Geochemical Tracers Research Articles

Groundwater and pore water inputs to the Bay of Bengal supported by geochemical tracers: Example from Tamil Nadu and Pondicherry, East Coast of India

Submarine groundwater discharge (SGD) and Saline water intrusion (SWI) are the two major processes that influence coastal aquifers resulting in severe water stress. It is essential to characterize groundwater dynamics and discriminate geochemical characterization to understand both approaches. The present study investigates the zones influenced by SGD and SWI along the coastal aquifers of Tamil Nadu and Pondicherry. Pore water (PW) and groundwater (GW) samples were collected during the monsoon season at low tide and analyzed for major ions adopting standard procedures. Hydrogeochemical characterization of water samples revealed by the piper, ionic ratio, ionic delta (Δmi), and seawater fraction (fSea) plots suggest that the PW samples, irrespective of location and GW samples in specific areas, were attributed to SWI, while the remaining samples suggested SGD. The average chloride-attributed SGD flux calculated for PW was 23.45 × 10−7 L cm−2 S−1 and for GW, 0.58 × 10−7 L cm−S−1. Higher fluxes observed in PW suggest seawater recirculation as the primary mechanism, and GW samples were found to be influenced by fresh, recirculated, and saline intrusions. Overall, the northern parts of the study region were influenced by freshwater discharge. However, the central and southern parts of the study regions were influenced by mixed RSGD and SWI water types. The present work suggests locations influenced by fresh, recirculated, and saline water zones that can benefit the stakeholders in planning strategies to identify proper aquifer recharge and suggest ideal pumping scenarios to sustain groundwater resources.

Cadmium isotope fractionation during sorption to soil minerals: Lab evidence and field implication

Stable isotope is a potent geochemical tracer unveiling the dynamic sources of cadmium (Cd) in the environment. However, the sorption process of aqueous Cd onto solid surfaces (e.g., soil) fractionates isotopic signatures, which makes it difficult to interpret its sources and migration processes. Understanding how Cd fractionates during sorption to soil minerals, therefore, provides necessary data to open the isotope fractionation black box of liquid-solid phase partition of Cd. In this study, we explored isotopic fractionation characteristics during Cd sorption to typical soil minerals. Distinct Cd isotope fractionation was observed during sorption, including goethite (∆114/110Cdsolid−solution=−0.51∼−0.47‰), montmorillonite (−0.34∼−0.32‰), quartz (−0.34∼−0.30‰), gibbsite (−0.29∼−0.25‰), and kaolinite (−0.09∼−0.07‰), where lighter isotopes tended to be preferentially sorbed to the solid phase in a reversible manner. We've also conducted a field survey in a historical flooding-affected region to explore Cd isotopic compositions of soil samples adjacent to a polluted creek. Distinct isotopic signatures for surficial soils and deep soils were observed, which was depicted by a binary mixing mode. Leaching of Cd from mine tailings to the creek, as well as its re-adsorption to soil during historical flooding events both led to preferential enrichment of light isotopes in the solid phase, which was consistent with findings from lab sorption experiments. Mineralogical analyses including EPMA, TOF-SIMS, Mössbauer spectra, XRD, and chemical extraction tests, were applied to unveil how Cd was bound to soil minerals at field. Possible linkage between lab and field data were discussed on the basis of these findings. Results from this study are encouraging for future application of Cd isotopes for source tracing.

Stable neodymium isotopic fractionation during chemical weathering

Stable Nd isotope ratio is a potentially useful tool to provide new constraints on the geological reservoir formation processes, complementing information from the radiogenic Nd isotope system. Here for the first time, we present the behavior of stable Nd isotopes during low-temperature weathering via a well-studied basaltic soil profile on Hainan Island, South China. The results showed that δ146/144Nd values spanned a range of approximately 0.21‰, from +0.058‰ in the lower profile to −0.152‰ in the upper soil profiles, while the τTh,Nd (%) values decreased from +387.7% to −68.2%, indicating that significant fractionation of stable Nd isotopes and migration of Nd elements occur during chemical weathering. Sequential extraction experiments suggest that the majority of Nd in this profile was hosted in the exchangeable and residual phases. The exchangeable phase was enriched with the heavy Nd isotope (146Nd) due to the adsorption of Nd onto gibbsite and the adsorption/precipitation of Fe-oxides from a heavier dissolved Nd pool in soils. The evidence for adsorption of Nd onto gibbsite is the positive correlation between the abundance of gibbsite and the proportion of Nd in the exchangeable phase, as well as the δ146/144Nd values. The evidence for the adsorption/precipitation of Nd on Fe-oxides comes from the positive correlations between Fe and Nd concentrations and δ146/144Nd values in the exchangeable fractions. The residual phases acquire depleted 146Nd signatures in the upper soil horizon, which could be caused by preferential desorption of heavy Nd isotopes from clay minerals or preferential incorporation of light Nd isotopes during kaolinite formation. These findings elucidate the mechanisms affecting stable Nd isotopic fractionation in low-temperature geochemistry and indicate that the stable Nd isotope ratio is a highly useful indicator for chemical weathering. This, combined with the radiogenic 143Nd/144Nd ratio, will be a powerful geochemical tracer for understanding global Nd cycles.

