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[1] Aerosol iron solubility is a major uncertainty in the global biogeochemical cycle of iron and, via its impact on ocean productivity, the carbon cycle and their influence on global climate. Previous studies have reported widely different values for this solubility (0.01 – 80%). Here we show that the primary control on aerosol iron solubility is the surface area to volume ratio of mineral aerosol particles, which changes during atmospheric transport as mineral aerosol concentration decreases due to preferential removal of larger particles (assuming particle morphology to be relatively constant with particle size). This important result indicates that aerosol iron solubility is not fixed, but will change predictably as an inverse function of dust concentration on both spatial and temporal (e.g. glacial – interglacial) scales.

Phosphorus (P) availability constrains both carbon uptake and loss in some of the world's most productive ecosystems. In some of these regions, atmospheric aerosols appear to be an important, if not dominant, source of new P inputs. For example, previous work suggests that mineral aerosols from North Africa bring significant amounts of new phosphorus to the P-impoverished soils of the Amazon Basin. Here we use recent observations and atmospheric transport modeling to show that the Amazon Basin itself appears to be losing atmospheric phosphorus to neighboring regions as a consequence of biomass burning emissions, anthropogenic sources of mineral aerosols and primary biogenic particles. Observations suggest that biomass burning emissions and human disturbance are responsible for ∼23% of the phosphorus flux in the Amazon. Although biomass burning and disturbance may bring new phosphorus into nondisturbed regions, as a whole the Amazon appears to be losing phosphorus through the atmosphere. Phosphorus lost via atmospheric transport from the Amazon is deposited in the adjacent oceans and in other regions downwind. These results suggest that land use change within the Amazon may substantially increase phosphorus availability to the remaining undisturbed forests, and that this fertilization mechanism could potentially contribute to recent changes in carbon uptake measured in undisturbed stands, as well as fertilizing downwind ocean regions.

[1] Since iron is an important micronutrient, deposition of iron in mineral aerosols can impact the carbon cycle and atmospheric CO2. This paper reviews our current understanding of the global dust cycle and identifies future research needs. The global distribution of desert dust is estimated from a combination of observations of dust from in situ concentration, optical depth, and deposition data; observations from satellite; and global atmospheric models. The anthropogenically influenced portion of atmospheric desert dust flux is thought to be smaller than the natural portion, but is difficult to quantify due to the poorly understood response of desert dust to changes in climate, land use, and water use. The iron content of aerosols is thought to vary by a factor of 2, while the uncertainty in dust deposition is at least a factor of 10 in some regions due to the high spatial and temporal variability and limited observations. Importantly, we have a limited understanding of the processes by which relatively insoluble soil iron (typically ∼0.5% is soluble) becomes more soluble (1–80%) during atmospheric transport, but these processes could be impacted by anthropogenic emissions of sulfur or organic acids. In order to understand how humans will impact future iron deposition to the oceans, we need to improve our understanding of: iron deposition to remote oceans, iron chemistry in aerosols, how desert dust sources will respond to climate change, and how humans will impact the transport of bioavailable fraction of iron to the oceans.

The complexation of copper was studied in rainwater collected in Norwich, UK, and during Atlantic and Indian Ocean cruises. The complexation was measured with Chelex resin, Sep-Pak columns and adsorptive cathodic stripping voltammetry with tropolone as a competing ligand. Strong organic complexation was observed in semi-urban and marine rain samples with conditional stability constants between 1011 and 1014. Model solutions of copper and humic matter found organic complexes of a similar strength to those observed in the rain samples suggesting humic material as a potential ligand. A large proportion of the copper in the rains was associated with strong organic complexes over the pH range 4-8 in both filtered and unfiltered rain samples suggesting organic complexation is an important process both in the atmosphere and on arrival to oceans. © 2005 Elsevier Ltd. All rights reserved.

In the context of the Water Framework Directive (2000/60/EC), EU Member States are required to introduce water quality objectives for all water bodies, including coastal waters. Given the impact of catchment fluxes on coastal water quality, decision-making at the catchment scale is essential. This chapter investigates the use of integrated assessment as an overall decision-support process and toolbox in the Humber estuary.

