Molybdenum isotope behaviour in aqueous systems

Molybdenum isotopes are used to quantify changes in Earth’s paleoredox conditions but their application relies upon a simplified model in which rivers dominate the ocean input with minor contributions from hydrothermal fluids. The effect of groundwater discharge is rarely considered. This study finds that cold groundwaters (δ98MoGROUNDWATER -0.1‰) are compositionally similar to their host rocks (δ98MoBASALT -0.15‰) whilst hydrothermal waters are enriched in heavy isotopes (δ98MoHYDROTHERMAL +0.2‰ to +1.8‰). Using flux estimates from the literature, the inclusion of these data results in the revaluation of the Mo ocean input from +0.5‰ (just rivers) to +0.35‰ (combined), in the modern day. As a bioessential element, Mo is important in many biogeochemical cycles: especially, as a cofactor in nitrogenase, the most common nitrogen fixing enzyme. Biological fractionations of some 1.5‰ are observed, with light Mo removed from Lake Mývatn by cyanobacterial uptake during an algal bloom. If preserved, these biological fractionations may need to be considered in the interpretation of the sedimentary record. Despite the growing evidence that the vapour-phase - formed through magma degassing and fluid boiling - can selectively concentrate and transport metals, the effects on metal stable isotopes remain poorly understood. For example, Mo isotopes show great variability in ore deposits, some of which is attributed to vapour-phase transport. Here we examine the vapour-phase in four geothermal systems in Iceland; the vapour-phase is always lighter than the brine with enrichment factors of some εV-L -2.9‰. This is an important first step towards understanding the mechanisms behind vapour transport and isotopic effects.Mólýbden (Mo) samsætur eru oft notaðar til að meta oxunarstig við yfirborð jarðar á ýmsum skeiðum jarðsögunnar. Aðferðin, sem beitt er, byggist á einföldu sjávarlíkani, þar sem styrkur og samsætur Mo í sjó stjórnast fyrst og fremst af árvatni, en jarðhiti á úthafshryggjum hefur til þessa verið talinn hafa lítil áhrif. Þessi rannsókn sýnir að kalt grunnvatn (δ98MoGROUNDWATER -0,1‰) er með svipaða samsætusamsetningu og berggrunnurinn sem það flæðir um (δ98MoBASALT -0,15‰), en jarðhitavatn inniheldur þyngri samsætur (δ98MoHYDROTHERMAL +0,2‰ til +1,8‰). Þessi gögn voru notuð, ásamt áður birtu mati á efnaflutningum til sjávar, til að endurreikna Mo-samsætuhlutföll innflæðis til sjávar við núverandi aðstæður, frá +0,5‰ (árvatn) í +0,35‰ (blanda árvatns og jarðhitavatns). Mólýbden er nauðsynlegt lífverum og hefur því áhrif á næringarefnahringrásina, sér í lagi sem þáttur í nítrógenasa sem er algengasta niturbindandi ensímið. Aðgreining Mo samsæta vegna ljóstillífunar bláþörunga („cyanobacteria”) í Mývatni mældist vera -1,5‰. Þetta er í fyrsta sinn sem þessi aðgreining er mæld í vatnaumhverfi þar sem létta samsætan binst í þörungunum og þunga samsætan verður eftir í vatninu. Nauðsynlegt er að hafa líffræðileg ferli í huga við túlkun og greiningu setlaga, því þessi samsætuaðgreining kann að varðveitast í lögunum. Í jarðhitakerfum myndast gufufasi vegna afgösunar kviku og suðu jarðhitavökva. Þrátt fyrir vísbendingar um að gufufasinn geti safnað í sig málmum og flutt þá, er lítið vitað um áhrif þessa flutnings á stöðugar samsætur málmanna. Til dæmis eru Mo samsætur í málmgrýti mjög breytilegar, en orsökina má að einhverju leyti rekja til þessa flutnings. Samsætuhlutföll mólýbdens í vatns- og gufufasa fjögurra íslenskra jarðhitakerfa voru rannsökuð í þessu verkefni. Samsætur gufufasans (V) reyndust ávallt léttari en jarðhitavökvans (L), og er auðgunin (εV-L) -2,9‰. Þetta er mikilvægt fyrsta skref í átt að skilningi á ferlum þeim sem stjórna gufuflutningum og túlkun á áhrifum flutninganna á samsætur.Initial Training Network grant number 290336, MetTran

