9Be Concentrations Research Articles

Simultaneous preconcentration of 9Be and cosmogenic 10Be for determination of the 10Be/9Be ratio in (coastal) seawater

AbstractBeryllium isotopes have emerged as a quantitative tracer of continental weathering, but accurate and precise determination of the cosmogenic 10Be and stable 9Be in seawater is challenging, because seawater contains high concentrations of matrix elements but extremely low concentrations of 9Be and 10Be. In this study, we develop a new, time‐efficient procedure for the simultaneous preconcentration of 9Be and 10Be from (coastal) seawater based on the iron co‐precipitation method. The concentrations of 9Be, 10Be, and the resulting 10Be/9Be ratio for Changjiang Estuary water derived from the new procedure agree well with those obtained from the conventional procedure requiring separate preconcentration for 9Be and 10Be determinations. By avoiding the separate preconcentration, our newly developed procedure contributes toward more time‐efficient handling of samples, less sample cross‐contamination, and a more reliable 10Be/9Be ratio. Prior to this, we validated the iron co‐precipitation method using artificial seawater and natural water samples from the Amazon Estuary regarding: (1) the “matrix effect” for Be analysis, (2) its extraction efficiency for pg g−1 levels Be in the presence and absence of organic matter, and (3) the data comparability with another preconcentration method. We calculated that for the determination of 9Be and 10Be in most open ocean seawater with typical 10Be concentrations of > 500 atoms g−1, good precisions (< 5%) can be achieved using less than 3 liters of seawater compared to more than 20 liters routinely used previously. Even for coastal seawater with extremely low 10Be concentration (e.g., 100 atoms g−1), we estimate a maximum amount of 10 liters to be adequate.

Spatial heterogeneity in beryllium isotopic distribution in the Indian Ocean

Beryllium-10 (10Be) has proven to be an essential tool for building chronology and understanding millennial-scale surface processes. Measurements in both the water column and authigenic fractions from various archives (such as surface sediments and Fe-Mn crusts) have provided valuable information on processes regulating Be isotopic distribution in the global oceans. Unlike the Pacific and the Atlantic Oceans, Be isotopic measurements in the Indian Ocean are sparse. Here, based on Be isotopic measurements on surface sediments from the central and northern Indian Ocean, an attempt is made to understand the processes controlling spatial Be isotopic distribution. Our data from the northern Indian Ocean suggests that terrestrial input is one of the primary contributors of 9Be. Owing to higher terrestrial flux, the sediment samples from the Bay of Bengal show higher 9Be concentrations and lower 10Be/9Be ratios. Our study suggests that scavenging by sediment particles plays a vital role in the distribution of Be isotopes in well-mixed open ocean water. Between carbonates and clay particles, carbonates are less efficient in scavenging Be from the water column.

Tracing Water Masses and Assessing Boundary Scavenging Intensity With Beryllium Isotopes in the Northern South China Sea

AbstractThe cosmogenic radionuclide 10Be and its stable isotope 9Be can be used as a tracer for water mass mixing, but such applications are rare in both open oceans and marginal seas. Here we report distributions of dissolved 9Be and 10Be concentrations of the seawater in the surface and water columns along a section from shelf to deep basin in the northern South China Sea (SCS). The concentrations of 9Be and 10Be in surface waters range between 8.8–43.6 pmol/kg and 118–576 atoms/g, respectively. The 9Be in the northern SCS is dominantly sourced from river waters, while 10Be has a prominent input from the western Pacific, resulting in the highest 10Be/9Be ratio of 10.9 × 10−8 closest to the Luzon Strait. Along the depth section, the 9Be concentrations decrease southward while 10Be concentrations increase with the maximum value of 1,237 atoms/g occurring at 2,843 m depth of Station A10. The 10Be/9Be ratios are interpreted with consideration of water mixing and boundary scavenging, which reveal evidence of a branch of the intruding Kuroshio Current (>7.7 × 10−8) in subsurface water and a deep cyclonic current (>8.9 × 10−8). A box model yields a sedimentation flux of 10Be around 1,167 atoms/m2/s, that is, 4.6 times of the atmospheric deposition flux, pointing to active boundary scavenging of 10Be. The residence time of 10Be in the deep water is estimated to be longer than 79 years in the northern SCS. The beryllium isotopes as a water mass tracer will find wide applications in basins where the endmembers are sufficiently differentiated.

