Stable silicon isotopes uncover a mineralogical control on the benthic silicon cycle in the Arctic Barents Sea

Ward, James; Hendry, Katharine R; Arndt, Sandra; Faust, Johan C.; Freitas, Felipe Sales de; Henley, Sian F.; Krause, Jeffrey W.; März, Christian; Ng, Hong Chin; Pickering, Rebecca A.; Tessin, Allyson

doi:10.1016/j.gca.2022.05.005

Cited by 21 publications

(53 citation statements)

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“…Given the changes forecast in the pelagic-benthic coupling of Si in the Arctic, it is important to understand the baseline benthic biogeochemical system in order to anticipate the implications of further perturbations. Based on Si isotopic data from various reactive sedimentary pools and the sediment pore water dissolved phase from the Barents Sea seafloor, Ward et al (2022) hypothesised that the Si cycle is isotopically coupled to the redox cycling of metal oxides, most likely solid-phase Fe (oxyhydr)oxides. The reductive dissolution of Fe (oxyhydr)oxides and release of adsorbed Si (FeSi) are thought to drive marked shifts in the isotopic composition of the Barents Sea sediment pore water DSi pool towards lower values.…”

Section: Introductionmentioning

confidence: 99%

“…The reductive dissolution of Fe (oxyhydr)oxides and release of adsorbed Si (FeSi) are thought to drive marked shifts in the isotopic composition of the Barents Sea sediment pore water DSi pool towards lower values. Further, Ward et al (2022) propose that sediment pore water undersaturation drives the contemporaneous dissolution of lithogenic silicate minerals (LSi) alongside BSi, some of which are reprecipitated as authigenic clay minerals (AuSi), representing a sink of isotopically light Si to the regional Si budget. Finally, Ward et al (2022) propose that seasonal pelagic phytoplankton blooms generate stark peaks in pore water DSi that dissipate on the order of weeks to months.…”

Section: Introductionmentioning

confidence: 99%

“…Further, Ward et al (2022) propose that sediment pore water undersaturation drives the contemporaneous dissolution of lithogenic silicate minerals (LSi) alongside BSi, some of which are reprecipitated as authigenic clay minerals (AuSi), representing a sink of isotopically light Si to the regional Si budget. Finally, Ward et al (2022) propose that seasonal pelagic phytoplankton blooms generate stark peaks in pore water DSi that dissipate on the order of weeks to months. However, to fully understand the early diagenetic cycling of Si within the seafloor of the Barents Sea, we must be able to quantify the relative contribution of LSi and BSi to the DSi pool, as well as establish whether AuSi precipitation removes a significant portion of that pool.…”

Section: Introductionmentioning

confidence: 99%

“…However, to fully understand the early diagenetic cycling of Si within the seafloor of the Barents Sea, we must be able to quantify the relative contribution of LSi and BSi to the DSi pool, as well as establish whether AuSi precipitation removes a significant portion of that pool. Here we employ steady state reaction-transport modelling to reconstruct the benthic cycling of Si in the Barents Sea, informed by our dataset of solid-and dissolved-phase Si isotopic compositions (Ward et al, 2022) to test these hypotheses. Such techniques allow for the disentangling and quantification of the aforementioned early diagenetic reactions (Geilert et al, 2020a;Ehlert et al, 2016a;Cassarino et al, 2020), as well as the return benthic flux of DSi to the overlying bottom water.…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, a recent isotopic assessment identified the need for an additional benthic sink of light Si to close the Si budget (Brzezinski et al,Figure 1. Map of the Barents Sea shelf, including ChAOS stations, the main hydrographic features and water masses from Ward et al (2022) (PF -oceanic polar front, AW -Atlantic Water, ArW -Arctic Water, NCCW -Norwegian Coastal Current Water, BSW -Barents Sea Water, BSO -Barents Sea Opening, BSX -Barents Sea Exit). Dashed red path refers to a subsurface water mass .…”

Section: Introductionmentioning

confidence: 99%

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Benthic silicon cycling in the Arctic Barents Sea: a reaction–transport model study

et al. 2022

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Abstract. Over recent decades the highest rates of water column warming and sea ice loss across the Arctic Ocean have been observed in the Barents Sea. These physical changes have resulted in rapid ecosystem adjustments, manifesting as a northward migration of temperate phytoplankton species at the expense of silica-based diatoms. These changes will potentially alter the composition of phytodetritus deposited at the seafloor, which acts as a biogeochemical reactor and is pivotal in the recycling of key nutrients, such as silicon (Si). To appreciate the sensitivity of the Barents Sea benthic system to the observed changes in surface primary production, there is a need to better understand this benthic–pelagic coupling. Stable Si isotopic compositions of sediment pore waters and the solid phase from three stations in the Barents Sea reveal a coupling of the iron (Fe) and Si cycles, the contemporaneous dissolution of lithogenic silicate minerals (LSi) alongside biogenic silica (BSi), and the potential for the reprecipitation of dissolved silicic acid (DSi) as authigenic clay minerals (AuSi). However, as reaction rates cannot be quantified from observational data alone, a mechanistic understanding of which factors control these processes is missing. Here, we employ reaction–transport modelling together with observational data to disentangle the reaction pathways controlling the cycling of Si within the seafloor. Processes such as the dissolution of BSi are active on multiple timescales, ranging from weeks to hundreds of years, which we are able to examine through steady state and transient model runs. Steady state simulations show that 60 % to 98 % of the sediment pore water DSi pool may be sourced from the dissolution of LSi, while the isotopic composition is also strongly influenced by the desorption of Si from metal oxides, most likely Fe (oxyhydr)oxides (FeSi), as they reductively dissolve. Further, our model simulations indicate that between 2.9 % and 37 % of the DSi released into sediment pore waters is subsequently removed by a process that has a fractionation factor of approximately −2 ‰, most likely representing reprecipitation as AuSi. These observations are significant as the dissolution of LSi represents a source of new Si to the ocean DSi pool and precipitation of AuSi an additional sink, which could address imbalances in the current regional ocean Si budget. Lastly, transient modelling suggests that at least one-third of the total annual benthic DSi flux could be sourced from the dissolution of more reactive, diatom-derived BSi deposited after the surface water bloom at the marginal ice zone. This benthic–pelagic coupling will be subject to change with the continued northward migration of Atlantic phytoplankton species, the northward retreat of the marginal ice zone and the observed decline in the DSi inventory of the subpolar North Atlantic Ocean over the last 3 decades.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%