Detrital Input Sustains Diatom Production off a Glaciated Arctic Coast

In the Arctic and subarctic oceans, the relatively low supply of silicon (compared to other nutrients) can make it limiting for the growth of diatoms, a fundamental building block of the oceanic food web. Glaciers release large quantities of dissolved silicon and dissolvable solid amorphous silica phases into high‐latitude estuaries (fjords), but the role of these glacially‐derived silica phases in sustaining diatom growth in the coastal and open‐water sectors remains unknown. Here we show how stable and radiogenic silicon isotopes can be used together to address this question, using southwest Greenland as a case study. This study finds enhanced levels of detrital (i.e., mineral) amorphous silica, likely glacially‐sourced, sustaining a large portion of diatom growth observed off the coast, revealing how the phytoplankton community can function during high‐meltwater periods. Plain Language Summary Through physical grinding and chemical reactions, glaciers release a large amount of nutrients, such as silicon, from the underlying rocks. The silicon released are present in two main forms: (a) silicon dissolved in seawater, and (b) soluble silicon in glacial debris. However, there has been an ongoing debate about the contribution of this glacier‐sourced nutrient to the coastal ecosystem in the high latitudes. This is because dissolved silicon concentrations in seawater have been found at low levels in glaciated fjords and coastal environments, and the offshore transportation pathways for reactive glacial debris are poorly understood. This study aims to address these outstanding questions by employing a suite of chemical and oceanographic analyses, using southwest Greenland as a case study. We find enhanced growth of a major microalgae group at sites with high glacial debris level off the coast. Our study supports the role of glacier‐sourced nutrient in sustaining high‐latitudinal coastal ecosystem through gradual dissolution of glacial debris, especially in regions with low levels of dissolved nutrient. Key Points Some of the highest levels of detrital amorphous silica in the Arctic Ocean are found off a glaciated Greenland coast Enhanced Arctic diatom production is found where detrital amorphous silica level is high, even when there is limited dissolved nutrient Gradual dissolution of detrital amorphous silica is estimated to sustain about half of diatom production off southwest Greenland coast