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We present new data on the rates of sedimentary denitrification and its component processes (canonical denitrification, anammox and dissimilatory nitrate reduction to ammonium) for intertidal and subtidal sites in the North Sea using nitrogen isotope addition methods. We find overall average denitrification rates of 6.3 (range 0.4–10.6) µmol m−2 h−1, similar to those previously reported for this region and other temperate shelf environments. We find canonical denitrification to be the dominant (>90%) process of the three. At the subtidal sites, most of the denitrification is supported by nitrate generated within the sediments, while at the intertidal site the main source is from the water column. We go on to consider the impact of these rates on nitrogen cycling within the North Sea region and compare the sediment core incubation rate results to estimates derived from modelling approaches. Model rates are somewhat higher than those directly measured and we consider possible reasons for this.

Evidence shows that habitats with potential to mitigate against greenhouse gases emissions, by taking up and storing CO2, are being lost due to the effects of on-going human activities and climate change. The carbon storage by terrestrial habitats (e.g. tropical forests) and the role of coastal habitats (‘Blue Carbon’) as carbon storage sinks is well recognised. Offshore shelf sediments are also a manageable carbon store, covering ∼9% of global marine area, but not currently protected by international agreements to enable their conservation. Through a scenario analysis, we explore the economic value of the damage of human activities and climate change can inflict on UK marine habitats, including shelf sea sediments. In a scenario of increased human and climate pressures over a 25-year period, we estimate damage costs up to US$12.5 billion from carbon release linked to disturbance of coastal and shelf sea sediment carbon stores. It may be possible to manage socio-economic pressure to maintain sedimentary carbon storage, but the trade-offs with other global social welfare benefits such as food security will have to be taken into account. To develop effective incentive mechanisms to preserve these valuable coastal and marine ecosystems within a sustainability governance framework, robust evidence is required.

We briefly review the role of atmospheric deposition measurements within the Atlantic Meridional Transect (AMT) programme and then go on to present new data on the soluble concentrations of a range of trace metals (Fe, Al, Mn, Ti, Zn, V, Ni and Cu) and major ions in aerosols collected along the AMT transect. The results allow us to identify emission sources of the trace metals particularly in terms of the relative importance of anthropogenic versus crustal sources. We identify strong gradients in concentrations and deposition for both crustal and anthropogenically sourced metals with much higher inputs to the North Atlantic compared to the South Atlantic, reflecting stronger land based emission sources in the Northern Hemisphere. We suggest anthropogenic sources of Ni and V may include an important component from shipping. We consider the extent to which these gradients are reflected in surface water concentrations of these metals based on the GEOTRACES water column trace metal data. We find there is a clear difference in the concentrations of surface water dissolved Al and Fe between the north and south Atlantic gyres reflecting atmospheric inputs. However for Mn, V or Ni, higher inputs to the North Atlantic compared to the South Atlantic are not clearly reflected in their water column concentrations.

Total and soluble trace metal concentrations were determined in atmospheric aerosol and rainwater samples collected during seven cruises in the south-east Atlantic. Back trajectories indicated that the samples all represented remote marine air masses, consistent with climatological expectations. Aerosol trace metal loadings were similar to previous measurements in clean, marine air masses. Median total Fe, Al, Mn, V, Co and Zn concentrations were 206, 346, 5, 3, 0.7 and 11 pmol m− 3 respectively. Solubility was operationally defined as the fraction extractable using a pH 4.7 ammonium acetate leach. Median soluble Fe, Al, Mn, V, Co, Zn, Cu, Ni, Cd and Pb concentrations were 6, 55, 1, 0.7, 0.06, 24, 2, 1, 0.05 and 0.3 pmol m− 3 respectively. Large ranges in fractional solubility were observed for all elements except Co; median solubility values for Fe, Al and Mn were below 20% while the median for Zn was 74%. Volume weighted mean rainwater concentrations were 704, 792, 32, 10, 3, 686, 25, 0.02, 0.3 and 10 nmol L− 1 for Fe, Al, Mn, V, Co, Zn, Cu, Ni, Cd and Pb respectively (n = 6). Wet deposition fluxes calculated from these values suggest that rain makes a significant contribution to total deposition in the study area for all elements except perhaps Ni.

We consider here first the nature of nutrient transport through estuaries and in particular the capacity of estuaries to modify that flux. We then focus particularly on the Wash system in the UK as an example of a particular type of “small estuary”, and also consider some tropical estuarine systems in Malaysia. We present nutrient budgets for the Wash system now and create estimates of these budgets 3000 years ago. These show that currently the system is a small sink for fluvial nitrate (∼30% removal) largely due to denitrification and dissolved inorganic phosphorus (∼24%) by burial. 3000 years ago, prior to large scale human intervention to reclaim wetlands for agriculture, the Wash system was much bigger and operated as a sink for all terrestrial nitrogen (albeit with much lower inputs) and also a sink for nitrate from the North Sea, predominantly via organic nitrogen burial. A similar change with time is evident in the phosphorus flux. We suggest that this change in function of this estuarine system has been replicated in many other estuarine systems. Given the key role of benthic processes of burial and denitrification we go on to suggest that the classification of estuaries in terms of area and river flow may offer a route to a typology of estuarine nutrient retention efficiency.

Iron has been found to limit primary productivity in high nutrient, low chlorophyll regions of the oceans, including the Southern Ocean. Here we assess the relative magnitudes and geographical distributions of the sources of iron (sedimentary, atmospheric, icebergs and sea ice) to the Southern Ocean, and their impact on productivity. We present an iron cycling model, based on the assumptions of iron and light limitation of primary production, which is embedded in an eddy resolving ocean general circulation model. We find that the injection depth of the various iron inputs determines their availability for driving production because dissolved iron may be scavenged prior to it entering the illuminated mixed layer where it can drive primary production. The model suggests that production is predominantly regulated by sediment-derived iron sources rather than icebergs, sea ice or atmospheric dust. We note non-linear response in productivity to changes in the strength of one or more iron sources due to scavenging. Sea ice influences productivity by modifying the timing of iron supply to the euphotic zone. We also show that in the Scotia Sea the majority of productivity is driven by sediment-sourced iron from the Antarctic Peninsula, with additional local hotspots driven by island sources.

The results of fine mode ( 2 or methane sulphonic acid (MSA). Using our estimates of marine biogenic sulphate and measurements of MSA concentrations we confirm that the ratio of MSA/sulphate from DMS oxidation increases systematically from low to high latitudes, consistent with the laboratory measurements, inferences from field studies and modelling predictions of others.

