Monsoon-controlled export fluxes to the interior of the Arabian Sea

As a part of the US-JGOFS Arabian Sea Process Study (ASPS), we deployed a m ooring array consisting of 16 Mark-7G time-series sediment traps on five mo orings, each in the mesopelagic and interior depths in the western Arabian Sea set along a transect quasiperpendicular to the Omani coast. The array w as deployed for 410 days to cover all monsoon and inter-monsoon phases at 4 .25-, 8.5- or 17-day open-close intervals, all of which were synchronized a t 17-day periods. Total mass flux, fluxes of organic, inorganic carbon, bio genic Si and lithogenic Al (mg m(-2) day(-1)) were obtained from samples re presenting 667 independent periods. The average total mass fluxes estimated in the interior depth along this sediment trap array at Mooring Stations 1 -5 (MS-1-5) during 1994-5 ASPS were 147, 235, 221, 164 and 63 mg m(-2) day( -1), respectively. Mass fluxes during the southwest (SW) Monsoon were alway s larger than during the northeast (NE) Monsoon at all divergent zone stati ons, but the difference was insignificant at the oligotrophic station, MS-5 . Four major pulses of export flux events, two each at NE Monsoon and SW Mo nsoon, were observed in the divergent zone; these events dominated in quant ity production of the annual mass flux, but did not dominate temporally. Ex port pulses were produced by passing eddies and wind-curl events, but the d irect processes to produce individual export blooms at each station were di versified and highly complex. The onset of these pulses was generally synch ronous throughout the divergent zone. Export pulses associated with specifi c biogeochemical signatures such as the ratio of elevated biogenic Si to in organic carbon indicate a supply of deep water to the euphotic layer in var ying degrees. The variability of mass fluxes at the oligotrophic station, M S-5, also represented both monsoon events. but with far less amplitude and without notable export pulses. (C) 1999 Elsevier Science Ltd. All rights re served.