Spatial and temporal variability of phytoplankton community composition in the tropical and subtropical atlantic ocean (40degreesN - 40degreesS).

• Main Author: Poulton, Alex J
• Format: Thesis
• Language: English
• Published: University of Southampton 2002
• Subjects: Bray; South Atlantic Ocean
• Online Access: https://eprints.soton.ac.uk/464715/; https://eprints.soton.ac.uk/464715/1/847114.pdf

Routine measurements of the phytoplankton community from the first 10 cruises (1995 - 2000) of the Atlantic Meridional Transect (AMIT) programme are examined in the context of spatial and temporal variations in community composition within the subtropical (10 - 40°N/S) and tropical equatorial (10°N - 10°S) Atlantic Ocean. Measurements include size-fractionated chlorophyll a concentration, High-Performance-Liquid-Chromatography (HPLC) determined pigment signature concentration and large (>5 mm) phytoplankton species abundance and identification. Ancillary measurements (CTD, nutrient concentrations and light levels) are used to examine spatial and temporal variations in the hydrographic environment and provide a regional framework for analysis of variations in the phytoplankton community composition. Multivariate statistical analyses (Bray-Curtis similarity) of the phytoplankton community composition from (HPLC) pigment measurements and species identification show both latitudinal and vertical differences in composition; an upper and deep flora in subtropical and equatorial Atlantic waters with a reduction in depth differences in upwelling waters off NW Africa. Such spatial differences are associated with regional changes in the mechanisms important for the formation of the ubiquitous Chlorophyll a Maximum. Analysis of the time-series measurements collected in South Atlantic Subtropical Waters (0 - 30°S) show marked interannual (post-winter) differences in the depth of the mixed layer. Examination of the phytoplankton community in South Atlantic Subtropical Waters indicates interannual variations in the phytoplankton community composition. It is hypothesised that a decrease in winter mixing associated with climatic variability in the South Atlantic Ocean reduce seasonal new nutrient inputs and favour oligotrophic components of the phytoplankton community.