Table of Contents

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

Water samples for nutrient analyses were collected from CTD Niskin bottles at discrete depths (15–100 m) from a single CTD cast. Approximately 40 mL of seawater was filtered onboard through 0.22 μm sterile syringe filters (Basix™ PES) and immediately frozen using an ethanol and dry ice bath prior to storage. Ammonia concentrations were determined using the o-phthaldialdehyde (OPA) fluorescence method following Holmes et al. (1999). Nitrite concentrations were measured spectrophotometrically using the sulfanilamide–NED method as described in Grasshoff et al. (1999). Nitrate concentrations were determined using the vanadium(III) chloride reduction method following García-Robledo et al. (2014).

For dark carbon fixation measurements, seawater was collected from CTD Niskin bottles from the same CTD cast and maintained in the dark at near in situ temperature. Four subsamples (90 mL each) were transferred into separate 110 mL acid-cleaned HDPE brown bottles. All subsamples were collected from the same Niskin bottle at each depth and divided into replicate incubations. All bottles were amended with approximately 6 μCi of 14C-labeled bicarbonate. One subsample was treated with 2.5% glutaraldehyde as a killed control, while the remaining three subsamples were incubated as biological replicates. Incubations were conducted in the dark at temperatures approximating in situ conditions (~15 °C for the 15m sample and ~11 °C for deeper samples). After ~60 hours of incubation, samples were processed following standard 14C carbon fixation protocols, including filtration and radioactivity measurement by liquid scintillation counting.

Carbon fixation rates were calculated from 14C incorporation measurements. Measured disintegrations per minute (DPM) were converted to carbon fixation rates using the known activity of added 14C-bicarbonate and the ambient dissolved inorganic carbon (DIC) pool. Background activity was corrected using the killed control sample. Rates are reported as carbon fixed per unit volume per day.

This section documents curation actions performed prior to publication review with the submitter, and additional information relevant to understanding and reusing this dataset. It distinguishes changes made to the submitted (meta)data from unresolved issues and/or enhancements that improve future reuse and interoperability.

CURATION ACTIONS PERFORMED ON DATA

- Loaded XLSX file "SPOT_nutrients and dark carbon fixation_20250219.xlsx" (sheet 1), naming the table spot_nutrients_dark_carbon_fixation, header row set to row 1, with preserve_formatting and adjust_floating_point_error enabled; set empty string and "nd" as missing values via schema override
- Renamed columns to fix a naming convention violation caused by a "/" character and to remove units from parameter names: DCF_nM_C/day to DCF, Depth_m to Depth, Ammonia_nM to Ammonia, Nitrite_nM to Nitrite, Nitrate_uM to Nitrate
- Output as 1005611_v1_spot_nutrients_dark_carbon_fixation.csv

CURATION ACTIONS PERFORMED ON METADATA

- Adjusted title to conform with BCO-DMO conventions

ISSUES POTENTIALLY IMPACTING REUSE

- The source or calculation of the ambient dissolved inorganic carbon (DIC) values used to calculate dark carbon fixation rates was not provided

NSF Award Abstract:

This project seeks to provide a deeper understanding of how major biogeochemical cycles that support all living marine resources will respond to climate warming in a changing ocean environment. It will train one postdoctoral researcher and three graduate students, and provides research training opportunities for undergraduate students in microbial physiology and ecology, bioinformatics, trace metal biogeochemistry, and oceanography. Project personnel also conduct K-12 education and outreach activities. All data is freely available through the Biological and Chemical Oceanographic Data Management Office (BCO-DMO).

This project investigates how climate warming will interact with the unique trace metal requirements of marine nitrifying microorganisms (nitrifiers) to affect ammonia and nitrite oxidation pathways in the rapidly changing ocean. Four investigators with diverse expertise in microbial global change physiology, nitrogen and trace metal biogeochemistry, and mechanistic transcriptomics and proteomics combine their efforts, using well-controlled pure culture-based laboratory studies along with field incubation experiments with natural communities to systematically investigate 1) thermal effects on iron (Fe) and copper (Cu) requirements and use efficiencies in isolated cultures and natural populations of marine ammonia-oxidizing archaea and bacteria (AOA, AOB) and nitrite-oxidizing bacteria (NOB), 2) the underlying molecular and biochemical mechanisms that facilitate such thermally-driven adaptive responses, and 3) system-level feedbacks between global change, trace metal biogeochemistry, and marine nitrifiers and their associated microbial communities in diverse marine environments. Together, these studies enhance our understanding of the marine nitrogen cycle and trace metal biogeochemistry, and ultimately contribute to a more detailed understanding of the impact of rapid ocean warming on critical major nutrient and micronutrient cycles.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.