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Atmospheric wet and bulk depositional fluxes of trace elements (Fe, Al, Mn, Zn, Pb, Cu, Cd, Ni, and Cr), 210Pb, and 7Be (bulk only) to the Sargasso Sea were measured at Bermuda from September 1996 to September 1997. Wet deposition was the dominant process of trace element deposition over most of the sampling seasons, based on the measured bulk versus wet depositional fluxes. Although about half of the Mn in Bermuda precipitation was calculated to originate from noncrustal sources, its seasonal trend is similar to the Fe and Al, suggesting primary sources from continental crustal materials. On the other hand, Cd, Zn, Pb, Cu, Ni, and Cr in Bermuda precipitation originate mainly from noncrustal sources (presumably anthropogenic) based on enrichment factor analyses. The noncrustal sources were highest during the fall-winter due to more frequent intrusion of U.S. continental air as the Bermuda High weakens. Atmospheric depositional fluxes of 210Pb showed a good correlation with the 7Be fluxes (r2=0.84) at Bermuda, indicating major transport of 210Pb via the upper troposphere from continents, along with other trace elements. Annual depositional fluxes of noncrustal elements (Cd, Zn, Pb, Cu, Ni, and Cr) at Bermuda were a factor of 2 to 3 lower than those at the mid-Atlantic Bight and were about 2–20 fold lower during the sampling year than those during the early 1980s. This confirms the rapid evolution of trace element inputs to the upper Sargasso Sea during the last few decades resulting from industrial emission controls in the surrounding continents.

A practical technique has been developed for the determinations of (234)Th simultaneously with (210)Po and (210)Pb in seawater samples, which greatly simplifies the on-board chemical procedures and enables an accurate correction of (234)Th ingrowth. A unique feature of this technique lies in the exact determination of co-precipitated (238)U following Fe(OH)(3) precipitation which leads to an exact correction of ingrown (234)Th between Fe(OH)(3) precipitation and U/Th separation. Such a correction eliminates several cumbersome on-board chemistry steps (such as Po plating, Fe(2+) oxidation, and 9 N HCl anion exchange) required in regular procedures to eliminate the (234)Th ingrowth. The total time required for on-board sample treatment (spike equilibration, Fe (OH)(3) co-precipitation and filtration) could be less than 10 h which significantly increases the sample processing efficiency and data throughput.

The distribution of 210 Po and 210 Pb (grand daughter–parent) in the dissolved and total (dissolved+particulate) phase of sea water samples has been measured in the upper 500 m at four stations along a western transect in the South-equatorial Atlantic. Such a transect allows one to make inference about the particle-associated scavenging processes in the equatorial versus subtropical regions of the South Atlantic. A common feature of the 210 Po profiles is that the dissolved activities in the surface waters are about one-third of the equilibrium concentrations, suggesting weeks to a month removal times of 210 Po by adsorption on settling particles. The mean dissolved 210 Po / 210 Pb activity ratios in the equatorial and South Atlantic are 0.27 and 0.39, respectively, representing a pronounced disequilibrium in surface waters. The box-model calculation yields a residence time of about 73 and 130 days for dissolved 210 Po in the surface water at the equatorial and southern sites, respectively. The gross deficiency of 210 Po extends throughout the upper 500 m; however, the 210 Po residence time in the intermediate depths is longer than that in surface water. The observed 210 Po – 210 Pb disequilibrium has been examined with respect to POC concentration, which yields a significant positive correlation (r2=0.61), suggesting that the 210 Po deficiency is mainly associated with biological removal. The 210 Pb distribution shows distinctively higher concentrations in the equatorial surface waters (19–22 dpm/100 l), suggesting an enhanced atmospheric flux of 210 Pb . The residence time of dissolved 210 Pb (400–780 days), with respect to atmospheric input, is longer than dissolved 210 Po and 234 Th residence times, and also shows a latitudinal decrease toward the equator in the surface ocean. The shorter residence time in the surface equatorial ocean (0–20 m) seems associated with higher productivity and more rapid particulate scavenging.

