Gradients3-KM1906-15N13C_2020-03-25_v1.0

Cruise: Gradients 3, KM1906

Project Name: Simons Foundation, Gradient NPSG

Dataset Description:

Standard protocols were used to measure in vitro primary productivity via the 13C radiotracer method [Lengendre et al., 1996] and N2-fixation rate measurements via 15N2 isotopic gas method described by Montoya et al., 1996. Briefly, water samples were collected before dawn in 4.3L polycarbonate bottles, a total of 120ml of cold enriched 15N2 seawater was added via syringe by inserting bevline tubing to the bottom of the sample bottle and slowly injecting the volume while overflowing. Bottles were then sealed with caps fitted with septum and injected with 0.5ml of 47mM 13C bicarbonate stock and gently mixed by inversion.  Bottles were incubated on deck in incubators screened to 48% of surface irradiance and plumbed with flow through surface seawater for temperature regulation. All bottles were incubated for ~ 24hr at 48% light level. Duplicate light bottles were paired with dark bottles and time final bottles that received no enrichment. Time zero bottles were also collected and sacrificed for each station. Following dawn to dawn incubations, each sample was filtered onto a combusted 25mm glass fiber filter, filters were folded in half and placed in combusted aluminum foil and stored at -80°C for later analysis. Post-cruise, all filters were thawed and dried overnight at 60°C. Samples were then balled into Sn boats and plated for analysis. The carbon and nitrogen isotopic composition (13C and 15N, respectively) were analyzed by continuous-flow isotope ratio mass spectrometry by the Stable Isotope Facility at UC Davis (https://stableisotopefacility.ucdavis.edu/13cand15n.html).