INFLUENCE OF SEA LEVEL AND MONSOON VARIABILITY ON SILICICLASTIC AND CARBONATE SEDIMENT ALONG A TROPICAL MIXED SYSTEM 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 that is seasonally influenced by the Asian-Australian Monsoon with heavy precipitation during the austral summer. Sediment cores from the slope and troughs of the GoP (300 to 2200 m water depth) record sediment delivery related to changes in sea level, monsoon strength, and oceanographic conditions. Late Quaternary patterns of sediment accumulation vary widely both spatially and temporally (glacial-interglacial and millennial cycles) based on elemental records measured with an XRF core scanner. In most slope and trough regions lowest siliciclastic fluxes occur during the Holocene when most river materials are stored on the inner shelf. However, highest siliciclastic fluxes do not occur consistently across the region during lowstands as predicted by reciprocal sedimentation models. Peak siliciclastic fluxes even vary within individual troughs. In many regions highest siliciclastic flux occurs during the regressive periods from MIS 3 to 5 and as short pulses during transgressions (MIS1/2). The high siliciclastic fluxes may be related to changing sea level during this time that mobilizes stored shelf sediment, cause tidal scour, and/or shift surface or deep-water currents. But increased precipitation related to stronger monsoons may also cause the higher flux. Paired Mg/Ca and oxygen isotope records from planktonic G. ruber indicate decreased salinity during these periods, which may indicate wetter conditions during MIS 3 to 5 compared to MIS 2. Siliciclastic fluxes are highest in a few longer cores during MIS 5b and 5d. These times correlate with high summer insolation over Australia, which may have increased the monsoon strength in the region resulting in an increase in precipitation over Papua New Guinea and a higher siliciclastic flux to the GoP. 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. In the GoP changes in sea level and shelf geometry influence sediment delivery, but changes in climate also play an important role.