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Benthic Dissolved Silicon and Iron Cycling at Glaciated Patagonian Fjord Heads.

Published version
Peer-reviewed

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Authors

Bertrand, Sebastien  ORCID logo  https://orcid.org/0000-0003-0374-4040
Summers, Brent A 

Abstract

Glacier meltwater supplies silicon (Si) and iron (Fe) sourced from weathered bedrock to downstream ecosystems. However, the extent to which these nutrients reach the ocean is regulated by the nature of the benthic cycling of dissolved Si and Fe within fjord systems, given the rapid deposition of reactive particulate fractions at fjord heads. Here, we examine the benthic cycling of the two nutrients at four Patagonian fjord heads through geochemical analyses of sediment pore waters, including Si and Fe isotopes (δ30Si and δ56Fe), and reaction-transport modeling for Si. A high diffusive flux of dissolved Fe from the fjord sediments (up to 0.02 mmol m-2 day-1) compared to open ocean sediments (typically <0.001 mmol m-2 day-1) is supported by both reductive and non-reductive dissolution of glacially-sourced reactive Fe phases, as reflected by the range of pore water δ56Fe (-2.7 to +0.8‰). In contrast, the diffusive flux of dissolved Si from the fjord sediments (0.02-0.05 mmol m-2 day-1) is relatively low (typical ocean values are >0.1 mmol m-2 day-1). High pore water δ30Si (up to +3.3‰) observed near the Fe(II)-Fe(III) redox boundary is likely associated with the removal of dissolved Si by Fe(III) mineral phases, which, together with high sedimentation rates, contribute to the low diffusive flux of Si at the sampled sites. Our results suggest that early diagenesis promotes the release of dissolved Fe, yet suppresses the release of dissolved Si at glaciated fjord heads, which has significant implications for understanding the downstream transport of these nutrients along fjord systems.

Description

Funder: University of South Florida; Id: http://dx.doi.org/10.13039/100008900


Funder: Royal Society Wolfson Merit Award

Keywords

early diagenesis, fjord biogeochemistry, reaction transport modeling, sediment nutrient cycling, silicon and iron, stable isotopes

Journal Title

Global Biogeochem Cycles

Conference Name

Journal ISSN

0886-6236
1944-9224

Volume Title

Publisher

American Geophysical Union (AGU)
Sponsorship
Natural Environment Research Council (NE/P003133/1‐PII20150106, NE/P006493/1)
European Research Council (678371)
HORIZON EUROPE Marie Sklodowska‐Curie Actions (793962)
Flemish Research Foundation (G0D7916N)
UGent BOF (01N02216)