Submarine groundwater discharge and associated metal elements into an urbanized bay

In this study, geochemical tracers (radium isotopes) and heavy metals (Pb, Zn, Cd, Cr and As) were analyzed to derive the submarine groundwater discharge (SGD) and associated metal fluxes during four seasons in an urbanized bay (Daya Bay, China). Results showed that Pb and Zn were the main pollutants in bay water. SGD was found to exhibit an obvious seasonal trend (autumn > summer > spring > winter). Such seasonal patterns may be related to the hydraulic gradient between groundwater level and sea level, storm surges and tidal range. SGD was a dominant source of marine metal elements, contributing 19 %–51 % of the total inputs of metals into Daya Bay. The bay water was classified as slight pollution to heavy pollution, which could be linked to SGD-derived metal fluxes. This study provides a better understanding of the important role that SGD plays in metal budgets and ecological environments of coastal waters.

Geochemical tracing of synoptic scale modern dust transport over the Northeast Arabian Sea during the southwest monsoon

During the Southwest monsoon (SWM), aeolian dust is mainly supplied via wet deposition over the northeast Arabian Sea (NEAS). To understand their impact on the biogeochemistry of the Arabian Sea, it is important to identify their sources and characteristics. In this context, wet deposit particulate (WDP) samples were collected at a coastal station (Goa; 15.4° N, 73.8° E) in the NEAS during the SWM for three years. These samples were used to characterize and identify mineral dust sources using mineralogical, elemental, and isotopic (Sr and Nd) signatures. The WDP samples were classified as Beginning of Monsoon (BM, June samples), Mid Monsoon (MM, July–August samples) and End of Monsoon (EM, September samples). Clay mineralogical composition indicate high palygorskite content during BM, which subsequently found to decrease in MM, and almost negligible in EM. However, smectite is highest during MM, with moderate presence of palygorskite during this period. The considerable variation in the relative percentages of clay minerals suggests significant temporal variability in dust sources which is further corroborated by the radiogenic isotopic composition. A strong seasonality in the isotopic composition is observed with 87Sr/86Sr ratio being relatively less radiogenic during MM than the BM and highly radiogenic at the EM. Whereas ƐNd values show an opposite trend to 87Sr/86Sr ratios throughout the monsoon, with more radiogenic ƐNd in the MM, and less radiogenic at the EM. End member mixing plot indicate dominant contribution of dust from the Arabian Peninsula (ARB) and Northeast African (NEA) sources during BM and MM, while a shift towards the Thar desert and Southwest Asian (SWA) sources at the EM. Trace elements associated with different sources were quantified and suggest high Fe concentration is associated with NEA dust sources, despite ARB being major supplier of aeolian dust to the Arabian Sea.

Geochemical behavior of rare earth elements (REE) in urban reservoirs: the case of Funil Reservoir, Rio de Janeiro State, Brazil.

