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Lecture 19
Stratigraphy of climate change
The predominant power in
this spectrum is at about
100,000, 41,000 and 1923,000 years
from Alley, 2000
The Milankovitch hypothesis: climate
change results from changes in Earth’s
orbital parameters
Barbados
Today we’ll look at
examples of climate
changes seen in the
stratigraphic record
that are NOT
controlled by orbital
parameters
Orbital Forcing – Ice Cores
• Ice core 18O
records temperature
• Orbital frequencies
are clearly
dominant, but
higher frequencies
are present
• Discovered
in 1988 in
marine
sediment
cores
• Recognized
as distinct
layers with
significant
increase in
lithic
fragments,
and large
clasts in
some areas
Heinrich Events
Heinrich Layer Isopachs
• Double maxima in isopachs
• Layers thicken to NW into Labrador Sea
Source of Heinrich events
• Black
areas are
regions
with large
carbonate
deposits
• Sediment
must have
been icerafted
Heinrich Layer 4 (~40,000 years BP)
18O in polar planktonic foraminifera
Modeling shows about 250-year duration and 2-m
rise in sea level
Nature, Roche et al., 2004
Modeling shows
about 250-year
duration and 2-m
rise in sea level
Nature, Roche et al., 2004
Heinrich
Events
in
context
• Occur at times of coldest weather in N. Atlantic
• Followed by a sharp warming
• No clear periodicity
Bond 1993 figure
Summary of Heinrich events
• Effects are global – signature of Heinrich
events has been found around the world
• Massive discharge of ice into N. Atlantic
from the Laurentide ice sheet is well
established
• No clear explanation for such dynamics in
the ice sheet
Dansgaard-Oeschger Events
• Characterized by
rapid warming in the
N. Atlantic, followed
by slower cooling
• Quasi-Periodic, with a
timescale of ~1400
years
• Recorded by diverse
climate proxies
• Evidence for global
climatic effects
(Data From ftp://ftp.ngdc.noaa.gov/paleo/icecore/greenland/summit/grip/isotopes/gripd18o.txt)
Greenland and D-O events
• Within the Greenland ice cores, several
independent variables all show D-O events
prominently
 18O – Temperature
– Ca/Dust concentrations – varying weather in Asia?
– Na/Cl concentrations – increased storminess in N.
Atlantic
– Etc…
Other Evidence of D-O events
• Sediment cores from
the Santa Barbara
Basin (Hendy and
Kennet, 1999)
Other Evidence of D-O events
• Stalagmites from
Eastern China (Wang
et al., 2001)
Global Map of D-O records
http://www2.ocean.washington.edu/oc540/lec01-31/
Theories for rapid climate change
• Heinrich, D-O periods are too rapid for
orbital frequencies
• Some combination of the
ocean/atmosphere/cryosphere must be
responsible
• Need a source with enough power to affect
global climate
Atlantic Circulation
Deep water
formation
•Deep Water is formed at
the Northern and Southern
extents of the Atlantic
Ocean
•This deep circulation has
an overturning timescale
of ~103 years
•Surface currents strongly
influence climate in many
areas, as in the N. Atlantic
Deep water formation
Stratigraphic Evidence
• Recent work (April 2004) has
investigated a proxy for Atlantic
circulation using a marine
sediment core from the Bermuda
Rise
• Th settles out of water faster than
Pa, so the ratio between the two
can provide information about
the strength of flow away from
source
• Result – Atlantic circulation
essentially shut down during
Heinrich events
Summary
• There is still no clear trigger for Heinrich or
Dansgaard-Oeschger events, nor an explanation
for their periods
• However, changes in Atlantic circulation seem to
account for many of the side effects of both
processes
• More stratigraphic records = more clues
Why it all matters
• Late Pleistocene
was not simply cold
– it was totally
chaotic
• Even modern
agricultural
processes probably
couldn’t overcome
such variability
Beginning of
Agriculture
End of
Agriculture???
A few references…
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Bradley, Raymond S. Paleoclimatology. Harcourt Press, 1999.
Siedov et al., Ed. The Oceans and rapid climate change. AGU, 2001.
Hesse, R. and Khodabakhsh, S. Depositional Facies of Late Pleistocene Heinrich Events
I nthe Labrador Sea. Geology 26:2 103-106, 1998.
Dansgaard, W et al. Evidence for general instability of past climate from a 250kyr icecore record. Nature 364, 15 July 1993.
Bond, G. et al. Evidence for massive discharges of icebergs into the North Atlantic
Ocean during the last glacial period. Nature 360, 19 Nov. 1992.
Sarnthein, M. et al. Exploring Late Pleistocene Climate Variations. Eos. 81:51 2000.
Bond, G. et al. Correlations between climate records from North Atlantic sediments and
Greenland ice. Nature 365, 9 Sept. 1993.
Bard, E. Climate Shock: Abrupt changes over Millennial time scales. Physics Today
Dec. 2002.
Hendy and Kennett. Dansgaard-Oeschger cycles and the California Current System:
Planktonic foraminiferal response to rapid climate change in Santa Barbara Basin,
Ocean Drilling Program hole 893A. Paleoceanography, 15:1, 2000.
Phillips, FM. Climatic and hydrologic oscillations in the Owens Lake basin and adjacent
Sierra Nevada, California. Science 274:5288, 1996.
Wang, YJ. A High-Resolution Absolute-Dated Late Pleistocene Monsoon Record from
Hulu Cave, China. 294:5550, 2001.