Estudos recentes têm demonstrado significativas variações na composição da fauna de ostracodes batiais decorrentes de mudanças climáticas. Visando verificar como esses eventos afetaram a ostracofauna batial da bacia de Campos foram analisadas 15 amostras provenientes de um testemunho a pistão recuperado a 1.287 m de lâmina de água. Espécies alóctones e autóctones foram identificadas sendo apenas as últimas estudadas. A idade das amostras foi obtida com base na análise de isótopos estáveis de oxigênio em testas do foraminífero planctônico Globigerinoides ruber, e os resultados comparados com dados do SPECMAP (Spectral Mapping Project). Foram identificadas 50 espécies autóctones distribuídas em 26 gêneros e 17 famílias. Os gêneros Krithe e Cytheropteron foram os mais diversificados (sete e cinco espécies, respectivamente). A família mais diversificada foi Cytheruridae, corroborando outros estudos paleoceanográficos. Foi estabelecida a idade de 42 ka para a base e 200 anos para o topo do testemunho. A análise de agrupamento por similaridade de Jaccard dividiu as amostras em dois grupos separados na amostra 12 (17,3 ka), no limite Holoceno-Último Máximo Glacial. A diversidade oscilou significativamente entre períodos glaciais e interglaciais, sendo menor no primeiro (3,0 nats/ind-1) e maior no último (3,4 nat/ind-1). Foi observado o predomínio de Argilloecia e Cytheropteron durante a deglaciação, Saida no interglacial, Apatihowella no UMG, Krithe no glacial e Macropyxis durante o UMG e glacial. Xestoleberis, por sua vez, ocorreu com diversidade relativamente constante ao longo de todo o testemunho. A distância taxonômica entre as espécies que ocorrem no glacial e interglacial se mostrou dentro dos limites esperados, com pequena proximidade entre os limites superiores e inferiores, respectivamente. A fauna de ostracodes da Bacia de Campos respondeu às variações climáticas ocorridas no Quaternário, o que reforça seu grande potencial como indicadora de mudanças paleoceanográficas. / Present studies have demonstrated significative changes in the composition of bathyal ostracode fauna caused by climatic events. With the objective of assess the influence of these events on the bathyal ostracodes from Campos Basin, 15 samples from a piston core taken at 1,287 m water depth were studied. Both allochthonous and autochthonous species were identified, however, only the latter were analyzed. The age of the samples was determined based on oxygen stable isotope data from tests of the planktonic foraminifer Globigerinoides ruber and compared to SPECMAP (Spectral Mapping Project) ones. Fifty autochthonous species belonging to 26 genera and 17 families were identified. The genera Krithe and Cytheropteron were the more diversified (seven and five species, respectively), while Cytheruridae was the most diversified family, supporting other paleoceanographic studies. The core bottom was dated as 42 ka, and the top 200 years. The Jaccard similarity grouping analysis shared the samples into two groups being the sample 12 (17.3 ka) the limit between them, which corresponds to the Holocene-Last Glacial Maximum transition. The diversity varied significantly between glacial and interglacial periods, being lower in the former (3.0 nats/ind-1) and higher in the latter (3.4 nat/ind-1). The predominance of Argilloecia and Cytheropteron during the deglacial, Saida during the interglacial, Apatihowella during LGM, Krithe on glacial, and Macropyxis during the glacial and LMG was recorded. Xestoleberis was registered with steady diversity values along the core. The taxonomic distances between the species in the glacial and interglacial presented ordinary values, with small distance between the upper and lower limits, respectively. The ostracode faunas from Campos Basin responded to the Quaternary climatic events, reinforcing the use of deep-sea ostracodes changes as a paleoceanographic proxy.

