Boundary Scavenging Research Articles

The behaviour of aluminium, manganese, iron, cobalt, and lead in the subarctic Pacific Ocean: boundary scavenging and temporal changes

AbstractAluminium (Al), manganese (Mn), iron (Fe), cobalt (Co), and lead (Pb) are trace metals that exhibit significant scavenging tendencies in the oceans. This study presents the full-depth distributions of the dissolved (d) and labile particulate (lp) fractions of these five elements in the subarctic Pacific Ocean, obtained during the GEOTRACES Japan KH-17-3 cruise. Along the 145° W meridional transect, the d and lp species of Al, Mn, Fe, and Co reflected fluvial supply from Alaska and benthic input from the continental shelf. We estimated that the boundary-scavenging zone has a width of approximately 250 km off Alaska. Along the 47° N zonal transect (GEOTRACES GP02 Line), we found input of trace metals from the Okhotsk and Bering Seas in the west, contrasting to the limited input of trace metals due to boundary scavenging in the east. The hydrothermal activity of the Juan de Fuca Ridge influenced the distribution of deep-water trace metals at the easternmost station, CL-21. Temporal change in the vertical profiles of dPb in the middle of the subarctic gyre highlighted a decline in anthropogenic Pb emissions from 2005 to 2017. Temporal change of the vertical profiles of Al, Mn, and Fe at 47° N, 160° E from 2011 to 2017 indicates the influence of the Great East Japan Earthquake. In particular, lp trace metals were brought by tsunami and ocean circulation in 2011, and decreased over time through scavenging.

Enhanced boundary scavenging of 241Am on the continental margin of the East China sea

The 241Am concentrations were determined by sector field high-resolution inductively coupled plasma mass spectrometry for settling particles and surface sediments collected on the continental margin in the East China Sea to discuss the behavior of 241Am in the studied area. A large and regular increase was noted from 97 m depth to 592 m depth in 241Am concentrations in settling particles from the cylindrical sediment traps, whereas only a slight increase in 239+240Pu concentrations was evident. The gradual increase in 241Am/239+240Pu activity ratios from the cylindrical trap settling particles also was observed. These results were attributed to 241Am being scavenged by settling particles at a more rapid scavenging rate than 239+240Pu. There was an obvious tendency for 241Am fluxes to increase linearly with depth with the highest fluxes at near-bottom, and these fluxes were due to large advective import to the near-bottom. There was a tendency for 241Am concentrations in surface sediments to increase almost linearly with depth, showing the same tendency as 210Pb concentrations, and this tendency indicated that the enhanced boundary scavenging of 241Am as well as 210Pb occurred in the East China Sea continental slope region due to the greater abundance of reactive finer particles. The 241Am concentrations in settling particles from the time-series sediment trap ranged from 1.05 to 4.20 mBq g−1, showing large variation. The 241Am concentrations from the time-series trap varied inversely with the total mass fluxes, indicating that 241Am concentrations were diluted by particles when mass flux increased. The 241Am fluxes showed large time-series variations and these variations were primarily controlled by mass flux variation. It seems that the high total mass flux events are due to resuspension of the underlying surface sediments and episodic lateral transport of particles that flow down the continental slope in the East China Sea.

Performance optimization of Ca and Y co-doped CeO2-based electrolyte for intermediate-temperature solid oxide fuel cells

The CeO2-based electrolytes of solid oxide fuel cells (SOFCs) with high ionic conductivity have attracted considerable attention. In this study, Ca and Y co-doped Ce0.8Y0.2−xCaxO2−δ (x = 0, 0.05, 0.1, and 0.15, abbreviated as YDC, YCDC05, YCDC10, and YCDC15) electrolytes were prepared, and their properties were investigated for intermediate-temperature solid oxide fuel cells (IT-SOFCs). All samples formed a cubic fluorite structure at a low sintering temperature (600 °C). At 800 °C, the YCDC05 electrolyte exhibited the highest conductivity (0.10 S cm−1), which was approximately 54% higher than that of the YDC electrolyte. The YCDC05 had the highest grain boundary scavenging factor and the smallest blocking factor. The blocking factor of YCDC05 was reduced by 49%, compared with that of YDC at 400 °C. The density functional theory calculation results showed that the oxygen vacancy formation energy of the Y and Ca co-doped (YCDC) electrolyte was lower than that of YDC. Therefore, Ce0.8Y0.15Ca0.05O2-δ may be a potential electrolyte material for IT-SOFCs.

