Marc Despinoy

Influence of upwelling, subsurface stratification, and heat fluxes on coastal sea surface temperature off southwestern New Caledonia

[1] Strong cooling events off the western barrier reef of New Caledonia have been recently observed and attributed to wind-driven coastal upwelling. A simple one-dimensional model based on a heat budget in the mixed laxer is developed and calibrated to explain the daily variations of sea surface temperature (SST) observed at a coastal station off southwestern New Caledonia from 1992 to 2005. This model takes into account the daily wind-forced vertical advection and air-sea heat fluxes, as well as seasonal variations of the subsurface temperature stratification. It can explain a large part of the daily SST variations and helps to quantify the relative contribution of the main vertical processes involved in these variations. The model shows that upwelling is the dominant process at daily timescale, and its SST signature is strongly modulated by the seasonal variations of the subsurface stratification. The surface heat fluxes have a smaller influence than upwelling on daily SST variations. Coastal chlorophyll a concentration increases during upwelling events.

Socioeconomic and environmental determinants of dengue transmission in an urban setting: An ecological study in Nouméa, New Caledonia

Background Dengue is a mosquito-borne virus that causes extensive morbidity and economic loss in many tropical and subtropical regions of the world. Often present in cities, dengue virus is rapidly spreading due to urbanization, climate change and increased human movements. Dengue cases are often heterogeneously distributed throughout cities, suggesting that small-scale determinants influence dengue urban transmission. A better understanding of these determinants is crucial to efficiently target prevention measures such as vector control and education. The aim of this study was to determine which socioeconomic and environmental determinants were associated with dengue incidence in an urban setting in the Pacific. Methodology An ecological study was performed using data summarized by neighborhood (i.e. the neighborhood is the unit of analysis) from two dengue epidemics (2008–2009 and 2012–2013) in the city of Nouméa, the capital of New Caledonia. Spatial patterns and hotspots of dengue transmission were assessed using global and local Moran’s I statistics. Multivariable negative binomial regression models were used to investigate the association between dengue incidence and various socioeconomic and environmental factors throughout the city. Principal findings The 2008–2009 epidemic was spatially structured, with clusters of high and low incidence neighborhoods. In 2012–2013, dengue incidence rates were more homogeneous throughout the city. In all models tested, higher dengue incidence rates were consistently associated with lower socioeconomic status (higher unemployment, lower revenue or higher percentage of population born in the Pacific, which are interrelated). A higher percentage of apartments was associated with lower dengue incidence rates during both epidemics in all models but one. A link between vegetation coverage and dengue incidence rates was also detected, but the link varied depending on the model used. Conclusions This study demonstrates a robust spatial association between dengue incidence rates and socioeconomic status across the different neighborhoods of the city of Nouméa. Our findings provide useful information to guide policy and help target dengue prevention efforts where they are needed most.

Regolith-geology mapping with support vector machine: A case study over weathered Ni-bearing peridotites, New Caledonia

Abstract Accurate maps of Earth’s geology, especially its regolith, are required for managing the sustainable exploration and development of mineral resources. This paper shows how airborne imaging hyperspectral data collected over weathered peridotite rocks in vegetated, mountainous terrane in New Caledonia were processed using a combination of methods to generate a regolith-geology map that could be used for more efficiently targeting Ni exploration. The image processing combined two usual methods, which are spectral feature extraction and support vector machine (SVM). This rationale being the spectral features extraction can rapidly reduce data complexity by both targeting only the diagnostic mineral absorptions and masking those pixels complicated by vegetation, cloud and deep shade. SVM is a supervised classification method able to generate an optimal non-linear classifier with these features that generalises well even with limited training data. Key minerals targeted are serpentine, which is considered as an indicator for hydrolysed peridotitic rock, and iron oxy-hydroxides (hematite and goethite), which are considered as diagnostic of laterite development. The final classified regolith map was assessed against interpreted regolith field sites, which yielded approximately 70% similarity for all unit types, as well as against a regolith-geology map interpreted using traditional datasets (not hyperspectral imagery). Importantly, the hyperspectral derived mineral map provided much greater detail enabling a more precise understanding of the regolith-geological architecture where there are exposed soils and rocks.

Wildfire risk for main vegetation units in a biodiversity hotspot: modeling approach in New Caledonia, South Pacific.

