Transcript Climate Change and the Oceans: A Geological Perspective William Curry

Climate Change and the Oceans: A
Geological Perspective
William Curry
Woods Hole Oceanographic Institution
75th Anniversary Symposium
September 21, 2005
Louis Agassiz (1807 – 1873)
• “Study nature, not books”
• 1837 – presented his theory of the Great Ice
Ages at the annual meeting of the Swiss Society
of Natural Sciences
Glacial Striations
(From Imbrie and Imbrie, 1979)
Glacial erratics,
moraines and
tills
(Agassiz, 1840; Figure from
Imbrie and Imbrie, 1979)
Agassiz’s theory
generally accepted by
the 1860s
Last ice advance
approximately 20,000
years ago
T. C. Chamberlain
reconstruction from
the 1890s
(From Imbrie and Imbrie, 1979)
Milutin Milankovitch (1879-1958)
• 1930 - Mathematical Climatology and the Astronomical
Theory of Climatic Changes
• Calculated the insolation variations at 8 different latitudes
and demonstrated the significance of changes in insolation at
65 oN
Modern Orbit
11,500 Years Ago
Milankovitch Insolation Curve
(ca. 1924)
(From Imbrie and Imbrie, 1979)
The Marine Record of Climate
Sediment Coring in the 1940s
• Charles S. Piggot – Carnegie Institution
• Henry Stetson – WHOI
• Borje Kullenberg – Goteberg, Sweden
David Ericson
• Worked at WHOI in late 1940s as an assistant to
Fred Phleger (who eventually moved to SIO) and
Henry Stetson
• Early expert on fossils in deep sea sea sediments
• Moved to LDEO in the early 1950s to work with
Maurice Ewing to study deep sea sediments
• Produced the first marine records of climate
change
Planktonic Foraminifera
11,000
yBP
G. menardii
Cesare Emiliani (1922-1995)
• Graduate student at University of Chicago with Harold
Urey
• 1955 - Produced the first oxygen isotope records using
deep sea sediments
• Often considered the “Father of Paleoceanography”
A179-4 - Caribbean Sea
Emiliani (1955)
11,000
yBP
A179-4
Ice Age Climate records
400,000
yBP
Emiliani, 1955
• 15 complete temperature cycles in last 600,000
• Good correspondence of temperature minima with
minima in Northern Hemisphere insolation
• Predicted the next ice age to begin in 10,000 years
The Current Era
• 1976 - Hays, Imbrie and Shackleton provide the
first spectral analysis documenting the presence of
the primary orbital frequencies
• 1976 (and 1984) - CLIMAP produces a global
reconstruction of the ice age climate
The CLIMAP Reconstruction
February Today
February 21,000 yrs ago
The Current Era
1980s and 90s - The hunt for other causes of
climate variability begins in earnest – unforced
suborbital climate variability
Glacier layering
Glacial Period
Large Scale Ocean Circulation
North Atlantic Circulation
Temperature Response
• Strong cooling in North Atlantic
• Warming everywhere else
• No net global change
Manabe and Stouffer, 1997
NADW
GEOSECS
Conservative Mixing
NADW High Salinity – High d13C
AABW Low Salinity – Low d13C
NADW
GEOSECS
NADW
Kroopnick (1985)
Core locations
New Brazil Margin Cores
(Curry and Oppo)
New Blake Ridge Cores
(Keigwin)
Curry and Oppo (2005)
Curry and Oppo (2005)
Curry and Oppo (2005)
NADW
Kroopnick (1985)
Curry and Oppo (2005)
Curry and Oppo (2005)
What about the rate of flow?
• Tracers only show geometry
• Geostrophy and radionuclides provide rate
information
Reduced North Atlantic MOC
• Key density gradients are reduced suggesting
that overturning was reduced
• Reduced export of particulate 231Pa suggests
that export of deepwater was reduced
• Large increases in the radiocarbon age of the
deep water track increased input of southern
ocean deep waters into the North Atlantic
231
Pa /
230
Th
GISP2
H1
YD
NADW on
NADW off
0.093
Bermuda Rise
McManus et al. (2004)
Summary
• There is clear evidence for forcing of the climate
changes through changes in the earth’s orbit
• At millennial time scales, there climate variability is
strong, but external forcing mechanisms are unknown
• Evidence is growing that reorganizations of oceanatmosphere systems were linked to the millennial
climate variability
• Marine sediments helped to unlock the secrets of the
ice ages and the response of the ocean circulation