Circulation and Flux of Suspended Particulate Matter in Ilha Grande Bay, SE Brazil

Ilha Grande Bay (IGB) is located in the southern tip of Rio de Janeiro state, SE Brazil. It is freely connected to the Atlantic ocean. In its central area lies a large, east-west trending island, separated from the continent by a narrow and deep feature, the Central Channel. IGB's eastern end is connected to Sepetiba Bay, a shallow, highly polluted environment and a potential source of fine-grained, contaminated sediment. The chief motivation of the present study was to identify scenarios conducive to the advection of suspended particulate matter (SPM) from Sepetiba Bay into IGB through the Central Channel where an anchor station was repeatedly occupied for 18-25 hours in December 2005, September 2006 and March, April and July 2007. The data set includes continuous measurements of water column currents; SPM concentration determined through filtration of water samples collected at 3-6 points from the water surface to the near-bed area; vertical profiles of seawater temperature and salinity. Sampling was carried out both under neap and spring tide conditions. Current speed usually remained under 0.5 in s(-1), except during the passage of a cold front in December 2005. Seawater properties suggest that the Central Channel is mostly filled by shelf waters; SPM concentration was low, rarely exceeding 20 mg L(-1). Within the domain of our observations, fluxes of SPM were strongly controlled by meteorological conditions and by the presence of low-frequency oscillations (internal seiches?). Results support the episodic occurrence of conditions that favor the introduction of particles originated in Sepetiba Bay into the Central Channel.