Biogeochemistry of marine dissolved organic Sulfur : quantification, distribution, molecular composition, and reactivity

Dissolved organic matter (DOM) is ubiquitous in natural waters and plays a central role in the biogeochemistry of riverine, estuarine and marine environments. The heteroatomic fraction of DOM consists mainly of nitrogen, phosphorous, and sulfur. While the biogeochemical cycling of C, N, and P has been intensely studied, dissolved organic sulfur (DOS) has been only marginally addressed. Nevertheless, it is an essential element for marine primary production and organic sulfur compounds play a critical role in biogeochemistry, ecology, and climate processes. The analysis of DOS quantity and distribution in marine environments as well as its chemical characterization is of urgent need to further understand the underlying processes of DOS biogeochemistry. This study is based on more than 600 samples from different marine environments, from the surface to the deep ocean, and thus, represents the so far most comprehensive dataset of DOS in the ocean. Within this thesis, a basin-scale distribution of extractable DOS in the East Atlantic Ocean, the Atlantic sector of the Southern Ocean, and the Weddell Sea is presented. A first conservative global inventory of the marine non-volatile DOS stock was calculated using a combination of state-of-the-art approaches. The results suggest that the marine DOS inventory is by far the largest oceanic reservoir of organic sulfur (OS), exceeding the atmospheric stock and the volatile marine DOS by several orders of magnitude. Decades of research on the marine DOS cycle have focused on only 2 % of the total OS inventory (DMSP cycle). The marine DOS distribution and stoichiometry was compared to radiocarbon age of dissolved organic carbon (DOC), suggesting a primarily autochthonous biogenic origin and an active involvement of this DOS in the microbial loop - similar to organic nitrogen. The contribution of the sulfur-containing amino acid methionine to extractable DOS was found to be only 2 %. Additionally, ultrahigh-resolution mass spectrometry identified a diverse suite of sulfur containing molecular formulas and their relative contribution suggested shorter residence times relative to DOC supporting the active involvement of DOS in biogeochemical cycles, ecological processes and ecosystem functions. Rivers are also important sources of (sulfur containing) organic matter to marine environments. Here I quantified DOS and trace metals along a salinity gradient and explored the complexation of trace metals with organic matter, in particular with sulfur-containing compounds. Despite decreasing DOM concentrations along the salinity gradient due to estuarine mixing, we showed that DOS is degrading faster than DOC, underpinning the active involvement of DOS in biogeochemical cycles and ecological processes. We found indication for complexation of trace metals with (sulfur containing) organic ligands and confirmed that the stability of metal-organic complexes followed the Irving-Williams order. The results of this thesis challenge current views of DOS dynamics and suggest that there remain major gaps in our understanding of the marine sulfur cycle, which will be of interest to ocean (biogeo-) chemists, atmospheric scientists, microbial ecologists, and ocean-/climate modelers

