The influence of dissolved inorganic macronutrient concentration and ratio on the elemental stoichiometry of sinking particulate matter and carbon export in the peruvian upwelling system

Dissertação de mestrado, Biologia Marinha, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2017Peruvian coastal waters are influenced by strong coastal upwelling events and an intense oxygen minimum zone, where large amounts of fixed nitrogen can be lost. In order to investigate some of the effects this oxygen minimum zone may have on these coastal waters, this study aimed to evaluate the influence of dissolved inorganic macronutrient concentration and ratio on the elemental stoichiometry of sinking particulate matter and carbon export. At the beginning of February 2017, eight mesocosms were deployed in coastal waters near Lima, Peru. 4 mesocosms were enriched with an OMZ derived water mass with a dissolved inorganic N:P ratio of 0.11, while the other 4 were enriched with OMZ water of N:P = 1.71. The amount of utilized reactive nitrogen was not associated to differences in carbon export rates, but the results of one individual mesocosm hint at stronger carbon export at low primary production. Furthermore, sinking particulate matter and its elemental stoichiometry did not show differences between treatments. However, our results showed clear deviations from the canonical Redfield ratio in sinking POM, hypothesized to be related with phytoplankton community composition.Os nutrientes inorgânicos dissolvidos são fundamentais para o funcionamento das redes alimentares marinhas e são, direta ou indiretamente, absorvidos por todos os organismos vivos. As regiões de afloramento costeiro apresentam elevada concentração de nutrientes inorgânicos, constituindo ecossistemas marinhos muito produtivos a nível biológico. Embora representam apenas 1% da área superficial do oceano global, as áreas de afloramento costeiro são responsáveis, em média,por cerca de 11% da produção primária anual nova. A variabilidade climática prevista, associada à crescente da pressão antrópica na atmosfera e no oceano, foi associada à intensificação e expansão da área ocupada pelas zonas mínimas de oxigénio (Oxygen Minimum Zones, OMZ), geralmente associadas aos sistemas de afloramento costeiro. Neste contexto, torna-se necessário avaliar e compreender as consequências do aumento das OMZ sobre os ciclos biogeoquímicos de nutrientes, de forma a prever com rigor a variabilidade futura do ambiente marinho e aplicar estratégias de gestão adequadas. Os eventos de afloramento costeiro ao largo da costa do Peru, bem como em outros sistemas similares, estão geralmente associados ao transporte de massas de água sub-superficiais, com elevada concentrações de nutrientes inorgânicos dissolvidos. Porém, a concentração de nutrientes inorgânicos dissolvidos e as proporções entre as formas contendo azoto e fósforo (ratio N:P) variam em função da intensidade dos eventos de afloramento e dos processos que influenciam a concentração e composição dos nutrientes em níveis inferiores à superfície. O azoto inorgânico é um elemento essencial ao crescimento do fitoplâncton e, muitas vezes, limita a produtividade primária, desempenhando assim um papel crucial na biogeoquímica marinha. As formas de azoto inorgânico biodisponíveis incluem o nitrato, nitrito e amónia, mas constituem apenas cerca de 6% da concentração total de azoto disponível na água do mar. O fósforo inorgânico é igualmente um elemento essencial ao crescimento do fitoplâncton, sendo a principal forma biodisponível o fosfato. Representa uma parte integrante da estrutura celular (ex.: ácidos nucleicos, incluindo DNA e RNA) e dos compostos associados ao armazenamento de energia química nas células, nomeadamente da molécula adenosina trifosfato (ATP). Assim, a análise do ciclo biogeoquimico do fósforo é relevante para determinar a estrutura e função dos ecossistemas. A exportação vertical de matéria orgânica a partir da superfície do oceano representa um processo chave para o funcionamento da bomba biológica de carbono, um componente importante do ciclo global do carbono. O carbono inorgânico é absorvido sob a forma de CO2 pelo fitoplâncton, transformado e acumulado no interior das células sob a forma de carbono orgânico, através da fotossíntese, e transportado verticalmente para o oceano profundo. Assim, o fluxo vertical de células fitoplanctónicas, em estado fisiológico variável, controla fortemente a capacidade do oceano como um coletor e reservatório de CO2. A exportação vertical de material particulado é determinada pela taxa de decomposição e velocidade de