Sediment efflux of silicon on the Greenland margin and implications for the marine silicon cycle

The polar region is experiencing one of the most rapid environmental changes driven by atmospheric warming, and feedbacks within the cryosphere. Under such a setting, it is crucial to understand the biogeochemical cycling of the nutrient silicon (Si) in the high latitudes, which is regulating the nutrient supply to polar ecosystems, and is linked to the global carbon cycle via diatom production. However, these efforts have been hindered by a lack of understanding of the benthic Si cycle, particularly the quantification of the sediment efflux of Si, and identification of the responsible mechanistic processes during early diagenesis. Here, we address these issues using new pore water profiles and incubation experiments on sediment cores collected from the Greenland margin and Labrador Sea, combined with Si isotope analysis and a mass balance model. Benthic Si flux at our study sites is found to be greatly heightened from values sustained by pore water molecular diffusion. The remainder of the flux is likely accountable with early dissolution of reactive biogenic silica phases at the upper sediments, and advective transport of pore waters. Our results highlight an active benthic Si cycle at a northern high-latitude continental margin, which could play a key role in recycling significant amounts of biologically available dissolved Si to the overlying water, and influencing the growth of benthic and planktonic communities in the polar region. (C) 2019 Elsevier B.V. All rights reserved.