The polar regions are biologically productive and play a critical role in regional and global biogeochemical cycling. A key nutrient is dissolved silicon, required for the growth of siliceous phytoplankton, diatoms, which form an important component of polar ecosystems. Glacial weathering is thought to be an important dissolved silicon source to coastal waters, especially critical in regions experiencing seasonal silicon limitation of diatom growth. However, complex physical and biogeochemical interactions in fjords and coastal regions modulate the downstream supply of dissolved and particulate nutrients, including silicon. Here, we review the biogeochemical complexities of glaciated margins and the insights into this system that silicon isotope geochemistry offer. We show that stable and radioisotopic measurements and biogeochemical numerical modelling provide a quantitative mechanistic understanding of subglacial silica mobilisation and its cycling across the land-ocean continuum. Subglacial weathering produces isotopically light amorphous silica, which dissolves in seawater to release dissolved silicon. Our findings show that isotopically light, detrital silica, likely containing glacial material, reaches the ocean and there could support a substantial proportion of diatom productivity, especially in the Arctic. Outstanding questions about silicon cycling in these crucial environments will be addressed through novel and cross-discipline approaches that overcome traditionally viewed ecosystem boundaries.

BGeosys Department of Geosciences Université libre de Bruxelles Brussels Belgium

British Antarctic Survey High Cross Cambridge UK

Dauphin Island Sea Lab Dauphin Island AL USA

Department of Biology University of Antwerp Wilrijk Belgium

Department of Earth and Environmental Science University of Pennsylvania Philadelphia PA USA

Department of Earth Sciences University of Cambridge Cambridge UK

Department of Ecology Faculty of Science Charles University Prague 2 Czechia

Department of Estuarine and Delta Systems Royal Netherlands Institute for Sea Research Yerseke The Netherlands

Department of Marine Science University of Otago Dunedin New Zealand

Greenland Climate Research Centre Greenland Institute of Natural Resources Nuuk Greenland

iC3 Centre for ice Cryosphere Carbon and Climate Department of Geosciences UiT The Arctic University of Norway Tromsø Norway

National Institute of Water and Atmospheric Research Wellington New Zealand

National Oceanography Centre Southampton Southampton UK

Plymouth Marine Laboratory Prospect Place The Hoe Plymouth UK

School of Earth Sciences University of Bristol Bristol UK

Stokes School of Marine and Environmental Sciences University of South Alabama Mobile AL USA

UK Centre for Ecology and Hydrology Environment Centre Wales Bangor UK

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