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Impacto dos processos físicos de mesoescala na produtividade primária : efeito de ilha
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Resumo(s)
In oligotrophic oceanic environments, islands can amplify primary productivity (PP) by reorganizing the nutrient field through orography–wind–ocean interactions. Around Madeira Island, the physical signature of the island effect is well described, but the impact on PP and the relative contribution of the underlying processes to the island mass effect (IME) remain poorly quantified. A coupled physical–biogeochemical model (ROMS+N2PZD) with a 3–1 km nested grid was applied and validated against remote sensing and coastal in-situ data. The model reproduces the main large-scale controls: wind (r > 0.9), sea surface temperature (SST; positive bias but realistic variability), surface chlorophyll-a (CHLa; overestimation at the surface and underestimation in depth), and the location of geostrophic eddies/currents (with caution regarding intensities near the coast). Physical structures were identified from simulated sea surface height anomalies (SSHA), in combination with SST, wind, current fields, and thermal profiles. The IME was assessed from vertical inventories of CHLa and nitrate (NO₃⁻) integrated down to the euphotic depth (Zₑᵤ) and 100 m, accounting for event duration. Results show that cyclonic eddies dominate the IME (~48% of CHLa enhancement at Zₑᵤ and ~60% at 100 m), followed by advection (~29–26%) and internal waves (~19–13%). The wake produces modest surface PP gains (<5%), whereas anticyclonic eddies act as inhibitors (net negative contribution). For NO₃⁻, cyclones and internal waves contribute similarly at Zₑᵤ (~40%), but cyclones dominate at 100 m (~67%). We conclude that mesoscale structures govern the IME. PP peaks when internal-wave-induced upwelling supplies nutrients that are redistributed by advection, while cyclones enhance residence time of fertilized waters and promote bloom grow.
Descrição
Tese de Mestrado, Ciências do Mar, 2026, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Primary productivity Madeira Island effect Physical–biogeochemical model Physical processes