Activities of 222 Rn and 226 Ra were measured in water samples from the Chesapeake Bay during two summers and one winter in 1995 and 1997 in order to develop a potential groundwater tracer. A major estuary to the Bay, the Potomac, was also sampled for these nuclides during 1997 in order to assess their inputs to the Bay. The 222 Rn activities ranged between about 20 and 140 dpm/100 l within the Chesapeake Bay. Higher activities were encountered at the northern end of the Bay. In the upper Potomac, activities as high as 200–300 dpm/100 l were observed. These activities are twice to as much as two orders of magnitude higher than coastal ocean 222 Rn . The activities generally decrease with salinity and depth to the south and show little change between summer and winter. The 222 Rn activities are much in excess of its parent 226 Ra which suggests an active disequilibrated source of 222 Rn to these waters. Considering the short half-life of 222 Rn (3.8 days) and its limited exchange with the atmosphere, another important source is suggested to be the exchange of groundwater in lower salinity regions of the Bay or its tributaries. The inverse trend of 222 Rn against salinity is consistent with a fresh groundwater end member from the Chesapeake Bay watershed. The 222 Rn concentrations of the Potomac tributary are even greater than in the Bay, increasing from 47 dpm/100 l at the Bay entrance to about 280 dpm/100 l upstream and suggest an even more significant groundwater discharge. Calculations suggest as much as 10% of freshwater inputs to the Chesapeake Bay could be from groundwater.

Measurements of gas-, particle- and precipitation-phases of atmospheric mercury (Hg) were made in the South and equatorial Atlantic Ocean as part of the 1996 IOC Trace Metal Baseline Study (Montevideo, Uruguay to Barbados). Total gaseous mercury (TGM) ranged from 1.17 to 1.99 ng m−3, with a weighted mean of 1.61±0.09 ng m−3. These values compare well with Pacific Ocean data and earlier results from the Atlantic. The open-ocean samples recorded a distinctive inter-hemispheric gradient, which is consistent with a long-lived trace gas emitted to a greater extent from the Northern than from the Southern Hemisphere. Correlations with surface 222Rn measurements indicate an influence of regional terrestrial sources on open-ocean TGM concentrations. Total Hg in precipitation ranged from 10 to 99 pM (volume-weighted average: 17.8±2.9 pM). On average, about 72% of the total Hg was “reactive” (i.e., reducible by SnCl2). The data showed an apparent rapid nonlinear decrease in concentration with event size (“washout curve”). The wet depositional flux was estimated at 18–36 nmol m−2 yr−1 (4–7 μg m−2 yr−1), which is slightly lower than that found in mid-continental locations of North America (6–12 μg m−2 yr−1). 210Pb analyses indicate a strong impact of particles on rain Hg concentrations. Particle-phase Hg (range 5–25 fmol m−3; mean 12±1 fmol m−3; 66% “reactive”) was comparable to values over the equatorial Pacific. The dry depositional flux is ca. 0.4 nmol m−2 yr−1, or 0.4–1.0% of the wet flux. Particle-phase Hg concentrations did not change significantly when African dust was present during sampling. However, the Hg/Al ratios were consistent with crustal values during the dust periods. The residence time of TGM was calculated to be 1.3–3.4 yr in this region, based on standing stock estimates. Incubation of rainwater added to surface seawater gave reduction rates [i.e., production of elemental Hg (Hg°); 1.6–4.3% d of total Hg added] comparable to additions of inorganic ionic standards, indicating that Hg+2 from precipitation is reduced in a similar manner in surface waters. Thus, precipitation-phase Hg is generally available for evasion to the atmosphere following deposition to the surface ocean, effectively enhancing the mobility and residence time of Hg at the Earth's surface.