Enhanced Boundary Scavenging Of 241am on the Continental Margin of the East China Sea

Enhanced Boundary Scavenging Of 241am on the Continental Margin of the East China Sea

10Be depositional flux variation in the central Indian Ocean during the last 43 ka

The advent of Accelerator Mass Spectrometer (AMS) enhanced the application of meteoric 10Be (half-life of 1.39 Ma) as a tracer for understanding earth surface processes on thousand to million-year time scales. However, for the majority of applications, an adequate understanding of the 10Be depositional flux is a prerequisite. A number of efforts have been made to understand both spatial and temporal variation of 10Be depositional flux. Yet, due to the limited globally distributed dataset and modulation of the 10Be signal by local processes, a significant offset is observed between model-derived and measured deposition rates of 10Be. In this study, an attempt has been made to determine the 10Be depositional flux from a marine sediment core from the central Indian Ocean chronologically constrained with the AMS radiocarbon dating and 10Be concentration measured with AMS. The 10Be depositional flux estimates using weak leaching method are found to be nearly 44% lower compared to the strong leaching method. The calculated 10Be depositional flux during the Holocene varies between 9.63 and 13.01 × 105 atoms/cm2/yr, which is 2-28% lower compared to the modeled depositional flux for the region. The difference observed in 10Be depositional flux could be due to the local processes (such as boundary scavenging, changing rate of sediment deposition at the location) affecting 10Be deposition into the sediment column or offset associated with the model estimations. The changes in 10Be depositional flux and the 10Be/9Be ratio have been reconstructed up to 43 ka. An increase in the 10Be/9Be ratio during 28 to 43 ka is observed due to the lower geomagnetic field intensity during the period. A high-resolution 10Be/9Be ratio reconstruction shows a peak at 41.2 ka, which can be attributed to the Laschamp event.

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.

Source and sinks of 210Pb in oceanic margins of east coast Peninsular Malaysia

• Both rivers received 210 Pb concentration through the physical and chemical weathering. • Rivers are a main contributor of 210 Pb into offshore sediment at the east coast Peninsular Malaysia. • Atmospheric deposition and transboundary mobilization may increase the total flux of 210 Pb at offshore sediments. A total of 97 surficial sediment samples were collected from the Kelantan River, Pahang River and offshore water of Peninsular Malaysia located in the east coast mainly in to investigate the sources and sinks of 210 Pb in the southern South China Sea region. At the locations studied, the concentration activity of 210 Pb was recorded from the Kelantan River (n = 28), Pahang River (n = 44) and offshore waters (n = 25), ranging from 2.7 ± 0.46 Bq/kg to 52.07 ± 5.23 Bq/kg, 8.65 ± 3.56 Bq/kg to 83.04 ± 6.71 Bq/kg, and 6.72 ± 2.92 Bq/kg to 42.2 ± 3.94 Bq/kg, respectively. Both riverine systems received huge amounts of 210 Pb concentrations via mobilised particulate matter, where erosional igneous rocks and weathered sedimentary layers were prominent in elevating the amount of 210 Pb from the source towards the sinks. In the offshore margins, the concentrations differed according to the source. As both rivers move towards the sinks in the coastal territories, boundary scavenging becomes prominent. In the offshore territories, a deficiency of 210 Pb leads to excess 226 Ra in the water column. Scavenged nuclide imported from several sources may increase the total concentrations lingering in the offshore waters of Peninsular Malaysia. Particulate matter mobilised from several sources via upwelling or downwelling in the bottom current through lateral transport further enhances the removal of particle-reactive nuclides from the water column. At the same time, atmospheric deposition via precipitation and transboundary mobilisation of aerosol by mineral dust may increase the total flux on the offshore waters of Peninsular Malaysia.

Coupled analysis of seawater and sedimentary 231Pa/230Th in the tropical Atlantic

