Banca de QUALIFICAÇÃO: CAIO CESAR RIBEIRO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : CAIO CESAR RIBEIRO
Date: 17/08/2026
TIME: 09:00
LOCAL: Sala 406 do Bloco B do Campus de Santo André da Universidade Federal do ABC.(híbrida)
TITLE:

ENVIRONMENTAL IMPACTS OF DEEP-SEA MINING: HYDROTHERMAL SULFIDES OF THE CENTRAL INDIAN RIDGE

PAGES: 303
BIG AREA: Ciências Biológicas
AREA: Ecologia
SUBÁREA: Ecologia de Ecossistemas
SUMMARY:

Deep-sea mining of seafloor massive sulfides (SMS) at hydrothermal vent systems is advancing toward prospective commercial development, driven by escalating global demand for critical metals essential to the energy transition. As of mid-2026, the International Seabed Authority (ISA) had issued eight exploration contracts for polymetallic sulfides in the Atlantic and Indian Oceans, including contracts on the Central Indian Ridge itself, while more than 40 States (43 as of mid-2026) have called for a moratorium or precautionary pause on mining, reflecting a governance gap in which regulatory frameworks have not kept pace with commercial and geopolitical pressures. This doctoral thesis presents an integrated, multidisciplinary environmental assessment of SMS mining impacts along the Central Indian Ridge (CIR), based on physical, chemical, biological, and ecotoxicological data collected during the KIOST MIRAE expedition (March-April 2023) aboard the R/V ISABU, with 17 ROV ROPOS dives across eight vent field clusters spanning 9°-16°S. The thesis is organized into six research chapters (Chapters 1 to 6), each written as a self-contained study, followed by a general conclusion (Chapter 7). Chapter 1 provides an integrated hydrographic characterization of the CIR water column from 24 CTD casts along the ridge axis (nine of them full-depth casts reaching the deep basin; ~9.8 to 15.5°S), identifying five water masses (TSW, SICW, AAIW, CDW, AABW) and documenting the AAIW oxygen-minimum layer (~68 to 74 μmol kg⁻¹) as an environmental vulnerability for mining-plume impacts. Chapter 2 presents high-resolution surface-ocean fCO₂ measurements from the GO168 underway system (7,396 observations), documenting CO₂ supersaturation (up to 691 μatm) associated with a cyclonic mesoscale eddy near the Mascarene Plateau, an estimated surface pH as low as 7.89 and a net CO₂ source during the survey; these carbon-system values are provisional pending final reference-gas calibration (the onboard reference-gas configuration is not yet reconciled). Chapter 3 reports an integrated multi-segment hydrothermal-plume survey of the mid-CIR (9 to 16°S), introducing a Hydrothermal Anomaly Index (HAI) applied to more than 313,000 ROV CTD records and identifying 34 candidate vent clusters, with the ONNARE sector producing the strongest thermal signals. Chapter 4 documents the biodiversity of the vent communities across 17 ROV dives, compiling an evidence-graded matrix of 18 megafaunal morphotaxa (operational taxonomic entries), 15 directly documented in the ROV imagery or in specimens and 3 supported only by regional literature records, organized within a six-zone habitat-zonation model. Chapter 5 presents an integrated ecotoxicological and geochemical assessment of CIR sulfide materials, combining whole-sediment tests, embryo-larval bioassays with three species and Phase-I Toxicity Identification Evaluation, which identify metals as the primary toxicants; bulk Cu and Zn reached the order of 10⁵ μg g⁻¹ and leachate Fe greatly exceeded the marine regulation for seawater. Chapter 6 analyzes the environmental governance and regulation of SMS mining, and Chapter 7 integrates the findings across the thesis. The integrated findings indicate that CIR SMS materials generate high toxicity under the laboratory exposure conditions tested, that CIR vent biodiversity is of high biogeographic conservation value, and that the oceanographic setting (strong density stratification, an AAIW oxygen-minimum layer and active vent-plume signatures) may constrain the rapid dilution of contaminants, although current velocities were not measured during the survey, so plume dilution and dispersal remain to be quantified with direct current measurements and hydrodynamic modelling. These results provide empirical support for a precautionary approach to SMS mining, mandatory pre-exploitation ecotoxicological characterization, and the establishment of a protected reference area network along the CIR. 

COMMITTEE MEMBERS:
Presidente - Interno ao Programa - 1834571 - OTTO MULLER PATRAO DE OLIVEIRA
Membro Titular - Examinador(a) Interno ao Programa - 1658925 - SIMONE RODRIGUES DE FREITAS
Membro Titular - Examinador(a) Externo à Instituição - ANDRÉ LUIZ BELÉM - UFF
Membro Suplente - Examinador(a) Interno ao Programa - 1768895 - GUSTAVO MUNIZ DIAS
Membro Suplente - Examinador(a) Externo à Instituição - ANA LUIZA SPADANO ALBUQUERQUE - UFF