Geographical distributions of organic-walled dinoflagellate cysts in surficial sediments of the Benguela upwelling region and their relationship to upper ocean conditions

The organic walled cyst content of 41 surface sediment samples from the sou th-eastern South Atlantic Ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions. In order to obtain insi ght into which environmental factors influence the distribution of individu al cyst species, the cyst associations have been compared with oceanographi c characteristics of the overlying water masses, i.e. temperature, salinity , density and stratification gradients. The associations and relationships have been established by Visual examination of the dataset and the multivar iate ordination techniques, Detrended Correspondence Analysis and Canonical Correspondence Analysis. Special attention has been given to the factors o f transport and preservation of the cysts. Five associations have been reco gnised as being characteristic of (1) areas influenced by coastal upwelling and/or river outflow, (2) open ocean, (3) Agulhas Current and southern Ben guela Current, (4) Benguela Current and (5) Walvis Bay, shelf break area. T he factors dominant in influencing either directly or indirectly the cyst d istributions appear to be the stratification in the upper 50 m of the water column, nutrient concentration and seasonality. Variations in sea surface temperatures and salinities have only minor effect on cyst distribution. (C ) 2001 Elsevier Science Ltd. All rights reserved.