ALBERT

Description: Phytoplankton community composition was assessed using chemotaxonomic pigments (including all chlorophyll types, accessory and photoprotective pigments) measured with high performance liquid chromatography (HPLC). Water samples from 7 depths spanning the euphotic zone were collected using a CTD-rosette during the five Lagrangian experimental cycles conducted during Salp Particle expOrt and Ocean Production (SalpPOOP), from October to November 2018 in the vicinity of the Chatham Rise (New Zealand). Depths varied according to experimental cycle, as it was adjusted based on PAR profiles to span the depth to 0.1% of surface irradiance. Chemotaxonomic pigments of phytoplankton in the water column were filtered onto GF/F filters (2L), then immediately flash-frozen in liquid nitrogen, and shipped frozen to Instituto Español de Oceanografía, Centro Oceanográfico de Gijón, where they were extracted for High-performance liquid chromatography (HPLC) analyses following established protocols (doi:10.4319/lom.2014.12.46). For this study, 2 profiles from each experimental cycle were analyzed, and vertically integrated to obtain areal estimates for each cycle. Pigment contributions were normalized by total chlorophyll a (Chl a) to account for potential losses and low yield, and are thus presented as integrated percentages per cycle. These proportions do not always sum to 100 because ancillary pigments/other compounds that cannot be positively identified are not included.

Description: Water was collected for net primary production (NPP) incubations and total and size-fractionated chlorophyll a from multiple depths spanning the euphotic zone, using a CTD-rosette equipped with 24 10L Niskin bottles. For NPP, water from 6 depths spanning the euphotic zone (0.1% of surface irradiance) were incubated in situ during the 5 Lagrangian cycles sampled during SalpPOOP. NPP was assessed using carbon-14 (14C) assays, with 24-hour incubations that integrated respiration/production balance over the dark and light periods of the diel cycle. Seawater samples (1.3 L) were collected into an acid-rinsed polycarbonate bottle from pre-dawn CTD casts (~2:00 h each day of each cycle) at six depths spanning the euphotic zone. The bottles were then spiked with 0.1 mCi 14C-bicarbonate (DHI, Denmark or Perkin-Elmer, USA) before triplicate controls on ethanolamine were taken to quantify initial radioactivity at each depth incubation. After gentle mixing, the 'hot' 1.3 L was dispensed into three light and one dark bottles (320 mL acid-cleaned polycarbonate) that were incubated in situ on the free-drifting array. After recovery, the entire content of the bottles were filtered onto 0.2 µm pore-size 25-mm polycarbonate filters and kept frozen until analysis. Once on land, filters were acidified with 200 µL 0.5 N HCL, Hi Safe 3 liquid scintillation cocktail was added and disintegrations per minute were then determined using a scintillation counter following procedures described in Gutiérrez‐Rodríguez et al (2020 doi:10.1029/2019JC015550). NPP of multiple casts (2 to 4) conducted during each experimental cycle were averaged to obtain cycle estimates of primary production. If only one estimate per depth was available, the std is indicated as n.d. Samples for total Chlorophyll a (Chl a) analysis were filtered on‐board on 25mm Whatman GF/F filters using low vacuum (〈200 mm Hg). The filters were folded, wrapped in aluminum foil, flash frozen in liquid nitrogen and kept at −80 °C until analysis. For size fractionated Chl a analysis (0.2–2, 2–20, and 〉20 μm), 250 ml of seawater were sequentially filtered through a 20 μm polycarbonate filter first (by gravity), and then sequentially through 2‐ and 0.2‐μm polycarbonate filters under low pressure vacuum. Filters were folded and stored in 1.5 ml cryovials, flash frozen in liquid nitrogen, and stored at −80 °C. Analyses was done following 90% acetone extraction using standard fluorometric methods with a Turner Design 10AU fluorometer after Strickland and Parsons (1972 doi:10.1002/iroh.19700550118).