Wildfire has been recognized as one of the most ubiquitous disturbance agents to impact on natural environments. In this study, our main objective was to propose a modeling approach to investigate the potential impact of wildfire on biodiversity. The method is illustrated with an application example in New Caledonia where conservation and sustainable biodiversity management represent an important challenge. Firstly, a biodiversity loss index, including the diversity and the vulnerability indexes, was calculated for every vegetation unit in New Caledonia and mapped according to its distribution over the New Caledonian mainland. Then, based on spatially explicit fire behavior simulations (using the FLAMMAP software) and fire ignition probabilities, two original fire risk assessment approaches were proposed: a one-off event model and a multi-event burn probability model. The spatial distribution of fire risk across New Caledonia was similar for both indices with very small localized spots having high risk. The patterns relating to highest risk are all located around the remaining sclerophyll forest fragments and are representing 0.012% of the mainland surface. A small part of maquis and areas adjacent to dense humid forest on ultramafic substrates should also be monitored. Vegetation interfaces between secondary and primary units displayed high risk and should represent priority zones for fire effects mitigation. Low fire ignition probability in anthropogenic-free areas decreases drastically the risk. A one-off event associated risk allowed localizing of the most likely ignition areas with potential for extensive damage. Emergency actions could aim limiting specific fire spread known to have high impact or consist of on targeting high risk areas to limit one-off fire ignitions. Spatially explicit information on burning probability is necessary for setting strategic fire and fuel management planning. Both risk indices provide clues to preserve New Caledonia hot spot of biodiversity facing wildfires.

Monitoring optical properties of the southwest tropical Pacific

We present data collected as part of ValHyBio- VALidation HYperspectral of a BIOgeochemical model in the South Western Tropical Lagoon of New Caledonia, a PNTS-sponsored program dedicated to chlorophyll satellite imaging and validation as affected by bathymetry. The specific goals of ValHyBio are to: - examine time-dependent oceanic reflectance in relation to dynamic surface processes, - construct field/satellite reflectance-based chlorophyll models, - investigate the feasibility of inverting the model to yield surface chlorophyll and turbidity, - validate the biogeochemical model with field/satellite observations. In situ bio-optical parameters include absorption coefficients by CDOM and particles, Secchi disk depth, backscattering coefficient, pigment concentration, suspended matter concentration, and K_dPAR. They are measured every month at 5 stations, of contrasted bathymetry and bottom reflectance, as well as at a reference station situated 4 miles offshore, and on a station over coral reefs. Remote sensing reflectance is calculated from the absorption and backscattering coefficients and compared with satellite data. SeaWIFS and MODIS AQUA match-ups collected over the period 1997-2010 (ValHySat-VALidation HYperspectral SATellite database) are used. Satellite retrievals are examined as a function of bathymetry. The feasibility of a longterm monitoring program of optical water retrieval with satellite remote sensing technique is examined in the frame of the GOPS (South Pacific Integrated Observatory).

A spatially explicit integrative model for estimating the risk of wildfire impacts in New-Caledonia

ABSTRACT In this study, we present a spatially explicit bayesian model which is able to predict the distribution of potential fire ignition at a grid resolution of over the entire main island of New-Caledonia. This statistical model, when used in conjunction with a mechanistic fire model (FlamMap), is able to estimate the comparative and spatialized risk of fire impact on specific areas for specific issues such as biodiversity or erosion. The input data includes variables related to the physical environment such as the topography, climate, and some geographical indicators relating to human influences such as population density and type of land property. Flowchart computation for the specific cell i. The grey rectangles denote the input data, the trapezoids denote the intermediate indices and the rounded corners rectangles denote the integrated wildfire risk indices. The connection legends indicates the corresponding equations and below certain nodes a drawing describes an example related to the main variables and the associated area used. Graphical Abstract

Mapping of the Regolith of New Caledonia with Airborne Hyperspectral Remote Sensing

Recently, regolith mapping based on hyperspectral remote sensing has stirred up a growing interest, in particular for mining exploration purposes. For an island like New Caledonia, which nickel resources are one of the most abundant on Earth, and which economy is mainly based on nickel exploitation, regolith mapping is of first interest. In 2010 airborne hyperspectral remote sensing data were acquired for the first time over several mining sites of New Caledonia. At the same time, field spectrometradiometric measurements were made on the same sites. One site was selected to evaluate the potential of airborne hyperspectral remote sensing for the mapping of the regolith. Combining the analysis of the field measurements and the processing of the airborne data, we managed to map the regolith with great results. In the following we present broadly the geological context of New Caledonia, the dataset acquired, the method developped and the results.