Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-05-03T16:41:23Z No. of bitstreams: 1 GASPAR_2014_TeseUFF.pdf: 5686020 bytes, checksum: 1a09a81a8e3faf6aa6834f79b7c46c47 (MD5) / Made available in DSpace on 2016-05-03T16:41:23Z (GMT). No. of bitstreams: 1 GASPAR_2014_TeseUFF.pdf: 5686020 bytes, checksum: 1a09a81a8e3faf6aa6834f79b7c46c47 (MD5) / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências-Geoquímica. Niterói, RJ / Este estudo teve como objetivo principal avaliar a saúde do ecossistema recifal do Atol das Rocas utilizando como indicadores as associações de foraminíferos bentônicos, Índice FORAM e saúde e cobertura de corais. Além disso, descrever a razão Mg/Ca em testas recentes de Nonion commune para identificar mais uma possível espécie para estudos paleoclimáticos. Um total de 276 transeções de ponto e faixa (20x1m) foram realizadas em 6 expedições (out/07, mar e dez/10, mai/11, mai e nov/12) e revelaram coberturas de corais variando entre ~3 e 50%, de acordo com o padrão de circulação de água nas piscinas. Relações entre branqueamento/doenças em corais e anomalias de temperatura foram registradas para 2010. O que pode ter causado uma redução significativa na cobertura de corais em 4 piscinas abertas, após março e dezembro de 2010. A prevalência de doenças, que lesionam e causam mortalidade parcial ou total dos corais, foi alta nessas piscinas. As doenças atingiram maiores porcentagens e persistem por mais tempo que o branqueamento. Em 2012, sem registro de temperatura muito elevadas, a cobertura para de apresentar sinais de declínio, embora ainda existam colônias doentes. Fatores como altos níveis de radiação solar, alta transparência da água, pouca profundidade, intenso fluxo de água, baixa diversidade de corais, dominância do gênero Siderastrea e o contato direto dos corais com muitas algas podem ter contribuído para os altos percentuais de doenças. Além disso, um total de 105 amostras de sedimento superficial foi coletado em dezembro de 2010 e maio de 2011 nas mesmas piscinas. Foram identificados 108 gêneros de foraminíferos bentônicos, porém a maioria com abundância inferior a 1%. Os gêneros Archaias, Quinqueloculina, Sorites, Amphistegina e Borelis dominaram nos dois períodos de amostragem, e juntos representam mais de 60% da abundância relativa em todas as piscinas. Uma relação positiva e significativa foi encontrada entre a granulometria e a densidade de foraminíferos. As menores densidades foram encontradas nas piscinas abertas com intenso fluxo de água. A alta transparência da água, pouca profundidade, intenso fluxo de água, abundância de algas e ambiente carbonático favorecem o domínio de Archaias angulatus nas associações de foraminíferos. A proporção dos foraminíferos que possuem endossimbiontes é superior a 40% em todas as piscinas, resultando em valores médios de Índice FORAM (IF) entre 5,76 e 9,15, com uma média geral para o Atol igual a 7,0. Portanto, o IF indica que a qualidade da água é favorável ao crescimento e/ou recuperação recifal, mas não apresentou correlação com cobertura de coral ou algas, assim como em outras regiões recifais do Brasil. Recomenda-se que o monitoramento da cobertura e saúde recifal e dos foraminíferos sejam complementares e não independentes. Para as análises de geoquímica elementar nas testas de foraminíferos recentes, com o método de ablação a laser (LA-ICP-MS) foram utilizados 50 exemplares de Nonion commune que estavam vivos no momento da coleta, com tamanhos entre 200-354 μm. As médias das razões de Mg/Ca registradas nesse trabalho - 6,12 a 7,85 mmol/mol - estão de acordo com a faixa de variação encontradas para foraminíferos bentônicos sem endossimbiontes e para águas rasas e quentes. A relação entre os valores de Mg/Ca e o tamanho da carapaça, sugerem que futuras análises considerem apenas testas maiores que 250 μm e, preferencialmente, com variações de apenas 50 μm no tamanho das mesmas. É possível sugerir que essa espécie possa ser usada em futuros estudos baseados em Mg/Ca com finalidade de reconstrução de paleotemperaturas, pois parecem ter relação com a temperatura de calcificação, embora um estudo mais detalhado em um ambiente com variações sazonais de TSM mais acentuadas, seja necessário para confirmar essa relação. A continuidade do monitoramento é essencial para compreender como esse ambiente tão importante irá se recuperar e/ou responder aos futuros eventos de anomalias térmicas / This study aimed to assess Rocas Atoll coral reef health by monitoring corals cover and health, as well the benthic foraminifera assemblages and the FORAM Index (FI) in 15 tide pools. Furthermore, the Mg/Ca ratios for recent (stained) foraminifera Nonion commune from Rocas Atoll were also described. A total of 276 point intercept transects and belt transects (20x1m) were surveyed during 6 expeditions (Oct/07, Mar and Dec/10, May/11, May and Nov/12) and revealed coral cover ranging between ~3 and 50% inside tide pools. Bleached and diseased corals were positive related to SST anomalies recorded for 2010, and might be the main reason of a significant coral cover decline in 4 open tide pools. Coral diseases reached higher percentages and persist longer than bleaching. In 2012 no high temperature was recorded and coral cover showing no signs of decline. High radiation levels, clear water, shallow depth, high water flow, low coral diversity, high abundance of one species (Siderastrea stellata) and direct algal contact might be influenced the high percentages of coral diseases. A total of 105 surface sediment samples were collected between December 2010 and May 2011 at the same tide pools. A total of 108 genera of benthic foraminifera were identified, however most of them showed abundance lower than 1%. The genera Archaias, Quinqueloculina, Sorites, Amphistegina and Borelis were dominant in the two sampling periods, and together represent more than 60% relative abundance in all tide pools. A significant and positive relation was found between the grain size and benthic foraminifera density. Lowest densities were founded in open tide pools with high water flow. Clear water, shallow depth, high water flow, high algae abundance and carbonate environment resulted in Archaias angulatus associations. Symbiont-bearing foraminifera proportion is above 40% in all tide pools, resulting FORAM Index (FI) values between 5.76 and 9.15, with mean value 7.0 for Rocas Atoll. Therefore, the FI indicates that the water quality is favorable to growth and/or reef recovery, but showed no correlation with coral cover and algae. It is recommended that monitoring coral cover and health and foraminifera to be complementary and not independent. Trace element composition analyses of recent foraminifera, using the laser ablation (LA-ICP-MS), were conducted in 50 tests of Nonion commune (alive at sampling time), tests sizes ranged from 200-354 μm. The mean Mg/Ca ratios recorded were - 6.12 to 7.85 mmol/mol - consistent with the range of variation found for smaller benthic foraminifera and to shallow and warm waters. The relation between Mg/Ca rations and test size, suggest that future analysis considers only tests greater than 250 μm, and varying only 50 μm. It is possible to suggest that this species may be used in future paleotemperatures research Mg/Cabased, since they appear to be related to the seawater calcification temperature, although a more detailed study in an environment with a higher seasonal SST variations is necessary to confirm this relation. Continuing monitoring is essential to understand how Rocas Atoll will recover and/or respond to future events of thermal stress anomalies

