A sampling day has two discrete modes, a CTD bio-cast and inline sampling from the underway seawater, plus instruments that record continuously. The notes below describe how a day is put together. The table that follows provides depths, timepoints, volumes, and replicates for each sample type.
CTD cast
Once per day, ideally within about two hours of local solar noon, the CTD rosette is cast on a dedicated bio-cast to a maximum depth of 1000 m. Cruises that accommodate Bio-GO-SHIP sampling use this separate cast for the biological bottles. DNA is filtered onto Sterivex cartridges at 1000, 200, 100, and 5 m (one filter per depth). RNA is collected only at 5 m (one filter). HPLC pigments are filtered onto GF/F filters at 100, 40, and 5 m. Particulate organic matter is collected at 5 m only: triplicate GF/F filters for POC/N and triplicate GF/F filters for POP. Flow cytometry samples (1.8 mL, glutaraldehyde-preserved in cryovials) are collected at eight depths spanning the profile: 1000, 500, 200, 150, 100, 75, 40, and 5 m.
At stations where a BGC-Argo float is deployed, that scheme changes. HPLC adds chlorophyll maximum and chlorophyll maximum + 50 m to the standard 100, 40, and 5 m. A small-volume POC/N sample, normally collected only from the inline seawater, is also drawn from the CTD at those same five depths so it can be submitted to NASA SeaBASS with the HPLC samples.
Two instruments record continuously on the CTD instead of from bottles. A transmissometer runs on every CTD cast, bio-casts and core hydrographic casts alike, when the team managing the rosette brings one. Its lenses are cleaned with isopropyl and deionized water once a day, and covered with electrical tape about once a week for a calibration dark cast. An Underwater Vision Profiler (UVP5) runs on full-depth casts and is switched off for bio-casts and other shallow casts. When the bio-cast itself falls within about two hours of solar noon, it takes the place of the noon inline timepoint.
Inline sampling
Inline sampling draws continuously from the ship's underway seawater supply. A diaphragm or positive-displacement pump is preferred, because impeller pumps do more damage to cells. Water is taken from a sink as close as possible to the surface-water inlet valve, which keeps the line short and reduces shear. The continuous instruments are set up near a sink that drains overboard.
Discrete samples are collected at four fixed local (ship) times: 06:00, 12:00, 20:00, and 00:00. The 06:00, 12:00, and 20:00 sets are DNA (one Sterivex), HPLC pigments (one GF/F), large-volume particulate organic matter (triplicate GF/F for POC/N and triplicate GF/F for POP), and flow cytometry (one cryovial). Noon also includes RNA (one Sterivex) and a small-volume POC/N sample (one GF/F, plus dry and wet blanks). Midnight is reserved for nucleic acids: DNA (one Sterivex) and RNA (one Sterivex).
In parallel, several instruments sample that same inline water continuously: an optical suite (a hyper-BB or BB3 for backscatter, an AC-S for absorption and attenuation, and a fast repetition rate fluorometer), an onboard flow cytometer and an Imaging FlowCytobot (IFCB), and a particulate inorganic carbon sensor paired with a salinity sensor and a fluorometer.
Bio-GO-SHIP also contributes validation data for NASA's PACE satellite. Each day the overpass time is determined for the PACE-OCI sensor, which tends to be close to local noon. Inline sampling at the overpass includes a small-volume POC/N regression (protocol details still needed), HPLC (triplicates when the sky is mostly free of clouds, and a single filter when it is cloudy), PIC, and flow cytometry (one cryovial).
CTD depths are for the 12:00 bio-cast. Inline timepoints are collected at 5 m.