Table of Contents

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

The cruise (KM1713) transited from Seward, AK to Honolulu, HI from 3-26 September 2017 onboard the R/V Kilo Moana. Six extended stations (Stn), three in subpolar waters (Stn 1 at 55°N, Stn 2 at 50°N, and Stn 3 at 46°N), one in the transition zone between subpolar and subtropical waters (Stn 4 at 42°N), and two in the subtropical gyre (Stn 5 at 34°N, and Stn 6 at 24°N) were occupied for 2-3 day periods during which continuous measurements of conductivity, temperature, O2, O2/Ar and beam attenuation were measured continuously on surface seawater supplied via the ships’ intake line and using CTD profiles of conductivity, temperature, pressure, oxygen, and the particulate beam attenuation coefficient conducted at ~2-hr intervals. An autonomous profiling float was deployed for ~ 2 days at four stations, retrieving CTD and oxygen profiles at approximately 3-hour intervals. Another float with same mission design was deployed near station ALOHA (22.45° N, 158° W) during July 2017 to provide mixed-layer averaged O2 near station 6. When available, the ship followed the trajectory of the profiling float, yielding a near-Lagrangian sampling strategy with the aim to minimize horizontal mixing effects.

Underway/continuous measurements of O2, O2/Ar and optically-based POC

Continuous measurements of surface O2, O2/Ar, POC, and beam attenuation coefficients used seawater supplied from an uncontaminated seawater intake line located at ~7m depth.  All continuous measurements were binned into hourly averages at each station. Continuous measurements of dissolved O2 concentration using an Optode (Aanderaa) and the dissolved O2/Ar  gas ratios using an equilibrator inlet mass spectrometer (EIMS) system [Cassar et al., 2009] were obtained at each station. Dissolved oxygen data (Optode) were corrected for pressure and salinity following Uchida et al. [2008]. O2/Ar measured by the EIMS were calibrated to O2/Ar measurements by mass spectrometer on discrete water samples collected in the mixed layer during the cruise (n=58). Saturated O2 concentrations and O2/Ar values were calculated using the solubility equations of García and Gordon [1992] for O2 and Hamme and Emerson [2004] for Ar. Diurnal changes in O2/Ar data measured by the EIMS instrument were corrected for fluctuations in total gas pressure based on concurrent changes in N2/Ar, yielding O2/Ar*, (i.e., % deviation in O2/Ar* = % deviation O2/Ar – a*% deviation N2/Ar, where ‘a’ represents a calibration factor between N2/Ar and O2/Ar deviations determined at each station). Diurnal changes in O2 were determined by multiplying the relative deviation from the mean O2 measured by the Optode by the mean surface Winkler O2 concentration measured at each station (Eq. 1), where i refers to each datapoint in time, and overbars denotes the mean values while on each station. The diurnal changes in O2/Ar and O2/Ar* were calibrated to Winkler concentrations using the same procedure.

Discrete water samples (collected on combusted GF/F filters with filter blank corrections following the Hawaiian Ocean Time Series (HOT) protocols, http://hahana.soest.hawaii.edu/hot/methods/pcpn.html) were collected from the ship’s uncontaminated seawater system to determine particulate organic carbon (POC) concentrations every ~2.5 hours (n=107 in total) using a semi-automated filtration device [based on the design of Holser et al., 2011]. Underway POC were scaled to mean near-surface (<10 m) samples collected at each station (n=12; r2=0.92) and these corrected values were then used to convert cp measurements to POC using Eq. 2, where  is the mean in situ POC measured at each station.

BCO-DMO Processing Notes:
- added conventional header with dataset name, PI name, version date
- modified parameter names to conform with BCO-DMO naming conventions
- added ISO Date format generated from date and time values
- combined POC and O2 continuous data

NSF Award Abstract:

The rate of primary production in the ocean is fundamental to the ocean's food web and the movement of carbon from surface waters to the deep ocean, known as the biological pump. Yet spatial and temporal variations in primary productivity are poorly known because the effort required for the current method of measuring primary productivity is significant, limiting its application, and the method has biases that are difficult to quantify. Using a novel combination of approaches, the investigators will estimate daily primary productivity in the ocean at three ecologically distinct sites. The research will significantly improve understanding of primary productivity variations and their impact on the ocean's biological pump, which will benefit the broader ocean community involved in carbon cycle modeling and benefit society via the impact of ocean primary productivity on atmospheric carbon dioxide uptake and future climate change. The research results will be incorporated into both undergraduate and graduate course curricula and outreach talks at the two institutions. There will be active undergraduate student participation in the project at both Oregon State University and the University of Washington.

Within the last decade, an in-situ primary productivity method based on measuring the isotopic composition of dissolved oxygen (O2) gas has gained traction within the oceanographic community because it yields a primary production estimate from a simple water sample collection. This method has yielded basin-wide snapshots of primary productivity based on underway sampling of the surface ocean by ships of opportunity. However, accurate estimates of oxygen/particulate organic carbon (O2/POC) produced during primary productivity are needed to convert oxygen-based primary production rates to carbon production. In this project, daily in-situ rates of primary production in the surface ocean at three ocean sites will be estimated from continuous measurements of diurnal cycles in the oxygen/argon dissolved gas ratio and POC and compared to simultaneous in vitro primary productivity estimates. Variations in the O2/POC produced during primary production will be determined. Autonomous float-based estimates of primary production based on measurements of diurnal cycles in O2 and POC will be validated using ship based measurements. Estimates of primary production based on autonomous measurements resulting from this research have the potential to revolutionize our knowledge on the spatial and temporal variations in primary productivity in the ocean.