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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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quaternary palaeoenvironments
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

proxy indicators of environmental change
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.

examples of the proxy approach
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.

what are the main kinds of proxies in quaternary research
What are the main kinds of proxies in Quaternary research?
  • glaciological
  • geological
  • historical
  • biological
glaciological archives
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

geological proxies
Geological proxies

Marine environmentsOrganics oxygen isotopesfaunal and floral componentsInorganics

mineralogy and texture

accumulation rates

geochemistry

geological proxies1
Geological proxies

Terrestrial environmentsglacial deposits

periglacial features

palaeo-shorelines

aeolian deposits (dunes, loess)

lacustrine deposits

palaeosols

speleothems

historical proxies
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..

historical proxies1
‘Historical’ proxies

Oral traditionse.g. Haida stories of flooding of Hecate Strait

(but native traditions tend to ‘float’ in time)

Imagerye.g. Breughel’s “Hunters in the Snow” records LIA winters in N. Europe, cave art in SW France records local game animals 20-30 ka.

multiple proxies phenological observations
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.

winter of 1740 in eastern england
Winter of 1740 in eastern England

For example, from Marsham’s 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 ….

biological proxies
Biological proxies

ecological

processes

taphonomic

processes

Physical

environment

(esp. climate)

biological

community

fossil

community

Reconstruction

(palaeoecological methods)

factors determining the utility of organisms as biological proxies
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?

bio proxies
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

determining organism abundance from body parts

1 spruce trunk = 1 tree

1 diatom frustule = 1 diatom

1 articulated shell = 1 clam

1 skull = 1 mammoth

1 articulated skeleton = 1 fish

2 spruce cones = ?

20 fish vertebrae = ?

40 fish scales = ?

200 spruce seeds = ?

2000 spruce pollen grains = ?

Estimates of absolute abundance possible

Estimates of relative

abundance possible

Determining organism abundance from body parts
factors determining the utility of organisms as biological proxies1
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?

factors determining the utility of organisms as biological proxies2
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 Earth’s surface.

factors determining the utility of organisms as biological proxies3
Factors determining the utility of organisms as biological proxies

Preservation factors

ANATOMY

Hard parts?

YESNO

YES

clams jellyfish

HABITAT

Rapid burial?

birds butterflies

NO

slide21

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

taphonomic stages in the preservation of a modern oyster community
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)

preservation potential of macrofauna baffin island fjords and continental shelf
Preservation potential of macrofauna, Baffin Island fjords and continental shelf

Fjords Nearshore Inner shelf Outer shelf

217

197

126

# genera

112

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.

differential preservation by habitat baffin island fjords and continental shelf
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.

differential preservation of trophic categories baffin island fjords and continental shelf
Differential preservation of trophic categories, Baffin Island fjords and continental shelf

Modern community Quaternary sediments

210 genera

36 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.

environmental controls on organic preservation
Environmental controls on organic preservation

1. Ambient temperature - fossils tend to be better preserved at low temperatures.

e.g. at water T>15°C fish carcasses float -> scavenged -> 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.

aeolian transportation
Aeolian transportation

Depositional shadows

(90% of total production)

needle/seed

shadow

pollen

shadow

cone

shadow

500 m?

40m?

5m?

parts may suffer mild abrasion

Result = homogenization of fossil assemblages

fluvial transportation and redeposition
Fluvial transportation and redeposition

Experiments with sheep and coyote bones in small streams

Not movedMoved 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?

habitat representation

Lake and bog sampling sites

Habitat representation?

alpine lakes

bogs and lakes

on floodplains

valley

sideslopes

common biological proxies
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

reconstructing palaeoenvironments temporal calibration of proxy
Reconstructing palaeoenvironments: temporal calibration of proxy

Past P.D.

warm

cold

calibration

period

Prehistoric

Historic

instrumental record (e.g. summer T)

proxy record (e.g. width of tree ring)

inferred summer T

proxy calibration spatial
Proxy calibration (spatial)

e.g. single species

morphology

% forams coiled to right

samples

e.g. cold warm

Present-day environmental gradient

proxy calibration spatial1
Proxy calibration (spatial)

e.g. species distributions

sp. C

sp. B

Relative abundance

sp. A

samples

e.g. cold warm

Present-day environmental gradient

transfer functions
Transfer functions

Quantitative reconstructionse.g. summer T(°C) = 12.5 + 1.7[ring] + 2.09[ring]2

summer T(°C) = 12.5 + 1.66(right-coiled)

summer T (°C) = f(abundance species A,B,C)

checking the reconstruction
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?
analyse archival record e g peat bog
Analyse archival recorde.g.peat bog

Depth

geochemical

proxy

sp. ABC

abundance

reconstruction from transfer function
Reconstruction from transfer function

geochemical proxy record

dominantspecies

reconstructed T

Past P.D.

checking with multiproxies deserted lake vi
Checking with multiproxies: Deserted Lake , VI

Vibracoring

DL in foreground; Hisnit Inlet (Nootka Sd.) in background

validation from 4 proxies
Validation from 4 proxies

Hutchinson et al., 2000. The Holocene10, 429-439