The Oligocene–Miocene boundary – cause and consequence from a Southern Ocean perspective
Published:January 01, 2007
H. A. Pfuhl, I. N. Mccave, 2007. "The Oligocene–Miocene boundary – cause and consequence from a Southern Ocean perspective", Deep-Time Perspectives on Climate Change: Marrying the Signal from Computer Models and Biological Proxies, M. Williams, A. M. Haywood, F. J. Gregory, D. N. Schmidt
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Understanding of Earth’s transition from a warm, ice-free Cretaceous to today’s bipolar glaciation is hotly debated. The Oligocene–Miocene boundary is marked by a brief glacial event followed by an interval of colder temperatures. Changes are small compared to the major Antarctic ice build-up at the Eocene–Oligocene boundary and establishment of a permanent Antarctic ice-sheet in the mid-Miocene. However, fossil evidence from low latitudes, including the faunal turnover which originally defined the Oligocene–Miocene boundary, indicates a reversal in trans-Atlantic flow, i.e. from westward to eastward, at this time. Modelling results suggest that a combined narrowing of the Tethys Seaway and deep opening of Drake Passage, and hence inception of Antarctic circumpolar circulation, drove reorganization of the patterns of ocean circulation. Despite evidence for a shallow Drake Passage opening in earliest Eocene time and subsequent deepening, a comparison of Southern Ocean isotopic records suggests that circumpolar circulation did not exist prior to c. 26 Ma. In fact, sedimentary records of a grain-size current-speed indicator from the Tasman Gateway reveal a singular, marked increase immediately preceding the initial Miocene event. The likely driver of this increase is inception of the full Antarctic Circumpolar Current. Among possible causes of early Cenozoic climate deterioration, the opening of seaways appears to play the major role. Extreme orbital configurations and pCO2-drawdown may act as reinforcing factors.
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Deep-Time Perspectives on Climate Change: Marrying the Signal from Computer Models and Biological Proxies
This book unites climate modelling, palaeoceanography and palaeontology to address fundamental events in the climate history of Earth over the past 600 million years. Understanding the ‘tipping points’ that have led to rapid changes in the Earth's climate is vitally important with the realization that humans modify global climate. In an effort to better understand past and future climate change, general circulation models have become the forerunners of attempts to simulate future climate. Although extraordinarily sophisticated, they remain imperfect tools that require ‘grounding’ in geological data. In this, the study of past major climate transitions like the Palaeozoic icehouse worlds and the extreme greenhouse of the Cretaceous are invaluable. Both the mechanisms that forced changes in the Earth's climate as well as the proxies that track these changes are discussed. The central message of the book is that general circulation models tested with geological data in an iterative ‘ground truth’ process provide the best estimates of the Earth's ancient climate.