![]() It is important to collect sufficient volume for analysis and to minimize surface area to volume ratio of the container (a minimum of 15 mL in a glass vial or 30 mL in an HDPE bottle for each analyte desired, DOC or TDN) while also taking care to not overfill the sample container. Rinse the sample container and cap three times with sample water prior to filling it three quarters full (refer to Supplementary SOP2 for step-by-step instructions). This type of platinum cured silicone tubing offers durability and minimizes organic leaching compared to Tygon ®. ![]() Samples should be gravity filtered at the rosette via an in-line filter cartridge housing a combusted GF/F filter and attached directly to the Niskin spigot via acid clean platinized silicone tubing (Cole-Parmer, Supplementary Appendix B). These results suggest that sorption of dissolved organic matter to combusted GF/F filters saturates the active sites on a combusted filter rapidly (within ~ 60 mL) and is not a DOC stripping concern when filtering samples for bulk DOM analysis. Tests after the filter and bottle rinsing step show no further stripping of organic carbon from DOC filtrate can be resolved at the µmol kg -1 level ( Supplementary Figure A3). Approximately 60 mL of sample are passed through a new filter during the flushing and vial rinsing procedure. Studies have shown that DOC can sorb to active sites on GF/F filters, which raises the question whether filtration through GF/F strips organic matter from the DOC filtrate ( Turnewitsch et al., 2007 Novak et al., 2018). It is recommended to filter samples from the greatest depth to the shallowest particulate concentrations will typically increase nearer the surface ocean, which could cause the filter to clog or the particles to disrupt, requiring more filters to be used for one station. In oligotrophic environments, one filter may be re-used for several consecutive samples around the rosette to conserve resources. For consistency when sampling in both oligotrophic and eutrophic environments, filtering is recommended, at a minimum, for all ≤ 250-m samples. As important components of global carbon cycles, accurate measurement of each fraction is critical for constraining mass balance of carbon in ocean models. ![]() Supplementary Appendix A (Figure A2) presents vertical profiles of TOC and DOC in contrasting regions as an example. In high productivity areas, a substantial portion of organic carbon in the euphotic zone may be present in particulate form, and many of those particles may be large and heterogeneously distributed in a sample, such that these sample types should be filtered. In addition, most of the standing stock of fixed nitrogen in the surface ocean ( 250 m away from ocean margins, DOC is the dominant component of TOC, exceeding the carbon inventory of organic particles by several orders of magnitude ( Cauwet, 1978 Hansell et al., 2012). Perturbations in the sources or sinks of the oceanic DOC pool impact the balance between oceanic and atmospheric CO 2, perhaps making it climatically significant ( Ridgwell and Arndt, 2014). At ~662 ± 32 Pg (10 15 g) C, oceanic dissolved organic carbon (DOC) is one of the largest bioreactive pools of carbon in the ocean ( Williams and Druffel, 1987 Hansell and Carlson, 1998 Hansell et al., 2009), and is comparable to the mass of inorganic C in the atmosphere ( MacKenzie, 1981 Eppley et al., 1987 Fasham et al., 2001). Resolving the dynamics of each DOM fraction helps to elucidate the greater questions of DOM biogeochemical cycling. Although written specifically for GO-SHIP oceanographic community practices, many aspects of sample collection and processing are relevant to DOM determination across oceanic regimes and this document aims to provide updated methodology to the wider marine community.ĭissolved organic matter (DOM), operationally defined as organic matter that passes through a submicron filter, is a complex mixture of organic molecules comprised of carbon, hydrogen and oxygen as well as nitrogen, phosphorus and sulfur. Included are SOPs for sample collection and storage, details for laboratory analysis using high temperature combustion analysis on Shimadzu TOC analyzers, and suggestions for best practices in quality control and quality assurance. This document describes best practices for analysis of dissolved organic matter (dissolved organic carbon and total dissolved nitrogen) in seawater samples. ![]() 2Department of Ocean Sciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, United States.1Marine Science Institute, Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara,.Elisa Halewood 1*, Keri Opalk 1, Lillian Custals 2, Maverick Carey 1, Dennis A. ![]()
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