The effect of fertilizer type, amount of fertilizer applied, growing medium, and water type on the nitrogen-15 content of carrots, tomatoes, and lettuces has been investigated. Crops grown using synthetic nitrogen fertilizer were isotopically lighter than those grown using pelleted chicken manure. For example, for equivalent amounts of nitrogen applied, carrots grown with ammonium nitrate fertilizer had delta15N values between 3 per thousand and 4 per thousand lower than those grown using pelleted chicken manure. Plants grown in peat-based compost were generally found to be isotopically lighter than those grown in composted bark based compost. Results suggest that nitrate content and the delta15N of the nitrate in irrigation water may also influence crop delta15N. Wider implications of using crop delta15N more generally as an indicator of whether synthetic nitrogen fertilizers have been applied to a crop and the possible application and limitations of using crop delta15N as an indicator of agricultural regime (organic/conventional) are discussed.

[1] The role of atmospheric deposition of iron, nitrogen and phosphorus in supplying nutrients to marine systems has been described, individually, in previous works. Here we examine atmospheric dry deposition of all these nutrients simultaneously, using samples collected during two meridional transects of the Atlantic Ocean. We find that, in line with previous work, desert dust supplies excess iron to the water column. However, primary production promoted by aerosol nitrogen can be sufficient to consume all of the soluble aerosol iron input in some situations. Aerosol N:P is universally very high, so that aerosol is always deficient in P relative to phytoplankton requirements. Nitrogen fixation stimulated by any excess atmospheric iron supply and phytoplankton utilisation of atmospheric nutrient inputs will therefore tend to drive the ecosystem towards P limitation. This emphasises the need to study the biogeochemical impact of atmospheric nutrient deposition in an integrated manner.

[1] Ammonium salts represent a major component of fine mode marine aerosol that play an important role in climate regulation, atmospheric pH control and nutrient supply to the oceans. We report here the results of analyses of aerosol samples collected in remote areas of the Atlantic Ocean. We show the isotopic abundance of aerosol ammonium varies with concentration, with isotopically light ammonium (−5 to −8‰) associated with the lowest ammonium concentrations compared to isotopically heavy ammonium (+10‰) associated with higher ammonium concentrations. We interpret the light ammonium signature as arising from marine emissions of ammonia. These results provide further evidence for the existence of a marine ammonia source and offers a method to define the relative contribution of marine and terrestrial ammonium to aerosols in remote areas and thereby investigate the role of these emissions in climate regulation.

The flux of nitrogen species from the atmosphere into the ocean, with emphasis on coastal waters, was addressed during the ANICE project (Atmospheric Nitrogen Inputs into the Coastal Ecosystem). ANICE focused on quantifying the deposition of atmospheric inputs of inorganic nitrogen compounds (HNO3, NO3-, NH3 and NH4+) into the North Sea and the processes governing this deposition. The Southern North Sea was studied as a prototype. Because the physical and chemical processes are described, as opposed to empirical relations, the results can potentially be transferred to other regional seas like the Mediterranean, the North Atlantic continental shelf area and the Baltic. Two intensive field experiments were undertaken, centred around the offshore tower Meetpost Noordwijk and the Weybourne Atmospheric Observatory in East Anglia (UK). Long-term measurements were made on a ferry sailing between Hamburg and Harwich/Newcastle. These measurements provided data for sensitivity studies of a variety of problems associated with the coastal region that are not easily evaluated with larger scale models, to constrain models and to test model results. Concentrations of nitrogen compounds over the North Sea and the resulting deposition presented in this paper were obtained with the Lagrangian transport-chemistry model ACDEP. The average annual deposition in 1999 was 906kg Nkm-2. The results are compared with experimental data from the ferry. Effects of temporal and spatial variations are evaluated based on experimental results and small-scale model studies. In particular, effects of the aerosol size distribution on the nitrogen deposition are discussed. © 2003 Elsevier Ltd. All rights reserved.

This Special Issue, “Climate change and coupling of macronutrient cycles along the atmospheric, terrestrial, freshwater and estuarine continuum” is dedicated to the career of Colin Neal, whose work over the years has generated so many concepts and so much data to support on-going research in this important research area. This note is concerned with Colin and his contributions to the scientific literature.

