Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean

Abstract

Abstract. The element silicon (Si) is required for the growth of silicified organisms in marine environments, such as diatoms. These organisms consume vast amounts of Si together with N, P, and C, connecting the biogeochemical cycles of these elements. Thus, understanding the Si cycle in the ocean is critical for understanding wider issues such as carbon sequestration by the ocean's biological pump. In this review, we show that recent advances in process studies indicate that total Si inputs and outputs, to and from the world ocean, are 57 % and 37 % higher, respectively, than previous estimates. We also update the total ocean silicic acid inventory value, which is about 24 % higher than previously estimated. These changes are significant, modifying factors such as the geochemical residence time of Si, which is now about 8000 years, 2 times faster than previously assumed. In addition, we present an updated value of the global annual pelagic biogenic silica production (255 Tmol Si yr−1) based on new data from 49 field studies and 18 model outputs, and we provide a first estimate of the global annual benthic biogenic silica production due to sponges (6 Tmol Si yr−1). Given these important modifications, we hypothesize that the modern ocean Si cycle is at approximately steady state with inputs =14.8(±2.6) Tmol Si yr−1 and outputs =15.6(±2.4) Tmol Si yr−1. Potential impacts of global change on the marine Si cycle are discussed.

Role of small Rhizaria and diatoms in the pelagic silica production of the Southern Ocean

“…Some forms of Rhizaria skeleton, and especially the polycystine radiolarians (Takahashi 1981), are much more resistant than diatoms' frustules. Moreover, Rhizaria remineralization occurs mostly on the sea-floor (Takahashi 1981), while diatoms dissolution occurs both in the water column and in the sediments (Tréguer and De La Rocha 2013;Tréguer et al 2021). These two processes combined, would lead to a preferential preservation of the Rhizaria at the sediment surface.…”

“…Up to 23.5% of the overall biogenic silica production occurs within polar oceans (Tréguer and De La Rocha 2013;Tréguer 2014;Tréguer et al 2021), most of it in the Southern Ocean. The Southern Ocean, sometimes referred to as the "silica ocean" (Honjo et al 2008), has among the highest oceanic silicic acid concentrations.…”

Assessment of C, N, and Si Isotopes as Tracers of Past Ocean Nutrient and Carbon Cycling

“…Several recent studies have reported a significant contribution of picoplankton to the bSi stock (Baines et al, 2012;Krause et al 2017). Their estimated contribution at a global ocean scale is relatively small (<10% according to the recent review of Tréguer et al, 2021) but will vary regionally. This represents an uncertainty for the use of Si isotope in (paleo-)oceanography since the Si isotopic fractionation of these organisms is unknown.…”

High Productivity Makes Mangroves Potentially Important Players in the Tropical Silicon Cycle

“…A variety of marine organisms are silicifiers including diatoms, radiolarians, silicoflagellates, select sponges, and even picocyanobacteria (Tréguer and De La Rocha, 2013). Photosynthesizing silicifiers (e.g., diatoms) take up significant amounts of Si along with nitrogen, phosphorus, and inorganic carbon, tightly coupling these biogeochemical cycles (Tréguer et al, 2021). Diatoms are responsible for ∼50% of oceanic primary productivity (Rousseaux and Gregg, 2013) and are an important source of carbon (C) export to the deep ocean (Tréguer et al, 2018).…”