Rare earth elements (REE) have unique chemical properties, which allow their use as geochemical tracers. In this context, the present study aims to assess the role of Funil Reservoir on REE biogeochemical behavior. We collected water samples upstream of the reservoir (P-01) in the city of Queluz, inside the reservoir (P-02), and downstream of Funil Reservoir (P-03) in the city of Itatiaia, RJ. In the field, physicochemical parameters were measured using a probe (pH, temperature, electrical conductivity, and dissolved oxygen). In the laboratory, water samples were filtered (0.45µm) and properly packed until chemical analysis. Chlorophyll a concentrations were determined by a spectrophotometric method and suspended particulate matter (SPM) by a gravimetric method. Ionic concentrations were determined by ion chromatography technique and REE concentrations were determined by ICP-MS. Chlorophyll a concentrations were higher in Funil Reservoir. Ionic concentrations in Queluz (P-01) suggest anthropic contamination. The sum of REE in the dissolved fraction ranged from 2.12 to 12.22µg L-1. A positive anomaly of La in Queluz indicates anthropic contamination. The observed patterns indicate that Funil Reservoir acts as a biogeochemical barrier, modifying the fluvial transport of REE. Nonetheless, another factor that probably influences REE behavior is the algal bloom that occurs in reservoirs during the rainy season. The seasonal behavior of algae can influence REE biogeochemistry through the incorporation and release of trace metals.

The origin of platinum group minerals in oceanic crust

Abstract Highly siderophile elements (HSEs), including Re and Os, are used extensively as geochemical tracers and geochronometers to investigate the formation and evolution of Earth’s crust and mantle. Mantle rocks are commonly serpentinized, but the effect of serpentinization on the distribution of HSEs is controversial because HSEs are commonly hosted by rare, micrometer- to sub-micrometer-scale grains of platinum group minerals (PGMs) of ambiguous origin that are challenging to identify, characterize, and interpret. In this study, atom probe tomography (APT) is used to characterize two spatially close PGM grains hosted by a partially serpentinized harzburgite from Macquarie Island, Australia. The APT data reveal an extraordinary level of detail that provides insights into the origin of a complex Cu–Pt alloy grain (average composition ~Cu4Pt). The grain hosts Fe-, Ni-, and Pt-rich sub-grains associated with Rh, variably overlapping networks of Pd- and Cd-enrichment, and OH-rich volumes identified as fluid inclusions. Osmium and Ru are hosted by an idioblastic laurite (RuS2) grain. Compositional, textural, and phase-diagram constraints are consistent with a modified pre-serpentinization origin for the PGMs, and a comparison between observed and calculated grain distributions indicate that while Os isotope ratios were probably unaffected by serpentinization, whole-rock and grain-scale HSE and isotopic ratios may have been decoupled during serpentinization.

Tracking the Provenance of Aeolian Loess in Northeastern China by Uranium Isotopes

AbstractThe aeolian loess deposits in northeastern China have substantial potential for reconstructing the paleoclimate in the East Asian monsoon boundary zone. Identifying the source of the aeolian dust is crucial to interpret the paleo‐proxies recorded in the loess deposits in northeastern China; however, traditional geochemical tracers such as Nd and Sr isotopes cannot discriminate between the potential source areas, that is, the Otindag Sandy Land, Horqin Sandy Land, and Hulun Buir Sandy Land regions. In this study, the (234U/238U) activity ratio is used to constrain the provenance of the loess deposits in northeastern China. The (234U/238U) of the studied loess‐paleosol sequences (from 0.935 to 0.910) decreases with increasing depositional age (from 10 to ∼1,000 ka), which is consistent with predictions from uranium isotope comminution age model. A derived (234U/238U) of 0.935 ± 0.003 for the newly deposited loess (zero depositional age) is most similar to that of the Otindag Sandy Land positioned at a proximal upwind direction, suggesting that the Otindag Sandy Land is the most likely source of the aeolian dust that formed the loess deposits in northeastern China. A transportation time of 432 ± 65 ka was calculated for these deposits, indicating extensive mixing of the fine dust in the source regions, which could partially explain the relative homogeneity of loess deposits in northeastern China. The transportation time longer than several glacial‐interglacial cycles suggests that reconstructions of regional paleoclimate on orbital timescales should be viewed with caution because the potential influence of climatic changes could largely be buffered.