The atmosphere and the oceans are intimately linked in a complex web of physical and chemical cycles that play an important role in regulating the biogeochemistry and climatology of Planet Earth. In this short paper, I will show first that atmospheric inputs are a major route by which some key nutrients for phytoplankton growth reach the ocean, and second that exchanges of a variety of gases and sea salt itself between the ocean and the atmosphere are of major importance in regulating climate and the properties of the atmosphere. These exchanges are regulated by biological and physical processes that are themselves sensitive to the inputs of nutrients, and to changes in physical forcing arising from climate change. We are beginning to understand the nature and regulation of some of these air-sea exchange processes, but the challenge for the next decade is to try to quantitatively understand the interactions and feedbacks between these systems. Only then can these processes be incorporated into Earth System models and contribute to improved predictions of global change.

Published observations of organic nitrogen (N) compounds in precipitation go back almost a century. Several different methods have been used to measure both the total and ionic concentrations of N. There is therefore some uncertainty as to whether reported �organic N� is real, or simply the result of uncertainties in chemical analyses or inadequate sampling methods. We found that the materials from which the collector was made (polypropylene, steel, or glass) had no significant effect on the composition of dissolved organic N (DON). The use of a biocide was found to be very important during sampling and storage of samples before analysis. We set up a network of seven collectors across the U.K., from the Cairngorms to Dorset, all operating to the same protocol, and including a biocide. Samples were analysed centrally, using proven methods. Over 6 months, organic N contributed about 20% to the total N in U.K. precipitation, but with a large variation across the country. This means that current estimates of wet deposited N to the U.K., which are based only on the ammonium and nitrate concentrations, are too small. Organic N is not an artefact, but a real problem that needs to be addressed.

This component of EUROTRAC has concentrated on two themes; the magnitude of atmospheric fluxes to the North Sea and the bioavailablity of such atmospheric inputs of metals as evidenced by their solubility. Good progress has now been made in both areas. The solubility of metals in rain-water is now reasonably well understood, and the atmospheric fluxes of metals and nitrogen to the North Sea have been quantified and the main factors controlling them rationalised. Furthermore much of what has been learnt about inputs to the North Sea is applicable to other coastal areas, providing evidence of several important processes in such environments which need to be included in transport and deposition models.

The Atmospheric Nitrogen Inputs into the Costal Ecosystem (ANICE) project was initiated to improve the accuracy and performance of model tools used to estimate the atmospheric nitrogen deposition to the sea. The experimental work includes the use of a ferry for long-term measurements of gaseous species, aerosols and rain water during one year, and two intensive field campaigns. During the first ANICE intensity experiment, situations were encountered in which the air flow connected the different stations. Differences in nitrate and ammonium concentrations between the various stations were analyzed in terms of the processes determining the concentrations of these species and to quantify their variations with fetch.

REVIEWThe coastal seas are one of the most valuable and vulnerable of Earth's habitats. Significant inputs of nutrients to the coastal zone arrive via rivers, groundwater, and the atmosphere. Nutrient fluxes through these routes have been increased by human activity. In addition, the N:P:Si ratios of these inputs have been perturbed, and many coastal management practices exacerbate these perturbations. There is evidence of impacts arising from these changes (in phytoplankton numbers and relative species abundance, and deep-water oxygen declines) in areas of restricted water exchange. Elsewhere, the nutrient fluxes through the coastal zone appear to be still dominated by large inputs from the open ocean, and there is little evidence of anthropogenic perturbations.

10 laboratories, using their routine methods, collaborated in a comparison of analyses of total carbon, nitrogen and organic carbon in a single sample of marine sediment and a pooled sample of settling particulate material collected by sediment trap. The standard error of the means from all individual laboratories was ±3% of the mean for all total carbon results, and for total nitrogen in the marine sediment, but was ±7% of the mean for total nitrogen in the sediment trap material. Larger errors (±8% of the mean) were found for organic carbon results from both the marine sediment and the sediment trap material, with a range of results (expressed as a percentage of the untreated dry weight) for the sediment trap sample analyzed here of 5.60–8.03%. When this range is compared with that of particulate organic carbon concentration in sediment trap material obtained by different workers at various deep ocean sites (2.4–10.2%) [Wefer, G., 1989. Particle flux in the ocean: Effects of episodic production, in: W.H. Berger, V.S. Smetacek, G. Wefer (Eds.), Productivity of the Ocean: Present and Past, John Wiley & Sons, pp. 139–154.] it is apparent that a large proportion of the observed oceanic variability could be accounted for by difference in analytical technique. We suggest that the problem stems from the difficulty of accurate separation of the organic and inorganic phases and discuss the inaccuracies involved in the separation. We present evidence that the range of results is partly due to either volatilisation of organic carbon during acid treatment, or incomplete removal of organic matter during thermal treatment. If results from different laboratories are to be compared, as is presently required for basin scale and global studies of ocean carbon cycling and budgets, there is clearly a need for suitable reference materials, rigorous intercalibration and technique development.

