Ecosystem services of dissolved organic matter in the oceans

• Autores: Ester Jerusalén Lleó
• Directores de la Tesis: M. Mar Nieto Cid (dir. tes.), Xosé Antón Álvarez Salgado (dir. tes.)
• Lectura: En la Universidade de Vigo ( España ) en 2025
• Idioma: inglés
• Tribunal Calificador de la Tesis: T. Ortega Díaz (presid.), Óscar Nieto Palmeiro (secret.), Cristina Romera Castillo (voc.)
• Materias:
  • Ciencias de la tierra y del espacio
    • Geoquímica
      • Geoquímica orgánica
    • Oceanografía
      • Oceanografía biológica
• Enlaces
  • Tesis en acceso abierto en: Investigo
• Resumen

  • Dissolved organic matter (DOM) is not only a vast reservoir of reduced carbon (662 Pg C) that plays a key role in oceanic biogeochemical cycles, but it also provides important regulating ecosystem services (ES), such as carbon sequestration, trace metal complexation, and absorption of UV radiation. This PhD thesis investigates how DOM contributes to these services by assessing its dependence on elemental, optical, and molecular composition in two study areas: the Cape Verde Frontal Zone (CVFZ; NW Africa) and the coastal, shelf, and oceanic waters of the NW Iberian Margin (Galicia). These areas are of particular oceanographic interest as they are regions where water masses of diverse origins circulate and mix, and where oceanographic processes such as coastal upwelling or continental water discharge occur, making them ideal scenarios to explore these ES. These ES are evaluated using DOM concentrates obtained through solid-phase extraction (PPL resins) or ultrafiltration of natural samples. The representativity of the isolated material varies depending on the isolation method used. PPL extracts are enriched in nitrogen-poor compounds and low molecular weight (LMW) recalcitrant DOM, while ultrafiltrates are depleted in fluorescent DOM (FDOM) and enriched in the high molecular weight (HMW) coloured DOM (CDOM) fraction. The CVFZ is characterized by a high molecular diversity, with 16% of the formulas common to all samples, representing 81% of the total amount. These common formulas are dominated by highly unsaturated compounds enriched in CHO, indicating strong microbial reprocessing. Exclusive molecules are dominated by heteroatomic groups including N, S, and P, which are associated with DOM production and transformation processes. The evaluation of the capacity of DOM to provide the studied ecosystem services showed that, in the CVFZ and the Iberian Basin, around 50% of the dissolved organic carbon (DOC) behaved similarly to refractory marine humic-like substances, while 10% resembled labile protein-like substances. Continental and marine waters of the Iberian Basin exhibit different copper complexation capacities. In the Oitavén River, this capacity is characterized by a marked seasonality, linked to DOM aromaticity, whereas in coastal and oceanic waters, it appears to be more related to the enrichment of LMW CDOM. Finally, photodegradation experiments followed by marine bacteria inoculation reveal high photosensitivity of the DOM concentrates, with significant and rapid losses of CDOM and FDOM. In the Oitavén River, this decline is most pronounced in autumn, linked to changes in the dominance of HMW and LMW compounds. The irradiated material predominantly favours bacterial growth as it is dominated by allochthonous DOM. In coastal and oceanic waters, photodegradation rates tend to increase with depth and, unexpectedly, are higher for protein-like than for humic-like fluorophores, attributed to the affinity of PPL for photodegradable protein-like fluorophores. Bacterial growth was neutral or negative, associated with the depletion of HMW compounds after extraction.