Argo Dataset production: Real‐time data‐management and delayed‐mode qualified dataset for O2, Chlorophyll‐a, backscattering and NO3

Assessment of Data flow and availability on the assembly centre. Description of the O2 delayed mode quality contro

BioGeoChemical‐Argo floats reveal stark latitudinal gradient in the Southern Ocean deep carbon flux driven by phytoplankton community composition

The gravitational sinking of particles in the mesopelagic layer (∼200–1,000 m) transfers to the deep ocean a part of atmospheric carbon fixed by phytoplankton. This process, called the gravitational pump, exerts an important control on atmospheric CO2 levels but remains poorly characterized given the limited spatio-temporal coverage of ship-based flux measurements. Here, we examined the gravitational pump with BioGeoChemical-Argo floats in the Southern Ocean, a critically under-sampled area. Using time-series of bio-optical measurements, we characterized the concentration of particles in the productive zone, their export and transfer efficiency in the underlying mesopelagic zone, and the magnitude of sinking flux at 1,000 m. We separated float observations into six environments delineated by latitudinal fronts, sea-ice coverage, and natural iron fertilization. Results show a significant increase in the sinking-particle flux at 1,000 m with increasing latitude, despite comparable particle concentrations in the productive layer. The variability in deep flux was driven by changes in the transfer efficiency of the flux, related to the composition of the phytoplanktonic community and the size of particles, with intense flux associated with the predominance of micro-phytoplankton and large particles at the surface. We quantified the relationships between the nature of surface particles and the flux at 1,000 m and used these results to upscale our flux survey across the whole Southern Ocean using surface observations by floats and satellites. We then estimated the basin-wide Spring-Summer flux of sinking particles at 1,000 m over the Southern Ocean (0.054 ± 0.021 Pg C)

Assessing the variability in the relationship between the particulate backscattering coefficient and the chlorophyll a concentration from a global Biogeochemical-Argo database

Characterizing phytoplankton distribution and dynamics in the world's open oceans requires in situ observations over a broad range of space and time scales. In addition to temperature/salinity measurements, Biogeochemical-Argo (BGC-Argo) profiling floats are capable of autonomously observing at high frequency bio-optical properties such as the chlorophyll fluorescence, a proxy of the chlorophyll a concentration (Chla), the particulate backscattering coefficient (bbp), a proxy of the stock of particulate organic carbon, and the light available for photosynthesis. We analyzed an unprecedented BGC-Argo database of more than 8,500 multi-variable profiles collected in various oceanic conditions, from subpolar waters to subtropical gyres. Our objective is to refine previously established Chla vs bbp relationships and gain insights into the sources of vertical, seasonal and regional variability in this relationship. Despite some nuances in the relationship considering one or another water column layer or region, a general covariation occurs at a global scale. We distinguish two main contrasted situations: (1) concomitant changes in Chla and bbp that correspond to actual variations in phytoplankton biomass, e.g. in subpolar regimes; (2) a decoupling between the two variables attributed to photoacclimation or changes in the relative abundance of non-algal particles, e.g. in subtropical regimes. The variability in the bbp:Chla ratio in the surface layer appears to be essentially influenced by the type of particles and photoacclimation processes. The dense BGC-Argo database helps identifying the spatial and temporal scales at which this ratio is predominantly driven by one or the other of these two factors

Temporal evolution of plankton and particles distribution across a mesoscale front during the spring bloom

The effect of mesoscale features on the distribution of planktonic organisms are well documented. Yet, the interaction between these spatial features and the temporal scale, which can result in sudden increases of the planktonic biomass, is less known and not described at high resolution. A permanent mesoscale front in the Ligurian Sea (north-western Mediterranean) was repeatedly sampled between January and June 2021 using a SeaExplorer glider equipped with an Underwater Vision Profiler 6 (UVP6), a versatile in situ imager. Both plankton and particle distributions were resolved throughout the spring bloom to assess whether the front was a location of increased zooplankton concentration and whether it constrained particle distribution. Over the 5 months, the glider performed more than 5000 dives and the UVP6 collected 1.1 million images. We focused our analysis on shallow (300 m) transects, which gave a horizontal resolution of 900 m. About 13,000 images of planktonic organisms were retained. Ordination methods applied to particles and plankton concentrations revealed strong temporal variations during the bloom, with a succession of various zooplankton communities. Changes in particle abundance and size could be explained by changes in the plankton community. The front had a strong influence on particle distribution, while the signal was not as clear for plankton, probably because of the relatively small number of imaged organisms. This work confirms the need to sample both plankton and particles at fine scale to understand their interactions, a task for which automated in situ imaging is particularly adapted

The Second SIMBIOS Radiometric Intercomparison (SIMRIC-2), March-November 2002

The second SIMBIOS (Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies) Radiometric Intercomparison (SIMRIC-2) was carried out in 2002. The purpose of the SIMRIC's was to ensure a common radiometric scale among the calibration facilities that are engaged in calibrating in-situ radiometrics used for ocean color-related research and to document the calibration procedures and protocols. The SeaWIFS Transfer Radiometer (SXR-II) measured the calibration radiances at six wavelengths from 411nm to 777nm in the ten laboratories participating in the SIMRIC-2. The measured radiances were compared with the radiances expected by the laboratories. The agreement was within the combined uncertainties for all but two laboratories. Likely error sources were identified in these laboratories and corrective measures were implemented. NIST calibrations in December 2001 and January 2003 showed changes ranging from -0.6% to +0.7% for the six SXR-II channels. Two independent light sources were used to monitor changes in the SXR-II responsivity between the NIST calibrations. A 2% variation of the responsivity of channel 1 of the SXR-II was detected, and the SXR-II responsivity was corrected using the monitoring data. This report also compared directional reflectance calibrations of a Spectralon plaque by different calibration facilitie

