Diatom silicification changes in high pCO2 seawater: a mesocosm experiment
Diatoms contribute significantly to the transfer of dissolved organic carbon from the surface ocean to the deep in a system called the biological pump. Understanding how diatoms silicify (incorporate silica into their cell wall) in response to high partial pressure CO2 (pCO2) seawater is important to understand how ocean acidification will affect this biological pump. A mesocosm experiment was performed at University of Washington’s Friday Harbor Laboratories to investigate these effects. Three pCO2 treatments were used in triplicate to determine whether or not diatom silicification is directly affected by ocean acidification. The control and high treatment, at 650ppm and 1250ppm, were held at constant pCO2 levels with additions of highly saturated CO2 seawater. The drift treatment started at 1250ppm and was allowed to drift as biological processes used the CO2. Biogenic silica was measured every other day and integrated with diatom cell counts to calculate silicification. Results showed no differences between pCO2 treatments for total silica in a population and silicification per diatom cell. A variety of potential stressors were explored to understand the changes in diatom silicification throughout the experiment. Factors other than CO2, such as light limitation, are more likely to explain data trends. Further research is necessary to see how CO2 will affect diatoms’ ability to sequester carbon especially when coupled with temperature increases.