Scavenging Isotopes and Particle Cycling

James W. Murray
Goal: To determine export of new production during the EqPac survey cruises from 12°N to 12°S along 140°W. The approach includes measurements of particle reactive radioisotopes and deployment of drifting sediment traps.

Survey No. 1:
James Murray, Jan Newton, Jennifer Young and Thomas Chapin
Survey No. 2:
Barbara Paul, Jan Newton, Thomas Chapin and Jennifer Young

Measurements, Protocols and QA/QC:

  1. Th, Pb and Po - Measurements will be made of dissolved, particulate and sediment trap Th, U, U, Pb and Po. Water column samples will be collected from 30 liter Go-Flo bottles. Particulate samples will be obtained by whole bottle filtration and from J. K. B. Bishop's in situ pump. Trap samples will be taken from both the Murray/Newton and Hedges et al. traps. There are no protocols for these analyses in JGOFS Report No. 6. For U and Th isotopes we use techniques that are very similar to those described in Anderson and Fleer (1982, Anal. Chem., 54:1142--1147). Yield tracers used are U and Th. For Po and Pb we plate Po onto silver plates following Flynn (1988, Anal. Chim. Acta, 43:221--227) and using Po, Po and stable Pb as yield tracers. Conventional alpha and beta counting procedures are used. Much of the beta counting of the total and dissolved Th will be done at sea using an at-sea counting system.

    QA/QC: Yield tracers will be exchanged with other radiochemists. For intercalibration of Th, Pb and Po the radiochemists on different cruises have agreed to analyze deep water samples at each common station from a mutually agreed upon depth. For Pb and Po we will also use the Stony Brook sediment sample. We will compare particulate isotopes using samples from the Bishop pump and whole bottle filtration from the same depths. We will analyze isotopes on both the Murray/Newton and Hedges et al. traps for a comparison of trap fluxes.

  2. Drifting sediment traps - Two-day drifting sediment trap arrays will be deployed at most of the survey cruise stations. The array includes both the Murray/Newton and Hedges et al. traps. The design of the array has taken into account and follows closely the recommendations of JGOFS Report No. 6 and U.S. JGOFS Report No. 10. At least one current meter (EG&G ACM) with tilt meter will be deployed on the array at each station. Our cylindrical traps are of the MLML design and have length to height ratios of >8:1. Baffles are placed in the top of the traps. We partially fill each trap with salt solutions (85 ppt) and use no preservative.

    Sediment trap samples will be analyzed for POC, CaCO, PN, PP, opal, chlorophyll, phaeopigments, HPLC pigments, major elements, trace elements, Th, Pb, Po, C (Quay) and N (Altabet). Supernatant solutions will be analyzed for nutrients, DOC and DIC in collaboration with other shipboard participants. Trace metals will be analyzed on the supernatant of the trace metal traps. Carbon and nitrogen will be analyzed on a Leeman Labs CHN analyzer, phosphorus by standard colorimetric techniques after combustion at 450°C and extraction into 0.5 M HCl (HOTS Protocols, 1990) and opal by colorimetric analyses following extraction into 0.5 % NaCO (Paasche, 1980, Limnology and Oceanography, 25:474--480). Chlorophyll and phaeopigments will be analyzed by standard fluorometric techniques. HPLC samples will be frozen in liquid nitrogen and returned to the lab for analyses. Major and trace elements will be analyzed by standard atomic absorption techniques (Jannasch, 1990, Ph.D. Thesis, University of Washington). The methods for radioisotopes were discussed above. Our techniques follow those given in JGOFS Report No. 9 for POC, PN, pigments and chlorophyll. No recommendations have been made for the other analyses.

    QA/QC: Several opportunities will be used for intercalibration. We will trade samples with Bishop, Leinen, Dymond/Collier for comparison of major and minor element analyses. Samples will be shared with Bidigare for HPLC pigment analyses. The Hedges et al. traps will be analyzed for isotopes, pigments and carbon/nitrogen. The latter will be an intercalibration with Hedges. Carbon/nitrogen will be analyzed on aliquots from several different MLML traps at each depth to determine the variability. Experiments are in progress to test the best way to remove CaCO for organic carbon analyses. Blanks for all elements will be determined using closed traps processed with the samples.

  3. Water column POC/PN/PP/CaCO/Opal/Pigments - Water column samples will be collected from the routine CTD hydrocasts (preferably 4 times per day) and analyzed for POC, PN, PP, CaCO, opal and chlorophyll/phaeopigment. The techniques were described above. Samples will be collected using 25 mm precombusted GF/F filters and 2 to 4 liter aliquots. We plan to do some whole bottle filtration as well. Frequent duplicates will be collected. Intercalibration will be conducted with the POC analyses person on the Time-Series cruises (Ducklow).