Cécile Dupouy

• PhD, HDR
• Chargée de recherche Hors Classe at Institute of Research for Development

The oceanic waters of the Southwest Tropical Pacific occupy a vast region including multiple Pacific Island Countries. The state of these waters is determinant for fisheries and the blue economy. Ocean color remote sensing is the main tool to survey the variability and long-term evolution of these large areas that are important for economic develop...

Marine diazotrophs convert dinitrogen (N2) gas into bioavailable nitrogen (N), supporting life in the global ocean. In 2012, the first version of the global oceanic diazotroph database (version 1) was published. Here, we present an updated version of the database (version 2), significantly increasing the number of in situ diazotrophic measurements...

La chlorophylle de surface observée par le satellite NIMBUS-7 dans une zone d'archipel (Nouvelle-Calédonie et Vanuatu). Une première analyse par CÉCILE DUPOUY Institut français de recherche scientifique pour le développement en coopération (OR5TOM) Centre OR5TOM B.P. AS, Nouméa (Nouvelle-Calédonie) RESUME

A powerful eruption within the Hunga Tonga-Hunga Ha’apai (HTHH) volcano (20.64°S, 175.19°W) in the Kingdom of Tonga, occurred on 15 January 2022. The volcanic blast was enormous, leading many scientists to investigate the full impact and magnitude of this event via satellite observations. In this study, we describe a new ocean color signature from...

The Copernicus Ocean State Report is an annual publication of the Copernicus Marine Service, established in 2014 by the European Commission for Copernicus 1 and renewed in 2021 for Copernicus 2. The report provides a comprehensive, state-of-the-art, scientific overview on the current conditions, natural variations, and ongoing changes in the global...

The photosynthetic cyanobacterium Trichodesmium is widely distributed in the surface low latitude ocean where it contributes significantly to N2 fixation and primary productivity. Previous studies found nifH genes and intact Trichodesmium colonies in the sunlight-deprived meso- and bathypelagic layers of the ocean (200–4000 m depth). Yet, the abili...

Monitoring chlorophyll-a concentration or turbidity is crucial for understanding and managing oligo- to mesotrophic coastal waters quality. However, mapping bio-optical components from space in such shallow settings remains challenging because of the strong interference of the complex bathymetry and various seabed colors. Correcting the total satel...

Contributions of filamentous and picoplanktonic cyanobacteria to the phytoplankton community structure were examined in New Caledonian waters during the 2001-2003 El Niño period at 2 ocean stations (Loyalty Channel and Santal Bay) and 1 coral-reef lagoon station (Ouinne). Morphometric characteristics of diazotrophic filamentous cyanobacteria are gi...

Rare earth elements (REEs) and Y, or REYs, are commonly used as geochemical proxies for water chemistry, history of the continental crust and provenance studies. At the continent-ocean interface, the estuarine geochemistry of REYs is commonly thought to be driven by large-scale removal of the dissolved fraction. Consequently, contributions of river...

Heavy rain events alter the biogeochemical outflows, affects water quality and ecosystem health within the coastal waters of small Pacific Islands. We characterized snapshots of the optical fingerprints of dissolved organic matter (DOM) sources together with the select nutrients, biogeochemical and physical variables for 10 stations in December 201...

An underwater volcanic eruption off the Vava’u island group in Tonga on 7 August 2019 resulted in the creation of floating pumice on the ocean’s surface extending over an area of 150 km2. The pumice’s far-reaching effects from its origin in the Tonga region to Fiji and the methods of automatic detection using satellite imagery are described, making...

Coastal and open ocean regions of the Western Tropical South Pacific ocean have been identified as a hotspot of N2 fixation. However, the environmental factors driving the temporal variability of abundance, composition, and activity of diazotrophs are still poorly understood, especially during the winter season. To address this, we quantified N2 fi...

Multispectral and hyperspectral sensor data of the bio-optical parameters with a high spatial resolution are important for monitoring and mapping of the coastal ecosystems and estuarine areas, such as the Kneiss Islands in the Gulf of Gabes. Sentinel 2 S2A and Hyperion Earth observing-1 (EO1) imaging sensors reflectance data have been used for wate...