We report the distributions of transition elements in the surface sediments of the Yellow Sea including the coastal areas of both Korea and China. The maximum concentrations of LOI (loss on ignition), Al, and transition elements (Ti, V, Cr, Fe, Co, Ni, Zn and Cu), except Mn, are found in the central Yellow Sea where clay minerals predominate. A good positive correlation between silt plus clay contents and most of the transition elements (Ti, V, Cr, Fe, Co, Ni, Zn, and Cu, r=0.72–0.91) suggests that the distribution patterns of these elements are strongly controlled by quartz dilution. The distribution pattern of Mn is opposite to the other transition elements, displaying the maximum concentrations in the shallower regions where coarse sediments predominate. Higher Mn enrichment factors (max. EF: 3.0) and higher Mn/Fe ratios in the coastal sandy regions (relative to those in the other study areas and in suspended matter of the source rivers) suggest the presence of authigenic Mn by forming an oxidizing condition due to higher porosity but lower organic contents. In contrast, relatively lower Mn/Al ratios and lower enrichment factors (mean EF: 0.7) are observed in the central Yellow Sea where maximum organic contents are present. This suggests that the dissolutions of Mn oxides take place in the central Yellow Sea sediments by oxygen reduction during decomposition of organic matters.

We report the presence of the fallout isotope 207Bi (half-life = 38 years) in salt marsh sediments collected from Wolf Glade Salt Marsh, Lewes, Delaware and evaluate its usefulness as a transient tracer for geochronology. The commonly used geochronological tracers of salt marshes. 210Pb and 137Cs, were also measured to corroborate the results. The average sedimentation rate based on a constant excess 210Pb flux model in three cores (2 plus 1 duplicate) is estimated to be 3.2 ± 0.1 mm/year. Based on 137Cs and 207Bi data and an assumption that the fallout activities of these nuclides peaked during 1963, average rates are 3.5 ± 0.7 and 3.7 ± 0.2 mm/year, respectively. The scatter on the down-core 210Pb activity is relatively large which may be ascribed to variations in the atmospheric deposition rate of 210Pb, core compaction, or sedimentation. The 137Cs is present in sediments older than 50 years and suggests that these sedimentation rates may be compromised by the post-depositional mobility of 137Cs in salt marsh environments. The presence of 207Bi is detected at similar depths in all three cores which is consistent with a pulsed input of this nuclide into the environment from nuclear detonations and a post-depositional immobility. A higher degree of reliability in sedimentation rate estimates may thus be obtained using 207Bi. Based on the measured flux of 207Bi into salt marsh and an assumed inventory ratio of 207Bi137Cs, the total production of 207Bi from nuclear weapon testings is estimated to be on the order of 1015 Bq.

A simplified technique for the direct analysis of 210Pb by γ-spectrometry is developed. This technique corrects for the sample geometry, counting efficiency and the effects of self-absorption by eliminating the need for making individual transmission measurements of the 46.5 keV gamma, on every sample. Results obtained by using this technique on three types of sediment samples show an excellent agreement with other techniques which use individual transmission measurements to determine and correct for the effects of self-absorption.

Many researchers have reported the widespread occurrence of excess 210 Po in the global atmosphere and suggested probable sources such as resuspension of top soils, stratospheric aerosols, sea spray of the surface micro-layer, volcanic emission, and bio-volatile 210Po species from the productive ocean. We have observed excess 210Po on aerosols in the coastal atmosphere of the Chesapeake and Delaware Bays. On-board measurements in the Chesapeake Bay atmosphere show that the increase of this excess 210Po is dependent upon wind speed. Simultaneously measured activity ratios of 7Be/210Pb and 210Pb/222Rn argue against either higher altitude air or continental soils as the source of this excess. We hypothesize that the excess 210Po originates mainly from surface waters either by the sea-spray of the surface microlayer, or more likely, by gas exchange. We conclude gas exchange as the mechanism since the polonium excess increases linearly with wind speed over a threshold of 3 m s-1(mean) similar to other gases (i.e., CO2, SF6 , and DMS). In addition, higher 210Po excess with lower 222Rn is observed in on-shore marine air at Lewes, DE. This suggests sea-air exchange of volatile Po along with other bio-volatile species (i.e., DMS, DMSe, and MMHg) in the coastal productive ocean during high wind speeds.DOI: 10.1034/j.1600-0889.2000.00975.x

