Benthic Ostracoda in the Benguela System (SE Atlantic): A multivariate analysis

Abstract

Q-mode factor analysis of ostracod faunas from 127 modern sediment samples associated with the Benguela System over the continental margin off Namibia and South Africa identifies ten Factor Associations of species (FA). These FA account for 93% of the variance, and can be related to nine sea-bottom variables: temperature, salinity, dissolved oxygen, total orgainc matter, elemental iron (=terrigenous component), calcium carbonate, glauconite, sand and mud. Transfer functions for these variables are calculated for future palaeo-environmental analyses. On the modern continental slope FA Henryhowella melobesioides and Krithe capensis are controlled primarily by cross-shelf temperature gradients, while on the uppermost slope and outer shelf dissolved oxygen values restrict the distribution of FA Cytherella namibensis (oxygen depleted) and Ruggieria cytheropteroides (“normal” oxygen levels) in the north and south, respectively. Inner and middle shelf faunal associations are controlled by high salinities north of 26°S (FA Palmoconcha walvisbaiensis), while substrate variables (terrigenous, glauconite, mud and organic matter) are the main determinants farther south (FA Bensonia knysnaensis knysnaensis, Pseudokeijella lepralioides, Bairdoppilata simplex, Ambostracon keeleri/flabellicostata and Paracypris lacrimata). These faunal/hydrographic relationships are linked to various dynamic oceanographic features such as upwelling, cross-shelf advection and shelf-parallel bottom currents.