Lakes as Records of Past Climates

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Lakes as Records of Past Climates
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Overview

• Climate change
• Paleolimnology
• Papers
• Discussion

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Climate Change

• variation in global or regional climate over time
• driven by external forces or human activities
  (CO2)

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External Factors

• Plate tectonics-continental vs. coastal climate
• Orbital variations-Milankovitch cycles
• Volcanism- large igneous provinces

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Anthropogenic Factors

• Fossil fuels-Industry, automobiles (SOx,NOx,CO2 )
• Land use-deforestation, agriculture,irrigation

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Evidence

• data taken from several ice cores(Fischer et al,
  1999Monin et al, 2004Ethridge et al, 1998)

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Evidence

• data taken from several ice cores(Fischer et al,
  1999Monin et al, 2004Ethridge et al, 1998)

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Paleolimnology

• Study of aquatic environments of the past

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Why?

• Curiosity-lake typology, evolution of ecosystems
  and organisms, biogeography
• Track anthropogenic changes-restoration
  implications, timelines, degree of changes
• Understanding past climates-predict future of
  ecosystems?

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How?

• Sediment cores
• Fossils
• Pigments
• Stable isotopes

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Fossils

• Diatoms
• Cysts-plankton
• Pollen, spores
• Invertebrates
• Vertebrates

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Pigments

• Distinctive to different algae
• Chlorophylls
• Accessory pigments

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Isotopes

• Time scale dependent
• Timing of environmental change
• Carbon, cesium,lead etc.
• Lead dating accurate to about 150 yrs ago

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Papers

• 1. Climate-driven regime shifts in the biological
  communities of arctic lakes (J. P. Smol et al,
  2005 PNAS)
• 2. Century-long synchrony of fossil algae in a
  chain of Canadian prairie lakes (Patoine and
  Leavitt, 2006 Ecology)

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1.Background

• Polar amplification of anthropogenic warming
• Glacier retreat
• Sea ice thinning
• Permafrost degradation

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1.Background

• High latitude lakes very responsive to climate
  change
• Degree of change local
• Slight warming leads to decreased ice/snow cover,
  longer growing season
• Higher primary production, new habitat available,
  taxonomic shifts

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1. Predictions

• Greater species turnover with higher latitude
• Biological response of arctic lake communities to
  changes in length ice free season
• Ice free season is modulated by climate
• As system passes through climate related
  thresholds, aquatic community composition
  turnover high

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1.Study Area

• A-Ellesmere Island
• B-Ellef Rignes Island
• C-Baffin Island
• D-NWT
• E-Quebec
• F-Spitsbergen
• G-Lapland
• H-Polar Urals

Sample site areas
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1. Methods

• 55 samples from 48 Arctic lakes
• Sediments cores
• Geochronology using 210Pb
• Biological indicators-diatoms, chrysophytes,
  cladocerans, chironomids

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1. Methods

• DCCA-quantitative estimates of compositional
  turnover-beta-diversity
• Looked at compositional change along temporal
  gradient (diatoms)
• Estimated species turnover in past 150 years

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1.Results and Discussion

• Northernmost sites-shifts from benthic taxa to
  littoral taxa (diatoms)
• Climate records show warming trend
• Consistent with longer growing season and habitat
  expansion

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1.Results and Discussion

• Deep water lakes -Baffin Island, Svalbard,
  Fennoscandia, Western subarctic lakes
• Climate records show warming trend
• Shift from benthic to planktonic diatom species

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1.Results and Discussion

• Labrador and Northern Quebec
• Little or no change in climate recorded
• Changes in diatom assemblages not observed

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1.Results and Discussion
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2. Background

• Lakes in same region can show similar annual
  patterns of fluctuation in biological parameters
  (algae)-synchrony (Kratz et al, 1998)
• High degree of synchrony influenced by large
  scale environmental factors-climate, land use,
  urbanization

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2. Background

• Lake synchrony greatest when sites are homogenous
• What factors responsible for driving changes in
  community composition in lakes?

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2. Predictions

• Degree of synchrony of algae between lakes taxon
  specific
• Synchrony arises from long term increases in
  algal abundance, not short term population
  variability
• Determination of relative importance of climate,
  resource use and urbanization on synchrony

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2. Study Area

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2. Study Area

• Since 1900
• 30 day increase in ice free season
• 25 increase in farming
• Exponential increase in population of nearest
  city-Regina
• 50-70 domestic waste water discharged upstream
  of Pasqua Lake

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2. Methods

• Sediments collected with freeze corer-1 per lake
  (Leavitt et al, 1989)
• Cores sectioned-annual resolution 210Pb dating
• Pigment extraction, isolation and identification
  each lake (period, 1776-1995)
• Analysis of fossil pigments -historical changes
  in abundance and synchrony

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• Analysis of fossil pigments

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2. Methods

• Determine if synchrony arises from long term or
  short term trends
• Time series model to describe long term trends in
  fossil pigment concentrations

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2. Methods

• gt85 changes explained by climate, resource use
  and urbanization in individual lakes
  (multivariate analysis)
• Relative importance of above factors on
  synchronous changes in all lakes (variance
  partitioning analysis)

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2. Results and Discussion

• Pasqua lake-increase in total algal biomass 20th
  century
• Less so in downstream lakes
• All lakes -increased concentration of sedimentary
  pigments since 1950 variable (siliceous algae
  and dinoflagellates nb.)

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2. Results and Discussion

• Three groups of pigments of varying chemical
  stability and synchronicity
• Algal synchrony in Quappelle lakes related to
  long term trends

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2. Results and Discussion

• Coherence of pigments greatest in labile
  compounds (Chl-a, fucoxanthin)
• Synchrony in spring blooming taxa
• Low overall synchrony of total algal
  abundance-low coherence of summer taxa

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2. Results and Discussion

• gt85 of algal variation in individual lakes
  explained by climate, resource use and
  urbanization (multivariate analysis)
• gt35 synchronous algal fluctuation in all lakes
  explained by climate, resource use and
  urbanization (multivariate analysis)
• Factors related to algal synchrony differ from
  those related to abundance

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Differences Between Studies

• Arctic lakes far from agriculture, forestry,
  cities climate only parameter
• Quapplelle lakes many other factors
• Scale of study, 48 vs. 7 lakes

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Conclusion

• Lakes can provide a record of past climates