The cobalt cycle in the Tropical Pacific Ocean

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2017Although over a dozen elements are needed to support phytoplankton growth, only a few are considered to be growth-limiting. As the central atom in vitamin B12, cobalt is crucial for metabolism, but its status as a limiting nutrient is uncertain. This thesis investigates the geochemical controls on oceanic cobalt scarcity and their biological consequences. Analysis of over 1000 samples collected in the Tropical Pacific Ocean reveals a dissolved cobalt distribution that is strongly coupled to dissolved oxygen, with peak concentrations where oxygen is lowest. Large cobalt plumes within anoxic waters are maintained by three processes: 1) a cobalt supply from organic matter remineralization, 2) an amplified sedimentary source from oxygen-depleted coastlines, and 3) low-oxygen inhibition of manganese oxidation, which scavenges cobalt from the water column. Rates of scavenging are calculated from a global synthesis of recent GEOTRACES data and agree with cobalt accumulation rates in pelagic sediments. Because both sources and sinks are tied to the extent of oxygen minimum zones, oceanic cobalt inventories are likely dynamic on the span of decades. Despite extremely low cobalt in the South Pacific gyre, the cyanobacterium Prochlorococcus thrives. Minimum cobalt and iron requirements of a Prochlorococcus strain isolated from the Equatorial Pacific are quantified. Cobalt quotas are related to demand for ribonucleotide reductase and methionine synthase enzymes, which catalyze critical steps in DNA and protein biosynthesis, respectively. Compared to other cyanobacteria, a streamlined metal physiology makes Prochlorococcus susceptible to competitive inhibition of cobalt uptake by low levels of zinc. Although phytoplankton in the Equatorial Pacific are subject to chronic iron-limitation, widespread cobalt scarcity and vulnerability to zinc inhibition observed in culture imply that wild Prochlorococcus are not far from a cobalt-limitation threshold.I am lucky to have benefitted from major financial support of the Saito Lab by the National Science Foundation and the Gordon and Betty Moore Foundation. Specifically, National Science Foundation grants for the Center for Microbial Oceanography Research and Education (CMORE, DBI-0424599), GEOTRACES Pacific and Artic projects (OCE-1233261 and OCE- 1540254), and OCE-1220484 funded my thesis work. National Science Foundation grants OCE- 1031271 and OCE-1337780 and Gordon and Betty Moore Foundation grants 3782 and 3934 to the Saito lab also provided instrumentation and funded field expeditions that enabled this work

Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES-Era Data

86 pages, 33 figures, 2 tables, 1 appendix.-- Data Availability Statement: The majority of the dissolved data were sourced from the GEOTRACES Intermediate Data Products in 2014 (Mawji et al., 2015) and 2017 (Schlitzer et al., 2018), and citations to the primary data sources are given in the caption for each figure. Data sources for Figure 1 are given below. Figure 1: Iron: Conway & John, 2014a (Atlantic); Conway & John, 2015a (Pacific); Abadie et al., 2017 (Southern). Zinc: Conway & John, 2014b (Atlantic); Conway & John, 2015a (Pacific); R. M. Wang et al., 2019 (Southern). Copper: Little et al., 2018 (Atlantic); Takano et al., 2017 (Pacific); Boye et al., 2012 (Southern). Cadmium: Conway and John, 2015b (Atlantic); Conway & John, 2015a (Pacific); Abouchami et al., 2014 (Southern). Molybdenum: Nakagawa et al., 2012 (all basins). Barium: Bates et al., 2017 (Atlantic); Geyman et al., 2019 (Pacific); Hsieh & Henderson, 2017 (Southern). Nickel: Archer et al., 2020 (Atlantic); Takano et al., 2017 (Pacific); R. M. Wang et al., 2019 (Southern). Chromium: Goring-Harford et al., 2018 (Atlantic); Moos & Boyle, 2019 (Pacific); Rickli et al., 2019 (Southern). Silver: Fischer et al., 2018 (Pacific); Boye et al., 2012 (Southern)Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth's climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth's climate historyThis contribution grew (and grew) out of a joint workshop between GEOTRACES and Past Global Changes (PAGES) held in Aix-en-Provence in December 2018. The workshop was funded by the U.S. National Science Foundation (NSF) through the GEOTRACES program, the international PAGES project, which received support from the Swiss Academy of Sciences and NSF, and the French program Les Envelopes Fluides et l'Environnement. [...] T. J. Horner acknowledges support from NSF; S. H. Little from the UK Natural Environment Research Council (NE/P018181/1); T. M. Conway from the University of South Florida; and, J. R. Farmer from the Max Planck Society, the Tuttle Fund of the Department of Geosciences of Princeton University, the Grand Challenges Program of the Princeton Environmental Institute, and the Andlinger Center for Energy and the Environment of Princeton University. [...] With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S

Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES-Era Data

Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth\u27s climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth\u27s climate history

Bioactive Trace Metals and Their Isotopes as Paleoproductivity Proxies: An Assessment Using GEOTRACES-Era Data

