Full details for collection and analyses of underway POM samples are provided by Holser et al., 2011 and Go\u00f1i et al., 2019 and Go\u00f1i et al., submitted. Brief summaries are provided below.
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Samples for this study were collected aboard RV Oceanus using the surface underway scientific system.
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Aboard the vessel we had access to uncontaminated seawater and collected samples at specific times that allowed us to determine location (latitude and longitude) and seawater characteristics (temperature and salinity) from the ships\u2019 navigation and sensor panels. We used a semi-automated filtration system (SAFS) described by Go\u00f1i et al., (2019) connected to Oceanus surface underway water to collect particulate organic matter samples. Surface underway water was connected to the SAFS through a manual flow-control valve via opaque polyethylene tubing.\u00a0 A fly wheel flow meter was placed in-line and connected to a laptop computer using a data acquisition system to measure and record flows during the filtration stage. A switching valve with 8 ports was placed downstream from the flow meter and controlled by the laptop.\u00a0 Under stand-by conditions, flow was directed to the \u2018waste\u2019 port, which was fitted with unobstructed tubing that drained into one of the ship\u2019s sinks and flowed back to sea.\u00a0 The 8-sample ports were fitted with tubing, quick-turn sockets\u00a0 and in-line stainless steel 13-mm Swinney filter holders.\u00a0 The flow from these filters was directed to the same sink as the \u2018waste\u2019 flow.\u00a0 In each holder, we placed one pre-combusted (400 oC for 3 hours) 13-mm glass fiber filter supported by a stainless steel screen and locked into place with a Teflon o-ring that prevents leakage and results in a filtration area of 78.5 mm2. Once filters were fitted in each of the sample ports, the filtration program was started to collect samples at selected intervals.
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Once the filtration run was completed, the filter housings were removed from the SAFS, opened, and each individual filter folded into pre-cleaned silver capsules, which were placed into sample trays that were frozen until CN analyses.\u00a0 Each sample was assigned a specific time stamp (start-end of filtration process) that coincided with the ship\u2019s clock and allowed us to retrieve location and oceanographic data for each sample, as well as determine an overall filtration volume, which was used to calculate particulate nitrogen and carbon concentrations once their contents were determined.\u00a0 During normal operations, we stacked two filter holders at specific positions in order to collect both particles from a sample using the first filter as well as measure blanks associated with dissolved organic matter sorption as filtered water goes through the second filter.
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Carbon and nitrogen analyses were conducted using high temperature combustion/reduction according to Holser et al., 2011 and Go\u00f1i et al., 2019. Sample and blank filters were exposed to concentrated hydrochloric acid fumes to remove carbonates and run in two CN analyzers (NC2500 Thermoquest and ECS 4010 Costech) using the manufacturers\u2019 recommendations for carbon and nitrogen analyses (e.g., specified temperatures for combustion and reduction furnaces, O2 loops/pressure, and the use of a water trap). In each run of a full auto-sampler, we typically included 6 standards (e.g., cystine, atropine) with different and known amounts of carbon and nitrogen to develop distinct calibration curves for each run. All filters were treated the same and we used the DOM blanks to correct for DOC and DN sorption. Detection limits for OC and N were 0.04 and 0.03 micromoles, respectively. Replicate analyses of selected samples yielded average standard errors for both measurements of ~2% of measured values.
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References cited: Holser et al., 2011; Go\u00f1i et al., 2019; Go\u00f1i et al., submitted.
These data are part of a manuscript submitted to Continental Shelf Research:
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Go\u00f1i, M.A., Welch, K.A., Alegria, E., Alleau Y., Watkins-Brandt, K., White, A.E. (submitted) Wintertime Particulate Organic Matter Distributions in Surface Waters of the Northern California Current System. Continental Shelf Research.
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The data are shown in figures in the manuscript (Figures 6, 8 and 9).
Data were acquired at approximately 1 Hz and then binned to correspond to the time stamps of discrete POM samples collected by the semi-automated filtration system (SAFS, see above). The transmission (Tr) data from the C-Star instrument (r = 0.25 m) was converted into beam attenuation coefficients (c = lnTr/r; m-1), which represent the sum of attenuation due to particles, water and colored dissolved organic matter. Particle beam attenuation data (Cp) were determined after correcting for the latter two by conducting attenuation measurements in low POC waters from offshore regions to adjust measured beam attenuation by an offset (e.g., Gardner et al., 2006). In the winter cruises, we verified these corrections by measuring beam attenuation signals of particle-free waters that were filtered through a 0.2 mm membrane filter (White et al. 2017; Slade et al. 2010). Navigation data were integrated into the sensor data set using the sample filtration time stamps to provide latitude and longitude information for each surface underway sample.
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BCO-DMO processing notes:
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\n- Concatenated all cruises
\n- added ISO_DateTime_UTC column
\n- Adjusted column names to comply with database requirements
\n- Adjusted all Date_Time_PST rows to following notation: mm/dd/yyyy HH:MM
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