Impactos das mudanças climáticas no Oceano Atlântico Equatorial e Sul: dos parâmetros biogeoquímicos à sensibilidade dos ecossistemas costeiros

Abstract

Climate change is a reality and a proven consequence of anthropogenic activities that increase the concentration of greenhouse gases in the atmosphere. Its impacts are diverse, affecting ecosystems as well as society and the economy. In some regions of the global oceans, it is still uncertain how climate change will influence biogeochemical parameters and how its effects, for example, increase of temperature, sea level rise, acidification and extreme events (e.g. marine heat waves, storms, storm surges and others) will affect marine and coastal ecosystems. Some of these regions are the South Atlantic and Equatorial Ocean, so this study aims to answer the following questions: i) How do biogeochemical parameters in the Atlantic Ocean respond to possible increases in CO2 in the atmosphere by 2100? ii) What is known about CO2 fluxes at the ocean-atmosphere interface on the Brazilian coast to date? iii) How sensitive and vulnerable are marine ecosystems in Brazil? For the latter, Guanabara Bay and adjacent regions were used as a case study. To answer these, an earth system model of intermediate complexity, ecoGENIE, was used with scenarios without climate change and two scenarios from the IPCC's 5th report (RCP 4.5 and RCP 8.5) up to the year 2100; a review of the available literature; and the basis for drawing up Environmental Sensitivity Charts for Oil Spills, respectively. The results show that (i) the intensity of the changes in biogeochemical parameters depends on the IPCC scenario, but both point to acidification of the ocean and a decrease in the export of carbon to the subsurface by 2100, in addition, the behavior of the regions changes from source to sink of CO2. (ii) It was possible to observe that over 20 years, only 50 scientific papers have been published on CO2 fluxes at the ocean-atmosphere interface off the coast of Brazil. The largest number of studies focused on the Amazonas River plume (14) and Rio de Janeiro coastal area (11). In general, the Brazilian continental margin behaves as a source of CO2 in the northeast, neutral in the southeast and a sink in the south, following the latitudinal variation, and there is a clear lack of information on the effects of seasonality, synoptic and mesoscale events on CO2 fluxes. For question (iii) 10 ecosystem sensitivity index were proposed, and an Environmental Sensitivity Map to Climate Change was developed. In Guanabara Bay and adjacent areas, 5 ecosystems were identified with 7 distinct sensitivity indices. Overall, climate change will cause alterations in the Atlantic Ocean and in the coastal ecosystems.