Phytoplankton productivity and export sequester climatically significant quantities of atmospheric carbon dioxide as particulate organic carbon through a suite of processes termed the biological pump. Constraining how the biological pump operated in the past is important for understanding past atmospheric carbon dioxide concentrations and Earth\u27s climate history. However, reconstructing the history of the biological pump requires proxies. Due to their intimate association with biological processes, several bioactive trace metals and their isotopes are potential proxies for past phytoplankton productivity, including iron, zinc, copper, cadmium, molybdenum, barium, nickel, chromium, and silver. Here, we review the oceanic distributions, driving processes, and depositional archives for these nine metals and their isotopes based on GEOTRACES-era datasets. We offer an assessment of the overall maturity of each isotope system to serve as a proxy for diagnosing aspects of past ocean productivity and identify priorities for future research. This assessment reveals that cadmium, barium, nickel, and chromium isotopes offer the most promise as tracers of paleoproductivity, whereas iron, zinc, copper, and molybdenum do not. Too little is known about silver to make a confident determination. Intriguingly, the trace metals that are least sensitive to productivity may be used to track other aspects of ocean chemistry, such as nutrient sources, particle scavenging, organic complexation, and ocean redox state. These complementary sensitivities suggest new opportunities for combining perspectives from multiple proxies that will ultimately enable painting a more complete picture of marine paleoproductivity, biogeochemical cycles, and Earth\u27s climate history

Geomicrobiology of the basal ice layer at Svínafellsjökull glacier, SE Iceland

Glaciers occupy 11% of Earth’s total surface and represent a significant but, as yet, poorly characterised ecosystem. As late as the mid-90s glaciers had been regarded as microbiologically sterile environments but there has since been major progress characterising diversity and functioning of glacier microbiota. The supraglacial environment has to-date been prioritised, but crucially the subglacial microbiota remains generally unknown despite their central importance in geochemical cycling. The dark and oligotrophic conditions typical to subglacial environments in general, and sediment entrained basal ice, in particular, are likely to select for chemolithotrophic carbon fixers that, by definition, will enable diverse heterotrophic microbial community development. Therefore, the basal ice microbiota, are likely to play fundamental roles in mineral weathering and geochemical cycling not only within basal ice but also subsequent foreland soil formation upon release. The main aim of this thesis is the first integrated geo-microbiological characterization, of geomorphologically distinct basal ice facies targeting an Icelandic temperate glacier, Svínafellsjökull. Here we show, via novel culture-dependent and -independent next generation molecular rRNA gene marker (16S and ITS) phylogenetics, that basal ice facies harbour a rich and diverse community of bacteria (Proteobacteria and Acidobacteria) and fungi (Ascomycota and Basidiomycota). An abundance of chemolithotrophic species (Thiobacillus, Gallionella, Nitrosospira) characterise the basal ice microbiome that is directly supported in the identified geochemical status of basal ice. The presence of reduced nitrogen species in the ice matrix and iron- and sulphur-rich minerals in basal ice sediment provides added functional support of the predominance of chemolithotrophs in basal ice. Based on total basal ice cell enumeration and export estimates (~1016 cells yr-1) it is clear that chemolithotrophic and heterotrophic microbial communities identified in foreland soils originate from basal ice, as opposed to supraglacial sources. Modelling highlights the importance of microbial activities on the geo-chemistry of the basal ice, e.g. oxidising minerals, acidifying the environment, and increasing the carbon content within the sediment. Once released, basal ice-derived microorganisms can survive the psychrophilic to mesophilic temperatures of the foreland and identified isolates from basal ice and the foreland were affiliated with species that play important roles in weathering and soil formation highlighting the functional importance of the basal ice microbiota both, in glacial and periglacial systems

Impacts of nanoparticles to microbes and invertebrates: from community responses to cellular targets

