Enrichment of dissolved silica in the deep equatorial Pacific during the Eocene-Oligocene

Summary, in English

Silicon isotope ratios (expressed as δ³⁰Si) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δ³⁰Si 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 δ³⁰Si. The δ³⁰Si 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 δ³⁰Si values around 37 Ma. The shift in radiolarian δ³⁰Si is interpreted as a consequence of changes in the δ³⁰Si of source DSi to the region. The decrease in sponge δ³⁰Si 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 δ³⁰Si 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.

• Author: Guillaume Fontorbe; Patrick J. Frings; Christina L. De La Rocha; Katharine R. Hendry; Jacob Carstensen; Daniel J. Conley
• Department/s: Quaternary Sciences
• Publishing year: 2017-08-18
• Language: English
• Pages: 848-863
• Publication/Series: Paleoceanography
• Volume: 32
• Issue: 8
• Links: http://dx.doi.org/10.1002/2017PA003090
• Document type: Journal article
• Publisher: John Wiley & Sons Inc.
• Topic: Geology
• Keywords: Eocene Oligocene; Ocean circulation; Silicon isotopes
• Status: Published
• ISBN/ISSN/Other: ISSN: 0883-8305