Anthropogenic Pb in settling particulate matter in the Northwestern Pacific examined using stable isotopes of Pb

We have investigated Pb concentrations and isotopic compositions in settling particles collected by sediment traps experiments over a period of two years, from May 2005 to April 2007, at two depths, 770 and 5100 m, at station KNOT in the Northwestern Pacific Ocean (44°N, 155°E). To the identify provenances of Pb, the samples were separated into two fractions by chemical leaching techniques, with the leachate expected to contain Pb of anthropogenic origin. Isotopic compositions of Pb and concentrations of Pb, Sc, Mn, La, Yb, and Th were measured by quadrupole ICP-MS. The isotope ratios of leachable Pb in settling particles were ²⁰⁷Pb/²⁰⁶Pb = 0.860 ± 0.001; ²⁰⁸Pb/²⁰⁶Pb = 2.116 ± 0.002 (mean ± 95% confidence intervals), which are similar to those of aerosols in China that are greatly affected by pollution from coal combustion. We estimated the mean contribution from anthropogenic Pb sources to the Pb in settling particles, using the conventional binary (anthropogenic and natural Pb) mixing equation for Pb isotopes, as 90% in the upper trap and 78% in the lower trap. Furthermore, we found a significant negative correlation between the isotope ratios of Pb and concentrations of leachable Mn, normalized to those of leachable Pb, suggesting that manganese oxides play an important role in transporting Pb from the upper layers of the ocean to the deeper layers. Our results support the speculation published in a previous study that Pb might be scavenged by Mn oxides in the Northwestern Pacific Ocean.     

Sediment bioavailable organic matter,deposition rates and mixing intensity in the Setúbal–Lisbon canyon and adjacent slope (Western Iberian Margin)

The role of the Setúbal–Lisbon canyon in accumulation and transport of labile organic matter from the coastal sea and ocean surface water towards the deep sea was assessed by investigating the distribution of organic matter of different quality in sedimentary aggregates and surface sediments of the canyon and adjacent slopes. Total hydrolysable amino acids (THAA) and organic carbon (Corg) were measured from aggregates, and contents of Corg, chlorophyll a (chl a), phaeopigments (phaeo), chloroplastic pigment equivalents (CPE) from sediments. As indices of organic matter (OM) quality THAA:Corg, degradation index (DI), chl a:phaeo, chl a:Corg and C:N ratio were determined. Sediment profiles of chl a and the isotope 210 of lead (²¹⁰Pb) were used as tracers in a transport model to estimate deposition rates and background levels of the tracers, and sediment mixing rates (Db). Whereas bulk Corg contents of canyon and slope sediments were practically similar at all depths, higher contents of THAA, chl a and CPE, as well as higher THAA:Corg, DI and chl a:Corg, in aggregates and sediments from the upper reaches of the canyon indicate that labile organic matter accumulates in the upper canyon. This is confirmed by higher chl a and ²¹⁰Pb deposition and Db calculated from the model. Hence, the Setúbal–Lisbon canyon, specially the upper region, acts as a natural trap of organic matter that is transported to the region via lateral transport and vertical settling from primary productivity. Organic matter might be further transported in downward canyon direction via rebound processes. The chl a and ²¹⁰Pb profiles reveal active sediment mixing by physical processes and/or animal reworking.     

Isotope ratios of Pb/Pb in eelgrass, Zostera marina, indicate sources of Pb in an estuary