Tese de doutoramento in Sciences Specialization in BiologyThe incredible development in nanotechnology since the last decade has brought the “nanoworld” to our regular life. However, the extensive global growth in commercial production and usage of nanomaterial-based products raised the question whether nanomaterials when released to the environment can constitute a potential risk to biota and ecosystem processes. Being large reservoirs, natural waters are likely to be the ultimate sink of nanomaterials. In forested streams, microbes, predominantly fungi, decompose plant litter from riparian vegetation and transfer carbon and energy via invertebrate shredders to higher trophic levels. Freshwater decomposers are sensitive to changes in water quality with implications to ecosystem functioning. Considering the recent development of nanotechnology, assessing the potential toxicity of nanomaterials against freshwater decomposers and examining their ecological and physiological responses to nanoparticle exposure will contribute to a safer use of nanomaterials. In this study, by using a microcosm approach, we found that nanocopper oxide (nanoCuO), nanosilver, and their ionic precursors severely affected leaf litter decomposition by stream-dwelling microbes, as indicated by a decrease in microbial biomass, fungal sporulation and species richness. Moreover, the analysis of fungal and bacterial communities, based on DNA fingerprints from denaturing gradient gel electrophoresis and fungal sporulating species, revealed shifts in species composition and changes towards a better adapted community under the stress induced by nano and ionic metals. Moreover, the negative effects of metal nanoparticles were less pronounced than those of their ionic forms. Nanoparticle size (12, 50 and 80 nm) and the presence of humic acid (HA) influenced the toxicity of nanoCuO against stream-dwelling microbial decomposers. The toxicity of nanoCuO increased in a dose-dependent manner and with the decrease in nanoparticle size. Bacteria were more sensitive than fungi to nanoCuO, because EC50 values for biomass of bacteria were much lower than those of fungi. Fungal reproduction was more sensitive to nanoCuO than leaf decomposition or microbial biomass. HA alone also had negative effects on microbial diversity and activity, but the presence of HA alleviated the negative effects of smaller size nanoCuO (12 or 50 nm). Alterations in leaf surface morphology further supported the impacts of nanoparticles and HA on microbial activity on decomposing leaves, as shown by scanning electron microscopy. We also showed that nanoCuO had lethal and sublethal effects on Allogamus ligonifer, a common invertebrate shredder in Southwest European streams that prefers high quality stream water. The feeding behaviour and growth of the invertebrate were affected in a dose-dependent manner. Effects were due to both nanoCuO and ionic copper leached from nanoCuO that adsorbed or accumulated in the shredder body. The feeding behaviour of the invertebrate shredder was more inhibited as nanoparticle size decreased. The toxicity of smaller size nanoCuO to the shredder was alleviated by the presence of HA. A postexposure feeding experiment showed a very low recovery of the invertebrate feeding behaviour after stress removal. The exposure of aquatic fungal populations to nanoCuO led to a decrease in biomass production, alterations in cell-wall morphology, increased biosorption of nanoCuO and induction of extracellular laccase activity in a time and dose-dependent manner. Fungal populations from metal-polluted streams were more resistant/tolerant to the stress induced by nanoCuO than those from non-polluted streams. Differences in laccase activity among fungi appeared to be related to the presence of laccase-like genes in the copper-binding domain. Exposure to nanoCuO or ionic copper led to lower intracellular accumulation of reactive oxygen species (ROS), plasma membrane disruption, and DNA-strand breaks in fungal populations isolated from metal-polluted streams than in those from non-polluted streams. The activities of glutathione reductase and superoxide dismutase were higher in fungi from metal-polluted than from non-polluted streams, but the opposite was found for glutathione peroxidase activity. Results suggested that fungi from metal-polluted streams have higher capacity to deal with the oxidative stress induced by nanoCuO, probably due to their ability to maintain a high ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG). In contrast to metal nanoparticles, polyhydroxy fullerene (PHF) nanoparticles stimulated the growth of the yeast Saccharomyces cerevisiae, which was used as model of eukaryotic organism. Moreover, the oxidative stress induced by cadmium ions to yeast cells was mitigated by the presence of PHF. A maximum growth recovery was obtained after 26h of exposure to 500 ppm PHF at pH 6.8. Results suggested that PHF nanoparticles have antioxidant and free-radical scavenging properties.Na última década ocorreu um desenvolvimento exponencial da nanotecnologia o que trouxe o "nanomundo" à nossa vida do dia a dia. No entanto, o crescimento a nível global da produção e do uso de produtos com base em nanomateriais levanta a questão de saber se os nanomateriais, quando libertados para o meio ambiente, podem constituir um risco potencial para as comunidades biológicas e para os processos dos ecossistemas a elas associados. Os ecossistemas de água doce são susceptíveis de constituir o reservatório final dos nanomateriais. Nos rios e ribeiros florestados, os