New Caledonia (Southwest Pacific), like all tropical Pacific Island countries, is impacted by weather events, climate change, and local anthropogenic forcing. Strong erosion of particles and dissolved organic matter (DOM) from ultramafic rocks, associated with trace metals dissemination (i.e., nickel, manganese and cobalt), potentially affects lago...

Workshop "Au fil de l'eau", Nouméa, NCL, 17-/09/2019 - 18/09/2019

Workshop "Au fil de l'eau", Nouméa, NCL, 17-/09/2019 - 18/09/2019

Fiji served as President of the UN General Assembly in 2017, linking climate (SDG13) and ocean (SDG14) as the foundation of blue economies for island and coastal states around the world. The resulting United Nations Oceans outcome statement stressed “the importance of enhancing understanding of the health and role of our ocean and the stressors on...

Chla, MES, CDOM, DOC and FDOM distributions were characterized to nutrients TOC, particulate absorption coefficients and TOC via flow cytometry and TRIOS(reflectance) from surveys within the Laucala Bay in the Fiji waters. The goal is to combine satellite measurements and a series of in-situ measurements in a variety of tropical lagoons to establis...

We assessed the influence of the marine diazotrophic cyanobacterium Trichodesmium on the bio-optical properties of western tropical South Pacific (WTSP) waters (18–22∘ S, 160∘ E–160∘ W) during the February–March 2015 OUTPACE cruise. We performed measurements of backscattering and absorption coefficients, irradiance, and radiance in the euphotic zon...

Trichodesmium is the major nitrogen-fixing species in the western tropical South Pacific (WTSP) region, a hot spot of diazotrophy. Due to the paucity of in situ observations, remote-sensing methods for detecting Trichodesmium presence on a large scale have been investigated to assess the regional-to-global impact of this organism on primary product...

Dinitrogen fixation is now recognized as one of the major sources of bio-available nitrogen in the ocean. Thus, N2 fixation sustains a significant part of the global primary production by supplying the most common limiting nutrient for phytoplankton growth. The “Oligotrophy to UlTra-oligotrophy PACific Experiment” (OUTPACE) improved the data covera...

The Eastern Lagoon of New Caledonia (ELNC) is a semi-enclosed system surrounded by an extensive coral reef barrier. The system has been suffering impacts from climate variability and anthropogenic activities, including mining exploitation. Satellite monitoring is thus an essential tool to detect such changes. The present study aimed to assess the b...

The fate of diazotroph (N2 fixers) derived carbon (C) and nitrogen (N) and their contribution to vertical export of C and N in the western tropical South Pacific Ocean was studied during OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment). Our specific objective during OUTPACE was to determine whether autocatalytic programmed cell death (...

Contributions of filamentous and picoplanktonic cyanobacteria to the phytoplankton community structure were examined in New Caledonian waters during the 2001-2003 El Niño period at 2 ocean stations (Loyalty Channel and Santal Bay) and 1 coral-reef lagoon station (Ouinne). Morphometric characteristics of diazotrophic filamentous cyanobacteria are gi...

Heterotrophic prokaryotic production (BP) was studied in the western tropical South Pacific (WTSP) using the leucine technique, revealing spatial and temporal variability within the region. Integrated over the euphotic zone, BP ranged from 58 to 120 mg C m-2 d-1 within the Melanesian Archipelago, and from 31 to 50 mg C m-2 d-1 within the western su...

Contributions of filamentous and picoplanktonic cyanobacteria to the phytoplankton community structure were examined in New Caledonian waters during the 2001−2003 El Niño period at 2 ocean stations (Loyalty Channel and Santal Bay) and 1 coral-reef lagoon station (Ouinne). Morphometric characteristics of diazotrophic filamentous cyanobacteria are gi...

