publications
history of publications and scientific production over the years
papers in peer-reviewed journals
2024
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Magnetization of Ferromanganese Crusts: Geochemical and Magnetic Insights From Rio Grande Rise and Tropic SeamountMuhammad Bin Hassan, Andrea Koschinsky, Gabriel Lucas Xavier da Silva, and 5 more authorsGeochemistry, Geophysics, Geosystems 2024Ferromanganese (FeMn) crusts are Fe and Mn oxides that typically form on deep-sea elevations by deposition of colloids from seawater. These mineral deposits are considered a source of critical metals and rare earth elements. Besides their potential economic value, FeMn crusts are extremely relevant in ocean science, since their very slow growth rates result in long-term paleoenvironmental and paleoceanographic records. In this study, we applied geochemical, mineralogical, and magnetic analyses to unravel paleoenvironmental changes at two locations on opposite sides of the Atlantic Ocean, the Rio Grande Rise in the SW Atlantic and the Tropic Seamount in the NE Atlantic. Our results show that the occurrence of amorphous (non-crystalline) Fe oxyhydroxides and the absence of Fe oxides in hydrogenetic, non-phosphatized FeMn crusts prevented the development of primary remanent magnetization. In contrast, phosphatized FeMn crusts may have contained a remanent magnetic signal. Phosphatization resulted from increased primary productivity and occurred at different stages during the growth of the FeMn crusts, leading to suboxic conditions and partial dissolution of pre-existing, remanence-carrying magnetic minerals. Carbonate Fluorapatite (CFA) accumulation in the phosphatized layers of FeMn crusts replaced Fe and Mn, decreasing their magnetic content. Thus, magnetic variations do not reflect a primary magnetization but rather result from geochemical alterations. The loss of primary magnetization may hamper the use of FeMn deposits for magnetostratigraphic purposes.
2022
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Connectivity patterns of Brazilian coral reefs associated with potential variation on thermal stress toleranceGabriel Lucas Xavier da Silva, and Milton KampelFrontiers in Marine Science 2022The rising trend in sea surface temperature presents a threat to tropical coral reefs, causing increased mass bleaching and mortality events. Brazilian reefs have been characterized as less susceptible to thermal stress, where the assessment of bleaching events based on temperature anomalies often overpredicts its actual occurrences in comparison with other regions of the global ocean. With coral reefs acclimatized to local environmental conditions, larval connectivity presents a potential role in introducing organisms adapted to different temperature conditions. In the present study, we evaluated the connectivity patterns of Brazilian coral reefs, verifying its potential influence on the variation of thermal stress tolerance supported by these communities. Connectivity was estimated based on 27-year larval dispersion simulations, from 1993 to 2019, among 180 reef sites distributed in seven ecoregions on the Brazilian continental margin. Simulations were performed using a biophysical model coupling ocean currents data and life history traits of Mussismilia hispida, a widespread stony-coral type species and one of the major endemic reef builders in the South Atlantic. The potential influence of larval connectivity on thermal stress tolerance was evaluated considering the probability of connections between each reef site, their respective bleaching thresholds, and the accumulation of sea surface temperature anomalies over 12-week periods. The results indicated that connectivity-influenced bleaching estimations were significantly closer to observations reported in the literature when compared to estimations without connectivity (p-value < 0.05). These findings present an evidence that larval connectivity may display a relevant role in the adaptation of Brazilian corals to changes in seawater temperature, leading to a potential variation of ± 0.3°C in local thermal stress thresholds. Different connectivity patterns assessed during the occurrence of El Niño–Southern Oscillation events were also observed in association with the migrations of the South Equatorial Current bifurcation. These conditions led to the disruption of connections between the Eastern and Northeastern reef sites during El Niño, and between the Northeastern and Amazon reef sites during La Niña. Ultimately, it is expected that those findings may contribute to the management of Brazilian coral reefs regarding changes in dispersal pathways and thermal stress tolerance given future climate change scenarios.
