Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Concentration measurements of water column phosphate, nitrate and nitrite, dissolved organic phosphorus, methane, and ethylene from samples collected during the R/V Niel Armstrong cruise AR16 in the western North Atlantic Ocean in May 2017.

Sampling was conducted aboard the R/V Neil Armstrong (cruise AR16) in May 2017. Seawater was collected from Niskin bottles deployed on a rosette with a CTD.

Samples for seawater methane (CH4) and ethylene (C2H4) concentration measurements were collected from the CTD rosette in 250 mL glass serum vials (pre-combusted) crimp-sealed with aluminum collars and with Teflon-lined septa. Samples were typically analyzed the same day of sampling aboard the R/V Armstrong with an Agilent 7980A gas chromatograph equipped with a flame ionization detector (FID) and a gas stripping and cryo-trap concentration method as described previously (Repeta et al. 2016). The FID was calibrated by injecting different sized loops of a gas mixture standard containing 10 ppm of CH4 and C2H4 in pure nitrogen gas (Scott-Marrin, Riverside, CA, USA).

Samples for nutrient analyses were collected in acid-clean HDPE plastic bottles. Samples were shipped frozen to the Center for Microbial Oceanography: Research and Education at the University of Hawaii at Manoa where they were stored frozen until analysis.

Seawater phosphate (PO4) concentrations were determined following the autoanalyzer colorimetric procedure of Foreman et al. (2019). Seawater nitrate+nitrite (NOx) concentrations were determined following the autoanalyzer colorimetric procedure outlined of Foreman et al. (2016). Both PO4 and NOx analyses were performed on a SEAL Analytics autoanalyzer model 3 HR.

Seawater samples with low level N+N (LLN) concentrations were measured using the modified chemiluminescent method based on titanium (III) trichloride reduction of N+N to nitric oxide gas and detection with an Antek model 7090 as described by Foreman et al. (2016).

MAGIC soluble reactive phosphorus (SRP) concentrations (i.e. phosphate) were determined in seawater samples using the MAGnesium Induced Coprecipitation (MAGIC) technique as described by Karl and Tien (1992) with modifications based on Thompson-Bulldis and Karl (1998) and Cavendar-Bares et al. (2001) to increase the concentration factor of phosphate. Specifically, SRP was concentrated from 150 mL sweater samples using 0.75 mL (0.5% v/v) of 1M NaOH to precipitate Mg(OH)₂ and the Mg(OH)₂ pellets were dissolved with 5.25 mL of 0.1M HCl.

Total dissolved P (TDP) concentrations were measured by a photo-oxidation procedure in which controlled exposure to ultraviolet (UV) radiation converts organic P in seawater to phosphate which is then measured by the modified molybdenum blue method adapted for the autoanalyzer technique. The UV photo-oxidation methodology for TDP analysis is described in Foreman et al. (2019). The difference between TDP and PO4 or TDP and SRP is calculated to estimate the concentration of dissolved organic phosphorus (DOP) in seawater.

nd = not determined; bdl = below detection limit.

BCO-DMO Processing:
- Re-formatted original date/time field into ISO8601 format;
- 2019-07-19: served version 2 of data (detection limits of ethylene gas were re-calculated).

NSF Award Abstract:
The "marine methane paradox" refers to observations of high concentrations of methane in surface waters of the ocean, even though these waters are well-oxygenated and high in sulfate, both features which generally do not favor the production of methane. This project aims to elucidate on the cause of this paradox. Based on preliminary results, the investigator identified the potential for methane production stimulated by microbial cycling of dissolved organic matter. Polysaccharides (carbonates such as starch) are a major component of high molecular weight dissolved organic matter (HMWDOM) and they can incorporate esters of methylphosphonate, which may be allowing for the production of methane in surface waters. When these HMWDOM polysaccharides were introduced to seawater samples, the researchers saw production of methane with an anomalous stable carbon isotope ratio comparable to what is seen in the paradoxical surface waters enriched in methane. By making measurements of trace gases, HMWDOM phosphonate, and stable carbon isotope measurements in the western North Atlantic Ocean, the investigator and his collaborators will reassess the preliminary data and the implications of these results for the entire oceanographic cycling of methane. Both educational and outreach efforts have been included. For the educational component, a postdoc, a graduate student, and summer undergraduate students will be work on the project, whereas for the outreach activities, the proponent plans to develop curricula on basic science and oceanography for high school students, include a high school teacher in the research cruise, and integrate results into an organic geochemistry course, the lectures of which will be publically available online.

This project seeks to evaluate the possibility that the "marine methane paradox", or the super-saturation of methane in high sulfate, well-oxygenated surface waters, is caused by microbial cycling of dissolved organic matter (DOM). There has been a great deal of preliminary evidence to support this theory. For example, samples from station ALOHA were amended with purified high molecular weight DOM (HMWDOM) polysaccharides, and methane, ethylene, and propylene productions were stimulated. HMWDOM polysaccharides incorporate esters of methylphosphonate (MPn), 2-hydroxyethylphosphonates (2-HEP), and other minor phosphonates, which are likely facilitating the production of methane, ethylene, and propylene. Carbon isotope data supports that this theory is the process behind the marine methane paradox; the d13C value of methane produced from HMWDOM polysaccharide enriched samples agrees well with the anomalous value associated with the super-saturated surface water. Only a small fraction of HMWDOM polysaccharides can easily explain the marine methane paradox, and this process could just as easily fully revise the current understanding of large scale methane cycling between the ocean and atmosphere. The researchers will assess the preliminary evidence and evaluate the microbial DOM cycling theory by making paired trace gas and HMWDOM phosphonate, as well as stable carbon isotope measurements in the western North Atlantic Ocean.