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 Ceratopogonidae Chaoboridae Chironomidae Culicidae Simuliidae Midges Biting midges, no-see-ums Phantom midges Non-biting midges, bloodworms Mosquitoes Black flies, buffalo gnats Larval Chaoborus flavicans T.P. Luoto Adult chironomid laying eggs 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 Some species live in tubes (sessile) while others free-living on the sediment surface Mostly detrivores Key components of aquatic ecosystems Epler (2001)
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 cm 3 ) 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
Laboratory procedure Bogorov counting tray Walker (2001)
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 ANTENNAL PEDESTAL VENTROMENTAL PLATE MENTUM POST-OCCIPITAL PLATE (POP) Corynocera ambigua
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 Smol 2008 Larocque & Hall (2003) Journal of Paleolimnology
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 (r 2 ) Root mean squared error of prediction (RMSEP) Mean and maximum biases
Available training sets
LWWA! Estimates! LWWA_Inv LWWA! Residuals! LWWA_Inv LWWA! Estimates! LWWA_Inv_X LWWA! Residuals! LWWA_Inv_X A Finnish chironomid-based calibration model Luoto et al. (2014) Quaternary Research 18 3.0 16 2.0 14 1.0 12 0.0 10-1.0 8-2.0 6 6 8 10 12 14 16 18 LWWA! Estimates! Obs_Tjul -3.0 6 18 3.0 16 2.0 14 1.0 12 0.0 10 8 N = 183 RMSEP = 0.74 C Jackknifed R2 = 0.90 6 6 8 10 12 14 16 18 LWWA! Estimates! Obs_Tjul -1.0-2.0-3.0 6
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
Luoto et al. (2014) The Holocene Air vs. water temperature
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 Spatial uniformity in depth optima Luoto (2012) Journal of Limnology
Chironomid-inferred effective precipitation Luoto & Nevalainen (2013) Climate Research
Chironomid relationship with stream flow
Luoto et al. (2013) Journal of Hydrology Chironomid-inferred stream flow
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 Important for the selection of suitable calibration model are the training set temperature gradient lenght and taxa representativeness Engels et al. (2014) Journal of Paleolimnology
How cold was the Little Ice Age? Southern Finland Zawiska et al. (in prep.) Luoto (2013) Environmental Earth Sciences
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 Similar patterns between past and present Implications for future changes in lake ecosystem functions Holocene Late Holocene Luoto & Nevalainen (2015) Hydrobiologia
Changes in benthic biodiversity and ecological functionality in the Alps Nevalainen et al. (2015) Aquatic Sciences
Regime shifts, the Alps Twenger Almsee Oberer Landschitzsee Luoto & Nevalainen (2013) Aquatic Biology Nevalainen & Luoto (2013) Journal of Paleolimnology
Regime shifts, high arctic Svalbard Kvalrosslaguna Luoto, Brooks & Salonen (2014) Journal of Paleolimnology Fugledammen Increase in bird-impact (observed population size) concurrent with climate warming Luoto, Oksman & Ojala (2015) Polar Biology
Future insights in chironomid-based paleoclimate research Stable isotope analysis (SIA) of head capsules δ 18 O δ 13 C Isotopic composition of lake water is controlled by the δ 18 O values of local precipitation > strongly correlated with mean annual surface temperatures in high latitude regions Biogeochemical cycles Also reflects the contribution of methane-oxidizing bacteria (MOB) in larval diet > indicator of past CH 4 emissions (?)
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