Ce travail avait pour but de reconstituer l'évolution de la température et du δ¹⁸O des eaux de surface et des eaux de la thermocline dans la Warmpool indo-pacifique (IPWP) en combinant la thermométrie Mg / Ca et la mesure des isotopes stables de l'oxygène sur des foraminifères planctoniques de surface et de sub-surface prélevés dans des carottes de sédiments situées dans l'océan Indien tropical oriental. Ce travail a permis de ré-évaluer les effets des différentes méthodes de nettoyage et de la dissolution in situ sur la thermométrie Mg/Ca des foraminifères planctoniques, mettant en évidence la nécessité de corrections différentes suivant les espèces. L’évolution de l’IPWP au cours des 270 000 dernières années a été reconstituée. Les résultats indiquent que le δ¹⁸O des eaux de surface reflètent principalement l'advection latérale plutôt que l'historique des précipitations régionales, et suggèrent que l'hydrologie de surface IPWP est contrôlée par la migration latitudinale de la zone de convergence intertropicale aux échelles de temps orbitales mais aussi en réponse aux événements climatiques abrupts de l'hémisphère nord (eg. événements de Heinrich). Les variations de salinité de surface sont étroitement corrélées aux changements d’export vers l’Atlantique au niveau du Courant des Aiguilles (Sud de l’Afrique). Puis, les changements dans le transport des eaux de la thermocline issues de l’ITF vers l'océan Indien ont été étudiés. Les résultats montrent que le transport était plus faible pendant les glaciations (ie. MIS 6 et 4-2) que pendant les périodes interglaciaires (ie. MIS 7, MIS 5 et Holocène) et exerçaient une influence significative sur les changements de la température de la thermocline dans l'Océan Indien. / This work aimed at reconstructing the late Quaternary evolution of surface and thermocline temperature and ocean surface water δ¹⁸O in the Indo-Pacific Warm Pool by combining Mg/Ca-thermometry and stable oxygen isotope analyses on surface and thermocline-dwelling planktonic foraminifers retrieved from sediment cores in the eastern tropical Indian Ocean. This study allowed to re-evaluate the effects of different cleaning methods and in-situ dissolution on the Mg-thermometry of planktonic foraminifers, evidencing the need for species-dependent corrections. Then, the IPWP evolution over the last 270,000 years has been explored. Results indicate that surface water δ¹⁸O chiefly reflects lateral advection rather than local precipitation history, and suggest that surface IPWP hydrology is controlled by the latitudinal migration of the Intertropical Convergence Zone at orbital timescale as well as during abrupt northern hemisphere climatic events (i.e. Heinrich events). Ocean surface salinity in the IPWP and Agulhas leakage region varied synchronously, implying their teleconnection through oceanic and atmospheric circulation. Moreover, changes in the transport of thermocline water to the Indian Ocean by the Indonesian Throughflow (ITF) have been reconstructed. Results show that thermocline water transport was weaker during glacials (i.e. MIS 6 and 4-2) than during interglacials (MIS 7, MIS 5 and Holocene), and exerted significant influence on Indian Ocean TWT change.

