Sedimentary Nutrient Supply in Productive Hot Spots off the West Antarctic Peninsula Revealed by Silicon Isotopes

Abstract

In this study we evaluate the benthic fluxes of silicic acid along the West Antarctic Peninsula (WAP). Silicic acid (DSi) is one of the macronutrients essential in fuelling biological hot spots of diatom‐dominated primary production along the WAP. Here we measure the concentration and stable silicon isotopic composition of DSi in porewater profiles, biogenic silica content (BSi), and diatom abundance from sediment cores collected along the WAP. We couple these measurements with reaction‐transport modeling, to assess the DSi flux and the processes that release this key nutrient from the sediment into the overlying waters. Our results show that the benthic DSi flux is dominated by the diffusive flux, which is estimated to be equivalent to 26.7 ± 2.7 Gmol yr−1 for the WAP continental shelf. The DSi isotope profiles reveal the important impact of sedimentary processes on porewater DSi and suggest that biogenic silica dissolution is the main source of DSi in porewaters and consequently of the benthic fluxes. Our integrated data‐model assessment highlights the impact of surface productivity on sedimentary processes and the dynamic environment of core‐top sediments where dissolution and reverse weathering reactions control DSi exchanges.

Stable Silicon Isotopes Uncover a Mineralogical Control on the Benthic Silicon Cycle in the Arctic Barents Sea

“…Previous assumptions as to the solubility of AuSi minerals (220-330 µM) would preclude precipitation of AuSi in Barents Sea and many North Atlantic sediments, as [DSi] remains undersaturated with respect to these minerals (Loucaides et al, 2010;Dixit et al, 2001;Ehlert et al, 2016a;Krissansen-Totton and Catling, 2020;Cassarino et al, 2020). However, dissolution experiments carried out over 8.5 years suggest that glauconite, an aluminosilicate and common weathering product of BSi (Odin and Fröhlich, 1988), has a solubility of ∼50 µM in seawater (Lerman et al, 1975).…”

“…As a result, recent work has begun to develop a better mechanistic understanding of this subject through measurement of stable Si isotopes (Ehlert et al, 2016a;Geilert et al, 2020;Ng et al, 2020;Cassarino et al, 2020).…”

“…However, while this isotopic similarity lends support to the dissolution of bloom derived BSi at B14, the hypothesis that both LSi dissolution and AuSi precipitation are active within the upper sediment would suggest that δ 30 Si DSi−P W and δ 30 Si Si−Alk may not be directly comparable. Preceeding studies have employed reactiontransport modelling to disentangle these processes (e.g Cassarino et al (2020)Ehlert et al (2016a);Geilert et al (2020)), which is the subject of ongoing work in this study.…”

Benthic Dissolved Silicon and Iron Cycling at Glaciated Patagonian Fjord Heads

“…k diss and k precip are fitted rate constants. ad, bd, ap, and bp are fitted coefficients defining the exponential decreases of the dissolution and precipitation reactions (Cassarino et al, 2020;Ehlert et al, 2016;Ward et al, 2022a).…”

Supplementary material to "Benthic Silicon Cycling in the Arctic Barents Sea: a Reaction-Transport Model Study"

“…An additional two reaction pathways have been introduced into our model relative to those of Cassarino (2018) and Ehlert et al (2016)-the dissolution of a lithogenic phase (LSi 30 and LSi 28 ) and two reaction rates representing the release of DSi 30 and DSi 28 from solid phase Fe (oxyhydr)oxides. As for BSi, LSi dissolution is assumed to be dependent upon the degree of pore water DSi undersaturation and follows equation S20, where k LSidiss is the dissolution rate constant and LSi sol represents the solubility of the lithogenic phase.…”