Title: Oligocene to middle Miocene Paleoceanography
1Oligocene to middle Miocene Paleoceanography
- Transitioning into the Ice House World
2Oligocene to Miocene
- Long-term Climate
- Deep-water Circulation
- Case Studies
- Boundary events
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4Transition into Psychrosphere
- In 1976, Jim Kennett and Nick Shackleton
published a paper proposing that the
Eocene-Oligocene boundary represented a
transition into a Psychrosphere (warm surface
ocean above a cold deep water mass).
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6Thermal Isolation
- In a series of papers, Kennett and Shackleton
laid the grounds for a tectonic trigger -
Thermal Isolation of Antartica - Two barriers cleared and allowed the Antarctic
Circumpolar Current to initiate. - Tasman Rise and Drake Passage
720-Dec-1998
8The Southern Ocean circles the world in the
Southern Hemisphere between latitudes 40 degrees
and 60 degrees South. Unlike the Northern
Hemisphere, there are no land masses to break up
this great continuous stretch of sea water.
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10The ACC and Climate
- The ACC and its effect on climate. They find it
controls climate in three ways - 1. By connecting the worlds oceans, the ACC
redistributes heat and other properties
influencing the patterns of temperature and
rainfall.
11The ACC and Climate
- 2. The vertical movement of water, caused by
antarctic freezing during the winter and warming
during summer, controls the renewal of deep water
in the worlds oceans. - 3. There is an exchange of gases, such as oxygen
and carbon dioxide, with the atmosphere at the
sea surface. The ocean contains 50 times more
carbon than the atmosphere, so the rate at which
carbon dioxide is absorbed by the Southern Ocean
can directly affect climate change.
12ODP Leg 189 Kennett and Exxon were Co-chief
Scientists. Constrained the opening of this
barrier to Eocene-Oligocene boundary
13Drake Passage
- Modeling efforts by
- Larry Lawver - UT Austin
- Reconstructions by
- Peter Barker
14Lawver Model
15Lawver Model
- In a conversation with Larry, I asked him when
the Drake opened. - His response was
- that we (paleoceanographers) would tell him.
The tectonic models get you into the ball park. - The answer is
- some time in the Oligocene
16Barker Reconstruction
- Argues that it is much more complicated that the
Antarctic Peninsula clearing South America
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19Barker Conclusion
- Argues that Drake Passage is a Miocene event.
- Best guess is 22-17 Ma
20Wright Analysis
- In the early 1990s, I borrowed an idea from
Kennett. I looked at the distribution of
sediments in the Southern Ocean recovered during
DSDP and ODP drilling. - The following was published in
- Wright and Miller 1993
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24Wright Conclusions
- Large-Scale Erosion
- Late Eocene
- Eocene-Oligocene boundary
- mid Oligocene
- Oligocene/Miocene boundary
- Middle Miocene
25Wright Conclusions
- Drake Passage
- Probably close to Oligocene/Miocene boundary
- Ongoing Discussion centers on effective opening
26Glacial History
- Zachos smoking gun
- Leg 120 drilled the Kerguelen Plateau. Zachos
showed IRD and d18O increase were co-incident at
Eocene/Oligocene boundary.
27Zachos results show that Antarctic Ice Sheet
reached the Continental shelf. Conclusion is
that part of this d18O increase is ice related.
28Northern Hemisphere Glaciation
- Traditional view based on Shackleton landmark
paper. - Northern Hemisphere glaciation began in late
Pliocene - 2.6 Ma
29Northern Hemisphere Glaciation
30Northern Hemisphere Glaciation
Site 659
Tiedemann et al., 1994
31Northern Hemisphere Glaciation
- Drilling in higher latitudes reveals different
story. - NHG during middle Miocene
32ODP LEG151
33The Miocene Perspective
34Generalization
- Middle to late Miocene Northern Hemisphere Ice
Sheets were small but present
35Higher Frequency Climate
- The million year events.
- Miller and Wright identified a series of d18O
cycles with a duration of 1 to 2 million years - Termed Oi and Mi events.
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37Icehouse Events
- Miller and Wright argued that these were Ice
Sheet Temperature - Covariance in PF and BF records
- Correspondence to Glacial Sediments
38Icehouse Events
- Overheads on Icehouse seds
39Katabatic Winds
The highest wind speeds ever recorded at sea
level anywhere in the world were at Cape Denison
in Adelie Land. Ninety years ago Sir Douglas
Mawson landed there and dubbed the area "Home of
the Blizzard" because the winds blew men off
their feet. Peak gusts have been clocked moving
faster than 100 mph.
40Katabatic Winds
41Antarctic Surface Water
42Antarctic Influence on Deep Water
- Go to Overheads on Cyclicty
43Northern Deep Water Circulation
- Erosion and Deposition
- Carbon Isotopes
44The Physical RecordErosion and Drifts
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46Gardar DriftSnorri DriftFeni Drift
47The Eirik Drift - S. Greenland
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49Erosion and Accumulation
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51Two Modes of Circulation
- Warm Mode
- N. Atlantic Deep Water
- Shallow Compensation
- Cold Mode
- N. Atlantic Intermediate and Upper Deep Water
- Deep Compensation
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62d13C Circulation Conclusions
- Brief Early Oligocene pulse
- Early Miocene interval 20 to 20 Ma
- Most recent phase began in late middle Miocene
(after 13 Ma) - Strongest in Pliocene (next lecture)
63Warm Saline Deep Water
- Woodruff and Savin championed this idea for the
Miocene. - Best evidence is found in early Miocene
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66A North Atlantic Valve
67Greenland-Scotland RidgeMean Depth 300 m
68Mechanism to Change Mean Depth along GSRMantle
Plume Peter VogtG. Ito Modeling
69Garrett ItosModel ofMantle Plume
VariationsAnomalies Extend to 500 km from
Plume axis
70V-Shaped Ridges and Escarpments
71Anomalous Crustal Production
72Cruise V23-03 (1969) crossed the Reykjanes Ridge
10 Times. Seismic and magnetic data allow
identification and dating of V-shaped
features(Talwani et al. 1971)
73 Tracing the Anomalies to Iceland16 cm/yr20
cm/yr33 cm/yr50 cm/yr100 cm/yr
74A Proxy for Mantle Plume Production
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