Open AccessEnrichment of dissolved silica in the deep equatorial Pacific during the Eocene‐Oligocene
Author(s) -
Fontorbe Guillaume,
Frings Patrick J.,
De La Rocha Christina L.,
Hendry Katharine R.,
Carstensen Jacob,
Conley Daniel J.
Publication year - 2017
Publication title -
paleoceanography
Language(s) - English
Resource type - Journals
eISSN - 1944-9186
pISSN - 0883-8305
DOI - 10.1002/2017pa003090
Subject(s) - geology , sponge spicule , paleogene , deep sea , oceanography , isotopes of silicon , biogenic silica , paleontology , range (aeronautics) , isotopes of carbon , paleoceanography , water column , dissolved silica , isotope , diatom , cretaceous , chemistry , physics , materials science , quantum mechanics , dissolution , composite material
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.