microrganismos, principalmente os fungos, decompõem o material vegetal proveniente da vegetação ribeirinha e promovem a transferência do carbono e da energia para os níveis tróficos superiores através da actividade dos invertebrados trituradores. Os decompositores de água doce são sensíveis a alterações na qualidade da água, com implicações para o funcionamento do ecossistema. Assim, a avaliação da potencial toxicidade dos nanomateriais para os decompositores de água doce e a análise das suas respostas ecológicas e fisiológicas à exposição a nanopartículas contribuirá para uma utilização mais segura dos nanomateriais. Neste estudo, usando uma abordagem em microcosmos, mostrámos que as nanopartículas de óxido de cobre, as nanopartículas de prata, e os seus precursores iónicos afectavam negativamente a decomposição da folhada por comunidades de microrganismos aquáticos, como indicado por uma diminuição da biomassa microbiana (fungos e bactérias), da esporulação dos fungos e da riqueza em espécies de fungos. A análise da comunidades de fungos, por electroforese em gradiente desnaturante do DNA microbiano e com base na morfologia das conídias libertadas da folhada em decomposição, revelou alterações na estrutura das comunidades no sentido de uma comunidade melhor adaptada ao stress induzido pelos metais quer nas formas nano quer iónicas. Além disso, os efeitos negativos das nanopartículas metálicas foram menos pronunciados do que os das suas formas iónicas. O tamanho das nanopartículas de óxido de cobre (12, 50 e 80 nm) e a presença do ácido húmico (HA) influenciou a toxicidade das nanopartículas para os microrganismos decompositores. A toxicidade das nanopartículas de óxido de cobre aumentou com a dose e com a diminuição do tamanho das partículas. As bactérias foram mais sensíveis do que os fungos às nanopartículas de óxido de cobre, porque os valores de EC50 para a biomassa de bactérias foram muito mais baixos do que os dos fungos. A reprodução dos fungos foi mais sensível à exposição às nanopartículas de óxido de cobre do que a decomposição da folhada ou a biomassa microbiana. O HA sozinho também teve efeitos negativos sobre a diversidade e a actividade dos microrganismos. Contudo, a presença de HA mitigou os efeitos negativos das nanopartículas de óxido de cobre de menor tamanho (12 ou 50 nm). As alterações na morfologia da superfície da folhada, reveladas por microscopia electrónica de varrimento, corroboraram os efeitos das nanopartículas e do HA na actividade microbiana nas folhas em decomposição. Os nossos resultados também mostraram que as nanopartículas de óxido de cobre tiveram efeitos letais e subletais em Allogamus ligonifer, um invertebrado detritívoro comum em rios do Sudoeste Europeu com elevada qualidade ecológica. A presença de nanopartículas de óxido de cobre afectou o comportamento alimentar e o crescimento do invertebrado de uma forma dependente da dose. Os efeitos negativos no animal pareceram ser devidos à adsorção ou acumulação no corpo do invertebrado de nanopartículas e de cobre iónico libertado das nanopartículas. O comportamento alimentar dos invertebrados foi mais inibido na presença de nanopartículas de menor tamanho comparativamente às de maior tamanho. A toxicidade das nanopartículas de óxido de cobre de menor tamanho para o invertebrado foi atenuada pela presença de HA. Uma experiência de alimentação de pósexposição mostrou uma baixa recuperação do comportamento alimentar dos invertebrados após a remoção do stress imposto pelas nanopartículas. A exposição de populações de fungos aquáticos às nanopartículas de óxido de cobre levou a uma diminuição da biomassa produzida, a alterações na morfologia da parede celular, ao aumento da bioadsorção das nanopartículas de óxido de cobre e à indução da actividade de lacases extracelulares de uma forma dependente da dose e do tempo. As populações de fungos isoladas de rios poluídos com metais foram mais resistentes/tolerantes ao stress induzido pelas nanopartículas metálicas do que as isoladas de rios não poluídos. As diferenças observadas na actividade das lacases entre os fungos pareceram estar associadas à presença ou ausência de genes do tipo das lacases. A exposição a nanopartículas de óxido de cobre ou a cobre iónico induziu menor acumulação intracelular de espécies reactivas de oxigénio e menos danos na membrana plasmática e no DNA de fungos isolados de rios poluídos com metais do que em fungos isolados de rios não poluídos. As actividades da glutationa reductase e da superóxido dismutase foram mais elevadas em fungos isolados de rios poluídos com metais do que em fungos isolados de rios não poluídos. Contudo, o oposto foi observado para a actividade da glutationa peroxidase. Os resultados sugerem que os fungos de rios poluídos com metais têm maior capacidade para lidar com o stress oxidativo induzido pelas nanopartículas de óxido de cobre provavelmente devido à sua capacidade de manter uma razão elevada de glutationa reduzida (GSH) em relação à glutationa oxidada (GSSG) nas células. Em contraste com o observado para as nanopartículas metálicas, as nanopartículas de poli-hidroxi-fulereno (PHF) estimularam o crescimento da levedura Saccharomyces cerevisiae, a qual foi utilizada neste trabalho como modelo de organismo eucariota. Por outro lado, o stress oxidativo induzido por iões de cádmio na levedura foi atenuado pela presença de PHF. A recuperação máxima do crescimento da levedura foi obtida após 26 horas de exposição a 500 mg L-1 de PHF e a pH 6,8. Os resultados sugerem que as nanopartículas de PHF têm propriedades antioxidantes

