Silicon isotopes in spring Southern Ocean diatoms: Large zonal changes despite homogeneity among size fractions

Silicon pool dynamics and biogenic silica export in the Southern Ocean inferred from Si-isotopes

“…3a, b). 30 Si enrichment was associated with a decrease in Si(OH) 4 concentration from south to north, as also reported in earlier studies (Varela et al, 2004;Cardinal et al, 2005). This condition is mainly driven by the preferential uptake of 28 Si by diatoms (De La Rocha et al, 1997) along the northward advection of surface waters (Varela et al, 2004) followed by diatom export out of the mixed layer.…”

“…The results are discussed in terms of source, pathway, and fate of silicon across the different Southern Ocean water masses and the interaction of the latter with the water masses from other oceanic basins. Results are compared with a similar transect sampled in spring and located in the Australian sector of the Southern Ocean (CLIVAR-SR3; Cardinal et al, 2005). The isotopic constraints allow us to quantify the annual net bSiO 2 production and the vertical summertime Si-supply into the mixed layer, both in the Antarctic Zone and Polar Front Zone, using the approach described in Fripiat et al (2011a).…”

A Review of the Stable Isotope Bio-geochemistry of the Global Silicon Cycle and Its Associated Trace Elements

“…This is often more pronounced for diatoms (and radiolarians; Abelmann et al, 2015) due to the ability for contaminant valve adherence and occlusion, over sponge spicules that can be picked. Clay δ 30 Si compositions are estimated between −2.95‰ and +2.5 (Douthitt, 1982;Georg et al, 2009;Opfergelt and Delmelle, 2012), which can significantly lower reported δ 30 Si diatom values [published values range between −0.07 and +3.05‰; (De La Rocha et al, 2000;Cardinal et al, 2007;Sun et al, 2013;Panizzo et al, 2014Panizzo et al, , 2016] and outside of analytical uncertainty, while high sample presence of different phases of bSiO 2 can have a similar effect (e.g., δ 30 Si sponge signatures vary between −5.72 and +0. 87‰ Douthitt, 1982;De La Rocha, 2003;Wille et al, 2010;.…”

“…The influence of environment on δ 30 Si composition in diatoms has yet to be shown under laboratory controlled conditions. Data from in-situ/natural settings, have not documented a species effect (e.g., Cardinal et al, 2007;Fripiat et al, 2012;Closset et al, 2015) although if anything this clearly demonstrates the need to better understand the variability of δ 30 Si in diatoms.…”

Evidence for a major change in silicon cycling in the subarctic North Pacific at 2.73 Ma

“…Results obtained from culture studies have not shown any species or temperature dependence of the Si isotope fractionation factor, which is e Si % À1.1% [De La Rocha et al, 1997]. This degree of mass fractionation has been confirmed by seawater modeling [Cardinal et al, 2005;Reynolds et al, 2006a], but fractionation into in situ formed biogenic opal appears to be somewhat larger, up to e Si % À1.6% [Varela et al, 2004;Cardinal et al, 2007]. For any one type of model used, there is only one other parameter relating the isotopic composition of the opal (d 30 Si) and the degree of utilization (f); the initial seawater composition.…”