Clipperton, A Meromictic Lagoon

In 2005, we participated in the Jean-Louis Etienne expedition to investigate the lagoon of Clipperton Island (10 degrees 17 ' N 109 degrees 13 ' W) and the surrounding oceanic waters. Since 3,000 years ago, the date of the first registered closure, the lagoon has suffered a succession of reopenings. Its actual situation, a meromictic lake, seems to have been the same for 150 years. Brackish waters of the upper layer (0-10 m) are oxygenated, while salted waters of the deep layer (>20 m) are anoxic. The transition layer between brackish and salted waters is characterized by a temperature inversion of 1.6 degrees C. Mean DIN (dissolved inorganic nitrogen) (0.39 +/- 0.08 mu M) and SRP (soluble reactive phosphate) (0.13 +/- 0.01 mu M) concentrations in the upper layer of Clipperton Lagoon were close to the values reported for other French Polynesian atoll lagoons. Taking into account the methodological problems of previous measurements, the physical characteristics of the lagoon do not seem to have changed significantly since the last expeditions (1980).