Mineral dust is a complex entity containing a range of iron minerals including poorly crystalline to crystalline iron oxides to clay minerals. Important progress has been made to characterize iron mineralogical compositions in the dust recently. These include the quantification of the content of crystalline hematite and goethite, which appear to show a regional variation in North Africa as a result of the differences in the degree of chemical weathering. Fractional Fe solubility (dissolved to total iron, FFS) in the atmospheric aerosols has been reported to range from 0.1% to 80%. However, FFS is usually less than 0.5% in the non-atmospherically-processed dust, suggesting that FFS can be enhanced by atmospheric processes. One of the atmospheric processes, gravitational settling of dust, which has been previously hypothesized to cause the abovementioned enhancement of FFS during dust transport has been shown to be insignificant. Cycling of dust particles in the clouds, in which pH is usually higher than 4, and in the aerosol phase, in which pH is usually substantially lower, can significantly affect iron speciation and FFS. Laboratory experiments showed that a significant amount of iron (>0.5%) can only be solubilized in the dust when pH is lower than 4. These laboratory data suggest that acid processing rather than cloud processing might be a prime mechanism to cause an increase in FFS in the dust during transport. Further laboratory studies, field measurements, and modelling are needed to increase the ability of models to quantify the atmospheric processing of iron in the dust. (c) 2012 Elsevier B.V. All rights reserved.

This review considers the ways in which atmospheric organic nitrogen has been measured and linked to potential sources. Organic N exists in gas, particle and dissolved phases and represents a large (ca. 30%) fraction of total airborne nitrogen, but with large variability in time and space. Although some components (e.g. amines) have been the subject of several studies, little information is available for the many other components of organic N that have been identified in individual measurements. Measurements of organic N in precipitation have been made for many decades, but both sampling and chemical analytical methods have changed, resulting in data that are not directly comparable. Nevertheless, it is clear that organic N is ubiquitous and chemically complex. We discuss some of the issues which have inhibited the widespread adoption of organic N as a routine analyte in atmospheric sampling, and identify current best practice. Correlation analysis is the most widely used technique for attributing likely sources, examining the co-variation in time and/or space of organic N with other components of precipitation or particulate matter, yet the shortcomings of such simple approaches are rarely recognised. Novel measurement techniques which can identify, if not yet quantify, many of the components of particulate or dissolved organic N greatly enhance the data richness, thereby permitting powerful statistical analyses of co-variation such as factor analysis, to be employed. However, these techniques also have their limitations, and whilst specific questions about the origin and fate of particular components of atmospheric organic N may now be addressed, attempts to quantify and attribute the whole suite of materials that comprise atmospheric organic N to their sources is still a distant goal. Recommendations are made as to the steps that need to be taken if a consistent and systematic approach in identifying and quantifying atmospheric organic N is to progress. Only once sources have been recognised can any necessary control measures to mitigate adverse effects of atmospheric organic N on human health or ecosystem function be determined.

The aim of this study was to investigate the cycling of dissolved inorganic and organic nutrients using moored instrumented buoys (SmartBuoys) during the spring bloom in the North Sea. The instrumentation on the buoys enabled high frequency measurements of water-column integrated irradiance and in situ chlorophyll to be made, and also preserved water sample collection which were used for dissolved inorganic and organic nutrient analyses. The SmartBuoys were located in the year-round well-mixed plume zone associated with the River Thames and in the summer stratified central North Sea. These site locations allowed comparison of nutrient concentrations and cycling, and spring bloom development at two contrasting sites. The spring bloom was expected to be initiated at both stations due to increasing insolation and decreasing suspended load leading to higher water-column integrated irradiance. Due to differences in suspended load between the sites, the spring bloom started ∼2 months earlier in the central North Sea. The spring bloom in the Thames plume also resulted in higher maximum phytoplankton biomass due to the higher pre-bloom nutrient concentrations associated with riverine input. The use of SmartBuoys is also shown to allow the cycling of dissolved organic nutrients to be examined over the critical, and often undersampled, spring bloom period. Dissolved Organic Nitrogen (DON) clearly increased during the spring bloom in the central North Sea compared to winter concentrations. DON also increased in the Thames plume although showing greater winter variability related to higher riverine and sedimentary dissolved organic matter input at this shallow (∼18 m) coastal site. DON increase during the spring bloom was therefore related to primary production at both sites probably due to active release by phytoplankton. At both stations DON decreased to pre-bloom concentrations as the bloom declined suggesting the released DON was bioavailable and removed due to heterotrophic uptake and production. The preserved nutrient samples from the central North Sea site were also suitable for Dissolved Organic Phosphorus (DOP) analysis due to their low suspended load with similar trends and cycling to DON, albeit at lower concentrations. This suggested similar processes controlling both DON and DOP. The variable timing of short term events such as the spring bloom makes sampling away from coastal regions difficult without the use of autonomous technology. This study demonstrates for the first time the applicability of using preserved samples from automated buoys for the measurement of dissolved organic nutrients.

The aims of the Atlantic Meridional Transect (AMT) Programme [www.amt-uk.org] are to quantify the nature and causes of ecological and biogeochemical variability in the planktonic ecosystems of the Atlantic Ocean, and to assess the effects of this variability on biological carbon cycling and air–sea exchange of radiatively active gases and aerosols (Fig. 1). Since 1995, marine and atmospheric data have been collected twice a year along a 13,500 km transect between 50°N and 52°S in the Atlantic Ocean. This transect encompasses a range of biogeographical provinces including the subtropical gyres and the equatorial and coastal upwellings. The sampling strategy is described in Robinson et al. (2006a), and for the last six cruises has involved continuous surface seawater and atmospheric sampling, and twice daily deployment of the CTD, bio-optical sensor rig and mesozooplankton nets. Up to 70 determinands were measured on each cruise (see Table 2 in Robinson et al., 2006a). The programme has included 18 research cruises, involving 180 scientists from 11 countries (Fig. 2), contributing to 170 refereed publications and 70 Ph.D. theses. This unique, spatially extensive, decadal dataset continues to be made available to the wider community through the British Oceanographic Data Centre (BODC) (www.bodc.ac.uk).

Concentrations of dissolved iron (DFe) and Fe-binding ligands were determined in the tropical Northeast Atlantic Ocean (12–30°N, 21–29°W) as part of the UK-SOLAS (Surface Ocean Lower Atmosphere Study) cruise Poseidon 332 (P332) in January–February 2006. The surface water DFe concentrations varied between 0.1 and 0.4 nM with an average of 0.22 ± 0.05 nM (n = 159). The surface water concentrations of total Fe-binding ligands varied between 0.82 and 1.46 nM with an average of 1.11 ± 0.14 nM (n = 33). The concentration of uncomplexed Fe-binding ligands varied between 0.64 and 1.35 nM with an average of 0.90 ± 0.14 nM (n = 33). Thus, on average 81% of the total Fe-binding ligand concentration was uncomplexed. The average logarithmic conditional stability constant of the pool of Fe-binding ligands was 22.85 ± 0.38 with respect to Fe3+ (n = 33). A transect (12°N, 26°W to 16°N, 25.3°W) was sailed during a small Saharan dust event and repeated a week later. Following the dust event, the concentration of DFe increased from 0.20 ± 0.026 nM (n = 125) to 0.25 ± 0.028 (n = 17) and the concentration of free Fe-binding ligands decreased from 1.15 ± 0.15 (n = 4) to 0.89 ± 0.10 (n = 4) nM. Furthermore, the logarithmic stability constants of the Fe-binding ligands south of the Cape Verde islands were distinctively lower than north of the islands. The absence of a change in the logarithmic stability constant after the dust event south of the Cape Verde islands suggests that there was no significant atmospheric input of new Fe-binding ligands during this dust event.

