Geochemistry of rare earth elements in pacific hydrothermal sediments

The concentrations and mass accumulation rates of rare earth elements (REE) in hydrothermal sediments from two Pacific sites support earlier predictions that hydrothermal REE inputs are significant to the overall marine REE mass balance. Although REE are enriched in hydrothermal vent fluids, they are rapidly and extensively scavenged from the water column by Fe oxyhydroxides and undergo some degree of fractionation prior to removal. Evidence for significant light REE (LREE) hydrothermal inputs tends to be masked by the fact that the LREE patterns and inter-element ratios of both proximal and distal hydrothermal precipitates are similar to those of seawater. However, the heavy REE (HREE) patterns clearly reflect a basaltic source and the HREE ratios from both sites are similar to each other but distinct from their seawater analogs. This suggests HREE ratios potentialy could be used as proxy indicators in our attempts to reconstruct the history of seafloor hydrothermal activity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27113/1/0000105.pd

The europium anomaly of seawater: implications for fluvial versus hydrothermal REE inputs to the oceans

Seafloor hydrothermal vent fluids are characterized by rare earth element (REE) enrichments and large positive Eu anomalies; however, this input is not recorded by seawater. Hydrothermal sediments from the southeast Pacific (DSDP Site 598) were examined to address this discrepancy between the observed and predicted REE pattern of seawater. "Scavenging indices", which reflect long-term REE scavenging by iron-rich hydrothermal precipitates, were calculated for each of eight REE's. Comparisons between these indices and the REE content of seawater indicate that the intensity of REE scavenging by hydrothermal precipitates is proportional to the concentration of REE's in the fluid phase. We predict that REE's are rapidly scavenged from hydrothermal solutions, and that Eu is removed disproportionately faster relative to its neighbors. Eu-anomaly values for Site 598 and other hydrothermal sediments support this prediction: a vent signature is recorded in sediments closest to the ridge axis and the Eu-anomaly values become more seawater-like with increasing distance and scavenging. This implies that the REE content of seawater cannot be used to constrain hydrothermal versus fluvial fluxes to the oceans.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29082/1/0000117.pd

REE/Fe variations in hydrothermal sediments: Implications for the REE content of seawater

Seafloor hydrothermal vent solutions exhibit rare earth element (REE) enrichments ranging between one to three orders of magnitude greater than average seawater. To assess the impact of these hydrothermal inputs on ocean chemistry, we have examined the behavior of REEs for hydrothermal sediments collected adjacent to two Pacific spreading ridge sites: the East Pacific Rise at 19[deg]S, and the Southern Juan de Fuca Ridge at 4S[deg]N. In general, the REE/Fe ratios for both proximal and distal hydrothermal sediments are greater than vent solutions by a factor of 2 to 500, and these ratios increase with increasing distance away from the ridge axis. An evaluation of these results in the context of previous models of REE behavior indicates that, in fact, seawater experiences a net depletion in REEs as a result of hydrothermal activity. This is due primarily to the large scavenging capacity of iron oxyhydroxides which precipitate from these solutions. Such an interpretation explains why the REE content of seawater collected in the vicinity of hydrothermal vents is anomalously lower than "normal" seawater sampled from a comparable depth.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28043/1/0000482.pd

Metalliferous sediments and the scavenging residence time of Nd near hydrothermal vents

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94674/1/grl5993.pd

Geochemistry of eolian dust in Pacific pelagic sediments: Implications for paleoclimatic interpretations

Geochemical data (REEs, Th, Sc) were determined for the operationally defined eolian dust (ODED) fraction (n = 57) from the north and equatorial Pacific Ocean. Paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions. This study shows, on the basis of geochemical data, published mineralogical data, and mixing models, that the ODED fraction actually is a mixture of materials from two endmember sources: the continental crust (eolian-transported weathering products) and the oceanic crust (primarily volcanogenic material). Mixing model results show that the average ash content is significant in the ODED fraction (equatorial Pacific = 43%; north Pacific = 24%). We have used this information to reconsider and refine the results of previous paleoclimate studies. In the northwest Pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35[deg]N and 42 [deg]N. Eolian fluxes are greatest during interglacial periods in the equatorial Pacific. These results are consistent with previous interpretations. In contrast to previous assumptions, eolian mass accumulation rates may not be a valid indicator of paleo-aridity because they are correlated with grain size. Furthermore, the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction (the continental crust component is associated with larger grains). This compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo-wind intensity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29219/1/0000274.pd

In-depth analysis of the antibody response of individuals exposed to primary dengue virus infection

Humans who experience a primary dengue virus (DENV) infection develop antibodies that preferentially neutralize the homologous serotype responsible for infection. Affected individuals also generate cross-reactive antibodies against heterologous DENV serotypes, which are non-neutralizing. Dengue cross-reactive, non-neutralizing antibodies can enhance infection of Fc receptor bearing cells and, potentially, exacerbate disease. The actual binding sites of human antibody on the DENV particle are not well defined. We characterized the specificity and neutralization potency of polyclonal serum antibodies and memory B-cell derived monoclonal antibodies (hMAbs) from 2 individuals exposed to primary DENV infections. Most DENV-specific hMAbs were serotype cross-reactive and weakly neutralizing. Moreover, many hMAbs bound to the viral pre-membrane protein and other sites on the virus that were not preserved when the viral envelope protein was produced as a soluble, recombinant antigen (rE protein). Nonetheless, by modifying the screening procedure to detect rare antibodies that bound to rE, we were able to isolate and map human antibodies that strongly neutralized the homologous serotype of DENV. Our MAbs results indicate that, in these two individuals exposed to primary DENV infections, a small fraction of the total antibody response was responsible for virus neutralization

