Ocean color response to an episode of heavy rainfall in the lagoon of New Caledonia

Inherent optical properties (IOPs) and remote sensing reflectance were measured in the southern part of the lagoon of New Caledonia during the VALHYBIO cruise (March-April 2008). The goal was to validate satellite chlorophyll data from MODIS and MERIS and to validate simulations of surface chlorophyll by a biogeochemical model. Physical parameters were collected from a Seabird CTD. Particulate and detritus absorption were measured with the filter pad technique. Backscattering was measured with a Hydroscat-6. Mapping of IOPs and Rrs were done for the whole southern lagoon area and compared with pigment maps. The cruise provided a description of the IOPs in different water types including bays, open ocean waters, mid-shelf lagoon, and above reefs. With respect to climatology, the heavy rainfall episode of March-April 2008 resulted in a large increase in chlorophyll-a concentration (by a factor of 3) attributed to increased nutrient availability from land drainage. Low backscattering ratios characterized the chlorophyll-rich plumes associated with the nutrient increase. The data are useful for the development of a specific algorithm for chlorophyll concentration retrieval by satellite in all oligotrophic lagoons during dry and wet seasons.