Pyrite as a Microtextural and Geochemical Tracer of Ore-Forming Processes, Central Zone Orogenic Gold Deposit, Gabgaba District, Sudan

Abstract Gold deposition in structurally controlled deposits is triggered by changes in the mineralizing fluid conditions. Recent research has demonstrated that in deposits with a well-established paragenesis, the processes that control the ore-forming fluid conditions, and thus the gold timing and deposition, can be inferred from the study of both textural and chemical characteristics of ore-bearing minerals such as sulfides, which are ubiquitous in almost every gold deposit type. In this contribution, we carried out a coupled investigation of (1) microscopic-scale expression of regional deformation, (2) textures of mineralized veins and pyrite generations, and (3) laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace element concentrations in pyrite from the Neoproterozoic Central Zone gold deposit, located in the poorly studied Gabgaba gold district, central Keraf suture, Sudanese Nubian shield. The Central Zone gold mineralization is associated with late-collisional Keraf strike-slip shearing. It is expressed by visible gold-bearing quartz-ankerite-(albite) conjugate veins hosted by metagranitoids surrounded by metasediments. Some structurally lattice-bound gold occurs in proximal As-Au-Ni–enriched pyrite associated with sericite-albite-ankerite alteration. Vein textures and proximal pyrite oscillatory zoning and geochemical signatures indicate that vein infilling occurred as a response to sudden pressure drops and boiling of the mineralizing fluid. We therefore interpret the Central Zone deposit as a typical orogenic gold deposit, with microtextural evidence and geochemical data supporting the existence of earthquake-induced fault-valve processes.

Monthly measurements of water dissolved inorganic radiocarbon in Lake Kawaguchi for three years indicating seasonal precipitation-groundwater variations

Understanding groundwater dynamics is important for projecting water resources of the Lake Kawaguchi, however, the difficulty of observation and the limited number of geochemical tracers are a problem. In this study, we investigated 14C concentration (Δ14C) of lake water for three years and employed a 14C box model to estimate the groundwater contribution. Seasonal variations of Δ14C were also observed in both 2019 and 2020, confirming that Δ14C in Lake Kawaguchi decreases from summer to fall and increases during winter. Heavy precipitation exceeding 300 mm in a few days because of tropical cyclon HAGIBIS (Typhoon#19) significantly increased Δ14C in the lake for one month and it could caused by temporal changes in the surface water pathway. The 14C box model demonstrated that 14C could semiquantitatively evaluate the groundwater flow in the lake. It is needed to add quantative evaluations inflow from rivers and other factors to understand of groundwater dynamics.

Using Deep Learning to Model the Groundwater Tracer Radon in Coastal Waters

AbstractSubmarine groundwater discharge (SGD) is an important driver of coastal biogeochemical budgets worldwide. Radon (222Rn) has been widely used as a natural geochemical tracer to quantify SGD, but field measurements are time consuming and costly. Here, we use deep learning to predict coastal seawater radon in SGD‐impacted regions. We hypothesize that deep learning could resolve radon trends and enable preliminary insights with limited field observations of groundwater tracers. Two deep learning models were trained on global coastal seawater radon observations (n = 39,238) with widely available inputs (e.g., salinity, temperature, water depth). The first model used a one‐dimensional convolutional neural network (1D‐CNN‐RNN) framework for site‐specific gap filling and producing short‐term future predictions. A second model applied a fully connected neural network (FCNN) framework to predict radon across geographically and hydrologically diverse settings. Both models can predict observed radon concentrations with r2 > 0.76. Specifically, the FCNN model offers a compelling development because synthetic radon tracer data sets can be obtained using only basic water quality and meteorological parameters. This opens opportunities to attain radon data from regions with large data gaps, such as the Global South and other remote locations, allowing for insights that can be used to predict SGD and plan field experiments. Overall, we demonstrate how field‐based measurements combined with big‐data approaches such as deep learning can be utilized to assess radon and potentially SGD beyond local scales.

Spatio-temporal suspended sediment fingerprinting under different land management practices

Understanding spatio-temporal suspended sediment dynamics is more important in large watersheds due to the decisive role of local source apportionment in sediment transport and yield. The Talar River with a large mountainous watershed in northern Iran, which plays a vital role in water supply for agriculture and drinking, recently has faced quality degradation. The current study explores the relative contribution of suspended sediment sources using geochemical tracers and fingerprinting techniques in high and low flow periods along this river. Soil samples were collected from four major land uses including rangeland, forest, rainfed agriculture, and irrigated agriculture, as well as riverbanks and riparian zones along the main river. Furthermore, suspended sediment was sampled at four sampling points along the main river in two seasons. Land use apportionment in suspended sediment yield was calculated using an unmixing model included in a newly developed package (FingerPro) in high flow and low flow, separately. The fingerprinting results showed a highly spatio-temporal dynamic for sediment source contribution along the main river in high and low flow periods. Natural land uses (forest and rangeland) in upstream reaches and agricultural land uses and riverbank sources in downstream reaches showed higher contributions to suspended sediment yield. The mean contribution of various land uses for both high and low flow periods indicated substantial contributions from forest (34%–41%) and riverbanks (31%–33%). The significant difference in sediment geochemical properties for the two flow seasons highlights the important role of the prevailing climatic-hydrologic condition on river sediment. Moreover, this issue indicates that sediment source contributions and transfer mechanisms are highly dynamic in Talar River watershed. The current study outcomes provide essential knowledge to create a robust strategy for mitigation of river sediment pollution.

