Seawater carbonate chemistry and the decrease of H+ concentration in the phycosphere and thickness of the pH boundary layer of marine diatoms Coscinodiscus wailesii

• Main Authors: Liu, Fengjie, Gledhill, Martha, Tan, Qiaoguo, Zhu, Kechen, Zhang, Qiong, Salaün, Pascal, Tagliabue, Alessandro, Zhang, Yanjun, Weiss, Dominik J, Achterberg, Eric Pieter, Korchev, Yuri
• Format: Dataset
• Language: English
• Published: PANGAEA 2022
• Subjects: Acid-base regulation; Alkalinity; total; Aragonite saturation state; Bicarbonate ion; Bottles or small containers/Aquaria (<20 L); Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Chromista; Coscinodiscus wailesii; Figure; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Hydrogen ion concentration; Laboratory experiment; Laboratory strains; Not applicable; OA-ICC; Ocean Acidification International Coordination Centre; Ochrophyta; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Pelagos; pH; Phytoplankton; Proton gradients; Salinity; Single species; Species; unique identification; Temperature; water; Thickness; Treatment; Type; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.951332; https://doi.org/10.1594/PANGAEA.951332

Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 μmol photons/m**2/s the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.