Dataset: GP17-OCE Size-fractionated particulate inorganic carbon (PIC)

Sampling:
Size-fractionated particles were collected using dual-flow McLane Research in-situ pumps (WTS-LV) and 142-millimeter (mm) "mini-MULVFS" filter holders (Bishop et al., 2012; Lam et al., 2018; Lam et al., 2015a; Xiang and Lam, 2020). At most stations through station 14, two casts of 8 pumps each and two filter holders per pump were deployed to collect samples at 16 depths throughout the water column. At one super station, a 24-depth profile was obtained with three casts. The targeted depths of the wire-out were corrected using pressure readings from a self-recording Seabird 19plus CTD at the end of the line.

At station 16, the entire string of 8 pumps and self-recording Seabird CTD was lost at sea. Starting at station 18, stations had 0-3 pump casts consisting of 1-4 pumps each.

One filter holder/flowpath was loaded with a Sefar polyester mesh prefilter (51-micrometers (um) pore size, called the "Qp" filter) and paired Whatman QMA quartz fiber filters (1 um pore size) in series ("QMA-side"). The other filter holder/flowpath was also loaded with a 51 um prefilter (called the "Sp" filter), but it was followed by paired 0.8 um Pall Supor800 polyethersulfone filters ("Supor-side"). A 150 um Sefar polyester mesh was placed underneath all 51 um prefilters and QMA filters as a support to facilitate filter handling but not analyzed. All filters and filter holders were acid leached before use based on the recommended methods in the GEOTRACES sample and sample-handling protocols (Cutter et al., 2010). QMA filters were pre-combusted at 450 degrees Celsius for 4 hours after acid leaching.

A special plate was manufactured for one of the pumps that could hold two additional mini-MULVFS filter holders that were loaded with full filter sets but not connected to plumbing. These 'dipped blank' filters included the full filter sets (51 um prefilter on top of paired QMA or paired Supor filters) with a 0.2 um Supor polyethersulfone filter on top of the 51 um polyester prefilters to exclude all particles from the main filter set. These were processed identically to the regular filters and functioned as full process blanks. Subsequent to the pump loss at station 16, dipped blank filter sets were wrapped in 1 um polyester mesh held in perforated plastic containers that were zip-tied to the pump frames.

In this dataset, data reported from the 51 um prefilter are referred to with an "LPT" suffix to indicate large particulate total concentrations (>51 um). Samples could come from the QMA side ("Qp" filter) or the Supor side ("Sp" filter) and are treated equivalently. Data reported from the main filters (QMA (1-51 um) or Supor (0.8-51 um)) are from the top filter of the pair only, and are referred to with an "SPT" suffix to indicate the small particulate total concentrations.

After Station 14, there were more instances of failed pumps. From Station 1 to 14, approximately 17% of the attempted samples failed, whereas from Station 18 to 34 approximately 45% failed. A failed pump did not move water through the filter, or it did not read the correct volume as the water entered, so particle concentration could not be determined. These samples are included in the dataset but have "NaN" entered for the values and errors, and a bad quality flag (QV=4). A few samples were missing; these have a missing quality flag (QV=9). (See "Data Processing" section for more on quality flags).

Analysis:
A UIC Carbon dioxide coulometer was used for PIC measurement. Briefly, PIC on SPT QMA punches or 1/16 LPT QMA-side prefilter was converted to CO2 by addition of 3 milliliters (mL) of 2 N sulfuric acid. CO2 produced is carried by a gas stream into a coulometer cell where CO2 is quantitatively absorbed by a cathode solution, reacted to form a titratable acid and measured based on the change in current. Machine blanks were run at the beginning of each run period until the CO2 values were stable and less than 1 microgram (ug). For every ten PIC samples run, a machine blank was run, which was the 3 mL H2SO4 with no filter. Three blanks were also collected at the end of each run period.