The 231Pa/230Th ratio of seawater and in ocean sediments is a potentially powerful tool in tracing oceanic processes such as the ocean circulation and marine primary productivity. However, 231Pa/230Th reflects the combined signal of multiple controls associated with scavenging and oceanic transport, limiting its use as a paleo-proxy. Given that links between seawater and sedimentary 231Pa and 230Th distributions are crucial for understanding the cycling and removal fluxes of these nuclides, we carry out analysis of 231Pa and 230Th in both seawater (dissolved phase) and modern sediment samples acquired from five depth transects across the northern tropical Atlantic open ocean. Overall, the sediment data support the dominance of 231Pa export in the deep Atlantic Ocean (>2.5 km) associated with the southward advection of North Atlantic Deep Water. However, the seawater data provide evidence for locally enhanced scavenging of 231Pa and 230Th near the western seamounts that is likely to be associated with the influence of hydrothermal activity or episodic formation of transient nepheloid layers. At shallower depths (0.5–1.5 km), paired sediment and seawater 231Pa/230Th data reveal enhanced burial of 231Pa at the eastern and mid-Atlantic sites that is likely related to elevated marine primary productivity and/or influence of boundary scavenging at the African margin, and a net input of 231Pa potentially maintained by the northward advection of intermediate water masses and an additional mechanism of upward diffusion. Our findings provide greater insights into the range of oceanic processes that play a significant role in the cycling of 231Pa and 230Th, with implications for the controls of 231Pa/230Th distribution in the Atlantic Ocean.

Rare earth elements in the East Sea (Japan Sea): Distributions, behaviors, and applications

The distributions of rare earth elements (REEs) were measured at 14 stations from 0 to 3365 m (n = 176) in the entire East Sea for the first time. The East Sea has its own deep-convection system, which operates on a time scale that is approximately one tenth that of the global ocean; it is also a downwind region of Asian dust. The vertical distributions of REE concentrations increased with depth, similar to those in the North Atlantic Ocean. However, the concentrations of REEs were 1.3–2.7 fold higher than those in the North Atlantic Ocean, associated with relatively larger atmospheric depositions of dust from the Asian continent. In this environmental condition, the removal of Ce relative to the other REEs was about an order of magnitude more efficient than that in the North Pacific Ocean. As such, in the deep layer below 750 m, large increases of heavy-REEs (HREEs) relative to light-REEs (LREEs), opposite to the re-mineralization trend, were observed suggesting that LREEs were preferentially re-scavenged by sinking particles. In addition, the boundary scavenging of REEs was also observed for all REEs in the bottom layer of the East Sea. On the other hand, the warm surface waters of REEs, Tsushima Warm Water (TWW) showed large fractionations, relative to the other water masses. This REE pattern traced the deep physical mixing proportions of TWW up to 750 m (∼10%). Thus, the unique distribution patterns of REEs in this sea illustrate the geochemical scavenging characteristics of REEs, which are concealed in the major oceans, as well as water mass mixing patterns in the upper ocean.

230Th Normalization: New Insights on an Essential Tool for Quantifying Sedimentary Fluxes in the Modern and Quaternary Ocean

Abstract230Th normalization is a valuable paleoceanographic tool for reconstructing high‐resolution sediment fluxes during the late Pleistocene (last ~500,000 years). As its application has expanded to ever more diverse marine environments, the nuances of230Th systematics, with regard to particle type, particle size, lateral advective/diffusive redistribution, and other processes, have emerged. We synthesized over 1000 sedimentary records of230Th from across the global ocean at two time slices, the late Holocene (0–5,000 years ago, or 0–5 ka) and the Last Glacial Maximum (18.5–23.5 ka), and investigated the spatial structure of230Th‐normalized mass fluxes. On a global scale, sedimentary mass fluxes were significantly higher during the Last Glacial Maximum (1.79–2.17 g/cm2kyr, 95% confidence) relative to the Holocene (1.48–1.68 g/cm2kyr, 95% confidence). We then examined the potential confounding influences of boundary scavenging, nepheloid layers, hydrothermal scavenging, size‐dependent sediment fractionation, and carbonate dissolution on the efficacy of230Th as a constant flux proxy. Anomalous230Th behavior is sometimes observed proximal to hydrothermal ridges and in continental margins where high particle fluxes and steep continental slopes can lead to the combined effects of boundary scavenging and nepheloid interference. Notwithstanding these limitations, we found that230Th normalization is a robust tool for determining sediment mass accumulation rates in the majority of pelagic marine settings (>1,000 m water depth).

231Pa and 230Th in the Arctic Ocean: Implications for boundary scavenging and 231Pa[sbnd]230Th fractionation in the Eurasian Basin

