Enrichment of dissolved silica in the deep equatorial Pacific during the Eocene‐Oligocene. (18th August 2017) - Fontorbe, Guillaume
Abstract: Silicon isotope ratios (expressed as δ 30 Si) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δ 30 Si of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (Ocean Drilling Program Leg 199) spanning the Eocene and Oligocene (~50–23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep waters and to examine upper ocean δ 30 Si. The δ 30 Si values range from −3.16 to +0.18‰ and from −0.07 to +1.42‰ for the sponge and radiolarian records, respectively. Both records show a transition toward lower δ 30 Si values around 37 Ma. The shift in radiolarian δ 30 Si is interpreted as a consequence of changes in the δ 30 Si of source DSi to the region. The decrease in sponge δ 30 Si is interpreted as a transition from low DSi concentrations to higher DSi concentrations, most likely related to the shift toward a solely Southern Ocean source of deep water in the Pacific during the Paleogene that has been suggested by results from paleoceanographic tracers such as neodymium and carbon isotopes. Sponge δ 30 Si provides relatively direct information about the nutrient content of deep water and is a useful complement to other tracers of deep water circulation in the oceans of the past. Key Points: Silicon isotope composition of BSi can complement other paleocirculation proxies to assess changes in ocean circulation The Equatorial Pacific became more silica‐rich from 37 Ma onward due to a change in the provenance of deep waters