Barium variation in Pagrus auratus (Sparidae) otoliths: A potential indicator of migration between an embayment and ocean waters in south-eastern Australia

Chronological variation in otolith chemistry can be used to reconstruct migration histories of fish. The use of otolith chemistry to study migration, however, requires knowledge of relationships between the chemical properties of the water and elemental incorporation into otoliths, and how water chemistry varies in space and time. We explored the potential for otolith chemistry of snapper, Pagrus auratus, to provide information on movement history between a large semi-enclosed bay, Port Phillip, and coastal waters in south-eastern Australia. Comparisons of water chemistry across two years demonstrated that ambient barium (Ba) levels in Port Phillip Bay were approximately double those in coastal waters (11 μg L⁻¹ versus 6 μg L⁻¹). Ba levels in otolith margins of wild juvenile snapper were highly positively correlated with ambient levels across 17 sampling locations, and levels in otolith margins of adult snapper collected from Port Phillip Bay were approximately double those of snapper collected in coastal waters. Mean partition coefficients for Ba (D_Ba) were similar for juvenile (0.43) and adult (0.46) otoliths, suggesting that otolith Ba incorporation relative to ambient levels was similar across life-stages. Low Ba variation across otoliths from adult snapper maintained in tanks for three years indicated that annual temperature and/or growth cycles did not strongly influence otolith Ba variation. We concluded that chronological Ba variation in snapper otoliths would be a reliable proxy for life-history exposure to variable ambient Ba. We used water chemistry data and Ba levels across otoliths of ocean resident snapper to estimate otolith Ba levels indicative of residence in Port Phillip Bay (>10 μg g⁻¹) or coastal waters (<6 μg g⁻¹). Peaks in Ba exceeding 10 μg g⁻¹ were common across otoliths of snapper collected in Port Phillip Bay and a nearby coastal region. The location of strong Ba peaks within otoliths was consistent with residence in Port Phillip Bay during the spring/summer when snapper move into the Bay from coastal waters to spawn. Our results for snapper support the use of otolith Ba as a proxy for ambient levels throughout the life-history, however, confident interpretation of migration history from otolith Ba chronologies will most likely require matching time series of ambient Ba in the water bodies of interest.     

Brine-induced mortality of non-indigenous invertebrates in residual ballast water

All transoceanic vessels entering the Great Lakes are required to manage ballast water and ballast tank residuals with ballast water exchange and tank flushing, respectively. While these management procedures effectively reduce the density and richness of biota in ballast waters and thereby reduce the risk of transferring non-indigenous species, some ships are unable to uniformly manage all tanks. Laboratory experiments were conducted to evaluate sodium chloride brine as an emergency treatment for ballast tanks with non-compliant residuals. Invertebrate communities collected from i) Detroit River, ii) exchanged ballast tanks arriving in the Great Lakes, and iii) North Sea ports, were exposed to a range of brine concentrations (15–115‰) until complete mortality was reached. Results indicate that a 1-h exposure to 115‰ brine is a broadly effective treatment (>99.9% mortality) regardless of treatment temperature, taxonomic group, or species’ source habitat salinity. A median of 0.00% (range 0.00–5.33) of individuals are expected to survive treatment and the expected number of viable individuals released after treatment is within Canadian and proposed international discharge standards. Before implementation, validation with ship-scale trials is recommended.     

Shipping traffic and introduction of non-indigenous organisms: Study case in two Italian harbours

In order to study the role of ballast water in introducing non-indigenous organisms in the Mediterranean Sea, the maritime traffic was analysed in the harbours of Naples and Salerno, which are important commercial ports in southern Italy. The 2001 data concerning the number of ships, the cruises’ length and the source of arrivals, were taken from harbours’ offices logbooks. In both harbours, the Mediterranean traffic was higher compared to the world sea-borne traffic that was mainly coming from North East Atlantic countries. The mean length of travels was of 1 week while the longest voyages were from Australia (3 weeks). A theoretical amount of ballast waters discharged during 1 year was provided by using an European model. A total of 55,738 and 118,339 ton of foreign ballast water are released annually in Naples and Salerno, respectively, to which theoretically correspond the entry of 4,977,403 (Naples) and 10,366,496 (Salerno) phytoplanktonic specimens.     