afundamento do material em afundamento, bem como pela migração vertical diária do zooplâncton ativo. O material particulado em afundamento no oceano é composto por agregados orgânicos, geralmente designados neve marinha, pelotas fecais do zooplâncton e fitodetritos. As partículas com reduzida velocidade de afundamento são geralmente consumidas ou degradadas antes de atingir o oceano profundo. Pelo contrário, as partículas com elevada velocidade de afundamento apresentam maior probabilidade de atingir o sedimento. A eficiência da bomba biológica depende ainda da composição da comunidade fitoplanctónica e, em consequência, das condições abióticas do ambiente marinho, incluindo a concentração e composição dos nutrientes inorgânicos dissolvidos. O presente estudo pretende avaliar a influência da concentração e composição (ratio) dos macronutrientes inorgânicos dissolvidos na água aflorada sobre a estequiometria da matéria em suspensão na plataforma continental do Peru. Os objetivos específicos do estudo abordaram as seguintes questões: (1) Estarão massas de água afloradas com diferente concentração e composição de nutrientes (ratio N:P) associadas a diferenças na estequiometria elementar das partículas em suspensão e sedimentação?; (2) Estarão a concentração e a taxa de absorção de nutrientes relacionadas com diferenças nas taxas de exportação do carbono orgânico? O presente estudo integrou-se no Collaborative Research Center (SFB 754) “Climate-Biogeochemistry Interactions in the Tropical Ocean” e baseou-se numa experiência iniciada em fevereiro de 2017, com recurso à plataforma Kiel Off-Shore Mesocosms for Ocean Simulations (KOSMOS), uma instalação móvel de mesocosmos, aplicável em experiências em larga escala, in situ. Os mesocosmos são unidades experimentais com um volume elevado, apropriadas para simular eventos de afloramento, em condições controladas quasi naturais, uma vez que permitem a manipulação eficiente das variáveis ambientais, incluindo a concentração de nutrientes. De forma a atingir os objetivos propostos, foram utilizados dois tratamentos experimentais, com quatro replicados cada (2 * 4 = 8 mesocosmos): massa de água com ratio N:P reduzido e massa de água com ratio N:P muito reduzido, a nível da composição de nutrientes inorgânicos dissolvidos. No início de fevereiro de 2017, foram implantados oito mesocosmos em águas costeiras ao largo de Lima (Peru), contendo armadilhas de sedimento no interior. A experiência decorreu durante um período de 50 dias, entre fevereiro e abril de 2017. Quatro mesocosmos foram enriquecidos com uma massa de água amostrada na OMZ, com um ratio N: P de 0,11, enquanto os restantes quatro mesocosmos foram enriquecidos com uma massa de água amostrada na OMZ com um ratio N: P de 1,71. Em cada um dos oito mesocosmos foram analisadas a concentração de nitritos, nitratos, amónia, fosfatos, silicatos, bem como os ratio associados, e clorofila-a (indicador da biomassa total do fitoplâncton) na coluna de água. Adicionalmente, foi amostrada a matéria particulada acumulada no interior de armadilhas de sedimento. Neste caso foram analisadas a concentração de carbono total, azoto total, carbono orgânico particulado, azoto orgânico particulado, carbono inorgânico particulado, sílica orgânica particulada e sílica biogênica. As diferenças entre os dois tratamentos experimentais, para todas as variáveis referidas, foram testadas estatisticamente. Os resultados obtidos não revelaram diferenças significativas em nenhuma das variáveis químicas ou biológicas entre os dois tratamentos experimentais. No entanto, observaram-se desvios claros nos ratios C: N: P, em relação aos valores propostos por Redfield (106: 16: 1), para os nutrientes inorgânicos dissolvidos e matéria orgânica particulada acumulada nas armadilhas de sedimento. Hipóteses para explicar estes desvios foram apresentadas, incluindo variações na composição da comunidade de fitoplâncton e mixotrofia. Os resultados indicaram que a concentração de azoto utilizado não se associou a diferenças significativas nas taxas de exportação vertical de carbono. No geral, a estratégia experimental utilizada apresentou alguns problemas incluindo uma similaridade entre as duas massas de água amostradas na OMZ e os distúrbios gerados pelas aves marinhas (ex.: entrada de guano e presas no interior dos mesocosmos). Experiências futuras deverão ativamente limitar estes problemas. A informação quantitativa sobre a composição da comunidade fitoplanctónica, disponível futuramente (após a data de submissão desta tese de mestrado), deverá ser utilizada para testar as hipóteses apresentadas no estudo

