CENOZOIC MOUNTAIN UPLIFT FORCING GLOBAL COOLING OR VISE VERSA: A CHICKEN AND EGG PROBLEM REVISITED

Refreshing a 10 year old debate, improvement of methods suggest to refocus on open questions. Accepting the validity of general coincidence between decreasing ocean floor spreading rates and volcanic activity, rising mountains, cooling ocean and cooling climate, increasing riverine fluxes and carbonate burial in the ocean, the question of causality remains open. This is due to numerous positive feedback mechanisms. E.g., if mountains rise above the treeline and the snowline, enhanced precipitation, glaciation, erosion and relief formation would force isostatic uplift of mountain tops and increase of albedo, which would result in further cooling. Lowering of these critical climatic threshold lines, however, would have the same effect. A major uncertainty for testing the hypothesis above is the paleoaltitude of mountain ranges and plateaus, since successful direct methods of determination like oxygen isotope studies of highly elevated lacustrine carbonates and the size of gas bubbles in basalt flows are brand new. A popular method for altitude estimates has been to study paleobotany, although this proxy is highly biassed by climate change. Proxys like Sr flux, Ge/Si ratio, sediment flux, and clay mineralogy have less but still serious disadvantages as paleoaltitude indicators. Integrating available data, Cenozoic mountain uplift is mainly forced by plate tectonic events (30, 17, 6 Ma) and rarely by climate change (2.7 Ma). Cenozoic climate changes coincide with paleoceanographic reorgansations (33, 14.5, 6, 2.7 Ma) in the course of opening and closing gateways. A runaway into icehouse conditions is prevented by negative feedbacks in the ocean, due to buffers in water chemistry, activity of life, and sea-level change. E.g, cold climate favors upwelling and high productivity of siliceous ooze, whereas productivity of carbonatic plankton, removing dissolved carbon dioxide from surface waters, is suppressed. The exposure of vast shelf areas during glaciations leads to oxydation of organic carbon, releasing greenhouse gases.