2020
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Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)Flaminia Cornaggia, Simone Bernardini, Martino Giorgioni, and 3 more authorsScientific reports 2020The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at around 40 Ma and lasted about 500 kyr. We study this event in an abyssal setting of the Tasman Sea, using the IODP Core U1511B-16R, collected during the expedition 371. We analyse magnetic, mineralogical, and chemical parameters to investigate the evolution of the sea bottom conditions at this site during the middle Eocene. We observe significant changes indicating the response to the MECO perturbation. Mn oxides, in which Mn occurs under an oxidation state around +4, indicate a high Eh water environment. A prominent Mn anomaly, occurring just above the MECO interval, indicates a shift toward higher pH conditions shortly after the end of this event. Our results suggest more acid bottom water over the Tasman abyssal plain during the MECO, and an abrupt end of these conditions. This work provides the first evidence of MECO at abyssal depths and shows that acidification affected the entire oceanic water column during this event.
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presentations in meetings and symposiums
2023
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Analyzing thermal modulation mechanisms and possible connectivity-induced variability in bleaching thresholds via multiscale hydrodynamics modelingAhmed Eladawy, Takashi Nakamura, Masaya Yoshikai, and 1 more authorInternational Conference on the Marine Environment of the Red Sea (ICMERS), Thuwal (Saudi Arabia), 2023Despite increasing attention to Red Sea hydrodynamics over the past few years, the interaction between the Gulf of Suez and the Red Sea, as well as the possible natural mitigation mechanisms of heat stress on the southern coral reef zones, have not been adequately examined. To understand the three-dimensional nature of thermal variability in the Red Sea, this study examines several Regional Ocean Modeling System (ROMS) simulations using a nesting approach in the southern parts of the GOS. On a TSUBAME 3.0 supercomputer operated by the Tokyo Institute of Technology, the regional ROMS model was used to simulate general circulation patterns and sea surface temperatures. Ultimately, satellite data spanning 2016-2020 were used to validate the regional model. An offline nesting approach was used to simulate the local 3-D thermal regimes of the northern islands region due to the scarcity of distributed depth-varying temperature data. Intriguingly, the nested model scenarios confirmed an unusual thermal moderating mechanism involving northern islands that act as barriers to influences from the eastern boundary current. A new approach is also presented to using higher-resolution models to precisely represent thermal indices in space and time that surpasses the widely used remote sensing methodologies. Shortly, multiscale modeling provides a valuable tool for assessing the thermal regimes around one of the Red Sea’s most precious marine ecosystems.
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Detecção de frentes oceânicas na Bacia de Santos a partir da temperatura da superfície do mar estimada por satéliteGabriel Lucas Xavier da Silva, Vitor Paiva, and Milton KampelXX Simpósio Brasileiro de Sensoriamento Remoto (SBSR), Florianópolis (Brasil), 2023As frentes oceânicas são definidas pelo encontro de massas d’água com diferentes propriedades físico-químicas. A temperatura da superfície do mar (TSM) pode ser utilizada para detecção de frentes oceânicas com base na magnitude do seu gradiente em determinado período e local. Neste estudo propomos caracterizar a variabilidade da ocorrência de frentes oceânicas na Bacia de Santos. Foram utilizadas imagens da TSM obtidas por satélite durante 2002-2022, as quais foram submetidas a um algoritmo de detecção de bordas para identificação das frentes oceânicas na região. A ocorrência de frentes oceânicas foi avaliada a partir de sua variabilidade sazonal e sua decomposição com base em funções ortogonais empíricas. Os resultados indicam a ocorrência de frentes oceânicas principalmente associadas a presença da Corrente do Brasil, também estando possivelmente relacionadas a fenômenos de ressurgência e intrusão de águas frias vindas de sul durante o inverno.
