Time-series rates of dissolved organic carbon production in the subtropical North Pacific Ocean
| Main Authors: | Church, Matthew J., Viviani, Donn |
|---|---|
| Format: | info dataset |
| Bahasa: | eng |
| Terbitan: |
, 2020
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/3712391 |
Daftar Isi:
- Over a 3-year period (April 2010-April 2013), we measured 14C-DOC production from vertical profiles used for determination of 14C-particle production, utilizing 0.2 um filtrates. Seawater for these experiments was collected from predawn CTD hydrocasts into acid-cleaned 500-ml polycarbonate bottles. A total of four replicate 500 ml bottles were subsampled per depth and each bottle was spiked with ~1.85 MBq 14C-bicarbonate. One hundred milliliters from one replicate per depth was vacuum filtered through a 0.2 mm polycarbonate filter and the filtrate served as a time zero blank. The remaining three bottles were hung on a free-drifting array, deployed before dawn, and incubated at their initial collection depths throughout the photoperiod (typically 11-13 hours). After sunset the array was recovered, and 100 ml subsamples of all bottles were filtered under gentle vacuum (<50 mm Hg) onto 0.2 mm polycarbonate filters. These 0.2 mm filtrates were stored frozen (-20oC) until subsequent processing for determination of 14C-DOC productivity. Samples were processed as follows: 100 ml of the 14C-PC filtrates were thawed, poured into 500 ml polyethylene separatory funnels, and acidified by the addition of 500 μl of 2 M sulfuric acid (H2SO4). Samples were vigorously bubbled with air in a fume hood to remove 14CO2. A 70 ml subsample was removed from each separatory funnel and poured into a 100 ml glass serum bottle containing 1 ml of 2 M sodium hydroxide (NaOH) and 10 ml of 0.37 M potassium persulfate (K2S2O8) in 1 M NaOH. Bottles were sealed with rubber stoppers, crimp sealed with an aluminum cap, and autoclaved at 126°C for 200 minutes; oxidizing 14C-DOC to 14C-DIC in an alkaline solution. Once cooled to room temperature, samples were uncapped and resealed using rubber sleeve stoppers holding plastic center wells containing ~2 x 2 cm pieces of fluted chromatographic filter paper (Whatman 2) soaked with 0.2 ml of β-phenylethylamine. A syringe was used to inject 4 ml of 9 N H2SO4 into the solution, converting the 14C-labeled dissolved inorganic carbon (hereafter 14C-DIC) to 14CO2. Samples were stored undisturbed at room temperature, passively trapping the 14CO2 on the β-phenylethylamine soaked wick. After at least 100 hours, rubber sleeve stoppers were removed and center wells and wicks were placed in scintillation vials, followed by the addition of 10 ml of Ultima Gold LLT scintillation cocktail. Samples were subsequently counted on a Perkin Elmer Tri-Carb 2800TR liquid scintillation counter. Rates of 14C-DOC production were computed for each cruise as the mean of the triplicate bottles from each depth minus the average 14C-activity of the time zero (blank) samples.