Effects of flow disturbances on Holocene planktonic foraminiferal ecostratigraphy

The ecostratigraphy of offshore North Coast of Trinidad and near Tobago is poorly resolved, although biogenic gas production for which it would be useful is widespread. Recent work has shown that a wake and eddy in the Guiana Current and Orinoco Plume to the lee of NWTobago influence benthic foraminiferal assemblages. This ecostratigraphical study of planktonic foraminiferal assemblages examines three piston cores taken on the lee of NW Tobago. Core 1 (upper bathyal) was most distal to the nutrient-rich Orinoco Plume and Core 3 (outer neritic) the most proximal. The assemblage turnover index (ATI) and analysis of variance (ANOVA) determined that the relative community stability at each site did not differ, showing similar community stabilities within the wake and plume. However, an abnormally high abundance of the deep-dwelling, nutrient-loving Globorotalia truncatulinoidesdextral in Core 2 indicated an oceanographic boundary between Cores 1 and 2 along which the Orinoco Plume abuts the oligotrophic ocean. This is reflected in the distributions of other planktonic foraminiferal morphotypes such as G. bulloides, Gn. obesa and G. ruberpink. SHE analysis detected two biozones in Cores 2 and 3, possibly marking a change in nutrient influx. Principal component analysis reinforced the nutrient influx as amajor factor acting at Cores 2 and 3 in thewake andOrinoco Plume, Core 2 being seasonally impactedwhile Core 3 lies permanently within the Orinoco Plume. We conclude that oceanographic complexity off NW Tobago affects the distributions of planktonic foraminiferal morphotypes at the kilometer scale. Our results will prove to be a powerful tool in deciphering the geological history of the Orinoco Plume.