2022
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Distribution and intensity of marine heatwaves over Brazilian coral reefs: relationships with bleaching eventsGabriel Lucas Xavier da Silva, Milton Kampel, and Vitor PaivaESA Living Planet Symposium, Boon (Germany), 2022The occurrence of Marine Heatwaves (MHWs) has intensified its frequency and intensity over the past years due to climate change and ocean warming. This phenomenon is characterized by abnormal sea surface temperature (SST) conditions, where SST stays above a climatological temperature threshold for at least five consecutive days. This anomaly pattern is associated with various impacts on marine ecosystems such as an increase in coral bleaching events, mass mortality of organisms, and loss of benthic habitat. This study aims to assess the occurrence of Marine Heatwaves on Brazilian coral reefs, tracking its spatiotemporal distribution, intensity, and potential relationship with historical coral bleaching events in the region. NOAA Coral Reef Watch (CRW) daily global 5km SST product, also known as CoralTemp, was extracted for 180 coral reef sites along the Brazilian continental margin in the period from 1985 to 2020. CoralTemp SST data were statistically compared against in situ buoy data available from the Brazilian National Buoy Program - PNBOIA (https://www.marinha.mil.br/chm/dados-do-goos-brasil/pnboia-mapa) in terms of the correlation coefficient (R = 0.99), root mean square error (RMSE = 0.55ºC) and bias (-0.06ºC). CoralTemp SST time series were decomposed in order to obtain its trend, seasonal and residual components. We then performed a normalization procedure by subtracting the seasonal component from the original time series, removing the influence of periodical variability in order to detect only anomalous events. Daily positive SST anomalies were calculated considering the deviation from the climatological mean at each coral reef site. Then, MHWs were identified on the basis of the 90th percentile threshold if presenting a minimum duration of five consecutive days. In addition, intervals of two or less days between continuous events above 90th percentile were considered as part of the same MHW. After the MHW identification, we calculated the intensity, duration and cumulative intensity (ºC days) for each event. These events were also classified according to their severity, considering the maximum intensity and the 90th percentile deviation from the climatological mean. In order to verify the potential relationship with coral bleaching events, the identified MHWs were grouped into five marine ecoregions according to the location of the coral reef sites: Eastern Brazil (EST), Trindade and Martim Vaz islands (TMZ), Northeastern Brazil (NST), Fernando de Noronha island and Atol das Rocas (FNA) and the Amazon region (AMZ). Then, the identified MHWs were matched with the bleaching events reported in the literature and/or registered in public databases. Preliminary results indicated that the average occurrence and intensity of MHWs on Brazilian coral reef sites varied greatly according to their marine ecoregion. An average of 78, 58, 70, 48, 63 MHWs were spotted at EST, TMV, NST, FNA and AMZ ecoregions, respectively. The intensity of MHWs were greater at coral reef sites farther from the equatorial region, reaching a maximum anomaly peak of 2.70 ºC at TMV and 2.62 ºC at EST. The cumulative intensity observed for TMV and EST were also > 104 (ºC days). Although northern coral reef sites also presented severe MHWs, their maximum anomaly peak and cumulative intensity were < 2 ºC and < 104 (ºC days). Also, 50% of the MHWs here identified were detected in the last 10 years, indicating a strong increase in the probability of occurrence of these events. Regarding coral bleaching, all the most intense and persistent MHWs occurrences seem to be associated with at least one reported bleaching event per marine ecoregion, indicating that although South Atlantic coral reefs are more resistant to positive temperature anomalies, periods of extreme and persistent warming are still threatening their health and conservation. Ultimately, our results show that the occurrence of MHWs on the Brazilian coral reefs are intensifying over the years, mainly in the southern communities. Further analyses are also being conducted to better understand the impacts of less severe MHWs on these ecosystems.