Understanding Geochemical Tracers in Deep-Sea Corals from a Biomineralization Perspective

Deep-sea corals have been developed as a useful archive of the chemistry and circulation of intermediate and deep waters in past oceans over the last three decades. However, applications of traditional paleoceanographic tracers in deep-sea corals remain a challenge due to our incomplete understanding of the biomineralization mechanisms underlying the incorporation of these tracers and their variabilities in the coral skeletons (a.k.a. the "vital effects"). In this thesis, an effort was made to understand the vital effects associated with the stable isotope as well as minor and trace element compositions of the aragonitic skeletons of the deep-sea coral species Desmophyllum dianthus, through a combination of empirical observations and a numerical model of coral calcification. Observations of the chemical and isotopic compositions of the coral skeletons were performed on four different spatial scales in a suite of modern D. dianthus specimens: bulk samples, micromilled samples, SIMS and nanoSIMS. These observations reveal tracer correlations in deep-sea corals that are coherent over different spatial scales and point toward a universal mechanism of the incorporation of these tracers through the biomineralization process. A few tracers emerge as promising proxies for the temperature (Li/Mg, Sr/Ca) and carbonate chemistry (U/Ca, B/Ca, Ba/Ca) of the oceans. The numerical model for coral calcification explains the strong δ18O and δ13C vital effects in individual deep-sea corals with an updated physicochemical basis, and carbonic anhydrase is found to play a key role in setting the slopes of the strong δ18O-δ13C correlations in different biogenic carbonates. The model also constrains the key physical parameters in the biomineralization process and is extended to explain the observed minor and trace element variabilities and correlations in deep-sea corals. The model can qualitatively explain the observed correlation patterns between Mg/Ca, Li/Ca, B/Ca and Sr/Ca in the coral skeletons, but quantitative data-model comparison is limited by both deficiencies in high-quality data and a lack of a well-constrained inorganic reference frame for aragonite. Future improvements in the geochemical tracers in biogenic carbonates will benefit from more extended empirical calibrations as well as a more complete mechanistic understanding of the key physicochemical and biological processes underlying the incorporation of tracers.</p