v Hypothesis: The uplift of the Tibetan Plateau is an active driver for global cooling of the Cenozoic period By Roslyn Gober 11 February 2015

Transcription

1 Objective Uplift of Tibetan Plateau as Active Driver for Cenozoic Climate Change v Use Paleoarchives from the Tibetan Plateau to support the uplift weathering hypothesis for global cooling over the last 50 million years v Hypothesis: The uplift of the Tibetan Plateau is an active driver for global cooling of the Cenozoic period By Roslyn Gober 11 February 2015 onebigphoto.com/stunning-dolomites-mountains-italy/ Cenozoic Period Global Cooling Cenozoic: CO2 & Climate Change Atmospheric CO2 Levels v Atmospheric CO2 and global temperature decline Uplift Weathering Hypothesis v Clear relationship between climate and atmospheric CO2 Tibetan Plateau v Need to identify driver of atmospheric CO2 removal Extensive High Terrain Physical Weathering Chemical Weathering (Beerling, 2011) 1

2 Cenozoic: Icehouse Climate Uplift Weathering Hypothesis Uplift is the cause of large-scale climate changes, through both direct physical impacts and indirect biochemical effects v Benthic foraminifera δ18o measurements over last 70 Myr v Trend toward more positive values of δ18o v Progressive cooling of deep ocean v Continental ice sheet growth v Proposed by Maureen Raymo in the late 1980 s v Physical impact v Changes in circulation of atmosphere and ocean v Chemical impact v Drawdown of atmospheric CO2 is a result of chemical weathering of silicate rocks (Raymo, 1992) Uplift Weathering Hypothesis (Ruddiman, 1997) Uplift Weathering Hypothesis Positive Feedback Negative Feedback 2

3 Extensive High Terrain: Tibetan Plateau v Collision between India and Asia created most extensive plateau on Earth v 55 Myr ago v 2.5 million km2 v Avg. elevation > 5 km v Marine limestones show plateau was below sea level 70 Myr ago Extensive High Terrain: Is it uniquely high? v Cannot prove modern elevations are unusually high or extensive based on age v India-Asia first major continental collision in 150 Myr v Sufficient evidence that amount of high terrain is more extensive than in earlier 3

4 Unusual Physical Weathering Unusual Physical Weathering: Himalayan Sediments v Ocean basin sediment influx is best record of physical weathering v Increase in sediment influx in last 40 Myr v Result of two factors: v Steep Terrain v Monsoons v Uplift of Tibetan Plateau led to increased physical weathering Himalayan Sediments in Indian Ocean Unusual Physical Weathering: Monsoons v Differential heating of Tibetan Plateau and Indian Ocean creates powerful monsoons v Causes greater physical weathering 4

5 Chemical Weathering of Continental Rocks v Removes CO2 from atmosphere through hydrolysis v Proxy of mantle processes and continental weathering v Preserved in marine carbonates v Isotopic composition inputs v Measure ions v Low Ratio: Mantle dissolved in rivers v High Ratio: Continental Weathering v Difficult to determine chemical weathering rates v Synthetic Stratigraphic Column of marine limestones v Continuous over past 500 million years (Edmond, 1992) v Increase in oceanic due to v Marine isotopic oscillations signal dampened v Seafloor spreading too slow to impact record v Weathering of Himalayas Late Cenozoic increase in (Edmond, 1992) caused dramatic increase in marine isotope ratio over last 40 Myr (Edmond, 1992) (Raymo, 1992) 5

6 and Atmospheric CO2 (Garzione, 2008) Conclusion v Global cooling and declining atm. CO2 levels in last 50 Myr v Evidence for Uplift Weathering Hypothesis in Cenozoic: v Creation of Tibetan Plateau 55 Myr ago v Increased rate of sediment influx to Indian Ocean v Increased Isotope Ratio in Marine Limestones v Hypothesis Supported v The uplift of the Tibetan Plateau is an active driver for global cooling during the Cenozoic period 6

7 3/8/15 References Beerling, D.J. and Royer, D.L., 2011, Convergent Cenozoic CO 2 History: Nature Geoscience V. 4, p Edmond, J.M., 1992, Himalayan tectonics, weathering processes, and the strontium isotope record in marine limestones: Science, V. 258, p ,597. Questions? Garzione, C. N., 2008, Surface uplift of Tibet and Cenozoic global cooling: Geology, V. 36, p Raymo, M.E. and Ruddiman, W.F., 1992, Tectonic Forcing of Late Cenozoic Climate: Nature, V. 359, p Ruddiman, W.F., 2014, Earth s Climate Past and Future: New York, W.H. Freeman and Company, 445 p. Ruddiman, W. F., 1997, Tectonic uplift and climate change. New York: Plenum Press. 7