DOWNWARD FLUX OF PARTICULATE FATTY-ACIDS IN THE CENTRAL ARABIAN SEA

Particulate matter collected at 732 and 2914 m during a time-series sediment trap experiment (sampling interval 13 days) in the Central Arabian Sea (14°29′N, 64°46′E; water depth 4016 m) was analysed for its fatty acid and organic carbon contents. The sampling period covered the summer monsoon of 1986. Contents of organic carbon and fatty acid decrease with increasing particle fluxes. At 732 m fatty acids account for 0.6-4% of organic carbon. Particulate organic matter collected during high-productivity and high-flux periods exhibits signs of less intense degradation within the surface layers. Furthermore, loss rates of organic carbon and fatty acids between 732 and 2914 m increase with increasing particle flux, which suggests that water column degradation is intensified during this period. Selective degradation of fatty acids diminishes their contribution to organic carbon in the deeper trap (0.3-0.7%). Despite this, the seasonality in fatty acid flux is maintained down to the deep ocean. Differences in fatty acid composition between the two depths are indicative of the organisms involved in the degradation of particulate organic matter in the water column, especially bacteria. Biological alteration of sinking particulate matter appears to occur mainly on particles. © 1990.