As the heaviest element of Group 6A, 210Po has a unique biogeochemistry in the environment that challenges our understanding. This chapter provides an overview of the research on 210Po in the atmosphere as well as in marine and other aqueous environments. Excess atmospheric 210Po has been attributed to external sources, such as volcanic emissions, resuspension of soil humus, incursion of stratospheric air, sea spray from the oceanic surface micro-layer, plant exudates including evapotranspiration, anthropogenic emissions (e.g., emission from coal combustion), and bio-volatilization through the formation of dimethyl polonide. Most of these sources have been qualitatively identified, yet they remain difficult to quantify. In the aqueous environment, 210Po is efficiently accumulated in plankton and bacteria and is biomagnified through the food webs, relative to its grandparent 210Pb, causing 210Po to be largely deficient in the euphotic zone. Globally, 210Po deficiency increases as ocean productivity decreases in the upper 1,000 m through biological transfer to the upper trophic levels. Smaller 210Po deficiencies in the productive areas of the ocean appear to be related to relatively active bacterial remineralization. Unusually high activities of 210Po are often found in the suboxic and anoxic waters in association with S, Mn, and Fe redox cycles. As many details of these processes remain elusive and under debate, we propose additional studies that should be conducted.

Submarine groundwater discharge (SGD) is an almost ubiquitous coastal feature that is driven by a combination of climatologic, hydrogeologic, and oceanographic processes. For example, terrestrial hydraulic gradients that reflect both short- and long-term climatic conditions almost always transport both surface- and groundwater toward the coast. In coastal oceans, physical processes such as wave setup, tidal pumping, and density-driven circulation may impact these hydraulic gradients and thus affect rates of SGD (Fig. 11.1.1) (Johannes 1980; Church 1996; Li et al. 1999; (year?); Taniguchi 2002; Burnett 2003). Although only fresh groundwater discharge has traditionally been accounted for in numerical simulations of coastal water budgets, saline groundwater discharge may be equally or even more important in terms of material transport across land/sea margins (Li et al. 1999; Kim et al. 2002; Burnett 2003; Kim et al. 2003a). In this chapter, we therefore define SGD to consist truly fresh groundwater, recirculated seawater, or a composite thereof.

The measurement of short-lived Ra-223 often involves a second measurement for supported activities, which represents Ac-227 in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of Ac-227, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles Ac-227 data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine end-members. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of Ac-227 near its potential sources.The average Ac-227 activities of nearshore marine end-members range from 0.4 dpm m(-3) at the Gulf of Mexico to 3.0 dpm m(-3) in the coastal waters of the Korean Strait. In analogy to Ra-228, we find the extension of adjacent shelf regions to play a substantial role for Ac-227 activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean Ac-227 inventory of 1.35 * 10(18) dpm Ac-227(ex) in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm m(-2) y(-1) from the deep-sea floor. For the shelf regions, we obtain a global inventory of Ac-227 of 4.5 * 10(15) dpm, which cannot be converted directly into a flux value, as the regional loss term of Ac-227 to the open ocean would have to be included.Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to Pa-231(ex). Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released [Moore, W.S., Ussler, W. and Paull, C.K., 2008-this issue. Short-lived radium isotopes in the Hawaiian margin: Evidence for large fluid fluxes through the Puna Ridge. Marine Chemistry]. Another potential mechanism of producing deviations in Ac-227/Ra-228 and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including Ac-227 in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution. (c) 2007 Elsevier B.V. All rights reserved.