Specialized prokaryotes performing biological dinitrogen (N2) fixation (“diazotrophs”) provide an important source of fixed nitrogen in oligotrophic marine ecosystems such as tropical and subtropical oceans. In these waters, cyanobacterial photosynthetic diazotrophs are well known to be abundant and active, yet the role and contribution of non-cyan...

We assessed the influence of the marine diazotrophic cyanobacterium Trichodesmium on the bio-optical properties of South West tropical Pacific waters (18–22° S, 160° E–160° W) during the February–March 2015 OUTPACE cruise. We performed measurements of backscattering and absorption coefficients, irradiance, and radiance, in the euphotic zone, and to...

Dinitrogen fixation is now recognized as one of the major sources of bio-available nitrogen in the ocean. Thus, nitrogen fixation sustains a significant part of the global primary production by providing an input of the most common limiting nutrient for phytoplankton growth. Evidences of the Western Tropical South Pacific being a hotspot of nitroge...

The fate of diazotroph (N2 fixers) derived carbon (C) and nitrogen (N) and their contribution to vertical export of C and N in the Western Tropical South Pacific Ocean was studied in OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment). Our specific objective during OUTPACE was to determine whether autocatalytic programmed cell death (PCD)...

Heterotrophic prokaryotic production (BP) was studied in the Western Tropical South Pacific using the leucine technique. Integrated over the euphotic zone, BP ranged from 58–120 mg C m−2 d−1 within the Melanesian Archipelago, and from 31–50 mg C m−2 within the subtropical gyre. Nitrogen was often one of the main factor controlling BP on short time...

Trichodesmium is the main nitrogen-fixing species in the South Pacific region, a hotspot for diazotrophy. Due to the paucity of in situ observations, methods for detecting Trichodesmium presence on a large scale have been investigated to assess the regional-to-global impact of these species on primary production and carbon cycling. A number of sate...

The eastern lagoon of New Caledonia (NC, Southwest Pacific), listed as a UNESCO World Heritage site, hosts the world's second longest double-barrier coral reef. This lagoon receives river inputs, oceanic water arrivals, and erosion pressure from ultramafic rocks, enriched in nickel (Ni) and cobalt (Co). The aim of this study was to characterize col...

Shortly after strong rains or tropical storms, chlorophyll-a concentration (Chla), turbidity, and colored dissolved organic matter (CDOM) in the lagoon of New Caledonia may be tripled. This effect is visible as far as 50 km offshore. The Eastern Coast of New Caledonia is more impacted than the Western Coast because of its geomorphological structure...

We assessed the influence of the marine dia-zotrophic cyanobacterium Trichodesmium on the bio-optical properties of western tropical South Pacific (WTSP) waters (18-22 • S, 160 • E-160 • W) during the February-March 2015 OUTPACE cruise. We performed measurements of backscattering and absorption coefficients, irradiance, and radiance in the euphotic...

The use of supervised learning for modeling biogeochemical parameters provides promising results. This presentation highlights why this method is very helpful in oligotrophic lagoons such as in New Caledonia. It provides two examples of implementation with chlorophyll-a concentration and turbidity assessment.

Particle transport by erosion from ultramafic lands in pristine tropical lagoons is a crucial problem, especially for the benthic and pelagic biodiversity associated with coral reefs. Satellite imagery is useful for assessing particle transport from land to sea. However, in the oligotrophic and shallow waters of tropical lagoons, the bottom reflect...

The New Caledonia lagoon (South Pacific Ocean) health is of prime importance to local island populations for food picking, local fisheries, water renewal and transport, recreation activities, and it includes zones classified with the Heritage of UNESCO. High run offs due to rain carrying abundant colored dissloved organic matter(CDOM) and particle...

In the framework of the VAHINE project, we investigated the spectral characteristics and the variability of dissolved and particulate chromophoric materials throughout a 23-day mesocosm experiment conducted in the south-west Pacific at the mouth of the New Caledonian coral lagoon (22°29.073 S–166°26.905 E) from 13 January to 4 February 2013. Sample...

