SCOPE 2016 Particle Enrichment Experiments, PC/PN, TOC, Picoplankton Abundances

SCOPE 2016 Particle Enrichment Experiments, PC/PN, TOC, Picoplankton Abundances Samples were collected during the HOT 286, HOT 291, HOT 292, and KOK 1703 cruises in the North Pacific Ocean. Concentrations of particulate carbon, nitrogen, and total organic carbon were determined from experiments where whole seawater was amended with sinking particles. Particles were collected using a large diameter (1 m), surface-tethered, 50 μm nylon mesh net trap. The net trap was hung at 175 m for 24 h. Collected particles were concentrated in the net's cod-end and subsampled using a Folsom plankton splitter; these sample splits were subsequently screened through a 335-μm mesh to remove large zooplankton. The screened splits were then further divided into ten 100 mL aliquots using a McLane Wet Sample Divider and triplicate splits were pooled. 300 mL of the pooled splits were added to triplicate 10-liter carboys containing seawater collected from the same depth as the net trap deployment (175 m). Unamended seawater controls (no particle amendments) consisted of triplicate 10-liter carboys filled with seawater collected from 175 m from the same cast as the seawater used for the particle-amended treatments. Carboys were subsampled for subsequent laboratory analyses of particulate carbon, nitrogen, and total organic carbon. For total organic carbon analyses, seawater from each carboy was subsampled into acid-cleaned 125 mL polyethylene bottles and frozen at −20°C. Total organic C concentrations were measured by high temperature combustion using a Shimadzu TOC-V. For particulate C determinations, 2–4 L of seawater was subsampled from each carboy and filtered onto precombusted glass fiber filters (Whatman GF/F) and filters were analyzed by using an Exeter CE-440 Elemental Analyzer. Picoplankton abundances were determined by flow cytometry. Aliquots (1.9 mL) were subsampled and preserved with 0.8% paraformaldehyde (final concentration; EM grade, Electron Microscopy Sciences). Samples were flash frozen in liquid nitrogen, and stored at -80C. Picoplankton abundances were quantified using an Attune NxT acoustic focusing cytometer after staining with SYBR Green I (488/530 nm excitation/emission wavelengths). The timestamp is in UTC.