Production of Globigerina bulloides generally increases during upwelling in the tropical ocean and, in particular, during southwest monsoon season in the Arabian Sea. We studied the delta sup(13) C signatures of Globigerina bulloides from Ocean Drilling Program (ODP) site 723A located in the intense upwelling area along the Oman Margin, Arabian Sea is studied. The delta sup(13) C signature of G. bulloides from the Oman Margin during the last 19 ka ranges from -2.65 ppt to -1.13 ppt. Strikingly, the delta sup(13) C values of G. bulloides are about 1 ppt lower than that of benthic foraminifera Uvigerina excellens at this site. Apparently, the vital effects induced carbon isotopic fractionation in G. bulloides results in abnormal delta sup(13) C values. During upwelling seasons, G. bulloides calcifies faster, perhaps because of high-nutrient availability. Faster calcification rates in this species require higher respiration, which involves more respired CO sub(2) enriched with sup(12)C accounting for nearly 10% of shell carbon. Therefore, the combination the foraminifera of faster calcification and involvement of respired CO sub(2) would induce more negative delta sup(13) C in G. bulloides compared to other foraminifera. Apart from vital effects, the environmental changes caused by the variations of upwelling intensity during Holocene and last glacial maximum also affected the down-core delta sup(13) C record of G. bulloides in the Arabian Sea. Significant ontogenic differences in both delta sup(18) O and delta (13) C occurred between large and small size classes of G. bulloides.