The first bimonthly resolved, paired δ18O and Sr/Ca time series from the slow-growing, tropical western Atlantic coral, Siderastrea siderea, from the Dry Tortugas, Florida has been generated and used to document that robust proxy climate records can be produced from this heretofore underutilized massive coral. The coral time series contains a 20-year long calibration window (1973-1992) for both δ18O and Sr/Ca and a 73-year long verification window (1900-1972) for Sr/Ca. These time series permits both the quantification of the relationship between coral δ18O-SST and Sr/Ca-SST using an augmented, 1° x 1° gridded SST record and the assessment of the stability of the proxy relationships over time. Both coral geochemical records are highly correlated with the augmented instrumental SST record through the calibration period and Sr/Ca remains highly correlated through the verification period both at the bimonthly (r = -0.97) and annual average level (r = -0.72). Additionally, both coral δ18O and Sr/Ca are highly reproducible within the same core, and Sr/Ca exhibits no extension-related vital effects. Sr/Ca-SST anomalies are also significantly correlated to the augmented SST anomalies, despite the removal of the serial autocorrelation. The skill of this proxy demonstrates its potential as a continuously growing, long-lived recorder of climate variability for the tropical Atlantic and Intra-American Seas. The relatively slow extension rate of the coral (~5 mm yr-1 during the 20th century) also suggests the potential for long records of climate variability (~200 years) of the region to be extracted from even modest-sized colonies (~1 m in height). The results of this study are important because relatively few century-long, sub-annually resolved time series of climate variability from massive Atlantic corals have been published, despite the significance of the tropical Atlantic climate modes of variability.

The Arctic and North Atlantic underwent significant climactic changes since the Last Glacial Maximum (25,000 years before present (1950 AD); ka BP), but offsets in the timing of events between the two regions are poorly constrained due to age model uncertainties that arise from changing radiocarbon reservoir ages. Here, we use a relatively high-resolution, multi-proxy stable isotope and sedimentologic dataset from Eastern Fram Strait (ODP Leg 162 Site 986) marine sediments to constrain the timing of Svalbard/Barents Sea Ice Sheet decay and infer deglacial reservoir ages over the last 30 ka. We use magnetic susceptibility, inorganic and organic carbon, foraminiferal assemblage counts, planktonic foraminiferal isotopes, and iceberg-rafted debris proxies to infer glaciomarine and paleoclimactic processes in Eastern Fram Strait. Significant negative Neogloboquadrina pachyderma (sinistral) δ18O episodes from background levels at 18.8 ka (-3.0 /) and 20.4 ka (-0.8 /) (on a radiocarbon-based age model) are shown to indicate meltwater discharge events from the Svalbard/Barents Sea Ice Sheet during the early glacial termination (21-14.7 ka). To allow for direct comparison between the timing of Eastern Fram Strait meltwater events and North Atlantic climate changes, the ODP Site 986 age model is correlated to the well-dated Greenland Ice Sheet Project 2 (GISP2) ice core δ18O record. The refined age model suggests that 16.0 and 18.1 ka are more realistic estimates for the meltwater events, inferring surface ocean reservoir age shifts of 1750 ± 1050 years in Eastern Fram Strait during the early glacial termination. Trends in reservoir ages throughout the last deglaciation mirror Nordic Sea deep ocean circulation changes and previously reported trends in the sub-polar North Atlantic; however, reservoir ages appear to be greater in Eastern Fram Strait. We hypothesize that processes affecting the distribution of reservoir ages in the North Atlantic and Arctic (e.g. sea ice cover, meltwater input, and ocean circulation) may have resulted in larger reservoir ages in polar regimes than in sub-polar ones during the last deglaciation, analogous to contemporary distributions. In contrast to previous radiocarbon age model-based studies in the Nordic Seas that predict a significant meltwater event at ~19 ka, these findings show that rapid Svalbard/Barents Sea Ice Sheet decay began at 16 ka and suggest that uncertainty on the order of thousands of years may exist in previous paleoclimate studies with radiocarbon-based age models from the deglacial Nordic Seas and Arctic.