Climate variability in the North Atlantic has been linked in part to the North Atlantic Oscillation (NAO). The NAO influences marine ecosystems in the northwestern Atlantic and the transport variability of the cold Labrador Current (LC). Understanding historic patterns and predicting future changes in LC transport require long-term and high-resolution climate records that are not available from instrumental data sets. This thesis presents the first century-scale sea surface temperature (SST)reconstructions from the Northwestern Atlantic using Mg/Ca ratios in the long-lived crustose coralline algae Clathromorphum compactum. which is characterized by a high Mg-calcite skeleton exhibiting annual growth increments. Results indicate strong correlations between interannual variations in Mg/Ca ratios and instrumental SST. The 131-year algal Mg/Ca record reveals NAO-type periodicities and evidence of past cold events and warming periods associated with basin-wide ecosystem shifts. Negative correlations between LC volume transport and algal Mg/Ca reflect the cooling influence of the LC on eastern Canadian shelf ecosystems.

Climate variability in the North Atlantic has been linked in part to the North Atlantic Oscillation (NAO). The NAO influences marine ecosystems in the northwestern Atlantic and the transport variability of the cold Labrador Current (LC). Understanding historic patterns and predicting future changes in LC transport require long-term and high-resolution climate records that are not available from instrumental data sets. This thesis presents the first century-scale sea surface temperature (SST)reconstructions from the Northwestern Atlantic using Mg/Ca ratios in the long-lived crustose coralline algae Clathromorphum compactum. which is characterized by a high Mg-calcite skeleton exhibiting annual growth increments. Results indicate strong correlations between interannual variations in Mg/Ca ratios and instrumental SST. The 131-year algal Mg/Ca record reveals NAO-type periodicities and evidence of past cold events and warming periods associated with basin-wide ecosystem shifts. Negative correlations between LC volume transport and algal Mg/Ca reflect the cooling influence of the LC on eastern Canadian shelf ecosystems.

