Combined processing and mutual interpretation of radiometry and fluorimetry from autonomous profiling Bio-Argo floats: Chlorophyll<i>a</i>retrieval

Xing, Xiaogang; Morel, A.; Claustre, Hervé; Antoine, David; D’Ortenzio, Fabrizio; Poteau, Antoine; Mignot, Alexandre

doi:10.1029/2010jc006899

Cited by 103 publications

(134 citation statements)

References 34 publications

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“…For other platforms than elephant seals (e.g., floats) where the implementation of radiometers is possible (and much easier), calibration methods that are synergistically using both measurements (Chla fluorescence and radiometry) can be developed (e.g., Xing et al 2011). These methods are based on robust global bio-optical relationships that allow establishing calibration coefficients that are pertinent over the platform lifetime .…”

Section: Discussionmentioning

confidence: 99%

“…Note that the method proposed by Xing et al (2011) relying on global bio-optical relationship is also a way to guarantee a coherence of the Chl a database through different fluorometers carried by different platforms. Recently a method was also proposed (Lavigne et al 2012) to make use of the Chl a concentration remotely detected through ocean color satellite as a reference value for establishing a calibration factor for the fluorescence profile co-located with the satellite measurement.…”

Section: Discussionmentioning

confidence: 99%

“…The calibration coefficients include the offset of the instrument (the so-called dark current) and a conversion factor. Nevertheless, these calibrations are generally established for a large range of Chl a concentrations, generally not representative of in situ conditions (see also Xing et al 2011). They can thus be considered only as a first guess of the actual fluorescence response to Chl a concentration.…”

Section: Fluorometer Descriptionmentioning

confidence: 99%

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Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)

Xing

Claustre

Blain

et al. 2012

Limnology & Ocean Methods

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It is recognized that open ocean properties, especially biological ones, are chronically undersampled. During the last decade, thanks to the emergence of sea glider and profiling float technology, the density of observations has nevertheless been drastically increased, especially for the description of temperature and salinity fields. However, most of the research conducted to date using this new technology has remained restricted to 60°N-60°S (e.g., Argo program). In order to develop observational capabilities in harsh polar conditions, the use of animals as an alternative platform has been progressively tested and proved to be efficient. This new field of biologging was made possible thanks to recent progress in microelectronics, miniaturization, and satellite telemetry. While the first objective was to provide a host of new information for biologists, the idea of simultaneously gathering oceanographic parameters has naturally emerged. A synergy between biologist's efforts to understand the marine life and physical oceanographic studies became possible in the early 2000s with the development of satellite-relay biologging devices incorporating high-accuracy oceanographic sensors. These Satellite Relay Data Loggers (SRDLs) were developed at the Sea Mammal Research Unit (SMRU-UK) and provide fundamental information not only for biologists, but also for oceanographers in the form of vertical profiles of temperature and salinity using a miniaturized conductivity-temperature-depth (CTD) cell (Fedak 2004;Charrassin et al. 2008 , and Christophe Guinet AbstractAs the proxy for Chlorophyll a (Chl a) concentration, thousands of fluorescence profiles were measured by instrumented elephant seals in the Kerguelen region (Southern Ocean). For accurate retrieval of Chl a concentrations acquired by in vivo fluorometer, a two-step procedure is applied: 1) A predeployment intercalibration with accurate determination by high performance liquid chromatography (HPLC) analysis, which not only calibrates fluorescence in appropriate Chl a concentration units, but also strongly reduces variability between fluorometers, and 2) a profile-by-profile quenching correction analysis, which effectively eliminates the fluorescence quenching issue at surface around noon, and results in consistent profiles between day and night. The quenching correction is conducted through an extrapolation of the deep fluorescence value toward surface. As proved by a validation procedure in the Western Mediterranean Sea, the correction method is practical and relatively reliable when there is no credible reference, especially for deep mixed waters, as in the Southern Ocean. Even in the shallow mixed waters, the method is also effective in reducing the influence of quenching.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Fluorometer Descriptionmentioning

confidence: 99%

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Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)

Xing

Claustre

Blain

et al. 2012

Limnology & Ocean Methods

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145

170

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“…The common procedure to convert a fluorescence profile (FLUO) into Chl a C (Boss et al, 2008;Cetinic et al, 2009;Xing et al, 2011) can be formalised by…”

Section: Overviewmentioning

confidence: 99%

“…simultaneous irradiance profiles, Xing et al, 2011), on the shape of fluorescence profile or on satellite ocean colour Chl a C observations (Boss et al, 2008). The last method (Boss et al, 2008), although developed to correct a profiling float fluorometer, also points to a reliable way to merge fluorescence profiles and satellite observations.…”

