Dataset: Division rates, grazing rates, and accumulation rates from phytoplankton dilution experiments conducted on cruises aboard the R/V Robert Gordon Sproul along the Southern California coast during July and August 2023

All surface seawater was collected just prior to local sunrise from a SBE-911+ Conductivity-Temperature-Depth (CTD, Sea-Bird Scientific) Niskin bottle rosette cast and then transferred or directly filtered into acid-cleaned 20-liter (L) carboys with platinum-cured silicone tubing.

Phytoplankton division and accumulation rates and zooplankton grazing rates (1/d) were estimated in 14 experiments, in which changes in group-specific phytoplankton cell abundances were measured using flow cytometry in a dilution series of total and filtered seawater after 24 hours (sampling at 0 hours and 24 hours). Phytoplankton apparent and instantaneous division rates, accumulation rates, and zooplankton grazing rates were quantified following Morison et al. (2019). For each experiment, 0.45-micrometer (µm) filtered seawater was generated directly from Niskin bottles using a polyethersulfone capsule filter (Polycap TC, Whatman) (Morison et al., 2019). Total seawater was diluted with the filtered seawater in 1-liter (L) acid-cleaned polycarbonate bottles to a final concentration of 100%, 75%, 50%, and 25% total seawater (Landry and Hassett, 1982). Each experiment included at least one biological replicate of one randomly selected dilution. Diluted water either remained unamended or was amended with ash leachate prior to being screened with mesh and incubated in a deck-board incubator with continuously flowing seawater. Ash leachates were added to a final amendment of ~4 micromoles carbon per liter (µmol C/L) as dissolved organic carbon (DOC). Incubations were screened to obtain a light level corresponding to the median intensity in the surface mixed layer.