URL | https://www.bco-dmo.org/dataset/805226 |
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Download URL | https://www.bco-dmo.org/dataset/805226/data/download |
Media Type | text/tab-separated-values |
Created | March 2, 2020 |
Modified | July 2, 2020 |
State | Final no updates expected |
Acquisition Description
Location:
Arctic Ocean: P-1-94-AR P21, 84o5' N, 174o58' W
California margin: W-2-98-NC TF1, 41o5' N, 125o1' W
Equatorial Pacific: TT013-06MC, 12o00' S, 134o56' W
Methodology:
Prior to the extraction, we freeze-dried, ground and sieved sediment samples to less than 125 μm (Ruttenberg 1992). For a given sample, we weighed four sample replicates (2 g) and placed each in 250 mL HDPE bottles. Sodium dithionite (F.W. 147.12 g/mol; 7.4 g) was added to each sample split, followed by 200 mL of citrate-bicarbonate solution (pH 7.6). This step produces effervescence, so the solution should be added slowly to the sample. We shook samples for 8 h and then centrifuged them at 3,700 rpm for 15 min. We filtered the supernatants with a 0.4 μm polycarbonate filter. We took 20 mL aliquots from the filtrate for each sample split for MRP and total P analyses, and kept them refrigerated until analysis within 24 h. We added 200 mL of ultrapure water to the solid residue for each sample split as a wash step after the above reductive step, shook samples for 2 h, and then centrifuged them at 3,700 rpm for 15 min. We filtered the supernatants with 0.4 μm polycarbonate filters and set aside 20 mL of filtrate from each sample split for MRP and total P analyses. We then extracted the solid sample residues in 200 mL of sodium acetate buffer (pH 4.0) for 6 h. At the end of this extraction step, we centrifuged the bottles at 3,700 rpm for 15 min, filtered the supernatants with 0.4 μm polycarbonate filters and took a 20 mL aliquot of filtrate from each sample split for MRP and total P analyses. We added 200 mL of ultrapure water to the solid residue for each sample split as a wash step, shook samples for 2 h, and then centrifuged them at 3,700 rpm for 15 min. We filtered the supernatants with 0.4 μm polycarbonate filters and set aside 20 mL of filtrate from each sample split for MRP and total P analyses. We repeated the water rinse step, and collected aliquots for MRP and total P analyses as in the previous steps. The concentrations of TP were determined as described below.
Solid sediment sample residues following the pretreatment described above were transferred to two 50 mL centrifuge tubes (2 sample replicates combined per tube). We added 20 mL of 0.25 M NaOH + 0.05 M Na2EDTA solution to each tube, vortexed until all sediment was resuspended and then shook samples for 6 h at room temperature (Cade-Menun et al. 2005). We used a solid to solution ratio of 1:5 for this step to minimize the amount of freeze-dried material that will need to be dissolved for the 31P NMR experiments. Large amounts of salts from the NaOH-EDTA concentrated in NMR samples lead to higher viscosity and increase line broadening on NMR spectra (Cade-Menun and Liu 2013). We chose an extraction time of 6 h to improve total P recovery while limiting the degradation of natural P compounds in the sample. At the end of the extraction, samples were centrifuged at 3,700 rpm for 15 min and supernatants decanted into 50 mL centrifuge tubes. We collected a 500 μL aliquot from each sample, which we diluted with 4.5 mL of ultrapure water. These were refrigerated until analysis for total P content on the ICP-OES. The sample residues and supernatants were frozen on a slant to maximize the exposed surface area during the lyophilization step; this was done immediately after the removal of the 500 μL aliquot. Once completely frozen, the uncapped tubes containing supernatants and residues were freeze-dried over the course of 48 h. Each tube was covered with parafilm with small holes from a tack to minimize contamination. Freeze-dried supernatants from identical sample splits were combined and dissolved in 500 μL each of ultrapure water, D2O, NaOH-EDTA and 10 M NaOH prior to 31P NMR analysis. The D2O is required as signal lock in the spectrometer (Cade-Menun and Liu 2013). Sample pH was maintained at a pH > 12 to optimize peak separation (Cade-Menun 2005; Cade-Menun and Liu 2013). Sample pH was assessed with a glass electrode, and verified with pH paper to account for the alkaline error caused by the high salt content of our samples (Covington 1985).
Freeze-dried sample residues were ashed in crucibles at 550oC for 2 h and then extracted in 25 mL of 0.5 M sulfuric acid for 16 h (Olsen and Sommers 1982; Cade-Menun and Lavkulich 1997). We centrifuged samples at 3,700 rpm for 15 min, filtered supernatants with 0.4 μm polycarbonate filters, and measured P content on an ICP-OES.
