under a specific climate regime.
The presence or absence of these characters in a fossil floral
assemblage allows for a paleoclimatic determination of the
assemblage site. Climatic interpretation is based on modern rela-
tionships between climate and specific plant characteristics.
Unlike the nearest-living-relative technique, foliar and wood phy-
siognomy approaches do not require specific or correct taxonomic
identification, although knowledge of the number of taxa present
and some aspects of their morphological or anatomical characters
are needed. This can be done using a parataxonomical or morpho-
type based approach (Woodcock and Ignas, 1994; Davies-Vollum,
1997), which interprets suites of morphologically similar plant
fossils as species groups. Exact taxonomic identification is needed
for stomatal indices and leaf venation density methods, as these
proxies are species dependent.
Leaves
Angiosperm leaves are often used in paleoclimatic reconstruc-
tions, with common proxies including leaf physiognomy,
stomatal density or stomatal index, and leaf venation density. Leaf
physiognomy is often used to determine annual and seasonal tem-
perature and precipitation. Stomatal density and stomatal index
are used to determine paleoCO
2
levels, moisture availability
and temperature. Leaf venation density is used to determine
transpiration stress.
Leaf physiognomic methods have their basis in numerous
qualitative relationships between leaves and climate that have
been quantified using modern climatic and floral data from a
range of climates and areas. By quantifying the proportions
of certain leaf characteristics present in specific modern
climates, predictive equations have been formed to determine
climate from fossil leaves. The most common equations corre-
late leaf morphological characters with mean annual tempera-
ture and mean annual precipitation, but others have been used
to quantify other climatic variables such as growing season pre-
cipitation, and cold month or warm month mean temperatures
(Wolfe, 1993; Gregory-Wodzicki, 2000; Jacobs, 2002).
Simple linear regression has been shown to be a relatively
direct and accurate means of predicting both mean annual
temperature and mean annual precipitation. The correlation
between leaf margin state (toothed or smooth) and mean annual
temperature is robust (Figure P4), and results in a fairly precise
and accurate predictive equation. As a consequence, this has
been the most studied and refined relationship within leaf phy-
siognomic studies (e.g., Dilcher, 1974; Wilf, 1997; Kowalski
and Dilcher, 2003). The resulting mean annual temperature esti-
mates generally have a suggested minimum standard error of
2
C(Wilf,1997). For precipitation, equations correlating leaf
area and mean annual precipitation have shown the most pro-
mise, and are slowly being refined by different researchers
(e.g., Wilf et al., 1998; Jacobs, 2002). However, most authors
have expressed caution in relying on the resulting mean annual
precipitation estimates, as the estimates have high standard errors.
Several authors have started using a multi-character
approach to climate prediction from leaf morphology, as the
morphology of most leaf characters is thought to be the result
of the complex interaction of many climate parameters. Multi-
ple regression equations using from two to nine or ten leaf
characters have shown some refinement of climate prediction
(e.g., Wing and Greenwood, 1993; Gregory-Wodzicki, 2000;
Jacobs, 2002), and are often more accurate than simple linear
regression equations for paleoclimate prediction (Kowalski,
2002). Wolfe (1993) has compiled a large, worldwide database
of modern climate and floral data, called CLAMP, to use with
canonical correspondence analysis, a multivariate statistical
approach for paleoclimate prediction. His database uses 31 leaf
characters to predict numerous climate parameters, including
mean annual temperature, growing season temperature and pre-
cipitation, enthalpy and range of temperature. Nearest neighbor
analysis uses only the sites from the CLAMP database that are
closest to the unknown site in multivariate space to form pre-
dictive equations for paleoclimate (Stranks and England,
1997). This technique has refined multivariate prediction
further by restricting the predictor set to similar floras and often
results in smaller estimate error.
Figure P3 A hypothetical list of modern relatives based on a flora from
southern Pennsylvania. If these modern taxa had represented the
modern relatives of a fossil flora, the estimated mean annual
temperature of the fossil site would be between approximately 10
C
and 12
C, the range of overlap between all taxa present.
680 PALEOBOTANY