Sediment trap data from four sites in the northeast Atlantic (48°N 20°W, 28°N 22°W, 24°N 23°W, 19°N 20°W) are presented for fluxes of total mass, organic matter, calcium carbonate, opal and lithogenous material. The results from these sites are compared with other published sediment trap data from this area to consider regional scale variations in the quantity and composition of settling ocean particulate matter along a transect at 20°W from 48°N to 19°N. There are clearly gradients of decreasing mass flux going south from 48°N which reverse around 25–30°N to increase again toward the North Africa upwelling regime. Flux seasonality is greater at the more northern sites. Opal fluxes are high at the more northern sites and the flux of lithogenic material is greater further south. Plankton species composition also changes along the transect. The changes in the mass and composition of sedimenting material along the transect are consistent with known changes in surface water plankton abundance and with fluxes inferred from sediment core results. Carbon fluxes measured by sediment traps and inferred from sediment core data in this area appear to be consistent with one another. These results provide increased confidence in the use of various ocean flux measurement techniques to derive estimates of ocean carbon cycling.

A 15 month survey was carried out into the distributions of trace metals, trace organics and nitrogen species in particulate and rainwater samples collected from the atmosphere over the southern North Sea. This is the first time a comprehensive and reliable data-set of this kind has been obtained for a coastal region from collections made at sea.

Atmospheric circulation patterns over the North Sea occasionally result in episodes of high concentrations of various contaminants. Synergistic chemical effects can act to enhance the deposition of nitrogen during these events resulting in highly episodic nitrogen inputs to the North Sea. Two such episodes are described and their causes interpreted. The problems of devising sampling strategies to quantify these events and assess their effects on phytoplankton communities are discussed.

The biogeochemistry of particulate organic matter was studied in the Great Ouse estuary draining to the North Sea embayement known as the Wash from March 1990 to January 1991. Eleven locations were sampled monthly on a 50 km transect across the shallow estuary from the tidal weir to the middle of the Wash. Particulate organic carbon (POC) and total carbohydrate, protein and lipid analyses were combined with the determination of stable carbon isotopes. δ13C often increased from −30‰ in the river to −22‰ in the tidal freshwater reach. The mixing zone between fresh and marine tidal waters displayed only a slight increase in δ13C to −19‰. The change in δ13C values in the freshwater tidal reach demonstrated that mixing of riverborne and marine suspended POC was not the only process affecting the carbon stable isotope composition. Complementary sources, interfering considerably with the two end-member sources, may be identified as autocthonous primary production and resuspension of sediment that may be transported upstream. The respective importance of these sources is subject to seasonal variation. From March to August, high concentrations in carbohydrate and protein through the whole estuary indicate that despite turbidity significant primary production occurred. The proportional importance of the uncharacterized fraction of POC, which is considered as complex organic matter, was high from September to January and low from March to August. During most of the year, the biochemical compositions of particulate organic matter in the turbidity maximum and the rest of the estuary were similar. This contradicted the principle that owing to the long residence times of particles degradation processes largely dominate the production processes within the turbidity maximum. The occurence of significant in situ production in such shallow water estuaries may partially compensate for the degradation of suspended particulate organics, resulting in a complex relationship between the biogeochemical cycling and the fate of nutrients.

Transfer of matter across gas-liquid interfaces is governed by the same physical and chemical principles irrespective of whether the interface separates laboratory or environmental media. Similarly, in the environment the same general principles apply whether the atmosphere is exchanging with fresh or saline waters. Two important advantages stem from this: (1) ideas and results developed in simple or idealized laboratory set-ups (e.g., in chemical engineering) can often be used in field situations, which are generally less tractable; (2) field studies conducted on lakes are applicable to oceanic and coastal situations, and vice versa.