Graduation date: 1987

The "Mystery Interval" (17.5-14.5 ka) is an unusual time period of abrupt global climate change during the late glacial between Heinrich event 1 and the Bølling-Allerød warm period (~17.5-14.5 ka). This period was characterized by extreme cooling in the North Atlantic region, warming in Antarctica, the rise of atmospheric greenhouse gases, and a variety of hydrologic changes around the globe, all of which may have stemmed from Heinrich event 1 and the possible collapse of the Atlantic?s meridional overturning circulation. A distinctive and unique gray clay layer was deposited in Cariaco Basin, Venezuela, within this time period, which has no apparent counterpart in the basin?s sediment record for at least the last full glacial-interglacial cycle. One hypothesis for the origin of the gray layer is that the initial pulse of deglacial sea level rise over the shallow Unare Platform, south of the basin, caused remobilization and rapid emplacement of previously deposited shelf sediments. However, analysis of the timing and extent of sea level rise as well as evidence from radiocarbon ages and a comparison of the organic content of gray layer sediments and known turbidites in the basin does not support this hypothesis. The alternative hypothesis, that the gray layer is related to increased fluvial discharge from local rivers as a result of elevated regional rainfall, is supported by a number of lines of evidence. The bulk sediment elemental content measured by scanning X-ray fluorescence (XRF) (this study) and clay mineralogy (Yu, 1996) support input of local river sediments. Coccolith abundances (Mertens et al., 2009), sea surface salinity (SSS) estimates and foraminiferal Ba/Ca analysis (this study) are also consistent with freshening of surface waters caused by elevated river runoff. This implies increased rainfall in the region which is corroborated by elemental and mineralogical ratios that point to increased precipitation and chemical weathering. Average terrigenous grain size and terrigenous fluxes are also in line with modern rainy season data. Despite prior suggestions that the Cariaco Basin region should be dry due to a southward-shifted Inter-tropical Convergence Zone (ITCZ) during cool periods in the North Atlantic, such as the Mystery Interval, data presented in this thesis suggest elevated rainfall and fluvial input related to deposition of the gray layer. Multiple lines of proxy evidence indicate that Cariaco Basin may have been characterized by a drier climate in the first part of the Mystery Interval but then shifted to a wetter climate in the second part, after ~16.5 ka, which might resolve this apparent conflict. The change to wetter conditions is most likely due to a northward shift in the position of the ITCZ, possibly due to warming tropical North Atlantic sea surface temperatures (SSTs) and/or extreme North Atlantic seasonality. Comparison of the Cariaco Basin climate records to climate observations from around the globe reveal a similar shift in climatic conditions around the same time, suggesting that the Mystery Interval may actually have been a two-phase event. Although many of the climatic observations from around the world can be explained by a shift from a southerly position of the ITCZ within the first part of the Mystery Interval to a more northerly position during the later part of the interval, many regions are not directly affected by the ITCZ and other complicating factors may play a role in the rapid climate changes observed globally.

We test the fidelity of shallow-water gastropod skeletons as multi-proxy archives of seasonal paleo-environmental change by performing isotopic and trace-metal analyses on specimens of Conus ermineus from the Gulf of Mexico. Four adult specimens were collected from Stetson Bank in the Flower Garden Banks National Marine Sanctuary during the summer of 2002. Shell samples were milled along axes of growth to produce time-series profiles spanning up to eight years. We corrected the profiles for growth rate effects and compared the tuned results with in situ temperature and salinity records at the reef surface and temperature profiles from nearby surface buoys. Examination of sample densities in δ18O cycles shows that shell growth is faster during summers and slower during winters. Tuning the profiles versus time yields δ18O values that co-vary closely with seasonal temperatures to a high degree of coherency (R2 = 0.84). The δ13C profiles show cyclic variation modified by ontogenetic decreases in δ13C. These ontogenetic trends are attributable to decreasing metabolic efficiency, while seasonal cycles reflect hydrographic changes in the gastropods’ habitat. Salinity and δ13C of dissolved inorganic carbon show a strong correlation at Stetson Bank (R2 = 0.80), and early summer shell δ13C minima coincide with local salinity minima during times of peak river discharge. The terminations of these δ13C minima occur during annual upcoast reversals of shelf currents in this area. These effects are augmented by summer stratification and productivity minima that further decrease seawater δ13C. Sr/Ca ratios increase through ontogeny, most likely due to decreasing metabolic efficiency. However, seasonal variations in Sr/Ca profiles show strong similarity with δ18O profiles, confirming the temperature dependence of Sr/Ca and minimal influence of salinity on shell δ18O at Stetson Bank. The results of this study show that tuned δ18O and Sr/Ca profiles can be used to reconstruct seasonal paleotemperatures. Carbon isotope profiles and environmental data also demonstrate the utility of Conus δ13C as a proxy for freshwater flux and shelf circulation.