[1] The magnitude of submarine fresh groundwater discharge (SFGD) was estimated using a freshwater budget of the coastal water, which was calculated from salinity anomalies off a volcanic island, Jeju, Korea. We obtained high-resolution profiles of salinity from the entire coastal area of Jeju Island using accurate CTD sensors. Lower salinity anomalies relative to the pristine offshore seawaters were observed and assumed to be a result of SFGD on the basis of negligible surface runoffs from the island and the relatively high levels of 222Rn in the low-salinity waters. The SFGD flux during the study period calculated from a freshwater budget of the water column was 2.5−3.8 × 106 m3 d−1, which is close to the long-term average based on the inland water balance. Our study shows that SFGD can be accurately and easily measured using a freshwater budget of the coastal waters off a highly permeable coastal zone with little surface runoff.

[1] In order to determine the physical and chemical factors controlling the outbreak of red tides, we monitored nutrients and other environmental parameters using a novel real-time monitoring buoy system during the summer of 2003 in the southern sea of Korea, where red-tide outbreaks occur every year. The real-time monitoring data on bioluminescence, which may indicate the presence of bioluminescent dinoflagellate species, showed a sudden increase under the lowest concentrations of dissolved inorganic nutrients. Our monitoring system for the first time provides real-time variations in nutrients and associated outbreaks of dinoflagellate red tides. This result supports the previous hypothesis by others that the outbreak of dinoflagellate red tides is associated with the limited growth of diatoms under depleted DIP or DIN conditions. We suggest that this real-time monitoring system can be utilized as a powerful tool for studying and predicting harmful dinoflagellate red tides in the coastal ocean.

We have investigated the cycling of naturally occurring 210 Po in waters from seasonally anoxic Pond B (South Carolina) and permanently anoxic Jellyfish Lake (Palau Islands, western Pacific Ocean). The maximum 210 Po activity in Pond B was about 14 mBq L -1 during summer. This activity was much higher than its parent 210 Pb activity, indicating excess 210 °Po inputs from bottom sediments. The summertime excess 210 Po activity was accompanied by increases in Fe and Mn, suggesting 210 Po diffusion from bottom sediments under reducing conditions. Activity of 210 Po was much lower under winter oxic conditions, most likely a consequence of efficient coprecipitation with Fe and Mn oxides that occurs with destruction of Pond B stratification. In permanently anoxic Jellyfish Lake, the maximum activity of 210 Po was 133 mBq L -1 , among the highest reported from any surface aqueous environment. A box model suggests that the release of only 2% of 210 Po, produced from the 210 Pb in the bottom sediments, would account for the observed excess. Our results suggest that 210 Po can be naturally enriched in anoxic environments to a high level, perhaps in concert with the Fe and Mn redox cycles.

Single cores from two Delaware salt marshes were used to reconstruct the historical deposition of trace metals (Cu, Pb, and Zn) and radionuclide tracers (U, 210Pb, and 137Cs) during the 20th century. Although the sedimentation rates of both cores were similar to the local sea-level rise (similar to 0.3 cm/yr), the two marshes have different depositional conditions. The Wolfe Glade salt marsh has maintained dense vegetation leading to almost complete preservation of the airborne-unsupported 210Pb, while the Great Marsh has a large fluvial soil input leading to some loss of unsupported 210Pb. The Wolfe Glade salt marsh accumulates more authigenic 238U from seawater but loses more 137Cs to seawater in association with larger organic decomposition relative to the Great Marsh. The reconstructed history shows that the atmospheric deposition of Cu, Pb, and Zn was maximum during the earlier 20th century, with a secondary peak during the 1970s for Pb. The anthropogenic stable Pb isotopic signature (206Pb/207Pb = 1.187) at this depth confirms that the source of Pb for this maximum is a nongasoline source, discounting postdepositional remobilization. This study suggests a possible strong regional pollution for Pb, along with Cu and Zn, in eastern Delaware during the earlier 20th century.

