Table of Contents

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

Measurements
Measurements for O2/Ar dissolved gas ratios, temperature, salinity, and fluorescence were continuously measured from an underway seawater system (10 m depth) on basin-wide transects of the North Pacific between Hong Kong and Long Beach, California onboard the M/V OOCL Tianjin and the M/V OOCL Tokyo (each individual transect has a unique Cruise ID). Sea surface temperature and salinity at the time of sample collection were determined using a Sea-Bird Electronics SBE45 thermosalinograph (TSG) installed in the ship’s seawater intake. Fluorescence was measured using a Seapoint Chlorophyll Fluorometer.  This dataset presents uncalibrated data; the discrete calibration data are in https://www.bco-dmo.org/dataset/626855.

Underway measurements of O2/Ar dissolved gas ratios were made using continuous flow equilibrator inlet mass spectrometry (EIMS), following the method of Cassar et al. (2009). Water from the underway seawater system was pumped into an equilibrator cartridge (Membrana MicroModule G569, 0.75” x 1”), the headspace of which was delivered to a quadrupole mass spectrometer (Pfeiffer Prisma QMS) that measured individual ion currents at one-second intervals. To prevent biofouling that could cause respiration in the ship’s seawater lines (Juranek et al., 2010), intake lines between the anticorrosive sea chest and the sampling port were purged with bleach and freshwater between every cruise.

NOTE: Since the samples were collected underway on a vessel moving ~24 knots and samples for all parameters were collected by a single shiprider, ship transit from the time that the location coordinates were recorded to the time of actual sampling could reflect a transit distance offset from the recorded location of up to 40 kilometers.

Methods and Calculations
Methods are described in detail in Clayton et al. (in preparation for JGR: Oceans). 

To aid in interpretation of the O2/Ar data provided here, we include calculations of the air-sea flux of biological oxygen driven by the biological saturation anomaly (O2Arbiosat), termed “bioflux” by Jonsson et al. [2013]:
                             Air_sea_flux = k*[O2]eq*(O2Arbiosat/100)

Where k represents the wind speed-dependent air-sea gas transfer velocity and [O2]eq is the oxygen concentration that would be expected in the mixed layer were it in equilibrium with the atmosphere. We calculate k from daily wind speed data from the NOAA National Climatic Data Center’s multiple-satellite Blended Sea Winds product (https://www.ncdc.noaa.gov/data-access/marineocean-data/blended-global/blended-sea-winds) following the Nightingale et al. (2000) equation and the 60-day (Reuer et al., 2007) time-dependent weighting scheme. We report k here as “Wkn” representing the weighted k value using the Nightingale algorithm. In conditions with limited influence of physical advection, entrainment, and transient changes due to non-steady state conditions over the dissolved gas residence time in the mixed layer, bioflux is equivalent to net community production. However, there are potential biases in quantifying net community production based on observed O2/Ar in dynamic western boundary current regions where steady state assumptions are likely invalid and strong vertical turbulent dissipation rates have been observed.

The following are additional details for relevant fields in this dataset:

• TrueO2Ar:  ratio of dissolved O2/dissolved Ar in surface seawater as measured by continuous underway equilibrator inlet mass spec, and calibrated with discrete samples from existing dataset (https://www.bco-dmo.org/dataset/626855).
• O2Arsat: O2/Ar ratio expected if both gases were in equilibrium with the atmosphere, which is a function of Salinity and Temperature (Garcia and Gordon, 1992; Hamme and Emerson, 2007)
• O2Arbiosat:  percent supersaturation of O2 in surface seawater, calculated from the TrueO2Ar and O2Arsat [O2Arbiosat = (TrueO2Ar/O2Arsat – 1)*100]
• MLD: climatological mixed layer depth from monthly World Ocean Atlas 2013 (with 1 degree gridded data)
• Wkn: air-sea gas transfer velocity in m/day, calculated using a relationship between wind speed and gas transfer from Nightingale et al. (2000) and the NOAA/NCDC Blended Sea Winds satellite wind speed product (Zhang et al. 2006), and using the Reuer et al. (2007) time-dependent weighting scheme and the MLD values given here.

Data processing: 
Data are reported as the mean over a three-minute measurement period, chosen to match the e-folding response time of O2/Ar ion current ratios for this EIMS setup. This yields a spatial resolution of ~2 km at the average ship speed of ~25 knots. For the Tokyo_3 cruise, a Loess filter with a 30-minute half-span was applied to remove high frequency instrument noise in the EIMS setup, reducing the spatial resolution to ~40 km, giving a marginal sampling for mesoscale fields. This filter was not applied to the May 2011 or July 2012 cruises in order to preserve the spatial resolution of the data.

BCO-DMO processing:​
- Data from all cruises were combined into a single dataset with an added column for Cruise ID
- Timestamp converted to ISO DateTime UTC format in additional column
- Longitude converted from a 360 degree scale to +/- 180 scale, and put in separate column
- Parameter names adjusted to comply with database requirements
- Added a conventional header with dataset name, PI name, version date
- Units added to parameter description metadata section
- Missing data identifier of 'nd' (no data) used

This project is an ongoing time-series beginning in 2008 of measurements relevant to ocean carbon cycling and productivity on basin-wide container ship transects across the North Pacific from Hong Kong to Long Beach, California, with transects made throughout the seasonal cycle beginning in October 2008. The goal of this project is to improve our understanding of the rates and mechanisms of ocean carbon uptake from the atmosphere throughout the seasonal cycle and across spatial gradients across the basin. Sampling includes both discrete samples and continuous underway measurements. Tracers sampled in this program include triple oxygen isotopes (δ17O and δ18O), a tracer of gross primary production, oxygen/argon dissolved gas ratios, a tracer of net community production or carbon export, and carbonate system parameters (pCO2, total alkalinity, DIC, and 13C-DIC) as tracers of ocean carbon uptake and carbon cycling.