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confidence: 99%

Towards a merged satellite and in situ fluorescence ocean chlorophyll product

et al. 2012

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Abstract. Understanding the ocean carbon cycle requires a precise assessment of phytoplankton biomass in the oceans. In terms of numbers of observations, satellite data represent the largest available data set. However, as they are limited to surface waters, they have to be merged with in situ observations. Amongst the in situ data, fluorescence profiles constitute the greatest data set available, because fluorometers have operated routinely on oceanographic cruises since the 1970s. Nevertheless, fluorescence is only a proxy of the total chlorophyll a concentration and a data calibration is required. Calibration issues are, however, sources of uncertainty, and they have prevented a systematic and wide range exploitation of the fluorescence data set. In particular, very few attempts to standardize the fluorescence databases have been made. Consequently, merged estimations with other data sources (e.g. satellite) are lacking.We propose a merging method to fill this gap. It consists firstly in adjusting the fluorescence profile to impose a zero chlorophyll a concentration at depth. Secondly, each point of the fluorescence profile is then multiplied by a correction coefficient, which forces the chlorophyll a integrated content measured on the fluorescence profile to be consistent with the concomitant ocean colour observation. The method is close to the approach proposed by Boss et al. (2008) to correct fluorescence data of a profiling float, although important differences do exist. To develop and test our approach, in situ data from three open ocean stations (BATS, HOT and DYFAMED) were used. Comparison of the socalled "satellite-corrected" fluorescence profiles with concomitant bottle-derived estimations of chlorophyll a concentration was performed to evaluate the final error (estimated at 31 %). Comparison with the Boss et al. (2008) method, using a subset of the DYFAMED data set, demonstrated that the methods have similar accuracy. The method was applied to two different data sets to demonstrate its utility. Using fluorescence profiles at BATS, we show that the integration of "satellite-corrected" fluorescence profiles in chlorophyll a climatologies could improve both the statistical relevance of chlorophyll a averages and the vertical structure of the chlorophyll a field. We also show that our method could be efficiently used to process, within near-real time, profiles obtained by a fluorometer deployed on autonomous platforms, in our case a bio-optical profiling float. The application of the proposed method should provide a first step towards the generation of a merged satellite/fluorescence chlorophyll a product, as the "satellite-corrected" profiles should then be consistent with satellite observations. Improved climatologies with more consistent satellite and in situ data are likely to enhance the performance of present biogeochemical models.

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Understanding the seasonal dynamics of phytoplankton biomass and the deep chlorophyll maximum in oligotrophic environments: A Bio‐Argo float investigation

Mignot

Claustre

Uitz

et al. 2014

Global Biogeochemical Cycles

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We deployed four Bio-Argo profiling floats in various oligotrophic locations of the Pacific subtropical gyres and Mediterranean Sea to address the seasonal phytoplankton dynamics in the euphotic layer and explore its dependence on light regime dynamics. Results show that there is a similar phytoplankton biomass seasonal pattern in the four observed oceanic regions. In the lower part of the euphotic layer, the seasonal displacement of the deep chlorophyll maximum (DCM) is light driven. During winter, the chlorophyll a concentration ([Chl a]) always increases in the upper euphotic mixed layer. This increase always results from a photoacclimation to the reduced irradiance. Depending on the location, however, the concentration can also be associated with an actual increase in biomass. The winter increase in [Chl a] results in an increase in irradiance attenuation that impacts the position of the isolume (level where the daily integrated photon flux is constant) and DCM, which becomes shallower. In summer when the [Chl a] in the upper layer decreases along with light attenuation, the DCM deepens and becomes closer to (and sometimes reaches) the nitracline, which enhances the phytoplankton biomass at the DCM. The bio-optical mechanisms and their relationship to light regimes that are revealed by the time series appear to be generic and potentially characteristic of all of the areas where a DCM forms, which is 50% of the open ocean.

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Combined processing and mutual interpretation of radiometry and fluorimetry from autonomous profiling Bio-Argo floats: Chlorophyllaretrieval

Cited by 103 publications

References 34 publications

Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)

Quenching correction for in vivo chlorophyll fluorescence acquired by autonomous platforms: A case study with instrumented elephant seals in the Kerguelen region (Southern Ocean)

Towards a merged satellite and in situ fluorescence ocean chlorophyll product

Understanding the seasonal dynamics of phytoplankton biomass and the deep chlorophyll maximum in oligotrophic environments: A Bio‐Argo float investigation

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