MIOCENE CLIMATE OPTIMUM AND COLUMBIA RIVER BASALT ERUPTIONS: USING SEDIMENTARY HG TO DETERMINE IF VOLATILE RELEASE OCCURRED PRIOR TO ACTIVE ERUPTIONS AND TRIGGERED GLOBAL WARMING

The warming of the Miocene Climate Optimum (MCO) has been attributed to Columbia River Basalt Group (CRBG) large igneous province (LIP) volcanism and release of volatile greenhouse gases including CO2. However, warming began several hundred ka before the first subaerial volcanic units erupted. This study tests if volatiles were released before the onset of active volcanism, using sedimentary Hg as a proxy for LIP emissions. Moreover, it tests the fundamental question of whether deep sea pelagic carbonate sediment records Hg loading during active CRBG eruptions. We measure Hg relative to total organic carbon (TOC) and insoluble residue (IR) in ODP Site 1000B from the Caribbean. Previously presented U-Pb dating of magmatic zircons from local arc-derived ash fall tuffs interspersed throughout the core provides a robust chronostratigraphic correlation with the CRBG volcanic units. This precision allows us to correlate the record of Hg abundance over time to timelines of MCO warming and CRBG eruptions. This approach also tests whether deep sea cores record Hg perturbations during periods of known LIP eruptions. Finding that our TOC-normalized Hg values increased prior to the first LIP volcanism would indicate that volatile release preceded eruption. Conversely, finding no evidence of Hg increase throughout the CRBG interval would indicate that our core site did not record Hg release during CRBG eruptions. An Hg increase indicating volatile release would indicate that solid earth processes like LIP eruptions can have a major impact on the climate and the feedbacks between atmospheric CO2, global temperature, and the timescale on which global warming can occur.