<p>The tropics are a significant source of heat and moisture export, which drive global circulation patterns, thus it is vital to systematically understand the land, ocean and sedimentological interactions within the tropics. The Brazilian continental margin is an ideal region to characterize the tropics due to its unique local oceanography and proximity to the atmospheric engine that is the Amazon Basin. A combination of: 1) terrestrial organics and hydrology; 2) oceanographic temperature, isotopic composition, and salinity and 3) early diagenesis and geochemistry of sedimentary interstitial water and methane hydrate, provide a detailed understanding of the primary constituents that influence the South American tropics.</p><p>Sedimentological, organic and paleoceanographic reconstructions of the Amazon Basin, Brazilian Nordeste, and western equatorial Atlantic have been undertaken on two sediment cores located on the Brazilian continental slope representing 30 and 110 ka, respectively. High-resolution XRF analyses of Fe, Ti, K and Ca are used to define the sedimentological history of the Amazon Basin and northern Nordeste. Here we present elemental ratios of Ti/Ca and Fe/K, in addition to magnetic susceptibility, to determine variability in Amazon Basin and Nordeste hydrology. Bulk organic proxies d13C and d15N of sedimentary organic carbon are used to define the organic history of the Amazon Basin. Peaks in Ti/Ca and Fe/K ratios largely correlate in both the Amazon Basin and in the Nordeste Record. These excursions correlate with commonly modeled global slowdown of the Atlantic meridional overturning circulation (AMOC) during increased northern hemisphere glaciation. Differences in the Fe/K and Ti/Ca records suggest periods of increased chemical weathering independent of precipitation driven sediment discharge in the Brazilian Nordeste. Bulk organic geochemistry indicates the vegetative history of the Amazon Basin has been relatively stable during the late Quaternary.</p><p>High-­resolution stable oxygen isotopic analysis and Mg/Ca paleothermometry undertaken on the near-­surface-dwelling planktic foraminiferal species Globierinoides ruber provide a picture of paleoceanographic forcings in the western equatorial Atlantic. The Nordeste core exhibits a rapid warming of ~3.5ºC between the last glacial maximum and the early Holocene. Furthermore, in almost all cases during the last glacial stage, there was a 0.5 to 2ºC warming of the western equatorial Atlantic during the periods of high Ti/Ca ratios that correlate with slowdown of AMOC. Thus, as observed in some previous studies, the western equatorial Atlantic was warm and the adjacent southern tropical continent was wet coincident with increased glaciation in the high latitude northern hemisphere.</p><p>Interstitial pore waters were analyzed from the Amazon Fan and Brazilian continental slope to determine early diagenesis, methane hydrate potential and its geographic variability. Interstitial waters were measured for total Mg, Ca, SO4, alkalinity, Cl, and d18O, combined with seismic bottom simulating reflectors (BSRs) to investigate early diagenesis. Interpolated maps of sulfate reduction, sedimentation rate and maximum alkalinity were produced to examine geographic variability in early diagenesis and methane hydrates. Inorganic precipitation of calcium and magnesium, likely via dolomite and siderite, correlates with a decrease in alkalinity through inorganic carbonate precipitation and methanogenesis, but alternatively increases through redox pathways, specifically sulfate reduction.