The University of Southampton
University of Southampton Institutional Repository

Iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids

Iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids
Iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids
Volcanogenic sediments are typically rich in Fe and Mn-bearing minerals that undergo substantial alteration during early marine diagenesis, however their impact on the global biogeochemical cycling of Fe and Mn has not been widely addressed. This study compares the near surface (0–20 cm below sea floor [cmbsf]) aqueous (<0.02 ?m) and aqueous + colloidal here in after ‘dissolved’ (<0.2 ?m) pore water Fe and Mn distributions, and ancillary O2(aq), NO-3 and solid-phase reactive Fe distributions, between two volcanogenic sediment settings: [1] a deep sea tephra-rich deposit neighbouring the volcanically active island of Montserrat and [2] mixed biosiliceous–volcanogenic sediments from abyssal depths near the volcanically inactive Crozet Islands archipelago. Shallow penetration of O2(aq) into Montserrat sediments was observed (<1 cmbsf), and inferred to partially reflect oxidation of fine grained Fe(II) minerals, whereas penetration of O2(aq) into abyssal Crozet sediments was >5 cmbsf and largely controlled by the oxidation of organic matter. Dissolved Fe and Mn distributions in Montserrat pore waters were lowest in the surface oxic-layer (0.3 ?M Fe; 32 ?M Mn), with maxima (20 ?M Fe; 200 ?M Mn) in the upper 1–15 cmbsf. Unlike Montserrat, Fe and Mn in Crozet pore waters were ubiquitously partitioned between 0.2 ?m and 0.02 ?m filtrations, indicating that the pore water distributions of Fe and Mn in the (traditionally termed) ‘dissolved’ size fraction are dominated by colloids, with respective mean abundances of 80% and 61%. Plausible mechanisms for the origin and composition of pore water colloids are discussed, and include prolonged exposure of Crozet surface sediments to early diagenesis compared to Montserrat, favouring nano-particulate goethite formation, and the elevated dissolved Si concentrations, which are shown to encourage fine-grained smectite formation. In addition, organic matter may stabilise authigenic Fe and Mn in the Crozet pore waters. We conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water, which may impact significantly on deep ocean biogeochemistry. Diffusive flux estimates from Montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved Mn to the bottom waters, and therefore a source for the widespread hydrogenous MnOx deposits found in the Caribbean region.
0016-7037
5032-5048
Homoky, W.B.
39da18e9-28b8-42c4-8e17-2cb66af8ee4d
Hembury, D.J.
4872a409-f5f7-4945-8796-0b62c9d3b4e3
Hepburn, L.E.
468ed9a0-ca00-4e5c-8aa2-a73d445eb19e
Mills, R.A.
a664f299-1a34-4b63-9988-1e599b756706
Statham, P.J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Fones, G.R.
5b71916c-4859-4a6f-b9ad-b6b1f541cbfa
Palmer, M.R.
d2e60e81-5d6e-4ddb-a243-602537286080
Homoky, W.B.
39da18e9-28b8-42c4-8e17-2cb66af8ee4d
Hembury, D.J.
4872a409-f5f7-4945-8796-0b62c9d3b4e3
Hepburn, L.E.
468ed9a0-ca00-4e5c-8aa2-a73d445eb19e
Mills, R.A.
a664f299-1a34-4b63-9988-1e599b756706
Statham, P.J.
51458f15-d6e2-4231-8bba-d0567f9e440c
Fones, G.R.
5b71916c-4859-4a6f-b9ad-b6b1f541cbfa
Palmer, M.R.
d2e60e81-5d6e-4ddb-a243-602537286080

Homoky, W.B., Hembury, D.J., Hepburn, L.E., Mills, R.A., Statham, P.J., Fones, G.R. and Palmer, M.R. (2011) Iron and manganese diagenesis in deep sea volcanogenic sediments and the origins of pore water colloids. Geochimica et Cosmochimica Acta, 75 (17), 5032-5048. (doi:10.1016/j.gca.2011.06.019).

Record type: Article

Abstract

Volcanogenic sediments are typically rich in Fe and Mn-bearing minerals that undergo substantial alteration during early marine diagenesis, however their impact on the global biogeochemical cycling of Fe and Mn has not been widely addressed. This study compares the near surface (0–20 cm below sea floor [cmbsf]) aqueous (<0.02 ?m) and aqueous + colloidal here in after ‘dissolved’ (<0.2 ?m) pore water Fe and Mn distributions, and ancillary O2(aq), NO-3 and solid-phase reactive Fe distributions, between two volcanogenic sediment settings: [1] a deep sea tephra-rich deposit neighbouring the volcanically active island of Montserrat and [2] mixed biosiliceous–volcanogenic sediments from abyssal depths near the volcanically inactive Crozet Islands archipelago. Shallow penetration of O2(aq) into Montserrat sediments was observed (<1 cmbsf), and inferred to partially reflect oxidation of fine grained Fe(II) minerals, whereas penetration of O2(aq) into abyssal Crozet sediments was >5 cmbsf and largely controlled by the oxidation of organic matter. Dissolved Fe and Mn distributions in Montserrat pore waters were lowest in the surface oxic-layer (0.3 ?M Fe; 32 ?M Mn), with maxima (20 ?M Fe; 200 ?M Mn) in the upper 1–15 cmbsf. Unlike Montserrat, Fe and Mn in Crozet pore waters were ubiquitously partitioned between 0.2 ?m and 0.02 ?m filtrations, indicating that the pore water distributions of Fe and Mn in the (traditionally termed) ‘dissolved’ size fraction are dominated by colloids, with respective mean abundances of 80% and 61%. Plausible mechanisms for the origin and composition of pore water colloids are discussed, and include prolonged exposure of Crozet surface sediments to early diagenesis compared to Montserrat, favouring nano-particulate goethite formation, and the elevated dissolved Si concentrations, which are shown to encourage fine-grained smectite formation. In addition, organic matter may stabilise authigenic Fe and Mn in the Crozet pore waters. We conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water, which may impact significantly on deep ocean biogeochemistry. Diffusive flux estimates from Montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved Mn to the bottom waters, and therefore a source for the widespread hydrogenous MnOx deposits found in the Caribbean region.

Full text not available from this repository.

More information

e-pub ahead of print date: 20 June 2011
Published date: 1 September 2011

Identifiers

Local EPrints ID: 194399
URI: http://eprints.soton.ac.uk/id/eprint/194399
ISSN: 0016-7037
PURE UUID: 2f5e0a20-9dbe-46c9-b18f-128199e9cd6f
ORCID for R.A. Mills: ORCID iD orcid.org/0000-0002-9811-246X

Catalogue record

Date deposited: 27 Jul 2011 15:20
Last modified: 18 Feb 2021 16:42

Export record

Altmetrics

Download statistics

Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.

View more statistics

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of http://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×