Ballasting outside port to prevent spread of butyltin from merchant ships

Most international discussions on ballast water management onboard ships have been virtually on the prevention of the transport of biotic alien species. This study focuses on how to improve this limited knowledge regarding the transport of butyltin compounds via ballasting. Butyltin compounds in ballast water, extracted from three sea-going merchant ships with similar voyage routes and berth ports but with different ballasting practices, were determined. Only monobutyltin (8–57 ng l^?1) and dibutyltin (10–32 ng l^?1) onboard two general cargo ships were detected in the ballast water taken outside the ports. In contrast, significant tributyltin (23–93 ng l^?1) was detected onboard the container ship in the ballast water pumped inside the loading/unloading ports. The comparison results from this study indicate that the risk of tributyltin transfer may be effectively prevented by ballasting outside the ports.     

Modelling of natural and synthetic polyelectrolyte interactions in natural waters by using SIT, Pitzer and Ion Pairing approaches

In this paper SIT and Pitzer models are used for the first time to describe the interactions of natural and synthetic polyelectrolytes in natural waters. Measurements were made potentiometrically at 25 °C in single electrolyte media, such as Et₄NI and NaCl (for fulvic acid 0.1 < I /mol L^− 1 < 0.75), and in a multi-component medium simulating the composition of natural waters at a wide range of salinities (for fulvic and alginic acids: 5 < S < 45) with particular reference to sea water [Synthetic Sea Water for Equilibrium studies, SSWE]. In order to simplify calculations, SSWE was considered to be a “single salt” BA, with cation B and anion A representing all the major cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) and anions (Cl⁻, SO₄²⁻) in natural sea water, respectively. The ion pair formation model was also applied to fulvate and alginate in artificial sea water by examining the interaction of polyanions with the single sea water cation. Results were compared with those obtained from previous speciation studies of synthetic polyelectrolytes (polyacrylic and polymethacrylic acids of different molecular weights). Results indicate that the SIT, Pitzer and Ion Pairing formation models used in studies of low molecular weight electrolytes may also be applied to polyelctrolytes with a few simple adjustments.     

Relationships between suspended particulate material, light attenuation and Secchi depth in UK marine waters

Measurements of sub-surface light attenuation (K_d), Secchi depth and suspended particulate material (SPM) were made at 382 locations in transitional, coastal and offshore waters around the United Kingdom (hereafter UK) between August 2004 and December 2005. Data were analysed statistically in relation to a marine water typology characterised by differences in tidal range, mixing and salinity. There was a strong statistically significant linear relationship between SPM and K_d for the full data set. We show that slightly better results are obtained by fitting separate models to data from transitional waters and coastal and offshore waters combined. These linear models were used to predict K_d from SPM. Using a statistic (D) to quantify the error of prediction of K_d from SPM, we found an overall prediction error rate of 23.1%. Statistically significant linear relationships were also evident between the log of Secchi depth and the log of K_d in waters around the UK. Again, statistically significant improvements were obtained by fitting separate models to estuarine and combined coastal/offshore data – however, the prediction error was improved only marginally, from 31.6% to 29.7%. Prediction was poor in transitional waters (D = 39.5%) but relatively good in coastal/offshore waters (D = 26.9%).SPM data were extracted from long term monitoring data sites held by the UK Environment Agency. The appropriate linear models (estuarine or combined coastal/offshore) were applied to the SPM data to obtain representative K_d values from estuarine, coastal and offshore sites. Estuarine waters typically had higher concentrations of SPM (8.2–73.8 mg l⁻¹) compared to coastal waters (3.0–24.1 mg l⁻¹) and offshore waters (9.3 mg l⁻¹). The higher SPM values in estuarine waters corresponded to higher values of K_d (0.8–5.6 m⁻¹). Water types that were identified by large tidal ranges and exposure typically had the highest K_d ranges in both estuarine and coastal waters. In terms of susceptibility to eutrophication, large macrotidal, well mixed estuarine waters, such as the Thames embayment and the Humber estuary were identified at least risk from eutrophic conditions due to light-limiting conditions of the water type.     