We deployed hydroponic eelgrass, Zostera marina L., to test its use as a sentinel accumulator and indicator of the source of water-borne lead (Pb) contamination in the marine environment. Eelgrass was deployed unrooted in the water column in the vicinity of the Portsmouth Naval Shipyard, located on Seavey Island in Portsmouth Harbor of New Hampshire and Maine, offshore from seepage sites near the Jamaica Island landfill (JIL). Deployed eelgrass, water samples from seepage sites, and sediment from the deployment sites were analyzed for Pb concentration and stable Pb isotopic composition. Isotopic composition was used to distinguish recent anthropogenic Pb inputs from background Pb in the estuary. Isotope ratios indicated that two groundwater seeps were a source of recent anthropogenic Pb (i.e. industrial Pb from the landfill) to Jamaica Cove. The eelgrass that showed the strongest presence of industrial Pb (having the lowest ²⁰⁶Pb/²⁰⁷Pb) was closest to a high volume seep that drained from the JIL and had a similar isotope signature as well as elevated Pb concentrations. These data confirm a source of water-borne industrial Pb in the estuary and show that eelgrass can function as a sentinel accumulator of Pb from anthropogenic sources.     

Identification of Pb sources in Yellow Sea sediments using stable Pb isotope ratios

Rapid economic developments in East Asian countries have inevitably resulted in environmental degradation in the surrounding seas, and concern for both the environment and protection from pollutants is increasing. Identification of sources of contaminants is essential to environmental pollution management. In this study, the provenance of anthropogenic lead (Pb), a major pollutant of Yellow Sea sediments, was determined for river mouth sediments, including those of the Changjiang, Huanghe, Han, and Geum Rivers, and for age-determined shelf core sediments through the measurement of Pb isotope ratios in the HCl-leached fraction using multi-collector inductively coupled plasma-mass spectrometry (MC ICP/MS). Anthropogenic Pb has accumulated in shelf core sediments since 1910, and its isotope ratios were estimated as 0.863–0.866 and 2.119–2.125 for ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb, respectively, from the mixing relationships of the two endmembers. River mouth sediments exhibited enough distinction in anthropogenic Pb isotope ratios to be discriminated: 0.874 (2.144) in the Huanghe, 0.856 (2.129) in the Han, 0.857 (2.122) in the Geum, and 0.854 (2.101) in the Changjiang for ²⁰⁷Pb/²⁰⁶Pb (²⁰⁸Pb/²⁰⁶Pb), respectively. Although isotope ratios of geogenic Pb in sediments dating before 1910 showed narrow ranges (0.842–0.845 and 2.088–2.100 for ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb, respectively), distinct isotope ratios in each core permitted source identification of sediments in the Yellow Sea based on geographic locations and the geogenic Pb of each river. By comparing the isotope ratios of the estimated anthropogenic Pb to source-related materials, the provenances of anthropogenic Pb in Chinese river sediments were presumed to be Chinese coal or ore, which is also a major source of atmospheric particulate Pb. The anthropogenic Pb in the shelf core sediments in the northern Yellow Sea originated from northern Chinese cities such as Beijing and Tianjin through atmospheric pathways. Pb isotope ratios indicated that Pb in Korean river sediments was characteristic of local Korean ores.     

Stable isotopic ratios of lead in surface waters of the Central Pacific

The geographic variation in the isotopic composition of lead in surface waters of the central Pacific provides new evidence of the global anthropogenic perturbation of the element's cycle. Ratios of ²⁰⁶Pb/²⁰⁷Pb decrease from 1.196 in the northern hemisphere (19°N, 158°W) to 1.176 in the southern hemisphere (15°S, 150°W). This decrease parallels the geographic variation in surface concentrations of soluble lead which decrease from 13 ng kg^?1 at the northern station to 4 ng kg^?1 at the southern station. Both the ²⁰⁶Pb/²⁰⁷Pb and the ²⁰⁶Pb/²⁰⁸Pb ratios of those waters fit between the isotopic ratios of Australian (Broken Hill) and North American (Mississippi Valley) leads which are the predominant sources of leads in anthropogenic emissions to the Pacific Ocean basin.     