231Pa, 230Th and 232Th were analyzed in filtered seawater (n = 70) and suspended particles (n = 39) collected along a shelf-basin transect from the Barents shelf to the Makarov Basin in the Arctic Ocean during GEOTRACES section GN04 in 2015. The distribution of dissolved 231Pa and 230Th in the Arctic Ocean deviates from the linear increase expected from reversible scavenging. Higher 232Th concentrations were observed at the shelf, slope and in surface waters in the deep basin, pointing at lithogenic sources. Fractionation factors (FTh/Pa) observed at the Nansen margin were higher compared to FTh/Pa in the central Nansen Basin, possibly due to the residual occurrence of hydrothermal particles in the deep central Nansen Basin. Application of a boundary scavenging model quantitatively accounts for the dissolved and particulate 230Th distributions in the Nansen Basin. Modelled dissolved 231Pa distributions were largely overestimated, which was attributed to the absence of incorporation of water exchange with the Atlantic Ocean in the model. 231Pa/230Th ratios of the suspended particles of the Nansen Basin were below the 231Pa/230Th production ratio, but top-core sediments of the Nansen margin and slope have high 231Pa/230Th-ratios, suggesting that scavenging along the Nansen margin partly acts as a sink for the missing Arctic 231Pa.

Major lithogenic contributions to the distribution and budget of iron in the North Pacific Ocean

Recent studies have elucidated that iron (Fe) is a critical trace metal that influences the productivity of marine ecosystems and the biogeochemical cycles of other elements in the modern ocean. However, our understanding of the biogeochemistry of Fe remains incomplete. Herein, we report basin-scale and full-depth sectional distributions of total dissolvable iron (tdFe), dissolved iron (dFe), and labile particulate iron (lpFe = tdFe – dFe) in the North Pacific Ocean, as observed during three cruises of the GEOTRACES Japan program. We found that lpFe dominates tdFe and is significantly correlated with labile particulate aluminum (lpAl): lpFe [nmol kg−1] = (0.544 ± 0.005) lpAl [nmol kg−1] + 0.11 ± 0.04, r2 = 0.968, n = 432. The results indicate a major lithogenic contribution to the distribution of particulate Fe. For dFe, the unique distribution is attributed to the combined effects of biogeochemical cycling, manganese reduction, and lithogenic contribution. Based on concurrent observations of Fe, Al, and manganese (Mn), we infer that the width of the boundary scavenging zone is approximately 500 km off the Aleutian shelf. We estimate the inventory of tdFe in the North Pacific as 1.1 × 1012 mol, which is approximately four times that of dFe. Our results emphasize the potential importance of lpFe in the ocean’s iron cycle.

Synergistic effect of lithium and calcium for low temperature densification and grain boundary scavenging in samarium doped ceria electrolyte

A highly dense electrolyte with lower grain boundary resistance is desirable for improving the performance of solid oxide fuel cell. This paper studies the synergistic role of calcium and lithium on the densification and ionic conductivity of samarium doped ceria (SDC) electrolyte. Nanosized powders of compositions, CaxLiySm0.2Ce0.78O2-δ (CLSDC, x + y = 0.02) were prepared by citrate - nitrate combustion method and subsequently sintered at 900 °C. A single phase cubic fluorite structure of CeO2 was observed in X-ray diffraction analysis. The segregation of the co-dopants was identified from Raman spectroscopic analysis and FESEM-EDX analysis. The presence of lithium enhanced the densification at 900 °C while calcium improved the grain boundary scavenging. The synergistic effect of an increase in configurational entropy and density in 0.5 mol% Ca and 1.5 mol% Li (0.5CLSDC900) resulted in the highest conductivity of 5.3 × 10−3 S/cm at 800 °C with a scavenging factor of 20.2. Thus the optimum ratio of Li+ and Ca2+ plays a key role in suppressing the ordering of oxygen vacancy and improve the ionic conductivity for its use as an electrolyte for solid oxide fuel cells.

Divalent cations modified grain boundary scavenging in samarium doped ceria electrolyte for solid oxide fuel cells

Grain boundary conductivity of samarium doped ceria electrolyte (SDC) depends on the space charge potential and oxygen vacancy concentration existing at the grain boundary region. Here, we report the effect of co-doping 1 mol% divalent alkaline earth metals in samarium doped ceria (Ce0.78Sm0.2A0.01O1.89, [ASDC], A = Mg, Ca, Sr, Ba) on the grain boundary conductivity. The increase (Ca2+, Sr2+, Ba2+) or decrease (Mg2+) in lattice parameter in comparison to SDC (0.5445 nm) depends on the ionic radii of the co-dopant. The oxygen vacancy concentration of ASDC system, quantified from the Raman spectra, increased from 2.98 × 1021 cm−3 (SDC) to 3.18 × 1021 cm−3. The samples sintered at 1400 °C for 5 h, resulted in a dense electrolyte with a relative density of 98–99%. Calcium co-doped SDC (CSDC) showed the highest conductivity of 2.04 × 10−3 S/cm at 700 °C with activation energy of 0.90 eV. The oxygen vacancy profile at the space charge layer was found to be higher for CSDC while the potential reduced from 0.24 V (SDC) to 0.18 V. The observed lower space charge potential in co-doped SDC, contributed to the enhancement in oxygen vacancy concentration at the space charge layer and increased the grain boundary conductivity. Thus the present study highlights the correlation of space charge potential, oxygen vacancy concentration to grain boundary conductivity and provide a profound insights on the grain boundary understandings for improving the performance of the electrolyte for solid oxide fuel cell application.

