Rates of diatom biogenic silica production, growth, and size-fractionated phytoplankton growth and microzooplankton grazing in the Bering and Chukchi Seas, spring 2017

During the Arctic Shelf Growth, Advection, Respiration and Deposition (ASGARD) cruise in the northern Bering Sea and Chukchi Sea (5 – 28 June 2017) we examined diatom production and phytoplankton growth and microzooplankton grazing losses. Quantification of total silica production can be a metric to estimate diatom production. Normalizing silica production to diatom biovolume-derived living-cell-associated silica using low-temperature allometric equations gave realistic growth values (considering the temperature at the time of sampling and a survey of literature measuring diatom growth in culture and field conditions). Field experiments to quantify grazing rates on phytoplankton showed that small phytoplankton, primarily non-diatoms, were heavily and consistently grazed, while larger phytoplankton (e.g. diatoms) were not. Out of 26 separate experiments, grazing on large-sized phytoplankton (e.g. diatoms) by microzooplankton was quantifiable in 14 experiments (54%) whereas grazing on smaller phytoplankton (non-diatoms) was quantifiable in 23 experiments (88%).