渤海中部沉积物铅来源的同位素示踪

本研究对渤海中部表层和柱状沉积物中Pb的含量和同位素进行了分析,研究了其时空分布规律,并探讨了其物质来源。结果表明,表层沉积物中Pb的含量为14.54×10-6~59.42×10-6,其含量在渤海湾近岸、黄河口附近、研究区的东北部较高,而在研究区的中部和渤海湾北部含量较低;Pb同位素207Pb/206Pb的值为0.8341~0.8489,208Pb/206Pb的值为2.0828~2.0980。岩心沉积物中Pb含量、同位素组成与表层沉积物相似,整体上较为稳定,但在1990s以来呈现增大的趋势。渤海中部沉积物中Pb以自然来源为主,黄河沉积物是其主要物质来源,但渤海湾北端则与滦河源物质或沿岸侵蚀相关;人类活动影响主要出现在1990s以后,与中国含Pb矿石的燃烧等工业活动相关,但影响微弱,仅在黄河口西北近岸海域、渤海湾等个别站位得到体现。     

Decline in heavy metal contamination in marine sediments in Jakarta Bay,Indonesia due to increasing environmental regulations

The ²¹⁰Pb geochronology, heavy metal concentrations (Zn, Cu, and Pb), and stable Pb isotope ratios (²⁰⁶Pb/²⁰⁷Pb) of three sediment cores collected from Jakarta Bay were analyzed to decipher the history of heavy metal contamination in the period 1900–2006. The chemical and isotopic analyses clearly suggest that anthropogenic metal accumulation in the sediments began in the 1920s and increased greatly from the 1970s until the end of the 1990s. From the end of the 1990s to 2006, accumulation rates were constant or decreased for Zn and Pb near the coastal industrialized area. Comparison of economic data and sociological information suggests that the decline in the concentrations of heavy metals could be attributed to the stricter environmental regulations which were enforced at the end of 1990s. However, metal contamination is currently still an important cause of concern in dealing with environmental preservation and protection in Jakarta Bay.     

Tracing the origin of Pb using stable Pb isotopes in surface sediments along the Korean Yellow Sea coast

To investigate the factors controlling lead (Pb) concentration and identify the sources of Pb in Yellow Sea sediments along the Korean coast, the concentration of Pb and Pb isotopes in 87 surface and 6 core sediment samples were analyzed. The 1 M HCl leached Pb concentrations had a similar geographic distribution to those of fine-grained sediments, while the distribution of residual Pb concentrations resembled that of coarse-grained sediments. Leached Pb was presumed to be associated with manganese (Mn) oxide and iron (Fe) oxy/hydroxide, while residual Pb was associated with potassium (K)-feldspar, based on good linear relationships between the leached Pb and the Fe/Mn concentrations, and the residual Pb and K concentrations. Based on a ratio–ratio plot with three isotopes (²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb) and the geographic location of each sediment, sediments were categorized into two groups of samples as group1 and group2. Group 1 sediments, which were distributed in Gyeonggi Bay and offshore (north of 36.5°N), were determined to be a mixture of anthropogenic and natural Pb originating from the Han River, based on a ²⁰⁸Pb/²⁰⁶Pb against a Cs/Pb_leached mixing plot of core and surface sediments. Group 2 sediments, which were distributed in the south of 36.5°N, also showed a two endmembers mixing relationship between materials from the Geum River and offshore materials, which had very different Pb concentrations and isotope ratios. Based on the isotopes and their concentrations in core and surface sediments, this mixing relationship was interpreted as materials from two geographically different origins being mixed, rather than anthropogenic or natural mixing of materials with the same origin. Therefore, the relative percentage of materials supplied from the Geum River was calculated using a two endmembers mixing model and estimated to be as much as about 50% at 35°N. The spatial distribution of materials derived from the Geum River represented that of fine-grained sediments originating from the Geum River. It was concluded that Pb isotopes in sediments could be used as a tracer in studies of the origin of fine-grained sediments along the Korean Yellow Sea coast.     

