Transcript What was the role of July temperature in determining the late

Question for Svante
What was the role of July
temperature in determining the
late-glacial vegetation patterns in
north-west Europe?
Hilary Birks and John Birks
Late Glacial: period of rapid and large climate changes
We infer these changes from proxy data, such as pollen, and
automatically interpret them as ‘Younger Dryas’ etc.
We usually ascribe these changes to changes in temperature;
• warming during the Bølling and Allerød following deglaciation;
• cooling in YD;
• rapid warming in early Holocene
But – are the vegetation changes the same across NW Europe?
– is temperature the major driving factor?
To determine if there are geographical patterns – we can take
pollen (and macrofossil) records across NW Europe as a
vegetation proxy to infer patterns in vegetation development
through the Late Glacial
To find the relationship to temperature, we need an
independent proxy for Mean July Temperature;
(Tjul) from Chironomid data
15 sites in NW Europe have published pollen data (proxy for
vegetation) and chironomid data (independent proxy for
temperature)
15 published sites
Jansvatnet
Lusvatnet, Andøya
Kråkenes (starts 14ka)
Loch Ashik (2 cores)
Abernethy Forest (2 cores)
Whitrig Bog
Hawes Water + 3 pollen sites nearby
Quidenham Mere (chiro) + Sea Mere
(pollen)
Loch Nadourcan
Fiddaun
Hijkermeer
Klein Ven (no YD)
Friedländer Grosse Wiese
Ech
Laguna de la Roya
Eriboll
Björkeröds mosse + 2 others
Slotseng
De Borchert
Usselo
= Additional sites with macros
Svante are you still
paying attention ?
Three late-glacial phases;
1.
2.
3.
Bølling
14.7 – 14.0
GI-1e
Allerød
14.0 - 12.7
GI-1d-a
GI-1d is a cold phase in Greenland ice cores (Older Dryas)
For AL, use period of warm temperature: GI-1c-a
Younger Dryas 12.7 - 11.55
GS-1
Method
• Poor chronologies: Take YD boundaries as synchronous.
• Correlate variations in the chironomid temperature curve with
interstadial (GI-1) oscillations and GS-1 (YD)
• Plot mean temperature for each phase geographically
• Plot temperature differences between phases (BØ→AL excludes GI-1d
cold phase)
• Also plot GI-1d temperatures and map extent of GI-1d
• Compare with pollen % curves for most abundant taxa:
Betula, Pinus, Empetrum, Salix, Juniperus, Artemisia
Gradients
Gradients
11
12
HOT SPOTS
in both BØ
and AL
11
12
increase
-1-1
-0.5
0
-1
+1
Small decrease or
no change
GI-1d ‘Older Dryas’
cooling
Temperature drop
from AL to
‘Older Dryas’
GI-1e to GI-1d
-1-3
-0.5
-1
-3-3
-4
-1.5
-2
Gradients
AL to YD temperature decrease
4.5
6
5
2.5+
0-1.5
4
6.5
5
4
10+
Really cold
10oC or more – warm
enough for tree birch
Betula pollen% - Bølling
Bølling temperatures
Tjul maybe marginal for
tree birch; ± on Tjul
T?
Bn; Betula nana (macros)
at highest % Betula pollen
T; Tree Betula (macros)
Suitable Tjul for tree birch;
but no tree birch, only Bn.
Why?
Migrational delay
Dry sandy soils
Arid windy climate
Betula - Allerød
6oC
High Empetrum,
Cyperaceae
10oC
Gramineae
assemblage
- grazing
Allerød temperatures
Ireland: sparse tree birch.
Cold winds from Atlantic
Dry limestone soil
Grazing
11
N limit Tree birch
12
Bn
S limit
dwarf birch
T = Tree birch macros
Bn = Dwarf birch macros
Spread of tree birch. Not
much change in Tjul.
Why?
More precipitation, less severe
winds, fewer spring frosts,
allowed spreading
Huge increase
Pinus
Pinus
Betula – Younger Dryas
Betula – % decrease AL to YD
Too cold
Tjul
6oC
-40 Huge decrease –
No tree-birch macros
B. nana spread south
favourable Tjul.
Why?
Cold, permafrost,
arid, windy (cover
sands)
Bølling: Pinus migrating from
central Europe
Bølling temperatures
Temperatures above 12oC
Migration delay
.
12oC +
Pinus in Allerød:
spread blocked Marginal temperature? Migrational lag?
Pinus sylvestris needs Tjul
12oC or more
An Iberian species?
Pinus in Younger Dryas
Huge decrease;
Tjul still favourable.
Why?