Neuro-Fuzzy Model for the Prediction and Classification of the Fused Zone Levels of Imperfections in Ti6Al4V Alloy Butt Weld

Weld imperfections are tolerable defects as stated from the international standard. Nevertheless they can produce a set of drawbacks like difficulty to assembly, reworking, limited fatigue life, and surface imperfections. In this paper Ti6Al4V titanium butt welds were produced by CO2laser welding. The following tolerable defects were analysed: weld undercut, excess weld metal, excessive penetration, incomplete filled groove, root concavity, and lack of penetration. A neuro-fuzzy model for the prediction and classification of the defects in the fused zone was built up using the experimental data. Weld imperfections were connected to the welding parameters by feed forward neural networks. Then the imperfections were clustered using the C-means fuzzy clustering algorithm. The clusters were named after the ISO standard classification of the levels of imperfection for electron and laser beam welding of aluminium alloys and steels. Finally, a single-value metric was proposed for the assessment of the overall bead geometry quality. It combined an index for each defect and functioned according to the criterion "the-smallest-the-best.

fe analysis of low density hemp epoxy composites produced by a new continuous process

Abstract This paper aims to present a new grid composite structure obtained by stacking hemp fabric layers impregnated by resin using a new continuous process. Both the process feasibility and the mechanical properties of the obtained specimens were investigated in terms of tensile and flexural response. In addition, the effect of the superimposition error of the layers, that can affect the density and the mechanical properties of the produced bio-composites, was studied both experimentally and numerically by finite element models (FEM). The results showed that the process is able to produce low density composites possessing interesting specific mechanical properties with a good level of repeatability

CFRPs drilling: comparison among holes produced by different drilling strategies

Abstract The drilling process of CFRPs is the most commonly employed machining operation owing to the need for joining these structures. However, these materials are prone to delaminate during the process and the presence of these defects can be a cause of rejection of these components. Therefore, this paper aims on the study of alternative drilling strategies such as: the orbital and a new drilling strategy (called circular drilling) to reduce the delaminations extension. Holes 8 mm in diameter were obtained by using different drilling strategies and cutting conditions and their influence on the cutting forces and delamination factor was studied

Recyclability Process of Standard and Foamed Gypsum

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Impact behaviour of a new Hemp/Carbon sandwich structure

Abstract This paper aims to present a new sandwich structure comprising of a grid hemp core and carbon skins. Two typology of hemp cores (7 and 8 mm in thickness) that mainly differ in the density values (0.36 and 0.63 g/cm3) were produced by an ad hoc manufacturing process and adopted to produce the sandwich structures under investigation. Aiming to extend the use of natural fibre composites (NFCs) for applications where high impact resistance is required and to replace common materials used as cores with more eco-friendly ones like the proposed hemp core, low velocity impact (LVI) tests and non-destructive (ND) tests were carried out

Selection of Optimal Process Parameters for Wire Arc Additive Manufacturing

Abstract This paper is about the optimal selection of process parameters for Wire Arc Additive Manufacturing technology, an emerging solution for additive production of metal parts. In particular, the selection of the process parameters is based on the evolution of the microstructure and on the mechanical properties of the final samples obtained through the successive deposition weld beads of a ER70S-6 steel, according to the AWS legislation. The feed rate and the heat input during the deposition of the weld beads have been varied, in order to understand how the temperature reached by the samples can affect the final product mechanical characteristics. The final cooling has been carried in calm air at room temperature and between the deposition of a weld bead and the following one it has been imposed a pause of 60s. The tests on mechanical properties carried out have been: A full experimental campaign that includes: macrographic observations, micrographic observations and Vickers microhardness. The analysis of these tests has highligthed that by varying the process parameters, the samples do not have substantial differences between them. Instead, a microstructure that evolves from pearlitic-ferritic grains until bainitic lamellae along the vertical direction of the samples has been observed by micrographic analysis and confirmed by microhardness measurements

Drivers of Particle Sinking Velocities in the Peruvian Upwelling System

As one of Earth’s most productive marine ecosystems, the Peruvian Upwelling System transports large amounts of biogenic matter from the surface to the deep ocean. Whilst particle sinking velocity is a key factor controlling the biological pump, thereby affecting carbon sequestration and O2-depletion, it has not yet been measured in this system. During a 50-day mesocosm experiment in the surface waters off the coast of Peru, we measured particle sinking velocities and their biogeochemical and physical drivers. We further characterized the general properties of exported particles under different phytoplankton communities and nutritional states. Average sinking velocities varied between size classes and ranged from 12.8 ± 0.7 m d-1 (particles 40–100 µm), to 19.4 ± 0.7 m d-1 (particles 100–250 µm), and 34.2 ± 1.5 m d-1 (particles 250–1000 µm) (±95% CI). Surprisingly, no relationship between opal ballast and sinking velocity could be identified, despite the presence of diatoms, questioning the importance of opal ballast in freshly produced material sinking from the surface. In contrast, we found higher sinking velocities with increasing particle size, compactness and roundness. Size had by far the strongest influence among these physical particle properties. Our study provides a detailed analysis of the drivers of particle sinking velocity in the Peruvian Upwelling System, which allows modelers to optimize local particle flux parameterization. This will help to better project oxygen concentrations and carbon sequestration in a region that is subject to substantial climate-driven changes

Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru

Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans