1,721,721 research outputs found
Rare earth element distribution in the Atlantic sector of the Southern Ocean: The balance between particle scavenging and vertical supply
Full text linkThe concentrations of rare earth elements (REEs) in seawater display systematic variations related to weathering inputs, particle scavenging and water mass histories. Here we investigate the REE concentrations of water column profiles in the Atlantic sector of the Southern Ocean, a key region of the global circulation and primary production. The data reveal a pronounced contrast between the vertical profiles in the Antarctic Circumpolar Current (ACC) and those south of the ACC in the Weddell Gyre (WG). The ACC profiles exhibit the typical increase of REE concentrations with water depth and a change in the shape of the profiles from near linear for the light REEs to more convex for the heavy REEs. In contrast, the WG profiles exhibit high REE concentrations throughout the water column with only the near surface samples showing slightly reduced concentrations indicative of particle scavenging. Seawater normalised REE patterns reveal the strong remineralisation signal in the ACC with the light REEs preferentially removed in surface waters and the mirror image pattern of their preferential release in deep waters. In the WG the patterns are relatively homogenous reflecting the prevalence of well-mixed Lower Circumpolar Deep Water (LCDW) that follows shoaling isopycnals in the region. In the WG particle scavenging of REEs is comparatively small and limited to the summer months by light limitation and winter sea ice cover. Considering the surface water depletion compared to LCDW and that the surface waters of the WG are replaced every few years, the removal rate is estimated to be on the order of 1 nmol m? 3 yr? 1 for La and Nd. The negative cerium anomalies observed in deep waters are some of the strongest found globally with only the deepest waters in parts of the Pacific having stronger anomalies. These deep waters have been isolated from fresh continental REE inputs during their long journey through the abyssal Indo-Pacific Ocean, which suggests that the high REE concentrations found in the ACC and WG reflect contributions from old deep waters.<br/
Online preconcentration ICP-MS analysis of rare earth elements in seawater
No full textThe rare earth elements (REEs) with their systematically varying properties are powerful tracers of continental inputs, particle scavenging intensity and the oxidation state of seawater. However, their generally low (∼pmol/kg) concentrations in seawater and fractionation potential during chemical treatment makes them difficult to measure. Here we report a technique using an automated preconcentration system, which efficiently separates seawater matrix elements and elutes the preconcentrated sample directly into the spray chamber of an ICP-MS instrument. The commercially available “seaFAST” system (Elemental Scientific Inc.) makes use of a resin with ethylenediaminetriacetic acid and iminodiacetic acid functional groups to preconcentrate REEs and other metals while anions and alkali and alkaline earth cations are washed out. Repeated measurements of seawater from 2000 m water depth in the Southern Ocean allows the external precision (2σ) of the technique to be estimated at <23% for all REEs and <15% for most. Comparison of Nd concentrations with isotope dilution measurements for 69 samples demonstrates that the two techniques generally agree within 15%. Accuracy was found to be good for all REEs by using a five point standard addition analysis of one sample and comparing measurements of mine water reference materials diluted with a NaCl matrix with recommended values in the literature. This makes the online preconcentration ICP-MS technique advantageous for the minimal sample preparation required and the relatively small sample volume consumed (7 mL) thus enabling large data sets for the REEs in seawater to be rapidly acquired
Rare earth elements as indicators of hydrothermal processes within the East Scotia subduction zone system
Full text linkThe East Scotia subduction zone, located in the Atlantic sector of the Southern Ocean, hosts a number of hydrothermal sites in both back-arc and island-arc settings. High temperature (> 348 °C) ‘black smoker’ vents have been sampled at three locations along segments E2 and E9 of the East Scotia back-arc spreading ridge, as well as ‘white smoker’ (< 212 °C) and diffuse (< 28 °C) hydrothermal fluids from within the caldera of the Kemp submarine volcano. The composition of the endmember fluids (Mg = 0 mmol/kg) is markedly different, with pH ranging from <1 to 3.4, [Cl-] from ∼90 to 536 mM, [H2S] from 6.7 to ∼200 mM and [F-] from 35 to ∼1000 μM. All of the vent sites are basalt- to basaltic andesite-hosted, providing an ideal opportunity for investigating the geochemical controls on rare earth element (REE) behaviour. Endmember hydrothermal fluids from E2 and E9 have total REE concentrations ranging from 7.3 – 123 nmol/kg, and chondrite-normalised distribution patterns are either light REE-enriched (LaCN/YbCN = 12.8 – 30.0) with a positive europium anomaly (EuCN/Eu∗CN = 3.45 – 59.5), or mid REE-enriched (LaCN/NdCN = 0.61) with a negative Eu anomaly (EuCN/Eu∗CN = 0.59). By contrast, fluids from the Kemp Caldera have almost flat REE patterns (LaCN/YbCN = 2.1 – 2.2; EuCN/Eu∗CN = 1.2 – 2.2).
