Quaternary%20palaeoenvironments

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Quaternary palaeoenvironments
Except for the observations made over the last
130 or so years at weather stations and on ships,
our knowledge of past climates is based on
records kept in sediment and ice. The task of
the palaeoclimatologist is to decipher these
proxies. Wally Broecker, 1993
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Proxy indicators of environmental change
Proxy (the action of) a substitute, or deputy
(OED) In palaeoenvironmental research the
properties of natural archives substitute for
direct measurement. Reconstruction of
palaeoenvironmental information requires that
these proxies be translated (qualitatively or
quantitively) into environmental parameters.
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Examples of the proxy approach
Research question 1 How warm were the summers
in Arctic Canada 6 000 years ago? Answer may be
derived from various temperature-sensitive
properties of lake sediments, bogs, or
glaciers. Research question 2 How frequent
were typhoons in Japan in the period before
records were kept? Answer may be derived from
proxies recording intense storms at sea and
flooding on land.
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What are the main kinds of proxies in Quaternary
research?

• glaciological
• geological
• historical
• biological

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Glaciological archives
Ice cores a) oxygen isotopes b) ice fabric
(size and shape of ice crystals) c) trace
elements (gases), and d) microparticle (dust)
concentration and composition
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Geological proxies
Marine environmentsOrganics oxygen
isotopes faunal and floral componentsInorganics
mineralogy and texture accumulation
rates geochemistry
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Geological proxies
Terrestrial environmentsglacial
deposits periglacial features palaeo-shorelines
aeolian deposits (dunes, loess) lacustrine
deposits palaeosols speleothems
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Historical proxies
Written records of paraclimatic phenomenae.g.
Hudson Bay factors journals record freeze-up and
breakup of Arctic rivers ships logs record
tropical storm frequency (e.g. logs of Manila-
Mazatlan voyages of Spanish galleons) whalers
catch records locate edge of sea ice in
Antarctica Norse sagas describe subpolar
landscapes (e.g. Greenland) arrival of spring
recorded in journals and diaries (phenological
records) size and date of crop harvest recorded
by merchants, etc..
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Historical proxies
Oral traditionse.g. Haida stories of flooding of
Hecate Strait (but native traditions tend to
float in time) Imagerye.g. Breughels Hunters
in the Snow records LIA winters in N. Europe,
cave art in SW France records local game animals
20-30 ka.
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European temperature records only begin in C18th
- but how cold/warm were previous years?
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Single proxies French grape harvest dates (AD
1484 -1880)
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Multiple proxies phenological observations
Phenology - study of the timing of natural events
e.g. Robert Marsham (1707-1797) kept a journal on
27 indications of Spring on his estate in
Norfolk (England) from 1736 until his
death. Indicators included flowering of spring
bulbs, leafing-out of shrubs and trees,
appearance of migratory birds and butterflies,
etc.
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Winter of 1740 in eastern England
For example, from Marshams journals we read that
the first few months of 1740 were so cold
that the gorse and heather died, the rabbits
starved in their warrens, the beer froze on the
dinner table, and the piss in his chamber pot
froze to a cake. In London the River Thames
froze .
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Biological proxies
taphonomic processes
ecological processes
biological community
Physical environment (esp. climate)
fossil community
Reconstruction (palaeoecological methods)
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Factors determining the utility of organisms as
biological proxies
Species-related factors 1. Is the species
abundant? 2. Is it (or are its parts) readily
identifiable? 3. Is the abundance of the
organism readily determinable from its
fossil components?
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Bio-proxies
Plant 1 trunk 102 cones 103 seeds 103
leaves 106 pollen grains
Vertebrate 1 skull 101 ribs 101 vertebrae 102
scales
annual production
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Determining organism abundance from body parts
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Factors determining the utility of organisms as
biological proxies
Environmental factors 1. Is the species
abundance primarily controlled by
environmental factors? 2. Is the relationship
between abundance and environment known or
readily determined?
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Factors determining the utility of organisms as
biological proxies
Taphonomic factors 1. Does the organism (or
ecological community) survive post-mortem
diagenesis? 2. What changes take place
pre-burial? 3. What changes take place
post-burial?
diagenesis processes affecting sediments at
temperatures and pressures characteristic of
the Earths surface.
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Factors determining the utility of organisms as
biological proxies
Preservation factors
ANATOMY
Hard parts?
YES NO
YES
clams jellyfish
HABITAT
Rapid burial?
birds butterflies
NO
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Live and dead assemblages of shelly invertebrates
