Sampling and Sample-handling Protocols for GEOTRACES Cruises Version 3 edited by the 2017 GEOTRACES Standards and Intercalibration Committee: Gregory Cutter, Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, Virginia 23529 USA; [email protected] Karen Casciotti, Department of Earth System Science, Stanford University, Stanford, California 94305 USA; [email protected] Peter Croot, Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland Galway, H91 TK33, Galway, Ireland; [email protected] Walter Geibert, Marine Geochemistry, Alfred Wegener Institute, Am Handelshafen 12, 27570 Bremerhaven Germany; [email protected] Lars-Eric Heimbürger, Méditerranéen Institute of Oceanography, Campus de Luminy – OCEANOMED Bâtiment Méditerranée, 13288 Marseille cedex 09, France; [email protected] Maeve Lohan, National Oceanography Centre Southampton, University of Southampton Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom; [email protected] Hélène Planquette, CNRS 6539/LEMAR/IUEM, Technopôle Brest Iroise, Place Nicolas Copernic, 29280 Plouzané, France; [email protected] Tina van de Flierdt, Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom; [email protected] Version 3.0; August 2017 Table of Contents I. INTRODUCTION ........................................................................................................... 4 II. GENERAL CONSIDERATIONS.................................................................................. 4 III. HYDROGRAPHY AND ANCILLARY PARAMETERS ........................................... 5 IV. RADIOACTIVE ISOTOPES ....................................................................................... 8 A. Protocols for 230Th and 231Pa .......................................................................................... 8 B. Protocols for 234Th ........................................................................................................ 12 C. Protocols for 226Ra and 228Ra Measurements in Sea Water ......................................... 15 D. Protocols for 210Po and 210Pb ........................................................................................ 27 E. Protocols for 7Be........................................................................................................... 36 F. Protocols for anthropogenic radionuclides (239Pu and 240Pu, and 137Cs) and limited information on other isotopes (90Sr, 237Np, 241Am, 236U and 129I) ..................................... 37 V. RADIOGENIC ISOTOPES ......................................................................................... 42 A. Protocols for 143Nd/144Nd ............................................................................................. 42 B. Protocols for 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, 206Pb/207Pb, 208Pb/207Pb ................ 48 VI. TRACE ELEMENTS ................................................................................................. 53 1. Pre-cruise Preparations ................................................................................................. 53 2. Sample Collection ......................................................................................................... 56 3. Sample Handling ........................................................................................................... 58 4. Shipboard Determinations of Selected Dissolved Trace Metals ................................... 63 5. Chemicals and Reagents ............................................................................................... 63 6. Analytical Considerations: Precision and Accuracy ..................................................... 64 7. References .................................................................................................................... 65 8. Protocols for Sampling and Determinations of Mercury and its Speciation ................ 66 2 9. Collection of particulate samples from GO-FLO sampling bottles ............................. 76 10. In-situ pump sampling protocols for particulate trace metals .................................... 91 11. Shipboard Aerosol Sampling ................................................................................... 107 VII. NITRATE, SILICON, AND CARBON ISOTOPES .............................................. 118 A. Protocols for Nitrate Isotopes .................................................................................... 118 C. Protocols for Carbon Isotopes in Dissolved Inorganic Carbon (DIC) ....................... 123 VIII. PROTOCOLS FOR OPTICS: TRANSMISSOMETER AND SCATTERING SENSORS ....................................................................................................................... 123 1. Transmissometers and Scattering sensors ................................................................... 124 2. Avoiding optical data dropouts ................................................................................... 126 3. Elimination of optics contamination and cast-to-cast offsets ..................................... 126 4. Compensation for Transmissometer Drift and CTD Digitizing Electronics .............. 127 5. References ................................................................................................................... 129 IX. BIOGEOTRACES PARAMETERS ........................................................................ 130 A. Active fluorescence (i.e., Fv/Fm and other biophysical metrics) ................................ 130 B. Metagenomics ............................................................................................................ 134 X. GLOSSARY OF TERMS .......................................................................................... 138 Appendix 1. Contributors to the GEOTRACES Cruise Protocols, Version 3.0 Appendix 2. GEOTRACES-recommended modifications to JGOFS 19 protocols Appendix 3. PICES Report 34, Determinations of DOC and DON, for GEOTRACES Cruises 3 I. Introduction The GEOTRACES Standards and Intercalibration (S&I) Committee is charged with ensuring that the data generated during GEOTRACES are as precise and accurate as possible, which includes all the steps from sampling to analysis. Thus, sampling methods for dissolved and particulate constituents must take a representative (of the water depth/water mass) and uncontaminated sample, the samples must be stored (or immediately analyzed) in a fashion that preserves the concentrations (activities) and chemical speciation, and the analyses of these samples must yield accurate data (concentration, activity, isotopic composition, and chemical speciation). To this end, experiences from the 2008-2010 GEOTRACES Intercalibration Program, actual GEOTRACES cruises from 2010-2017, and other related intercalibration efforts, helped to create the protocols in this document. However, methods continually evolve and the GEOTRACES S&I Committee will monitor these advances as validated by intercalibrations and modify the methods as warranted. The protocols here are divided into trace element and isotope groups: Hydrography and Ancillary Parameters, Radioactive Isotopes, Radiogenic Isotopes, Trace Elements, Nutrient Isotopes, Optics, and BioGEOTRACES parameters. Those who contributed to preparing these protocols are listed in Appendix 1 and are sincerely thanked for their efforts in helping GEOTRACES and the worldwide TEI community. II. General Considerations The following items must be included as a part of a standard intercalibration effort during all GEOTRACES cruises: A. Every GEOTRACES Section cruise must occupy at least one GEOTRACES Baseline Station (where previous intercalibration cruises have established the concentrations, activities, and/or speciation of at least the key GEOTRACES TEIs), or an overlap/cross- over station with a previous GEOTRACES cruise, to affect an intercalibration for sampling through analyses. B. If there are no GEOTRACES Baseline Stations or crossover stations to occupy, an intercalibration must be conducted via replicate sampling during each cruise. Cruises without a crossover station are required to sample at least 3 depths in replicate at 2 different stations, at least for all key parameters (defined in Table 2 of the GEOTRACES Science Plan), and samples from these intercalibration depths must be distributed to at least one other laboratory for TEI determinations. Where two labs share the analyses for a parameter on a cruise, this requirement can be satisfied by alternating samples between labs. Exceptions to this requirement can be made if an alternative method to demonstrate intercalibration can be provided and approved by the Standards and Intercalibration Committee. The results from this effort should be examined later for data integrity and coherence. 4 C. The number of detectable parameters is constantly growing, and the analytical state- of-the-art for certain transient and/or large volume parameters sometimes does not allow the use of crossover or baseline stations, or sample exchanges. Therefore, the intercalibration for such short-lived, transient, very large volume, or new parameters may include different approaches for establishing accuracy. This can include the measurement of reference materials, comparisons with nearby stations, analyses of sites with known concentrations, or other methods of external validation. The Standards and Intercalibration