Over the past decade it has become apparent that the atmosphere is a significant pathway for the transport of many natural and pollutant materials from the continents to the ocean. The atmospheric input of many of these species can have an impact (either positive or negative) on biological processes in the sea and on marine chemical cycling. For example, there is now evidence that the atmosphere may be an important transport path for such essential nutrients as iron and nitrogen in some regions. In this report we assess current data in this area, develop global scale estimates of the atmospheric fluxes of trace elements, mineral aerosol, nitrogen species, and synthetic organic compounds to the ocean; and compare the atmospheric input rates of these substances to their input via rivers. Trace elements considered were Pb, Cd, Zn, Cu, Ni, As, Hg, Sn, Al, Fe, Si, and P. Oxidized and reduced forms of nitrogen were considered, including nitrate and ammonium ions and the gaseous species NO, NO2, HNO3, and NH3. Synthetic organic compounds considered included polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs), DDTs, chlordane, dieldrin, and hexachlorobenzenes (HCBs). Making this assessment was difficult because there are very few actual measurements of deposition rates of these substances to the ocean. However, there are considerably more data on the atmospheric concentrations of these species in aerosol and gaseous form. Mean concentration data for 10° × 10° ocean areas were determined from the available concentration data or from extrapolation of these data into other regions. These concentration distributions were then combined with appropriate exchange coefficients and precipitation fields to obtain the global wet and dry deposition fluxes. Careful consideration was given to atmospheric transport processes as well as to removal mechanisms and the physical and physicochemical properties of aerosols and gases. Only annual values were calculated. On a global scale atmospheric inputs are generally equal to or greater than riverine inputs, and for most species atmospheric input to the ocean is significantly greater in the northern hemisphere than in the southern hemisphere. For dissolved trace metals in seawater, global atmospheric input dominates riverine input for Pb, Cd, and Zn, and the two transport paths are roughly equal for Cu, Ni, As, and Fe. Fluxes and basin-wide deposition of trace metals are generally a factor of 5-10 higher in the North Atlantic and North Pacific regions than in the South Atlantic and South Pacific. Global input of oxidized and reduced nitrogen species are roughly equal to each other, although the major fraction of oxidized nitrogen enters the ocean in the northern hemisphere, primarily as a result of pollution sources. Reduced nitrogen species are much more uniformly distributed, suggesting that the ocean itself may be a significant source. The global atmospheric input of such synthetic organic species as HCH,PCBs, DDT, and HCB completely dominates their input via rivers.

A general introduction to the current state of knowledge of the long- range transport of trace elements is given in Chapter 2 (p. 37). In this chapter we present four case studies to illustrate our level of understanding of the processes and to draw attention to the gaps in the current knowledge. Each case has been treated differently to reflect the complexity of the case and the available data base. The approaches we used are exploratory and our results, preliminary. However, these results do illustrate ways in which we might improve our undertanding of the processes involved in long-range transport. The themes common to each case are explored in the final section.

Throughout the earth’s geological history trace elements have been atmospherically transported from continent to continent and from continent to ocean; this long-range atmospheric transport is now recognized as an important, if not the most important, mode of global transport for a variety of trace substances ad elements. The anthropogenic trace substances found in remote locations attest to the rapidity and extent of such transport.

Environmental context. Iron is an essential component of many enzyme systems of marine plants (phytoplankton), but in large areas of the global ocean iron is in such short supply as to hinder phytoplankton growth. This is of major environmental interest because phytoplankton growth can remove carbon from the atmosphere. This contribution seeks to improve the understanding of how dust transported through, and processed within, the atmosphere helps to supply usable iron to the plants of the remote ocean. Abstract. Soil dust mobilised from arid regions is transported through and processed within the atmosphere before deposition to marine and terrestrial ecosystems remote from the source regions. This process represents a significant source of iron to the oceans, which creates feedback loops throughout the Earth’s system. The very limited solubility of iron from dust makes the determination of this solubility, how it varies and how this may influence ocean biogeochemistry of considerable importance. In this short communication we summarise a series of recent studies of mechanisms that control solubility and then consider how these results influence the inputs of iron to the oceans and their isotopic signature.