The carbon dioxide system and net community production within a cyclonic eddy in the lee of Hawaii

The dynamics of dissolved inorganic carbon (DIC) and processes controlling net community production (NCP) were investigated within a mature cyclonic eddy, Cyclone Opal, which formed in the lee of the main Hawaiian Islands in the subtropical North Pacific Gyre. Within the eddy core, physical and biogeochemical properties suggested that nutrient- and DIC-rich deep waters were uplifted by 80 m relative to surrounding waters, enhancing biological production. A salt budget indicates that the eddy core was a mixture of deep water (68%) and surface water (32%). NCP was estimated from mass balances of DIC, nitrate+nitrite, total organic carbon, and dissolved organic nitrogen, making rational inferences about the unobserved initial conditions at the time of eddy formation. Results consistently suggest that NCP in the center of the eddy was substantially enhanced relative to the surrounding waters, ranging from 14.1±10.6 (0–110 m: within the euphotic zone) to 14.2±9.2 (0–50 m: within the mixed layer) to 18.5±10.7 (0–75 m: within the deep chlorophyll-maximum layer) mmol C m⁻² d⁻¹ depending on the depth of integration. NCP in the ambient waters outside the eddy averaged about 2.37±4.24 mmol C m⁻² d⁻¹ in the mixed layer (0–95 m). Most of the enhanced NCP inside the eddy appears to have accumulated as dissolved organic carbon (DOC) rather than exported as particulate organic carbon (POC) to the mesopelagic. Our results also suggest that the upper euphotic zone (0–75 m) above the deep chlorophyll maximum is characterized by positive NCP, while NCP in the lower layer (>75 m) is close to zero or negative.     

Sorption model for dissolved and particulate aluminium in the Conway estuary, UK

Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, K_d, which varies from 0.67 × 10⁵ to 3.38 × 10⁶ ml g⁻¹ for suspended particle concentrations of 2–64 mg l⁻¹. The K_d values in general decrease with increasing suspended particulate matter and this tendency termed the “particle concentration effect” is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for K_d values of 10⁵, 10⁶ and 10⁷ ml g⁻¹ with various values of α. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with K_d value 10⁷ ml g⁻¹ and C₀ values 16 × 10⁻⁶ mg ml⁻¹ and 92 × 10⁻⁶ mg ml⁻¹. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.     

Photochemical production of molecular hydrogen in lake water and coastal seawater

Samples of lake water and coastal seawater from Nova Scotia, Canada, were irradiated with natural or artificial sunlight to investigate the potential for photochemical hydrogen production. Hydrogen photo-production was observed in all natural water samples. Rates of hydrogen formation were highest in coloured lake water (range: 98–163 pmol L^− 1h^− 1) and lower in seawater (range: 19–45 pmol L^− 1 h ^− 1). Dilutions of the most highly coloured lake sample (Kejimkujik Lake) showed a positive linear relationship between H₂ production rates and CDOM concentration. Photo-production rates normalised to UV absorption coefficients at 350 nm indicated that the photochemical efficiency of hydrogen formation varied between samples, perhaps due to differences in the CDOM composition. Photochemical hydrogen formation was also seen in solutions of syringic acid and acetaldehyde: two low-molecular-weight carbonyl compounds found in natural waters. Photochemistry may therefore offer least a partial explanation for the persistently high levels of hydrogen observed in the low-latitude surface ocean.     