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Shifts in connectivity patterns of a major coral reef builder sp. during ENSO eventsGabriel Lucas Xavier da Silva, and Milton KampelXIX Congresso Latinoamericano de Ciencias del Mar (COLACMAR), Panama City (Panama), 2022Despite being sessile organisms in their adult phase, corals have a high migratory capacity due to the characteristics of their life cycle. During their reproduction phase, hundreds of larvae are released into the water column allowing its dispersion over large distances. When larvae are successfully transported from one population to another, we have a process known as connectivity. Studies on coral reef connectivity are essential for securing marine biodiversity in general. Here we proposed to evaluate the connectivity metrics of Brazilian coral reefs and verify the potential influence of El Niño–Southern Oscillation events in its patterns. Connectivity metrics were estimated through larvae dispersal simulations from 1993 to 2019, between 180 reef sites distributed in seven regions on the Brazilian continental margin. Simulations were performed using a biophysical model coupling ocean currents data and life-history traits of Mussismilia hispida, a widespread endemic species and one of the major reef builders in the region. The results indicated a variation in connectivity patterns according to the occurrence of ENSO events. El Niño years were marked by a shutdown of connectivity between Northeastern and Eastern reefs, whereas La Niña years were marked by a shutdown of connectivity between Northern and Northeastern reefs. These results can be associated with changes in larvae dispersion due to the migration of the South Equatorial Current southern branch. Ultimately, these findings may help elucidate the dynamics of larvae connectivity between Brazilian coral reefs and their conservation in the face of a changing climate.
2021
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Occurrence of Marine Heatwaves along the Northeastern Brazilian coast during 2002 - 2020Gabriel Lucas Xavier da Silva, Lorena Moura Joia Gomes, Milton Kampel, and 1 more authorXXII Brazilian Symposium on Geoinformatics (GEOINFO), Virtual, 2021Marine Heatwaves (MHWs) are defined as high-impact events in which the Sea Surface Temperature (SST) stays anomalously high during at least five consecutive days. This events are directly related to mass mortality of organisms, loss of benthic habitat and changes on the biological, economic and political structure. Here we proposed to identify the occurrence of MHWs along the Northeastern Brazilian coast, during 2002-2020. We used MODIS-Aqua/L3SMI products for retrieving the SST, then applied spatial reductions to obtain the temporal series for three major polygons created along the coastline. Time series analysis was carried in order to remove seasonality effects and to identify consecutive extreme events above 98th percentile. The obtained results indicated the presence of eight MHWs between the years 2009, 2010, 2019 and 2020. Ultimately, all these occurrences were classified as strong, severe or extreme events.
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Caracterização espaço-temporal da turbidez na Baía de Santos (SP) em relação à variáveis ambientaisGabriel Lucas Xavier da Silva, and Milton KampelXVI Semana Temática de Oceanografia (STO), Virtual, 2021Entender como variáveis ambientais interferem na qualidade da água de ecossistemas marinhos é muito relevante para a sociedade, especialmente para populações associadas às metrópoles costeiras e portuárias, como é o caso das que circundam a Baía de Santos no litoral do Estado de São Paulo. A turbidez, um dos índices utilizados para modelar a qualidade da água, pode ser estimada através de técnicas de sensoriamento remoto e ajudar a compreender a saúde destes sistemas aquáticos. Neste estudo propomos identificar o padrão de distribuição espacial da turbidez na Baía de Santos (SP) e verificar sua possível relação com as variáveis ambientais de uso-cobertura da terra, precipitação e dinâmica de ventos durante o período de 2002 a 2018. Para isso utilizamos um algoritmo de estimação indireta da turbidez via satélite, aplicado sobre os produtos do sensor MODIS-Aqua; bem como conjuntos de imagens e dados de reanálise dos bancos MAPBIOMAS, CHIRPS e ERA5. Foram aplicados algoritmos de agrupamento para identificar a distribuição espacial da turbidez e obter seu padrão regionalizado. Em seguida, realizamos análises de séries temporais e modelos de regressão linear para comparar a possível relação entre variáveis apresentadas ao longo do tempo. Os resultados indicam a existência de três zonas principais de turbidez na Baía de Santos: Z1 (𝜇T = 8.29 FNU), Z2 (𝜇T = 6.56 FNU) e Z3 (𝜇T = 5.27 FNU). Foi possível observar uma relação linear significativa entre a tendência de crescimento da turbidez (Z1 e Z2) e o aumento da infraestrutura urbana, diminuição de agro-pastagem e variações na cobertura de manguezal. Por fim, a turbidez da água também apresentou uma forte correlação positiva com a tensão de cisalhamento do vento durante o outono.
