Assessment of organic matter preservation and coastal constraints (SE Algarve, Portugal)

Abstract

Surface sediments were sampled at 18 stations from 7 to 64 m depth off the SE coast of Algarve to characterize the organic matter contents in the inner and middle shelf. For each sediment sample, grain size, mineralogy and total organic carbon analyses were carried out, as well as pigment analyses (19’ but-fucoxanthin, fucoxanthin, 19’ hex-fucoxanthin, chlorophyll-a, chlorophyll-b, pheophytin-a, pheophorbide-a, alpha-carotene, beta-carotene, anteraxanthin, diadinoxanthin, diatoxanthin, lutein and zeoxanthin). In addition, the ratios between each pigment and the total organic carbon (TOC) percentage, and between the chlorophyll-a concentration and the pheophytin-a and the pheophorbide-a concentrations were calculated to establish pigment indices. A Multidimensional scaling (MDS) analysis highlights three regions in the SE coast of Algarve according to depth, percentages of TOC, sediment grain size and mineralogy, concentration of pigments highly susceptible to degradation, concentration of refractory pigments (pigments not susceptible to degradation) and different preservation conditions (based on the pigment index values). The results highlight a correlation between pigments concentration and environmental variables, showing the eastern limit of West coastal upwelling plumes influence along the Algarve continental shelf.