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Publication MIO : Chloé Martias (MIO), Marc Tedetti (MIO), François Lantoine, Léocadie Jamet, Cécile Dupouy (MIO) - Characterization and sources of colored dissolved organic matter in a coral reef ecosystem subject to ultramafic erosion pressure (New Caledonia, Southwest Pacific) in Science of the Total Environment

Version imprimable de cet article

Article history :
Received 3 September 2017
Received in revised form 23 October 2017
Accepted 24 October 2017

Abstract

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 char- acterize colored dissolved organic matter (CDOM), as well as to determine its main sources and its possible rela- tionships (through the use of Pearson correlation coefficients, r) with biogeochemical parameters, plankton communities and trace metals in the NC eastern lagoon. Water samples were collected in March 2016 along a se- ries of river/lagoon/open-ocean transects. The absorption coefficient at 350 nm (a350) revealed the influence of river inputs on the CDOM distribution. The high values of spectral slope (S275–295, N 0.03 m−1) and the low values of specific ultraviolet absorbance (SUVA254, b 4 L mg-C−1 m−1) highlighted the photodegradation of CDOM in surface waters. The application of parallel factor analysis (PARAFAC) on excitation-emission matrices (EEMs) allowed the identification of four CDOM components : (1) one humic- and one tyrosine-like fluorophores. They had terrestrial origin, exported through rivers and undergoing photo- and bio-degradation in the lagoon. These two fluorophores were linked to manganese (Mn) in southern rivers (r = 0.46–0.50, n = 21, p b 0.05). (2) A tryptophan-like fluorophore, which exhibited higher levels offshore. It would be potentially released from the coral reef. (3) A second tyrosine-like (“tyrosine 2-like”) fluorophore. Linked to Prochlorococcus cyanobacteria (r = 0.39, n = 47, p b 0.05), this fluorophore would have an oceanic origin and enter in the lagoon through its southern and northern extremities. It also displayed relationships with Ni and Co content (r = 0.53–0.54, n = 21,p b 0.05). This work underlines the diversity of CDOM sources in the NC eastern lagoon.

Keywords :
CDOM
Fluorescence
Trace metals
Southwest Pacific
Coral reef lagoon
Rivers