Mo thio and oxo-thio molecular complexes film as self-healing catalyst for photocatalytic hydrogen evolution on 2D materials

2D semiconducting nanosheets of Transition Metal Dichalcogenides are attractive materials for solar energy conversion because of their unique absorption properties. Here, we show that Mo thio- and oxo-thio-complexes anchored on 2D p-WSe2 nanosheets considerably boost water splitting under visible light irradiation with photocurrent density up to 2.0 mA cm−2 at -0.2 V/NHE. Besides developing high electro-catalytic activity, the Mo-complexes film is also shown to be capable of healing surface defects. We propose that the observed healing of surface defects arises from the strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-, (Mo2S6O2)2- as supported by DFT calculations. In addition, the thio-, oxo-thio Mo complexes films are shown to enhance charge carrier separation and migration favouring the hydrogen evolution reaction, putting forward the use of thio-, oxo-thio-Mo complexes as a multicomponent passivation layer exhibiting multiple properties

The suspended small-particles layer in the suboxic Black Sea: a proxy for delineating the effective N<sub>2</sub>-yielding section

Abstract. Upper suboxic water masses confine a majority of the microbial communities that can produce up to 90 % of oceanic N2. This effective N2-yielding section encloses a suspended small-particle layer, inferred from particle backscattering (bbp) measurements. It is thus hypothesized that this layer (hereafter, the bbp-layer) is linked to N2-yielding microbial communities such as anammox and denitrifying bacteria – a hypothesis yet to be evaluated. Here, data collected by three BGC-Argo floats deployed in the Black Sea are used to investigate the origin of this bbp-layer. To this end, we evaluate how key drivers of anammox-denitrifying bacteria dynamics impact on the vertical distribution of bbp and the thickness of the bbp-layer. In conjunction with published data on N2 excess, our results suggest that the bbp-layer is at least partially composed of anammox-denitrifying bacteria for three main reasons: (1) strong correlations are recorded between bbp and nitrate; (2) the top location of the bbp-layer is driven by the ventilation of oxygen-rich subsurface waters, while its thickness is modulated by the amount of nitrate available to produce N2; (3) the maxima of both bbp and N2 excess coincide at the same isopycnals where denitrifying-anammox bacteria coexist. We thus advance that bbp and O2 can be exploited as a combined proxy to delineate the N2-yielding section of the Black Sea. This proxy can potentially contribute to refining delineation of the effective N2-yielding section of oxygen-deficient zones via data from the growing BGC-Argo float network

The suspended small-particle layer in the oxygen-poor Black Sea: a proxy for delineating the effective N 2 -yielding section

International audienceThe shallower oxygen-poor water masses of the ocean confine a majority of the microbial communities that can produce up to 90 % of oceanic N 2. This effective N 2yielding section encloses a suspended small-particle layer, inferred from particle backscattering (b bp) measurements. It is thus hypothesized that this layer (hereafter, the b bp-layer) is linked to microbial communities involved in N 2 yielding such as nitrate-reducing SAR11 as well as sulfur-oxidizing, anammox, and denitrifying bacteria-a hypothesis yet to be evaluated. Here, data collected by three BGC-Argo floats deployed in the Black Sea are used to investigate the origin of this b bp-layer. To this end, we evaluate how the key drivers of N 2-yielding bacteria dynamics impact the vertical distribution of b bp and the thickness of the b bp-layer. In conjunction with published data on N 2 excess, our results suggest that the b bp-layer is at least partially composed of the bacteria driving N 2 yielding for three main reasons: (1) strong correlations are recorded between b bp and nitrate; (2) the top location of the b bp-layer is driven by the ventilation of oxygen-rich subsurface waters, while its thickness is modulated by the amount of nitrate available to produce N 2 ; and (3) the maxima of both b bp and N 2 excess coincide at the same isopycnals where bacteria involved in N 2 yielding coexist. We thus advance that b bp and O 2 can be exploited as a combined proxy to delineate the N 2-yielding section of the Black Sea. This proxy can potentially contribute to refining delineation of the effective N 2-yielding section of oxygendeficient zones via data from the growing BGC-Argo float network

Particulate concentration and seasonal dynamics in the mesopelagic ocean based on the backscattering coefficient measured with Biogeochemical-Argo floats

International audienceWe explore a novel and spatially extensive data set obtained from Biogeochemical-Argo (or BGC-Argo) floats, containing 16,796 profiles of the particulate backscattering coefficient at 700 nm (b bp (700)) measured with three different sensors. We focus at the 900-950m depth interval (within the mesopelagic), where we found values to be relatively constant. While we find significant differences between estimates of b bp (700) obtained with different sensors (≈30% disagreement), the median values in most oceanic regions obtained with a single type of sensor are within 50% of each other and are consistent with measurements of suspended mass conducted in the early 1970s. Deviations from the quasi-constant background value likely indicate times and locations associated with higher particulate export to depth. Indeed, we observe that in productive high-latitude regions, a deep seasonal signal is observed, with enhanced values recorded a few months after surface spring/summer maximal concentrations. In addition, the deep b bp (700) is highest in regions exhibiting suboxic-anoxic conditions (e.g., Northern Indian Ocean), which have been associated with local particulate production as well as reduced particle flux attenuation