210Pb sedimentation rates from the Northwestern Mediterranean margin

A total of 83 cores were collected in the Gulf of Lions continental margins and analysed for ²¹⁰Pb_xs (excess ²¹⁰Pb) in order to understand sedimentation patterns. Apparent sedimentation rates (ASR) range from 0.65 cm year⁻¹ in the vicinity of the Rhône River mouth to 0.01 cm year⁻¹ in the deep basin. Except for the prodelta area, rates decrease with depth linearly with the water depth. On the slope, ASR do not differ between canyons and open slope, except for the western area where the rates are slightly higher in the Lacaze–Duthiers canyon compared to its adjacent, open slope. In the canyon and open slope areas, mass accumulation rates determined from ²¹⁰Pb_xs profiles (0.10 and 0.08 g cm⁻² year⁻¹, respectively) are in good agreement with particulate fluxes calculated from 5 years of near-bottom sediment trap data, even when the trap particle fluxes and the apparent accumulation rates are overestimated in response to resuspension and bioturbation effects.However, differences in sediment trap data, between west and east portion of the slope, are not observed in the sedimentation rates calculated with ²¹⁰Pb_xs. The outer shelf area may have an important role in trapping sediment but it is not sufficiently documented. Sediment surface mixed layer depths decrease with water depth, with a mean value for the whole margin of 8±6 cm.²¹⁰Pb_xs inventories in the sediment are systematically higher than the net ²¹⁰Pb export flux estimated from the above water column. Over the margin, the ratio between accumulated ²¹⁰Pb and available ²¹⁰Pb is about 3, suggesting boundary scavenging effects and advective transport.     

Nematode diversity and its relation to the quantity and quality of sedimentary organic matter in the deep Nazaré Canyon,Western Iberian Margin

Samples collected in the deep Nazaré Canyon and at the adjacent slope, during the HERMES RRS Discovery D297 cruise (2005), were analysed for metazoan meiofauna, nematode structure and diversity and its relation to quality and quantity of sedimentary organic material. The amount and quality of organic matter available for direct consumption was much higher in the canyon compared to the slope and positively correlated with high nematode abundances (795–1171 ind. 10 cm^?2) and biomass (93.2–343.5 μg dry weight 10 cm^?2), thus leading to higher standing stocks. Canyon nematode assemblages also showed particular adaptations (e.g. higher trophic complexity, variability of nematode morphology, and presence of opportunistic genera) to canyon conditions, particularly in the deeper sediment layers. The Nazaré Canyon's nematode diversity was slightly lower than that of the adjacent slope and its assemblages were characterised by a higher dominance of certain genera. Still, the canyon contributes considerably to total Western Iberian Margin diversity due to different assemblages present compared to the slope. Furthermore, the harsh conditions in terms of hydrodynamic disturbance and the high organic matter flux are likely to have a negative impact on the establishment of species rich meiobenthic communities, especially in the canyon axis.     

Heavy metals in sinking particles and bottom sediments from the eastern Turkish coast of the Black Sea

Concentrations of Cd, Cu, Cr, Co, Ni, Zn, Fe, Mn, Pb, As, and Sb were determined in sediment trap and bottom sediment samples collected seasonally from a station on the eastern Turkish coast of the Black Sea. Cd, Pb and Mn concentrations were highest in the sediment trap samples except during the summer period, whereas Co, Ni, Zn and Fe levels were much lower than corresponding levels found in the surface sediments. Cu, Cr, As and Sb levels showed no definite trend with sediment type. In general, with the exception of Cr, relatively lower metal concentrations in the sediment trap material were determined in the summer period. The highest mass flux, 56.5 g m⁻² day⁻¹, was measured during autumn. The highest flux of heavy metals also occurred during autumn and was strongly dependent on particle mass flux. Based on these results, we suggest that the downward vertical transport of particulate heavy metals in this region is related to the high degree of land erosion and the resultant particulate flux dynamics, which occur here. It was noteworthy that the highest concentrations of Cd, Cu, Co, Zn, Fe and Sb in particles were measured during winter a finding which suggests that enhanced fossil fuel combustion, which occurs during this period in adjacent urban and industrial areas plays an important role in the metal composition of sinking particles in nearshore waters.     