The results of measurements of sea-to-air fluxes of methyl iodide and air-to-sea wet depositional fluxes of iodide and iodate over the southern North Sea are reported. The estimated average annual flux of methyl iodide out of the southern North Sea is 8 × 10 5 moles yr −1 while the iodine deposition flux, based on average rainwater concentrations, is 6 × 10 5 moles yr −1 . Both emission fluxes of methyl iodide and deposition fluxes of total iodine show a modest seasonality with minimum fluxes in winter. The average concentration of iodine in the rainwater samples ( n = 40) over a one year period was 6.8 + 7.5 nm for total iodine, 3.1 + 2.7 nm for iodate and 3.7 + 6.6 nm for iodide. There is no evidence of seasonality in the iodide/iodate ratio in rainwater over the year. DOI: 10.1034/j.1600-0889.1996.00010.x

An assessment of atmospheric inputs of nitrogen to the southern North Sea (south of 56°N) has been made following a series of research cruises between August 1988 and October 1989, during which wet and dry sampling for aerosol and gaseous species was undertaken. Wet and dry deposition appear to contribute approximately equally to total deposition, yielding fluxes of 126 × 10 3 t N a -1 and 102 × 10 3 t N a -1 , respectively. A tentative assessment for the northern North Sea has been made based on extrapolation from data generated here and from coastal sites. When combined with fluxes calculated for the southern area, the total atmospheric deposition of nitrogen to the whole North Sea is estimated to be 412 × 10 3 t a -1 . In terms of gross nitrogen inputs to the North Sea, the contribution from the atmosphere is relatively minor, the budget being dominated by the influence of the North Atlantic inflow. However, it does represent at least 26% of the terrestrial input. Furthermore, the effects of both seasonality in inputs and remoteness from estuarine influence suggest that during the growing season, when primary production in the North Sea is often nutrient limited, the atmosphere may provide the dominant source of nitrogen in stratified areas away from the coast, and at a time when the long-term trend in European emissions of NH 3 and NO x to the atmosphere is upward. DOI: 10.1034/j.1600-0889.1993.00005.x

Trace metal distributions in ocean waters are dominated by internal recycling processes. However, fluxes out of the water column must balance inputs if steady state is to be maintained. We use deep-sea particle fluxes at 3200 m in the Sargasso Sea as measured by sediment traps to define the flux to the sediments beneath the Sargasso Sea and compare this flux to the atmospheric input for a group of trace metals. Despite the uncertainties associated with the comparison, several important features are revealed. For elements predominantly associated with crustal particles (Al, Mn, Fe, and V), lateral advection provides a significant part of the deep-sea particle flux. For Cd, Cu, Ni, Pb, and Zn this lateral component is minor, and atmospheric inputs to the Sargasso Sea exceed deep-sea particle fluxes. These excesses appear to be consistent with calculations of the export of these metals from the Sargasso Sea arising from ocean boundary scavenging (Pb) and release from decomposing organic matter in the southward flowing North Atlantic Deep Water (Cd, Cu, Ni, and Zn). In the atmospheric deposition itself, wet deposition exceeds dry deposition for Cd, Cu, Mn, Ni, Pb, and Zn, while wet and dry deposition are of similar magnitudes for V, Fe, and Al.

The concentration of the trace metals Cd, Cu, Fe, Mn, Ni, Pb, V and Zn has been measured in atmospheric precipitation events at the middle Atlantic coast (Lewes, DE) and on the western Atlantic island of Bermuda. The purpose is to assess the sources, transport, and wet deposition of trace metals to the western Atlantic during non-summer months when trace metals are likely to be transported by westerly air mass flow from N America to the open Atlantic. The concentrations, and wet deposition of trace metals are greater at the coast than on Bermuda, and the other at both sites (Fe > Zn > Pb > Cu, Mn, Ni > V > Cd) is similar. The trace metal enrichment factors for all metals but Mn, based on crustal Fe, are significantly greater than unity, and the order (Cd > Pb > Zn > Cu > Ni > V) is also the same at the coast as on Bermuda. This evidence suggests common sources from North America for trace metals in western Atlantic precipitation and important atmospheric transport of trace metals to the Atlantic Ocean. Calculations using enrichment factors from sea salt aerosol (Na based) indicate recycling of trace metals from the sea surface, while generally considered not to be important, could be a potentially significant process contributing to Mn and V enrichments in open western Atlantic precipitation.

The sedimentation rates of aluminium, cadmium, copper, iron manganese, nickel, phosphorus, lead, vanadium, and zinc in the Sargasso Sea have been determined from samples collected in a sediment trap 3200 m below the ocean surface. The fluxes are temporally variable, being driven by the seasonal cycle of primary production in the surface waters. There is evidence to suggest anthropogenic perturbation of the copper, lead, and zinc fluxes. The measured fluxes imply short (>150 day) lifetimes of particulate trace elements in the surface layers.

