Tracing sinking organic matter sources in the NW Iberian upwelling system (NE Atlantic Ocean): comparison between elemental, isotopic and molecular indicators

•Pyrolysis-GC-MS study of settling organic matter in coastal upwelling region.•Molecular characterization confirmed common assumptions for δ13Coc and C/N proxies.•Marine primary production dominates organic matter in upwelling/downwelling seasons.•Terrestrial signal more intense when high river discharge occurred during downwelling.•Downwelling/upwelling dynamics dominates variability in molecular fingerprints.