Abstract:
The sediment record from Arabian Sea shows oscillations of environmental changes in the coastal upwelling off Oman. The upwelling is driven by the summer southwest monsoon over Indian Ocean. The sediment record at ODP Sites 727 and 728 covers 2 m.y., and shows higher biological productivity during interglacial periods than glacial periods. The productivity drop occurs twice at 1.37-1.36 Ma and 0.93-0.88 Ma through the Quaternary, when productivity continuously decreased. Planktonic foraminiferal abundance (#/g) and carbonate carbon content were higher during interglacial periods, but their accumulation rates were not high. Rather, they were higher during glacial periods. This suggests that carbonate dissolution effect occurred in the surface sediments. The fact that the dissolution effect, judged from the estimates of the amount of fragmented foraminifera tests, was stronger during interglacial periods than during glacial periods supports this suggestion. The amounts of organic carbon in the samples suggest that much organic materials were supplied to the bottom during interglacial periods than during glacial periods. Sediments rich in organic matters lead, when decomposed, to stronger carbonate dissolution effect. And a large amount of organic carbon supply to the bottom relates to higher productivity in the surface water mass, caused by coastal upwelling driven by southwestern monsoon during interglacial periods. Accordingly this proves that biological productivity is higher during interglacial periods.