Sediment Trap Particle Flux data during the North Atlantic Bloom Experiment

Dr. Susumu Honjo and Dr. Steven J. Manganini
Woods Hole Oceanographic Institution

The following methods documentation was extracted from:

Honjo, S, and S. J. Manganini, 1992.
Biogenic Particle Fluxes at the 34N 21W and 48N 21W Stations, 1989-1990: Methods and Analytical Data Compilation. Woods Hole Oceanographic Institution, Technical Report 92-15


A. Deployment of Sediment Traps and Mooring Arrays

  1. Location, depths and timing:

    Two deep ocean mooring arrays were deployed at about 34N (depth to seafloor: 5,261 m and 5,083 m, for phase 1 and 2) and 48N (depth to seafloor: 4,418 m and 4,451 m). Table 1 gives more detailed information on mooring locations, trap depths and names of ships that were used for deployment and recovery. Three PARFLUX Mark 7G-13 time-series sediment traps with 13 rotary collectors on each were deployed on both moorings for a total of 6 traps. At each of the stations, traps were moored at approximately the same depth relative to the surface and the sea- floor (for the deepest trap); 1 km and 2 km from the surface and 0.7 km above bottom.

                                  TABLE 1
    Sediment Trap deployments, North Atlantic Bloom Exp., Dr. S. Honjo
    Mooring Stations and Trap Depths 
    Phase 1:  Periods 1 to 13, April 3, 1989 to Sept. 26, 1989 
    Phase 2:  Periods 14 to 27, Oct. 16, 1989 to April 16, 1990 
    Hiatus :  Sept. 26 1989 to Oct 16, 1989
                        34N 21W Station                48N 21W Station            
                    Phase 1         Phase 2         Phase 1         Phase 2 
    Latitude        3349.3'N       3348.4'N       4742.9'N       4743.6'N 
    Longitude       2100.5'W       2102.2'W       2052.5'W       2051.5'W 
    Bottom Depth ** 5,261 m         5,083 m         4,418 m         4,451 m 
    Trap Depth      1,070 m         1,248 m         1,018 m         1,202 m 
      "    "        2,067 m         1,894 m         2,018 m         2,200 m 
      "    "        4,564 m         4,391 m         3,718 m         3,749 m 
    Deployed by     R/V Atlantis II R/V Endeavor    R/V Atlantis II R/V Endeavor 
    Recovered by    R/V Endeavor    RRV Darwin      R/V Endeavor    RRV Darwin 
    **       Depths are all corrected values 
    Arrays were deployed in March and April 1989, recovered and redeployed in September 1989, and totally recovered in April 1990 (Table 1). During the 376-day deployment (including 20 days of hiatus in the middle), each sediment trap was opened and closed 26 times, providing continuous time-series sampling at 14-day intervals, except for two periods. Table 2 lists open/close schedules for which all the traps were uniformly programmed during the experiment. An independent monitoring mechanism installed with each trap (Honjo and Doherty, 1988) confirmed that the entire program was executed correctly and on schedule.

                                  TABLE 2 
    Synchronized Open/Close Schedule for All Traps 
    at the 34N and 48N, 21W Stations
    Period    Mid Date        Open/Close Date     Days Open   Elapsed Days
            JD*     CD*        JD*     CD*             
    1       96      04/06/89   93      04/03/89        5       5
    2      105      04/15/89   98      04/08/89       14      19
    3      119      04/29/89  112      04/22/89       14      33
    4      133      05/13/89  126      05/06/89       14      47
    5      148      05/29/89  140      05/20/89       17      64
    6      164      06/13/89  157      06/06/89       14      78
    7      178      06/27/89  171      06/20/89       14      92
    8      192      07/11/89  185      07/04/89       14     106
    9      206      07/25/89  199      07/18/89       14     120
    10     220      08/08/89  213      08/01/89       14     134
    11     234      08/22/89  226      08/15/89       14     148
    12     248      09/05/89  241      08/29/89       14     162
    13     262      09/19/89  255      09/12/89       14     176
    14     279      10/06/89  269      09/26/89       20     196 (hiatus)
    15     296      10/23/89  289      10/16/89       14     210
    16     310      11/06/89  303      10/30/89       14     224
    17     324      11/20/89  317      11/13/89       14     238
    18     338      12/04/89  331      11/27/89       14     252
    19     352      12/18/89  345      12/11/89       14     266
    20       1      01/01/90  359      21/25/89       14     280
    21      15      01/15/90    8      01/08/90       14     294
    22      29      01/29/90   22      01/22/90       14     308
    23      43      02/12/90   36      02/05/90       14     322
    24      57      02/26/90   50      02/19/90       14     336
    25      71      03/12/90   64      03/05/90       14     350
    26      85      03/26/90   78      03/19/90       14     364
    27      99      04/09/90   92      04/02/90       14     378
    *CD = Calendar Date;  JD = Julien Date
  2. Time-series sediment traps:

