The marine geochemistry of the rare earth elements

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 September 1983Novel methods were developed for the determination of 12 of the 14 Rare Earth Elements (REE) in seawater. Initial extractions of the REE by chelating ion exchange chromatography is followed by cation exchange for removal of co-extracted U and remaining traces of major ions. Finally traces of U are removed by anion exchange before irradiation for 8 hours at a flux of 5 x 1013 neutrons.cm-2.sec-l. After post-irradiation separation of 24 Na, the gamma spectra are recorded over four different time intervals with a Ge(Li) detector. An internal standard (144Ce) is carried all along the procedure for improved precision by avoidance of counting geometry errors. Vertical profiles are reported for three stations in respectively the Northwest Atlantic Ocean, the Eastern Equatorial Pacific Ocean and the Cariaco Trench, an anoxic basin. This data set represents the first detailed profiles of Pr, Tb, Ho, Tm and Lu in seawater, together with profiles of La, Ce, Nd, Sm, Eu, Gd and Yb. The first observations of positive Ce anomalies in seawater are ascribed to regeneration of Ce under reducing conditions. The first reported positive Gd anomalies are ascribed to the unique chemical properties of the Gd(III)-cation, which has an exactly half-filled 4f electron shell. Concentrations of the REE range from 0.3 pmol.kg-l (Lu) to 86 pmol.kg-l (Ce) and are among the lowest reported so far for trace elements in seawater. The REE as a group typically exhibit a quasi-linear increase with depth. In the deep water there appears to be some degree of correlation with silicate. Concentration levels in the deep Pacific Ocean are 2-4 times those in deep Atlantic waters. Ce has an opposite behaviour, with very strong depletions in deep Pacific waters. In the Cariaco Trench all REE, but especially Ce, are strongly affected by the chemical changes across the oxic/anoxic interface. The REE distributions normalized versus shales (crustal abundance) exhibit four major features: i) a gradual enrichment of the heavy REE, most strongly developed in the deep Pacific Ocean. This is compatible with the stabilization of heavy REE by stronger inorganic complexation in seawater as predicted by the TURNER- WHITFIELD-DICKSON speciation model. ii) the first description of positive Gd anomalies, in agreement with the anomalously strong complexation of the Gd(III)-cation predicted by the same speciation model. iii) most commonly negative, but sometimes positive, Ce anomalies. iv) a linear Eu/Sm relation for all samples. Distributions of the dissolved REE in ocean waters seem to be dominated by their internal cycling within the ocean basins. With a few notable exceptions, the ultimate external sources (riverine, aeolian, hydrothermal) and sinks (authigenic minerals) appear to have little impact on the spatial distribution of the REE in oceanic water masses. Analogies with distributions of other properties within the oceans suggest that the REE as a group are controlled by two simultaneous processes: A) cycling like or identical to opal and calcium-carbonate, with circumstantial evidence in support of the latter as a possible carrier. B) adsorptive scavenging, possibly by manganese-oxide phases on settling particles. The latter mechanism is strongly supported by the parallels between REE(III) speciation in seawater and the 'typical 1 seawater REE pattern. This general correspondence is highlighted by the very distinct excursions of Gd in both Gd(III) speciation and the observed seawater REE patterns. Combination of both apparent mechanisms, for instance scavenging of REE by adsorptive coatings (Mn oxides) on settling skeletal material, is very well conceivable. Upon dissolution of the shells at or near the seafloor the adsorbed REE fraction would be released into the bottom waters. The observations of positive Ce anomalies in Northwest Atlantic surface waters, enhanced Ce anomalies and Mn levels in the OZ-minimum zone of the Eastern Equatorial Pacific Ocean, and enhanced Ce concentrations in anoxic waters all support the contention that a vigorous cycling driven by oxidation and reduction reactions dominates both Ce and Mn in the ocean basins. Under conditions of thermodynamic equilibrium, Ce tends to become depleted in well-oxygenated open ocean waters, and normal or enriched in waters below a pOZ threshold of about 0.001-0.010 atm partial pressure. The latter threshold level generally lies below the sediment/water interface. However, the kinetics of oxidation (and reduction) of Ce appears to be slow relative to various transport processes. This leads to disequilibria, i.e. a major uncoupling of the pOZ threshold level and the Ce anomaly distribution. The REE are definitely non-conservative in seawater and in general the REE pattern or 143Nd/144Nd isotopic ratio cannot be treated as ideal water mass tracers. The continuous redistribution of Ce within the modern ocean, combined with the likelihood of active diagenesis, precludes the use of Ce anomalies as indicators of oxic versus anoxic conditions in ancient oceans. On the other hand, the Eu/Sm ratio, possibly combined with 143Nd/144Nd , would have potential as a tracer for understanding modern and ancient processes of hydrothermal circulation.This research was supported by Department of Energy contract DE-AS02-76EV03566 and Office of Naval Research Contract NOOOl 4-82-C-00l 9 NR 083-004

MEMS based hair flow-sensors as model systems for acoustic perception studies

Arrays of MEMS fabricated flow sensors inspired by the acoustic flow-sensitive hairs found on the cerci of crickets, have been designed, fabricated and characterized. The hairs consist of up to 1 mm long SU-8 structures mounted on suspended membranes with normal translational and rotational degrees of freedom. Electrodes on the membrane and on the substrate form variable capacitors allowing for capacitive read-out. Capacitance versus voltage, frequency dependency and directional sensitivity measurements have been successfully carried out on fabricated sensor arrays, showing the viability of the concept. The sensors form a model-system allowing for investigations on sensory acoustics by their arrayed nature, their adaptivity via electrostatic interaction (frequency tuning and parametric amplifica- tion) and their susceptibility to noise (stochastic resonance

Klimaat onderzoek bij het Nederlands Instituut voor Onderzoek der Zee

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Bank pull or bar push: what drives scroll-bar formation in meandering river?