A mesocosm experiment coupled with optical measurements to assess the fate and sinking of atmospheric particles in clear oligotrophic waters

It has recently been postulated that lithogenic particles such as Saharan dust strongly influence particulate organic carbon export to the deep ocean by acting as mineral ballast. However, our understanding of the processes involved remains scant. In the present study, optical measurements were performed to monitor variations in the concentration, composition and size distribution of particles in suspension within the water column after simulating a Saharan dust event in very clear Mediterranean waters off Corsica in June 2010. A new methodology set up in large mesocosms proved very successful in this regard. Values obtained simultaneously from three instruments (WetLabs ECO-BB3, WetLabs ac-9, Sequoia Scientific LISST-100) provided evidence that (1) part of the Saharan dust pool has a rapid settling velocity (∼24–86 m day⁻¹), (2) particulate export following a dust event is a nonlinear multi-step process and (3) export is controlled in part by the formation of organic-mineral aggregates. This experimental study provides the first insight of the complex export processes occurring after a dust event involving both physical and biogeochemical forcings in clear oligotrophic waters.     

Carbon cycling in a high-arctic marine ecosystem – Young Sound, NE Greenland

Young Sound is a deep-sill fjord in NE Greenland (74°N). Sea ice usually begins to form in late September and gains a thickness of 1.5 m topped with 0–40 cm of snow before breaking up in mid-July the following year. Primary production starts in spring when sea ice algae begin to flourish at the ice–water interface. Most biomass accumulation occurs in the lower parts of the sea ice, but sea ice algae are observed throughout the sea ice matrix. However, sea ice algal primary production in the fjord is low and often contributes only a few percent of the annual phytoplankton production. Following the break-up of ice, the immediate increase in light penetration to the water column causes a steep increase in pelagic primary production. Usually, the bloom lasts until August–September when nutrients begin to limit production in surface waters and sea ice starts to form. The grazer community, dominated by copepods, soon takes advantage of the increased phytoplankton production, and on an annual basis their carbon demand (7–11 g C m⁻²) is similar to phytoplankton production (6–10 g C m⁻²). Furthermore, the carbon demand of pelagic bacteria amounts to 7–12 g C m⁻² yr⁻¹. Thus, the carbon demand of the heterotrophic plankton is approximately twice the estimated pelagic primary production, illustrating the importance of advected carbon from the Greenland Sea and from land in fuelling the ecosystem.In the shallow parts of the fjord (<40 m) benthic primary producers dominate primary production. As a minimum estimate, a total of 41 g C m⁻² yr⁻¹ is fixed by primary production, of which phytoplankton contributes 15%, sea ice algae <1%, benthic macrophytes 62% and benthic microphytes 22%. A high and diverse benthic infauna dominated by polychaetes and bivalves exists in these shallow-water sediments (<40 m), which are colonized by benthic primary producers and in direct contact with the pelagic phytoplankton bloom. The annual benthic mineralization is 32 g C m⁻² yr⁻¹ of which megafauna accounts for 17%. In deeper waters benthic mineralization is 40% lower than in shallow waters and megafauna, primarily brittle stars, accounts for 27% of the benthic mineralization. The carbon that escapes degradation is permanently accumulated in the sediment, and for the locality investigated a rate of 7 g C m⁻² yr⁻¹ was determined.A group of walruses (up to 50 adult males) feed in the area in shallow waters (<40 m) during the short, productive, ice-free period, and they have been shown to be able to consume <3% of the standing stock of bivalves (Hiatella arctica, Mya truncata and Serripes Groenlandicus), or half of the annual bivalve somatic production. Feeding at greater depths is negligible in comparison with their feeding in the bivalve-rich shallow waters.     

Hydrobiological studies of the ballast waters of cargo ships in Russian Sea ports

The results of the first studies on the ballast waters of commercial vessels in Novorossiysk and Vladivostok ports are presented. Data on the composition of the flora and fauna, their abundance, viability, and the origin of the species were obtained. In the zooplankton from the ballast waters sampled in the Novorossiysk port, 31 species of holoplankton and 15 species of meroplankton were found. The total number of zooplankton varied from 1.3 to 60 thousand ind./m³. The Mediterranean basin, providing 62% of the ballast waters, represents a vector of the greatest risk. In the port of Vladivostok, in the ballast waters of the vessels of the Russian-Japanese and Russian-Chinese lines, 45 species of microalgae, 24 species of zooplankton, 22 species of meroplankton, and 10 groups of meiofauna were revealed. In addition, 24 species of microscopic filamentous fungi were identified and 28 morphologically distinguishable strains of bacteria were isolated (in total not less than 153 species). The basic “groups of risk” for bioinvasions in the basins of the Black Sea and the seas of the Far East were revealed. The need for control of ships’ ballast waters in Russia, which is presently lacking relevant national methodical guidelines and legislation, is substantiated.     