    Each sediment trap had an aperture of 0.5 m2, covered by baffles with 25mm diameter cells with the aspect ratio of 2.5. The included cone angle was 42 degrees and the structural frame was built of welded titanium The opening and closing of all 6 traps was synchronized with an error of less than one minute. The sample containers, 13 for each trap, were filled with in situ deep sea water were collected by a 30 liter Niskin bottle prior to the deployment. Analytical grade formalin (S. Wakeham; personal communication, 1988) was added to make a 3% solution buffered with 0.1% sodium borate. Each of the 13 sample containers was completely filled with this sea water solution with preservative before the deployment of a trap. Individual sample containers were mechanically sealed from the ambient water before and after each collecting period (Honjo and Doherty, 1988).

  3. Mooring array:

    The mooring design was based on the PARFLUX Sediment Trap Mooring Dynamics Package that has been used by us since 1979 (Honjo et al., 1992). A detailed design, parts listing and tension calculation of the NABE mooring array is available in Manganini and Krishfield, 1992, Cruise Report. The arrays were designed to maintain an average of 180 kg of vertical tension throughout the tautline, with a total buoyancy of 1,114 kg that was balanced with a 1,590 kg (in-water weight) cast-iron anchor. Sediment traps were attached to a mooring in-line with three 1-m polyethylene-jacketed bridles. The automatic collection mechanism (Honjo and Doherty, 1988) of the 6 sediment traps worked flawlessly throughout the duration of the experiment and provided us with a total of 156 samples each of which represents an individual key to the time-space matrix for the NABE experiment.

B. Laboratory Analysis

  1. Pre-analysis treatment of samples:

    We measured the pH in supernatant in sample containers immediately after recovery of traps (Manganini and Krishfield, 1992, Cruise Report). Sample containers were then refrigerated on board at approximately 2 to 4 degree C. Particle samples in (original) 250 ml, polyethylene centrifuging sample containers were transported to Woods Hole under refrigeration at approximately 1 to 2 degree C. We identified no swimmers from all samples collected by our experiment. The impact of swimmers, if any, was relatively small; it appears that they were all included with the >1 mm fractions.

  2. Supernatant analysis:

    In the shore laboratory, first the liquid in a sample container was decanted and then filtered through a 0.45 um pore size Nucleopore filter leaving approximately 1/3 of the original volume. About 50 ml of filtered liquid was then analyzed for total N, NO2, NO3, NH4, P, PO4 and SiO2 using an automatic nutrient analyzer (e.g. Grasshoff et al. 1983). We regarded all excess quantities above the ambient concentration as being dissolved from the trapped particles while stored in situ before the recovery and added to the particle fluxes after being stochastically converted to solids. The remaining liquid in the sampling containers was used as rinse water in the processing of the particulate portion in each specific sample. When additional rinse water was required during the course of analysis, for example, for sample splitting we used filtered and buffered deep Sargasso Sea water containing 3% formalin.

  3. Water sieving:

    Particle samples were water-sieved through a 1-mm Nitex mesh. This was necessary to maintain precision during splitting of the major portion of the sediment that was <1 mm. Common particles in the >1 mm fraction were large aggregates and fragmented gelatinous zooplankton. A sample caught in the 1 mm mesh was then re-suspended in the original seawater, stirred gently and poured onto a grid-printed, 47-mm Nucleopore filter with 2-um pore size, while applying gentle vacuum suction. While a sample on a filter was wet, the filter with the >1 mm fraction was cut into 4 equal pieces along the printed grid by a Teflon-coated blade; each aliquot was then immediately put back into the filtered original water for storage. When a >1 mm sample was too small to split, it was dried and homogenized by pulverization.

