Paleoceanography II Telluric Effects on Oceanography

Transcription

1 Paleoceanography II Telluric Effects on Oceanography Geological Oceanography OCN 622 Gary McMurtry

2 Telluric Effects Tellus = Earth Distribution of Continents at 100 Ma BP and Present Comparison of Earth s Albedo in Cretaceous Period versus Present: What Happened? From: Kennett (1982)

3 Cambrian Period From: S. M. Stanley, Earth and Life Through Time (1989)

4 Ordovician Period From: S. M. Stanley (1989)

5 Silurian- Devonian Periods From: S. M. Stanley (1989)

6 Carboniferous Period Lycopod trees From: S. M. Stanley (1989)

7 Permian Period From: S. M. Stanley (1989)

8 Triassic Period From: S. M. Stanley (1989)

9 Early Cretaceous Period From: S. M. Stanley (1989)

10 Late Cretaceous Period Water World! From: S. M. Stanley (1989)

11 Tertiary: Late Eocene From: S. M. Stanley (1989)

12 Eocene-Oligocene Transitions Opening of Drake Passage at 28 Ma B.P.: Before & after inferred circulation patterns Separation of Australia from Antarctica at South Tasman Rise, 38 Ma B.P. (stippled) Antarctica Isolated! From: Kennett (1982)

13 Early & Middle Miocene: Tethys Seaway Closes in East From: S. M. Stanley (1989)

14 Late Miocene: The Mediterranean Sea Dries Up Messinian Event or Crisis From: S. M. Stanley (1989)

15 Mid-Miocene Sinking of the Iceland- Faeroe Ridge: Formation of North Atlantic Deep Water (NADW) Inferred paleo-circulation Subsidence history of top of Iceland-Faeroe Ridge From: Kennett (1982)

16 Plio-Pleistocene Period: Our World Glaciers as they existed in a typical glacial interval of the Pleistocene Sea-level changes during the Neogene Gulf Stream From: S. M. Stanley (1989)

17 Deep-Sea Sediment Core Record Note: evidence for two cycles in Pleistocene Period

18 The Pliocene Paradox: Mechanisms for a Permanent El Nino Warmer Colder Ice Core Data Human Impact Fedorov et al., Science (2006)

19 Milankovitch & the Astronomical Theory of Climate Variations Causes of variation in intensity and distribution of solar insolation on Earth 1. Orbital Eccentricity --Varies from near 0 (a perfect circle) to 6% over a 100,000 year period, as originally calculated by Leverrier (1843). The value today is about 1%. --Variation is caused by gravitational pull of the planets. Leverrier s s calculations led to the discovery of Neptune. --Resulting variations in solar insolation average out over a year, but are different from season to season.

20 Milankovitch & the Astronomical Theory of Climate Variations (cont.) 2. Nutation (tilting) of the Earth s s axis --Varies from 22 to 25,, or about 1.5 about the present value of 23.5 from the vertical, as defined by the plane of Earth s s orbit, every 41,000 years. Dominates the radiation input at high latitudes. --Variation results mainly from the gravitational pull of the Moon and Jupiter. 3. Precession of the Equinoxes --Varies with a period of 22,000 years (d Alembert, 1754) as a result of: 1) Axial wobble: Earth s s axis rotates around a full circle every 26,000 years, in a clockwise direction when viewed from above the North Pole, because of the gravitational pull of the Sun and Moon on Earth s s equatorial bulge. It dominates the radiation input at low latitudes. 2) Precession of perihelion: Earth s s orbital ellipse also rotates, in the opposite direction to the axial wobble but independently and much more slowly.

21 Milankovitch Cycles From: Kennett (1982)

22 The Cenozoic Deviation of the Benthic and Planktonic O-isotope Record Savin & Yeh (1981)

23 Major Telluric Events in Cenozoic Time (Ma) Event Result Consequence for Global Climate 38 Separation of Antarctica from Australia (Tasmania) Initiate circum-polar current Buildup of Antarctic Glaciation on Land, Global Cooling 28 Drake Passage Opened Full circum-polar current continued Isolation of Antarctica Further buildup of Glaciation on Land, more Global Cooling 15 Sinking of Iceland- Faeroe Ridge NADW formation and Transport of moisture to Ant. via upwelling Antarctic Ice Sheet Formation, even more Global Cooling 3.2 Formation of Isthmus of Panama; Tethys Seaway closure between N. & S. America Deflection of moisture to N. Atlantic via Gulf Stream formation Initiate North American Glaciation; Planet now cold enough for glacial- interglacial fluctuations from orbital variations (Milankovitch cycles)

24 Have a Blast for Christmas!