Temporal changes in the amino acid contents of particulate organic matter sedimenting in the Bay of Banyuls-sur-Mer (northwestern Mediterranean)

We monitored gross sedimentation rates (GSR) together with organic carbon, total hydrolysable (THAA) and enzymatically available (EHAA) amino acid con tents of the particulate organic matter collected within 2 sediment traps m oored during a 4 yr period at a shallow station (18 m) in the Bay of Banyul s-sur-Mer (northwestern Mediterranean). GSRs were between 0.26 and 470.55 g DW m(-2) d(-1) They were low during spring and summer, and usually higher but much more variable during fall and winter. Organic carbon concentration s were between 1.21 and 6.94% DW, versus 3.36 and 29.16 mg g(-1) DW, and 0. 54 and 14.44 mg g(-1) DW for THAA and EHAA, respectively. EHAA/THAA ratios were between 13.91 and 65.78 %. These 4 parameters showed an annual periodi city and correlated negatively with GSR, which supports the role of resuspe nsion in controlling sedimentation. THAA and EHAA spectra were both dominat ed by glycine, aspartic acid, glutamic acid and alanine. However, there wer e consistent differences between the 2 kinds of spectra. EHAAs were enriche d in threonine, glutamic acid, leucine and aspartic acid; and depleted in a rginine, lysine, glycine and histidine. EHAA spectra showed fewer temporal changes than THAA spectra. In all cases but one, significant changes in THA A spectra were related to glycine, aspartic acid, glutamic acid and threoni ne, and were indicative of the presence of degraded material, probably due to resuspension. We computed degradation indexes based on both THAA and EHA A spectra. THAA degradation index was between -0.318 and 1.363 versus 0.051 and 1.006 for EHAA. Both of these indexes showed an annual periodicity and correlated positively (although weakly) with EHAA/THAA ratios. None of the m correlated negatively with GSR. This last result suggests that EHAA/THAA ratios constitute a better index of the lability of particulate organic mat ter than degradation indexes.