So, if evidence is accumulating that the Younger Dryas event was due to a shutdown of circulation in

1
So, if evidence is accumulating that the Younger
Dryas event was due to a shut-down of circulation
in the North Atlantic caused by freshwater
floods from Lake Agassiz. Which drained into the
region south of Greenland and Iceland where
bottom water is formed Then could the
catastrophic draining of OTHER pro-glacial lakes
also cause regional or global climate
change? Pro-glacial Lake Missoula in our own
backyard.
2
Pro-Glacial Lake Missoula Floods our own
pro-glacial lake with the potential impact on
North Pacific climate.
Lake Missoula floods About 90 floods over 2000
years (about every 25 to 50 years). Water volume
was about 2500 km3 per flood. Lake Bonneville
floods (at same time) was about 4700 km3. About
0.5 to 1 cm SL rise.
3
About 18,000 years BP, the Purcell lobe of the
Cordilleran Ice Sheet advanced into nothern
Idaho. This ice advance dammed the melt water
from the ice sheet into the (very) deep valleys
of western Montana, forming a large pro-glacial
lake.
When Lake Missoula level reached 80 of the
height of the ice dam, the dam floated, and was
catastrophically destroyed (in hours).
The lake waters then flooded E. Washington (a
desert), and entered the Columbia River drainage
at Wallula Gap.
The flood waters roared past the site of
Portland, OR as a 600 ft high wall of water at
60 mph. Then filled the Willamette Valley,
almost to California. There are glacial erratics
from Missoula icebergs in southern Oregon.
4
The Purcell Lobe of the Ice Sheet kept advancing
rapidly, and the dam re-formed and Lake Missoula
re-filled. Photo near Missoula, Montana, showing
paleo-lake levels cut into the hill-side. Lake
bottom sediments have been cored, showing many
(near 90) periods of the empty/re-fill cycle.
5
By doing land geology in the slack water areas
of the Missoula floods, it is possible to count
the number of floods, and to establish what other
events were going on at the same time (Lake
Bonneville floods, Mt St Helens eruptions, etc)
6
Previous studies of Lake Missoula floods have
stopped at the mouth of the Columbia River. But
the water from the Lake continued, out into
Cascadia Basin. The Astoria Fan, which fills
most of eastern Cascadia Basin is sediment from
the Lake Missoula floods.
7
And the sediments didnt stop with filling
Cascadia Basin Sediment cores in the NE Pacific
showed that the flood sediments extended for 1500
miles from the mouth of the Columbia
River. Similar to a landslide on Mt Baker that
ended up in Los Angeles.
8
The largest of the individual Missoula floods had
nearly the same volume as the Agassiz flood
suggested to produce the climatic changes during
the Younger Dryas (Bond et al, 1992 Clark, et
al, 2001).
More importantly, the integrated Missoula
freshwater influx over the entire 2,000 years (1
x 105 km3, estimated as 80 floods x ½ lake
volume) approaches the largest of the Agassiz
floods (R1 1.6 x 105 km3, Clark et al, 2001).
BUT there is NO DEEP WATER FORMATION in the NE
Pacific, and these floods would not have shut
down THC circulation.
9

• When the flood waters entered the Pacific Ocean,
  they did it in TWO modes.
• Hypopycnal floods where the freshwater floats
  out onto the top of the water column. Or
• Hyperpycnal floods where the sediment load
  (from E. Washington) is so large that the flood
  waters are HEAVIER than seawater. These types of
  turbidites flow ALONG THE SEAFLOOR.
• Hyperpycnal turbidites gradually release
  freshwater as giant plumes as they flow along
  the seafloor.

If the floods were hypopycnal, the freshwater
would have reduced the surface water salinity,
and the ice pack in the NE Pacific would have
extended farther south. If the floods were
hyperpycnal, the rising freshwater plumes would
have stirred the entire NE Pacific, and -
released CO2 from the bottom waters, brought
nutrients up to the surface (phytoplankton
blooms), and disrupted the surface circulation
patterns in the entire Northern Pacific. Any of
these things would (should) have caused major
climate changes.
10
What else is going on in the world (climate)
during the Missoula floods?
Missoula floods coincided with H-1 (Heinrich
event) in the Atlantic.
And the beginning of the global warming at the
end of the LGM, including the rise in atmospheric
CO2 levels.
11
But the change in water volume (0.5 cm for 1
flood 0.5 meter for 90) is too small to see in
the sea level record.
12
Can you see the impact of Missoula floods in the
d18O record? (why should you?). Cores taken
from the Gorda Basin, off Oregon, that cover
Missoula flood time..
13
Data Cores from the Gorda Plate. Cores from
Vancouver Island, Drill holes from the Gorda
plate.
14
Can you see the impact of Missoula floods in
giant piston core records off Vancouver Island?
The question is still open and requires
additional study.
15
Moving back in time, before the LGM.
Millenial Scale Oscillations in Climate.
Greenland Ice Cores show large (but short in
time) variations in temperature during the last
glacial period. These variations (abrupt warm
periods) are short (100s to a 1000 years in
period) but intense. About half (or more) the
temperature variation associated with the Dryas
Event.
Dansgaard-Oschger Cycles warm. Heingrich Events
glacial debris, cold.
16
(No Transcript)