Deposition and retention of meteoric 10Be in Holocene Taiwan river terraces

The cosmogenic meteoric 10Be that is produced in the atmosphere and mainly scavenged by rainfall is a valuable tool for determining dates and rates of Earth surface processes. A key prerequisite for its applications is the knowledge of the long-term 10Be depositional flux to Earth's surface. Previous efforts on obtaining 10Be depositional fluxes include general atmospheric circulation modelling (GCM), empirical fitting of rainfall 10Be records, and determining the inventory of soil profiles of known age. Here, we derive 10Be depositional fluxes from Holocene river terrace 10Be inventories across the Taiwan mountain belt. We measured 10Be and 9Be concentrations from three terrace profiles, with 14C ages ranging between 3.83 and 9.05 cal. kyr BP and sampling depths of up to 6.2 m.Based on 10Be inventories of our river terraces, the calculated long-term 10Be depositional fluxes vary from 0.32 to 0.49 × 106 at/cm2/yr in the Taiwan orogen. We identify partial Be retention, surface erosion, multi-phase sediment deposition, and incomplete sampling depth in these terraces as potential causes of flux underestimation. When accounting for each of these factors and their uncertainties, the resulting flux estimates of each terrace show an overlapping range of 0.66–0.88 × 106 at/cm2/yr. This newly constrained flux range representative over millennial timescales is thus recommended for Earth surface applications in the fast-eroding Taiwan orogen, especially in regions with similar climatic conditions as the studied terraces. When comparing to flux estimates from other approaches, the flux from the rainfall-based fitting equation exceeds our new terrace-derived flux by more than a factor of two. We consider such high flux to be unlikely for the Taiwan orogen, and suggest that the control of precipitation on the 10Be flux here may be overestimated in rainfall data fitting. The GCM-derived flux overestimates the 10Be depositional flux in this setting to a smaller degree (at least 23%), which is in accordance with findings from previous global data compilation of 10Be fluxes.

Dissolved and Particulate Beryllium Isotopes in the Pearl River Estuary: Their Geochemical Behavior in Estuarine Water and Potential Contributions From Anthropogenic Sources

The ratio of cosmogenic 10Be and its stable isotope 9Be has been used as a proxy of long-term continental weathering fluxes and denudation rates, but transport processes of these isotopes from river water to estuarine water and seawater, as well as interference of potential anthropogenic source of 9Be on natural 10Be/9Be around populated estuaries are not well constrained. Here, we present results of 10Be and 9Be concentrations of dissolved and reactive particulate phase in the Pearl River Estuary (PRE) and its eight major outlets. The concentrations of Cu, Cd, and Pb are also measured, allowing us to assess their contamination levels and anthropogenic source together with 9Be by the geo-accumulation index (Igeo–reac) and enrichment factor (EF). A wide distribution pattern of dissolved 10Be (137–1,194 at/gwater) and 9Be (0.781–8.31 × 10–12 g/gwater) among these outlets is observed. The distribution coefficients (Kd) of both isotopes between sediment and water are in the order of 105, and on average only 5% of 10Be exists as dissolved form. Compared with total meteoric 10Be deposited on the river basin, 23% of the meteoric 10Be is retained while 38% of 10Be finally escape the estuary and is transported into coastal seawater. Despite the high contamination levels of Cu and Cd, the lower Igeo–reac and EF values of 9Be indicate that 9Be is hardly polluted by anthropogenic source. Thus, the 10Be/9Be in the PRE area is mainly associated with natural processes instead of human activities.

