oa Variation in the Source of Organic Matter to the Iberian Margin Over the Millennia

The Iberian Margin, influenced by wind-driven coastal upwelling, plays an important role in ocean productivity and climate regulation. However, the impact of climate change on primary production (PP) and marine ecosystems remains uncertain due to natural variability and future ocean dynamics. This study, part of the ICW3P project, aimed to assess the temporal variation of organic matter (OM) sources along the Iberian Margin over the last millennium using lipid biomarkers and isotopic compositions. Sediment records from three sites (Douro, Tagus and Algarve) were analyzed. Results showed significant differences in OM provenance, particularly at the Algarve site, and revealed that the isotopic approach was less effective in distinguishing sources where both terrestrial and marine inputs were substantial. Principal component analysis (PCA) of lipid biomarkers revealed more informative variations in OM sources, with marine OM dominating in Porto during the industrial era and some periods of the Little Ice Age, and terrestrial OM dominating in the Tagus in certain years. In the Algarve, marine algal OM dominated during the industrial era and earlier periods. The study found that upwelling and flooding events influenced OM dominance, with temporal shifts in the dominance of vegetation and phytoplankton groups along the Iberian Margin.