Paleoceanography of the Gulf of Papua using multiple geophysical and micropaleontological proxies

Abstract

Recent marine and late Pleistocene sediments examined from the Gulf of Papua (GoP), Papua New Guinea investigate the flux and fate of detrital sediments and organic carbon over the last glacial-interglacial cycle. Based on surface sediment magnetic susceptibility (MS) and calcium carbonate concentrations, recent marine sediment is exported off the narrow shelf and into deeper regions via the Kerema Canyon of the northern Pandora Trough. Detrital clastic sediment is then dispersed deeper into the central and southern Pandora Trough. Except for pelagic deposition, very little detrital material reaches the Ashmore Trough and Eastern Plateau adjacent to the Great Barrier Reef. Rock-Eval pyrolysis data and organic petrography indicate that late Pleistocene and recent organic matter were strongly degraded prior to burial. Late Pleistocene depositional records come from two, 12 m piston cores retrieved from the slope of the northern Pandora Trough. MV-54 was taken at the mid-slope of the central Pandora Trough (923 m) and MV-51 was collected from a bathymetric high in the northeastern Pandora Trough (804 m). Core sediments were analyzed with MS, calcium carbonate, organic geochemistry, and benthic foraminiferal assemblages. Both cores show two periods of rapid sediment accumulation. High accumulation rates characterize 15,800-17,700 Cal. yrs B.P. in MV-54 and correspond to the early transgression when rivers delivered sediments closer to the shelf-edge. Benthic foraminiferal assemblages in MV-51 indicate a seasonally variable flux of organic carbon during late LGM (~18,400-20,400 Cal. yrs B.P.), suggesting enhanced contrast between monsoon seasons. The oldest section, >32,000 14C yrs B.P., contains the highest mass accumulation rates and TOC fluxes, with >50% of the organic carbon derived from C3 vascular plant matter. MS and benthic foraminiferal accumulation rates are orders of magnitude higher during this interval than any younger time indicating a greater influence of detrital minerals and labile organic carbon. Because mineralogy and detrital input are shown to be the main controls on MS variability, the MS data in this interval suggest more direct dispersal pathways from central and eastern PNG Rivers to the core site when sea level was lower and dispersal gradients were higher.