Gradients2-MGL1704-PPPCPN-UW_2020-03-11_v1.0

Cruise: Gradients 2, MGL1704

Project Name: Simons Foundation Gradient NPSG, SCOPE

The phosphorus content of particulate material (PP) was collected by semi-automated and sequential filtration of the ship’s underway flow through seawater onto acid-washed and combusted GFF filters. Select samples had a piggybacked GFF filter holder in sequence for collection of dissolved organic material and/or evaluation of trapping efficiency of GFF.  Following filtration, 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).  The carbon and nitrogen content of particulate material (PC, PN) was collected by semi-automated and sequential filtration of the ship’s underway flow through seawater onto a combusted GFF filter. Select samples had a piggybacked GFF filter holder in sequence for collection of dissolved organic material and/or evaluation of trapping efficiency of GFF. Following filtration, 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, acidified, 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).  The ship’s location, sea surface temperature and salinity from ship’s underway instrumentation are matched to the mid-point of each PCPN filtration time, and PP data were matched to the closest PCPN filtration.  Samples were corrected for DOC/DON/DOP. Depth of 5m refers to the depth of the seawater intake on the R/V Marcus G. Langseth.