230Th in the eastern South Pacific Ocean: Boundary scavenging and bottom scavenging by metal oxides derived from hydrothermal vents

The vertical distribution of total 230Th was investigated in the eastern South Pacific Ocean. Among the stations studied, 230Th inventories in the depth range 1000‒2500 m generally decrease with increasing net primary productivity and export production, which implies that the spatial variability of particle flux controls the 230Th distribution. On the other hand, at equatorial stations, 230Th inventories in the depth range 0‒1000 m were similar to those found at stations in lower productivity regions, and the effect of lateral input of 230Th by equatorial zonal flow was considered. The large-scale bottom scavenging effect on 230Th in deep layers arising from hydrothermal activity in the vicinity of the East Pacific Rise was observed at stations in the Southwest Pacific Basin and the Peru Basin. Corresponding to the pattern seen in the map of iron and manganese oxide content of surface sediment, the observed 230Th depletion was higher in the Peru Basin than the Southwest Pacific Basin, suggesting that these oxides contribute to the observed bottom scavenging.

Grain boundary scavenging through reactive sintering of strontium and iron in samarium doped ceria electrolyte for ITSOFC applications

Lowering the operational temperature of ceria based electrolytes is important for commercialization of solid oxide fuel cells. Here, we report the effect of iron, strontium and iron/strontium co-addition in samarium (20 mol %) doped ceria (SDC) with respect to sintering, microstructural modifications and ionic conductivity. The nanoparticle synthesized through glycine-nitrate combustion method was sintered at 1000, 1200 and 1300 °C. An increase in density was observed in iron doped SDC due to viscous flow sintering while co-addition of strontium and iron lead to the reactive sintering at 1300 °C by forming a eutectic liquid phase which resulted in the density of 99%. The presence of iron and strontium generated a compensatory tensile strain in the lattice and an enhancement in oxygen vacancy concentration which resulted in higher ionic conductivity. Co-addition of strontium and iron in SDC, not only increases the density but also reduces the activation energy for grain boundary conductivity.

Thorium and protactinium isotopes as tracers of marine particle fluxes and deep water circulation in the Mediterranean Sea

Abstract 231Pa, 230Th and 232 Th were analyzed in unfiltered seawater samples (n = 66) and suspended particles (n = 19) collected in the Mediterranean Sea during the MedSeA-GA04-S cruise along the GEOTRACES section GA04S and used to investigate mechanisms controlling the distribution and fractionation of Pa and Th in an ocean margin environment. 231Pa and 230 Th are particle reactive radionuclides and are often used as tracers of processes such as boundary scavenging, particle transport and ocean circulation. The depth profiles of total 231Pa and 230Th concentrations in the Mediterranean Sea displayed non-linear shapes. Higher total 232Th concentrations were observed at the straits and in deep waters pointing at lithogenic sources. Fractionation factors FTh/Pa ranged from 1.4 to 9. Application of a box-model illustrated that 94% of the 231Pa and almost all of the 230Th (99.9%) produced in the Mediterranean Sea is removed to the sediment by scavenging. The negligible export of 230Th to the Atlantic Ocean, leads to a reevaluation of the mean settling speed of the filtered particles, which is now estimated to 500–1000 m/y. The low FTh/Pa fractionation factors are attributed to the efficient scavenging and lack of transport of 231Pa to the Atlantic Ocean.

