1. The impacts of the North American ice-sheet on glaciation conditions over northern Europe: an atmospheric circulation study with the LMDZ model*
Pauline Beghin1, Sylvie Charbit1, Masa Kageyama1
Christophe Dumas1, Catherine Ritz2
1: Laboratoire des Sciences du Climat et de l’Environnement/IPSL, Gif-sur-Yvette, France
2: Laboratoire de Glaciologie et de Géophysique de l’Environnement, Grenoble, France
*A study published in
Beghin et al, Climate of the Past Discussions, 11, 26-61, 2015

2. Glacial-interglacial cycles
Main contributors to glacial-interglacial sea-level changes: North American and European ice sheets
Massive mid-latitude ice-sheets  strong disturbance to atmospheric circulation
Interplay between these two ice-sheets via the atmospheric circulation?
Here, we study the impact of the North American ice-sheet on European climate
Relative sea level (m)
Waelbroeck et al, 2002
time (ky)

3. Model and experiments
model
LMDZ5 atmospheric model, 96x95x39, as in IPSL_CM5A_LR
Atmospheric composition, insolation, land-sea mask as in IPSL LGM PMIP3-CMIP5 simulation
SSTs and sea-ice from IPSL LGM PMIP3-CMIP5 run (Kageyama et al, Climate Dynamics 2012)
5 experiments with/without North American ice-sheet albedo and varying topography from PI to LGM; no European ice-sheet
boundary conditions

4. Winter atmospheric circulation changes
no ice sheet
flat ice sheet
Atlantic jet stream more zonal
Winds more northerly for NE Europe
full ice sheet
m/s

5. Winter circulation and European climate
temperature anomalies
( K)
precipitation anomalies
(mm/day)
Atlantic jet stream more zonal
Winds more northerly for NE Europe
m/s

6. Relationship between precipitation and jet changes
precipitation anomalies
(mm/day)
Jet stream latitudinal position change
Precipitation changes over Scandinavia
So…
A higher North American ice-sheet drives a drier Scandinavia/Barents/Kara area
… not so good for building an ice-sheet!

7. Summer climate change SUMMER WINTER flat ice sheet strong cooling over
Barents-Kara Seas
cooling decreases as
North American ice sheet gets higher
cooling increases as
North American ice sheet gets higher

8. Summer atmospheric circulation changes
temperature anomalies
( K)
trough over North American ice sheet
southerlies reach further north

9. atmospheric circulation
Summary
change in
annual precip
change in
annual snowfall
North American ice sheet
atmospheric circulation
(stationary waves)
WINTER over NE Europe
cooler temperatures
less precip (jet shifts S’d)
SUMMER over NE Europe
flat ice  colder
but cold anomaly decreases as N America altitude increases
 Impact on potential NE European ice sheet?

10. Ice sheet growth from GRISLI ice sheet model
flat North American ice sheet favours growth of NE European ice sheet
North American ice sheet growth
inhibits
NE European ice sheet growth

11. Conclusions & perspectives
Atmospheric circulation changes due to North American ice sheet are large enough to impact on ice sheet growth over NE Europe
Our results suggest a succession of ice sheet states with
1/ low North America ice sheet, built up of European IS 2/ growth of North America IS, smaller European IS
BUT
Our experiments are highly idealised, North American ice sheet did not appear all at once
Need to refine experiments, e.g. using recent reconstructions from Kleman et al (2013)

12. Thank you!
Cosquer
Lascaux