The annual phytoplankton bloom occurring north of the Crozet Plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high-nutrient low-chlorophyll (HNLC) conditions normally associated with the Southern Ocean. Therefore, during CROZet natural iron bloom and EXport experiment (CROZEX), a large multidisciplinary study performed between November 2004 and January 2005, measurements of total dissolved iron (DFe⩽0.2 μm) were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples. DFe concentrations were determined by flow injection analysis with N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD) catalytic spectrophotometric detection. DFe concentrations varied between 0.086 and 2.48 nM, with low values in surface waters. Enrichment of dissolved iron (>1 nM) at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron. Waters farther north also appear to be affected by this input of coastal and shelf origin, although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of ∼0.07 nM km−1 at the time of sampling. Using lateral and vertical diffusion coefficients derived from Ra isotope profiles and also estimates of atmospheric inputs, it was then possible to estimate a DFe concentration of ∼0.55 nM to the north of the islands prior to the bloom event, which is sufficient to initiate the bloom, the lateral island source being the largest component. A similar situation is observed for other Sub-Antarctic Islands such as Kerguelen, South Georgia, that supply dissolved iron to their surrounding waters, thus enhancing chlorophyll concentrations.

Ammonium (NH4 ) concentration was measured at 15 stations in the NE Atlantic during the declining phase of the spring diatom bloom as part of the FISHES 2001 cruise. The NE Atlantic temperate spring bloom is one of the largest seasonal events in the oceanic cycle of primary productivity and represents the conversion of large amounts of oxidized nitrogen to organic (reduced) nitrogen by planktonic photosynthesis, much of which is recycled by heterotrophs as reduced N (DON and ammonium). We might expect recycled ammonium to be rapidly re-used by photosynthesizers. However, during the FISHES cruise the decline of the bloom was accompanied by a substantial buildup of dissolved ammonium (from ∼100 nM to >500 nM near the sea surface) caused by a temporary imbalance in production and consumption processes. Calculations of air–sea ammonia (NH3) flux under assumed ‘normal ’‘ peak bloom’ and ‘post-diatom-bloom’ conditions are presented and these demonstrate that over a wide range of temperatures, post-bloom accumulation of ammonium will lead to changes in the magnitude and direction of air–sea ammonia flux. If our results are generally applicable then the seasonal succession of plankton communities may be accompanied by periods of anomalously high ammonium concentration and hence be disproportionately important for air–sea ammonia flux. Once in the atmosphere, ammonia neutralizes acidity and in doing so plays a potentially significant role in climate forcing via aerosol formation.

A hydrodynamic model is developed for the Blackwater estuary (UK) and used to estimate nitrate removal by denitrification. Using the model, sediment analysis and estimates of sedimentation rates, we estimate changes in estuarine denitrification and intertidal carbon and nutrient storage and associated value of habitat created under a scenario of extensive managed realignment. We then use this information, together with engineering and land costs, to conduct a cost benefit analysis of the managed realignment. This demonstrates that over a 50–100 year timescale the value of the habitat created and carbon buried is sufficient to make the large scale managed realignment cost effective. The analysis reveals that carbon and nutrient storage plus habitat creation represent major and quantifiable benefits of realignment. The methodology described here can be readily transferred to other coastal systems.

The presence of a surface iodide maximum in seawater is commonly attributed to biological activity, however laboratory studies on the influence of phytoplankton on inorganic iodine speciation have yielded somewhat contradictory results. Here, we report changes in the speciation of inorganic dissolved iodine in nutrient-enriched seawater during the growth of a variety of phytoplankton taxa, including the cold water pennate diatoms Nitzschia and Navicula. Unialgal batch cultures were grown under axenic conditions in f/20 media; iodate was kept at ambient seawater levels or raised to 10 μM. The ability of algal cultures to reduce iodate to iodide varied considerably between the different algal species studied. Nitzschia sp. cultures removed close to 100% of iodate from growth media and produced iodide at rates of 0.03 and 3 nmol I μg chl-a− 1 day− 1 at ambient and elevated iodate levels, respectively. At elevated iodate levels, iodate depletion in Nitzschia cultures was matched by iodide production such that applying a linear regression to the concentrations of the two iodine species gave slopes of − 1 with R2 values greater than 0.9. At ambient iodate levels, only 50 to 100 nM of iodide was produced in Nitzschia cultures despite more than 200 nM of iodate being consumed, suggesting production of some other iodine species. Additionally, iodide levels peaked at the end of the exponential growth phase suggesting that an iodide consuming mechanism began to operate in the stationary growth phase. Cultures of the cold water diatom Navicula sp. and the temperate phytoplankton Emiliania huxleyi, Thalassiosira pseudonana and Dunaliella tertiolecta also exhibited iodate uptake, although the extent of this was variable and always less than in the Nitzschia cultures. Navicula and E. huxleyi also showed iodide production at both ambient and elevated iodate levels, but T. pseudonana and D. tertiolecta did not. In both the cold water algal cultures 50% to 100% of the lost iodate appeared to have been converted to an organic or particulate form, or lost by volatilisation.

Atmospheric concentrations of trace metals over the oceans are investigated through analysis of aerosol samples collected during cruises from the UK to the Falkland Islands and from South Africa to Australia. The readily soluble concentrations of Cu (4–256 pmol m−3), Ni (0.1–54 pmol m−3), Ba (0.2–60 pmol m−3), Zn (6–316 pmol m−3), Cd (0.01–0.29 pmol m−3) and Pb (0.4–22 pmol m−3) were measured in the aerosols, along with total concentrations of crustal elements (Fe, Al and Mn) to evaluate the crustal contributions. Air mass back trajectories suggested most of the aerosol samples had spent several days over the ocean prior to collection. The highest metal concentrations were observed in aerosols close to South Africa, Australia and major cities in South America, although these concentrations were lower than had been reported previously in the literature. Apart from Ba, which had a major crustal source, the trace metals were enriched relative to crustal sources in most samples, including some collected thousands of kilometers from emission sources. The mean trace metal concentrations in the remote Indian Ocean were lower than those measured in the Atlantic Ocean. Even lower concentrations are reported in the literature for the remote Pacific Ocean. In contrast to previous studies, no clear north–south gradient is observed in the concentrations of the trace metals in the aerosols. Lead isotope measurements were also carried out on aerosol samples using a multicollector inductively coupled plasma mass spectrometer to assist in source apportionment. Clear differences were noted in the isotope ratios collected on either side of the Indian Ocean with Australian lead ore dominating over much of the eastern and mid-southern Indian Ocean. Samples collected over the western Indian Ocean and Atlantic Ocean under South African influence had lead isotopes quite different from those seen in South African cities in the past, and are closer in ratio to the coal signature of the region.

