Jean-Michel Fernandez

Circulation and suspended sediment transport in a coral reef lagoon: The south-west lagoon of New Caledonia

The south-west lagoon of New Caledonia is a wide semi-open coral reef lagoon bounded by an intertidal barrier reef and bisected by numerous deep inlets. This paper synthesizes findings from the 2000-2008 French National Program EC2CO-PNEC relative to the circulation and the transport of suspended particles in this lagoon. Numerical model development (hydrodynamic, fine suspended sediment transport, wind-wave, small-scale atmospheric circulation) allowed the determination of circulation patterns in the lagoon and the charting of residence time, the later of which has been recently used in a series of ecological studies. Topical studies based on field measurements permitted the parameterisation of wave set-up induced by the swell breaking on the reef barrier and the validation of a wind-wave model in a fetch-limited environment. The analysis of spatial and temporal variability of suspended matter concentration over short and long time-scales, the measurement of grain size distribution and the density of suspended matter (1.27 kg l(-1)), and the estimation of erodibility of heterogeneous (sand/mud, terrigenous/biogenic) soft bottoms was also conducted. Aggregates were shown to be more abundant near or around reefs and a possible biological influence on this aggregation is discussed. Optical measurements enabled the quantification of suspended matter either in situ (monochromatic measurements) or remotely (surface spectral measurements and satellite observations) and provided indirect calibration and validation of a suspended sediment transport model. The processes that warrant further investigation in order to improve our knowledge of circulation and suspended sediment transport in the New Caledonia lagoon as well as in other coral reef areas are discussed, as are the relevance and reliability of the numerical models for this endeavour.

Benthic foraminifera records of complex anthropogenic environmental changes combined with geochemical data in a tropical bay of New Caledonia (SW Pacific).

During the 1950s, open-cast mining led to an increasing input of heavy-metal-rich terrigenous particles in the bays near Nouméa, detected by geochemical and sedimentological analyses. Even though most of terrigenous metal is unavailable, an impact on the benthos was suspected. Simultaneously, the population of Nouméa increased dramatically, which may impact the neighboring bays. Foraminifera were used for assessing this double impact. Thirteen surface samples were collected as a basis for the interpretation of 27 samples from a 54 cm long core. Paradoxically, the general trends in foraminiferal assemblages with time were consistent with a decreasing impact of pollution and continental influence (e.g., increasing species richness, diversity, density, and decreasing percentages of Ammonia tepida). Explanations were found in the urban planning that led to a decrease of freshwater and pollutant inputs. Multiple and contradictory impacts of anthropic activities could be assessed only by a set of complementary tools (i.e., geochemistry and bioindicators).