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!