The oxygen minimum zone in the Arabian Sea

This paper focuses on the characteristics of the oxygen minimum zone (OMZ) as observed in the Arabian Sea over the complete monsoon cycle of 1995. Dissolved oxygen, nitrite, nitrate and density values are used to delineate the OMZ, as well as identify regions where denitri"cation is observed. The suboxic conditions within the northern Arabian Sea are documented, as well as biological and chemical consequences of this phenomenon. Overall, the conditions found in the suboxic portion of the water column in the Arabian Sea were not greatly di!erent from what has been reported in the literature with respect to oxygen, nitrate and nitrite distributions. Within the main thermocline, portions of the OMZ were found that were suboxic (oxygen less than &4.5 lM) and contained secondary nitrite maxima with concentrations that sometimes exceeded 6.0 lM, suggesting active nitrate reduction and denitri"cation. Although there may have been a reduction in the degree of suboxia during the Southwest monsoon, a dramatic seasonality was not observed, as has been suggested by some previous work. In particular, ther