. Lateglacial summer temperature changes and vegetation development along a west to east transect across NW-Europe

M i n i m u m t e m p e r a t u r e f o r b i r c h / p i n e f o r e s t

Ireland The Netherlands

Belgium

M i n i m u m t e m p e r a t u r e f o r b i r c h / p i n e f o r e s t Summer temperatures restrict forest

INTRODUCTION

Nelleke van Asch

*, Oliver Heiri

and Wim Z. Hoek

RESULTS

Lateglacial summer temperature changes and vegetation

development along a west to east transect across NW-Europe .

Lateglacial climatic changes, such as the Younger Dryas cold phase, are associated with changes in the North Atlantic

thermohaline circulation. Presumably, Lateglacial temperature

changes were most pronounced in regions close to the ocean and decreased further inland.

Here we infer longitudinal temperature gradients in northwest Europe during the Lateglacial. These are based on existing

chironomid-based temperature reconstructions from the region.

Reconstructed summer temperatures are compared with

Lateglacial vegetation development to gain insight into the effect of summer temperature on vegetation in the region. Vegetation

development is generalised from existing pollen records.

CONCLUSIONS AND FURTHER RESEARCH

 Large range of Interstadial temperatures: centennial-scale cold oscillations

 Strong temperature decline during the YD: minimum values are 3-6 °C below average interstadial values.

 Enhanced longitudinal temperature gradient during coldest phase YD increased influence of Atlantic Ocean

 Vegetation development reflects a combination of environmental (e.g. migration) and climatic gradients (e.g. summer temperature, seasonality)

 TO DO: include additional chironomid-based temperature reconstructions from this region for more reliable gradient inferences

1 Faculty of Geosciences, Utrecht University, the Netherlands. * N.vanAsch.uu.nl@gmail.com

2 Institute of Plant Sciences and Oeschger Centre for Climate Change Research, University of Bern, Switzerland.

Pictures by Hanneke Bos, Wim Hoek

RESEARCH SITES

Open landscape, herbaceous grassland with local stands of birch Birch and pine forests

Open landscape, shrub-tundra with birch

Increasing distance from Atlantic Ocean

Shrub/forest-tundra with birch and pine Open pine forest with birch and juniper

Chironomid-based temperature

reconstructions and pollen records are used from the mid-latitudes

(50-56°N) in northwest Europe:

• South of the ice sheets during the Lateglacial period.

• Focus on longitudinal

temperature gradient: influence of the Atlantic Ocean

• Narrow latitudinal range to

minimise the N-S temperature gradient.

Open birch forest with juniper shrubs Pine dominated forest with birch

Migration of pine

I N T E R S T A D I A L Y O U N G E R D R Y A S

Increasing summer temperatures & seasonality

Summer temperatures do not restrict forest

15 10

5 0

-5 -10

12 10

6 8

18 16 14 12 10

Scotland

England Germany

Minimum YD chironomid- inferred mean July air temperature (°C)

R ange of Int ers tadial chironom id -inf erred m ean July air t em perat ures (° C)

Longitude (°)

Forest limited by other factors

FID LN NW-E WhB

Hijk FGW

FID LN

NW-E

WhB

Hijk

FGW KV

MB

FID: Fiddaun (Van Asch et al., 2012, PPP-315-316) LN: Lough Nadourcan (Watson et al., 2010, JQS-25) WhB: Whitrig Bog (Brooks and Birks, 2000, JQS-15)

NW-E: Five northwest-England sites (Lang et al., 2010, QSR-29) MB: Moerbeke (Gelorini et al., in prep.)

KV: Klein Ven (Van Asch et al., 2013, Bor-42) Hijk: Hijkermeer (Heiri et al., 2011, QSR-30)

FGW: Friedlander Groβe Wiese (Van Asch et al., 2012, JQS-27)

Lateglacial chironomid records

FID

LN WhB NW-E

MB

KV Hijk

FGW

55°N

50°N YD ice sheet

10°W 0° 10°E 20°E

Tundra with some willow and birch shrubs

Veget at ion Tem per at ur e Tem per at ur e Veget at ion