Two databases derived from BGC-Argo float measurements for marine biogeochemical and bio-optical applications

Since 2012, an array of 105 Biogeochemical-Argo (BGC-Argo) floats has been deployed across the world’s oceans to assist in filling observational gaps that are required for characterizing open-ocean environments. Profiles of biogeochemical (chlorophyll and dissolved organic matter) and optical (single-wavelength particulate optical backscattering, downward irradiance at three wavelengths, and photosynthetically available radiation) variables are collected in the upper 1000m every 1 to 10 days. The database of 9837 vertical profiles collected up to January 2016 is presented and its spatial and temporal coverage is discussed. Each variable is quality controlled with specifically developed procedures and its time series is quality-assessed to identify issues related to biofouling and/or instrument drift. A second database of 5748 profile-derived products within the first optical depth (i.e., the layer of interest for satellite remote sensing) is also presented and its spatiotemporal distribution discussed. This database, devoted to field and remote ocean color applications, includes diffuse attenuation coefficients for downward irradiance at three narrow wavebands and one broad waveband (photosynthetically available radiation), calibrated chlorophyll and fluorescent dissolved organic matter concentrations, and single wavelength particulate optical backscattering. To demonstrate the applicability of these databases, data within the first optical depth are compared with previously established bio-optical models and used to validate remotely derived bio-optical products. The quality-controlled databases are publicly available from the SEANOE (SEA scieNtific Open data Edition) publisher at https://doi.org/10.17882/49388 and https://doi.org/10.17882/47142 for vertical profiles and products within the first optical depth, respectively

ProvBioII: biogeochemical floats become more flexible

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ProVal A profiling float dedicated to radiometric measurements

International audienceIn-situ high quality measurements of radiometric quantities are mandatory to enable a "system vicarious calibration" (SVC) of satellite sensors dedicated to Ocean Color Radiometry (OCR) as well as to validate their derived products. High density of acquisition is particularly critical during the early stages of an OCR satellite activity. The ProVal float measures downward irradiance and upwelling radiance at seven wavelengths on two arms that allow radiometer redundancy and shading mitigation. We analyzed more than 500 profiles sampled in the Southern Ocean and Mediterranean Sea to date. We find that 45% and 85% of data in the surface layer exhibit tilts lower than 10°in the Southern Ocean and Mediterranean Sea respectively. Floats deployed in the Mediterranean Sea were recovered allowing post-deployment calibrations of radiometers that confirmed the low sensor drift. In addition, platform shading, estimated from the difference between the two radiometers, shows good agreement with Monte-Carlo simulations. Finally, comparisons of Remote Sensing Reflectance with the OLCI sensor (Sentinel-3A) show results in agreement with other sources of in-situ data but with extended coverage capabilities

Past and new technological developments at LOV for core and new BGC applications

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Characterization of Bio‐Optical Anomalies in the Kerguelen Region, Southern Indian Ocean: A Study Based on Shipborne Sampling and BioGeoChemical‐Argo Profiling Floats

International audienceAbstract The Southern Ocean (SO) is known for its atypical bio‐optical regime. This complicates the interpretation of proxies measured from satellite and in situ platforms equipped with optical sensors, which occupy an important niche for monitoring the vast and remote SO. A ship‐based field study in concert with time series observations from BioGeoChemical‐Argo (BGC‐Argo) profiling floats were used to investigate spatial and temporal variations in bio‐optical relationships in the open ocean waters surrounding the Kerguelen Plateau in the Indian sector of the SO. Compared to other regions with similar chlorophyll concentrations, chlorophyll‐specific phytoplankton absorption in the blue waveband presented a consistent negative anomaly. The anomaly was uniform over deep mixed layers and correlated with phytoplankton size, photoacclimation and atypically high concentrations of fucoxanthin. The BGC‐Argo observation‐based proxies revealed that the blue absorption anomaly increased with chlorophyll concentration both spatially and temporally and, while particularly pronounced in the naturally iron‐fertilized waters, was also found in the High Nutrient Low Chlorophyll region. While phytoplankton size was an important driver of the anomaly, photoacclimation associated with self‐shading of phytoplankton cells was also involved during intense booms. The backscattering coefficient exhibited negative and positive anomalies in the low and high biomass regimes, respectively. The large positive anomaly in high biomass regimes was attributed to the variable non‐algal particles characteristics associated with a relatively high production of bloom by‐products. With clear understanding of the bio‐optical anomalies, BGC‐Argo floats stand as unique tools for monitoring the bio‐optical spatio‐temporal complexity of the SO

Development and validation of the new ProvBioII float

In the last ten years, a productive collaboration has grown between the Laboratoire d’Océanographie de Villefranche (LOV), NKE and IFREMER to implement biogeochemical sensors on profiling floats. A first project (2003) was dedicated to the design of the so-called ProvBio floats (models A and B) that consisted of a PROVOR-CTS3 float instrumented with three new optical sensors: a Wetlabs transmissometer (C-Rover), a 3-wavelength Satlantic radiometer (OCR-503) and an “ECO3” Wetlabs sensor, measuring chlorophyll-a fluorescence, colored dissolved organic matter and particle backscattering coefficients (see First Success of ProvBio floats, Coriolis Letter n°5). Then, the integration of biogeochemical sensors continued in the framework of ProNuts project (2009, autonomously profiling the nitrate concentrations in the ocean: the pronuts project, Coriolis Letter n°8), by equipping a PROVOR with a nitrate concentration sensor. In parallel within the framework of the Carbocean EU project, the ProvCarbon and ProvDo floats were developed as in 2006 by fitting on a PROVOR a C-Rover and a 3830 Aanderaa optode, respectively. They were used to investigate new tools to assess marine carbon sources and sinks. These initial developments have led to a first invaluable dataset and to subsequent papers (Xing et al. 2012, Xing et al. 2011) and report (IOCCG 2011). Nevertheless, the above projects have grown partially dissociated, as related to specific and project-related needs, while a more integrated solution may have a lot of advantages. Undoubtedly, the scientific exploitation of data would be strongly improved if a unique multidisciplinary float, able to measure all accessible parameters, was available. Such a multidisciplinary float would also strongly reduce costs, by sharing the float itself, and by reducing deployment, validation and communication costs. The idea to merge all these sensors on the same profiling float was thus at the origin of the ProvBioII float project, which was developed in the framework of the remOcean and NAOS programs