Sampling was conducted aboard the CCGS John P. Tully during five cruises (2018-2020) in the northeast Pacific from Vancouver Island to Station P (50°N, 145°W).
Fisheries and Oceans Canada (DFO) Cruise numbers: 2018-40, 2019-001, 2019-006, 2019-008, 2020-001
Particulate Nitrogen and Carbon
Cruise 2018-040: Prior to use, Whatman 25 mm GF/C filters (~1.2 μm pore size) were placed in aluminum foil packets and baked at 450°C for 4.5 hours and allowed to cool overnight, sealed, and stored in a zip-lock bags in plastic Tupperware containers previously cleaned with a dilute solution of RBS-35 (Thermo Scientific) in deionized water. Filters were not pre-weighed for this cruise. Particulate concentration was determined using the amount of water filtered.
Cruises 2019-001, 2019-006, 2019-008, and 2020-001: Whatman 25 mm GF/F filters (~0.7 μm pore size) were used for all other cruises. Prior to use, GF/F filters were baked at 450°C for 4 hours and allowed to cool in the muffle furnace overnight. Further cooling took place in a desiccator. Once cooled to air temperature, filters were weighed on a Sartorius LE225B balance and then stored in individual PALL plastic 47mm filter holders until use.
All Cruises:
For all cruises, all water bottles and silicone tubing used for sampling were initially cleaned in a dilute Extran solution and thoroughly rinsed with Type 1 deionized water. Water samples were collected from Niskin bottles directly into 330 mL to 1L HDPE bottles, through silicon tubing or, at times, directly from the Niskin. Sample bottles were rinsed three times with aliquots from the Niskin and then filled. Volumes varied depending on availability of bottles. Samples were filtered immediately. People doing the sampling wore either vinyl or nitrile gloves. Sample bottles/tubing were reused through the cruise and well-rinsed with sample water between Niskins/casts.
Pre-combusted filters were placed onto a filtration manifold and samples were filtered under vacuum at 5 mm Hg or less. For total particulate carbon, 0.2 μm filtered seawater was used as a final rinse down the sides of the filtration cups. For particulate organic carbon, acidified seawater (10% HCl) was used as a final rinse to purge off the carbonate.
Cleaned forceps were used to remove filters from the manifold and returned to their original containers. After sampling, the filters were oven dried at 30°C. Filters were then stored at -80°C until returned to the lab where they were dried at 30°C for 24 hours. Samples were cooled in a dessicator. They were then sent to Stanford University for further chemical analysis. Samples that arrived at Stanford were placed into plastic petri dishes.
At Stanford University, filters from all cruises were loaded into a Costech Analytical Technologies Zero Blank carousel attached to a Carlo Erba NA1500 Series 2 elemental analyzer (EA) at the Stanford University Stable Isotope Laboratory Facility. The EA was configured with a 10 ml oxygen loop, a combustion oxidation reactor set at 1080°C, reduction reactor at 650°C, magnesium perchlorate column to remove water, the chromatography column set to 60°C, and the thermal conductivity detector set at 190°C. The UHP grade helium flow rate was 65 ml per minute and the UHP oxygen used to enhance combustion was 20 ml per minute.
All standards were loaded into 5×9 mm tin capsules (Costech Analytical Technologies). An empty 5×9 mm tin was analyzed with each run sequence for blank correction. All GF/C and GF/F filters were loaded into 9×10 mm tin capsules and one pre-combusted GF/C or GF/F filter was loaded into a 9×10 mm tin capsule for blank correction. Each 31-drop run sequence was composed of 2 conditioners, 1 5×9 mm tin blank, 1 9×10 mm filter blank, 2 acetanilide standards, 7 unknown filters, 1 acetanilide standard, 7 unknown filters, 1 acetanilide standard, 7 unknown filters, 2 acetanilide standards.
Though instrument precision is relatively high (± 1 µg N, and ± 2 µg C), overall uncertainty is strongly tied to the sampling procedure, with errors anticipated to range from 10% to 25%.
Dissolved Inorganic Carbon, Total Alkalinity, and pH
Samples were collected following standard protocols (Dickson et al., 2007) into 500 mL borosilicate glass bottles and preserved with 200 μL saturated mercuric chloride for later analysis. Samples were shipped to and analyzed at the Monterey Bay Aquarium Research Institute (MBARI). Three parameters (DIC, TA, and pH) were measured from each 500 mL sample bottle. All samples were run in triplicate, and the results were averaged. DIC and TA instrument performance was monitored by measuring Certified Reference Material (CRM; provided by Andrew Dickson at SIO) approximately hourly.
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