Sepik River, Papua New Guinea

Funding Agency: NSF

Summary: A sediment budget was constructed for the shelf and slope influenced by the Sepik River plume in order to estimate the relative importance of surface and subsurface turbid flows versus transport through a near-shore submarine canyon in distributing river sediments across this narrow margin.  210Pb geochronology and inventories of Kasten cores are consistent with northwestward dispersal of sediment from the river mouth via surface plume and possible subsurface isopycnal transport.  Sediment accumulation rates are highest on the upper slope just off of the Sepik mouth, decreasing gradually toward the northwest (~1 cm yr-1 in the western part of the study area), and decreasing abruptly offshore (<0.2 cm y-1 at 1200 m water depth).  A first-order sediment budget indicates that only about 7-15% of the estimated Sepik River sediment discharge accumulates on the adjacent open shelf and slope.  The remainder of the Sepik River sediment discharge presumably escapes offshore through a submarine canyon that extends upstream about 1 km from the river mouth.  The divergent sediment pathways observed off the Sepik may not be uncommon along high yield collision margins of the Indo-Pacific archipelago, and perhaps represents the norm for most margins during Late Quaternary low sea-level conditions.