Dataset: Protist carbon from microscopy samples collected in the Argo Basin of the Eastern Indian Ocean on R/V Roger Revelle cruise RR2202 from Feb to Mar 2022

Field Collection

We conducted four Lagrangian experiments (hereafter referred to as “cycles”) that lasted three to five days.  The mixed layer was followed in a Lagrangian frame of reference using subsurface drogues attached to satellite-tagged marker buoys (Landry et al. 2009; Stukel et al. 2015). Six depths were chosen to span the euphotic zone (based on chlorophyll fluorescence measured during the conductivity-temperature-depth (CTD) downcast profiles).We used a 12-place 6-L Niskin bottle rosette equipped with a Seabird Conductivity, Temperature, and Depth (CTD) sensor and profiling chlorophyll fluorometer to sample water daily at six depths spanning the euphotic zone for phytoplankton community samples.

Epifluorescence Microscopy Sampling

From each depth, two different volumes of water were sampled: 50 mL for nanoplankton- epifluorescence microscopy (filtered through a 0.8-µm pore-size black polycarbonate filter) and 400 mL for microplankton epifluorescence microscopy (filtered through an 8-µm pore-size filter). Utilizing two different sized filters and sampling volumes allowed for appropriate, adjustable filtered volumes and avoid overlapping cells on the slides. 20 µm backing filters were utilized as data has indicated that they support the membrane filters and ensure even dispersal of sample on the filter (Kemp et. al., 1993; Taylor et al., 2015). The samples were preserved using buffered formalin, alkaline Lugol’s solution, and sodium thiosulfate then stained using proflavine and 4’, 6-diamidino-2phenylindole (DAPI) (modified protocol from Sherr and Sherr, 1993 in Kemp et. al., 1993). During and immediately after filtration, filters were covered with tin foil to prevent photochemical quenching. Filters were mounted onto a glass slide and frozen in a -80º C freezer for later analysis.