Correction: In-Depth Analysis of the Antibody Response of Individuals Exposed to Primary Dengue Virus Infection

Humans who experience a primary dengue virus (DENV) infection develop antibodies that preferentially neutralize the homologous serotype responsible for infection. Affected individuals also generate cross-reactive antibodies against heterologous DENV serotypes, which are non-neutralizing. Dengue cross-reactive, non-neutralizing antibodies can enhance infection of Fc receptor bearing cells and, potentially, exacerbate disease. The actual binding sites of human antibody on the DENV particle are not well defined. We characterized the specificity and neutralization potency of polyclonal serum antibodies and memory B-cell derived monoclonal antibodies (hMAbs) from 2 individuals exposed to primary DENV infections. Most DENV-specific hMAbs were serotype cross-reactive and weakly neutralizing. Moreover, many hMAbs bound to the viral pre-membrane protein and other sites on the virus that were not preserved when the viral envelope protein was produced as a soluble, recombinant antigen (rE protein). Nonetheless, by modifying the screening procedure to detect rare antibodies that bound to rE, we were able to isolate and map human antibodies that strongly neutralized the homologous serotype of DENV. Our MAbs results indicate that, in these two individuals exposed to primary DENV infections, a small fraction of the total antibody response was responsible for virus neutralization

In-Depth Analysis of the Antibody Response of Individuals Exposed to Primary Dengue Virus Infection

Humans who experience a primary dengue virus (DENV) infection develop antibodies that preferentially neutralize the homologous serotype responsible for infection. Affected individuals also generate cross-reactive antibodies against heterologous DENV serotypes, which are non-neutralizing. Dengue cross-reactive, non-neutralizing antibodies can enhance infection of Fc receptor bearing cells and, potentially, exacerbate disease. The actual binding sites of human antibody on the DENV particle are not well defined. We characterized the specificity and neutralization potency of polyclonal serum antibodies and memory B-cell derived monoclonal antibodies (hMAbs) from 2 individuals exposed to primary DENV infections. Most DENV-specific hMAbs were serotype cross-reactive and weakly neutralizing. Moreover, many hMAbs bound to the viral pre-membrane protein and other sites on the virus that were not preserved when the viral envelope protein was produced as a soluble, recombinant antigen (rE protein). Nonetheless, by modifying the screening procedure to detect rare antibodies that bound to rE, we were able to isolate and map human antibodies that strongly neutralized the homologous serotype of DENV. Our MAbs results indicate that, in these two individuals exposed to primary DENV infections, a small fraction of the total antibody response was responsible for virus neutralization

Investigations of the geochemistry of the rare earth elements in the exogenic cycle.

This study investigates the REE geochemistry of three common sediment types (hydrothermal, eolian, and benthic layers) in order to underst and their role in the exogenic cycle. The impact of seafloor hydrothermal activity upon the REE content of seawater was investigated by comparing REE/Fe ratios of hydrothermal sediments with end-member plume values. Hydrothermal sediments are 2-500 times greater than vent solutions, and increase with distance away from the ridge-axis. Hydrothermal activity results in a net depletion in REE's from seawater, primarily due to the large scavenging capacity of iron oxyhydroxides which precipitate from these solutions. The discrepancy between the predicted (positive) versus observed (negative) Eu anomaly of seawater was investigated by calculating REE scavenging indices for DSDP Site 598 hydrothermal sediments. Overall, the intensity of REE scavenging by hydrothermal precipitates is proportional to REE concentration in the fluid phase. Rapid removal of all REE's from hydrothermal vent solutions is predicted, and would be the greatest for Eu. This is supported by the Eu anomaly values of Site 598 sediments. The REE content of Lake Superior benthic layers are dominated by lithogenous sources, with minor contributions from the water column. The mechanism of REE removal from the water column may involve scavenging by Fe-rich phases. The nepheloid layer contains 24-57% more REE's on a per-unit Fe basis suggesting longer exposure to lake waters than fluff. Benthic particulate layers may play a major role in chemical transport processes. The eolian dust component of Pacific sediments is derived from two sources: the continental crust and oceanic crust, probably ash from circum-Pacific volcanism. The relative amount of the two end-members influences the median grain size. An eolian flux maximum exists between 35$\\sp\\circ$N and 42$\\sp\\circ$N in the northwest Pacific. This region also receives more eolian materials during glacial versus interglacial stages. A comparison of chemically treated versus untreated loess samples suggests that eolian dust is not a significant source of dissolved REE's to the oceans.Ph.D.GeochemistryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/162506/1/9013982.pd