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Assessment of sedimentary pigments and phytoplankton determined by CHEMTAX analysis as biomarkers of unusual upwelling conditions in summer 2014 off the SE coast of Algarve
- Sañé, E., Valente, A., Fatela, F., Cabral, M.C., Beltrán, C., Drago, T.
- Journal of sea research 2019 v.146 pp. 33-45
- Bacillariophyceae, Miozoa, biomarkers, chlorophyll, coasts, computer software, data collection, organic matter, phytoplankton, pigments, remote sensing, satellites, sediments, spatial distribution, spring, summer, taxonomy, Portugal
- In this study we tested the validity of sedimentary pigments and phytoplankton as biomarkers of upwelling events. Based on the evidence from satellite and reanalysis datasets that unusually intense upwelling conditions occurred in summer 2014 off the SE coast of Algarve (Portugal), we looked at pigments and phytoplankton before and after summer 2014 in order to test their use as biomarkers of upwelling conditions. From the analysis of summer anomalies with respect to the 2003–2014 average, we show that summer 2014 was characterized by exceptional westerly winds, colder waters and higher chlorophyll, pointing to unusual upwelling conditions. In order to confirm or not the intense upwelling in summer 2014 suggested by satellite data, the concentration of sedimentary pigments has been quantified. Sediments were sampled off the SE Algarve coast in spring and in summer-autumn 2014, above 60 m depth. Labile sedimentary pigments have been used as indicators of recently produced and non-degraded organic matter available as good quality food for consumers. We tested if the particular oceanographic conditions observed in summer 2014 were registered by sedimentary pigments by comparing their concentration and vertical distribution in spring and in summer-autumn. Based on the data on sedimentary pigments, also the phytoplankton composition has been studied. CHEMTAX software has been used to quantify the taxonomic composition of the phytoplankton community and it has been found that the relative contribution of dinoflagellates and diatoms to Chl-a was highest both in spring and in summer-autumn. Based on the SIMPER test, the contribution of dinoflagellates and diatoms to the average square distance between seasons was low, suggesting weaker stratification of the water column also in summer-autumn, maybe related to the intense upwelling conditions of summer 2014. Oceanographic data, together with the distribution of sedimentary pigments and phytoplankton taxa in spring and in summer-autumn, suggest that exceptional upwelling events occurred in summer 2014 off the SE coast of Algarve.