Ostracodes, bi-valved crustaceans, are potentially excellent proxies for salinity.They are abundant, react to changes in salinity, and secrete low-magnesium calcite shells that preserve information about their host water chemistry. Changes in valve trace element concentration, stable isotope composition, and sieve pore shape values have been linked to changes in salinity. This study analyzed the response of the euryhaline ostracode, Cyprideis americana, to salinity in six lakes from two Bahamian islands across two seasons. The purpose of this work was to determine which compositional and morphological variables in C. americana are the most useful for paleosalinity reconstructions.Ostracode and water samples were collected from lakes of varying water chemistry on San Salvador Island (winter and summer seasons), and Exuma (winter season). Dissolved oxygen, pH, salinity, and temperature measurements were taken for each lake. The best-preserved valves from each lake were analyzed for sieve pore circularity, Mg and Ca concentrations, and δ18 O isotopic composition. Mg/Ca ratios and Kd[Mg] values were calculated for each lake. Each parameter was plotted against salinity for all of the lakes and for lakes from each season and island. Only the samples collected during the summer followed expected trends: with increases in lake water salinity, Mg/Ca ratio decreased, δ18 O composition increased, and sieve pore circularity decreased. Samples collected from the winter field sessions did not follow expected trends, potentially due to the breeding and moulting habits of C. americana. Temperature was more correlative with valve composition than a previous study of C. americana suggests, but is supportive of similar correlations of Cyprideis species in continental and other island settings. The valve Mg/Ca ratio and mean sieve pore circularity showed the best correlation with salinity and are the variables that will be most useful in paleosalinity studies from sediment cores. Future work should further investigate the relationship between mean sieve pore circularity and lake salinity as well as the breeding and moulting habits of C. americana. Such work may allow for past salinity ranges to be reconstructed from fossil C. americana samples.

Yes / The Mg/Ca ratios of biogenic calcite is commonly seen as a valuable palaeo-proxy for reconstructing past ocean temperatures. The temperature dependence of Mg/Ca ratios in bivalve calcite has been the subject of contradictory observations. The palaeoceanographic use of a geochemical proxy is dependent on initial, rigorous calibration and validation of relationships between the proxy and the ambient environmental variable to be reconstructed. Shell Mg/Ca ratio data are reported for the calcite of two bivalve species, Mytilus edulis (common mussel) and Pecten maximus (king scallop), which were grown in laboratory culturing experiments at controlled and constant aquarium seawater temperatures over a range from 10 to 20 C. Furthermore, Mg/Ca ratio data of laboratory- and fieldgrown M. edulis specimens were compared. Only a weak, albeit significant, shell Mg/Ca ratio¿temperature relationship was observed in the two bivalve species: M. edulis (r2=0.37, p<0.001 for laboratory-cultured specimens and r2=0.50, p<0.001 for field-cultured specimens) and P. maximus (r2=0.21, p<0.001 for laboratory-cultured specimens only). In the two species, shell Mg/Ca ratios were not found to be controlled by shell growth rate or salinity. The Mg/Ca ratios in the shells exhibited a large degree of variability among and within species and individuals. The results suggest that the use of bivalve calcite Mg/Ca ratios as a temperature proxy is limited, at least in the species studied to date. Such limitations are most likely due to the presence of physiological effects on Mg incorporation in bivalve calcite. The utilization is further limited by the great variability both within and among shells of the same species that were precipitated under the same ambient conditions

No / The potential of Mg in Arctica islandica as a climate proxy is explored through analysis of live-collected shells from Irvine Bay, NW Scotland. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis of the right hand valve from two specimens indicates that seasonal Mg/Ca variations do not correlate with seawater temperature. The highest Mg/Ca typically occurs at the annual growth checks in ~ November¿February. Mg/Ca variations between growth checks are significant in one specimen but usually not significant in the other. Mg/Ca measurements taken laterally across the band (i.e. perpendicular to direction of the growth) to determine heterogeneity of the aragonite deposited at the same time indicates that Mg/Ca concentration decreases with increasing distance from the periostracum in both shells. X-ray Absorption Near Edge Spectroscopy (XANES) indicates that Mg is not substituted into aragonite but is hosted by a disordered phase e.g. organic components or nanoparticles of an inorganic phase. Shell Mg/Ca variations may reflect changes in the concentration or composition of the disorded phase, as well as changes in the composition of the extrapallial fluid used for calcification. Such changes could reflect the relative transportation rates of Mg and Ca to the calcification site.

