EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Benthic dissolved silicon and iron cycling at glaciated Patagonian fjord heads

Katharine R Hendry1,2, Hong Chin Ng2, Jon Hawkings3, Sebastien Bertrand4, Brent Summers5, Matthew Sieber5, Tim Conway5, Felipe Sales de Freitas2,6, James Ward2, Helena Pryer7, Jemma Wadham8, and Sandra Arndt6
Katharine R Hendry et al.
  • 1British Antarctic Survey, Polar Oceans, United Kingdom of Great Britain – England, Scotland, Wales (
  • 2School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ, UK
  • 3Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA, USA
  • 4Renard Centre of Marine Geology, Ghent University, Gent, Belgium
  • 5College of Marine Science, University of South Florida, St Petersburg, FL, USA
  • 6BGeosys, Department of Geosciences, Université libre de Bruxelles, Brussels, Belgium
  • 7Department of Earth Sciences, University of Cambridge, Cambridge, UK
  • 8Department of Geosciences, Centre for Arctic Gas Hydrate, Environment and Climate (CAGE), UiT The Arctic University of Norway, Tromsø, Norway

Glacier meltwater supplies a significant amount of silicon (Si) and iron (Fe) sourced from weathered bedrock to downstream ecosystems. However, the extent to which these essential nutrients reach the ocean is regulated by the processes occurring within fjords, which act as conduits from glacial rivers and subglacial discharge and the ocean. One key – but understudied – component of biogeochemistry within fjords is benthic cycling, especially in regions of rapid deposition of reactive particulates at fjord heads. Here, we explore the benthic cycling of Si and Fe at four Patagonian fjord heads through geochemical analyses of sediment pore waters, including stable Si and Fe isotopes (δ30Si and δ56Fe respectively), and novel reaction-transport modelling for Si. A high diffusive flux of dissolved Fe from the fjord sediments compared to open ocean sediments is supported by both reductive and non-reductive dissolution of glacially-sourced reactive Fe phases, as reflected by the range of pore water stable Fe isotopes (δ56Fe from -2.7 to +0.8‰). In contrast, the diffusive flux of dissolved Si from the fjord sediments is relatively low. 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 but suppresses the release of dissolved Si at glaciated fjord heads. The redox sensitive coupling of Si and Fe has significant implications for our understanding of how essential nutrients are transport along fjord systems.

How to cite: Hendry, K. R., Ng, H. C., Hawkings, J., Bertrand, S., Summers, B., Sieber, M., Conway, T., Sales de Freitas, F., Ward, J., Pryer, H., Wadham, J., and Arndt, S.: Benthic dissolved silicon and iron cycling at glaciated Patagonian fjord heads, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2341,, 2023.