GERMANIUM-SILICON RATIOS AS A RECORD OF MID MIOCENE SILICA FLUXES TO THE OCEANS

Abstract

A warm climate interval from 17 to 14.8 Ma is known as the Mid Miocene Climatic Optimum (MMCO). This interval was followed by a progressive cooling that continued to the Pleistocene. Several isotopic tracers indicate global climate and possibly weathering changes during the mid-Miocene. Germanium-silicon (Ge/Si) ratios are fractionated by silicate weathering processes and so can be an effective tracer of weathering intensity, and one potential consequence of a warm climate is increased silicate weathering intensity. We present a Ge/Si ratio record of 81 samples from IODP U1337A for ~12-18 Ma. The Ge/Si data for this interval do not show an overall temporal trend, but they are higher than present day ratio in seawater. The data show considerable scatter outside of analytical precision, and this scatter data may be in part result from diagenetic alteration. With a box model of the oceanic balance of Ge/Si and δ7Li we find that mid-Miocene weathering fluxes and weathering intensity were likely higher than at present, consistent with a warmer climate at that time.