Biogeochemistry of surface sediments in an Antarctic nearshore area affected by recent glacier retreat: Collins Harbour, King George Island

Biochemical composition of sedimentary organic matter, grain size, major and trace elements were analysed at 10 sampling stations in Collins Harbour, Maxwell Bay, to evaluate sources of particulate material in the seafloor. Surface sediment samples were taken with a grab, during the ANTAR XXV expedition in January 2018, onboard the BAP Carrasco from the Peruvian Navy. Coarse sediment fractions decreased, while mud content increased towards the centre of the bay. Positive correlation between mud and the biopolymeric carbon (BPC) indicated depositional conditions and organic material accumulation in the deepest central area. Proteins (PRT) predominated over other biochemical classes contributing to labile organic carbon, followed by lipids (LIP) and carbohydrates (CHO). PRT positive correlation with Ba, Ca and Al indicated that labile organic carbon inputs derived from marine primary production. Whereas, PRT positive correlation with K and Ti suggested also the influence of terrestrial supply through Collins Glacier meltwater runoff. Mn/Ti, Mn/Al and Fe/Al ratios decreased towards the centre of the bay, while the Ba/Al ratio showed the opposite trend. This distributional pattern suggested the diminish of glacial and terrigenous sedimentation towards the deepest central area of the bay, with the increment of marine particulate material deposition and accumulation. Igeo values between 0 and 1 showed unpolluted conditions in Collins Harbour for Cr, Ni, Cu, Zn, As and Pb, which concentrations may reflect background values for this area. Natural inputs from weathering, glacial runoff and marine primary production are main sources of particulate material in Collins Harbour, with none detected anthropogenic contributions

Radiocarbon geochronology of the sediments of the São Paulo Bight (southern Brazilian upper margin)

The aim of this work was to generate an inventory of the data on radiocarbon datings obtained from sediments of the São Paulo Bight (southern Brazilian upper margin) and to analyze the data in terms of Late Quaternary sedimentary processes and sedimentation rates. A total of 238 radiocarbon datings from materials collected using differents ampling procedures was considered for this work. The sedimentation rates varied from less than 2 to 68 cm.kyr-1. The highest sedimentation rate values were found in a low-energy (ría type) coastal system as well as in the upwelling zones of Santa Catarina and Cabo Frio. The lowest rates were found on the outer shelf and upper slopes. Our results confirm the strong dependency of the shelf currents, with an emphasis to the terrigenous input from the Río de La Plata outflow which is transported via the Brazilian Coastal Current, as well as of the coupled Brazil Current - Intermediate Western Boundary Current (BC-IWBC) dynamics on the sedimentary processes. At least three indicators ofthe paleo sea level were found at 12200 yr BP (conventional radiocarbon age) (103 meters below sea level - mbsl),8300-8800 cal yr BP (13 mbsl) and 7700-8100 cal yr BP (6 mbsl).O objetivo deste trabalho foi a geração de um inventário dos dados de datação de radiocarbono obtidos de sedimentos do Embaiamento de São Paulo (Margem Continental Superior do Sul do Brasil) e analisar os dados em termos de processos sedimentares quaternários e taxas de sedimentação. Um total de238 datações ao radiocarbono de materiais coletados com autilização de procedimentos amostrais diferentes foi considerado neste trabalho. As taxas de sedimentação variaram de menor que 2 a 68 cm.kyr-1. As taxas de sedimentação mais altas foram encontradas em um sistema costeiro de baixa energia (tipo ría), bem como nas zonas de ressurgência de Santa Catarina e Cabo Frio. As taxas mais baixas foram encontradas na plataforma externa e talude superior. Nossos resultados confirmam a forte dependência do sistema de correntes de plataforma, com ênfase no aporte terrígeno oriundo do Rio daPrata, transportado através da Corrente Costeira do Brasil, e da dinâmica da Corrente do Brasil - Corrente de Contorno Intermediária (CB-CCI) nos processos sedimentares. Pelo menostrês indicadores de paleo-níveis marinhos foram encontrados a 12200 anos AP (idade radiocarbônica convencional) (103 metros abaixo do nível do mar atual - manm), 8300-8800 cal anos AP (13 manm) e 7700-8100 cal anos BP (6 manm).Fundação de Amparo à Pesquisado Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Biogeochemical and oceanographic conditions provide insights about current status of an Antarctic fjord affected by relatively slow glacial retreat

