Increasing iron concentration inhibits the Al-incorporation into the diatom biogenic silica: From laboratory simulation of ocean iron fertilization

Abstract

Incorporated aluminum (Al) in diatom biogenic silicon (BSi) by biological behaviors shows a dissolution-inhibition effect for BSi, thus affecting the organic carbon export driven by diatoms. Ocean iron fertilization (OIF) aims to reduce the amount of atmospheric CO2 by promoting diatom blooms to enhanced the biological pump. However, BSi dissolved in a short time, leading to low efficacy of the carbon export. Considering the key role of incorporated Al in BSi dissolution, it is necessary to investigate the influence of increasing iron concentrations during OIF on Al incorporation of BSi. A lab simulation experiment, whereby Thalassiosira weissflogii was selected as a model marine diatom, was performed to reveal the effects of increasing iron concentrations on Al incorporation to BSi. Microanalyses including focused ion beams (FIB), high-resolution transmission electron microscopy (HRTEM), and high-resolution energy dispersive X-ray spectrometry (EDS) were used to identify the incorporated Al in BSi and evaluate its content. Results showed that increasing the iron concentration in the culture medium increased the cell yields but decreased the relative content of incorporated Al in BSi. The Al decrease resulted in the reduction of its effects in dissolution-habitation of BSi, which most likely also occurred during OIF. Therefore, the coupled SiAl biogeochemical cycle and the export of organic carbon from the surface ocean driven by diatoms would be influenced by the addition of iron during OIF.