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: “ (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

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?

•glaciological•geological•historical•biological

Glaciological archives

Ice cores:a) oxygen isotopesb) ice fabric (size and shape of ice crystals)c) trace elements (gases), andd) microparticle (dust) concentration and composition

Geological proxies

Marine environmentsOrganics

oxygen isotopesfaunal and floral components

Inorganicsmineralogy and textureaccumulation ratesgeochemistry

Geological proxies

Terrestrial environmentsglacial depositsperiglacial featurespalaeo-shorelinesaeolian deposits (dunes, loess)lacustrine depositspalaeosolsspeleothems

Historical proxiesWritten records of paraclimatic phenomena

e.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’ 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.

European temperature records only begin in C18th - but how

cold/warm were previous years?

Single proxies: French grape harvest dates (AD 1484 -1880)

Multiple proxies: phenological observationsPhenology - study of the timing of natural events

e.g. Robert Marsham (1707-1797) kepta 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

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

biologicalcommunity

Physicalenvironment(esp. climate)

fossilcommunity

Reconstruction(palaeoecological methods)

taphonomic processes

ecologicalprocesses

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

Vertebrate: 1 skull

101 ribs101 vertebrae

102 scales

Plant: 1 trunk

102 cones*103 seeds*

103 leaves*106 pollen grains*

*annual production

Determining organism abundance from body

parts1 spruce trunk = 1 tree1 diatom frustule = 1

diatom1 articulated shell = 1 clam

1 skull = 1 mammoth1 articulated skeleton = 1

fish2 spruce cones = ?

20 fish vertebrae = ? 40 fish scales = ?

200 spruce seeds = ?2000 spruce pollen grains =

?

Estimates of absolute abundance

possible

Estimates of relativeabundance

possible

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 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 proxies

Preservation factors

Rap

id b

uri

al?

YES

NO

Hard parts?

YES NO

clams jellyfish

birds butterflies

ANATOMY

HA

BIT

AT

1

10

100

1000

1 2 3 4 5 6 7 8 9 10

LiveDead

1 2 3 4 5 6 7 8 9 10

Re

lativ

e a

bu

nda

nce

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 lewisii10. Polinices reclusianus

Live and dead assemblages of shelly invertebrates in the main tidal channel, Mugu Lagoon, California

Taphonomic stages in the preservation of a modern oyster

communityStage

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

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.

Fjords Nearshore Inner shelf Outer shelf

many fossils

few fossils

nofossils

112 217 197 126# genera

Differential preservation by habitat, Baffin Island fjords and continental

shelf

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.

Fjords Nearshore Inner shelf Outer shelf

Quaternaryfossilsno

fossils

Differential preservation of trophic categories, Baffin Island fjords and

continental shelf

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.

Carnivores

Suspension feeders

Deposit feeders

Browsers

Modern community Quaternary sediments

36 genera210 genera

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 scattered2. Oxygenation - oxidation may destroy organic materials; anoxic water reduces scavenger activity3. Water status - some organic material degrades when dry (see #2 above)4. pH - acidic porewaters may destroy some organic materials.

Aeolian transportation

parts may suffer mild abrasion

Result = homogenization of fossil assemblages

needle/seed shadow

coneshadow

5m?40m?500 m?

Depositional shadows (90% of total production)

pollenshadow

Fluvial transportation and redeposition

these parts may suffer severe abrasion

Result = homogenization of species? sorting by body part?

Experiments with sheep and coyote bones in small streamsNot moved Moved gradually Moved

immediately (traction)

(saltation/suspension)skulllower jaw

femurtibia

humeruspelvis

ribsvertebraesternum

finger/toe bones

Habitat representation?

bogs and lakeson floodplains

alpine lakes

valleysideslopes

Lake and bog sampling sites

Common biological proxies

Terrestrial organismsplants (macrofossils, pollen, tree rings)fauna (esp. insects, molluscs and mammals)

Aquatic organismsdiatoms, coccolithophoresforaminifers, ostracodes, coralschironimids, molluscs, fish

Reconstructing palaeoenvironments: temporal calibration of proxy

HistoricPrehistoric

Past P.D.

instrumental record (e.g. summer T)proxy record (e.g. width of tree ring)inferred summer T

calibrationperiod

warm

cold

Proxy calibration (spatial)

e.g. cold warm

Present-day environmental gradient

samples

e.g. single speciesmorphology

% f

ora

ms

coile

d t

o

rig

ht

Proxy calibration (spatial)

e.g. cold warm

Present-day environmental gradient

samples

sp. Asp. B

sp. C

Rela

tive a

bu

nd

an

ce

e.g. species distributions

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

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

recorde.g.peat bog

geochemical proxy

Depth

sp. A B Cabundance

Reconstruction from transfer function

Past P.D.

geochemical proxy recorddominant

species

reconstructed T

Replication

of results at local, regional, or global

scales

Checking with multiproxies: Deserted Lake , VI

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

Vibracoring

Validation from 4 proxies

Hutchinson et al., 2000. The Holocene 10, 429-439

Elk Lake, Itasca Park,

Minn.

Multiproxy validation and complementarity :

Elk Lake: Minn. - pollen, lake geochemistry and diatoms