Quantitative source-to-sink processes and carbon cycling effect of sediment on the continental slope of the western Philippine Sea since 156 ka

We analyzed the stable carbon isotopic composition (δ¹³C_org) of organic matter in Core MD06-3052 retrieved from the continental slope of the western Philippine Sea. The new data, together with the published ones from the same core, including total organic carbon content, total nitrogen content, fluxes of different sediment components, and continental weathering and erosion proxies, were combined to constrain the quantitative source-to-sink processes, main controlling factors, and their carbon cycling effects of organic matter in the study area since 156 ka during glacial-interglacial cycles. Results show that the δ¹³C_org values fluctuate between −27.4‰ and −18.6‰ on average of −22.2‰, and are characterized by a variation characteristic of relatively negative values during the glacial periods and relatively positive values during the interglacial periods. The sources of organic matter included marine organisms and terrestrial C3 plants, dominated by terrestrial provenance (about 67% on average) and marine provenance (average 83%) during the glacial and interglacial periods, respectively. The variation trends of terrigenous organic carbon content and flux are very similar to those of the total organic carbon, and characterized by higher values during the glacial periods and lower values during the interglacial periods, indicating that the main reason for the increased organic carbon fluxes is continental shelf exposure during the glacial periods at sea level drop, and thus the strong weathering and erosion of loose silicate sediments. Combined with similar records of other cores in the tropical Western Pacific, we conclude that strong weathering and erosion of silicates on the widely exposed continental shelves and the associated high organic carbon burial flux in the sea during three stages could contribute greatly to the reduction of atmospheric carbon dioxide concentration, and consequent global cooling.