| Popis: |
Measurements of dissolved aluminium (Al) in surface microlayer (SML) samples from the eastern Arabian Sea during the southwest (summer) and northeast (winter) monsoon periods have revealed much higher concentrations (23–657 nmol kg−1) than in the sub-surface layer (SSL; collected at 1 m depth). Higher concentrations observed during the summer monsoon and directional trends in the distribution, with concentration maxima situated away from the influence of fluvial discharge, are best explained by the atmospheric deposition of mineral dust aerosol and its subsequent dissolution in the surface seawater. The low Al concentrations in the SSL (11–296 nmol kg−1) varied in line with those in the SML. However, Al was significantly higher there than in the rest of the water column (up to 3000 m), indicating that much of the dissolved aerosol Al was removed in the upper few metres of the water column. The non-nutrient-type behaviour of dissolved Al did not support a mechanism of Al removal by biological uptake. High Al levels in the SML observed during the summer monsoon were associated with low primary productivity. The considerably lower values observed during the winter monsoon, a period of higher primary productivity in the Arabian Sea, could be due to removal from solution by adsorption onto biogenic particles. |
