Seasonal and Spatial Patterns of Deeply Buried Calanoid Copepods on the Amazon Shelf: Evidence for Periodic Erosional/Depositional Cycles

Seasonal sampling of Amazon shelf deposits revealed that calanoid copepods as well as other pelagic zooplankton were often buried along with benthic infauna throughout the upper 25 cm of the sea-bed. During February through March, the period of rising to peak riverine discharge and maximum trade wind stress, shelf-wide maxima occur in numbers and depth of burial. Buried copepods were present in all stations with abundances reaching 5168 copepods m−3in the 10–25-cm depth interval off the river mouth in 18 m of water (Station RMT-2). The intact nature of the buried copepods and presence of phytoplankton within the digestive tracts of many, supports the notion that burial was sudden and rapid ( hours). In contrast, from August to October, the period of falling to low riverine discharge and minimum wind stress, burial of zooplankters was restricted to stations along a southern transect (ST) and at the innermost river mouth station (RMT-1). Burrowing macroinfauna, meiofauna and bacterial inventories increase dramatically at all shelf stations during the time of minimum zooplankton burial. Successful recolonization by benthos and lack of entrainment of water-column organisms show that the bottom is most stable during seasons of falling to low river flow. Sedimentologic and chemical, as well as biological, evidence indicates rapid turnover of 20–30 cm of the sea-bed during rising- and peak-flow periods when the sea-bed is most unstable.