Beryllium cycling through deciduous trees and implications for meteoric 10Be systematics

Application of meteoric 10Be inventories and 10Be/9Be ratios to determine surface ages, erosion rates, and denudation rates requires understanding the conditions under which meteoric 10Be functions as an open vs. closed system near the Earth's surface. Here, we investigate biologically mediated beryllium isotope mobility in an oak-hickory forest in eastern North America. We report meteoric 10Be and 9Be concentrations in soils, roots, and leaves of four deciduous tree species. The data show that beryllium is readily taken-up from the soil by roots, cycled through leaves, and redeposited on the forest floor with autumn leaf abscission. Hickory (genus Carya) dominates beryllium cycling with a spatially averaged annual 10Be flux to the soil surface through litterfall that is four times higher than the atmospheric 10Be deposition rate. Biocycling may thus modulate the shape of meteoric 10Be concentration and 10Be/9Be ratio depth profiles in soils. We present a biocycling model that describes beryllium uptake by roots, redeposition on the surface through litterfall, and retention according to an exponential adsorption rule. This model reproduces the observed form of meteoric 10Be and 9Be depth profiles and the beryllium isotope ratio in foliage at the study site. The model also indicates that both declining and bulge-type meteoric 10Be depth profiles may result from biocycling, even where beryllium loss by leaching is significant, implying that declining meteoric 10Be depth profiles may not be indicative of quantitative 10Be retention. We recommend that biocycling be considered in models of beryllium isotope systematics where hickory or other beryllium accumulating taxa are present and where litter production rates are high.

Measurements of beryllium isotopes in ice wedges in Alaska

To explore the possibility of using ground ice archives for studies of the cosmogenic radionuclide 10Be, we analyzed the beryllium isotopes in ice wedges exposed in the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel and the Barrow Permafrost Tunnel in Alaska. We determined the concentrations of 10Be and 9Be in samples pretreated following two procedures: acidification before (procedure A) and after (procedure B) removal of particles. The 10Be and 9Be concentrations spanned wide ranges. Concentrations in procedure A samples were higher than those in procedure B samples. The 10Be/9Be ratios fell within a narrow range, and values from CRREL (about 8.5 × 10−9) and Barrow (about 7 × 10−9) were of the same order of magnitude. Further studies are needed to validate our findings and assess the feasibility of using the 10Be/9Be ratio of syngenetic ice wedges for reconstruction of 10Be variations due to cosmogenic and environmental changes, and radiometric dating of ice-wedge sequences that contain very old (beyond 1 Ma) ice.

Investigation of the Dashigil mud volcano (Azerbaijan) using beryllium-10

We collected and analyzed five sediments from three mud volcano (MV) vents and six suspended and bottom sediment samples from the adjoining river near the Dashgil mud volcano in Azerbaijan for 10Be. These three MV are found among the 190 onshore and >150 offshore MV in this region which correspond to the western flank of the South Caspian depression. These MVs overlie the faulted and petroleum-bearing anticlines. The 10Be concentrations and 10Be/9Be ratios are comparable to the values reported for mud volcanoes in Trinidad Island. It appears that the stable Be concentrations in Azerbaijan rivers are not perturbed by anthropogenic effects and are comparable to the much older sediments (mud volcano samples). The 10Be and 9Be concentrations in our river sediments are compared to the global data set and show that the 10Be values found for Kura River are among the lowest of any river for which data exist. We attribute this low 10Be concentration to the nature of surface minerals which are affected by the residual hydrocarbon compounds that occur commonly in the study area in particular and Azerbaijan at large. The concentrations of 40K and U-Th-series radionuclides (234Th, 210Pb, 226Ra, and 228Ra) indicate overall homogeneity of the mud volcano samples from the three different sites. Based on the 10Be concentrations of the mud volcano samples, the age of the mud sediments could be at least as old as 4myr.

Carrier free 10Be/9Be measurements with low-energy AMS: Determination of sedimentation rates in the Arctic Ocean

Using the TANDY AMS facility (600kV) at ETH Zurich the seawater-derived (authigenic) 10Be/9Be ratio of marine sediment samples is measured without the addition of 9Be carrier. This novel method reduces systematic uncertainties because the 10Be/9Be ratio of a sample is determined in only one (AMS) measurement. A challenge of carrier-free AMS is to avoid any contamination of the sample with 9Be during the chemical preparation. Further, the leaching procedure has to be reproducible and ideally should attack the authigenic Be of the sediments only, leaving the detrital Be untouched. The low amount of stable 9Be in the unspiked samples causes low currents during the AMS measurement. This requires a good stability and sensitivity of the AMS setup. Our first results show that the new preparation method is reliable and that background from stable 9Be is avoided.For a comparison study, sediment samples from two cores located in the Arctic Ocean (HLY0503-09JPC, HLY0503-14JPC) were used. The authigenic 10Be/9Be ratio of these samples had been determined previously applying the conventional method where 10Be and 9Be concentrations are measured separately by AMS and ICP-MS, respectively. The resulting sedimentation rates are in discrepancy with values derived from biomarkers. To cross check the 10Be/9Be based age model two samples from each core were measured again with the new carrier-free method. The carrier-free results show systematically higher authigenic 10Be/9Be ratios. The calculated sedimentation rates of about 0.2cm/kyr, however, are consistent for the carrier free and the conventional method.

