Table of Contents

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

This data is provided free for educational and non-profit research purposes.  Please cite the publication listed under Acquisition Description in any work that uses this database. If you would like to be apprised of any future corrections or updates to the data, send an e-mail to rhamme@uvic.ca. If you discover what you believe to be an error in the database, it is your responsibility to send an e-mail to rhamme@uvic.ca before using the data in a publication.

Both MatLab .mat databases and comma-delimited .csv text files are provided. These two formats contain identical information. The data from the paper is listed in order of collection (date). Different cruises can be identified by the cruise name or date.

Download the Matlab file: LabSea_Hammeetal2017-12-06

Methodology is given in Hamme et al. (2017).  Briefly, samples are collected through CO2-flushed tubing into ~180mL evacuated glass flasks until half full.  Samples are weighed. The water is equilibrated with the headspace, then removed.  Headspace gases are cryogenically purified to remove H2O and CO2 for N2/Ar samples or to remove all gases except noble gases for the noble gas samples.  An additional aliquot of 38Ar is added to the noble gas samples along with a balance gas of either N2 or He. Samples are analyzed on a MAT 252 or 253 isotope ratio mass spectrometer for the noble gas and UVic N2/Ar samples, and on a Delta XL for the N2/Ar samples run at UW.  Samples are analyzed against standards of similar composition.  Standard gases are calibrated relative to air with assumed dry mole fractions of 1.818e-5 for Ne,  9.34e-3 for Ar, 1.141e-6 for Kr, and 0.78084 for N2.

Related Reference:
These data were published in Figures 1, 2 and 4 of:
Hamme, R. C., Emerson, S. R., Severinghaus, J. P., Long, M. C., & Yashayaev, I. (2017). Using noble gas measurements to derive air-sea process information and predict physical gas saturations. Geophysical Research Letters, 44, 9901–9909. https://doi.org/10.1002/2017GL075123

All samples were collected in duplicate.  Only data for which both duplicates were successfully analyzed and whose standard deviation was within three times the overall dataset pooled standard deviation are included in this dataset.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- replaced commas and colons with semicolons

The role of nitrate in the ocean carbon cycle and its relatively short residence time make it crucial to understand the marine nitrogen cycle; however, there is currently insufficient experimental evidence to accurately determine present day fluxes. Denitrification and nitrogen fixation are the main sink and source for dissolved inorganic nitrogen in the sea.

In this study a research team at the University of Washington will collaborate with colleagues at the University of Victoria to study changes in the N2/Ar ratio in seawater caused by denitrification. Previous research has demonstrated the utility of this tracer in the oxygen minimum zones of the Pacific and Indian Ocean, but they will investigate observed changes in the "background" distribution of the ratio. The investigators already have unpublished data that indicate the N2/Ar ratio increases by about 0.5 % from the Atlantic to Pacific Oceans in waters below 1000 meters. If this increase is assumed to be caused by denitrification in deep ocean sediments it amounts to roughly 80 Tg/yr of denitrification. This is a significant portion of estimated global denitrification (between 200 and 400 Tg/yr) and within the range of the largely untested predictions of deep-ocean sediment denitrification using global sediment diagenesis models. Presently it is not possible to unequivocally attribute the observed deep water column N2/Ar increase to denitrification because it could also be caused by deep-water formation processes in the Antarctic.

The investigators will separate the fraction of the N2/Ar ratio increase due to the physical processes of atmosphere or ice-water interaction from that due to denitrification by measuring other noble gas ratios (primarily Ne/Ar and Kr/Ar) that change only in response to ocean surface cooling and bubble processes. They will measure deep water-column profiles of N2/Ar, Ne/Ar and Kr/Ar in strategically-located sites where there are ships of opportunity: the Labrador Sea, the North Atlantic at the Bermuda time-series site, the Drake Passage, the Indian Ocean south of Madagascar, the subtropical North Pacific at the Hawaii Ocean time-series site, and the subarctic North Pacific at Station P. Preliminary measurements of all of the gas ratios have been made, and extensive testing has been done to identify sources of contamination in the sampling methods. This proposal involves a two-laboratory collaboration to make it possible to sample a large number of ocean sites, minimize atmospheric contamination by rapid sample analysis, and create maximum accuracy through laboratory intercalibration.

Broader Impacts: This project will promote international ocean science collaboration between the U.S.and Canada. It will support the research of an assistant professor to apply analytical methods that she has helped develop to an important problem in oceanography. A PhD candidate at the University of Washington will be trained in the area of chemical oceanography using analytical methods of gas ratio and isotope ratio mass spectrometry.