The atmosphere can be an important source of nutrients to remote ocean waters, e.g., in supplying iron to nitrogen fixers in the tropical North Atlantic. We use results obtained from aerosol collection during four meridional transect cruises of the Atlantic Ocean in an attempt to identify sources of soluble nutrient species (Fe, N, P and Si) to the Atlantic atmosphere. The Sahara desert was the dominant source of soluble aerosol Fe and Si and also a significant source of aerosol P. Biomass burning and another source, possibly primary particles derived from vegetation, also contribute to the aerosol P loading. Industrial (NOx) and agricultural (ammonium) sources contribute to high nitrogen concentrations in the northern hemisphere, while biomass burning appears to be a significant seasonal source of N to the southern hemisphere. This work is an initial step in our aim to describe the atmospheric nutrient inputs to the Atlantic basin using a much larger set of aerosol and rain samples that will be obtained during the Atlantic Meridional Transect (AMT) project and other field campaigns. © 2006 Elsevier Ltd. All rights reserved.

The aims of the Atlantic Meridional Transect (AMT) programme [www.amt-uk.org] are to quantify the nature and causes of ecological and biogeochemical variability in the planktonic ecosystems of the Atlantic Ocean, and to assess the effects of this variability on biological carbon cycling and air–sea exchange of radiatively active gases and aerosols. Marine and atmospheric data have been collected twice a year along a 13,500 km transect in the Atlantic Ocean between 50°N and 52°S since 1995. The cruise track enables biogeochemical measurements to be made within the poorly studied North and South Atlantic oligotrophic gyres as well as within equatorial and coastal upwelling regions. The range of ecosystems sampled during AMT has facilitated the calibration and validation of newly developed optical, microbiological, molecular and analytical techniques and provided a testbed for comparative ecology and the development of atmospheric and oceanographic models. This paper describes the rationale and methodology of the programme. Upper-ocean measurements of density, nitrate and chlorophyll a (Chl a) are presented to illustrate seasonal, inter-annual and decadal variability in hydrography. Seasonal distributions of dissolved nitrous oxide (N2O) and methane (CH4) are used to derive estimates of the sea–air flux of these gases in the South Atlantic Gyre. Observations made during AMT and published since 2000 are reviewed, and the key findings are highlighted. The extent to which the programme aims have been achieved is discussed and improvements for the future suggested.

Increasing inputs of reactive nitrogen have led to excessive phytoplankton growth in some coastal waters. Until recently, rivers were thought to be the most important nitrogen source but we now know that atmospheric inputs are large and can equal, or exceed, those from the rivers. These atmospheric nitrogen compounds have both agricultural sources (ammonia emitted from animal wastes) and combustion sources (nitrate derived from NOx emitted by vehicles and power stations). Our hypothesis is that atmospheric nitrogen deposition in summer to nutrient depleted, well lit, surface waters in coastal seas stimulates phytoplankton blooms. This paper summarises and compares studies conducted in the North Sea, the North East Atlantic Ocean and the Kattegat Sea. Budgeting approaches imply that the atmosphere can, under certain meteorological conditions and over short time periods, provide enough nitrogen to support a large increase in phytoplankton growth. This is not true in all areas and at all times and this emphasises the highly episodic nature of atmospheric deposition. However, productivity-based approaches suggest that atmospheric nitrogen inputs have little effect on phytoplankton growth. This may be because productivity in the North Sea and the Kattegat is controlled by internal recycling of nitrogen, even in the summer when inorganic nitrogen levels are very low. Over longer time scales, atmospheric inputs do increase the overall nitrogen stock in the water column. Reducing the input of nitrogen from the atmosphere will, therefore, reduce total nitrogen loads to coastal seas and hence may decrease eutrophication problems.

A new method is presented to analyse the isotopic abundance of organic matter in aerosols. The method involves water extraction of aerosol filters, elution through an ion retardation resin to remove inorganic components and lyophilising the eluent to concentrate the fraction prior to isotopic analysis. Results of analyses of a series of aerosol samples collected in the UK, for the fraction of organic matter passing through the resin, are presented. Carbon and nitrogen isotopic abundances ranged from −23.0‰ to −35.5‰ (versus PDB) and −14.6‰ to +12.5‰ (versus AIR), respectively.

This review considers the nature and relative importance of atmospheric, groundwater and riverine inputs of nitrogen, phosphorus and silicon, and how these influence coastal eutrophication pressures. The effect of modification of riverine fluxes within estuaries is also discussed. The extent of the perturbation of these fluxes by human activity is considered along with possible future changes in the fluxes.

This paper reviews what is presently known about sediment contamination in the macro-tidal Humber estuary on the east coast of the UK, with particular reference to the trace elements arsenic, copper, lead and zinc. The Humber is a post-industrial estuary, with an industrial and mining legacy of contaminated sediments throughout the river catchment. Surface and near-surface sediments in the estuary also show significant contamination of trace metals over background values. Inputs of dissolved and particulate trace elements to the estuary from the rivers are reviewed, and atmospheric deposition to the catchment and estuary calculated as a potential additional source of contamination. The necessity of maintaining the sediment balance within the estuary means that contaminated sediments dredged from the estuary harbours are deposited to other sites within the estuary, rather than being removed. Trace metal concentrations in recent dredged sediments, and sediments from the period of peak contamination in the 1970s, are compared with background values. Current inputs to the estuary from point sources, and trends over the last decade are considered. Our calculation of the current depositional fluxes of trace metals to the estuary intertidal sediments, and comparison with the inputs, reveals that the estuary sediments are today capable of storing 55–97% of the input load of As, 15–27% of the Cu, 17–50% of the Pb and 11–12% of the Zn annually. Sediment quality in the estuary is currently far from its 'background' state with respect to trace metals. This has implications for the future water and sediment quality of the Humber under the terms of the EU Water Framework Directive. One management option being considered to improve sea defences in the estuary, managed realignment, may also act to dilute contaminated sediments in the estuary, and thereby to improve future water quality. We look at the effect on sediment contaminant storage of three possible future managed realignment scenarios.

Nitrate and ammonium uptake rates were measured during a series of cruises in the well-mixed region of the southern North Sea from February to September. Water column-integrated uptake rates ranged between 0.01 and 8.7 mmol N m−2 d−1 and 0.01 and 12.2 mmol N m−2 d−1 for nitrate and ammonium, respectively, with ammonium uptake dominating after the phytoplankton spring bloom in May. A moored buoy continuously measuring nitrate and chlorophyll a and seabed current meters were also deployed in the central southern North Sea in the region of the East Anglian plume—a permanent physical feature which transports nutrients towards continental Europe. This enabled the flux of water and hence of nutrients across the southern North Sea to be determined and an assessment of the contribution of freshwater nutrients to the flux to be made. A simple box model is developed to relate the phytoplankton uptake of nitrate and ammonium to the transport of nitrate, ammonium and particulate organic matter (POM) across the southern North Sea. This showed the importance of the plume region of the North Sea in the processing of nitrogen, with nitrate dominating total nitrogen transport prior to the spring bloom ( 10 340×10 3 kg N inflow to the plume in March) and transport of nitrogen as ammonium, nitrate and POM in approximately equivalent amounts during summer (2560, 2960 and 2151×10 3 kg N inflow to the plume, respectively, in July). The box model also demonstrates more generally the need to assess nitrogen transport as nitrate, ammonium and POM if an improved understanding of the impact of nutrient input in shelf seas is to be achieved.

