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Abstract Detail



The Miocene vegetation and environment of Western North America

GRAHAM, ALAN [1].

The Miocene- Before and After.

The Miocene was a pivotal time in the modernization of global ecosystems.  The geological, biological, and climatic events were complex and interactive and can best be understood in the context of what went on before and immediately following the interval between ca. 23 and 5 Myr.  There was an episodic warming from the early Paleocene to the Paleocene-Eocene Thermal Maximum at ca. 55 Myr when MATs were ca. 11-12o warmer than at present (CO2 concentration ca. 900-1100 ppmv) and communities with a strong subtropical to warm temperate component extended into the high northern (and southern) latitudes.  There followed a gradual decline until the Middle Miocene Climatic Optimum at ca. 15 Myr (MAT ca. 3o warmer than at present, CO2 450 ppmv) with widespread deciduous forests, then continued cooling (interrupted by the Middle Pliocene Climatic Optimum, CO2 380 ppmv) into the glacial cycles of the Quaternary (CO2 at glacial maxima ca. 190 ppmv; presently 392 ppmv).  Elements coalesced into the prominent grasslands evident in the late Miocene (earlier regionally due to physiographic and edaphic factors) and into modern arid communities in the late Miocene, Pliocene, and the 18-20 drying glacial cycles of the Quaternary (beginning ca. 2.5 Myr).  Climate forcing mechanisms such as the Milankovitch variations become expressed as CO2 declined, Heinrich and Dansgaard-Oeschger events of a few thousand to several hundred years developed in the Quaternary, and even faster changes occurred at each glacial-interglacial boundary.  Renovations are required in some previous concepts such as geofloras (too static as formerly applied); regional physiography (higher elevations earlier in the Rocky Mountains and Sierra Nevada); global uplift of the Himalayas as a major cause of CO2 drawdown and mid- to Late Cenozoic cooling; and some proposed land bridges (e.g., GAARLANDIA through the Antilles).  Caution is recommended to avoid over-extending emerging data on western American physiographic history, land bridges elsewhere, and on the age/place-of-origin of lineages as each new record is discovered.  The conservation implication of a dynamic view of Late Cenozoic vegetation history is that parks and reserves, rather than protecting existing biotas in perpetuity, are actually way-stations for accommodating communities of ever-changing range and composition.


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1 - Missouri Botanical Garden, PO Box 299, St. Louis, MO, 63166, USA

Keywords:
Miocene
vegetation
western American.

Presentation Type: Symposium or Colloquium Presentation
Session: C2
Location: Salmon/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 1:30 PM
Number: C2001
Abstract ID:78
Candidate for Awards:None


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