Arctic River Dissolved and Biogenic Silicon Exports—Current Conditions and Future Changes With Warming

Abstract

Silicon (Si) exports from terrestrial to marine systems can dictate phytoplankton species composition in Arctic coastal waters. Diatoms are often the dominant autotroph in Arctic waters, making Si an important control on Arctic marine primary productivity. Yet even as Arctic regions are among the fastest warming on Earth, we lack baseline knowledge on the magnitudes and controls of Arctic river Si exports. To address uncertainties in current and future Si behavior, we used a combination of field data and modeling to quantify daily yields of dissolved Si (DSi) and biogenic Si (BSi) from a 400 km space‐for‐time latitudinal gradient of seven basins across the boreal‐Arctic transition in Alaska (United States) over the course of 2 years (2015–2016). Mean annual DSi concentrations (33–149 μM) and yields (13–49 kmol km−2 year−1) were significantly and positively correlated with mean basin active layer depth, indicating that permafrost thaw will likely increase DSi fluxes to Arctic coastal waters. Conversely, BSi concentrations (7–16 μM) and yields (2.6–4.5 kmol km−2 year−1) were more uniform across the seven basins, indicating that warming may not substantially alter BSi loads to coastal systems in the near future. Our data also indicate that climatic warming will advance the timing of Si delivery to coastal waters in the spring, although the ratios of Si to nitrogen in Arctic river exports will likely remain steady. These results highlight the important role of basin hydrology, largely driven by permafrost extent, as a key driver of Si exchange at the land‐sea interface in the Arctic.

The Importance of Benthic Nutrient Fluxes in Supporting Primary Production in the Laptev and East Siberian Shelf Seas

“…The benthic DSi flux and the riverine flux of DSi together account for over 85% of DSi required for primary production in the Laptev Sea. In a warming Arctic, riverine DSi export has been predicted to increase and to occur earlier in the spring, but the DSi/DIN ratio is expected to remain unchanged (Carey et al., 2020). The increase in the DSi and biogenic Si from land to the ocean could stimulate productivity, but only provided a sufficient supply of nitrogen will exist.…”

New Constraints on the Physical and Biological Controls on the Silicon Isotopic Composition of the Arctic Ocean

“…In addition to dissolved silicon, Arctic rivers discharge 0.02-0.08 Tmol Si a −1 as particulate bSi into the Arctic Ocean (Carey et al, 2020; Table 2). Assuming that about half of that material dissolves before burial (Tréguer et al, 2021), the total riverine input offsets about 53-68% of the estimated net removal of Si from the Arctic Ocean.…”

“…Carey et al (2020). l 0.16 Tmol Si a −1 from main text; 0.30 Tmol Si a −1 estimate fromMacDonald et al (2010).…”

Controls on Riverine Dissolved Organic Matter Composition Across an Arctic‐Boreal Latitudinal Gradient

“…We sampled six rivers and streams within the Yukon River Basin and the North Slope of Alaska spanning a gradient of latitude from the Salcha River, just south of Fairbanks to the Sagavanirktok River on the North Slope of Alaska (Figure 1; Table 1) during the ice-free season in 2016 (May-October) and the period of peak discharge in May 2017. Methods used to derive landscape characteristics such as permafrost coverage, active layer thickness, and land cover are described in Carey et al (2020). The watersheds are underlain by a south to north gradient of discontinuous to continuous permafrost (50%-90%, and greater than 90% underlain by permafrost, respectively).…”