Influence of sea level and monsoon variability on sedimentation in the Western Tropical Pacific, Gulf of Papua

The Gulf of Papua (GoP) is a tropical mixed carbonate-siliciclastic system located along the southeast continental margin of Papua New Guinea. GoP sediments contain a record of late Quaternary climate changes at the edge of the Western Pacific Warm Pool in an area seasonally influenced by movement of the Intertropical Convergence Zone. Results are presented from a suite of sediment cores from the slope of the GoP that document changes in sediment delivery as a result of changes in sea level, monsoon strength, and climate. Patterns of sediment accumulation vary widely on both glacial-interglacial and millennial time scales. High siliciclastic flux occurs during MIS 2. However, even higher siliciclastic fluxes occur during the regressive periods from MIS 3 to 5 and as short pulses during the transgressions (MIS1/2 and 5/6). The greater siliciclastic flux is likely related to falling sea level during this time that remobilized shelf sediment and/or increased tidal scour. Alternating sandy/muddy turbidities and hemipelagic sediment in many trough cores during MIS 3 may be related to fluctuations in sea level and/or climate changes at millennial scale, such as the Dansgaard/Oeschger cycles or Antarctica Warm/Cold Intervals. Short warming events during MIS 3 are documented by Mg/Ca data from G. ruber. Siliciclastic fluxes on the Eastern Plateau are highest during MIS 5b and 5d, which correlate with high summer insolation over Australia that may have increased the strength of the monsoon resulting in an increase in precipitation over Papua New Guinea and a higher siliciclastic flux to the GoP. Initial estimates from paired Mg/Ca and oxygen isotope records from G. ruber indicate decreased salinity during these periods. Spectral analysis of elemental data from X-ray fluorescence shows predominant forcing by precession, but an obliquity signal is also present. In the Gulf of Papua changes in sea level and shelf geometry influence sediment delivery, but changes in climate forcing mechanisms also play a role. A simple model cannot be applied to the carbonate and siliciclastic sediment deposition between glacial and interglacial cycles.