Dendroclimatology

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Dendroclimatology

• 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

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Lagarostrobos franklinii
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Sequoiadendron giganteum
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Tree Rings

• 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"

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Tree Ring Banding
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Splicing Tree Ring Records
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Sampling Tree Rings
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Climate Information from Trees

• 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

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Extreme Ecological Niche
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Sediments

• 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

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Biogenic Sediments

• 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 cold-water
  species
• The morphological variations in particular
  species resulting from environmental factors

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Isotopic Composition of Shells

• 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

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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

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Glacial/Interglacial change in 18O
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.
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.
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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

• Isotopic records of deep water organisms can help
• Bottom water temperatures ( -1C to 2C) 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

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Other Complications Vital Effects

• 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

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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 paleo-temperatures of the
  oceans
• Other variations include differences in test
  size, shape and surface structure

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Corals

• 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

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Coral Growth

• 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

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Annual Banding in Coral

• 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

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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

• d18O function of SST and salinity (fresh water
  influx and precipitation)
• Close correspondence between ?18O and
  instrumental measurements
• Red spikes in ?18O record match up with red
  spikes in the SST record
• Coral ?18O 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

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Long Records

• Detailed records of ?18O provide information on
  SST and El Nino activity for last 350 years
• Longer records obtained by splicing records

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Other Coral Geochemical Proxies

• 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?

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Terrigenous Material in Marine Environments

• 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

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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

• 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

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Glacial Fluctuations

• 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

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Records of Glacial Movements

• 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

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Dating Glacial Movements

• 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

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Lake Level Fluctuations

• 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

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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

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Problems with Pollen

• 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

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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 gt100 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

• 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

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Climate Reconstruction Facies Analysis

• 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

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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