Dataset: Phytoplankton and heterotrophic bacterial cell abundance in seawater collected during R/V Savannah cruise SAV-19-02 in the NW Atlantic Ocean in the Spring of 2019

Sampling and analytical procedures:

 Seawater samples were collected in triplicate from Niskin bottles (12 L), at three stations (St. 1, St. 2 and St. 3) along a transect from coastal Georgia to offshore waters. Latitude (lat) and longitude (lon) of sampling sites are provided in .mat files. Stations 1 and 2 were on the continental shelf (15–30 m depth), while Station 3 was on the shelf break (220 m depth) adjacent to the Gulf Stream. At each station, samples were collected at 2-3 depths between the surface (4–5 m) and 50 m for Picoeukaryotes, Nanoeukaryotes, Synechococcus (PhytoplanktonCellAbundance. mat) and heterotrophic bacteria (HetertrophicBacteriaCellAbundance.mat). 

Samples for cell abundance (2 mL) were fixed with 0.5% glutaraldehyde (final concentration), flash frozen in liquid nitrogen and then transferred into a -80 °C freezer until analysis. Frozen samples were thawed at room temperature and were analyzed using the Guava EasyCyte HT flow cytometer (Millipore). Instrument specific beads were used to calibrate the cytometer.

Samples were analyzed at a low flow rate (0.24 µL s-1) during 3 min. For heterotrophic bacteria cell counts, samples were incubated with SYBR Green II solution 1:10 (Molecular Probes) for 15 min in the dark, in order to stain the nucleic acids. Bacterial cells were detected and enumerated based on diagnostic plots of forward scatter vs. green fluorescence.  Group-specific phytoplankton were distinguished based on plots of forward scatter vs. orange fluorescence (phycoerythrin containing Synechococcus sp.), and SSC vs. red fluorescence (eukaryotes).

Instruments:  Sampling was performed using Niskin bottles (12 L) mounted on a rosette. Cell abundance of both phytoplankton and heterotrophic bacteria were determined using the Guava EasyCyte HT flow cytometer (Millipore).

Location:  Northwestern Atlantic surface waters. Depth: surface-50 m.