Basin-scale seawater lead isotopic character and its geological evolution indicated by Fe-Mn deposits in the SCS

Abstract

The geochemical characteristics and Pb isotope variations in Fe-Mn deposits collected from the South China Sea (SCS) were studied in this paper. The mineralogical and chemical composition data indicate that the deposits are almost all hydrogenetic in origin. Compared with the Fe-Mn deposits in other oceans, the SCS Fe-Mn deposits have a significantly higher Pb content because of higher material supply in addition to a lower growth rate of the deposits. Pb isotope ratios in the surface of the SCS Fe-Mn deposits are relatively uniform, with a characteristic of relatively lower ²⁰⁶Pb/²⁰⁴Pb ratio. The Pb isotopic compositions of the SCS Fe-Mn deposits are controlled by the Pacific Deep Water and local inputs, which include eolian dust from the Asian continent and weathering products from Taiwan, Luzon and SCS submarine volcanic rocks. The continuously increasing ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios along the transect of nodule D581 over the past 3.5?Ma are affected by the stepwise closure of the Luzon Strait that reduced volcanic material supply and the deep current strengthen at the same time.     

Origin and variability of downward biogeochemical fluxes on the Rhone continental margin (NW mediterranean)

A one year study of downward particle fluxes conducted in the northwestern Mediterranean Sea is presented. Two mooring lines equipped with sediment traps and current meters were deployed at around 1000 m depth on the northeastern continental slope of the Gulf of Lions, one inside the Grand-Rhône canyon and the other outside on the adjacent open slope. Mean total mass fluxes increased slightly with trap depth inside the canyon, a feature quite typical of fluxes in continental margin environments. The near-bottom trap inside the canyon collected more material than its counterpart deployed at equivalent depth on the open slope, indicating a preferential transport of material within the canyon. Major biogeochemical constituents (organic and inorganic carbon, opal, and siliciclastic residue) revealed a marked difference in particle composition between the sub-surface (80 m) and deeper traps, suggesting the existence of at least two sources of material. The two shallower traps showed a clear biological signal: flux peaks were related to periods of surface biological production, especially perceptible in summer and autumn. The particulate matter trapped at deeper levels in the canyon and on the open slope was characterized by a more stable composition with a major lithogenic contribution, originating from sedimentary material most probably resuspended on the upper- or mid-slope. The seasonal variability was dominated by the summer/winter alternation; the latter period was characterized by a weak stratification of the water column and an enhanced current variability favoring vertical exchanges. The present results are compared with those obtained previously in the Lacaze-Duthiers canyon on the southwestern side of the Gulf of Lions. The comparison shows strong differences between the NE entrance and the SW exit of the gulf, with respect to the general along-slope circulation of water masses, both in terms of intensity of particulate fluxes and transport processes.     

Lead pollution in subtropical ecosystems on the SE Gulf of California Coast: a study of concentrations and isotopic composition