One of the most striking features of meandering rivers are quasi-regular ridges of the point bar, evidence of a pulsed lateral migration of meander bends. Scroll bars formed on the inner bend are preserved on the point-bar surface as a series of ridges as meanders migrate, and in the subsurface of the point bar as inclined heterolithic stratification with lateral accretion surfaces. It is necessary to understand the formation and sedimentary architecture of these point bars, which are fundamental geomorphic building blocks of meandering rivers and potential reservoirs for water, oil, and gas. However, it remains unresolved whether the scroll-bar pattern forms in response to outer bend bank erosion during floods (i.e., bank pull), or is forced by bank progradation (i.e., bar push). Here we use experimentally formed meandering rivers with a set of static and migrating bends to isolate the effects of sediment supply to the point bar, bank protection, and forced bank retreat. We find that channel widening caused by bank retreat near the bend apex causes deposition of new scroll ridges along the inner bend point bar, whereas scroll bars cannot be forced by sediment pulses. Thus channel width variations along meander bends cause bank pull, which is necessary for scroll-bar formation. Furthermore, we find that each newly attached scroll bar overlies a nonpermeable layer of finer-grained sediment caused by the temporary flow expansion, which explains the fining-upward tendency of point bars

Distribution and redox speciation of dissolved iron on the European continental margin

To investigate the biogeochemistry of iron in the waters of the European continental margin, we determined the dissolved iron distribution and redox speciation in filtered (<0.2 μm) open-ocean and shelf waters. Depth profiles were sampled over the shelf slope southeast of the Chapelle Bank area (47.61°N, 4.24°W to 46.00°N, 8.01°W) and a horizontal surface-water transect over the shelf and through the English Channel (la Manche) and the southern North Sea (46°N, 8°W to 52°N, 4°E). An abrupt trace-metal front was found near the shelf slope, indicated by a horizontal gradient of dissolved iron (DFe) and aluminium (DAl), which correlated with changing salinities (r2 = 0.572 and 0.528, respectively, n = 92). Labile Fe(II) concentrations varied from <12 pmol L-1 in North Atlantic surface waters to >200 pmol L-1 in the near bottom waters of the shelf break. Labile Fe(II) accounted for ∼5 of the dissolved iron species in surface shelf waters (mean 5.0 ± 2.7), whereas higher Fe(II) fractions (i.e., >8) were observed near the sea bottom on the shelf break and during a midday solar maximum in surface waters in the vicinity of the Scheldt river plume. Benthic processes (resuspension and diagenesis) constituted important sources of Fe(II) and DFe in this region, and photoreduction of Fe(III) species in shelf waters caused enhanced labile Fe(II) concentrations. These processes increased the lability of iron and its potential availability to marine organisms in the shelf ecosystem. © 2007, by the American Society of Limnology and Oceanography, Inc

The Rotterdam Elderly Pain Observation Scale (REPOS):A new behavioral pain scale for non-communicative adults and cognitively impaired elderly persons

Several observation scales have been developed to measure pain in elderly persons with cognitive impairments. Most scales, however, do not provide cut-off scores for pain, and previous studies do not include data on non-verbal patients with diagnoses other than dementia. Objective: The development of an easy-to-use, reliable and valid pain observation scale, the Rotterdam Elderly Pain Observation Scale (REPOS), for use in nursing home residents incapable of reporting pain themselves. Methods: In this multicenter case-control study 174 residents of various cognitive levels were videotaped at rest and during a potentially painful activity. Prevalences and co- occurrences of behaviors were examined, and interrelationships were identified. To reduce number of items, multiple linear regression analysis was used. Interrater-, and intrarater agreements and internal consistency were investigated. To estimate validity, REPOS was related to Numeric Rating Scale (NRS) and Pain Assessment in Advanced Dementia-Scale (PAINAD), and activity and rest situations were compared. Results: A one-dimensional model with a good fit was found. After redundancy analysis, ten items remained. Interrater- and intrarater agreements of two observers were good. Internal consistency was moderate. Correlations between REPOS and NRS were small to medium, and between REPOS and PAINAD large. REPOS-scores for the two situations differed significantly. A total score of 3 and higher indicates pain. Conclusions: REPOS appears to be promising for identifying pain in residents of various cognitive levels. To improve pain management, a cut-off score for pain was determined, together with a treatment protocol. Its conciseness suggests good usefulness in daily practice.</p