Atmospheric iron and underway sea-surface dissolved (

Despite over a century of published reports of dissolved organic nitrogen (DON) in precipitation, its implications are still being appraised. The number of studies focusing on atmospheric organic nitrogen deposition has increased steadily in recent years, but comparatively little has been done to draw together this disparate knowledge. This is partly a consequence of valid concerns about the comparability of analysis and sampling methodologies. Given the current global trends in anthropogenic nitrogen fixation, an improved qualitative and quantitative understanding of the organic nitrogen component is needed to complement the well-established knowledge base pertaining to nitrate and ammonium deposition. This global review confirms the quantitative importance of bulk DON in precipitation. This cumulative data set also helps to resolve some of the uncertainty that arises from the generally locally and temporally limited scale of the individual studies. Because of analytical and procedural changes in recent decades, assessments are made of the comparability of the data sets; caution is needed in comparisons of individual studies, but the overall trends in the compiled set are more robust. Despite the large number of reports considered, evidence for long-term temporal changes in rainwater organic nitrogen concentrations is ambiguous. With regard to sources, it is likely that some of the organic material observed is not locally generated, but undergoes extensive or long-range atmospheric transport. The compiled data set shows a land-to-sea gradient in organic nitrogen concentration. Possible precursors, reported data on the most likely component groups, and potential source mechanisms are also outlined.

Emissions from the Black Triangle Region were considered to be the major source of air pollution problems in Europe during the 1990s. This discussion reviews the changes in emissions and pollution concentrations in the Krusne Hory Region (Czech Republic) in the winter half of the year during most of the past decade, and describes the relationships with meteorology. Sulfur dioxide (SO2) is used as the example pollutant. The results show a decrease in pollution concentrations since 1996, as air pollution control and management strategies for important point sources take effect. The winter of 1995–1996 was especially harsh in the number of pollution episodes. Correlations between SO2 and meteorological parameters are inconsistent. Wind direction provides the best relationship at monitoring stations along the Krusne Hory Plateau, with wind speed and temperature more variable depending on month and location. For the valley stations, higher SO2 concentrations are strongly related to colder temperatures, higher relative humidities, and lower wind speeds. A case study during the winter of 1995–1996 (November 9–15) illustrated the importance of synoptic high pressure and a low-level inversion in minimizing plume dispersion from point sources. Specific sources of SO2 affecting each station could thus be identified.

The study of aerosols and rainwater presented here demonstrates that episodic atmospheric deposition events associated with southeasterly flow are quantitatively significant for large areas of the North Atlantic Ocean. This paper considers aluminium and manganese, with predominantly crustal sources, and lead and zinc, which are mobilised into the atmosphere primarily through anthropogenic activity. High levels of all trace metals are associated with southeasterly flow from Europe as the air passes over heavily populated and industrialised regions before reaching the northeast Atlantic Ocean. Fluxes calculated using the 1% HNO3 acid soluble metal concentration show that, although the climatological norm for this area is westerly flow, short-lived southeasterly transport events dominate the input of trace metals to this ocean region. This material may be toxic to phytoplankton or may be represent a new source of nutrients to the biological community. A significant decrease in atmospheric lead levels in polluted air is seen between June 1996 and May 1997, reflecting the decrease in use of leaded fuels in Europe. Comparing atmospheric flux values to sediment trap metal fluxes shows that the atmosphere represents the dominant source of zinc to the deep ocean, whereas an additional, non-atmospheric, manganese source this required, perhaps from mobilisation of sedimentary material from the continental shelf or long range advection of manganese rich Saharan material.

Atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters. Stable nitrogen isotope data can provide important information regarding the sources and processing of atmospheric fixed-nitrogen species and is thus important in controlling eutrophication. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland and also aboard the RRS Challenger in the Eastern Atlantic Ocean. Aerosol concentrations of ammonium and nitrate were determined prior to δ 15 N isotopic analysis. The isotopic enrichment factor, e , was calculated for both the species by subtracting the respective δ 15 N values of the coarse-mode fraction (>1 μm diameter) from those of the fine-mode fraction ( 4 NO 3 followed by scavenging of the HNO 3 produced appears to be significantly more important than in samples of onshore, marine dominated air. In contrast, ammonium appears to be transferred to the coarse mode during offshore flow largely via the dissolution and coagulation of aerosol ammonium, nitrate and sulphate-containing species. During onshore flow, the uptake of gaseous NH 3 , arising from the continued dissociation of NH 4 NO 3 , seems to become increasingly important.

Direct atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters and can be enhanced by heterogeneous reactions between gaseous atmospheric nitrogen species and aerosol sea salt, which increase deposition rates. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland. Major-ion aerosol concentrations were determined and temporal patterns were interpreted with the use of air-mass back trajectories. Low levels of terrestrially derived material were seen during periods of clean, onshore flow, with respective concentration ranges for nitrate and ammonium of 0.47–220 and below detection limit to 340 nmol m −3 . Corresponding levels of marine derived material during these periods were high, with sodium concentrations ranging from 39 to 1400 nmol m −3 . Highest levels of terrestrially derived material were seen during polluted, offshore flow, where the air had passed recently over strong source regions of the UK and northern Europe, with concentration ranges of nitrate and ammonium of 5.6–790 and 9.7–1000 nmol m −3 , respectively. During polluted flow ∼40–60% of the nitrate was found in the coarse mode (>1 μm diameter) and under clean marine conditions almost 100% conversion was seen. In addition, our data suggests strong evidence for dissolution/coagulation processes that also shift nitrate to the coarse mode. Furthermore, such processes are thought also to give rise to the size-shifting of aerosol ammonium, since significant coarse-mode fractions of this species (∼19–45%) were seen at both sites. A comparison of the relative importance of nitrate and ammonium in the overall dry deposition of inorganic fixed-nitrogen at each site indicates that at Weybourne the mass-weighted dry deposition velocity of the latter is around double that seen at Mace Head with its resultant contribution to the overall inorganic nitrogen dry flux exceeding that of nitrate.

Atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters. Stable nitrogen isotope data can provide important information regarding the sources and processing of atmospheric fixed-nitrogen species and is thus important in controlling eutrophication. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland and also aboard the RRS Challenger in the Eastern Atlantic Ocean. Aerosol concentrations of ammonium and nitrate were determined prior to δ15N isotopic analysis. For both species a significant difference in mean isotopic composition was seen between samples from Weybourne ( +6±6‰ for ammonium and +7±6‰ for nitrate) and Mace Head and RRS Challenger campaigns ( −9±8‰ for ammonium and −1±3‰ for nitrate). At each site a strong dependence of isotopic composition on the geographical origin of the sampled air mass was also observed. For aerosol ammonium, marine and terrestrially dominated samples were found to be isotopically distinct, perhaps reflecting the presence of oceanic sources of ammonia in addition to anthropogenic or natural terrestrial sources. Further distinctions were made within terrestrially dominated samples, possibly indicative of different types of animal husbandry regimes or other forms of anthropogenic activity. For aerosol nitrate, there was found to be generally less variation between samples at each site, although at Weybourne a significant difference was observed between the mean isotopic composition of samples originating from the northern UK ( +15±3‰ ) and that of those originating from the southern UK (+10±3‰) , suggesting that aerosol δ15N data might possibly facilitate source apportionment between NOx emissions from power stations and those from vehicle exhausts. The nitrate data also appeared to show seasonality with higher concentrations and lower δ15N values seen in the summer.

Iodine has been determined in aerosol samples collected at a coastal site in southeast England using instrumental neutron activation analysis (INAA) and by an electrochemical technique, after aqueous extraction. Size distribution and enrichment factor data for the samples are consistent with a non-sea-salt source of iodine, presumably gas-to-particle conversion of volatile iodocarbons. On average, only ∼70% of INAA (i.e. total) iodine could be released from the aerosols as inorganic iodine by aqueous extraction at 95°C. Extraction at a more environmentally realistic temperature (20°C) decreased this yield to ∼25%. Through the use of high-energy UV light, which is known to destroy organic matter, the yield of aqueous extractable iodine at the lower temperature was increased for some samples. Thus, it appears likely that iodine is present in aerosol in varying proportions as soluble inorganic iodine, soluble organic iodine and insoluble, or unextractable, iodine. The different characteristics of these fractions are likely to have significant impacts on the cycling and reactivity of iodine in the atmosphere.

Approximately 400 paired measurements of total organic nitrogen (TON) and total organic phosphorus (TOP) were made on a hydrographic transect across Drake Passage by a uv photooxidation technique. Latitudinal variations in TON and TOP concentrations were observed, with the continental margins having surface-water concentrations approximately 50% greater than those in the centre of Drake Passage. This may be due to enhanced primary production on the continental shelves leading to increased production of organic nutrients. The vertical distributions of TON and TOP were characterised by surface maxima, declining to approximately constant levels of about 2.5 ?M TON and levels of TOP below detection by about 800 m. TON and TOP can be related by the equation TON=(15.7±1.7)TOP+(2.48±0.17), r2=0.44, n=397. This is interpreted as reflecting two weakly connected pools of organic material, the first a substantial refractory pool containing about 2.5 ?M TON and undetectable levels of TOP, which dominates in deep water, and the second a surface labile pool containing TON and TOP in quasi-Redfield stoichiometry. This relationship between TON and TOP is not significantly different from a similar regression of data from the HOTS site in the central Pacific, implying that the composition of organic material, and hence the processes controlling its formation, are not substantially different in these two biogeochemically very different environments. Our postulation of two different pools of organic material with different chemical compositions and residence times leads us to suggest that the cycles of TON and TOP are more strongly coupled than is often thought.

During a 17-month study at a site on the Porcupine Abyssal Plain of the northeast Atlantic (approx. 48°N 20°W), the downward flux of particulate material within and above the benthic nepheloid layer (BNL) was measured using sediment traps 1455 m above bottom (mab) (3100 m depth) and 90 mab (4465 m depth). Flux at 90 mab is usually higher than the primary flux at 3100 m depth, and this enhancement is especially pronounced during the winter. The additional material found in the near-bottom trap comprises recently deposited resuspended material (rebound flux), but with an admixture of refractory sediment. It is unlikely that scavenging of either BNL particles or dissolved material contributes greatly to the near-bottom flux. Fluxes of metal tracers (232Th and Al) and cyanobacteria into traps were used to examine the process of resuspension. The ratio of tracer flux at 90 mab to that at 3100 m depth was taken as a measure of the strength of the resuspension process (the resuspension factor RF) and reflects clearly the enhanced resuspension in winter. This seasonal variation appears to be related to both the magnitude of near-bottom currents and to the wave height at the surface 40 days before. It is also possible that recently deposited material forms a partly cohesive blanket on the sediment surface that restricts resuspension to the benthic boundary layer.

Aluminosilicate mineral aerosol (dust) is traced from its predominant North African source to the Sargasso Sea. The mechanisms of dust production, atmospheric transport and atmospheric transformation are briefly reviewed highlighting the issue of solubilisation during long range transport. The deposition and transformation of dust in the surface ocean are then considered together with estimated upwelling fluxes to derive estimates of the residence time of dissolved and total aluminium, manganese and iron in the euphotic zone of the Sargasso Sea. The flux estimates for dissolved iron are also compared to export production estimates for iron as an independent check.

Iodide and iodate concentrations are reported and discussed for the WOCE A23 transect from the Weddell Sea north to about 25°S. Iodide concentrations are very low in the surface waters of the Weddell Sea (20 nM) and increase steadily northwards to about 100 nM in the surface waters of the south Atlantic gyre. In deep waters iodide concentrations are low but detectable at 0.5–2 nM. There is no detectable total iodine depletion in the surface waters south of the polar front although there is a small depletion evident north of the front. The results are discussed in terms of the hydrography, nutrient concentrations and phytoplankton activity along the transect. In particular, a systematic change in the relationship between iodide and nitrate along the transect is discussed.

Two well established methods that are widely applied in the determination of marine dissolved organic nitrogen (DON) have been investigated in their application to the determination of rainwater DON and the water-soluble organic nitrogen component of atmospheric aerosol. Empirical observation highlighted some difficulties in the analysis of DON in these non-marine matrices, so some practical suggestions for the extension of the oxidative methods to atmospheric samples are proposed. Ten rain samples, 20 aqueous aerosol extracts, and a suite of commercially obtained organic nitrogen compounds were both chemically oxidised by persulfate and oxidised by exposure to high-intensity ultraviolet light. The total dissolved nitrogen concentration of the rains in this study ranged from 4 to 35 μM nitrogen. The aerosol extracts were diluted to a pre-oxidation concentration range of 12–65 μM N for oxidation and analysis. Both UV and persulfate methods require the aqueous extract of the aerosol organic nitrogen to be diluted approximately to rainwater concentrations for optimal oxidation efficiency, since sub-optimal recoveries and high analytical variability arise at high concentration. Some potential causes of analytical interference at higher concentration are discussed. This study shows that total dissolved nitrogen results obtained by the two methods are linearly correlated (with an R 2 of 0.87 for 30 samples) over the full range of natural rainwater concentrations, but results obtained using the persulfate oxidation are about 30% lower than those obtained by photo-oxidation.

