Abstract: Based on the grain size systematic analysis of D3-7 sedimentary column, including grain size probability diagram, size parameter scatter diagrams, and CM patterns, the palaeosedimentary environment of the Northwest Weddell Sea since MIS3 is studied. The results show that the sediment mainly exists in the form of hydrostatic suspension status before arriving sea bottom. The sedimentary hydrodynamic environment can divided into four stages, with cyclic characteristics. The first stage is from 33.4-35.0ka, between 241-319cm(bottom of D3-7),and belongs to single hydrostatic suspended deposition. The second stage is from 29.6-33.4ka, between 143-241cm,and belongs to multi hydrostatic suspended deposition. The third stage is from 26.8-29.6ka, between 52-143cm, and belongs to single hydrostatic suspended deposition again. The fourth stage is from 0-26.8ka, between top of D3-7 and 52cm, and belongs to multi hydrostatic suspended deposition. The transport of coarse sediments requires large starting power, inferred some sediment provenance linked to ice rafting and volcanic activity.

Key words: South Ocean, Powell Basin, MIS 3, D3-7 column, grain size, palaeosedimentary environment