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12.740 Paleoceanography
Spring 2008
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Early B-P 14C results: Sonne II
Effect of bioturbation on sedimentary 14C
Laminated sediment
Bioturbated sediment
The role of sampling statistics in foraminiferal property analysis
Keigwin Atlantic LGM vertical 14C profile
Apparent ventilation age, years
-500
1000
0
500
1000
1500
2000
Water depth, m
2000
3000
4000
5000
Summary of apparent ventilation ages for (a) the YD and LGM time slices, and (b) benthic
foram dates during the YD and planktonic dates on the LGM benthic peaks. For each panel,
YD data are solid squares, and LGM data are open squares.
KEIGWIN: VENTILATION IN THE WESTERN NORTH ATLANTIC Paleoc. 19:PA4012 (2004)
Figure by MIT OpenCourseWare.
Deep-sea Corals
• solitary: generally don’t build
reefs (some exceptions, however)
• live for 100-1000 years, but
submersibles and dredge hauls can
bring in specimens >100,000 yrs
old
• reveal banding that is reminiscent
of surface corals - although these
may or may not be annual, they at
least give a sense of the direction
of time
• contain U, so can be 230Th/U
dated
• can be carbon dated to calculate
initial 14C
• can measure G18O, G 13C, Cd, Ba,
Sr, U etc., but none of these at
present appear to be reliable
indicators
Images removed due to
copyright restrictions.
231Pa/230Th
as a deep sea
circulation tracer
Western North Atlantic '14C, 26-10 ka
(from deep corals and abundance maxima benthic-planktonic pairs)
Images removed due to copyright restrictions.
Boyle and Keigwin (1987): North Atlantic LGM
nutrient profile shows reductions in upper
waters, enrichments in deeper waters
0
0
Depth (km)
1
Phosphorus (μmol kg-1)
1
2
3
Modern (GEOSECS 120)
2
3
Glacial
4
5
0.00
0.10
Cd/Ca (μmol mol-1)
0.20
Glacial depth profile of phosphorus in the modern western North Atlantic
(GEOSECS station 120) compared to glacial profile.
Figure by MIT OpenCourseWare.
Boyle and Keigwin (1987): deep N. Atlantic
nutrient enrichment occurred during Younger
Dryas
Images removed due to copyright restrictions.
Warren 1983 abstract
At cold temperatures, salt is more important than temperature
Tropical-polar water vapor
transport and MOC
Pore water chlorinity and oxygen isotopes
Images removed due to copyright restrictions.
Adkins, Schrag, and McIntyre (2002)
Temperature and salinity for LGM as estimated from
foram G18O and pore water G18O and salinity
Manabe and Stouffer multiple stable states
Manabe and Stouffer, 1988 C-OA-GCM
34
Greenland
35
North America
Europe
36
37
Africa
South America
Model 1: Warm High Latitude North Atlantic
With NADW
32.5
Greenland
32
North America
34
Europe
33
35
36
Africa
South America
Model 2: Cold High Latitude North Atlantic
No NADW
Figure by MIT OpenCourseWare.
Rahmsdorf and
Weaver (??)
0
a
0
0
Depth (km)
-1
9
-2
12
6
3
0
3
-3
-4
0
0
0
b
Depth (km)
-1
6
3
-2
9
0
-3
-3
-4
Depth (km)
-1
0
c
0
0
6
3
-2
-3
12
9
0
-3
-4
-64 -48 -32 -16 0 16 32
Latitude (degrees)
48
64
Zonally integrated meridional mass transport in 106 m3 s-1 in the Atlantic model
basin: (a) for the spin-up conveyor state; (b) for the equilibrium reached after the
first freshwater perturbation; (c) for the equilibrium after the second perturbation.
These three coupled equilibria exit under the same forcing. Note that in b and c
the North Atlantic Deep Water (NADW) cell does not reach down to the bottom
of the North Atlantic.
Figure by MIT OpenCourseWare.
Multiple stable states of ocean circulation?
PACIFIC
x
x
60
O
PACIFIC
ATLANTIC
64
N
O
64
N
O
O
60
60
O
0
S
48
O
x
x
x
60
O
O
O
60
0
O
60
x
64
S
O
O
O
O
O
S
48
S
48
64
N
x
60
O
64
S
O
64
S
64
N
O
O
60
0
ATLANTIC
0
O
O
S
48
O
x
O
O
64
S
x denotes sinking; larger is stronger.
Model domain of the global GFDL model.
Figure by MIT OpenCourseWare.
Marotzke and Willebrande
Events that may be related to fresh water pulses
• Younger Dryas? - diversion of outflow from Mississippi
drainage to St. Lawrence but no evidence for freshwater
signal in the North Atlantic at this time
• 8200 year cold event - possibly due to disintegration of
ice-dammed glacial Lake Aggasiz