General Context

The choice of the core variables for the Biogeochemical-Argo network results from a compromise between (1) the research and management requirement of the network and (2) the readiness of the sensors with respect of delivering accurate, long-term and reliable measurements. These core variables are:

These variables include some of the so-called Essential Ocean Variables (EOVs), Ecosystem EOVs (eEOVs), or Essential climate variables (ECVs) (Table 1) that allow to better constrain the biogeochemical cycles of carbon, oxygen, nitrogen, and biomass. These variables are the fundamental measurements that are required to address significant scientific and societal ocean/climate-related issues.

The suite of sensors to be used in a global observing system that will be deployed in the near future must be operational now. These sensors must provide robust measurements of the core Biogeochemical-Argo variables that include several essential (ocean, ecosystem or climate) variables. They must also provide data that directly addresses the research and management needs of the network (Table 2). Here we briefly summarize the sensors that meet these criteria.

Autonomous sensors for key oceanic biogeochemical variables
Variable Sensor Type Accuracy/Precision Reference
Oxygen (1,3,4)
Lifetime optode
1% of surface O2 / 0.2 μmol kg-1
[Körtzinger et al., 2004]
[Johnson et al., 2015]
[Bittig et al., 2015]
Nitrate (1,4)
Ultraviolet absorbance
1 μmol kg-1 / 0.1 μmol kg-1
[Johnson et al., 2013]
pH (1,4)
Ion Sensitive Field Effect Transistor
0.01 pH / 0.0005 pH
[Johnson et al., 2016]
Chlorophyll a(2,3,4)
Max (30%,0.03 mg Chla m-3) / 0.025 mg Chla m-3
[Boss et al., 2008]
Max (24%,0.03 mg Chla m-3 ) / 0.025 mg Chla m-3
[Xing et al., 2011]
Suspended particles (3) Optical backscatter
Suspended particles: Max (50%, 1.5 µg kg-1) / 1 µg kg-1
[Boss et al., 2015]
Backscattering coefficient: Max (10%, 10-5m-1) / 4 x10-6 m-1
[Sullivan et al., 2013]
POC : Max (30%, 20 mg m-3) / 10 mg m-3
[Cetinic et al., 2012]
PC: Max (30%, 6 mg m-3) / 3 mg m-3
[Graff et al., 2015]
Downwelling irradiance (3,4)
PAR: Max (3%, 5 μmol photons m-2 s-1) / 1 μmol photons m-2 s-1
[Manufacturer web site]
Spectral: Max (3%, 5 X10-3 µW cm-2 nm-1) / 2.5 X 10-3 µW cm-2 nm-1
  • Boss, E., D. Swift, L. Taylor, P. Brickley, R. Zaneveld, S. Riser, M. J. Perry, and P. G. Strutton (2008), Observations of pigment and particle distributions in the western North Atlantic from an autonomous float and ocean color satellite, Limnology and Oceanography, 53(5), 2112-2122, doi:10.4319/lo.2008.53.5_part_2.2112.
  • Johnson, K. S., J. N. Plant, S. C. Riser, and D. Gilbert (2015), Air Oxygen Calibration of Oxygen Optodes on a Profiling Float Array, Journal of Atmospheric and Oceanic Technology, 32(11), 2160-2172, doi:10.1175/jtech-d-15-0101.1.
  • Johnson, K. S., L. J. Coletti, H. W. Jannasch, C. M. Sakamoto, D. D. Swift, and S. C. Riser (2013), Long-Term Nitrate Measurements in the Ocean Using the in situ Ultraviolet Spectrophotometer: Sensor Integration into the APEX Profiling Float, Journal of Atmospheric and Oceanic Technology, 30(8), 1854-1866, doi:10.1175/jtech-d-12-00221.1.
  • Johnson, K. S., H. W. Jannasch, L. J. Coletti, V. A. Elrod, T. R. Martz, Y. Takeshita, R. J. Carlson, and J. G. Connery (2016), Deep-Sea DuraFET: A Pressure Tolerant pH Sensor Designed for Global Sensor Networks, Analytical Chemistry, 88(6), 3249-3256, doi:10.1126/science.1102557.
  • Körtzinger, A., J. Schimanski, U. Send, and D. Wallace (2004), The ocean takes a deep breath, Science, 306(5700), 1337-1337, doi:10.1021/acs.analchem.5b04653.
  • Xing, X., A. Morel, H. Claustre, D. Antoine, F. D'Ortenzio, A. Poteau, and A. Mignot (2011), Combined processing and mutual interpretation of radiometry and fluorimetry from autonomous profiling Bio-Argo floats: Chlorophyll a retrieval, Journal of Geophysical Research-Oceans, 116, doi:10.1029/2010jc006899.