in the main tidal channel, Mugu Lagoon,
California
1. Sanguinolaria nuttalli 2. Cryptomya
californica 3. Dendraster excentricus 4.
Diplodonta orbella 5. Olivella plicata 6.
Chione californiensis 7. Spisula dolabriformis
8. Nassarius fossatus 9. Lunatia lewisii 10.
Polinices reclusianus
Relative abundance
1 2 3 4 5 6
7 8 9 10
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Taphonomic stages in the preservation of a modern
oyster community
Stage A B C
phyla 9 7 7 species 80 45 18
preservation 100 56 23
A original community B all hard parts
preserved (e.g. late Quaternary subfossils).
These are mainly molluscs and other species
with hard skeletons C aragonitic,
calcitic and siliceous skeletons lost (e.g.
mid-Tertiary sediments)
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Preservation potential of macrofauna, Baffin
Island fjords and continental shelf
Fjords Nearshore Inner shelf
Outer shelf
217
197
126
112
genera
many fossils
no fossils
few fossils
Aitken, A.E. 1990. Fossilization potential of
Arctic fjord and continental shelf benthic
macrofaunas. In Dowdeswell, J.A. and Scourse,
J.D. (eds.) Glacimarine Environments Processes
and Sediments. Geological Society Special
Publication No. 53 pp. 155-176.
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Differential preservation by habitat, Baffin
Island fjords and continental shelf
Fjords Nearshore Inner shelf
Outer shelf
Quaternary fossils
no fossils
Aitken, A.E. 1990. Fossilization potential of
Arctic fjord and continental shelf benthic
macrofaunas. In Dowdeswell, J.A. and Scourse,
J.D. (eds.) Glacimarine Environments Processes
and Sediments. Geological Society Special
Publication No. 53 pp. 155-176.
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Differential preservation of trophic categories,
Baffin Island fjords and continental shelf
Modern community Quaternary sediments
36 genera
210 genera
Aitken, A.E. 1990. Fossilization potential of
Arctic fjord and continental shelf benthic
macrofaunas. In Dowdeswell, J.A. and Scourse,
J.D. (eds.) Glacimarine Environments Processes
and Sediments. Geological Society Special
Publication No. 53 pp. 155-176.
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Environmental controls on organic preservation
1. Ambient temperature - fossils tend to be
better preserved at low temperatures. e.g.
at water Tgt15C fish carcasses float -gt scavenged
-gt bones scattered 2. Oxygenation -
oxidation may destroy organic materials
anoxic water reduces scavenger activity 3. Water
status - some organic material degrades when
dry (see 2 above) 4. pH - acidic porewaters may
destroy some organic materials.
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Aeolian transportation
Depositional shadows (90 of total production)
needle/seed shadow
pollen shadow
cone shadow
5m?
40m?
500 m?
parts may suffer mild abrasion Result
homogenization of fossil assemblages
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Fluvial transportation and redeposition
Experiments with sheep and coyote bones in small
streams
Not moved Moved gradually Moved
immediately
(traction) (saltation/suspension)
skull lower jaw
femur tibia humerus pelvis
ribs vertebrae sternum finger/toe bones
these parts may suffer severe abrasion
Result homogenization of species?
sorting by body part?
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Habitat representation?
alpine lakes
bogs and lakes on floodplains
valley sideslopes
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Common biological proxies
Terrestrial organisms plants (macrofossils,
pollen, tree rings) fauna (esp. insects,
molluscs and mammals) Aquatic organisms diatoms,
coccolithophores foraminifers, ostracodes,
corals chironimids, molluscs, fish
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Reconstructing palaeoenvironments temporal
calibration of proxy
Past P.D.
warm cold
calibration period
Historic
Prehistoric
instrumental record (e.g. summer T)
proxy record (e.g. width of tree ring)
inferred summer T
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Proxy calibration (spatial)
e.g. single species morphology
forams coiled to right
samples
e.g. cold warm
Present-day environmental gradient
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Proxy calibration (spatial)
e.g. species distributions
sp. C
sp. B
Relative abundance
sp. A
samples
e.g. cold warm
Present-day environmental gradient
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Transfer functions
Quantitative reconstructionse.g. summer
T(C) 12.5 1.7ring 2.09ring2 summer
T(C) 12.5 1.66(right-coiled) summer T (C)
f(abundance species A,B,C)
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Checking the reconstruction

• Replication does the same proxy produce
  equivalent results at another site?
• Validation do several proxies produce equivalent
  results?
• Complementary information do alternative proxies
  provide useful supplementary data?

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Analyse archival recorde.g.peat bog
Depth
geochemical proxy
sp. A B C
abundance
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Reconstruction from transfer function
geochemical proxy record
dominantspecies
reconstructed T
Past P.D.
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Replicationof results at local, regional, or
global scales
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Checking with multiproxies Deserted Lake , VI
Vibracoring
DL in foreground Hisnit Inlet (Nootka Sd.) in
background
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Validation from 4 proxies
Hutchinson et al., 2000. The Holocene 10, 429-439
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Elk Lake, Itasca Park, Minn.
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Multiproxy validation and complementarity Elk
Lake Minn. - pollen, lake geochemistry and
diatoms