[1] During a 3-year record of 228Ra/226Ra ratio profiles (from nine cruises) in the Sargasso Sea, two profiles in the Spring (April 1997 and 1998) show distinct subsurface maxima. Such maxima in the radium isotope ratio record the subsurface advection of surface waters, such as subtropical mode waters. The April 1997 maximum occurred below the euphotic zone (between 300–400 m) and was also coincident with that of POC and dissolved oxygen, supporting the subsurface advection of surface waters. This single event represents a large isopycnal injection (23 g m−2) of organic carbon into the subsurface ocean. Although we cannot quantify carbon export by this process on a basin scale based on these single-site measurements, it may be an important pathway for short-term oceanic carbon export.

[1] We measured seepage rates of coastal groundwater from a volcanic island, standing in the South Sea of Korea. The seepage rates measured along the sandy coast were in the range 50–300 m/yr, which are much higher than those reported from typical continental coast. The 18O tracer in potential seeping waters signifies that they are mixtures of basal groundwater and pristine seawaters. On the eastern coast of Jeju, almost all groundwater discharge is attributed to recirculating seawater, while fresh groundwater contributes about 20% of the total submarine groundwater discharge (SGD) on the western coast of Jeju. Thus, SGD appears to be important for the management of water resources in western Jeju. The measured radionuclides (228Ra, 226Ra, and 222Rn) and nutrients in the groundwater suggest that the discharge of both fresh and recirculated seawater will have a significant influence on the budget of coastal nutrients and other chemical constituents in this region.

We have measured 90 Sr activities in the marine environment (seawater, sediments and organisms) off the two Korean atomic power stations at Gori and Weolseong. The marine sampling sites were chosen in the vicinity of the power stations to investigate the dispersion of any local 90 Sr sources. The 90 Sr activities in seawater ranged from 1.3 to 1.9 mBq/l (mean: 1.4, n =16) and 0.9 to 1.5 mBq/l (mean: 1.3, n =29) at the Gori and Weolseong sites, respectively. These activities are comparable with those reported for the remote open ocean, suggesting that the 90 Sr at these sites originated primarily from global fallout, which occurred during the 1960s, rather than from any local sources. The 90 Sr activities in marine sediments ranged from 116 to 1277 mBq/kg (mean: 565, n =12) and from 304 to 1799 mBq/kg (mean 933, n =6) at the Gori and Weolseong sites, respectively. The horizontal distribution of 90 Sr in surface sediments appears to be affected by grain size as well as local sedimentation rate. The enrichment of 90 Sr in fish (5.5±2.6 mBq/kg, n =5) and shellfish (7.1±1.2 mBq/kg, n =2) was much lower than that in seaweed (57±33 mBq/kg, n =5).

Large (approximately 10 g) soil and sediment samples are often required for analysis of low-level man-made actinides for monitoring environmental radioactivity. However, use of large environmental samples often results in significant chemical losses during chemical separations due to matrix interferences. We present a technique based on the ion-exchange resin Diphonix which selectively collects actinides and lanthanides into a common form, which then behaves uniformly and predictably during subsequent separation schemes. Diphonix is attractive for this purpose because it has an extremely high affinity for actinides and a low affinity for most common ions and is resistant to hydrofluoric acid. After being adsorbed onto Diphonix resin in a column mode at a pH approximately 1, actinides are completely eluted with 0.5 M 1-hydroxyethylidene-diphosphonic acid (HEDPA). After destruction of the HEDPA by ozonation or use of Fenton's reagent, Am, Pu, U, and Th are separated from each other and the remaining matrix by use of extraction chromatographic resins. We obtained high and consistent chemical recoveries (mean, 85%), as well as excellent chemical separations, for Am, Pu, U, and Th through the entire procedure for several 10-g soil and sediment samples.

