Dataset: TEP and CSP particle concentrations from incubations collected from Station ALOHA and 31ºN at 5m and 125m in the North Pacific in June 2021 on the R/V Kilo Moana cruise KM2108

Seawater samples were collected from 22˚45’N  (S(5m), S(125m)) and  31˚N (N(5m), N(125m)) in June 2021 at 5m and at 125m. At each station and depth, approximately 100 liters of seawater were collected and the following treatments were conducted in triplicate by placing 10L of initial volume into acid-cleaned and rinsed 10 L HDPE amber carboys (Justrite ®): (1) Whole water (W), 100% seawater; (2) Filtrate (F), 0.2 µm-filtered water; and (3) Mixed (M), 80% filtrate and 20% whole water. 

For the F and M treatments, gravity filtration was used through an in-line Pall Acropak 1000 (0.8/0.2 µm) filter attached directly to the 50 L carboy spigot with silicone tubing. The incubation carboys were then stored in the dark within two deckboard environmental chambers maintained at the in-situ temperatures by use of recirculating surface or chilled (closed loop) seawater. The experiments were performed over a period of 80-100 hours, experiments S(5m), S(125m), and N(125m) were sampled at 4 discrete time points, and experiment N(5m) at 3 time points, after the incubation initiation, spaced at ~1-1.5 day intervals.

TEP and CSP particles were collected onto 0.4 µm polycarbonate filters from 1 liter each of incubation subsample filtrate collected for nutrient analysis. Filtration was achieved using a peristaltic pump and silicone tubing through a 25 mm polycarbonate filter holder. Filters containing particles were immediately stained with Alcian blue (TEP) or Coomassie blue (CSP) dyes and stored frozen at -20 degC until analysis on shore back at the University of New Hampshire. TEP and CSP concentrations were determined spectrophotometrically following the protocols of Bittar et al., (2018) for TEP and Cisternas-Novoa et al.,(2015) for CSP with minor modifications, and standardized with xanthan gum and bovine albumen, respectively. 

Incubation samples collected from TEP/CSP filtering were put into 40 mL glass EPA vials with silicone septa tops and frozen at -20degC until analysis on shore back at the University of New Hampshire. Phosphate concentrations were measured using Shimadzu UV-1800 Dual Beam UV-Vis Spectrophotometer, and Nitrate concentrations were measured using Thermo Scientific 42iQ NO-NO2-NOx Analyzer. Total organic carbon was measured Shimadzu TOC-V CSH with TNM-1 and ASI-V Autosampler. All were measured at the University of New Hampshire. Dissolved organic phosphorus and dissolved organic nitrogen were computed after subtracting the relevant inorganic nutrient concentrations from the measured total dissolved phosphorus (TDP) and total dissolved nitrogen concentrations (TDN). 

For INT, at each incubation time point, incubation water was subsampled and analyzed following the García-Martín et al., (2019) method. The INT reagent was added to the sample and placed in the incubation tank for 1.5 hours, and then placed in a -20ºC freezer for later laboratory analysis. Once samples were at the UNH laboratory, samples were then added to acrylic 1 cm pathlength cuvettes and run on a Shimadzu UV-Vis spectrophotometer to measure the absorbance at 485 nm. 

For cells, at each time point, samples were fixed with 0.01% glutaraldehyde and stored in a -80 °C freezer until they were measured at the UNH laboratory using a flow cytometer (Miltenyi BiotecMACSQuant VYB) with SYBR green as a DNA stain (Gasol & Del Giorgio, 2000). For measuring α-glucosidases, the incubated water was subsampled and 25 µL of 1mM MUF-a-D-glucopyranoside solution was added and shaken. During a 24-hours- period the fluorescence readings were performed at an excitation of 365-395 nm and emission of 440-470 nm using a handheld Turner® TBS-380 mini UV fluorometer. The fluorescence readings were calibrated using the MUF standard solution which was prepared within the range 10 – 250 μM MUF, with the slope and time duration of the 4-point glucosidase incubation at each time used to convert to nM C hr-1 rates.