Spatial and temporal dynamics of phytoplankton biomass and water turbidity can provide crucial information about the function, health and vulnerability of lagoon ecosystems (coral reefs, sea grasses, etc.). A statistical algorithm is proposed to estimate chlorophyll-a concentration ([chl-a]) in optically complex waters of the New Caledonian lagoon...

The accurate determination of light absorption coefficients of particles in water, especially in very oligotrophic oceanic areas, is still a challenging task. Concentrating aquatic particles on a glass fiber filter and using the Quantitative Filter Technique (QFT) is a common practice. Its routine application is limited by the necessary use of high...

In the framework of the VAHINE project, we investigated the spectral characteristics and the variability of dissolved and particulate chromophoric materials throughout a 23 day mesocosm experiment conducted in the South West Pacific at the exit of the New Caledonian coral lagoon (22°29.073 S–166°26.905 E) from 13 January to 4 February 2013. Samples...

The giant clam Tridacna maxima presents a strong potential for paleoclimatic reconstructions but its use remains limited by the fact that the relationship between the shell stable oxygen isotopes ratio (δ 18Oshell), the sea surface temperature (SST), and the stable oxygen isotopes ratio of seawater (δ 18Osw) has not been calibrated yet. In this stu...

Biogenic dissolution of carbonates by microborers (or microbioerosion) is one of the main destructive forces in coral reefs. This process seems to be enhanced by eutrophication and ocean acidification and the chlorophyte Ostreobium sp., the main agent of this process, appears as the most responsive microboring species to those environmental factors...

We propose a statistical algorithm to assess chlorophyll-a concentration ([chl-a]) using remote sensing reflectance (Rrs) derived from MODerate Resolution Imaging Spectroradiometer (MODIS) data. This algorithm is a combination of two models: one for low [chl-a] (oligotrophic waters) and one for high [chl-a]. A satellite pixel is classified as low o...

In recent years great progress has been made in global mapping of phytoplankton from space. Two main trends have emerged, the recognition of phytoplankton functional types (PFT) based on reflectance normalized to chlorophyll-a concentration, and the recognition of phytoplankton size class (PSC) based on the relationship between cell size and chloro...

Ocean color of tropical lagoons is dependent on bathymetry and bottom type, as well as input of coastal living and mineral particles and chromophoric dissolved organic matter (CDOM). The New Caledonia lagoon lies in the Southwestern Tropical Pacific around 21° 30’S and 166° 30’E, with a great marine biodiversity in UNESCO Heritage coral reefs, bent...

The extent of light absorption in the near-infrared spectral region (NIR; 700–900 nm) of natural suspended particles was investigated by determining the absorption and mass-specific absorption coefficients of samples from different environments: river, coastal waters, tropical lagoon, and oceanic waters. Large amounts of sample were collected onto...

Features on the seabed can be mapped from remote sensing multi/hyperspectral imagery, provided that their effects on the measured reflectance spectrum can be made independent of those produced by the atmosphere and water column. The nonlinear effect of water column light attenuation can then be corrected to obtain the absolute reflectance of the se...

The SPOT station (168°E-20°S,-4500 m) is a recent deep-sea and multidisciplinary marine research observation station which objective is the establishment of the first long time series of basic parameters in the South West Pacific. The main studies concerns the biodiversity, the productivity of key Plankton Functional Types, the biogeochemistry of c...

The Coral Sea, located at the southwestern rim of the Pacific Ocean, is the only tropical marginal sea where human impacts remain relatively minor. Patterns and processes identified within the region have global relevance as a baseline for understanding impacts in more disturbed tropical locations. Despite 70 years of documented research, the Coral...

Retrievals of inherent optical properties (IOPs) and chlorophyll-a concentration (Chla) were investigated for AVNIR-2 images with 30 m spatial resolution and four bands in the southwest tropical lagoon of New Caledonia. We corrected the atmospheric and sea-surface reflectance iteratively through the retrieval of IOPs. After an additional correction...