Lead pollution was investigated in environmental matrices and biological indicators collected from two typical subtropical coastal ecosystems in the southeast Gulf of California, Mexico. Lead concentrations and isotopic compositions ((206)Pb/(207)Pb and (208)Pb/(207)Pb) were measured using high resolution inductively-coupled plasma-mass spectrometry (HR-ICP-MS) and thermal ionization mass spectrometry (TIMS), respectively. Lead in surface estuary sediments (10.0-34.2microgg(-1)) and particulate Pb (25.0-128.7microgg(-1), >98% of total Pb) in the water column were significantly higher than levels in natural bedrock soils (15.1+/-8.3microgg(-1)) and river runoff (1.9+/-1.4microgg(-1)). Aquatic plants had Pb concentrations between 2.5 and 7.2microgg(-1), while those in macroalgae ranged from 3 to 5microgg(-1). The ranges of mean Pb concentrations in the aquatic animals studied (ranges in microgg(-1)) were as follows: zooplankton 32+/-3, mussels 2.3-3.9, oysters 1.9-7.9, snail 2.0-7.7, barnacles 0.1-18.5, fish 1.4-8.9, crab 6.3-40.2 and polychaetae 8.5-16.7. Pb values in 20-40% of oyster and fish samples and in all samples of crab exceeded acceptable levels for a food source for human consumption. Pb isotope ratios (206)Pb/(207)Pb, (208)Pb/(207)Pb in biota ranged from 1.188 to 1.206 and 2.448 to 2.470, respectively. A plot of (206)Pb/(207)Pb versus (208)Pb/(207)Pb for the environmental and biological samples collected from two study areas indicates that they contain lead from ores mined in Mexico and used in the past to produce leaded gasoline in use until 1997, natural Pb weathered from the Sierra Madre Occidental mother rock, and the later influence of inputs from a more radiogenic source related to industrial activity in the United States. Statistical software IsoSource results revealed that the Pb contained in environmental matrices and biomonitors is mostly derived from gasoline (20-90%) and US emissions (10-40%).     

Stable C and N isotopic composition of sinking particles and zooplankton over the southeastern Bering Sea shelf

Stable carbon and nitrogen isotopic composition of zooplankton, suspended particulate organic matter (SPOM), and sinking particles collected using sediment traps were measured for samples obtained from the southeastern Bering Sea middle and outer shelf during 1997–1999. The quantity of material collected by the middle shelf sediment trap was greater in both spring and late summer and fall than in early and mid-summer. The δ¹⁵N of SPOM, sinking material and zooplankton showed greater inter-annual variability at the middle shelf site (M2) than at the outer shelf site (M3). Zooplankton and sinking organic matter collected by M2 sediment traps became more depleted in ¹⁵N from 1997 through 1999, associated with a change from unusually warm to unusually cold conditions. Suspended and sinking organic matter and zooplankton collected from M3 decreased only slightly in δ¹⁵N from 1998 to 1999. SPOM, zooplankton, and sediment trap samples collected at M2 were usually enriched in δ¹⁵N and δ¹³C over those from M3. However, in 1999 sediment trap samples from the middle shelf were enriched in ¹³C over M3 material, but the δ¹⁵N of samples from the two sites was similar. The geographic pattern could be explained greater productivity over the middle shelf, associated with either isotopically heavy nitrogen being regenerated from sediments, or with utilization of a greater fraction of the available inorganic nitrogen pool during most years.     

Temporal and spatial variation in the Nazaré Canyon (Western Iberian margin): Inter-annual and canyon heterogeneity effects on meiofauna biomass and diversity

The Nazaré Canyon on the Portuguese Margin (NE Atlantic) was sampled during spring-summer for three consecutive years (2005–2007), permitting the first inter-annual study of the meiofaunal communities at the Iberian Margin at two abyssal depths (~3500 m and ~4400 m). Using new and already published data, the meiofauna standing stocks (abundance and biomass) and nematode structural and functional diversity were investigated in relation to the sediment biogeochemistry (e.g. organic carbon, nitrogen, chlorophyll a, phaeopigments) and grain size. A conspicuous increase in sand content from 2005 to 2006 and decrease of phytodetritus at both sites, suggested the occurrence of one or more physical disturbance events. Nematode standing stocks and trophic diversity decreased after these events, seemingly followed by a recovery/recolonisation period in 2007, which was strongly correlated with an increase in the quantity and bioavailability of phytodetrital organic matter supplied. Changes in meiofauna assemblages, however, also differed between stations, likely because of the contrasting hydrodynamic and food supply conditions. Higher meiofauna and nematode abundances, biomass and trophic complexity were found at the shallowest canyon station, where the quantity, quality and bioavailability of food material were higher than at the deeper site. The present results suggest that even though inter-annual variations in the sedimentary environment can regulate the meiofauna in the abyssal Nazaré Canyon, heterogeneity between sampling locations in the canyon were more pronounced.     

