A MICROPALEONTOLOGICAL INVESTIGATION OF DOWNSLOPE SEDIMENT TRANSPORT ON THE WAIPAOA RIVER MARGIN, NEW ZEALAND

Previous work has shown that benthic foraminifera can be used to determine sediment transport pathways on the seafloor. As part of the MARGINS Source-to-Sink (S2S) Initiative, a primary goal of this project is to use benthic foraminifera to determine the degree to which shelf sediments are moved to the slope setting in the New Zealand study area. The Waipaoa River drains into Poverty Bay, off the east coast of the North Island, New Zealand. While its catchment is relatively small (2200 km²), the river's suspended sediment yield is unusually large (15 million tonnes yr^-1) and off-shelf sediment transport has been suggested by earlier seismic reflection and coring research. In 2005 and 2006, three research cruises obtained approximately 200 cores by means of multi-, box-, gravity- and piston-coring. From these, approximately 60 surface samples (0-2 cm) from shelf and slope settings (water depths ranging from 25-1250 m) were analyzed to establish the pattern of foraminiferal depth zonation. The shelf-to-slope displacement of sediment was assessed by comparing the abundances and distributions of species within three slope cores with the depth-zonation model. The slope cores were examined at 2-6 cm intervals, providing an indication of shelf-to-slope transport over the past approximately 180 years. Preliminary results suggest that benthic foraminifera from a wide range of shelf water depths (25-150 m) are found in significant amounts within slope cores.