The shedding of mesoscale anticyclonic eddies from the Alaskan Stream and westward transport of warm water

The south-flowing waters of the Kamchatka and Oyashio Currents and west-flowing waters of the Alaskan Stream are key components of the western sub-Arctic Pacific circulation. We use CTD data, Argo buoys, WOCE surface drifters, and satellite-derived sea-level observations to investigate the structure and interannual changes in this system that arise from interactions among anticyclonic eddies and the mean flow. Variability in the temperature of the upstream Oyashio and Kamchatka Currents is evident by warming in mesothermal layer in 1994–2005 compared to 1990–1991. A major fraction of the water in these currents is derived directly from the Alaskan Stream. The stream also sheds large anticyclonic (Aleutian) eddies, averaging approximately 300 km in diameter with a volume transport significant in comparison with that of the Kamchatka Current itself. These eddies enclose pools of relatively warm and saline water whose temperature is typically 4 °C warmer and salinity is 0.4 greater than that of cold-core Kamchatka eddies in the same density range. Aleutian eddies drift at approximately 1.2 km d⁻¹ and retain their distinctive warm and salty characteristics for at least 2 years. Selected westward pathways during 1990–2004 are identified. If the shorter northern route is followed, Aleutian eddies remain close to the stream and persist sufficiently long to carry warm and saline water directly to the Kamchatka Current. This was observed during 1994–1997 with substantial warming of the waters in the Kamchatka Current and upstream Oyashio. If the eddies take a more southern route they detach from the stream but can still contribute significant quantities of warm and saline water to the upstream Oyashio, as in 2004–2005. However, the eddies following this southern route may dissipate before reaching the western boundary current region.     

Origin of iron and aluminium in large particles (> 53 µm) in the Crozet region, Southern Ocean

Natural iron fertilization processes are occurring around the Crozet Islands (46°26′S–52°18′E), thus relieving the water masses from the normally encountered High Nutrients Low Chlorophyll (HNLC) conditions of the Southern Ocean. During austral summers 2004/2005 and 2005/2006, iron and aluminium concentrations were investigated in large particles (> 53 µm) collected from just below the mixed layer at stations under the influence of island inputs, and also in adjacent HNLC waters. These large particles are anticipated to sink out of the mixed layer, and to reflect the net effects of input and cycling of these elements in the overlying mixed layer. Labile and refractory fractions were determined by a two-stage leaching technique. Data showed that water masses downstream of the islands were enriched in total iron and aluminium (0.25–2.68 nmol L^− 1 and 0.34–3.28 nmol L^− 1 respectively), relative to the southern HNLC control sites (0.15–0.29 nmol L^− 1 for Fe and 0.12–0.29 nmol L^− 1 for Al), with only a small fraction (typically < 1%) being acid leachable in both environments. Particulate iron predominantly derived from the island system represents a significant fraction of the total water column iron inventory and may complement dissolved Fe inputs that help support the high summer productivity around the Crozet islands.     

