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Chironomids as a paleoclimate proxy
Tomi P. Luoto, PhD Department of Geosciences and Geography
University of Helsinki, Finland
Department of Biological and Environmental Science
University of Jyväskylä, Finland
List of contents
• Chironomid ecology
• Fossil chironomids in paleoecology
– methods
– indicator potential
– potential problems
• Examples of chironomid-based paleoclimate reconstructions
Midges (Insecta: Diptera: Nematocera)
Nematocera Midges Ceratopogonidae Biting midges, no-see-ums Chaoboridae Phantom midges Chironomidae Non-biting midges, bloodworms Culicidae Mosquitoes Simuliidae Black flies, buffalo gnats
Larval Chaoborus flavicans Adult chironomid laying eggs
© T.P. Luoto © T.P. Luoto
Chironomids
• Family (Chironomidae) of two-winged flies (Diptera)
• 5000-15 000 species
Larva Adult
Ecology of chironomids
• Life cycle – Eggs
– Larvae (mostly aquatic)
– Pupae
– Adult (flying insects)
• Ecologically important bottom dwellers in lakes
• Sensitive to environmental conditions
K.P. Brodersen
Larval stage
Epler (2001)
• Some species live in tubes (sessile) while others free-living on the sediment surface
• Mostly detrivores
• Key components of aquatic ecosystems
Fossil midge remains
a) Biting midge (Ceratopogonidae) head capsule
b) Chironomid head capsule
c) Phantom midge (Chaoboridae) mandible
Factors influencing chironomid distribution and abundance
• Regional scale – Temperature
• Local scale – Water quality
• Site-specific scale – Habitat Luoto (2012)
Entomologica Fennica
Multiple responses
Luoto (2011) Aquatic Insects
TWINSPAN
Luoto (2012) Entomologica Fennica
Chironomids in paleolimnology
• Diverse and abundant group
• Ecologically sensitive
• Rapid response to environmental changes
• Head capsules preserve well in lake sediments and are identifiable to genus/species type/species level
Sergentia coracina
Methodology
• Field techniques
• Laboratory procedures
• Identification
Field techniques
• Coring strategy – 1 g (or 1 cm3) of wet
sediment is usually enough to gain 50 head capsules in boreal lakes
– Core from the deepest point vs. intermediate depth • Representation of
littoral/offshore communities
• Fit to training set
• Disturbance
Patchy within-lake distribution
Walker (2001)
Laboratory procedure
Bogorov counting tray
Microscopy
1. Hand-sorting of fossil chironomid headcapsules with fine forceps under a stereomicroscope at ~25 x magnification
2. Head capsules ventral side up on preparation slides
3. Mounted in Euparal, Canada balsam, etc.
4. Identification from microscope slides under a light microscope at 100 x to 400 x magnification
Identification of fossil chironomids
MANDIBLE
MENTUM
VENTROMENTAL PLATE
POST-OCCIPITAL PLATE (POP)
Corynocera ambigua
ANTENNAL PEDESTAL
Indicator potential
• Salinity
• Hydrology (water depth, stream flow)
• Productivity
• Hypolimnetic oxygen
• Acidification
• Environmental assessments (e.g. pollution)
• Ecosystem health
• Temperature
Why chironomids and paleoclimate ? • Rapid response to climate changes especially in northern lakes
• Response times at annual resolution
• Established paleoclimatic tool to better understand the ongoing changes
Larocque & Hall (2003) Journal of Paleolimnology
Smol 2008
Quantitative reconstructions • Assemblages dependent on
multiple environmental stressors
• Similar assemblages are from
similar environmental conditions
• Transfer function connects a
particular assemblage to a particular environmental variable
• Transfer function produces a reconstruction from fossil core assemblages using the environmental optima derived from modern assemblages Luoto (2010)
Model types
• Modern analogue technique (MAT)
• Weighted-averaging (WA)
• Partial least squares (PLS)
• WA-PLS
• Locally weighted WA (LWWA)
• Maximum likelihood (Gaussian logit model)…
Model performance • Cross-validation
– Jackknifing or bootstrapping
• Correlation coefficient (r2)
• Root mean squared error of prediction (RMSEP)
• Mean and maximum biases
Available training sets
