Find in Library

This study aims to validate the stable carbon isotopic composition (<i>δ</i>¹³C) of phytoplankton as a tool for detecting submarine leakages of anthropogenic CO_2(g), since it is characterised by <i>δ</i>¹³C values significantly lower than the natural CO₂ dissolved in oceans. Three culture experiments were carried out to investigate the changes in <i>δ</i>¹³C of the diatom <i>Thalassiosira rotula</i> during growth in an artificially modified medium (ASW). Three different dissolved inorganic carbon (DIC) concentrations were tested to verify if carbon availability affects phytoplankton <i>δ</i>¹³C. Simultaneously, at each experiment, <i>T. rotula</i> was cultured under natural DIC isotopic composition (<i>δ</i>¹³C_DIC) and carbonate system conditions. The available DIC pool for diatoms grown in ASW was characterised by <i>δ</i>¹³C_DIC values (−44.2 ± 0.9‰) significantly lower than the typical marine range. Through photosynthetic DIC uptake, microalgae <i>δ</i>¹³C rapidly changed, reaching significantly low values (until −43.4‰). Moreover, the different DIC concentrations did not affect the diatom <i>δ</i>¹³C, exhibiting the same trend in <i>δ</i>¹³C values in the three ASW experiments. The experiments prove that phytoplankton isotopic composition quickly responds to changes in the <i>δ</i>¹³C of the medium, making this approach a promising and low-impact tool for detecting CO_2(g) submarine leakages from CO_2(g) deposits.