The dependence of meteoric 10Be concentrations on particle size in Amazon River bed sediment and the extraction of reactive 10Be/9Be ratios

Concentrations of meteoric 10Be extracted from detrital Amazon River sediment are strongly particle size-dependent. Such grain size dependency presents a formidable obstacle to routine applications of meteoric cosmogenic 10Be to basin-wide erosion studies. In this study, we explore means to eliminate these grain size effects in bedload from rivers of the Amazon basin by measuring 10Be/9Be ratios after selective chemical extraction of reactive authigenic phases. These phases mainly comprise Fe–Mn-(hydr)oxides that are the main carriers of 9Be and 10Be. We explore the distribution of 10Be and its stable 9Be counterpart between these phases and the partitioning of Be into remaining silicate fractions. This extraction procedure was carried out on bedload samples comprising the three main tectonic units of the Amazon basin, namely the Andes, the Guyana and Brazilian Shields, and the central Amazonian lowlands. For all samples, extracted 10Be concentrations show a strong decrease with increasing particle size, with up to 20 times more 10Be extracted from the finest analyzed (<30μm) grain size when compared to the coarsest (90–125μm) grain size. We attribute this decrease in 10Be concentrations mostly to subsequent dilution by quartz in coarse bedload. However, when normalized to stable 9Be concentrations that are also extracted from reactive phases, grain size effects are effectively removed and the resulting “reactive” 10Be/9Be ratio is uniform for all particle sizes. The reactive 10Be/9Be ratio thus offers important advantages over methods employing single meteoric 10Be concentrations, such that this ratio can now be developed as quantitative tracer for Earth surface processes.

The dissolved Beryllium isotope composition of the Arctic Ocean

We present the first comprehensive set of dissolved 10Be and 9Be concentrations in surface waters and vertical profiles of all major sub-basins of the Arctic Ocean, which are complemented by data from the major Arctic rivers Mackenzie, Lena, Yenisey and Ob. The results show that 10Be and 9Be concentrations in waters below 150 m depth are low and only vary within a factor of 2 throughout the Arctic Basin (350–750 atoms/g and 9–15 pmol/kg, respectively). In marked contrast, Be isotope compositions in the upper 150 m are highly variable and show systematic variations. Cosmogenic 10Be concentrations range from 150 to 1000 atoms/g and concentrations of terrigenous 9Be range from 7 to 65 pmol/kg, resulting in 10Be/ 9Be ratios (atom/atom) between 0.5 and 14 × 10 −8. Inflowing Atlantic water masses in the Eurasian Basin are characterized by a 10Be/ 9Be signature of 7 × 10 −8. The inflow of Pacific water masses across the Bering Strait is characterized by lower ratios of 2–3 × 10 −8, which can be traced into the central Arctic Ocean, possibly as far as the Fram Strait. A comparison of the high dissolved surface 10Be and 9Be concentrations (corresponding to low 10Be/ 9Be signatures of ∼2 × 10 −8) in the Eurasian Basin with hydrographic parameters and river data documents efficient and rapid transport of Be with Siberian river waters across the Siberian Arctic shelves into the central Arctic Basin, although significant loss and exchange of Be on the shelves occurs. In contrast, fresh surface waters from the Canada Basin also show high cosmogenic 10Be contents, but are not enriched in terrigenous 9Be (resulting in high 10Be/ 9Be signatures of up to 14 × 10 −8). This is explained by a combination of efficient scavenging of Be in the Mackenzie River estuary and the shelves and additional supply of cosmogenic 10Be via atmospheric fallout and melting of old sea ice. The residence time of Be in the deep Arctic Ocean estimated from our data is 800 years and thus similar to the average Be residence time in the global ocean.

