Dendroclimatology
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Dendroclimatology (relationship between annual
tree growth and climate) offers high resolution
paleoclimate reconstruction for most of the
Holocene
Huon pine - Lagarostrobos franklinii
 A conifer endemic to Tasmania is recognized
as the longest living tree (or organism) known
 A medium sized specimen growing on the
west coast of Tassie is estimated to be
about 10,000 years old
Lagarostrobos franklinii
Sequoiadendron
giganteum
Tree Rings
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Cross section of temperate forest tree trunks
reveal alternation of light and dark bands
 Seasonal growth increments consisting of
earlywood (light growth band from early part
of the growing season) and denser latewood (a
dark band produced towards the end of the
growing season)
 Mean width of tree rings are a function of
tree species, tree age, soil nutrient availability
and a whole host of climatic factors
Dendroclimatologist must extract climatic
signals available in the tree-ring data from
remaining background "noise"
Tree Ring Banding
Splicing Tree Ring Records
Sampling Tree Rings
Climate Information from Trees
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Tree growth can be limited directly or indirectly by some
climate variable
 If the limitation can be quantified and dated,
dendroclimatology can be used to reconstruct some
information about past environments
Trees growing near the extremes of their ecological
niche are subject to climatic stresses – typically
moisture and temperature stress
 Trees in semi-arid regions are frequently limited by
the availability of water
 Dendroclimatic indicators reflect water
 Trees growing near the latitudinal or altitudinal tree
line are frequently temperature limited
 Dendroclimatic indicators reflect temperature
Extreme Ecological Niche
Sediments
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Marine sediments accumulating in ocean basins can
indicate climate conditions in the surface ocean or
on the adjacent continents
 Sediments are composed of both biogenic and
terrigenous materials
 Biogenic components include planktonic and
benthic organisms
 The nature and abundance of terrigenous
materials provides information about
continental weathering and the intensities and
directions of winds
Ocean sediment records have been used to
reconstruct climate change ranging from thousands
of years to tens of millions of years in the past
Biogenic Sediments
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Calcareous or siliceous oozes
Three types of analysis of calcareous and
siliceous tests are typically used for climate
reconstruction
 The oxygen isotopic composition of calcium
carbonate
 The relative abundance of warm- and coldwater species
 The morphological variations in particular
species resulting from environmental factors
Isotopic Composition of Shells
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First general rule of isotope geochemistry
 Heavy isotopes concentrate in the compound
where bond energy is strongest
When a mineral forms in water, heavy isotope
concentrates in the mineral
 The isotopic composition is a function of
 The isotopic composition of the water
 The temperature of formation
• Fractionation decreases as temperature
increases
The d18O of Shells
Temperature dependent
 T = 16.9 - 4.2 (dc - dw) + 0.13 (dc - dw)2
 Isotopic variations in carbonates small
 For modern analyses, dw can be measured
directly in ocean water samples; in fossil
samples, however, the isotopic composition
of sea water is unknown and cannot be
assumed to have been the same as it is
today

Glacial/Interglacial change in
Interglacial scenario: High sea-level
stand coupled with little ice at the
poles and relatively little storage of
16O in ice caps leads to relatively
sea-water rich in 16O. Calcareous
organisms living in the oceans will
incorporate more 16O in their
carbonate shells. Clouds contain high
proportion of the light isotope
because of it's higher vapor
pressure.
18O
Glacial scenario: Low seal level
stands with much polar ice will store
more 16O and thus sea water will
contain a higher proportion of 18O;
this proportion will be mirrored by
calcareous organisms that live and
fractionate this water when they
form their shell. Clouds contain high
proportion of the light isotope
because of it's higher vapor
pressure.