</p><p>Through multiple lines of evidence it is likely that there is extensive methane hydrate occurrence on the Amazon continental shelf. A combination of: 1) A rapid linear decline in sulfate at an unusually shallow depth; 2) Uncommonly high sedimentation rates and terrestrial organic carbon input; 3) Significant variability in what should be conservative chloride concentrations; 4) Large variability in interstitial oxygen isotopes; 5) Widespread occurrence of BSRs provide substantial support for the presence of methane hydrates. Sulfate reduction rates are lowest along the main Amazon channel, with highest values distal of the main channel. Sedimentation rates are relatively low on the continental shelf and surrounding the main channel and highest toward the distal end of the main channel. Sulfate reduction rates provide key insights to the potential geographic variability of methanogenesis and methane hydrate formation. Given the tremendous influx of sediment from the Amazon River, this region is prone to massive sediment failures, subsequent release of methane hydrates, as well as significant potential for natural gas hydrates.</p> / Dissertation

We test the fidelity of shallow-water gastropod skeletons as multi-proxy archives of seasonal paleo-environmental change by performing isotopic and trace-metal analyses on specimens of Conus ermineus from the Gulf of Mexico. Four adult specimens were collected from Stetson Bank in the Flower Garden Banks National Marine Sanctuary during the summer of 2002. Shell samples were milled along axes of growth to produce time-series profiles spanning up to eight years. We corrected the profiles for growth rate effects and compared the tuned results with in situ temperature and salinity records at the reef surface and temperature profiles from nearby surface buoys. Examination of sample densities in &#948;18O cycles shows that shell growth is faster during summers and slower during winters. Tuning the profiles versus time yields &#948;18O values that co-vary closely with seasonal temperatures to a high degree of coherency (R2 = 0.84). The &#948;13C profiles show cyclic variation modified by ontogenetic decreases in &#948;13C. These ontogenetic trends are attributable to decreasing metabolic efficiency, while seasonal cycles reflect hydrographic changes in the gastropods’ habitat. Salinity and &#948;13C of dissolved inorganic carbon show a strong correlation at Stetson Bank (R2 = 0.80), and early summer shell &#948;13C minima coincide with local salinity minima during times of peak river discharge. The terminations of these &#948;13C minima occur during annual upcoast reversals of shelf currents in this area. These effects are augmented by summer stratification and productivity minima that further decrease seawater &#948;13C. Sr/Ca ratios increase through ontogeny, most likely due to decreasing metabolic efficiency. However, seasonal variations in Sr/Ca profiles show strong similarity with &#948;18O profiles, confirming the temperature dependence of Sr/Ca and minimal influence of salinity on shell &#948;18O at Stetson Bank. The results of this study show that tuned &#948;18O and Sr/Ca profiles can be used to reconstruct seasonal paleotemperatures. Carbon isotope profiles and environmental data also demonstrate the utility of Conus &#948;13C as a proxy for freshwater flux and shelf circulation.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Geological Sciences." Includes bibliographical references.

Στην παρούσα εργασία πραγματοποιήθηκαν μικροπαλαιοντολογικές αναλύσεις σε επιλεγμένα δείγματα ιζήματος από πυρήνα που συλλέχθηκε στο Λιβυκό πέλαγος. Σε αυτόν τον πυρήνα έχουν εντοπιστεί ορίζοντες σαπροπηλικής ή παρόμοιας σύστασης καθώς και αποθέσεις λασπούχων ροών. Σκοπός της εργασίας είναι ο προσδιορισμός των παλαιοωκεανογραφικών και παλαιοκλιματικών συνθηκών που αναπτύχθηκαν κατά το χρονικό διάστημα απόθεσης των ιζημάτων που μελετήθηκαν, καθώς και η συσχέτιση τους με αποτελέσματα ερευνών των γειτονικών περιοχών. Η έρευνα πραγματοποιήθηκε από το εργαστήριο Θαλάσσιας Γεωλογίας και Φυσικής Ωκεανογραφίας του Πανεπιστήμιου Πατρών. / --