Determination of 9Be in geological standard samples, JA-2 and JB-2, and of 9Be and 10Be in a basaltic rock sample for evaluation of uncertainty involved in 10Be/9Be ratio measurements

We determined the concentrations of 9Be in JB-2 and JA-2 geological standard samples using an inductively coupled plasma mass spectrometer (ICP-MS). We determined 9Be abundance in standard samples of JA-2 and JB-2 as 2.26 ± 0.10 and 0.241 ± 0.010 ppm, respectively, after comparing and selecting 9Be concentration data obtained by the internal standard method, the standard addition method and the column separation method. In the course of comparison, we identified a problem in the internal standard method, which is usually used for abundance analyses using an ICP-MS. Repeated analyses of a basalt lava gave a standard deviation of 10Be abundance of 9% (1σ, n = 5). From the results, we estimated the uncertainty of 10Be/9Be ratio as 10% (1σ), considering a law of propagation of errors.

O.144 Controlled lower border split of mandibular body – Modification of BSSO

The cosmogenic meteoric 10Be that is produced in the atmosphere and mainly scavenged by rainfall is a valuable tool for determining dates and rates of Earth surface processes. A key prerequisite for its applications is the knowledge of the long-term 10Be depositional flux to Earth's surface. Previous efforts on obtaining 10Be depositional fluxes include general atmospheric circulation modelling (GCM), empirical fitting of rainfall 10Be records, and determining the inventory of soil profiles of known age. Here, we derive 10Be depositional fluxes from Holocene river terrace 10Be inventories across the Taiwan mountain belt. We measured 10Be and 9Be concentrations from three terrace profiles, with 14C ages ranging between 3.83 and 9.05 cal. kyr BP and sampling depths of up to 6.2 m.Based on 10Be inventories of our river terraces, the calculated long-term 10Be depositional fluxes vary from 0.32 to 0.49 × 106 at/cm2/yr in the Taiwan orogen. We identify partial Be retention, surface erosion, multi-phase sediment deposition, and incomplete sampling depth in these terraces as potential causes of flux underestimation. When accounting for each of these factors and their uncertainties, the resulting flux estimates of each terrace show an overlapping range of 0.66–0.88 × 106 at/cm2/yr. This newly constrained flux range representative over millennial timescales is thus recommended for Earth surface applications in the fast-eroding Taiwan orogen, especially in regions with similar climatic conditions as the studied terraces. When comparing to flux estimates from other approaches, the flux from the rainfall-based fitting equation exceeds our new terrace-derived flux by more than a factor of two. We consider such high flux to be unlikely for the Taiwan orogen, and suggest that the control of precipitation on the 10Be flux here may be overestimated in rainfall data fitting. The GCM-derived flux overestimates the 10Be depositional flux in this setting to a smaller degree (at least 23%), which is in accordance with findings from previous global data compilation of 10Be fluxes.

Beryllium geochemistry constraints on the hydraulic behavior of mud volcanoes: the Trinidad Island case

To constrain Trinidad mud volcanoes hydraulic behavior, both cosmogenic 10Be (t1/2=1.5 Myr) and 9Be concentrations have been measured in fluid and associated expelled mud. As previously evidenced [A.N. Dia, M. Castrec, J. Boulègue, P. Comeau, Trinidad Mud Volcanoes: where do the expelled fluids come from? Geochim. Cosmochim. Acta 63 (1999) 1023–1038] from δ18O values and Cl concentrations, 9Be concentrations in the fluids mostly reflect the mixing of two deep components: REM I and REM II. REM I (δ18O=10.5‰, Cl≈275 mM and 9Be≈0.05 nM) has characteristics of a continental fluid while REM II (δ18O=3‰, Cl≈350 mM and 9Be≈1 nM) results from seawater–volcanogenic derived sediment interaction. Although 10Be concentrations in the fluid samples are close to the detection limit, the distribution of both beryllium isotopes between the hydroxylamine leachable and residual phases indicates exchange reaction with fluid younger than 15 Myr. Comparison between the lowest REM I 10Be/9Be ratio in fluid recorded by the hydroxylamine leachable phase (TD5 mud sample) and the 10Be/9Be ratio representative of meteoric contribution in the recharge area (TD8 fluid sample) yields a circulation rate of REM I fluid in the Trinidad mud volcanoes of several 10−1 m/yr.

