The cold event
8,200 year ago:
Cosmopolitan
consequences of
a provincial
perturbation.
Don Barber
Geology Department
Bryn Mawr College
The cold event 8,200 years ago: “Cosmopolitan”
consequences of a provincial perturbation.
perturbation
(note: “cosmopolitan” includes Vancouver and Seattle,
but generally doesn’t include California or the Southwest)
but generally doesn’t include California or the Southwest)
ut generally doesn’t include California or the Southwest)
t generally doesn’t include California or the Southwest)
The 8,200 yr BP cold event is anomalous enough, in the
context of Holocene climate variability to be worth a look.
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GISP2 1-meter Oxygen Isotopes
δ18O (per mille)
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0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
7,000
8,000
9,000
10,000
age (yrs before 1950)
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GRIP 20-yr Oxygen Isotopes
δ18O (per mille)
-33
-34
-35
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-37
-38
0
1,000
2,000
3,000
4,000
5,000
6,000
age (yrs before 1990)
8.2 cal ka cold event: cosmopolitan?
(well, it affected Europe; what else matters?)
Gorham et al., Quat. Sci. Rev. 2007.
Gorham et al., QSR 2007.
Menounos et al., (2004) Early Holocene glacier advance, southern Coast
Mountains, British Columbia, Canada. Quat. Sci. Reviews v. 23, p. 1543–1550.
Menounos et al., (2004) Early Holocene glacier advance, southern
Coast Mountains, British Columbia, Canada. Quat. Sci. Reviews v.
23, p. 1543–1550.
What caused the 8.2 cal ka cold event?
5
6
14C
ka
7
8
9
200
195
190
Cariaco Basin
sediment greyscale
185
8.2 cal ka
Cold Event
freshwater pulse
from lake outburst
-34
-35
Summit, Greenland
GISP2 δ18O ice (‰)
-36
5
6
7
8
Calendar kyrs BP
9
10
Coldest interval lasted ~40 yrs
Barber et al., 1999
Clarke et al., Science 2003.
Modeling of the subglacial outburst drainage of Lake
Agassiz suggests that drainage was very rapid (<1 yr) and
fluxes were high (4-8 million m3/sec).
Probable
subglacial
meltwater
routings
Clarke et al., 2004. Quaternary Science Reviews,
23, pp 389-407.
max. sea-level rise in Mississippi delta
Estimated meltwater volumes and sea-level rise due to
Lake Agassiz drainage from various studies.
Calculations based on Earth radius of 6400 km & ocean fraction = 0.7. Stippled line: max. sealevel rise in Mississippi delta study area from Törnqvist et al., 2004. Geophys. Res. Lett.
70 N
Baffin
Bay
Baffin
Greenland
Island
Denmark
Strait
Iceland
DSOW
50
0
Cmb.
Snd.
00
10
Irminger
Huds
on
2
St rait
0 Basin
00
ne
ja
k
y
Re
Labrador
Sea
area enlarged
3000
LSW
ge 2000
id
sR
ISOW
60 N
00
30
NEADW
40
00
4000
G ulf
o
St . f
Lawr
ence
60 W
Orphan
Knoll
50 N
km
WBUC
40 W
0
500
1000
20 W
Meltwater routing and ocean currents of the
northwestern North Atlantic.
ECBilt-CLIO global
climate model
response to
0.75 Sv freshwater
pulse lasting 20
years
(= 4.67 x 1013 m3
total lake drainage)
Hans Renssen et al.,
2001, Geophys. Res.
Lett.; Paleoceanography, 2002
Renssen et al., 2002, Paleoceanography
temperature anomaly; deg. C
Wiersma & Renssen, 2006. Model–data comparison for the 8.2 ka BP
event: confirmation of a forcing mechanism by catastrophic drainage of
Laurentide Lakes. Quat. Sci. Rev., v. 25, p. 63.
“… model–data agreement confirms the
hypothesis that the 8.2 ka BP event was forced by
a freshwater-induced weakening of the
thermohaline circulation.”
“Other forcings are unlikely, since they would result
in an alternative geographical distribution and
expression of the climate response.”
Wiersma & Renssen, 2006. Model–
data comparison for the 8.2 ka BP
event: confirmation of a forcing
mechanism by catastrophic drainage
of Laurentide Lakes. Quat. Sci. Rev.,
v. 25, p. 63.
Simulated Jan SST, sea ice
extent and ocean
convection sites:
Before freshwater
perturbation
--Æ
After freshwater
perturbation
Wiersma & Renssen, 2006. Model–data comparison for the 8.2 ka BP event:
confirmation of a forcing mechanism by catastrophic drainage of Laurentide
Lakes. Quat. Sci. Rev., v. 25, p. 63.
simulated strength of North Atlantic meridional overturning
circulation, in Sverdrups (i.e., deepwater formation)
Wiersma and Renssen, 2006
time
Alley & Agustdottir (2005)
GCM- modeled storm
tracks:
strong Atlantic meridional
overturning circulation
(MOC)
vs.
perturbed
(reduced MOC)
conditions.
Correspondence
of winter air temp
with NAO index
Correspondence
of winter air temp
with North Pacific
SST index
Correlation fields, decadal precipitation
Rotated Principal Components (RPCs) for SW
US (top) and NW US (bottom) vs SLP over
global grid, 1900–91 .
Correlation fields, decadal precip.
RPCs for SW US (top) and NW US
(bottom) vs SST over global grid,
1900–91 .
Cayan et al., (1998) Decadal Variability of Precipitation over Western
North America. J. Clim. v. 11, pp. 3148-3166.
8.2 cal ka cold event: cosmopolitan maybe,
but not very Californian.
Thank You!