During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.

Previous studies showed that sea surface salinity (SSS) in the Florida Straits as well as Florida Current transport covaried with changes in North Atlantic climate over the past two millennia. However, little is known about earlier Holocene variability in the Florida Straits. Here, we combine Mg/Ca-paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber (white variety) from Florida Straits sediment core KNR166-2 JPC 51 (24 degrees 24.70? N, 83 degrees 13.14?W, 198m deep) to reconstruct a high-resolution (~30 yr/sample) early to mid Holocene record of sea surface temperature and delta18OSW (a proxy for SSS) variability. We also measured Ba/Ca ratios in the same shell material as a proxy for riverine input into the Gulf of Mexico over the same time interval. After removing the influence of global delta18OSW change due to continental ice volume variability, we propose that early Holocene SSS enrichments were caused by increased evaporation/precipitation ratios in the Florida Straits associated with periods of reduced solar output, increased ice rafted debris in the North Atlantic and the development of more permanent El Nino-like conditions in the eastern equatorial Pacific. When considered with previous high-resolution reconstructions of early Holocene tropical atmospheric circulation changes, our results provide evidence that solar output variability over the Holocene had a significant impact on the global tropical hydrologic cycle over the last 10,000 years.

During the Late Pliocene, between 3.3 Ma and 2.6 Ma, tectonic events changed ocean basin interactions against a background of shifting orbital forcing mechanisms and a global cooling trend. A climate system that had been locked in a stable, warm state gradually transformed into one typified by the high-amplitude glacial–interglacial fluctuations characteristic of the later Quaternary. The onset of Northern Hemisphere glaciations in the Late Pliocene marks an important step in this transition, due to the role of feedback mechanisms including ice albedo. A crucial factor in this Northern Hemisphere ice sheet expansion is the North Atlantic surface ocean circulation. To evaluate how they are linked, a ca. 200-kyr time slab spanning 2782-2520 ka (Late Pliocene–Early Pleistocene) was analyzed at millennial scale resolution from eastern North Atlantic Deep Sea Drilling Project (DSDP) Site 610 and Integrated Ocean Drilling Program (IODP) Site U1313. The causes of the Plio-Pleistocene climatic turnover are compared to that of the well-documented Marine Isotope Stage (MIS) M2 occurring in the Late Pliocene (3.3 Ma). MIS M2, a severe glacial event seen as a precursor to later Quaternary-style glaciations, was investigated from western North Atlantic DSDP Site 603. Utilizing a same-sample methodology, two paleoceanographic proxies were used: (1) dinocyst assemblages, and (2) foraminiferal geochemistry (δ18O and Mg/Ca). Dinocysts are proven tracers of sea-surface temperature (SST), salinity, nutrient supply, and sea ice cover, and are analyzed here to characterize the overlying water masses at the studied sites. Strong dinocyst assemblage fluctuations attest to variations in the influence of the North Atlantic Current (NAC). Using Mg/Ca ratios for the planktonic foraminifer Globigerina bulloides to determine absolute SSTs allows salinity changes to be reconstructed when combined with stable oxygen isotopes. This study shows a persistent Gulf Stream–NAC in the western North Atlantic during MIS M2, favoring a southern shift of the NAC over a shutdown of the thermohaline circulation. At the newly established Plio-Pleistocene boundary, a profound turnover in dinoflagellate cyst assemblages reveals a shift in ocean mode during MIS 104 (2.6 Ma). Three distinct dinocyst ecozones demonstrate this fundamental reorganization of the North Atlantic circulation.