Total dissolvable cobalt, copper, manganese and nickel have been measured in two water column profiles from the Sargasso Sea. The nickel results suggest cycling in association with nutrients, with relatively low concentrations in surface waters and an increase in concentration with depth. The cycling of manganese, by contrast, appears to be dominated by abiogenic scavenging processes with a concentration maximum near the surface declining to low and rather constant values at depth, except near the sediment-water interface where sediment resuspension can increase the concentration. The profiles of copper and cobalt are influenced by both biogenic and abiogenic scavenging processes. For copper, recycling at the sediment-water interface is also important while for cobalt concentrations vary in different water masses, probably as a function of the relative age of the water since it sank from the surface.

Methods have been developed for the measurement of iodate and total iodine in ocean waters based on the spectrophotometric method of Truesdale and Spencer (Mar. Chem., 2 (1974) 33–47). Total iodine is measured as iodate after photo-oxidation of reduced forms of iodine with UV light, and iodide is then calculated by difference. A complex interference from nitrate is reported and discussed. Measurements of iodine concentrations in the Sargasso Sea and the Bermuda inshore waters suggest a seasonal cycle. This seasonality appears to be the result of water masses becoming isolated by hydrographic effects for a sufficient time for iodate reduction to significantly change the iodate/total iodine ratio. The mechanisms for the reduction are at least partly biological, but other mechanisms may also play a part.

Inland marine caves have served as biological refugia and, as such, frequently contain unique assemblages of taxonomically significant relict populations known only from a single cave or cave system. However, the absence of photosynthesis in this totally lightless environment and the presence of a highly stratified water column and long residence times for cave waters, characteristically result in depleted dissolved oxygen levels. Under such circumstances, organic pollution, even at low levels, can produce anoxic conditions and may consequently result in the extinction of entire species of cavernicolous fauna. We here present data on the normal environment of marine caves in Bermuda and cite as an example a cave which has become grossly polluted as a result of indiscriminate dumping.

Increased acidity of precipitation due to combustion of fossil fuels has been well documented for both the eastern USA1 and Canada2. The SO2 and NOxemitted by the burning of coal, natural gas, fuel oil and petrol are oxidized in the atmosphere to sulphuric and nitric acids which subsequently give rise to acid precipitation1. However, the SO2 and NOx emitted, and their oxidation products, are not all removed by atmospheric deposition over the North American continent; a large fraction is advected east out of North America3. In a study between 1 May 1980 and 30 April 1981, we have detected acid precipitation (pH

Recently, it has been suggested that marine primary productivity can be influenced by direct inputs of fixed inorganic nitrogen (NO−3, NO−2 and NH+4) from atmospheric deposition, and that this may be important in shaping trends of productivity in coastal areas1. It is known that anthropogenic contaminants are transported from North America to the Sargasso Sea, affecting the chemistry of rain water over this oligotrophic ocean area. Here we present data collected between 1982 and 1984 as part of the Western Atlantic Ocean Experiment (WATOX) by a wet-only precipitation collector on Bermuda. Our measurements of the anthropogenic fixed nitrogen in the rainwater samples are discussed in the context of the amount of nitrogen required to support ‘new’ primary production in the Sargasso Sea. We show that the effects of atmospheric deposition are insignificant

Concurrent measurements of particle concentrations in the near-surface water and of particle fluxes in the deep water of the Sargasso Sea show a close coupling between the two for biogenic components. The concentrations of suspended matter appear to follow an annual cycle similar to that of primary production and deepwater particle flux. Although the concentration of particulate aluminum in the surface water appears to vary randomly with respect to that cycle, the removal of aluminum to deep water is intimately linked to the rapid downward transport of organic matter.

