The Characteristics And Source-sink Processes Of Sediments In The New Britain Trench Of Western Pacific Ocean And Their Temporal And Spatial Variations

Papua New Guinea?PNG?,located in the Western Pacific Warm Pool?WPWP?,is a critical component of the global source-to-sink system,where New Britain Trench?NBT?is a narrow region adjacent an island.Trenches are unique regions in the world,which have the deepest zones?Hadal zones?,funnel-like terrain and extreme environments.In order to further understand trenches,the NBT closed to the land and islands is chosen as research objects.Sediments from box cores NBT01,NBT02,NBT03,NBT05,NBT06,NBT07,NBT10 and gravity core GC02 and three parallel surface sediments NBT09 in the NBT are analyzed by major elements,trace elements,rare earth elements,bulk minerals and clay minerals,grain size,Sr-Nd isotope,total organic carbon and total nitrogen content,total organic carbon isotope,bio-silica,pollen and AMS-¹⁴C dating.Source,transportation and accumulation process of sediments?inorganic materials and organic materials?in the NBT and their difference of spatial characteristics of accumulation are discussed in this paper with the changes of their provenance and the paleoproductivity and their driving factors since the Last Deglacial.Geochemical elements and minerals results show that sediments of the near-land type NBT are mainly derived from intermediate volcanogenic materials of the surrounding islands,and the contribution of volcanogenic materials is about 90%.The NBT is affected by volcanogenic materials from Rabaul Volcano and Bagana Volcano,the TLTF volcanic chain?volcanoes Tabar-Lihir-Tanga-Feni?,the northern volcanoes of the New Britain Island,and the Solomon Islands.Moreover,volcanogenic materials from Rabaul Volcano have a significant effect in the western NBT,and the eastern NBT is more strongly affected by the TLTF volcanic chain.In addition,combined with the evidence of pollen,it is found that the surface sediments of NBT01 in the western trench axis are distinctly affected by river sediments and the high content of carbonate is in the lower layer of NBT01,which may be related to the funnel-like topography of the trench.The content of organic carbon and total nitrogen and the composition of organic carbon isotope indicate that the organic matter of NBT is obviously affected by the soil organic matter of PNG forest.But the inputs of terrestrial organic matter are controlled by the terrain and offshore distance of the trench.Based on the changes in clay minerals contents in the sediments of the NBT and the distribution of clay minerals in the PNG,it is found that the illite content in the southern PNG is higher,while it is higher smectite content in the northern PNG.And the clay minerals distribution of the NBT is located between them,but it is closer to the southern region.Thus,it shows that the ocean currents flowed northward in the PNG resist the materials of the northern New Britain Island to be transported southward.In addition,the differences of deposited characteristics in the NBT are discussed by AMS-¹⁴C age and grain size of sediments.It reveals that the sedimentation rate in the continental slope is higher than that in the oceanic slope due to the complex terrain in the NBT.However,the deposited environment in the continental slope is unstable,and it is difficult for the materials to be accumulated for a long time.The materials are transported to the trench axis by mass-wasting event.The examinations of geochemical elements,clay minerals and grain size in the sediments of the gravity core GC02 in the NBT showed that although sediments of the NBT were mainly derived from intermediate volcanogenic materials of the surrounding islands since the Last Deglacial,the inputs of intermediate volcanogenic materials were gradually decreased with the increasing inputs of terrestrial rivers sediments.However,there might be the new inputs of acid volcanogenic materials in the late Holocene.The rainfall was stronger during the Last Deglacial and mid-late Holocene,while the rainfall was weaker during early Holocene due to Intertropical Convergence Zone migration.In addition,the results of biogenic component and total organic carbon isotope illustrated that the sources of organic matter in the NBT were mainly derived from marine origin in the Last Deglacial and Holocene,but the highest contribution of the soil organic matter of PNG forest was 50%during the Last Deglacial.Meanwhile,a large number of inputs of terrestrial organic matter promoted the increasing of productivity in the region,but the accompanying allochthonous detritus diluted the calcium carbonate content.And the carbonate content increased during the later period of the early Holocene due to the weakness of the accompanying inputs,which reflected the rise of productivity.The inputs changes were distinct in the Last Deglacial and Holocene,which were affected by the comprehensive effects of the equatorial convergence zone?ITCZ?,sea level and climate changes.