Chironomids as a paleoclimate proxy

Transcription

1 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

2 List of contents Chironomid ecology Fossil chironomids in paleoecology methods indicator potential potential problems Examples of chironomid-based paleoclimate reconstructions

3 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

4 Chironomids Family (Chironomidae) of two-winged flies (Diptera) species Larva Adult

5 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

6 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)

7 Fossil midge remains a) Biting midge (Ceratopogonidae) head capsule b) Chironomid head capsule c) Phantom midge (Chaoboridae) mandible

8 Factors influencing chironomid distribution and abundance Regional scale Temperature Local scale Water quality Site-specific scale Habitat Luoto (2012) Entomologica Fennica

9 Multiple responses Luoto (2011) Aquatic Insects

10 TWINSPAN Luoto (2012) Entomologica Fennica

11 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

12 Methodology Field techniques Laboratory procedures Identification

13 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

14 Laboratory procedure Bogorov counting tray Walker (2001)

15 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

16 Identification of fossil chironomids MANDIBLE ANTENNAL PEDESTAL VENTROMENTAL PLATE MENTUM POST-OCCIPITAL PLATE (POP) Corynocera ambigua

17 Indicator potential Salinity Hydrology (water depth, stream flow) Productivity Hypolimnetic oxygen Acidification Environmental assessments (e.g. pollution) Ecosystem health Temperature

18 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

19 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)

20 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

21 Available training sets

22 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 LWWA! Estimates! Obs_Tjul N = 183 RMSEP = 0.74 C Jackknifed R2 = LWWA! Estimates! Obs_Tjul

23 Weaknesses Multiple responses Air temperature vs. water temperature Taxonomy Preparation time Brooks et al. (2007)

24 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

25 Luoto et al. (2014) The Holocene Air vs. water temperature

26 Reconstruction of water and air temperature Luoto et al. (2014) The Holocene

27 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

28 Chironomid relationship with water depth Spatial uniformity in depth optima Luoto (2012) Journal of Limnology

29 Chironomid-inferred effective precipitation Luoto & Nevalainen (2013) Climate Research

30 Chironomid relationship with stream flow

31 Luoto et al. (2013) Journal of Hydrology Chironomid-inferred stream flow

32 Chironomid relationship with temperature Eggermont & Heiri (2012) Biological Reviews

33 Local or regional temperature model? Engels et al. (2014) Journal of Paleolimnology

34 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

35 How cold was the Little Ice Age? Southern Finland Zawiska et al. (in prep.) Luoto (2013) Environmental Earth Sciences

36 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

37 Chironomid-inferred water temperature Luoto & Nevalainen (2013) Scientific Reports

38 Chironomid-based evidence for large-scale climatic modes Luoto & Helama (2010) Quaternary Science Reviews

39 Chironomid-inferred continentality Engels et al. (2014) Journal of Paleolimnology

40 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

41 Changes in benthic biodiversity and ecological functionality in the Alps Nevalainen et al. (2015) Aquatic Sciences

42 Regime shifts, the Alps Twenger Almsee Oberer Landschitzsee Luoto & Nevalainen (2013) Aquatic Biology Nevalainen & Luoto (2013) Journal of Paleolimnology

43 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

44 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 (?)

45 Thanks!