Wildfire effects on the hydrogeochemistry of a river severely polluted by acid mine drainage

This study evaluates for the first time the impact of a large wildfire on the hydrogeochemistry of a deeply AMD-affected river at the beginning of the wet season. To accomplish this, a high-resolution water monitoring campaign was performed within the basin coinciding with the first rainfalls after summer. Unlike similar events recorded in AMD-affected areas, where dramatic increases in most dissolved element concentrations, and decreases in pH values are observed as a result of evaporitic salts flushing and the transport of sulfide oxidation products from mine sites, a slight increase in pH values (from 2.32 to 2.88) and decrease in element concentrations (e.g.; Fe: 443 to 205 mg/L; Al: 1805 to 1059 mg/L; sulfate: 22.8 to 13.3 g/L) was observed with the first rainfalls after the fire. The washout of wildfire-ash deposited in the riverbanks and the drainage area, constituted by alkaline mineral phases, seems to have counterbalanced the usual behavior and patterns of the river hydrogeochemistry during autumn. Geochemical results indicate that a preferential dissolution occurs during ash washout (K > Ca > Na), with a quick release of K followed by an intense dissolution of Ca and Na. On the other hand, in unburnt zones parameters and concentrations vary to a lesser extent than burnt areas, being the washout of evaporitic salts the dominant process. With subsequent rainfalls ash plays a minor role on the river hydrochemistry. Elemental ratios (Fe/SO4 and Ca/Mg) and geochemical tracers in both ash (K, Ca and Na) and AMD (S) were used to prove the importance of ash washout as the dominant geochemical process during the study period. Geochemical and mineralogical evidences point to intense schwertmannite precipitation as the main driver of reduction in metal pollution. The results of this study shed light on the response of AMD-polluted rivers to certain climate change effects, since climate models predict an increase in the number and intensity of wildfires and torrential rain events, especially in Mediterranean climates.

Determination of the origin of surface water in the Saijo Plain, Japan, using antimony as a geochemical tracer

Determination of the origin of surface water in the Saijo Plain, Japan, using antimony as a geochemical tracer

Tracing the dominant sources of sediment flowing towards Lake Victoria using geochemical tracers and a Bayesian mixing model

PurposeLake Victoria has been increasingly silting over the past decades, impacting water quality and loss of biodiversity. Sediment control strategies require information on the relative and absolute contributions of sediment from different sources. However, to date, there is no continuous monitoring of sediment flux or water quality in any of the tributaries, prohibiting an assessment of the scale of the problem. The aim of this study was to trace the dominant sources of riverine sediment using geochemical fingerprinting, thereby generating a knowledge base for improving land management and reducing sediment yields in Simiyu River catchment, one of the main contributing rivers to Lake Victoria.Materials and methodsGeochemical tracer concentrations were analyzed in transported sediment from the main river and two tributaries (riverbed sediments) and from soils in five dominant land use types (agricultural land, bush land, forest land, channel banks, and main river banks). Dominant sources to the Simiyu main river sediment were attributed using the Bayesian MixSIAR model.Results and discussionThe mixing model outputs showed that the Simiyu tributary was the dominant source of sediment to the Simiyu main river with 63.2%, while the Duma tributary accounted for 36.8%. Cultivated land was shown to be the main land use source of riverine sediment, accounting for 80.0% and 86.4% in Simiyu and Duma sub-tributaries, respectively, followed by channel banks with 9.0% in both sub-tributaries. Direct unmixing of the Simiyu main river sediment to the land use sources yielded 64.7% contribution of cultivated land and 26.5% of channel banks.ConclusionThe demonstrated application of sediment source tracing provides an important pathway for quantifying the dominant sources of sediment in the rivers flowing towards Lake Victoria. Eroded soil from agricultural areas is the biggest contributor to transported sediment in the Simiyu River. This information is vital for the design of catchment wide management plans that should focus on reducing soil erosion and sediment delivery from farming areas to the river networks, ultimately supporting both food security and water quality in the Lake Victoria Basin.

