Hydrography, phytoplankton biomass and photosynthesis in shelf and oceanic waters off southeastern Brazil during autumn (may/june, 1983)

Abstract

Spatial distribution of chlorophyll-a, phytoplankton photosynthesis and nutrients were studied in relation to the hydrographic environment of the southeastern Brazil from May 3 to June 31 of 1983 during an oceanographia cruise conducted by the R/V "Almirante Saldanha" of the Brazilian Navy. Temperature and salinity at 5 meters depth ranged from 21 to 25º C and from 33.00 to 37.11, respectively. The concentration of nutrients varied, nitrate + nitrite-N from 1.0-3.0 µg-at/l, phosphate-P 0.1-0.9 µg-at/l and silicate-Si 5-25 µg-at/l. The chlorophyll-a concentrations along the coast varied from 0.35 to 1.48 mg/m³ with maxima in front of Paranaguá Bay (PR) and over the southern shelf of Santa Catarina State. Low concentrations around 0.20 mg/m³ of uniform distribution were observed in shelf and off-shelf areas. Comparatively high concentrations were measured over the shelf break zone in front of Paranaguá Bay indicationg the occurrence of shelf break upwelling of deep nutrient rich waters. The pattern of vertical distribution was stratified and irregular in coastal stations and uniform in shelf and oceanic waters although some subsurface peaks were sometimes detected. The integrated chlorophyll values within the euphotic layer varied between 2.70 and 28.06 mg/m². The surface photo synthetic capacity varied from 0.4 to 7.7 mgC/mgChl.a/hr with higher values obtained in coastal areas.. The vertical distributions were variable in coastal areas and more uniform in mid-shelf stations. Sub-surface maxima of photosynthesis were detected in both nearshore and off-shore stations, and surface inhibition was not observed.