Biogeochemical significance of fatty acid distribution in the coastal upwelling ecosystem off Concepciَn (36°S), Chile

The distribution of fatty acids (FAs) in the water column and surface sediment of the coastal upwelling ecosystem off Concepción (central Chile; almost monthly from February 2007 to November 2008) was analyzed using gas chromatography–mass spectrometry. The concentration of FAs in the water column ranged from 3.4 to 67.7 μg l−1 and showed higher values in surface water than in bottom water, and under upwelling vs. non-upwelling conditions. The content in surface sediment ranged from 21.6 to 328.5 μg g dw−1 and had a higher abundance in February 2007, and January–March and June 2008. In surface water 16:0, 18:0 and 16:1n-7 made up ca. 47% of the FAs during the study period, while in bottom water 16:0, 18:0 and 18:1n-9 accounted for ca. 45%, and in surface sediment ca. 43% was accounted for by 14:0, 16:0, 16:1n-7 and 18:1n-7 FAs. Seasonal variability in the relative abundance of saturated and polyunsaturated FAs (PUFAs) was observed in surface water, while in bottom water and surface sediment no major temporal change in FA composition was observed. A negative exponential relationship between bacterial FAs and PUFAs from surface water and sediment suggests that bacteria may be responsible for ca. 80% of PUFA removal during sinking. We suggest that the FA composition of the surface sediment of the ocean is a consequence of rapid alteration of the FA pool by biological activity in the water column and sediment, driven by the removal of the labile fraction of FAs.