The chemical mass balance in the Amazon plume I: The nutrients

Abstract

In May and June 1976, the Amazon plume was dominated by a diatom blood centered on the 10 x 10−3 isohaline. The bloom was apparently initiated by the increased transparency produced by the rapid settling of the fluvial detrial load. The bloom removes the nitrate and phosphate from the surficial layer. The underlying salt wedge was enriched by remineralisation of planktonic debris. A balance between the dissolved and particulate material shows that the regeneration was essentially complete for carbon and phosphorus; but about 50% of the nitrogen was unaccounted for, having been solubilised to species other than nitrate and nitrite. Only 20% of the silica removed as diatoms (∼25% of the river dissoled flux) could be accounted for as salt wedge enrichment. The rest must have been incorporated in the sediment. The composition of the river waters was strongly affected, before entry to the mixing zone, by remineralisation of a large fraction of the fluvial particulate organic material in the broad area of multi-channel flow above the mouth.