There are literature reports suggesting that some estuaries are sinks for dissolved inorganic phosphorus (DIP) whilst other estuaries appear to be sources of DIP. Here a simple Kd model is presented that is able to rationalize these disparate patterns of behaviour. This model suggests that riverine DIP levels are an important regulator of DIP behaviour in estuaries. DIP concentrations have increased in many rivers over the last 50 years as a result of human activity. The model results presented suggest that increases in riverine DIP concentrations from 5 μM, consistent with documented changes in some systems over the last 50 years, can change estuaries from being sources to sinks for DIP. The model results demonstrate that suspended solid concentrations in estuaries (based on simulations over the range 100–2000 mg 1−1) are also an important regulator of DIP behaviour and hence the modification of suspended solids via dredging and land reclamation activities in estuaries can alter their DIP removal capacity.

The measurement of urea (CO(NH2)2) in rainwater samples from predominantly marine-influenced locations in Bermuda, and Ireland, and in rains and aqueous aerosol extracts from a rural site at UEA, Norwich indicates that urea is not generally a major contributor to atmospheric water-soluble organic nitrogen. At UEA, where anthropogenic and natural sources of urea are expected to be most intense, urea accounts for 40% of the DON measured in those samples. This may be a consequence of strong local sources, or it could possibly result from the partial breakdown of other DON compounds to urea during sample transport and storage. However, the similarity in urea concentrations observed in Pacific samples in this present study and in a previous one ( Timperley et al., 1985 , Canadian Journal of Fisheries and Aquatic Science 42, 1171–1177) suggests that this may reflect a difference in rain chemistry between Atlantic and Pacific rains, perhaps resulting from differences in levels of agricultural urea usage between Asia and the rest of the world.

A programme of surveys of the Great Ouse estuary (England) was conducted to investigate the cycling of nutrients during mixing and to quantify nutrient budgets for the estuary. The Great Ouse estuary is shallow, well mixed and relatively turbid, and the dominant source of fresh water to The Wash. Surveys were conducted once or twice a month between February 1992 and January 1994 at high tide to yield seasonal and interannual information. High levels of chlorophyll a(>100 μg l−1), oxygen supersaturation (>120%) and non-conservative nutrient distributions during spring and summer periods of low freshwater flow strongly suggest that primary production in the low-salinity reaches of the estuary may significantly modify nutrient fluxes to The Wash, despite the relatively high turbidity. In support, calculated nutrient budgets indicate that biological removal in the river and estuary during the growing season results in depleted nutrient fluxes and higher N:Si and P:Si ratios which may affect primary production in coastal waters by contributing to the shift in species dominance from diatoms to flagellates and affecting the likelihood of bloom conditions occurring during the summer months. However, the influence of estuarine biological processes on riverine nutrient fluxes is interrupted by periods of high freshwater flow, more characteristic of the winter months, which result in high flushing rates. Under such conditions, nutrient distributions revert to a more conservatively mixed regime. This fundamental control exerted by freshwater flow generally limits the significance of estuarine processes on an annual basis, the exception being the inorganic removal of phosphate in the low-salinity reaches of the estuary which accounts for one-third of the annual input to the head of the salinity gradient. Given the character of this agriculturally impacted estuary, which permits the relatively straightforward identification and quantification of nutrient cycling processes, results from this study may have wider application.

Estuarine profiles of dissolved barium are reported from six estuarine systems in the U.S.A. and Europe. All show clear evidence of mid-estuarine barium concentration maxima, although the location and scale of these maxima vary. These differences are rationalized in terms of low-salinity desorption of particulate barium, estuarine particle dynamics, riverine sediment supply and barium storage and subsequent slow release in salt marshes. Low-salinity removal of barium also occurs in some estuaries, apparently related to dissolved iron and manganese removal.

The Humber is a large and complex estuarine system on the east coast of England fed by several rivers. Fluxes of dissolved inorganic nutrients to, through and from this estuary over 1990–1993 are estimated from point flux calculations and property salinity plots. Internal nutrient sources and sinks are quantified. Fluxes of nutrients to the system are highly seasonal; fluxes of nitrate and phosphate are dominated by winter flows in the River Trent, the ammonium flux is dominated by the Rivers Aire and Don. The tidal Trent has a large internal source of ammonium, removes about 80% of its dissolved phosphate load and functions as a sink for nitrate. The tidal Ouse has large internal sources of nitrate, phosphate and ammonium, removes over 60% of its dissolved phosphate load, is an overall source of nitrate and a large sink for ammonium. The main estuary, below the confluence of the two tidal river systems, removes about 6% of the phosphate and 50% of the ammonium entering at the confluence or about 50% and 80%, respectively, if internal sources are taken into account. Nitrate behaves conservatively within the main estuary; thus any conversion of ammonium to nitrate is balanced by a nitrate sink of comparable size. Buffering mechanisms in the outer estuary may release phosphate in similar magnitudes to the direct dissolved export. The seasonality in nitrate flux to the system is preserved throughout the system. The seasonality of the phosphate flux to the system is almost eliminated in the lower part of the tidal rivers at the early part of the salinity gradient. This, combined with phosphate buffering, may render the offshore region nitrogen-limited under conditions suitable for algal growth. Overall the Humber system removes 85% of its dissolved phosphate load, and 4% of its dissolved inorganic nitrogen load.

The cycling of dissolved inorganic nutrients in the Great Ouse estuary, Norfolk, U.K. was studied over a 50-day period in the early summer of 1994. The cycling of nutrients within the estuary and the export of nutrients to the surrounding coastal waters is quantified using mass balancing and conservative mixing considerations. Overall, the estuary was a minor sink for nitrate+nitrite (8%), a modest sink for silicate and phosphate (12 and 22%, respectively), a large source of ammonium (95%), and, overall, a small sink for dissolved inorganic nitrogen (2%). Water-column processes account well for the observed silicon and phosphorus removals; however, sedimentary processes are required to account for most of the ammonium source and some of the nitrate sink. The most significant water-column processes were primary production and nutrient regeneration from particulate material. The former process appears to be driven mainly by nitrogen imported directly at the head of the estuary, not recycled nitrogen. Regenerative processes returned approximately half of the silicate assimilated in primary production to the water column, and reduced the inferred respiratory releases of nitrogen and phosphorus by 40 and 60%, respectively. The two approaches to quantifying export, mass balancing and conservative mixing considerations, complement each other well, with the mixing analysis suggesting magnitudes and locations for nutrient-cycling processes not quantified by the mass-balance model.

