Dataset: Particulate organic carbon concentrations and monosaccharide composition of POM-derived carbohydrates from samples taken during R/V Endeavor cruise EN638 in the Western North Atlantic in May 2019

Collection

Water was collected via Niskin bottles mounted on a rosette, equipped with a CTD. Seawater was transferred to carboys that were rinsed three times with water from the sampling depth and then filled with seawater from a single Niskin bottle.

Particulate organic matter (POM) was harvested by filtering between 5-15 liters of seawater through a 47-mm pre-combusted (400℃ for 6 hours) glass fiber filter (GF/F; nominal pore size 0.7 μm; for volumes filtered at each depth and station, see the dataset). Filers were stored at -80C until further analysis. The same filter was used for both particulate organic carbon (POC) measurements and monosaccharide composition analysis.   

Analysis

Particulate organic carbon was measured as described in Becker et al. (2020). In brief, triplicate filter punches from samples collected on pre-combusted (400℃ for 6 hours) glass fiber filters (GF/F) were placed in an acidic environment (concentrated HCl fumes) for 24 h to remove inorganic carbon. After drying for 24 h at 60 °C, the samples were packed in pre-combusted tin foil. C was quantified using an elemental analyzer (cario MICRO cube; Elementar Analysensysteme) using sulfanilamide for calibration. Limits of detection for POC was 0.001 mg C/L, based on the standard deviation of blank measurements.

The monosaccharide constituents of total combined carbohydrates (i.e., polysaccharides, glycoproteins, glycolipids, etc.) of POM (collected as described above) were determined from triplicate filter punches (11.2 mm diameter). Samples were acid hydrolyzed by adding 1 M HCl to each filter piece, flame sealing each piece in a glass ampule, and placing the ampules in an oven at 100°C for 24 hours. After acid hydrolysis, the samples were dried on a speed-vac and resuspended in Milli-Q water to remove any HCl. The quantity and composition of the resulting monosaccharides were measured using a modified protocol (Engel and Handel (2011), as described by Vidal-Melgosa et al. (2021)). In brief, neutral, amino, and acidic sugars were quantified using high performance anion exchange chromatography on a Dionex ICS-5000+ system with pulsed amperometric detection (HPAEC-PAD). Peaks were identified using retention times of purified monosaccharide standards; abundance was quantified from standards using the peak area for a given monosaccharide. The limit of detection for monosaccharides varied from 0.5 – 1 ug/L, depending on the specific monosaccharide measured.