Silicon Cycling in Greenlandic fjords: Comparison of Marine and Land-Terminating Glaciers

Melting of Arctic glaciers and ice sheets is accelerating, potentially providing significant fluxes of key nutrients to downstream ecosystems, impacting biogeochemical cycles. Previous work has shown silicon (Si) exported from glacial environments also has a distinct isotopic signature compared to silicon in non-glacial rivers, which has potential implications for the wider Si cycle, if glacially derived Si is exported to the polar oceans. However, the extent to which glacially-derived Si and other bioavailable nutrients reach the open ocean is much debated, due to biological uptake and complex physical processes within heterogeneous fjord environments.

We assess the impact of glacial meltwater from marine and land-terminating glaciers on fjord biogeochemistry, with a focus upon silicon (Si) cycling, by sampling two fjords (Godthåbsfjord and Ameralik Fjord) in southwest Greenland over two melt seasons. We combine silicon isotope measurements of dissolved and biogenic silica (DSi and BSi, respectively) with a range of complementary physical and chemical parameters to evaluate the role of glacially derived nutrients and benthic recycling on biological productivity within the two contrasting fjord environments. Data from two consecutive melt seasons also enables us to begin to assess inter-annual variability and continuous DSi and nitrate concentrations from Godthåbsfjord for the 2019 melt season, obtained using novel sensor technology, allow us to assess intra-annual variations in nutrient export. Our targeted field campaigns have provided a range of nutrient, trace element and isotopic data that will improve the current understanding of the complex biogeochemical cycling occurring within fjord environments and allow a better assessment into the importance of glacial meltwater for nutrient export and primary productivity in downstream ecosystems.