Organic complexation has been suggested to be an important mechanism by which the biogeochemistry of transition metals is altered in natural waters. We have conducted complexing ligand titrations on rainwater, collected during the winter and spring from a semi-urban U.K. location, using cathodic stripping voltammetry with tropolone as the added ligand. The results show that organic ligands capable of binding copper are present in all the precipitation samples measured. As a consequence of the method used, only those copper-natural ligand complexes with conditional stability constants (1 : 1 stoichiometry-log K CuL ′) between 11 and 14 have been identified. Within this stability region, ligand concentrations vary from 10.2 to 34.5 nM, very similar to the total copper levels which range between 10.2 and 33.2 nM. While total copper has a concentration of the order of 10 −8 M, free Cu 2+ ions exist at levels of just 10 −11 −10 −12 M, showing that copper is largely complexed in the rainwater samples measured. The existence of such low free ion concentrations must be considered when assessing the catalytic role of rain and aerosol trace metals in atmospheric reactions and determining the impact of atmospheric inputs on surface water biogeochemistry. Conditional stability constants increase with the detection window used (from log K CuL ′) = 11.4 at a detection window centred at log α CuAL = 2.68 to log K CuL ′) = 12.57 at log α CuAL = 4.47). As the method is specific to a limited range of conditional stabilities, dependent on the strength and amount of competitive ligand used, this concentration dependence suggests the presence of a wider range of natural ligands than those identified here. The source of the organic complexant in precipitation is unclear. We postulate, based on stable isotope measurements made on rains collected at the same location (Cornell et al. , 1995), that the organic ligands are likely to be terrestrial in origin.

Measurements of the particulate rain of biogenic opal, the flux of dissolved SiO2 across the sea water-sediment interface, pore-water profiles of dissolved SiO2, and opal burial at the Bermuda Atlantic Time Series site are reported for a 5-year period, 1988–1993. Opal rain was determined on samples collected by a sediment trap deployed at 3200 m, 1200-m above the sea floor. Samples were collected almost continuously over the 5-year period (94% of the time). Benthic dissolution fluxes were measured in situ with benthic chambers several times each year. SiO2 diagenesis was defined with pore-water profiles of SiO2 concentration determined on samples collected in situ. The data collected are used to describe the benthic biogeochemical cycle of biogenic opal for this oligotrophic ocean environment. Despite strong seasonal variation in the rain of opal at 3200 m, driven by the cycle of primary production in the surface waters, dissolution fluxes from the sediments were constant throughout the period of our study. Pore-water profiles indicate that ∼90% of SiO2 dissolution within the sediments takes place in the upper 5 cm, and that the residence time of opal in this interval is 100–350 years. The long residence time is consistent with the lack of response to seasonal variation in opal input. Dissolution fluxes, determined with benthic chambers and estimated from pore-water profiles, provide no evidence of SiO2 dissolution at the water-sediment interface. The average particulate opal rain and the benthic dissolution flux, 0.0052 and 0.0047 μmol cm−2 day−1, respectively, are not significantly different, indicating little opal burial. The burial efficiency of opal based on mass balance considerations is estimated to be ∼6%.

The results of analyses of samples from the Bermuda Atlantic Time Series (BATS) and Hawaii Ocean Time-series (HOT) for dissolved iodine speciation are presented. At both sites iodate is reduced to iodide in surface waters by biological processes, but the iodide concentrations in the upper 100 m at the HOT site are approximately twice those at the BATS site. Using published estimates of surface water residence times and primary productivity at each station we use the differences between the two sites to derive an estimate of the in situ rate of iodide oxidation and the relationship between iodate reduction and primary production using a simple mass balance model. The model results suggest that on an annual basis iodide oxidation is relatively fast (half-life about 70 days) and that biological iodate reduction to iodide is about 100 times faster than iodide incorporation into particulate organic carbon.

Analyses of samples from a 14-year series of sediment-trap deployments in the deep Sargasso Sea reveal a significant trend in the ratio of the sinking fluxes of biogenic calcium carbonate and silica. Although there are pronounced seasonal cycles for both flux components, the overall opal/CaCO3 ratio changed by 50% from 1978 to 1991 (largely due to a decrease of opal flux), while total flux had no significant trend. These results suggest that plankton communities respond rapidly to subtle climate change, such as is evident in regional variations of wind speed, precipitation, wintertime ventilation and midwater temperatures. If the trends we observe in the makeup of sinking particulate matter occur on a large scale, they may in turn modify climate by modulating ocean-atmosphere CO2 exchange and albedo over the ocean.

During an intercomparison field experiment, organized at the Atlantic coast station of Mace Head, Ireland, in April 1991, aerosol samples were collected by four research groups. A variety of samplers was used, combining both high- and low-volume devices, with different types of collection substrates: Hi-Vol Whatman 41 filter holders, single Nuclepore filters and stacked filter units, as well as PIXE cascade impactors. The samples were analyzed by each participating group, using in-house analytical techniques and procedures. The intercomparison of the daily concentrations for 15 elements, measured by two or more participants, revealed a good agreement for the low-volume samplers for the majority of the elements, but also indicated some specific analytical problems, owing to the very low concentrations of the non-sea-salt elements at the sampling site. With the Hi-Vol Whatman 41 filter sampler, on the other hand, much higher results were obtained in particular for the sea-salt and crustal elements. The discrepancy was dependent upon the wind speed and was attributed to a higher collection efficiency of the Hi-Vol sampler for the very coarse particles, as compared to the low-volume devices under high wind speed conditions. The elemental mass size distribution, as derived from parallel cascade impactor samplings by two groups, showed discrepancies in the submicrometer aerosol fraction, which were tentatively attributed to differences in stage cut-off diameters and/or to bounce-off or splintering effects on the quartz impactor slides used by one of the groups. However, the atmospheric concentrations (sums over all stages) were rather similar in the parallel impactor samples and were only slightly lower than those derived from stacked filter unit samples taken in parallel.

A method by which estuarine water samples have been successfully analysed for the dissolved trace metals Mn, Fe, Cu and Zn using an ion chromatograph (IC) coupled directly to an inductively coupled plasma-atomic emission spectrometry (ICP-AES) system is described. Direct determination by ICP-AES of these metals in the samples was not possible since detection limits of this instrument are too high in the estuarine water matrix. The coupling of the IC to this ICP-AES system lowers detection limits sufficiently to allow analysis in two ways. First, the sample is pre-concentrated on-line; second, much of the background emission caused by the matrix is removed prior to analysis, which improves the signal-to-noise ratio. This latter feature of the method is shown to remove observable matrix effects from sample analysis, precluding the need for the use of the method of standard additions, and allowing samples from the entire salinity gradient to be accurately measured against an aqueous standard calibration line. The only required pre-treatment for samples is filtration (0.2 μm) and buffering to pH 5·4 with ammonium acetate; multi-elemental analysis is complete within 10 min. For the metals determined, the limits of determination were Cu:1·11, Fe:1·46, Mn:0·20, Zn:0·75 μg l −1 (17, 26, 4 and 11 nM, respectively). Precision on saline samples was estimated at Cu:1·41, Fe:1·23, Mn:0·27, Zn:1·11 μg l −1 (22, 22, 5 and 17 nM, respectively), which improved for freshwater samples. The method has a large linear range and is accurate based on analyses of standard reference material.

The estimates of atmospheric inputs of metals and nutrients to the oceans and some coastal areas are reviewed and the uncertainties in these estimates considered. The evidence that these inputs significantly modify oceanic chemistry is presented. However, there are still major uncertainties in our understanding of the interactions between the atmosphere and the ocean for these elements. Two of these areas of uncertainty, atmospheric deposition processes and the ecological effects of atmospheric inputs, are considered in detail.