The development and decline of phytoplankton blooms in the Southern Benguela upwelling system. 2. nutrient relationships

Abstract

Five drogue studies on phytoplankton bloom dynamics in nutrient-rich newly upwelled water in the southern Benguela provided an opportunity to investigate the applicability of Redfield ratios to coastal upwelling regions. Mean atomic ratios of nutrient utilization and oxygen production (ΔP:ΔN:ΔSi:ΔO), as estimated from regression analyses (1:15, 9:11, 6:−283) and elemental changes along the drogue tracks (1:15, 7:13, 8:−206), were roughly similar to the equivalent Redfield ratios (1:16:15:−276). This implies that phytoplankton in upwelling areas also take up (or produce) these elements in proportions similar to those in which they occur in the cells themselves. As the upwelled water ages, changes in the ratios of N, Si and P imply that nitrate was used up fastest and is thus most likely to limit phytoplankton productivity in the southern Benguela region. However, regression analyses, calculations of times of nutrient depletion and published information on relative rates of nutrient regeneration suggest that silicate may also sometimes limit photosynthesis in this region. © 1987 Taylor & Francis Group, LLC.