Comprender el origen, el transporte y el carácter de la materia orgánica que ingresa a los fiordos antárticos es esencial, ya que son componentes importantes del ciclo y presupuesto global del carbono. Se analizaron como indicadores de fuente depósitos macromoleculares de materia orgánica particulada, geoquímica orgánica a granel, elementos principales y traza en sedimentos superficiales de la Bahía de Collins. Como factores de control ambiental se consideraron las condiciones oceanográficas, la batimetría (multihaz) y el tamaño de grano. Las muestras de sedimentos fueron tomadas con una cuchara van Veen, durante la XXV expedición peruana ANTAR (febrero 2018), a bordo del B/O “ BAP Carrasco” de la Armada del Perú. La composición biopolimérica reveló el predominio de materia orgánica marina fresca rica en proteínas en el fondo marino de la Bahía de Collins, lo que denota un recurso alimentario de alta calidad para los heterótrofos bentónicos marinos. Según los valores de Igeo (entre 0 y 1), la Bahía de Collins se puede considerar no contaminada con niveles naturales de As, Cd, Cr, Cu, Fe, Mn, Ni, Pb y Zn. La distribución de la mayoría de estos elementos con un gradiente de disminución desde el fiordo interior poco profundo hacia el fiordo exterior más profundo, sugiere su asociación con la deposición de material detrítico y partículas litogénicas suministradas por la ablación frontal y la escorrentía del glaciar Collins. Esta primera información de referencia integral ayudaría a interpretar las reconstrucciones sedimentarias descendentes y los futuros cambios inducidos por el clima

Coastline changes and sedimentation related with the opening of an artificial channel: the Valo Grande Delta, SE Brazil

The role played by human activity in coastline changes indicates a general tendency of retreating coasts, especially deltaic environments, as a result of the recent trend of sea level rise as well as the blockage of the transfer of sediments towards the coast, especially due to the construction of dams. This is particularly important in deltaic environments which have been suffering a dramatic loss of area in the last decades. In contrast, in this paper, we report the origin and evolution of an anthropogenic delta, the Valo Grande delta, on the south-eastern Brazilian coast, whose origin is related to the opening of an artificial channel and the diversion of the main flow of the Ribeira de Iguape River. The methodology included the analysis of coastline changes, bathy metry and coring, which were used to determine the sedimentation rates and grain-size changes over time. The results allowed us to recognize the different facies of the anthropogenic delta and establish its lateral and vertical depositional trends. Despite not being very frequent, anthropogenic deltas represent a favorable environment for the record of natural and anthropogenic changes in historical times and, thus, deserve more attention from researchers of different subjects.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [06/04344-2]info:eu-repo/semantics/publishedVersio

Biogeochemical and oceanographic conditions provide insights about current status of an Antarctic fjord affected by relatively slow glacial retreat

Abstract Understand the origin, transport, and character of organic matter entering Antarctic fjords is essential as they are major components of the global carbon cycle and budget. Macromolecular pools of particulate organic matter, bulk organic geochemistry, major and trace elements in surface sediments from Collins Bay were analysed as source indicators. Oceanographic conditions, bathymetry (multibeam) and grain size were considered as environmental controlling factors. Sediment samples were taken with a van Veen grab, during the ANTAR XXV Peruvian expedition (February 2018), onboard the R/V “BAP Carrasco” from the Peruvian Navy. Biopolymeric composition revealed the predominance of fresh marine protein-rich organic matter in the seafloor of Collins Bay, denoting high quality food resource for marine benthic heterotrophs. Based on Igeo values (between 0 and 1) Collins Bay can be considered unpolluted with natural levels of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Distribution of most of these elements with a gradient of decrease from the shallow inner fjord towards the outer deepest fjord, suggest their association with the deposition of detrital material and lithogenic particles supplied by Collins Glacier frontal ablation and runoff. This first comprehensive baseline information would assist in interpreting downcore sedimentary reconstructions and future climate-induce changes

Sedimentary changes on the Southeastern Brazilian upper slope during the last 35,000 years

A first evaluation of the sedimentary changes, including accumulation of inorganic and organic carbon on the upper slope off Southeastern Brazil under different climatic conditions, based on the analysis of a sedimentary core, is here presented. Results indicate that sedimentation rate as well sedimentary characteristics, including the nature of the organic carbon deposited during the LGM (Last Glacial Maximum), were different from the present deposition, indicating higher primary productivity during the LGM, to be accounted for by the higher values of marine organic carbon. Nevertheless, the higher values of Accumulation Rate of calcium carbonate and organic carbon can be credited to the higher values of the sedimentation rates. Conditions prevailing during Isotope Stage 3 may be considered intermediate as between the LGM and the present day. The conditions for a higher primary productivity associated with the deposition of finer terrigenous sediments may be explained as a response to the off shoreward displacement of the main flow of the Brazil Current.<br>Este trabalho apresenta uma primeira avaliação das mudanças sedimentares, incluindo a acumulação de carbono orgânico e inorgânico, no talude continental superior do Brasil, sob diferentes condições climáticas, baseadas em análises de um testemunho. Os resultados indicam que a taxa de sedimentação, assim como as características sedimentares, incluindo a natureza do carbono orgânico depositado durante o UMG (Último Máximo Glacial), foram diferentes dos processos deposicionais atuais, indicando maior produtividade primária durante o UMG, como determinado pelos maiores valores de carbono orgânico marinho. Entretanto, os maiores valores de Taxa de Acumulação de carbonato de cálcio e carbono orgânico podem ser creditados aos valores mais altos de taxas de sedimentação. As condições prevalentes durante o Estágio Isotópico 3 podem ser consideradas intermediárias entre o UMG e as condições atuais. As condições para maior produtividade primária, associada à deposição de sedimentos mais finos, podem ser explicadas como uma resposta ao deslocamento, em direção ao mar aberto, do fluxo principal da Corrente do Brasil