The nitrogen isotope biogeochemistry of sinking particles from the margin of the Eastern North Pacific

The nitrogen isotopic composition of time-series sediment trap samples, dissolved NO^-₃, and surficial sediments was determined in three regions along the margin of the eastern North Pacific: Monterey Bay, San Pedro Basin, and the Gulf of California (Carmen and Guaymas Basins). Complex physical regimes are present in all three areas, and each is influenced seasonally by coastal upwelling. Nevertheless, sediment trap material evidently records the isotopic composition of new nitrogen sources, since average δ¹⁵N is generally indistinguishable from δ¹⁵N values for subsurface NO^-₃. Surficial sediments are also very similar to the average δ¹⁵N value of the sediment traps, being within 1‰. This difference in δ¹⁵N between trap material and sediment is much less than the previously observed 4‰ difference for the deep sea. Better organic matter preservation at our margin sites is a likely explanation, which may be due to either low bottom O₂ concentrations or higher organic matter input to the sediments. All sites have δ¹⁵N for sub-euphotic zone NO^-₃ (8–10‰) substantially elevated from the oceanic average (4.5–5‰). This isotopic enrichment is a result of denitrification in suboxic subsurface waters (Gulf of California) or northward transport of denitrification influenced water (Monterey Bay and San Pedro Basin). Our results therefore suggest that downcore δ¹⁵N data, depending on site location, would record the intensity of denitrification and the transport of its isotopic signature along the California margin. Temporal variations in δ¹⁵N for the sediment traps do appear to respond to upwelling or convective injections of NO^-₃ to surface waters as a result of isotopic fractionation during phytoplankton uptake. Overall, though, the coupling between NO^-₃ injection, δ¹⁵N, and flux is looser than previously observed for the open-ocean, most likely the result of the smaller time/space scales of the events. In the Gulf of California, wintertime convective mixing/upwelling does produce distinct δ¹⁵N minima co-occurring with particle flux maxima. Interannual variations are apparent in this region when these winter-time δ¹⁵N minima fail to occur during El Niño conditions. There appears to be a positive relationship between the Southern Oscillation Index (SOI) anomaly and annual average δ¹⁵N. One explanation calls for hydrographic changes altering the δ¹⁵N of subeuphotic zone NO^-₃.     

Mass balance of lead through a small macrotidal estuary: The Morlaix River estuary (Brittany,France)

Dissolved and particulate lead were measured over an annual cycle (12 surveys between February 1998 and January 1999) in the Morlaix River estuary (Brittany, France). The concentrations were investigated in both the water column and the sediment of the river bottom in relation to hydrological conditions. In the water column, dissolved and particulate lead concentrations ranged from 0.1 to 4.4 nM and from 0.04 to 1.9 μmol g^− 1, respectively. Lead concentrations in surface sediment varied from 0.04 to 0.19 μmol g^− 1 and concentrations in the sediment pore water of the estuary were below the detection limit. Compared with the ranges known for pristine estuaries, concentrations of Pb in the water column of the Morlaix River estuary were found to be much higher. Concentrations of Pb also exceeded the lower range of those known for industrialized estuaries. Extensive agricultural activities in the drainage basin may be responsible for Pb levels above pristine conditions. Furthermore, the sediment appeared not to be contaminated. A mass balance was constructed quantifying all known sources and sinks for the Pb in the estuary. Riverine input accounts for most of the total annual metal flux. Burial in sediments was the major sink within the estuary, which acts as a trap especially for the particulate lead. The mass balance shows that the metal accumulation ranged between 414.6 and 446.0 kg year^− 1.     