Earliest YD temperatures
Continental; arid;
permafrost; windy; fires
Salix - Bølling
Sp
Macros give species info
Dwarf Salix macros only
Sp = Salix polaris macros
Cold, dry, continental
Sh, Sp
Sp
Sr
Sh = Salix herbacea
macros Cold, snowy
Sr = S. reticulata macros
at Usselo – heliophilous
vegetation
Sp
Sh
Sh (Sp)
Sh
Allerød
Salix polaris (Sp) in north
Norway and inner fjords –
Continental and cold
Salix herbacea (Sh) in west
Norway and north Scotland –
Oceanic, wet and cold, snowcover i.e. precipitation is
important
No macro evidence
further south
Sp
Younger Dryas
Salix polaris Sp in North
Norway arid and cold
Sh
Sh
‘Younger Salix
herbacea’ zone
Salix herbacea Sh widespread
in South Norway and Scotland.
Oceanic, snowy
Also in Ireland. Sh macroevidence from many sites –
Jessen: «Younger Salix
herbacea zone» rather than
Younger Dryas
Commonest in W Scotland
and W Ireland
Huge amounts at Loch
Nadourcan (acid bedrock)
Too cold and dry in N Norway
In UK and N Europe;
competition from shrubs, e.g.
Juniperus, B. nana, and Salix
Empetrum - Allerød
Empetrum – Younger Dryas
Too cold
Cold, wet, acid soils
Too cold
Colder,
wetter.
Inwash
from
AL soils
Too snowy
Too arid,
permafrost
Juniperus – Bølling
peaks
Juniperus – Allerød
Grazing?
Rumex Juniperus
assemblage
Mirrors Empetrum
Open birch woodland with Juniperus
Juniperus Younger Dryas
Rare everywhere
? An Iberian species at Laguna
de la Roya ?
Cold winters, windy,
permafrost, arid
Iberian species?
Artemisia - Bølling
Artemisia - Allerød
Long distance transport
Warm soil,
dry steppe
Long distance transport
Abundant in eastern Scotland
Rain shadow and high
insolation → warm dry soils
‘Artemisia
assemblage’
‘Artemisia assemblage’
in Ireland
Climate pattern Arctic
Sea ice
Ice sheet
Oceanic
dry land
Continental
Vegetation pattern -
Sparse
Pioneer grass- Rumex
→ Empetrum Juniperus
Open dry grassland
with Dryas + Bn
Open dry grassland
+ Bn
Steppe
Migration
lag trees
Arid
Oceanic
Wet
Snow
Ice retreat
11
12
Megaherbivore
grazing
Continental
Dry
Vegetation pattern -
Sparse
Arctic alpines
11
12
Birch tree line
grassland
Pine tree line
Dry - Birch - Pine
Birch - Pine
Migration lags
Climate pattern -
Arctic
Ice sheet
readvance
Arid, cold winds, stormy,
permafrost, aeolian
sands, fires
Vegetation pattern -
Polar
desert
Snow beds
The classic Younger Dryas area
Dry open grassland,
unstable soils
Let me get my
head round this
That’s
fascinating!
Conclusions
At this coarse geographical scale and time scale, July
temperature is not a good predictor of pollen %
patterns, and hence of vegetation patterns
Climate
Direct
Indirect
Temperature
Precipitation
Permafrost Soil moisture
Sea ice
Land ice
Humidity ;
P:E
Seasonality
Oceanicity
Wind
Direct effects of climate on vegetation
+
Temperature
Precipitation
-
Geographical limits
Snow
Aridity : Desert
Spread
e.g. Betula Pinus
Extinction
e.g. trees in YD;
Empetrum + Juniperus
in NE UK in YD
e.g. Salix herbacea
in NW Scotland
and Norway , esp.
in YD
North Norway
in whole LG;
Netherlands in
YD
Artemisia in East
Scotland YD
Ecosystem processes =
indirect effects or responses
Species
Temperature Climate
Precipitation envelope
Soil
Competition Grazing
Migration
Extinction
Vegetation
Realised
Niche
Species composition
Succession
Competition
Expansion
or reduction/extinction
Immigration of keystone
spp
Extinction of keystone spp
Catastrophes -Fire/disease
• Late-glacial vegetation patterns are responses to
Climate patterns, mainly Temperature and
Precipitation
• The ecological tolerances of species and the complex
and interacting climate patterns lead to complex
vegetation patterns and responses to changes.
In the future: facing 2+oC warming, but from an already temperate
base-line.
• However, plants, animals, and vegetation in NW Europe will still
respond in accordance with their ecological tolerances, and
vegetation changes will depend on the complex combination of
direct and indirect ecosystem effects.
• But, a new factor in the equation is human impact, which is now
universal. It facilitates vegetation change (e.g. forest clearance)
landscape change, burning, invasion of exotic species, including
diseases, and more recently, climate warming.
Now I get it!
_
Isn’t science
&_
fun
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Do you still enjoy Scrabble? –
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