The distribution of 10Be and 9Be in the South Atlantic

Vertical and surface-water distributions of 10Be and 9Be in the South Atlantic Ocean were studied. The major input of 9Be to the surface waters of the region is from the partial dissolution of eolian dusts, with the extent of the dissolution being about seven times that of aluminum from the dust particles. The gradients in surface-water 10Be concentrations appear to reflect the magnitude of the local precipitation. The imprinting of the surface water signals onto the deep water masses appears rapid, particularly in regions of enhanced productivity. Bottom waters of Antarctic origin have characteristic isotope signatures that can be traced along their advective route into the Guinea Basin of the eastern Atlantic. Elevated 9Be concentrations in the Angola Basin are indicative of diagenetic input in this region of restricted circulation. The corresponding anomalous 10Be in the bottom waters indicates historically lower surface-water 10Be/ 9Be ratios in the region, perhaps as a result of the further southward penetration of the Inter-Tropical Convergence Zone at those times. The budgets of 10Be and 9Be in the South Atlantic were estimated. The results show that crossequator transport of 10Be and 9Be from the North Atlantic is 0.3 ± 10 23 atoms/year and 5.7 ±10 6 mol/year, respectively, accounting for less than 5% of 10Be and about 10% of 9Be entering the North Atlantic. There is a net export across 50°S to the Antarctic/Indian/Pacific Oceans of 0.9 ±10 23 atoms/year for 10Be and 7.5 ± 10 6 mol/year for 9Be. Using 10Be as a tracer, we evaluate accumulation rates of lithogenic minerals to be 1.7 ± 10 14 g/year in the North Atlantic and 4.8 ± 10 13 g/year in the South Atlantic. While the North Atlantic rate agrees with the observed eolian dust input, the estimated lithogenic flux in the South Atlantic is about twice the eolian input, suggesting that the riverine input of 9Be to the open ocean may become non-negligible in areas of low eolian dust flux.

Separation of 9Be and cosmogenic 10Be from environmental materials and SIMS isotope dilution analysis

A recently developed high-resolution secondary ion mass spectrometer (SIMS) allows direct determination of the ratio of cosmogenic 10Be to stable 9Be. In this paper a new method for high-purity separation of nanogram amounts of Be from environmental materials, such as silicates, oxides, or water is described. The separation employs a flexible combination of ion exchange columns with optional hydroxide coprecipitation. The natural 10 Be 9 Be ratio is measured directly by multi-collector SIMS. Secondly, an isotope dilution method for determination of 9Be concentrations is described. This approach uses a 10Be-enriched solution as tracer, and offers considerable advantages over methods, of which concentration results are sensitive to matrix effects (ICP-MS, AAS). We illustrate the methods with examples from oceanic FeMn-oxide sediments.

Beryllium isotope geochemistry of hydrothermally altered sediments

Profiles of both 10Be and 9Be concentrations have been measured in sediments from the DSDP, Leg 64, Site 477 core. Established in the deep Guaymas Basin, in an area of high heat flow, this site offers the opportunity of studying hydrothermal alteration induced by two distinct hydrothermal systems, those caused (i) by the intrusion of hot sills into porous sediments and (ii) by heat associated with a magma chamber. The results show that the distribution of both beryllium isotopes between two operationally defined sedimentary phases (material susceptible to hydroxylamine leaching and residual material) changes with the degree of hydrothermal alteration. A decrease in 10Be/ 9Be in the leachable phase of altered sediments relative to unaltered sediments indicates that hydrothermal alteration is not limited to a simple chemical leaching but involves redistribution of the beryllium isotopes between metamorphosed sedimentary phases. In addition, the similarity of the mean 10Be/ 9Be ratios associated with the leachable and the residual phases in the part of the core which has experienced greenschist facies metamorphism suggests that this process leads in the prevailing geophysical conditions to isotopic homogenization. A close relationship exists between 10Be and MgO concentrations in altered sediments from this core. This supports earlier observations that beryllium is not easily removed from the sedimentary column and indicates that this remains the case even under the conditions encountered in submarine hydrothermal systems.