    Sediment that passed through the 1 mm mesh was further water- sieved through a 62-um Nitex sieve. Each fraction was split into 1/4 aliquots and then into 1/40 aliquots by a rotating wet- sediment splitter with 4 and 10 splitting heads (Honjo, 1980). The average error during the splitting of NABE samples into 4 or 10 aliquots was 3.7% for the <1 mm fraction. Wet splitting of the trap-collected sample is justified for multi-disciplinary research including biocoenosis studies. Once particle samples are dried, each becomes inseparable and unidentifiable. Consequently, biocoenosis research such as picking up foraminifera tests or identifying diatom frustules becomes impossible.

  4. Total dry mass measurement:

    Dry mass was determined by weighing two 1/4 aliquots of >1 mm (whose flux was usually insignificant) and three 1/10 aliquots of <1 mm samples on pre-weighed 47 mm, 0.45 um Nucleopore filters. Before weighing, the samples were rinsed 3 times with distilled water, dried in an oven at 60 deg. C for 24 hours and cooled in a desiccator for 4 hours. Total flux was calculated from dry weight of the above aliquots divided by aperture area of the trap and the time it was opened.

  5. Sedimentary component analyses:

    The dried sample was pulverized and homogenized, then the two size fractions were recombined proportionally and analyzed with respect to concentrations of:

           a)   Carbonate: as CaCO3
           b)   Biogenic Opal
           c)   Organic carbon, nitrogen and hydrogen in the decalcified
           d)   Phosphorus
    a) Carbonate content was determined by a method based on a vacuum-gasometric technique developed by Ostermann, et al. (1989). A preweighed sample is introduced into a sealed reaction vessel containing concentrated phosphoric acid. The pressure due to the evolution of CO2 gas is proportional to the carbonate content when calibrated with appropriate standards and was recorded by a transducer. The results were calculated and reported as carbonate percent in the total sample.

    b) Biogenic opal was estimated from particulate, reactive Si, selectively leaching decalcified samples in a sodium carbonate solution (Eggimann, et al., 1980) and converting the Si content to SiO2 fluxes. A preweighed sample of approximately 10 mg along with 10 ml of 1 M Na2CO3 was sealed in a Teflon container. The samples were placed in a shaker bath at 90 deg. C for 3 hours and then filtered through a 47-mm-diameter, 0.45 um pore size Nucleopore filter using an all-plastic filtering apparatus. The filtrate at room temperature was neutralized with 0.2 N HCl using methyl orange as an indicator. After appropriate dilution, content of Si was determined spectrophotometrically (Strickland and Parsons, 1972). The Si content was then converted to SiO2 and reported as particulate opal flux.

    c) Organic carbon, nitrogen and hydrogen were analyzed using a Perkin-Elmer Elemental Analyzer Model 240C. Preweighed samples on precombusted glass fiber filters were decalcified using 1N phosphoric acid.

    d) Reactive (biogenic) phosphorus content was determined by the Solorzano and Sharp method that was based on the dissolution of phosphorus by an acid after ashing, using MgSO4 as an oxidant. A preweighed sample was placed into a glass centrifuge tube along with 2 ml of 0.017 M MgSO4 and was dried at 90 degree C. The centrifuge tube containing the sample was ashed at 500 deg. C for 2 hours. After cooling, 5 ml of 0.2 M HCl was added and, with the centrifuge tube capped, was heated at 80 deg. C for 30 min. At room temperature, 5 ml of distilled H2O with one ml of reagent (Strickland and Parsons, 1972) was added and the centrifuge tube was shaken in a vortex shaker, then centrifuged. The concentration of phosphorus was determined spectrophotometrically in the supernatant and the results were reported as particulate phosphorus flux.

    Using the reported method, the lithogenic particles were too small to detect and were usually within the analytical error.

C. Restoration of dissolved components to particulate flux

The dissolution of collected particles in a bottle may occur as soon as particles arrive in the bottle while it is open, or later when it is sealed. Assuming that all dissolved portions remained in the recovered bottle, we restored the dissolved components of Si, P and N by analyzing the supernatants in sample bottles. We assumed that the elevated concentration above the sea water initially used to fill the bottles was caused by dissolved components. During the deployment of a trap, the sample bottles were open to the water column only for the duration of collecting periods. While a bottle was open, the bottle water which was placed in the bottle before deployment is exchanged with ambient water. In case the nutrient concentration of the initial bottle water is not equal to that of the ambient water, a correction had to be made; we assumed that one half of the initial water was diluted by the ambient water while the bottle was open. In practice, the effect on calculating particle flux by the difference of nutrients in the initial sea water was within analytical error.

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