Trends in d18O
During glacial times
 Sea water enriched in 18O
 Surface water colder
 d18O of planktonic calcareous
organisms more positive
 During interglacial times
 Sea water enriched in 16O
 Surface water warmer
 d18O of planktonic calcareous
organisms more negative
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Constraining d18O of Seawater
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Isotopic records of deep water organisms can
help
 Bottom water temperatures (» -1°C to 2°C)
have changed little since glacial times
 Therefore increases in the d18O of deep water
organisms mostly reflect changes in the
isotopic composition of the glacial ocean
Concluded that 70% of the changes in the
isotopic composition of surface dwelling
organisms was due to changes in the isotopic
composition of the oceans, and only 30% due to
temperature variations
Other Complications – Vital Effects
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Unfortunately calcareous marine organisms
never took a course in chemical thermodynamics
 They do not precipitate their shell in oxygen
isotope equilibrium with seawater
Calcareous organisms commonly display “vital”
isotope effects
 For example, incorporation of metabolically
produced carbon dioxide
Vital isotope effects are not a problem if
 They are known
 They are constant
Other Biotic Climate Data

Climate reconstruction can be achieved by
studying
 Relative abundances of species
 Species assemblages
 Morphological variations
 Test coiling directions, either right-coiling
(dextral) or left-coiling (sinistral), reveal
proxy information about paleotemperatures of the oceans
 Other variations include differences in test
size, shape and surface structure
Corals
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Coral skeleton are colonies
composed of polyps
Symbiotic algae (zooxanthellae)
 Zooxanthellae supply both with
food and oxygen
 Food caught by the coral
supplies both with phosphorous
and nitrogen
Algae are crucial to calcium
carbonate deposition
 Without algae corals unable to
produce substantial reef
structures
Complicates geochemical records
from corals
Coral Growth
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Polyps are seated in aragonite
secreted by the epidermis
 CaCO3 is deposited beneath
living tissue
 Interconnected polyp
networks completely covers
the skeleton
Corals periodically encapsulate
a portion of their skeleton and
seal it off from contact with
sea water or living tissues
 Over the course of years,
each polyp lifts itself
hundreds of times leaving
new skeleton behind
Annual Banding in Coral
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Density of skeleton depends on coral
growth rate
 Related to temperature and cloud
cover
 Winter growth slow and skeleton is
dense (dark)
 Spring and summer growth rapid
and skeleton is less dense (light)
Seasonal coral banding may be visible to
the naked eye or apparent in an x-ray
Age of corals determined by counting
bands
 Uneven banding can reveal significant
weather events
Sample Collection
Hydraulic drill
used to collect a
core through the
coral
 Cores taken to
coral's plane of
maximum growth
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Coral Records of SST
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d18O function of SST and
salinity (fresh water influx and
precipitation)
Close correspondence between
d18O and instrumental
measurements
 Red spikes in d18O record
match up with red spikes in
the SST record
 Coral d18O data nearly as
accurate as instrumental
data
Coral records can cover the
past 500-800 years
Instrumental records are only
available for the last 50-100
years
Long Records
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Detailed records of d18O provide information on
SST and El Nino activity for last 350 years
Longer records obtained by splicing records
Other Coral Geochemical Proxies
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Cd/Ca and Ba/Ca proxy for upwelling
Cd and Ba have nutrient-like distributions in
seawater and therefore are sensitive indicators
of vertical mixing -- Other proxies?
Terrigenous Material in Marine Environments
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Weathering and erosion processes in different
climatic zones on continental land masses
produce characteristic inorganic products
Those products are transported to oceans (wind,
rivers or floating ice) and deposited on the sea
floor
 Carry information about the climate of their
origin or transportation route, at the time of
deposition
Terrestrial detritus dilutes the relatively
constant influx of calcium carbonate
 Most basic information is carbonate purity
Terrestrial Sediments
Several types of non-marine sediments can
provide relevant climatic information
 Aeolian, glacial, lacustrine and fluvial
deposits are a function of climate
 Often difficult to distinguish specific
causes of climatic change
 Erosional features such as ancient
lacustrine or marine shorelines, or glacial
striae also reveal climatic information
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Periglacial Features
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Morphological features associated with continuous
(permafrost) or discontinuous (diurnal or seasonal
freezing) periods of sub-zero temperatures
 Features such as fossil ice wedges; pingos;
sorted polygons; stone stripes; and periglacial
involutions
Climate reconstructions are subject to a fair
degree of uncertainty
 The occurrence of periglacial activity can only
indicate an upper limit on temperatures
 These features are difficult to date
 Dating of associated sediments provides only a
maximum age estimate
Glacial Fluctuations
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Glacier fluctuations result from changes in the
mass balance of glaciers
 Glacial movements lag climate forcing
 Different glaciers have different response
times to mass balance variations
Interpreting glacial movements in terms of
climate complex
 Many combinations of climatic conditions
might correspond to specific mass balance
fluctuations
 Temperature, precipitation (snowfall) and
wind speed are three main factors
Records of Glacial Movements
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Record of glacial front movements is
derived from moraines
 Piles of sediments carried by advancing
glaciers and deposited when they
retreat
 Periods of glacial recession, and the
magnitude of recession, are harder to
identify
 Repeated glacial movements can
destroy evidence from earlier
advances
Dating Glacial Movements
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Dating glacial movements prone to considerable
error
 Radiocarbon dates on organic material in soils
on moraines provides a minimum age for glacial
advance
 Considerable time lag may exist between
moraine deposition and soil formation
Lichenometry (lichens) and tephrochronology
(lava flows) can sometimes be to date glacial
events
 Reliability is restricted
Lake Level Fluctuations
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In regions where surface water discharge (via rivers
and other waterways) is restricted to inland basins
 Changes in the hydrological balance can provide
evidence for past climatic fluctuations
 In land-locked basins, water loss is almost
entirely due to evaporation
• During times of positive water budgets
(wetter climates), lake levels rise and lakes
expand
• During times of negative water budgets
(drier climates), lake levels drop and the
aerial expanses recede
Lake studies particularly useful in arid or semi-arid
areas
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Lake Titicaca, Altiplano, Andes
What can the lake level of high altitude lakes tell us about
oceanic circulation and atmosphere-oceanic interactions?