Organic nitrogen (N) is an important component of the atmospheric deposition of reactive N, but its sources are essentially unknown. Assessing whether this dissolved organic N (DON) is of natural, anthropogenic or mixed origin is critically important in attempting to determine the scale of human perturbation of the global N cycle. Here we report evidence for atmospheric organic N deposition and its anthropogenic sources in China. Precipitation samples were collected and analyzed from 15 rural, Suburban and urban sites during 2005 and 2006. The average deposition of DON was 8.6 kg ha(-1) yr(-1) with a volume-weighted concentration of 111 mu mol L-1, which was much higher than in other regions of the world. The contribution of DON to total dissolved N (TDN) was approximately 30% on average, agreeing well with other reported data in the literature. Parallel collections of wet-only and bulk deposition showed wet deposition to be 68% on average, indicating a significant dry deposition component. Combining data from the Chinese sites with those from elsewhere in the world, significant (p < 0.0001) correlations between DON and NH4-N, TDN and TDN suggest that atmospheric organic N originates from similar sources to dissolved inorganic N (DIN) (NH4-N and NO3-N), which are largely attributed to anthropogenic emissions from both agricultural and industrial sources.

Based on an international workshop (Gothenburg, 14–16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas.

This work reports on the current status of global modelling of iron (Fe) deposition fluxes and atmospheric concentrations and analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry-transport (CTMs) and general circulation (GCMs) models have participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, The Atmospheric Input of Chemicals to the Ocean. The global total Fe (TFe) emissions strength in the models is equal to ~ 72 Tg-Fe yr−1 (38–134 Tg-Fe yr−1) from mineral dust sources and around 2.1 Tg-Fe yr−1 (1.8–2.7 Tg-Fe yr−1) from combustion processes (sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg-Fe yr−1, accounting for mineral dust and combustion aerosols together. The multi model ensemble global TFe and LFe deposition fluxes into the global ocean are calculated to be ~ 15 Tg-Fe yr−1 and ~ 0.3 Tg-Fe yr−1, respectively. The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parametrizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicate that most models overestimate surface level TFe mass concentrations near the dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe loading near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (~ 14), larger than the Southern Hemisphere (~ 2.4) for the ensemble model mean. This model intercomparison and model–observation comparison study reveals two critical issues in LFe simulations that require further exploration: 1) the Fe-containing aerosol size distribution and 2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions.

The ANICE (Atmospheric Nitrogen Inputs into the Coastal Ecosystem) project addressed the atmospheric deposition of nitrogen to the North Sea, with emphasis on coastal effects. ANlCE focused on quantifying the deposition of inorganic nitrogen compounds to the North Sea and the governing processes. An overview of the results from modelling and experimental efforts is presented. They serve to identify the role of the atmosphere as a source of biologically essential chemical species to the marine biota. Data from the Weybourne Atmospheric Observatory (UK) are used to evaluate the effect of short episodes with very high atmospheric nitrogen concentrations. One such episode resulted in an average deposition of 0.8 mmol N m-2 day-1, which has the potential to promote primary productivity of 5.3 mmol C m-2 day-1. This value is compared to long-term effects determined from model results. The total calculated atmospheric deposition to the North Sea in 1999 is 948 kg N km-1, i.e. 0.19 mmol N m-2 day -1 which has the potential to promote primary productivity of 1.2 mmol C m-2 day-1. Detailed results for August 1999 show strong gradients across the North Sea due to adjacent areas where emissions of NOx and NH3 are among the highest in Europe. The average atmospheric deposition to the southern part of the North Sea in August 1999 could potentially promote primary production of 2.0 mmol C m-2 day-1, i.e. ∼ 5.5% of the total production at this time of the year in this area of the North Sea. For the entire study area the atmospheric contribution to the primary production per m2 is about two-third of this value. Most of the deposition occurs during short periods with high atmospheric concentrations. This atmospheric nitrogen is almost entirely anthropogenic in origin and thus represents a human-induced perturbation of the ecosystem. © 2003 Elsevier Ltd. All rights reserved.

This paper summarises the results of the EU funded MEAD project, an interdisciplinary study of the effects of atmospheric nitrogen deposition on the Kattegat Sea between Denmark and Sweden. The study considers emissions of reactive nitrogen gases, their transport, transformations, deposition and effects on algal growth together with management options to reduce these effects. We conclude that atmospheric deposition is an important source of fixed nitrogen to the region particularly in summer, when nitrogen is the limiting nutrient for phytoplankton growth, and contributes to the overall eutrophication pressures in this region. However, we also conclude that it is unlikely that atmospheric deposition can, on its own, induce algal blooms in this region. A reduction of atmospheric nitrogen loads to this region will require strategies to reduce emissions of ammonia from local agriculture and Europe wide reductions in nitrous oxide emissions. 2005 Elsevier Ltd. All rights reserved.