One of the most remarkable and profound past global changes during the Quaternary and Tertiary was the uplift of the Tibetan Plateau and the consequent set of Indian Ocean-Asia monsoon climate system. That is a multi-sphere interactive process originated from lithosphere plate tectonic movement, transferred to atmosphere and hydrosphere. This process was well recorded in the northwestern Arabian Sea. Previous work usually focused on the Tertiary record and used planktonic indicators (e.g., Prell WL, Niitsuma N et al., 1991). However, benthic fauna is also fairly good proxy indicator to be explored because they can not only reflect the sea surface condition, but also is unique record of bottom environment.

Much of the Arabian Sea is characterized by a narrow continental shelf bordered by an extremely steep continental slop. The western Arabian Sea currently is characterized by intense summer monsoonal upwelling that induces high primary productivity and distinctive assemblages.

The benthic foraminiferal fauna were sampled in 32 Recent coretop sediment samples covering a water depth from 247 to 1474 m during the regional survey cruise RC27-04.

Characteristics of benthic foraminiferal fauna are: (1) high abundance (large standing stocks); (2) high species dominance and low diversity; (3) relatively small, thin shelled specimens; (4) particular test morphology and ornaments that are adaptations to opportunistic infaunal mode of life; (5) more than 90% of tests are stained or filled by pyrite; (6) dominated by a relatively small number of opportunistic species, mainly species belonging to genera such as Bolivina, Bulimina, Buliminella, Cassidulina, Chilostomenella, Ehrenbergina, Globobulimina, Uvigerina, etc. Benthic foraminiferal record in Hole 723B of ODP Leg 117 reveals that the Indian summer monsoon and upwelling were intensified 9 ky, 18 ky, 50 ky , 100 ky , 200 ky and 240 ky, 340, 440 ky, 480 ky, 600 ky and 700 ky ago. These benthic foraminiferal records are highly coherent with record of eolian detritus flux from deserts and highlands of adjacent lands, and grain size of lithogenic component in the sediments deposited on the western Arabian Sea continental shelf. Compared to the Tertiary, the Quaternary monsoon/upwelling/OMZ conditions revealed by benthic foraminiferal record were more intense, which implies the increasing in global changes effect from the uplift of the Tibetan Plateau.

* Project (No. 49606073)supported by National Natural Science Foundation.