Fatty acid reactivities in sediment cores from the northern Gulf of California

Fatty acids were determined in three sediment cores from Delfin Basin, Northern Gulf of California (NGC), Mexico. Steady-state apparent degradation rate constants (k′) were determined to assess the reactivity of the total organic carbon (TOC) pool, the total fatty acids (TFA) and selected individual fatty acids. k′ values for TFA were higher than those for TOC, indicating that fatty acids are at least 5 times more labile than the organic carbon pool. A comparison of k′ values for selected fatty acids indicates that the long-chain terrigenous fatty acids are less labile than the shorter chained fatty acids from autochthonous sources. The general order of reactivity by source was plankton>bacteria>terrestrial. There are at present essentially no inputs of terrigenous material from the Colorado River. Therefore, the lower reactivity of the terrigenous fatty acids in the Delfin Basin probably suggests that the contemporary source of terrestrial organic matter to the NGC is the eroding Colorado River Delta, which contains already degraded organic carbon. In spite of the high primary productivity in the region, k′ values for fatty acids from the NGC were low when compared with those from other marine ecosystems. These results suggest that fatty acid diagenesis during particle settling through the water column in the NGC is intense, allowing only for the deposition of relatively refractory organic matter.