The Miocene Climate at 20 and 14 Ma: A Model Study With the Focus on Freshwater

Gradual cooling of the Cenozoic, including the Miocene epoch, was punctured by many warming and cooling episodes. The early and middle Miocene was the time when some elements of the young southern cryosphere might have become unstable and generated significant freshwater impacts on the ocean circulation. It is highly probable that the ocean and eventually the entire climate system responded to those impacts differently in the cases of different land-ocean geometries. We examine the role of freshwater disturbances and significance of ocean geometry in a series of coupled ocean-atmosphere computer experiments. These experiments suggest that relatively small and short-lived fluctuations in ocean-cryosphere interactions could be responsible, at least partially, for notable Miocene climate excursions that cannot be explained by changes in greenhouse gas concentrations, volcanic activities, and/or changes in orbital configuration. The focus of our study is on the Miocene climate response to possible freshwater inputs into the ocean from the Antarctic cryosphere. To simulate freshwater inputs and test our hypothesis of abrupt climate shifts, the freshwater balance at the ocean surface is disturbed by injecting and removing freshwater around paleo- Antarctica. The individual and combined effects of changes in land-sea and ocean bathymetry changes from 20 to 14 Ma are under intense scrutiny. We conclude that recurrent freshwater impacts inside this interval of Cenozoic history could cause significant climate swings with durations from thousand to tens of thousand years.