Geochemistry and rare-metal potential of coals of the Sakhalin coal basin, Sakhalin island, Russia

The study presents new data on the geochemistry coal deposits of the Cretaceous, Paleogene, and Neogene age in the Sakhalin Basin. A wide range of trace elements were studied in 240 coal samples and 138 coal-bearing rock samples from the main fields of the Basin that are under development and available for study. This study demonstrated that the coals in the Sakhalin Basin are generally characterized by concentrations of most trace elements close to the average estimates for the world coals along with, in addition, a mixed chalcophile-siderophile and lithophile geochemical assemblage typical for the transition areas of the continent-ocean zone. On average for the Basin, the coals are enriched in Sc, V, Co, Br, Sr, and Ba compared to the world average. Ash of coals from the Sakhalin Basin is characterized by the above-Clarke content of rare alkali metals (Li, Rb, Cs), Cr, Ni, Cu, Y, and Zr, in addition to the above elements. HREE, Br, Cu, Ag, Hg, Nb, Ge, Mo, W, As, Ni, and Pb specialization was identified for some coalfields. The levels of accumulation of Sc, Y, Sr and heavy lanthanides in coal ash in some coalfields exceed the minimum possible commercial concentrations.The study demonstrated that the geochemical trace element characteristics of coal-bearing sediments in the Sakhalin Basin reflects the peculiarities of the geological evolution of this crustal block. Despite the high tectonic activity and volcanism in the Cenozoic, the specific composition of the rocks in the flanks and the basement of the coal-bearing depressions defined the low rare-metal potential of the basin. Scandium, V, Co, Ni, Ba, and Sr anomalies are associated with the predominantly basic composition of the flanks of the depressions, while local Hg, Sb, W, Cu, and Ge anomalies are connected to the hydrothermal activity.

Fast Spin‐Up of Geochemical Tracers in Ocean Circulation and Climate Models

AbstractOcean geochemical tracers such as radiocarbon, protactinium and thorium isotopes, and noble gases are widely used to constrain a range of physical and biogeochemical processes in the ocean. However, their routine simulation in global ocean circulation and climate models is hindered by the computational expense of integrating them to a steady state. Here, a new approach to this long‐standing “spin‐up” problem is introduced to efficiently compute equilibrium distributions of such tracers in seasonally‐forced models. Based on “Anderson Acceleration,” a sequence acceleration technique developed in the 1960s to solve nonlinear integral equations, the new method is entirely “black box” and offers significant speed‐up over conventional direct time integration. Moreover, it requires no preconditioning, ensures tracer conservation and is fully consistent with the numerical time‐stepping scheme of the underlying model. It thus circumvents some of the drawbacks of other schemes such as matrix‐free Newton Krylov that have been proposed to address this problem. An implementation specifically tailored for the batch HPC systems on which ocean and climate models are typically run is described, and the method illustrated by applying it to a variety of geochemical tracer problems. The new method, which provides speed‐ups by over an order of magnitude, should make simulations of such tracers more feasible and enable their inclusion in climate change assessments such as IPCC.

Formation and pathways of dense water in the Nordic Seas based on a regional inversion

Dense waters formed in the Nordic Seas spill across gaps in the Greenland-Scotland Ridge into the abyss of the North Atlantic to feed the lower limb of the Atlantic Meridional Overturning Circulation. The overflow water transport is well known, but open questions remain regarding where and how the dense overflow waters are formed and transported to the ridge. Here we develop a regional high-resolution version of an inverse method called Total Matrix Intercomparison, which combines hydrographic and geochemical tracer observations between 2000 and 2019 to resolve the pathways that connect the overflows to their origins. Consistent with previous studies we find two main pathways feeding the Denmark Strait Overflow Water (DSOW): the East Greenland Current and the North Icelandic Jet. Most of the water supplied by the North Icelandic Jet originates in the Greenland Sea (82 ± 2%) and flows southward along an outer core of the East Greenland Current, as well as along a previously unknown pathway crossing the Jan Mayen Ridge into the Iceland Sea. In total, 39 ± 2% of the DSOW originates in the Greenland Sea, while the Iceland Sea and the Atlantic Domain of the Nordic Seas account for 20 ± 3% and 19 ± 2%, respectively. The majority of the Faroe Bank Channel Overflow Water originates in the Greenland Sea (46 ± 8%) and the Arctic Ocean (25 ± 9%). These dense waters approach the sill in the Iceland-Faroe Slope Jet and along the eastern side of the Jan Mayen Ridge. The inversion reveals unprecedented details on the upstream sources and pathways of the overflows, which have not previously been obtained using observations.

