Full details for collection and analyses of underway Chl samples are provided by Goñi et al., submitted . Brief summaries are provided below.

Samples for this study were collected aboard RV Oceanus using the surface underway scientific system.

Aboard the vessel we had access to uncontaminated seawater and collected samples at specific times that allowed us to determine location (latitude and longitude) and seawater characteristics (temperature and salinity) from the ships’ navigation and sensor panels. We used a semi-automated filtration system (SAFS) described by Goñi et al., (2019) connected to Oceanus surface underway water to collect particulate samples for chlorophyll analyis. Surface underway water was connected to the SAFS through a manual flow-control valve via opaque polyethylene tubing.  A fly wheel flow meter was placed in-line and connected to a laptop computer using a data acquisition system to measure and record flows during the filtration stage. A switching valve with 8 ports was placed downstream from the flow meter and controlled by the laptop.  Under stand-by conditions, flow was directed to the ‘waste’ port, which was fitted with unobstructed tubing that drained into one of the ship’s sinks and flowed back to sea.  For Chlorophyll (Chl) measurements, samples were collected via the SAFS using 25 mm pre-combusted GF/F membranes placed inside stainless steel filter holders. Once filters were fitted in each of the sample ports, the filtration program was started to collect samples at selected intervals.

Once the filtration run was completed, the filter housings were removed from the SAFS, opened, and each individual filter placed in a closed container and stored in -80oC freezer until analyses.  Each sample was assigned a specific time stamp (start-end of filtration process) that coincided with the ship’s clock and allowed us to retrieve location and oceanographic data for each sample, as well as determine an overall filtration volume, which was used to calculate total chlorophyll concentrations once analyses were completed.

Samples were processed and analyzed following the method outlined in Strickland and Parsons (1972). Brifely, chlorophyll a concentrations were determined using the method of where samples were extracted in 90% acetone for 48 hours at -20°C in the dark and measured fluorometrically using a Turner Designs 10-AU fluorometer.

References cited: Strickland & Parson, 1972; Goñi et al., 2019; Goñi et al., submitted.