We demonstrate that the REE geochemistry of fluids from the East Scotia back-arc spreading ridge is variably influenced by ion exchange with host minerals, phase separation, competitive complexation with ligands, and anhydrite deposition, whereas fluids from the Kemp submarine volcano are also affected by the injection of magmatic volatiles which enhances the solubility of all the REEs. We also show that the REE patterns of anhydrite deposits from Kemp differ from those of the present-day fluids, potentially providing critical information about the nature of hydrothermal activity in the past, where access to hydrothermal fluids is precluded
Environmental versus biomineralization controls on the intratest variation in the trace element composition of the planktonic foraminifera G. inflata and G. scitula
No full textThe intratest variation in the chemical composition of Globorotalia scitula and G. inflata recovered from a sediment trap sample collected at 3000 m in the North Atlantic in early spring has been investigated using laser ablation inductively coupled plasma–mass spectrometry and electron microprobe. Mg/Ca, Li/Ca, B/Ca, Mn/Ca, and Ba/Ca vary by up to a factor of 10 through the test walls. Water column properties, including temperature and salinity, are well documented at the trap site, and the observed variations are too large to be explained by vertical migration of the foraminifera. However, changes in calcite precipitation rate, crystal structure, or the chemical composition of the internal calcification reservoir also cannot, by themselves, fully account for the pattern of intratest variability. Nevertheless, the average Mg/Ca for each chamber generally produces a Mg/Ca temperature that matches that measured in the water column. The exception is small, morphologically distinct G. inflata tests that have anomalously high Mg/Ca. <br/
Radiogenic Sr, Nd and Pb isotope data and clay mineral abundances of the < 2 µm size fraction of ODP Hole 121-758A
No full textThe clay size fraction of the sediments from ODP Site 758 located in the southern Bay of Bengal on top of the Ninetyeast Ridge were studied to better understand South Asian Monsoon induced silicate weathering over the last 27 million years. The radiogenic Sr, Nd and Pb isotope data were measured by multi-collector ICP-MS and the the clay mineral abundances were calculated from X-Ray diffraction measurements. The age model used here incorporates age constraints from both ODP Site 758 and new data from a new multiple hole drill site nearby (International Ocean Discovery Program Site U1443)
Laser ablation ICP-MS screening of corals for diagenetically affected areas applied to Tahiti corals from the last deglaciation
No full textFossil corals are unique archives of past seasonal climate variability, providing vital information about seasonal climate phenomena such as ENSO and monsoons. However, submarine diagenetic processes can potentially obscure the original climate signals and lead to false interpretations. Here we demonstrate the potential of laser ablation ICP-MS to rapidly detect secondary aragonite precipitates in fossil Porites colonies recovered by Integrated Ocean Drilling Program (IODP) Expedition 310 from submerged deglacial reefs off Tahiti. High resolution (100 ?m) measurements of coralline B/Ca, Mg/Ca, S/Ca, and U/Ca ratios are used to distinguish areas of pristine skeleton from those afflicted with secondary aragonite. Measurements of coralline Sr/Ca, U/Ca and oxygen isotope ratios, from areas identified as pristine, reveal that the seasonal range of sea surface temperature in the tropical south Pacific during the last deglaciation (14.7 and 11 ka) was similar to that of today
Dissolved neodymium and hafnium isotope data of surface water samples during RV METEOR cruise M147
No full textThe dataset contains the isotope compositions of dissolved Nd and Hf together with those of particulate Nd, and the concentrations of rare earth elements and yttrium (REY) and Hf ([Hf]) in surface waters along the entire salinity gradient of the Amazon estuary, including the Pará River. Samples were obtained in April–May 2018 during RV Meteor cruise M147, which was official process study Gapr11 of the international GEOTRACES program
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dissolved neodymium and hafnium isotopes and rare earth element data of near-bottom water samples from RV Meteor cruise M147
No full textThe dataset comprises isotope compositions of dissolved neodymium (Nd) and hafnium (Hf), together with particulate Nd and Hf isotope data from surface estuarine sediments. It further includes concentrations of rare earth elements and yttrium (REY) as well as dissolved hafnium ([Hf]) in near-bottom waters and surface sediments collected across the Amazon shelf and slope. All samples were obtained during RV Meteor cruise M147 (April–May 2018), conducted as the official process study GAPR11 within the framework of the international GEOTRACES program
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