Abstract
The watershed of the Amazon River discharges about 120,000 m3·s-1 of freshwater into the adjacent platform and oceanic region. The aim of this work was to analyze the distribution of oceanographic parameters, chlorophyll a and primary productivity under the influence of the Amazon River plume, during the period of greatest extension of the Amazon plume. Collections were carried out in September 14 in 16 stations including continental platform and oceanic region. It was possible to observe superficial currents along the coast in the northwest direction, but with less intensity and currents with greater speeds towards the east due to the North Brazil Current retroflexion at this time of the year, transporting the plume to the central Atlantic Ocean. The spatial influence of the plume was observed in the salinity, which ranged from 28 to 36.75, although the high precipitation in the region may also have contributed as a source of freshwater. However, the sampled region showed strong negative linear correlation of silicate, chlorophyll a and primary productivity with salinity. The primary productivity values ranged from 0.04 to 18.81 mg C m-3 day-1, whereas chlorophyll a concentrations ranged from 0.15 mg·m-3 to 1.83 mg·m-3, decreasing their values as they move away from the coast. The Amazon River plume can reach and influence the oceanographic and biological parameters in a large area of this oligotrophic region. However, the results also suggest that the export of material from the adjacent coastal region is another determinant of the region’s productivity.
Highlights
Primary production and chlorophyll a concentrations are always dependent on synergistic effects among meteorological, physical, chemical and biological factors that limit or stimulate the activity of photosynthetic planktonic organisms [1] [2]
The spatial influence of the plume was observed in the salinity, which ranged from 28 to 36.75, the high precipitation in the region may have contributed as a source of freshwater
The objective of this work was to analyze the distribution of oceanographic parameters, chlorophyll a and primary productivity under the influence of the Amazon River plume, during the period of greatest extension of the Amazon plume
Summary
Primary production and chlorophyll a concentrations are always dependent on synergistic effects among meteorological, physical, chemical and biological factors that limit or stimulate the activity of photosynthetic planktonic organisms [1] [2]. The watershed of the Amazon River discharges about 120,000 m3·s−1 of freshwater, but is responsible for about 30% of the freshwater flow to the Atlantic Ocean [8] [9] It presents a surface plume of approximately 3 - 10 m thick, which covers an area that varies between 2.31 × 106 km and 5.26 × 106 km. It significantly influences the flow of nutrients, and other suspended materials, interfering in the biogeochemistry of many elements present along the continental platform [10] [11] [12] [13] Due to this influence, the plume has a differentiated phytoplankton structure in relation to the adjacent oceanic region, with high concentrations of photosynthetic pigments [14]
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