Distributions and seasonal variability of dissolved organic nitrogen in two estuaries in SW England

Nitrogen loadings to coastal waters have increased over the last century, resulting in deterioration in water quality. In this study we investigated the distributions and seasonality of dissolved organic nitrogen (DON), and its relationship to total dissolved nitrogen (TDN), for two anthropogenically influenced estuarine systems in southwest England. Concentrations of DON in both estuaries were generally < 80 μM. DON showed non-conservative distributions, resulting from external and internal inputs and in situ reactivity. DON contributed 38 ± 22% (range 4–79%, Yealm) and 36 ± 17% (range 4–84%, Plym) to the TDN pool, with lower values generally observed in the fresher samples relative to the more saline samples. DON was a larger fraction of the TDN pool during the summer and autumn relative to winter and spring, indicating the influence of bacterioplankton release on nitrogen cycling in the estuaries. Ammonification and nitrification were observed in the estuaries, processes which were reproduced in incubation experiments using bioreactors. The bioreactor experiments showed that 12% h^− 1 of the DON flux from the River Plym may be available to bacteria, indicating significant removal of DON during the residence time of the water in the estuary (a few days). The bioavailable nature of the DON means that this N fraction significantly adds to the eutrophication burden of the receiving coastal waters, and therefore cannot be ignored in environmental assessments.     

The behaviour of dissolved Cd, Co, Zn, and Pb in North Atlantic near-surface waters (30°N/60°W–60°N/2°W)

In September 1993 (M26) and June/July 1996 (M36), a total of 239 surface samples (7 m depth) were collected on two transects across the open Atlantic Ocean (224 samples) and northwest European shelf edge area. We present an overview of the horizontal variability of dissolved Cd, Co, Zn, and Pb in between the northwest and northeast Atlantic Ocean in relation to salinity and the nutrients. Our data show a preferential incorporation of Cd relative to P in the particulate material of the surface ocean when related to previously published parallel measurements on suspended particulate matter from the same cruise. There is a good agreement with results recently estimated from a model by Elderfield and Rickaby (Nature 405 (2000) 305), who predict for the North Atlantic Ocean a best fit for α_Cd/P=[Cd/P]_POM/[Cd/P]_SW of 2.5, whereas the approach of our transect shows a α_Cd/P value of 2.6. The Co concentrations of our transects varied from <5 to 131 pmol kg⁻¹, with the lowest values in the subtropical gyre. There were pronounced elevations in the low-salinity ranges of the northwest Atlantic and towards the European shelf. The Co data are decoupled from the Mn distribution and support the hypothesis of marginal inputs as the dominant source. Zinc varied from a minimum of <0.07 nmol kg⁻¹ to a maximum of 1.2 and 4.8 nmol kg⁻¹ in regions influenced by Labrador shelf or European coastal waters, respectively. In subtropical and northeast Atlantic waters, the average Zn concentration was 0.16 nmol kg⁻¹. Zinc concentrations at nearly three quarters of the stations between 40°N and 60°N were <0.1 nmol kg⁻¹. This suggests that biological factors control Zn concentrations in large areas of the North Atlantic surface waters. The Pb data indicated that significant differences in concentration between the northwest and northeast Atlantic surface waters presently (1996) do not exist for this metal. The transects in 1993 and 1996 exhibited Pb concentrations in the northeast Atlantic surface waters of 30 to 40 pmol kg⁻¹, about a fifth to a quarter of the concentrations observed in 1981. This decline is supported by our particle flux measurements in deep waters of the same region.     

Seasonal and depth-related dynamics of prokaryotes and viruses in surface and deep waters of the northwestern Mediterranean Sea

The study site located in the northwestern Mediterranean Sea was visited nine times in 2005–2006 to collect water samples from the epi- (5 m), meso- (200, 600 m), and bathypelagic (1000, 2000 m) zone. Total abundance of prokaryotes and viruses was determined by flow cytometry (FCM). Prokaryotic abundance in the epi-, meso-, and bathypelagic varied between 0.9 and 15.9×10⁵, 0.6 and 2.1×10⁵, and 0.3 and 1.3×10⁵ ml⁻¹, respectively. Variation of viral abundance in the epi-, meso-, and bathypelagic was between 1.2 and 57.5×10⁶, 0.5 and 3.5×10⁶, and 0.4 and 1.3×10⁶ ml⁻¹, respectively. The fraction of low (LNA) and high (HNA) nucleic acid prokaryotes averaged 42.9% and 57.1% throughout the water column and did not differ between depth layers. Throughout the water column the fraction of low, medium, and high fluorescent viruses (Vir-LF, Vir-MF, Vir-HF) averaged 66.3%, 30.2%, and 3.5%. Vir-LF and Vir-MF did not differ between depth layers; however, Vir-HF showed a preference for surface waters. The fraction of LNA cells decreased in the epi- and increased in the bathypelagic with decreasing stratification. The fraction of Vir-LF viruses increased in the epipelagic and decreased in the bathypelagic with increasing prokaryotic abundance. Also, the relationship between viral abundance and the bacterial community was different in surface and deep waters. The data suggest that different mechanisms of interaction between viruses and their prokaryotic hosts prevail at the surface and in deep waters.     