Multi-Isotope Geochemical Baseline Study of the Carbon Management Canada Research Institutes CCS Field Research Station (Alberta, Canada), Prior to CO2 Injection

Carbon capture and storage (CCS) is an industrial scale mitigation strategy for reducing anthropogenic CO2 from entering the atmosphere. However, for CCS to be routinely deployed, it is critical that the security of the stored CO2 can be verified and that unplanned migration from a storage site can be identified. A number of geochemical monitoring tools have been developed for this purpose, however, their effectiveness critically depends on robust geochemical baselines being established prior to CO2 injection. Here we present the first multi-well gas and groundwater characterisation of the geochemical baseline at the Carbon Management Canada Research Institutes Field Research Station. We find that all gases exhibit CO2 concentrations that are below 1%, implying that bulk gas monitoring may be an effective first step to identify CO2 migration. However, we also find that predominantly biogenic CH4 (∼90%–99%) is pervasive in both groundwater and gases within the shallow succession, which contain numerous coal seams. Hence, it is probable that any upwardly migrating CO2 could be absorbed onto the coal seams, displacing CH4. Importantly, 4He concentrations in all gas samples lie on a mixing line between the atmosphere and the elevated 4He concentration present in a hydrocarbon well sampled from a reservoir located below the Field Research Station (FRS) implying a diffusive or advective crustal flux of 4He at the site. In contrast, the measured 4He concentrations in shallow groundwaters at the site are much lower and may be explained by gas loss from the system or in situ production generated by radioactive decay of U and Th within the host rocks. Additionally, the injected CO2 is low in He, Ne and Ar concentrations, yet enriched in 84Kr and 132Xe relative to 36Ar, highlighting that inherent noble gas isotopic fingerprints could be effective as a distinct geochemical tracer of injected CO2 at the FRS.

Study of Ra desorption processes in an estuary system with high-turbidity at the Southeast China

Radium (Ra) isotopes are extensively used as geochemical tracers for studying water mass mixing and submarine groundwater discharge in marginal and coastal seas. However, river-borne particles and seafloor sediments are an important source of Ra in marine systems due to Ra desorption. Therefore, it is necessary to study the desorption behaviors of Ra isotopes in river sediment or suspended particles. Here, the desorption behaviors of four Ra isotopes (223Ra, 224Ra, 226Ra, and 228Ra) in the Zhangjiang River sediments were investigated by a series of designed variable-controlling experiments in the laboratory. Within the designed salinity range, desorption amounts of Ra isotopes increased with increasing salinity, and when the salinity was greater than 15 ppt, Ra desorption reached an equilibrium state. Overall, desorption of Ra isotopes increased with the decrease of particle grain size, however, the desorption fractions of 224Ra and 228Ra decreased with decreasing particle size due to the increase of original Ra activities in smaller sediment particles. In the experiments, we found that two sediment samples with similar mean grain size (3.8 μm and 3.3 μm) and similar grain size distributions had significantly different Ra desorption under the same conditions. The results of mineral composition analysis based on X-ray diffraction showed that these two samples had different percentages of kaolinite, quartz, and plagioclase, which indicated that the mineral composition of particles had an important effect on Ra isotope desorption. In conclusion, salinity, particle grain size, and mineral composition all had significant effects on Ra desorption behaviors of sediment particles. Based on the above desorption experiments, the desorbed fluxes of four Ra isotopes from river-borne sediments to the Dongshan Bay were estimated to be (5.95 ± 1.47) × 107 Bq yr−1 for 223Ra, (1.95 ± 0.27) × 109 Bq yr−1 for 224Ra, (2.73 ± 0.47) × 108 Bq yr−1 for 226Ra, and (1.26 ± 0.20) × 109 Bq yr−1 for 228Ra, respectively.