Table of Contents

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

The NCD cruise steamed northwest of Oahu until ~35^oN, then transited west along ~35^oN to ~170^oE. We then transited S. to ~11^oN, targeting frontal zones between mesoscale features based on sea surface height anomalies and enhanced chlorophyll features, before returning to Oahu. We had daily CTD casts where we deployed the CTD (<300 m). The CTD had sensors for measuring conductivity (calculated salinity), temperature, depth, beam transmission, beam attenuation, photosynthetically active radiation, and fluorescence.

Data processed with Seabird CTD processing software (1m-binned).  Software Version Seasave V 7.26.7.107.  These data were concatenated and provided as Data File 969967_v1_ctd.csv in this dataset.  

The data is also available in the following formats (See Supplemental Files):

* "km2206_binavg.cnv.zip" - The processed seabird .cnv file format. Example file: S18C02binavg.cnv contains data for station 18 cast 2.

* "KM2206_ct1.zip" - WHP Exchange format (standardized, text-based format (CSV) for exchanging hydrographic data, specifically for CTD (Conductivity-Temperature-Depth) and bottle samples).  Parameter explanation can be found here: https://exchange-format.readthedocs.io/en/latest/parameters.html (Barna et al., 2024). Example file: KM2206_s18c02_ct1.csv contains data for station 18 cast 2.  All files include suffix _ct1.csv indicating data from one cast.

WOCE Bottle Quality Codes

1: Bottle information unavailable.

2: No problems noted.

3: Leaking.

4: Did not trip correctly.

5: Not reported.

(6): (Significant discrepancy in measured values between Gerard and Niskin bottles.)

(7): (Unknown problem.)

(8): (Pair did not trip correctly. Note that the Niskin bottle can trip at an unplanned depth while the Gerard trips correctly and vice versa.)

9: Samples not drawn from this bottle.

* Data within .csv files by cast (see supplemental file "KM2206_ct1.zip") were concatenated into a combined table (attached to this dataset as 969967_v1_ctd.csv) with LATITUDE,LONGITUDE,DEPTH,STNNBR,CASTNO,SECT_ID,DATE,TIME, EXPOCODE fields extracted from header comments in each .csv cast file and added as individual columns in the combined data table. The last row of each cast table "END_DATA" was not included in the combined table. An additional column Cruise_ID was added with KM2206 (identifier as used at R2R https://www.rvdata.us/search/cruise/KM2206).

Missing Data Identifiers:
* In the BCO-DMO data system missing data identifiers are displayed according to the format of data you access. For example, in csv files it will be blank (null) values. In Matlab .mat files it will be NaN values. When viewing data online at BCO-DMO, the missing value will be shown as blank (null) values.

In all cast files, the header contained:
CTD = "20220704ESSSTNFRDGVD" which was added to the instrument information for this dataset's metadata.

NSF Award Abstract:
Nitrogen (N) is an important element in the ocean that limits the growth of the microscopic marine plants, phytoplankton. Estimates suggest N inputs and losses may not be balanced in the modern ocean, and thus an underestimation of N inputs may explain this imbalance. The conversion of gaseous N2 to biologically available N (N2 fixation) is the largest source of new N to the ocean. It is possible that the "missing" N can be explained by identifying new sources of N2 fixation. N2 fixation relies on a group of microorganisms, termed "diazotrophs", that utilize N2 for growth, unlike other marine microorganisms. Diazotrophs fall into two groups, cyanobacterial diazotrophs, which are able to derive energy through photosynthesis, and non-cyanobacterial diazotrophs (NCDs), which require a non-light-based energy source. Next to nothing is known about the ecology and biology of NCDs, except that they are ubiquitous in the ocean and contain the nitrogen fixing gene, but no direct measurements of their N2 fixation activity exist. Recent molecular advances for studying organisms at the single cell level now makes the measurement of N2 fixation by NCDs possible. This study is focused on determining whether marine NCDs are actually fixing N2 in the environment and understanding how their N2 fixation is modulated. Determining if NCD activity is an important missing N source in the global oceans has the potential to fill a critical gap in our understanding of the marine N cycle. This project supports early career STEM researchers including a graduate student and a postdoctoral scientist, as well as undergraduate students through several programs including UCSC's California Alliance for Minority Participation (CAMP).

Nitrogen fixation, the microbial process of converting N2 into biologically available ammonia, is an important source of N in the oceans. Historically, research has focused on the most conspicuous diazotrophs, such as Trichodesmium, but the discovery of unicellular cyanobacterial and non-cyanobacterial diazotrophs (NCDs) in the open ocean revealed a broader diversity than previously thought. Much of what is known about NCDs is restricted to presence, abundance estimates and transcriptional activity from gene surveys. NCDs are globally distributed throughout coastal and oligotrophic environments, however, it is not known whether NCDs supply N to support primary productivity. Measurements of marine NCDs are needed to determine if NCDs are actively fixing N2. This study is focused on measuring single cell NCD N2 fixation rates from a variety of taxa living in well-lit, oxygen-rich coastal and oligotrophic surface waters in the North Pacific and Arctic Oceans. The investigators are using a cultivation-independent technique called geneFISH to microscopically visualize and localize NCDs and measuring the incorporation of 15N2 into single cells using nanoscale secondary ion mass spectrometry. Beyond measuring in situ NCD N2 fixation rates, experiments are being conducted to determine environmental controls on single cell NCD N2 fixation (light, temperature, dissolved organic matter, dissolved inorganic N, and iron). Obtaining single cell NCD N2 fixation rates from a range of taxa, under different experimental conditions and in coastal and oligotrophic environments will provide information to link their presence to N2 fixation activity, determine the quantitative significance of NCDs in the marine environment, and set the stage for their inclusion in biogeochemical models.

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.