Sedimentation in mangroves and coral reefs in a wet tropical island, Pohnpei, Micronesia

A six-month-long study was conducted of the fate of turbid river plumes from the Enipein watershed in Pohnpei, Federated States of Micronesia. Pohnpei is one of the wettest places on earth, with a mean annual rainfall exceeding 4 m in the lowlands and 8 m in the highlands. The river waters were clear of sediment except after major storms with rainfall exceeding 5 cm day⁻¹. Following a storm, the river plume spread in the mangrove fringed estuary and in the coral reef lagoon. The waters were highly stratified in temperature, salinity, and suspended sediment concentration. The brackish water was flushed out in four days, while the suspended sediment all settled out in the estuary, in the mangroves, and in the lagoon including on the coral reefs, in less than one day. The mean rate of sedimentation exceeded 35 mg cm⁻² d⁻¹ both over the mangroves and on the adjacent coral reefs. While this leads to no detrimental effects on the mangroves, sediment smothers corals and leads to substantial coral mortality in the lagoon. The mud is not flushed out from the lagoon because there are no strong currents from waves or tides. This high sedimentation rate is attributable to poor farming and land-use practices on the upland areas.     

Daily variability of dissolved inorganic radiocarbon in Sargasso Sea surface water

Surface water samples were collected daily in June 2000 at a site in the Sargasso Sea to observe variability of Δ¹⁴C values in dissolved inorganic carbon (DIC). Temperature, salinity, DIC concentration, alkalinity, and δ¹³C and Δ¹⁴C values of DIC were measured in the samples. Ten Δ¹⁴C measurements averaged 81 ± 8‰ and had a range of 24‰ over the sixteen-day cruise. Δ¹⁴C values were more variable during the latter half of the cruise. Salinity and temperature measurements in the mixed layer throughout the cruise indicate that there were changes in water mass that occurred at our site. We conclude that the daily range of DIC Δ¹⁴C values in the surface ocean at our site is several times greater than the annual change in surface waters in the Sargasso Sea during the last two decades of the 20th century. This points to the importance of obtaining multiple measurements of the surface ocean to adequately define the true variability of DIC Δ¹⁴C measurements.     

Distributions, sources and atmospheric fluxes of nitrous oxide in Jiaozhou Bay

The distributions, sources and atmospheric fluxes of nitrous oxide (N₂O) in the seawater of Jiaozhou Bay were investigated during four surveys in 2003 to evaluate this area as a source of N₂O to the atmosphere. N₂O concentrations in both the surface and bottom waters of Jiaozhou Bay showed obvious variability with both seasons and tidal cycles. Atmospheric fluxes of N₂O in Jiaozhou Bay showed seasonal and spatial variations, with the highest values occurring in summer and the lowest in winter. The annual emission of N₂O from the bay was estimated to be 1.09 × 10⁶–2.23 × 10⁶ mol yr⁻¹. N₂O in the water column of Jiaozhou Bay was found to come from several external sources including riverine water, sewage water and groundwater input, among which the riverine input was dominant while the groundwater input was rather limited. The spatial variation in distribution and atmospheric fluxes of N₂O in Jiaozhou Bay was influenced by the input of polluted river waters and sewage effluent along the eastern coast, which highlights the effects of human impacts on N₂O emission rates.