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Abstract: Widespread seagrass dieback in central Torres Strait, Australia has been anecdotally linked to the delivery of vast quantities of terrigenous sediments from New Guinea. The composition and distribution, and sedimentological and geochemical properties, of seabed and suspended sediments in north and central Torres Strait have been determined to investigate this issue. In northern Torres Strait, next to Saibai Island, seabed sediments comprise poorly sorted, muddy, mixed calcareous–siliciclastic sand. Seabed sediments in this region are dominated by aluminosilicate (terrigenous) phases. In central Torres Strait, next to Turnagain Island, seabed and suspended sediments comprise moderately sorted coarse to medium carbonate sand. Seabed sediments in this region are dominated by carbonate and magnesium (marine) phases. Mean Cu/Al ratios for seabed sediments next to Saibai Island are 0.01, and are similar to those found in New Guinea south coastal sediments by previous workers. Mean Cu/Al ratios for seabed sediments next to Turnagain Island are 0.02, indicating an enrichment of Cu in central Torres Strait. This enrichment comes from an exogenous biogenic source, principally from foraminifers and molluscs. We could not uniquely trace terrigenous sediments from New Guinea to Turnagain Island in central Torres Strait. If sediments are a factor in the widespread seagrass dieback in central Torres Strait, then our data suggest these are marine-derived sediments sourced from resuspension and advection from the immediate shelf areas and not terrigenous sediments dispersed from New Guinea rivers. This finding is consistent with outputs from recently developed regional hydrodynamic and sediment transport models. [Copyright &y& Elsevier]

Surface sediments of the Northern and Middle Adriatic shelf were studied during five cruises, from 1977 to 1990, in order to map the distribution of Ca and Mg carbonates in bottom sediments of the Adriatic Sea. The aim of this work was to trace the preferential depositional areas of sediments derived from Italian rivers by distinguishing among the contributions from northeastern Italian rivers, the Po and Apenninic streams. The pattern distribution of dolomite concentration proved to be a good tracer of the alongshore transport of particulate material from the Northern toward the Middle and Southern Adriatic. Moreover, dolomite and textural sedimentary parameters such as grain size distributions discriminate between local, recent sources, and regional, older sources of bottom sedimentary material. The analysis of the main pathways of sediment transfer between different shelf compartments shows that a huge amount of material is transferred from north to south. This occurs in two main shelf sectors: along the Romagna coast, sediments moving inside the belt delimited by the 20 m isobaths are influenced by the local river input and minor coastal gyres, whereas offshore sediments, coming from the northern Adriatic Sea, are transported southward by the Northern Adriatic Coastal Current (NACC); along the Marche and Abruzzo coasts, the “local” belt extends offshore on the outer shelf. In order to obtain a quantitative estimate of sediment accumulation of fine sediments of Northern Adriatic origin along the shelf sectors, a mass budget was calculated for bulk sediments and for dolomite contributions. The budget shows that the amount of sediment transferred between adjacent boxes is always of the order of 50% of the fluvial input to the sea. [Copyright &y& Elsevier]