R/V Neecho, WHOI
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Salar de Uyuni, Bolivia
World's largest salt flat contains a record of alternating wet/dry
periods on the Altiplano
Factors Affecting Lake Level
Factors affecting the rates of evaporation
include
 Temperature, cloudiness, wind speed,
humidity, lake water depth and salinity
 Factors influencing the rate of water
runoff include
 Ground temperature, vegetation cover,
soil type, precipitation frequency,
intensity and type (i.e. rain, snow etc.),
slope gradients and stream sizes and
numbers
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Identifying Lake Levels
Episodes of lake growth identified by
 Abandoned wave-cut shorelines, beach
deposits, perched river deltas and
exposed lacustrine sediments
 Episodes of lake retreat
 Identified in lake sediment cores or by
paleosols and evaporites developed on
exposed lake bed
 Stratigraphy, microfossil analysis and
geochemistry may be used to decipher lake
level history
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Pollen Analysis
Pollen and spores accumulations
 Record past vegetation
 Changes in the vegetation of
an area can be due to
changes of climate
Pollen grains and spores form
ideal records
 Extremely resistant to decay
 Produced in huge quantities
 Distributed widely from
their source
 Can possess unique
morphological
characteristics
Problems with Pollen
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Differences in pollen productivity and dispersion rates
pose significant problems
 Relative abundances of pollen grains in a deposit
cannot be directly interpreted in terms of species
abundance
 Calibration of pollen abundance and spatial
distribution to species frequency is necessary
Pollen is a wind-blown sediment
 Accumulates on any undisturbed surface
 Sediments containing fossil pollen include peat
bogs, lake beds, alluvial deposits, ocean bottoms
and ice cores
 When pollen is deposited in water, differential
settling, turbulent mixing and sediment bioturbation
can bias record
Pollen Uses
Pollen analysis usually allow only qualitative
reconstructions
 The climate was wetter/drier or
warmer/colder
 Sometimes it is possible to quantify
climatic variations by the use of individual
indicator species rather than total pollen
assemblages
 The occurrence of plants that may not
be abundant but which are limited by
specific climatic conditions
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Sedimentary Rocks
Marine sediments >100 my subducted
 If sediments uplifted and exposed, can be
used to reconstruct past climates
 As sediments become progressively buried
undergo lithification and diagenesis
 Geochemical proxies must take into
account chemical alteration
 Record can be compressed
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Climate Reconstruction – Rock Type
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Rock type provides valuable information
 Evaporites
 Lithified salt deposits and evidence of dry
arid climates
 Coals
 Lithified organic matter and evidence of
warm, humid climates
 Phosphates and cherts
 Lithified siliceous and phosphate material
and evidence of ocean upwelling
 Reef limestone
 Lithified coral reef and evidence of warm
surface ocean conditions
Climate Reconstruction – Facies Analysis
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Investigates how rock type changes over time
 A formation consisting of a shale layer
interbedded between two sandstone layers
 Evidence of a changing sea level
 Potentially linked to climatic change (e.g.,
glacial ice formation)
 Sedimentation rates, sediment grain
morphology and chemical composition
 Provide information on the climatic
conditions at the time of parent rock
weathering
Biotic Indicators
Type and distribution of marine and
continental fossils within fossil-bearing
rocks
 Principally limestones and mudstones,
occasionally sandstones
 Microfossil type, abundance and
morphology
 Paleotemperatures can sometimes be
derived from oxygen isotope analysis
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