A Finnish chironomid-based calibration model
Luoto et al. (2014) Quaternary Research
6 8 10 12 14 16 18
6
8
10
12
14
16
18
LWWA ! Estimates ! Obs_Tjul
LW
WA
! E
stim
ate
s ! L
WW
A_
Inv
6 8 10 12 14 16 18
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
LWWA ! Residuals ! Obs_Tjul
LW
WA
! R
esid
ua
ls ! L
WW
A_
Inv
6 8 10 12 14 16 18
6
8
10
12
14
16
18
LWWA ! Estimates ! Obs_Tjul
LW
WA
! E
stim
ate
s ! L
WW
A_
Inv_
X
6 8 10 12 14 16 18
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
LWWA ! Residuals ! Obs_Tjul
LW
WA
! R
esid
ua
ls ! L
WW
A_
Inv_
X
N = 183 RMSEP = 0.74 °C
Jackknifed R2 = 0.90
Weaknesses
• Multiple responses
• Air temperature vs. water temperature
• Taxonomy
• Preparation time Brooks et al. (2007)
Sampling site selection
• Deep sites have cold water fauna
• Sampling depth must be similar between the downcore site and the training set
Luoto (2010) Ecological Monographs
Air vs. water temperature
Luoto et al. (2014) The Holocene
Reconstruction of water and air temperature
Luoto et al. (2014) The Holocene
What can be reconstructed? • Spatially and temporally case-specific
• Always multiple stressors
– Primary vs. surrogate variables
• Primary forcing factors can change in time
How to select the variable to reconstruct? • Depends on the site and environmental gradient
• Direction of the primary ordination axis
• Indicator taxa (e.g. generalized linear modelling)
• A variaty of statistical approaches
• Multiproxy approach
• Comparison with instrumental data
Chironomid relationship with water depth
Luoto (2012) Journal of Limnology
Spatial uniformity in depth optima
Chironomid-inferred effective precipitation
Luoto & Nevalainen (2013) Climate Research
Chironomid relationship with stream flow
Chironomid-inferred stream flow
Luoto et al. (2013) Journal of Hydrology
Chironomid relationship with temperature
Eggermont & Heiri (2012) Biological Reviews
Local or regional temperature model?
Engels et al. (2014) Journal of Paleolimnology
Comparison of Norwegian, Finnish and russian models
Engels et al. (2014)
Journal of Paleolimnology
Important for the selection of suitable calibration model are the training set temperature gradient lenght and taxa representativeness
How cold was the Little Ice Age ?
Luoto (2013) Environmental Earth Sciences
Zawiska et al. (in prep.)
Southern Finland
Holocene climate dynamics
Northern Finnish Lapland
• Warm or cold early Holocene?
• Timing of the Holocene Thermal Maximum?
• Late Holocene cooling?
• Recent warming?
Luoto et al. (2014) Quaternary Research
Chironomid-inferred water temperature
Luoto & Nevalainen (2013) Scientific Reports
Chironomid-based evidence for large-scale climatic modes
Luoto & Helama (2010) Quaternary Science Reviews
Chironomid-inferred continentality
Engels et al. (2014) Journal of Paleolimnology
Climate forced patterns in feeding guilds Modern distribution
Holocene Late Holocene
Luoto & Nevalainen (2015) Hydrobiologia
• Similar patterns between past and present
• Implications for future changes in lake ecosystem functions
Changes in benthic biodiversity and ecological functionality in the Alps
Nevalainen et al. (2015) Aquatic Sciences
Regime shifts, the Alps Twenger Almsee
Luoto & Nevalainen (2013) Aquatic Biology
Oberer Landschitzsee
Nevalainen & Luoto (2013) Journal of Paleolimnology
Regime shifts, high arctic Svalbard Kvalrosslaguna
Luoto, Brooks & Salonen (2014) Journal of Paleolimnology
Fugledammen
Luoto, Oksman & Ojala (2015) Polar Biology
Increase in
bird-impact
(observed
population
size)
concurrent
with climate
warming
Future insights in chironomid-based paleoclimate research
• Stable isotope analysis (SIA) of head capsules
– δ18O
• Isotopic composition of lake water is controlled by the δ18O values of local precipitation – > strongly correlated with mean annual surface temperatures
in high latitude regions
– δ13C
• Biogeochemical cycles
• Also reflects the contribution of methane-oxidizing bacteria (MOB) in larval diet – > indicator of past CH4 emissions (?)
Thanks!