2019
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O Ótimo Climático do Eoceno Médio no Mar de Tétis (Bacia Elazig, Leste da Turquia): uma abordagem estatísticaGabriel Lucas Xavier da Silva, and Luigi JovaneII Simpósio Brasileiro de Geologia e Geofísica Marinha (SBGGM), Porto Alegre (Brasil), 2019O presente estudo propõe a interpretação de registros geológicos referentes ao Eoceno Médio obtidos ao longo do afloramento de Baskil, localizado na Bacia Elazig (Leste da Turquia - 38°36’30.34’’N, 38°36’03.46’’L). No estudo utilizamos dados referentes a propriedades magnéticas, mineralógicas, isotópicas e geoquímicas que foram submetidos a algoritmos estatísticos capazes de gerar padrões de agrupamento baseados em suas semelhanças. Os resultados obtidos foram interpretados com o intuito de identificar a presença de diferentes processos climáticos e oceanográficos nos registros geológicos da seção. Em última análise, o projeto teve como foco analisar a influência do evento Ótimo Climático do Eoceno Médio (MECO).
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thesis
2022
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Padrões de conectividade em recifes de coral brasileiros associados ao estresse termal estimado por satéliteGabriel Lucas Xavier da SilvaMestrado em Sensoriamento Remoto, Instituto Nacional de Pesquisas Espaciais (INPE), 2022A tendência de aumento da temperatura da superfície do mar representa uma ameaça para os recifes de coral tropicais, causando branqueamento e mortalidade em massa. Os recifes brasileiros tem sido caracterizados como menos suscetíveis ao estresse termal. A previsibilidade de eventos de branqueamento com base em anomalias da temperatura da superfície do mar pode ser menos precisa do que em outras regiões do oceano global. Como os recifes de coral são aclimatados às condições ambientais locais, a conectividade larval tem potencial para desempenhar um papel relevante na introdução de organismos adaptados a diferentes condições de temperatura. No presente estudo propõe-se avaliar os padrões de conectividade em recifes de coral brasileiros, verificando sua influência potencial na variação da tolerância ao estresse termal nestas comunidades. Foram estimadas métricas de conectividade com base em simulações de dispersão larval no período de 1993 a 2019, entre 180 células recifais distribuídas em sete regiões na margem continental brasileira (Leste-sul, Leste-centro, Lestenorte, Trindade e Martim Vaz, Nordeste, Fernando de Noronha e Atol das Rocas e Amazônia). As simulações foram realizadas utilizando um modelo biofísico acoplado a dados de correntes oceânicas e características biológicas da espécie Mussismilia hispida, um coral endêmico e amplamente difundido na costa brasileira. A influência potencial da conectividade larval na tolerância ao estresse termal foi avaliada considerando a probabilidade de conexões entre cada célula recifal, seus respectivos limiares de branqueamento e o acúmulo das anomalias de temperatura da superfície do mar estimadas por satélite durante 12 semanas. Os resultados obtidos indicam uma variação nos padrões de conectividade de acordo com a ocorrência de eventos El Niño–Southern Oscillation, quando se observam mudanças na dispersão larval associadas a deslocamentos da bifurcação do ramo sul da Corrente Sul Equatorial. As métricas de conectividade indicam uma variação do limiar de branqueamento de ±0,3 °C, com células recifais apresentando variações relevantes na tolerância ao estresse termal. As estimativas de branqueamento considerando a conectividade foram significativamente mais próximas das observações reportadas na literatura (valor-p < 0,05), em comparação com as estimativas sem a conectividade. Os resultados obtidos indicam que a conectividade larval pode ter um papel relevante na adaptação dos corais brasileiros a variações na temperatura da água do mar. Quando considerada, observa-se uma melhora nas estimativas de branqueamento desses corais. Espera-se que o presente estudo possa contribuir no monitoramento ambiental e no manejo de recifes de coral brasileiros, considerando os cenários futuros de mudanças climáticas.