Beryllium isotope systematics of submarine hydrothermal systems

Both 10Be and 9Be concentrations have been measured in a hydrothermal fluid from the sediment-starved East Pacific Rise at 21°N as well as in fluids and associated sediments from the sediment covered Guaymas Basin and Escanaba Trough hydrothermal systems. The results show that while the 9Be concentrations in fluids from both types of systems are comparable, about three orders of magnitude higher than that of the seawater supplying the systems, their 10Be concentrations are significantly different. The 10Be concentration in the solution emanating from the studied sediment-starved hydrothermal system is at least two times lower than that of the Pacific bottom water. By contrast, the 10Be concentration in hydrothermal solutions from sediment-hosted environments are enriched over ambient seawater and are at least one order of magnitude higher than that measured in the 21°N fluid. The sedimentary cover being the only available source of 10Be in these systems, these data demonstrate that 10Be is an unambiguous tracer of interactions between hydrothermal fluids and recent sediments. As an example, this study examines hydrothermal solutions from the sediment-starved Mariana Trough back-arc basin which have compositions similar in many respects to those from sediment-hosted environments. However, these fluids are depleted in 10Be relative to ambient seawater, which precludes interaction with recent sediment as the cause of their peculiar chemical composition.

Be isotopes in rivers/estuaries and their oceanic budgets

10Be and 9Be have been determined in several North American rivers and in the estuaries of San Francisco Bay and the Pearl River (China). The average fluvial concentration of dissolved 10Be in the rivers is 3220 ± 1960 (1σ) atoms/g, almost an order of magnitude higher than the observed estuarine values and slightly higher than the 10Be concentration in the ocean ( ∼ 1700 atoms/g). For dissolved 9Be, a similar order-of-magnitude drop in concentration also occurs in going from rivers (750 ± 740 pM) to estuaries (80–140 p M). However, in contrast to the 10Be situation, there appears another order-of-magnitude drop from estuaries to the ocean, which has 9Be concentrations of 5–30 p M. In spite of the wide range of concentrations for both isotopes in river and estuarine waters, 10Be/ 9Be ratios range mostly from 2 to 12 × 10 −9, with a median value of 7 × 10 −9 (atom/atom), and are much lower than the seawater ratio of ∼ 10 −7. In the rivers studied, a given volume of water contains roughly equal amounts of particulate and dissolved 10Be. The 10Be concentration in particulate matter ranges from 2 × 10 6 to 1 × 10 9 atoms/g-particulate with a median value of about 5 × 10 7 atoms/g-particulate. A two-box model calculation shows that coastal regions play an important role in the removal of Be isotopes from the ocean and that eolian dusts may be the chief source of oceanic 9Be. Because of the marginal removal effect, the overall oceanic residence time of Be should be shorter than the residence time of 500–1200 yr estimated for the open ocean.

Beryllium isotope distribution in the western North Atlantic: a comparison to the Pacific

The surface depletion/deep enrichment of the 10Be and 9Be distributions observed in the Pacific is not as conspicuous in the western North Atlantic Ocean between 33° and 42°N. In the case of 9Be, a surface excess sometimes even exists. While 10Be concentrations in the surface waters of the two oceans are comparable, 9Be concentrations in the surface North Atlantic are about five times those in the surface Pacific. Deep waters show an increase of concentrations from the Atlantic (via Antarctic) to the Pacific, but the degree of increase for the two isotopes is different: about 10% for 9Be and 2.5-fold for 10Be. Thus there is a systematic increasing trend in the ration 10Be/ 9Be ( atom/ atom × 10 −7) along the advective flow lines: surface North Atlantic (0.4)→ deep North Atlantic (0.6) → Circumpolar (1.0) → deep Pacific (1.2) → surface Pacific (1–3). These distributional patterns and contrasting North Atlantic-Pacific features can be explained in terms of: (a) a strong fluvial and continental dust input of 9Be to the North Atlantic and an ocean-wide, more-or-less uniform pluvial input of cosmogenically produced 10Be; (b) active participation of Be in the particle recycling involving surface uptake and deep water regeneration; and (c) mean removal time of Be from the ocean, which, based on the 10Be/ 230Th ratios in surface sediments of two deep-sea cores, are estimated as ∼1200 y in the open Pacific and ∼500 a in the open Atlantic, values that are close to water mixing times of the individual ocean basins.