Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • BCO-DMO Processing Description
• Related Publications
• Parameters
• Project Information
• Funding

Sample Collection:
Surface water was sampled at Mo'orea's North Shore (French Polynesia) (-17.47722, -149.84258) mid-day aboard kayaks or small motor boats in September 2017, May 2019, and April 2022. At every station on the backreef, salinity and temperature were measured using a YSI Professional Plus (Yellow Springs Instruments). Seawater samples were collected directly into 5-liter (L) polycarbonate carboys from the surface waters approximately 30 centimeters (cm) below the seawater surface and immediately transported to the shore for further processing. One milliliter (mL) of whole seawater was collected by pipette and added to a cryovial with 16 microliters (µL) of 32% paraformaldehyde, mixed by inversion, and immediately frozen and stored at -40 degrees Celsius (°C) for subsequent flow cytometric analysis of plankton abundance. Subsequent samples were processed using a multi-channel peristaltic pump and acid-washed silicone tubing initially flushed with approximately 300 mL seawater sample. For microbial community composition analysis, 300 to 500 mL sample was filtered through 0.2-micrometer (µm) polyethersulfone filter cartridges (Sterivex, Millipore, UK) and frozen at -40°C. The sterivex filtrate was used to rinse bottles to collect samples for inorganic nutrients, which were frozen and stored at -40°C. For particulate organic matter samples, 3 to 4L of seawater samples were filtered through pre-combusted GF/F (25mm, Whatman) filters, folded into combusted aluminum foil, and frozen at -40°C. For DOC measurements, GF/F filtrate was used to triple sample-rinse borosilicate vials with Teflon septa caps before collecting 40 mL (for deployment 2 and 3 in duplicates). Additionally, 2 liters of filtrate were also collected in triple-rinsed polycarbonate bottles for solid-phase DOM extraction. In total, 3 to 5 liters of sample were filtered through this G/FF filter via peristaltic pumps using acid-cleaned silicone tubing for analysis of particulate organic matter (POM). The filters were folded in half, wrapped in aluminum foil, and promptly frozen and stored at -80°C until analysis. DOC and DOM samples were acidified to pH 2 using trace metal grade HCl. Duplicates of acidified 1L DOM samples were solid-phase extracted using the multichannel pump operating at a flow rate of 18 milliliters per minute (mL/min) onto Bond Elut PPL resin cartridges (200 milligrams (mg) bed mass, Agilent 2105005, USA), according to (Dittmar et al., 2008) and (Petras et al., 2017). After desalinating the resin with LC-MS grade water (Fisher Chemical, Belgium), the cartridges were dried using Ultra High Purity compressed N₂ gas and kept frozen at -40°C.

Biogeochemical Measurements:
The following inorganic nutrients were analyzed using a Seal AA3 Segmented Flow Injection Autoanalyzer at the University of Hawai'i SOEST Laboratory for Analytical Biogeochemistry: Nitrate+nitrite (N+N) and silicate concentrations (Grasshoff et al., 1983), ammonium (Kérouel and Aminot, 1997), phosphate (Murphy and Riley, 1962). Additionally, total dissolved nitrogen and total dissolved phosphorus were determined through separate injections, with UV and alkaline or acid persulfate in-line oxidation, respectively. DOC samples were analyzed using high-temperature platinum catalytic oxidation on a Shimadzu TOC-V at the University of Santa Barbara, according to (Carlson et al., 2010) for data collected in 2017 and 2019. Data collected in 2022 were analyzed at Scripps Institution of Oceanography according to https://ccelter.ucsd.edu/dissolved-organic-carbon-and-total-nitrogen/. Particulate organic carbon (POC) and nitrogen (PON) concentrations were determined via filter combustion after acid fumigation to remove particulate inorganic carbon, drying, weighing, and packing into tin capsules (https://ccelter.ucsd.edu/particulate-organic-carbon-and-nitrogen/). Samples from 2017 were analyzed for carbon and nitrogen concentrations and stable isotope composition (δ13C and δ15N) at the SIO Stable Isotope Facility on a Thermo Finnigan DeltaPlus Isotope-Ratio mass spectrometer interfaced with a Costech 4010 elemental combustion analyzer. Filters from 2019 were analyzed on an Exeter Analytical CE 440 Elemental Analyzer in the SOEST Analytical Laboratory (http://www.soest.hawaii.edu/S-LAB/). The analysis of fluorescent dissolved organic matter (fDOM) was conducted using a Horiba Aqualog scanning fluorometer, according to the methodology outlined in (Nelson et al., 2015). Samples for bacterioplankton enumeration were thawed and 200 µL of each sample was stained with SYBR Green I stain for a final concentration of 1X. Bacterial cell counts were enumerated using an Attune Acoustic Focusing Cytometer (Applied Biosystems, Part No. 4445280ASR) as described in (Nelson et al., 2015).

currently being processed

NSF Award Abstract:
Dissolved organic matter is an important component of the global carbon cycle. Dissolved organic matter provides food and energy for microbes living in the ocean and influences microbial diversity. Microbes convert some dissolved organic matter to CO2 (respiration) whereas other forms of dissolved organic matter are altered by microbial processes and persist in the ocean. Thus, it is important to understand how microbes change dissolved organic matter composition and reactivity. This project will examine the chemical structure of dissolved organic matter to identify: 1) molecules that fulfill carbon demand (biomass produced minus losses from respiration) and 2) transformation processes that result from microbial activity. The project will combine lab experiments and field studies at the Moorea Coral Reef Long Term Ecological Research site. The project will support training for three graduate students in marine biogeochemistry. Undergraduate training is aimed at sustained mentoring of underrepresented minority (URM) students. Undergraduates will be recruited from existing programs at Minority Serving Institutions at San Diego State University and the University of Hawaiʻi at Mānoa. Undergraduates will participate in the Scripps Institution of Oceanography SURF Research Experiences for Undergraduates program, where they will conduct research in marine chemistry. The goal is to provide a mentoring approach that can successfully overcome roadblocks to URM engagement in STEM and increase retention of these students in marine science.

This work will combine field and lab studies using advanced molecular-level chemical characterization tools to explore how bacteria alter the composition and bioreactivity of organic compounds dissolved in seawater. Additionally, this project will develop informatics-based tools to identify a larger proportion of chemical structures in marine dissolved organic matter (DOM) than is currently possible using traditional approaches. The project will use tandem mass spectrometry and networking techniques to comprehensively classify organic compounds into molecular families and determine common chemical transformations. Then, using a well-developed field-based experimental ecosystem to produce diverse labile DOM pools the research team will track microbial transformation using expression of hydrolytic enzymes and measure selection for particular microbial taxa and metabolisms. This approach defines the reactivity of individual molecules and broader compound classes participating in carbon fluxes that underpin DOM-microbe interactions. Field surveys conducted within the Moorea Coral Reef Long Term Ecological Research program will explore methods to track transformation of specific molecules in the environment and validate experimental observations of compound classes that appear to accumulate as semi-labile DOM. By integrating laboratory and field experiments and oceanographic surveys with the refinement of analytical tools for untargeted metabolomics, this project will characterize the fate of reactive DOM in the ocean.