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Oligocene to middle Miocene Paleoceanography

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Northern Hemisphere Glaciation Traditional view based on Shackleton landmark paper. Northern Hemisphere glaciation began in late Pliocene ... – PowerPoint PPT presentation

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Title: Oligocene to middle Miocene Paleoceanography


1
Oligocene to middle Miocene Paleoceanography
  • Transitioning into the Ice House World

2
Oligocene to Miocene
  • Long-term Climate
  • Deep-water Circulation
  • Case Studies
  • Boundary events

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Transition 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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Thermal 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

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20-Dec-1998
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The 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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The 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.

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The 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.

12
ODP Leg 189 Kennett and Exxon were Co-chief
Scientists. Constrained the opening of this
barrier to Eocene-Oligocene boundary
13
Drake Passage
  • Modeling efforts by
  • Larry Lawver - UT Austin
  • Reconstructions by
  • Peter Barker

14
Lawver Model
  • Switch to AKOG PPT

15
Lawver 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

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Barker Reconstruction
  • Argues that it is much more complicated that the
    Antarctic Peninsula clearing South America

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Barker Conclusion
  • Argues that Drake Passage is a Miocene event.
  • Best guess is 22-17 Ma

20
Wright 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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Wright Conclusions
  • Large-Scale Erosion
  • Late Eocene
  • Eocene-Oligocene boundary
  • mid Oligocene
  • Oligocene/Miocene boundary
  • Middle Miocene

25
Wright Conclusions
  • Drake Passage
  • Probably close to Oligocene/Miocene boundary
  • Ongoing Discussion centers on effective opening

26
Glacial History
  • Zachos smoking gun
  • Leg 120 drilled the Kerguelen Plateau. Zachos
    showed IRD and d18O increase were co-incident at
    Eocene/Oligocene boundary.

27
Zachos results show that Antarctic Ice Sheet
reached the Continental shelf. Conclusion is
that part of this d18O increase is ice related.
28
Northern Hemisphere Glaciation
  • Traditional view based on Shackleton landmark
    paper.
  • Northern Hemisphere glaciation began in late
    Pliocene - 2.6 Ma

29
Northern Hemisphere Glaciation
30
Northern Hemisphere Glaciation
Site 659
Tiedemann et al., 1994
31
Northern Hemisphere Glaciation
  • Drilling in higher latitudes reveals different
    story.
  • NHG during middle Miocene

32
ODP LEG151
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The Miocene Perspective
34
Generalization
  • Middle to late Miocene Northern Hemisphere Ice
    Sheets were small but present

35
Higher 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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Icehouse Events
  • Miller and Wright argued that these were Ice
    Sheet Temperature
  • Covariance in PF and BF records
  • Correspondence to Glacial Sediments

38
Icehouse Events
  • Overheads on Icehouse seds

39
Katabatic 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.
40
Katabatic Winds
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Antarctic Surface Water
42
Antarctic Influence on Deep Water
  • Go to Overheads on Cyclicty

43
Northern Deep Water Circulation
  • Erosion and Deposition
  • Carbon Isotopes

44
The Physical RecordErosion and Drifts
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Gardar DriftSnorri DriftFeni Drift
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The Eirik Drift - S. Greenland
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Erosion and Accumulation
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Two 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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d13C 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)

63
Warm Saline Deep Water
  • Woodruff and Savin championed this idea for the
    Miocene.
  • Best evidence is found in early Miocene

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A North Atlantic Valve
67
Greenland-Scotland RidgeMean Depth 300 m
68
Mechanism to Change Mean Depth along GSRMantle
Plume Peter VogtG. Ito Modeling
69
Garrett ItosModel ofMantle Plume
VariationsAnomalies Extend to 500 km from
Plume axis
70
V-Shaped Ridges and Escarpments
71
Anomalous Crustal Production
72
Cruise 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
74
A Proxy for Mantle Plume Production
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