Hyperspectral remote sensing reflectance (Rrs) was measured by a TriOS radiometer system along the East Coast of New Caledonia during the R/V Alis 03-13 October 2011 CALIOPE cruise. The TriOS system consists of radiance and irradiance sensors measuring in the spectral range 320-950 nm, at a spectral resolution of about 10 nm (sampled by every 3.3 n...

Optical remote sensing was used to provide scientific information to support environmental management in the Gulf of Gabes located on the southeastern coast of Tunisia. This region is characterized by a shallow continental shelf with semi-diurnal tides. Since the early 1970s, industrial activity in this area may have contributed to the degradation...

Satellite and in situ chlorophyll concentration data collected as part of VALidation HYperspectral of a BIOgeochemical model (ValHyBio), a PNTS-sponsored project dedicated to satellite ocean-colour imaging of the Southwest Pacific, are analyzed to describe chlorophyll variability in the Coral Sea, a vast oligotrophic region characterized by a deep...

An estimation of bathymetry in the optically complex lagoon of New Caledonia was performed from the spectroradiometer MeRIS satellite sensor. Bathymetric estimation was obtained with different MeRIS images acquired at different dates. The method is based on the rotation of a pair of spectral bands. One of the resulting images is depth-dependent. A...

Trichodesmium, a major colonial cyanobacterial nitrogen fixer, forms large blooms in NO3-depleted tropical oceans and enhances CO2 sequestration by the ocean due to its ability to fix dissolved dinitrogen. Thus, its importance in C and N cycles requires better estimates of its distribution at basin to global scales. However, existing algorithms to...

The retrieval of chlorophyll-a concentration from remote sensing reflectance (Rrs) data was tested with the NASA OC4v4 algorithm on the inner New Caledonian lagoon (Case 2) and adjacent open ocean (Case 1) waters. The input to OC4v4 was Rrs measured in situ or modeled from water's inherent optical properties (2001-2007). At open ocean stations, bac...

The upwelling events that follow strong trade wind episodes have been described in terms of their remarkable signature in the sea surface temperature southwest off New Caledonia. Upwelling brings deeper, and colder waters to the surface, causing 2-4 degrees C drops in temperature in a few hours, followed by a slower relaxation over several days. Up...

We present data collected as part of VALidation HYperspectral of a BIOgeochemical model (ValHyBio), a PNTS-sponsored program dedicated to chlorophyll satellite imaging and validation as affected by bathymetry in the South Western Tropical Lagoon of New Caledonia. The specific goals of ValHyBio are to: - examine time-dependent oceanic reflectance in...

Coastal ocean-color estimation needs to retrieve not only molecular and aerosol scattering (rhoa), but also high spatial resolution sea-surface reflectance (rhoa) because rhog has fine temporal and spatial scales due to variable winds and air-sea stability caused by the coastal geographical structure. Murakami and Frouin 2008 showed a possibility o...

The major part of the New Caledonia (NC) lagoon was classified as UNESCO Natural Site of Humanity Patrimony. Indeed, 22 175 km2 of tropical coral lagoon area exhibit high biodiversity. The NC lagoon is semi enclosed and connected to the Coral Sea through a barrier reef segmented by narrow passes. The environment is oligotrophic, due to important fl...

No map of the sea floor is available yet on the whole lagoon of New Caledonia. We tried to validate a method to map it with MeRIS images on the south western part of the lagoon. The non-linear effect of water column light attenuation can then be corrected to obtain the absolute reflectance of the seabed. Light attenuation by the water column can be...

During the Echolag cruise (13 February-8 March 2007), the effect of 16-30 knot trade winds on abundance, community structure and dynamics of phytoplankton was investigated in the southern part of the New Caledonian coral reefs and surrounding oceanic waters. In this area, the coral reefs form two horn-like structures (hereinafter referred to as 'ho...

Features on the sea bed can be mapped from remote sensing multi/superspectral imagery provided that their effects on the measured reflectance spectrum can be rendered independent of those produced by the atmosphere and water column. The non-linear effect of water column light attenuation can then be corrected to obtain the absolute reflectance of t...