Sources of sediment to the Neuse River estuary, North Carolina

The Neuse River estuary is part of the large Albemarle/Pamlico estuarine/lagoonal system (APES) of North Carolina. Exchange between the APES and the open ocean is restricted to inlets in the Outer Banks barrier islands. Freshwater discharge of the Neuse River is low in relation to the size of its estuary, so that the estuary is normally brackish over most of the area which accumulates fine-grained sediments. Mud (silt + clay) accumulation rates are low ( 6 mm year⁻¹).From the mud distribution and the dynamics of suspended sediment in the estuary it has been inferred that the Neuse retains fines efficiently, with probable episodic (high discharge) losses seaward, to Pamlico Sound.As part of a study of particle transport, deposition, and accumulation in the Neuse estuary, we have collected radiochemical data (10 cores) and chemical data (seven cores) on sediment cores from the main channel of the estuary between New Bern, North Carolina and the estuary mouth. K/Al increases in the lower estuary, consistent with earlier reports of increasing illite in the clay fraction. Landward transport of sediment from Pamlico Sound is the most plausible explanation for the increasing K/Al (illite). A marine sediment source may, therefore, be important for the lower estuary.The distribution of sediment inventories (quantities per cm² of sediment column) of particle-reactive radionuclides is consistent with the hypothesis of landward sediment transport. Inventories of excess ²¹⁰Pb, ¹³⁷Cs, and ^239,240Pu are coherent through the estuary and show the effects of particle redistribution processes on regionally uniform inputs. To obtain excess (anthropogenic) Zn and Cu, we use metal/Al normalization to estimate natural backgrounds. Anthropogenic metal inputs are concentrated at the head of the estuary, and sediment inventories of excess Zn and Cu generally decrease seaward. Normalization of the excess Zn and excess Cu inventories to excess ²¹⁰Pb inventories corrects the raw metal inventories for effects of lithology and sediment redistribution. The normalized excess Zn inventory decreases smoothly seaward, while the normalized excess Cu inventory shows an unexplained mid-estuary maximum. Low normalized inventories of anthropogenic metals at the estuary mouth indicate that little modern riverine sediment is stored there.Increasing K/Al (illite) and decreasing anthropogenic Zn and Cu in the lower estuary are thus both consistent with a predominantly marine sediment source. We conclude that landward transport of muds from Pamlico Sound has contributed significantly to the sediment balance of the lower Neuse estuary.     

Deep slope currents and suspended particle fluxes in and around the Foix submarine canyon (NW Mediterranean)

Deep slope currents and particulate matter concentrations were studied on the Barcelona continental margin in and around the Foix submarine canyon from May 1993 to April 1994. This year-long moored experiment revealed that near-bottom slope currents are strongly influenced by the bottom topography, being oriented along isobaths and along the canyon axis. The deep slope current fluctuations are controlled by the local inertial motion (18.3 h) and also by low-frequency oscillations at periods of 6–10 days, related to the passage of atmospheric pressure cells. Particulate matter concentrations recorded during the experiment do not show a clear seasonal variability, except outside the canyon, where significant peaks of particulate matter concentrations were recorded only during the winter-fall deployment. In addition, the temporal evolution of suspended particulate matter concentration is not linked to changes in the cross-slope or along-slope current components and did not show a clear relationship with river avenues or wave storm events. This suggests that suspended particulate matter exported from the shelf is dispersed on the slope by advective processes, which attenuate the signal of the shelf-slope sediment transfer. Mean particulate matter concentrations differed among sampling sites, but the magnitude of the mean horizontal suspended particle flux reflects a quite similar value in the whole study area, ranging from 2.53 to 4.05 mg m⁻² s⁻¹. These horizontal suspended particle fluxes are 27 (canyon head) to 360 (open slope) times higher than the settling particle fluxes measured at the same sampling sites, indicating that the suspended particulate transport on the Barcelona continental slope dominates over the settling particle fluxes, even inside the Foix submarine canyon.