Cruise: Gradients 1, KOK1606 Project Name: Simons Foundation Gradient NPSG Method: The phosphorus, carbon, and nitrogen content of particulate material (PP, PC, PN) was collected from rosette niskin bottles at specific depths and filtered at low vacuum through a combusted glass fiber filter (PCPN) or acid washed combusted glass fiber filter (PP). At select stations a secondary set was collected and size fractionated using a 3um polycarbonate filter to provide the <3um size fraction of PP and PCPN. Following filtration, filters for PCPN 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 Ag and Sn boats and plated for analysis. Organic carbon and total nitrogen content was analyzed using high-temperature combustion (1020 C) on a ThermoQuest NC 2500 elemental analyzer. Three standards with known %C and %N were weighed, folded in tin boats, and analyzed with the samples to develop the calibration equation for each run. The calibration equation was then used to calculate the mass (mg) of carbon and nitrogen in each sample using EAS Clarity Chromatography Station software. The standards are Cystine (Elemental Microanalysis, B2035, 11.66 %TN, 29.99 %TC), Atropine (Elemental Microanalysis, B2002, 4.84 %TN, 70.56%TC), and GoniLab Secondary Standard (low %C)-A1 (an internal standard of sediment from the Gulf of Mexico, MV0803, with low carbon - 0.12 %N, 1.3 %C). Following filtration, PP filters were placed in histoprep capsules and stored at -80°C for later analysis. Post-cruise, all filters were thawed overnight, combusted at 450°C for 4.5 hours, then extracted with 0.15 M HCl for 1 hour at 60°C. PP was then analyzed spectrophotometrically as SRP in a 1.0 cm cell at 880 nm following Strickland and Parsons (1972). Recovery efficiency was assessed from the analysis of a known dry weight of certified reference material (National Institute of Standards, NIST 1515, apple leaves, certified 0.159% P by weight).