New insights into cycling of 231Pa and 230Th in the Atlantic Ocean

We use the Bern3D model of intermediate complexity to examine the marine cycle of isotopes 231Pa and 230Th and the relationship between the particle-bound ratio Pap/Thp and changes in the formation of the North Atlantic Deep Water (NADW). Model parameters describing reversible scavenging of isotopes by organic particles, opal, calcite and resuspended sediments were systematically varied and alternative sink parametrisations explored. It proves difficult to simultaneously achieve a good agreement with observations of dissolved and particle-associated concentrations of 231Pa and 230Th (Pad, Thd, Pap, Thp) as well as the particle-bound ratio Pap/Thp within the classical concept of reversible scavenging alone.Agreement between simulated and observed Pad, Thd and estimates of mean ocean residence times is improved by taking into account simplified representations of additional sinks at the sea floor (bottom scavenging) and at continental boundaries (boundary scavenging). We also find improved agreement between model and data by increasing lateral advection, in particular for Pad. These results point to the importance of sink processes that act in addition to reversible scavenging to shape the steady state distribution of 231Pa and, to a lesser degree, of 230Th.In transient experiments in which the strength of the Atlantic meridional overturning circulation (AMOC) is periodically turned on and off, we find a strong statistical relationship between variations in AMOC strength and Pap/Thp at great depths in the Northwest Atlantic region. These conclusions are robust across the range of sink parametrisations, that are consistent with estimates in the mean ocean residence time of 231Pa and 230Th. Our results indicate that the relationship between Pap/Thp and AMOC-strength may not be fundamentally affected by uncertainties in sink processes, at least on the large spatial and temporal scale considered here, and support the idea that changes in Pap/Thp in sediments of the Northwest Atlantic are indicative of changes in AMOC strength. Taking into account our simplified approach, our results indicate that the relationship between Pap/Thp and AMOC-strength in the deep Northwest Atlantic is not affected by boundary scavenging or bottom scavenging. Our results thus support the idea that changes in Pap/Thp in sediments of the Northwest Atlantic are indicative of changes in AMOC strength.

Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications

Authigenic 10Be/9Be ratios and 10Be-fluxes reconstructed using the 230Thxs normalization, proxies of the cosmogenic radionuclide 10Be production rate in the atmosphere, have been measured in a sedimentary core from Baffin Bay (North Atlantic) spanning the last 136 ka BP. The normalization applied on the exchangeable (authigenic) 10Be concentrations using the authigenic 9Be isotope and 230Thxs methods yield equivalent results strongly correlated with sedimentological parameters (grain-size and mineralogy). Lower authigenic beryllium (Be) concentrations and 10Be/9Be ratios are associated with coarse-grained carbonate-rich layers, while higher authigenic Be values are related to fine-grained felspar-rich sediments. This variability is due to: i) sediment composition control over beryllium-scavenging efficiency and, ii) glacial history that contributed to modify the 10Be concentration in Baffin Bay by input and boundary scavenging condition changes. Most paleo-denudation rates inferred from the 10Be/9Be ratio vary weakly around 220 ± 76 tons.km−2.yr−1 (0.09 ± 0.03 mm.yr−1) corresponding to relatively steady weathering fluxes over the last glacial cycle except for six brief intervals characterized by sharp increases of the denudation rate. These intervals are related to ice-surging episodes coeval with Heinrich events and the last deglaciation period. An average freshwater flux of 180.6 km3.yr−1 (0.006 Sv), consistent with recent models, has been calculated in order to sustain glacially-derived 10Be inputs into Baffin Bay. It is concluded that in such environments, the authigenic 10Be measured mainly depends on climatic effects related to the glacial dynamics, which masks the 10Be production variation modulated by geomagnetic field changes. Altogether, these results challenge the simple interpretation of 10Be-concentration variation as a proxy of Interglacial/Glacial (interstadial/stadial) cycles in Arctic and sub-Arctic regions. They rather suggest the effect of higher-frequency paleoclimatic changes and local glacial dynamics on 10Be signature.

Seasonal distribution patterns of 7Be and 210Pb in surface sediments in the Changjiang Estuary, China and their implication

The estuarine-inner shelf region of the East China Sea (ECS) is heavily impacted from the riverine input from the Changjiang River. In this study, the grain size and activities of radionuclides (7Be and 210Pb) of surface sediments collected from the Changjiang Estuary to the southern inner shelf of the ECS in June and November 2010, were measured to provide the study of the sources and the transportation pathways of surface sediments in this region. The results indicated that the grain size of surface sediments ranged from 8.1 to 251.1μm and from 5.8 to 128.3μm with an average of 85.1μm and 56.6μm in June and November 2010, respectively. Relatively large particle sizes were observed in the northwest and southeast of our study area. Meanwhile, the grain size increased offshore. The activities of 7Be in the surface sediments were high in the nearshore stations and the activities of 210Pbex in the surface sediments increased from north to south. For 7Be, more than 90% was decayed before deposition into the surface sediment. However, most 210Pb (99%) was deposited into the sediment. Both7Be and 210Pb need to be input into the inner shelf by boundary scavenging processes to balance the budget.