Sources of nutrients and seasonal dynamics of chlorophyll in the inner shelf off Paraná State-South Brazil Bight

Abstract

The seasonal dynamics of phytoplankton chlorophyll and nutrients were studied between August 1997 and March 1999 along a cross-shelf section of the inner coastal of Paraná State, southern Brazil. Vertical thermohaline stratifications in the rainy summer alternated with winter homogeneities. Nitrate-N varied from 0.17 to 1.13 µM, nitrite-N from 0.04 to 1.10 µM, phosphate-P from 0.37 to 0.73 µM, and silicate-Si from 2.5 to 10.2 µM, all presenting maximum concentrations at the bottom layers at the outer stations. Chlorophyll concentrations varied from <0.02 to 10.8 µg·L−1 throughout the study period, with maxima at subsurface and bottom layers depending on the season. Seasonal differences in the distributional patterns of nutrients and chlorophyll were caused by two main wind-driven physical processes: (i) onshore intrusions of South Atlantic Central Waters and (ii) remote continental runoff from La Plata River. These were considered the main sources of new nutrients in summer and winter periods, respectively. Phytoplankton biomass (indicated by chlorophyll concentrations) tends to accumulate at subsurface layers, representing the primary source of organic matter for pelagic and benthic habitats in the inner shelf off Paraná State.