Table of Contents

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

The floats were deployed in different ocean basins: Northwest, Central and Eastern Pacific, Atlantic, Arabian Sea and Indian Ocean. These floats are standard Argo APEX floats with a variety of sensors in addition to those for pressure, temperature, and salinity. 

Most of the data (47 floats that are called SOS-Argo floats) have an Aanderaa pO2 sensor (optode) installed on a 61 cm stalk above the end cap of the float, which allows the float to capture uncontaminated atmospheric pO2 for the purpose of in-situ calibration while the float is at the surface. 

In addition to the SOS-Argo floats there are five equatorial floats with sensors for nitrate (NO3) and pH in addition to a pO2 sensor on a stalk that is 10 cm high rather than the 61 cm on the SOS-Argo floats.  We refer to these floats as BGC floats (here meaning they carry a NO3 and pH sensor in addition to the standard P,T and S sensors). The numbers of these floats are 8474, 8482, 11017, 12788, 17862 and 18608; and are marked with two asterisks ** on the UW website.

There are an additional six standard Argo floats without a 61 cm optode stalk. The numbers of these floats are 12632, 12780, 12783, 12792, 18827 and 18822; and are marked with a single asterisk * on the UW webpage.

Measurements of pO2 in the air when the floats reach the surface were used calibrate the optodes against atmospheric pO2.  The procedure for doing this is described in detail in the paper by Bushinski et al., 2016. Briefly, we used a two-stage process in which each optode was calibrated as a function of pO2 and temperature in the Emerson Lab.  This procedure resulted in the following polynomial for pO2 as a function of temperature and optode t-phase.  The “C” values are presented in "Data Files" under the “Optode calibration table”.

pO2 = (((C(5)*T+C(4))/(C(6)+C(7)*y))-1)/(C(1)+C(2)*T+C(3)*T^2)                         

where: T is optode temperature (deg C), y is optode t-phase (degrees), “C” values are given in the table below

Laboratory-calibrated oxygen sensors were recalibrated at sea against in situ atmospheric pO2 values calculated  from NCEP reanalysis atmospheric pressure, P, and humidity, pH2O, for the float location and sampling time along with the oxygen mole fraction in air (XO2=0.20946).”

pO2 (atm) = XO2 (P – pH2O)

When the SOS-Argo float surfaced the pO2 measurements were made every two minutes for a period of one hour.  Profile timing was adjusted so that the float surfaced during night time to avoid heating of the optode foil by direct exposure to the sun.  Surface profile pO2 measurements were adjusted to equal the mean of the atmospheric measurements while the float was on the surface.  

* Merged data of all floats into a single dataset

NSF Award Abstract:
In the sunlit surface waters of the world's oceans, phytoplankton combine nutrients and carbon dioxide to form organic matter and release oxygen. Some of this surface water biological production ends up in the deep ocean, resulting in a net removal of carbon from the surface ocean and atmosphere. One way to estimate this export of carbon to the deep ocean, also called the "biological pump," is by carefully measuring the amount of oxygen that is produced along with the organic matter. Oxygen dissolved in seawater can be measured very precisely by sensors that can be deployed for years at a time on instrument platforms like moorings, floats, or gliders. In this project, a team of investigators will deploy twelve floats in the equatorial Pacific Ocean to measure ocean profiles of temperature, salinity, oxygen, and nitrate (a nutrient for phytoplankton). The data will be transmitted by satellite and combine with computer models of ocean circulation to understand the biological pump in this productive area of the ocean. The project will support two early-career researchers: a graduate student and a postdoctoral research fellow.

The project will be a combination of in situ measurements of oxygen and nitrate on specially-equipped profiling floats with data interpretation using a high-resolution Global Circulation Model (GCM). The plan is to construct 12 Argo floats with specially-mounted Aanderaa Optode oxygen sensors and ISUS nitrate sensors, and to deploy them in the region between 8 degrees N and 8 degrees S from about 95 degrees W to 140 degrees W; the location where carbon export is greatest in both satellite-based and GCM-based maps of global carbon export. The data will be interpreted in terms of net biological oxygen production, which is stoichiometrically related to Annual Net Community Production (ANCP) and annual organic carbon export, using a Regional Ocean Model System (ROMS) physical transport model with a Biogeochemical Elemental Cycling (BEC)-like ecosystem. Previous NSF research has shown that it is possible to determine the air-sea pO2 difference using oxygen sensors on profiling floats to an accuracy of plus or minus 0.2 % by calibrating the sensors against atmospheric oxygen when the floats surface to transmit data to shore. Since the air-sea flux and net biological production are usually the dominant terms in the upper ocean oxygen mass balance, it has been possible to determine ANCP in subarctic and subtropical gyre locations using a one-dimensional, upper-ocean model. The goal in this project is to determine the ANCP in the strongly advective equatorial region, and compare it to carbon export values determined from satellite-based and GCM-based methods that so far have not been tested with observations.