The diatom Thalassiosira pseudonana grown in mesocosms at contemporary and elevated CO2 over the diel cycle

To test whether elevated CO2 , which drives seawater below pH 7.9, would shift the dynamical expression patterns diatoms in a more natural environment, we designed a controlled mesocosm study at Friday Harbor Laboratories (FHL) Ocean Acidification Environmental Laboratory (OAEL). Briefly, four independent mesocosm tanks were set up with continuous flow (10-12 mL/min) of filtered seawater from the Puget Sound to simulate mid-century (pH 7.9) and acidified oceanic conditions (pH 7.6) in duplicate. Mesocosm reservoirs were supplemented with nutrients and inoculated with T. pseudonana acclimated in FHL seawater. Mesocosms were outfitted with custom enclosures to simulate a 12:12 light:dark diel cycle. Cells for RNA extraction were sampled in the middle of the light and dark cycle and sequenced on Illumina NextSeq 500 platform. Duplicate mesocosms at mid-century (pH 7.9) and acidified oceanic conditions (pH 7.6) were inoculated with T. pseudonana and grown over a 12:12 diel cycle (275 μM photons/m2/s). Cells were collected for gene expression analysis in the middle of the light and dark cycle over 2 days. Result: 16 total transcriptomes (n=4 at pH 7.9 in the light, n=4 at pH 7.9 in the dark, n=4 at pH 7.6 in the light, and n=4 at pH 7.6 in the dark).