Omotayo Fadina

and 8 more

Marine sediments from the Western and Eastern South Atlantic continental margins are used to reconstruct mercury (Hg) accumulation over the last glacial/interglacial cycle. Sediment core GL-1248, collected from the continental slope off northeastern Brazil, and sediment core ODP1077, retrieved from the Congo deep-sea fan area, both dated to the last 128 ka and 130 ka respectively. Mercury concentrations in GL-1248 ranged between 14.95 and 69.43ng/g, and varied with periodicities of 56 ka and 900 yr suggesting the presence of glacial-interglacial changes and millennial-scale variability respectively. Parallel trends of Hg and XRF-Fe plots suggest that following atmospheric Hg deposition onto the continent, Hg is incorporated with iron (Fe) minerals before transportation and eventual immobilization at the NE Brazil continental slope. Mercury concentrations in ODP1077 varied significantly, having concentrations between 23.12 ng/g and 256 ng/g, and its plot exhibits an anti-phase pattern with the Fe/Ca ratio plot, that distinguishes between periods of increased and decreased terrigenous material delivery. This inverse trend in the plots of mercury concentration and Fe/Ca ratio shows that during periods of increased (decreased) terrigenous material delivery, less (more) mercury accumulates in the marine sediment. Although Hg concentration is poorly correlated with total organic carbon (TOC), it correlates positively with XRF-Ca implying that marine organic matter played a significant role in mercury distribution and accumulation in the ODP1077 marine sediment core. Despite the fact that both marine sediment cores were retrieved from the tropics and cover the same glacial/interglacial periods, their mercury variations and the main drivers of mercury accumulations are dissimilar. Accordingly, we identified two different pathways by which mercury is incorporated into marine sediments for prolonged storage and inclusion in the global mercury biogeochemical cycle. The outcome of this study suggests that regional climate processes and geochemical conditions are essential to Hg variations in environmental archives. Another obvious finding is that the source of sedimentary organic carbon is a key determinant of their affinity for mercury.

Luthiene Dalanhese

and 5 more

Extratropical cyclones are weather phenomena with significant transfer of energy between the surface (over the ocean or on land) and the atmosphere. Recurrently, reanalysis data are used to understand the behavior of cyclonic tracks and to study extreme events, with constant updates and validations with the observational base in the Northern Hemisphere. However, studies using cyclone tracking in the Southwestern Atlantic, has proven more difficult. This disagreement seems to be in function of the structure and intensity of the forcing factors that influence both cyclogenesis and the displacement to the South Atlantic, when compared to the Northern Hemisphere. In this work, synoptic pressure charts at sea level, manually made and processed by the Brazilian Navy every 12 hours between the years 2010 and 2020, as a product resulting from a consensus among Navy meteorologists, were used to study the cyclonic pathways in the Southwestern Atlantic (METAREA V). Data obtained for all cyclones identified in the charts, based on their position and displacement, formed a database with 10737 cyclones, containing speed, dimensions, and pressure gradient. The cyclones identified have a higher radius frequency between 200/400 km and a faster-moving center shift. In addition, about 60% of cyclones associated with cold fronts have a life cycle ranging from 3 to 4 days. There is also a expressive cyclogenesis between latitudes 23ºS and 43ºS where, in austral autumn winter, increases its frequency over the ocean and close to the southern Brazilian coast. During spring, the greater cyclogenesis frequency occurs over the continent, close to Chaco area in Argentina and Uruguay. The impacts of these statistical figures on the south and southeastern Brazilian coast, mainly the continental insertion point of the cold fronts and cyclonic displacement that influence rough seas and storm surges, are discussed in this work. Keywords: EXTRATROPICAL CYCLONES, CYCLONE TRACK, SYNOPTIC CHARTS, SOUTHWESTERN ATLANTIC