ALBERT

Description: Biomass accumulation was assessed by subtracting phytoplankton mortality (due to microzooplankton) from phytoplankton growth rates. Rates of phytoplankton growth and microzooplankton grazing were assessed daily with the dilution technique (Landry and Hassett 1982; doi:10.1007/BF00397668), following the two treatment approach (Landry, Haas et al. 1984 doi:10.3354/meps016127), at six depths within the euphotic zone. We implemented this mini-dilution approach to generate vertically resolved growth and grazing rates, but also conducted a full dilution experiment on the last day of each of the cycles (n = 5) to test linearity assumptions of the method. Seawater collected with the Niskin bottles attached to the CTD rosette at 02:00 h was used to fill a pair of 2.2-L polycarbonate bottles (100%, B and C) while a third bottle (A) was filled with 25% whole seawater diluted with 0.2-µm filtered seawater obtained immediately before by gravity filtration using an Acropak filter cartridge (Pall) directly from the same Niskin bottle. Nutrients (final concentrations in 2.2L bottles; nitrate 0.18 μM, ammonium 4.16 μM, phosphate 15.08, silicate 44.2 μM, and vitamins) were added to bottles A and B in order to ensure the assumption that the same phytoplankton intrinsic growth rate was occurring in WSW and FSW bottles despite dilution (Gutiérrez‐Rodríguez, Safi et al. 2020 doi:10.1029/2019JC015550). Bottles were then incubated in situ at the same six depths of collection using a drifting array. Rates were calculated from changes in Chl a concentration and picophytoplankton abundance between the beginning and end of the experiment assuming exponential growth of phytoplankton. Microzooplankton grazing rate was estimated from: µ = (kA – kB)/(1-x) where kA and kB are the observed net rates of change of chl a in bottles A and B, respectively, and x is the fraction of whole seawater in the diluted bottle A (0.25). Phytoplankton growth rate was estimated from µ =m+kB. Photoacclimation effects were corrected from changes in cell chl a fluorescence estimated by flow cytometry during incubations as a proxy of cell chl a content (Gutierrez-Rodriguez, Latasa et al. 2010 doi:10.1016/j.dsr.2009.12.013). These include estimating the photoacclimation index (Phi) from changes in FL3: FSC and calculating an average value from Phi index obtained for pico- and nanoeukaryotic populations weighted by their biomass contribution. Accumulation was calculated by subtracting the C-based estimates of microzooplankton grazing (from the dilution experiments) from the 14C-based NPP.

Description: Salps were collected using double oblique Bongo tows, with 0.7m diameter frames equipped with 202 µm nets, General Oceanics flow meters, and an RBR temperature depth recorder. Salp specimens (typically 10) from each tow had their guts excised, and chl a and phaeopigments gut contents were measured. A power function was used to fit the size-specific Gpig (chl a + phaeo) contents for each tow, allowing the estimation of Gpig for each size bin per tow, and this was multiplied by the abundance in each size bin. Gut passage time (GPT) was calculated using a modified equation, based on (von Harbou, Dubischar et al. 2011 doi:10.1007/s00227-011-1709-4) where GPT(h) = 2.607*ln(OAL, mm) - 2.6. Grazing was estimated as: G (h-1) = Gpig /GPT, and scaled using a Q10=2. Daily salp grazing rates were obtained by assuming 14 h of day and 10 h of night, coincident with the times and latitudes at which we sampled these communities during the Salp Particle expOrt and Ocean Production (SalpPOOP) campaign. Cycle estimates were calculated by first averaging all day and all night tows separately, and then adding the two estimates. Fecal pellet production was calculated by assuming an egestion efficiency of 0.36 (Huntley, Sykes et al. 1989 doi:10.1007/BF00238291, Pakhomov 2004 doi:10.1016/j.dsr2.2001.03.001, Pakhomov and Froneman 2004 10.1016/j.dsr2.2000.11.002) and converting to carbon values using C:Chl ratios from the phytoplankton growth and grazing experiments combined with NPP, and reported in mg C m-2 d-1. Data is reported by size after binning in 5mm size bins (ranging 1-135mm), and for oozooids and blastozooids separately.

Description: Water collection for nutrient analysis was done using a CTD rosette equipped with 24 10L Niskin bottles, at different depths throughout the water column depending on the cast, spanning the euphotic zone to a maximum depth of 200m. Multiple casts were done during 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). Water was filtered through 25mm Whatman GF/F filters onto clean polyethylene bottles (250ml) and frozen at -20 °C. Analysis was done at the NIWA Hamilton Water Quality Laboratory (New Zealand), using an Astoria Pacific API 300 microsegmented flow analyzer (Astoria-Pacific, Clackamas, OR, United States) following colorimetric the methods outlined in Law et al. (2011; doi:10.1016/j.dsr2.2010.10.018).

Description: In situ data was collected between 2008-2014 in upper ocean. This data set includes the date, local time, coordinate, lifetime value, and variable fluorescence values.

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: Double oblique zooplankton net tows from 200 m water depth to the sea-surface were carried out using a 0.7 m diameter Bongo frame with paired 200 µm mesh nets, a General Oceanics Flow meter affixed to each net to measure the volume of water filtered, and a temperature-depth recorder. Tows were conducted at least twice daily (day and night), with one additional day per cycle of sampling every 2-3 hours for further studies of diel patterns. A quantitative subset of salp specimens were identified to species using keys (Foxton 1965, doi:10.1017/S0025315400016519; Bone 1998), classified into oozooid or blastozooid stage, and measured for total length and corrected to oral to atrial (OAL). For plots and calculations, Salpa thompsoni lengths were divided into 5 mm bins, and abundance was calculated for each size bin.

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).

Description: 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 photosynthetically active radiation (PAR) profiles to span the depth to 0.1% of surface irradiance. The physiology of the phytoplankton community was evaluated using the Mini-Fire fast repetition rate fluorometer (FRRF), using approximately 5ml per depth. Fv/Fm and reoxidation of Qa-, the first quinone acceptor of PSII, were evaluated using the Mini-Fire FRRF, which provided indications of phytoplankton stress most likely caused by iron-limitation following the procedure outlined in Gorbunov and Falkowski (2020 doi:10.1002/lno.11581).