Total P concentrations in sediment extracts were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). Standards were prepared with the same solutions as those used for the extraction procedure in order to minimize matrix effects on P measurements. Sediment extracts and standards (0 μM, 3.2 μM, 32 μM and 320 μM) were diluted to lower salt content to prevent salt buildup on the nebulizer (1:20 dilution for step 1, 1:10 for steps 2 – 4). Concentration data from both wavelengths (213 nm and 214 nm) were averaged to obtain extract concentrations for each sample. The detection limit for P on this instrument for both wavelengths is 0.4 μM. The MRP concentrations were measured on a QuikChem 8000 automated ion analyzer. Standards were prepared with the same solutions used for the extraction step to minimize matrix effects on P measurements. Sediment extracts and standards (0 – 30 μM PO4) were diluted ten-fold to prevent matrix interference with color development. The detection limit for P on this instrument is 0.2 μM. We derived MUP concentrations by subtracting MRP from total P concentrations.
Processing Description
Data were processed in Excel.
BCO-DMO data manager processing notes:
* Excel file Data_TP_sediments with pretreatment_v3.xlsx with four sheets (one per Step) exported to csv. The four tables were combined into one table. There is a column Step with values 1-4 already so there was no need to add another column to capture the original sheet names “Step #”
Instruments
Parameters
unique sample identification or number; any combination of alpha numeric characters; precise definition is file dependent
Dataset Maintainers
Name | Affiliation | Contact |
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Adina Paytan | University of California-Santa Cruz (UC Santa Cruz) | ✓ |
Delphine Defforey | University of California-Santa Cruz (UC Santa Cruz) | ✓ |
Amber York | University of California-Santa Cruz (UC Santa Cruz) | |
Amber York | University of California-Santa Cruz (UC Santa Cruz) | |
Amber York | Woods Hole Oceanographic Institution (WHOI BCO-DMO) |
BCO-DMO Project Info
Project Title | A new marine sediment sample preparation scheme for solution 31P NMR analysis |
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Acronym | Marine Sediment Analysis 31P NMR |
URL | https://www.bco-dmo.org/project/664054 |
Created | November 7, 2016 |
Modified | February 27, 2020 |
Project Description
We developed and tested a new approach to prepare marine sediment samples for solution 31P nuclear magnetic resonance spectroscopy (31P NMR). This approach addresses the effects of sample pretreatment on sedimentary P composition and increases the signal of low abundance P species in 31P NMR spectra by removing up the majority inorganic P from sediment samples while causing minimal alteration of the chemical structure of organic P compounds. The method was tested on natural marine sediment samples from different localities (Equatorial Pacific, California Margin and Arctic Ocean) with high inorganic P content, and allowed for the detection of low abundance P forms in samples for which only an orthophosphate signal could be resolved with an NaOH-EDTA extraction alone. This new approach will allow the use of 31P NMR on samples for which low organic P concentrations previously hindered the use of this tool, and will help answer longstanding question regarding the fate of organic P in marine sediments. We developed and tested a new approach to prepare marine sediment samples for solution 31P nuclear magnetic resonance spectroscopy (31P NMR). This approach addresses the effects of sample pretreatment on sedimentary P composition and increases the signal of low abundance P species in 31P NMR spectra by removing up the majority inorganic P from sediment samples while causing minimal alteration of the chemical structure of organic P compounds. The method was tested on natural marine sediment samples from different localities (Equatorial Pacific, California Margin and Arctic Ocean) with high inorganic P content, and allowed for the detection of low abundance P forms in samples for which only an orthophosphate signal could be resolved with an NaOH-EDTA extraction alone. This new approach will allow the use of 31P NMR on samples for which low organic P concentrations previously hindered the use of this tool, and will help answer longstanding question regarding the fate of organic P in marine sediments.
NSF C-DEBI Award #156246 to Dr. Adina Paytan
NSF C-DEBI Award #157598 to Dr. Delphine Defforey
Data Project Maintainers
Name | Affiliation | Role |
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Adina Paytan | University of California-Santa Cruz (UC Santa Cruz) | Principal Investigator |
Delphine Defforey | University of California-Santa Cruz (UC Santa Cruz) | Co-Principal Investigator |
Barbara J. Cade-Menun | Agriculture and Agri-Food Canada (AGR GC) | Co-Principal Investigator |