Iron availability influences silicon isotope fractionation in two Southern Ocean diatoms (Proboscia inermis and Eucampia antarctica) and a coastal diatom (Thalassiosira pseudonana)

<p>The fractionation of silicon (Si) isotopes was measured in two Southern Ocean diatoms (<i>Proboscia inermis</i> and <i>Eucampia Antarctica</i>) and a coastal diatom (<i>Thalassiosira pseudonana</i>) that were grown under varying iron (Fe) concentrations. Varying Fe concentrations had no effect on the Si isotope enrichment factor (ε) in <i>T. pseudonana</i>, whilst <i>E. Antarctica</i> and <i>P. inermis</i> exhibited significant variations in the value of ε between Fe-replete and Fe-limited conditions. Mean ε values in <i>P. inermis</i> and <i>E. Antarctica</i> decreased from (± 1SD) −1.11 ± 0.15‰ and −1.42 ± 0.41 ‰ (respectively) under Fe-replete conditions, to −1.38 ± 0.27 ‰ and −1.57 ± 0.5 ‰ (respectively) under Fe-limiting conditions. These variations likely arise from adaptations in diatoms arising from the nutrient status of their environment. <i>T. pseudonana</i> is a coastal clone typically accustomed to low Si but high Fe conditions whereas <i>E. Antarctica</i> and <i>P. inermis</i> are typically accustomed to High Si, High nitrate low Fe conditions. Growth induced variations in silicic acid (Si(OH)₄) uptake arising from Fe-limitation is the likely mechanism leading to Si-isotope variability in <i>E. Antarctica</i> and <i>P. inermis</i>. The multiplicative effects of species diversity and resource limitation (e.g., Fe) on Si-isotope fractionation in diatoms can potentially alter the Si-isotope composition of diatom opal in diatamaceous sediments and sea surface Si(OH)₄. This work highlights the need for further <i>in vitro</i> studies into intracellular mechanisms involved in Si(OH)₄ uptake, and the associated pathways for Si-isotope fractionation in diatoms.</p>