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A silicon depleted North Atlantic since the Palaeogene : Evidence from sponge and radiolarian silicon isotopes

Fontorbe, Guillaume LU ; Frings, Patrick J. LU ; De La Rocha, Christina L. LU ; Hendry, Katharine R. and Conley, Daniel J. LU (2016) In Earth and Planetary Science Letters 453. p.67-77
Abstract

Despite being one of Earth's major geochemical cycles, the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica (DSi) concentration through geologic time remain poorly constrained. Silicon isotope ratios (expressed as δ30Si) in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling. In particular, the δ30Si of siliceous sponge spicules has been demonstrated to be a useful proxy for past DSi concentrations. We analysed δ30Si in radiolarian tests and sponge spicules from the Blake Nose Palaeoceanographic Transect (ODP Leg 171B) spanning the Palaeocene–Eocene (ca. 60–30 Ma). Our δ30Si... (More)

Despite being one of Earth's major geochemical cycles, the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica (DSi) concentration through geologic time remain poorly constrained. Silicon isotope ratios (expressed as δ30Si) in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling. In particular, the δ30Si of siliceous sponge spicules has been demonstrated to be a useful proxy for past DSi concentrations. We analysed δ30Si in radiolarian tests and sponge spicules from the Blake Nose Palaeoceanographic Transect (ODP Leg 171B) spanning the Palaeocene–Eocene (ca. 60–30 Ma). Our δ30Si results range from +0.32 to +1.67‰ and −0.48 to +0.63‰ for the radiolarian and sponge records, respectively. Using an established relationship between ambient dissolved Si (DSi) concentrations and the magnitude of silicon isotope fractionation in siliceous sponges, we demonstrate that the Western North Atlantic was DSi deplete during the Palaeocene–Eocene throughout the water column, a conclusion that is robust to a range of assumptions and uncertainties. These data can constitute constraints on reconstructions of past-ocean circulation. Previous work has suggested ocean DSi concentrations were higher than modern ocean concentrations prior to the Cenozoic and has posited a drawdown during the Early Palaeogene due to the evolutionary expansion of diatoms. Our results challenge such an interpretation. We suggest here that if such a global decrease in oceanic DSi concentrations occurred, it must predate 60 Ma.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
ODP Leg 171B, Palaeogene, radiolarians, silicon isotopes, sponges
in
Earth and Planetary Science Letters
volume
453
pages
11 pages
publisher
Elsevier
external identifiers
  • Scopus:84983431717
ISSN
0012-821X
DOI
10.1016/j.epsl.2016.08.006
language
English
LU publication?
yes
id
e0806f47-6253-40eb-b94e-e60bc47db964
date added to LUP
2016-10-13 10:34:48
date last changed
2016-10-13 10:34:48
@misc{e0806f47-6253-40eb-b94e-e60bc47db964,
  abstract     = {<p>Despite being one of Earth's major geochemical cycles, the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica (DSi) concentration through geologic time remain poorly constrained. Silicon isotope ratios (expressed as δ<sup>30</sup>Si) in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling. In particular, the δ<sup>30</sup>Si of siliceous sponge spicules has been demonstrated to be a useful proxy for past DSi concentrations. We analysed δ<sup>30</sup>Si in radiolarian tests and sponge spicules from the Blake Nose Palaeoceanographic Transect (ODP Leg 171B) spanning the Palaeocene–Eocene (ca. 60–30 Ma). Our δ<sup>30</sup>Si results range from +0.32 to +1.67‰ and −0.48 to +0.63‰ for the radiolarian and sponge records, respectively. Using an established relationship between ambient dissolved Si (DSi) concentrations and the magnitude of silicon isotope fractionation in siliceous sponges, we demonstrate that the Western North Atlantic was DSi deplete during the Palaeocene–Eocene throughout the water column, a conclusion that is robust to a range of assumptions and uncertainties. These data can constitute constraints on reconstructions of past-ocean circulation. Previous work has suggested ocean DSi concentrations were higher than modern ocean concentrations prior to the Cenozoic and has posited a drawdown during the Early Palaeogene due to the evolutionary expansion of diatoms. Our results challenge such an interpretation. We suggest here that if such a global decrease in oceanic DSi concentrations occurred, it must predate 60 Ma.</p>},
  author       = {Fontorbe, Guillaume and Frings, Patrick J. and De La Rocha, Christina L. and Hendry, Katharine R. and Conley, Daniel J.},
  issn         = {0012-821X},
  keyword      = {ODP Leg 171B,Palaeogene,radiolarians,silicon isotopes,sponges},
  language     = {eng},
  month        = {11},
  pages        = {67--77},
  publisher    = {ARRAY(0xb55a2c8)},
  series       = {Earth and Planetary Science Letters},
  title        = {A silicon depleted North Atlantic since the Palaeogene : Evidence from sponge and radiolarian silicon isotopes},
  url          = {http://dx.doi.org/10.1016/j.epsl.2016.08.006},
  volume       = {453},
  year         = {2016},
}