We obtained real-time monitoring data of water temperature, salinity, wind, current, CH 4 and other oceanographic parameters in a coastal bay in the southern sea of Korea from July 8 to August 15, 2003, using an environmental monitoring buoy. In general, the transfer velocity of environmental gases across the air–sea interface is obtained exclusively from empirical relationships with wind speeds. However, our monitoring data demonstrate that the agitation of the aqueous boundary layer is controlled significantly by tidal turbulence, similar to the control exercised by wind stress in the coastal ocean. The sea-to-air transfer of CH 4 is enhanced significantly during spring tide due to an increase in the gas transfer velocity and vertical CH 4 transport from bottom water to the surface layer. Thus, our unique time-series results imply that the sea-to-air transfer of gases, such as CH 4 , DMS, DMHg, N 2 O, CO 2 and 222 Rn, from highly enriched coastal bottom waters, is controlled not only by episodic wind events but also by regular tidal turbulence in the coastal ocean. DOI: 10.1111/j.1600-0889.2005.00170.x

[1] Atmospheric samples were collected aboard ship in the South and equatorial Atlantic (35°S–10°N) between 19 May and 20 June 1996. We measured 222Rn in air, 210Pb in aerosol, and trace elements (Fe, Mn, Zn, Pb, Cu, Cd, Ni, and Cr), 210Pb, and 210Po in precipitation samples. The large variation of 222Rn in air suggests a significant change in the incursion of continental air with time and latitude in the remote Atlantic. In the equatorial and subtropical Atlantic (20°S–10°N), 222Rn activity was lower but 210Pb/222Rn ratios were higher than those at higher latitudes. The higher 210Pb/222Rn ratios in the equatorial Atlantic appear to be due to prevailing trade easterly winds which transport a supported source of 210Pb in Saharan dust from the African Sahel. The enrichment of noncrustal trace elements in precipitation samples from the remote equatorial Atlantic was small on account of the remoteness from the continental emission regions and as a result of dilution with Saharan dust. The wet depositional fluxes of major crustal elements (Fe and Mn) were two- to three-fold higher, while those of Cd and Zn were two- to ten-fold lower, in the South and equatorial Atlantic relative to the western North Atlantic (Bermuda) or North Atlantic coast (Lewes, Delaware). Thus, dominant wet precipitation of Saharan dust in the Intertropical Convergence Zone (ITCZ) areas of the equatorial Atlantic appears to be a large potential source of micronutrients (i.e., Fe) to surface seawater.

[1] There has emerged a recognition that the submarine discharge of fresh, brackish, and marine groundwaters into the coastal ocean is comparable to the inputs via river discharge. However, the factors controlling submarine groundwater discharge (SGD) are poorly understood owing to a lack of SGD measurement tools in dynamic coastal waters. We observed bi-hourly variations of the natural SGD tracers, 222Rn and CH4, at a coastal seawater station over two seasons using novel monitoring techniques. This unique data set suggests that SGD increases sharply from neap to spring tide during the wet season. The observed increase is much greater than what would be expected from the rainfall and tidal-height changes. We conclude from this that the temporal variation of SGD is regulated predominantly by a semi-monthly fluctuation of a tidal oscillating pumping force in this environment.

[1] We observed a sudden initiation of bottom-water formation in the East/Japan Sea associated with a severely cold winter in 2000–2001. An increase in dissolved oxygen concentration as well as decreases in temperature and nutrient concentrations for the bottom waters provides unequivocal evidence that cold, oxygen-rich and nutrient-poor surface waters were injected directly to the bottom. Since the conveyor-belt in the East Sea has been undergoing dramatic change with a complete halt to bottom-water formation since the mid-1980s, this sudden episode of bottom-water formation could easily be detected. Though the amount of bottom water formed was rather small, being only about 0.03% of the volume in the past time, the observation clearly demonstrates that the conveyor-belt is directly connected to the weather system.

Many researchers have reported the widespread occurrence of excess 210 Po in the global atmosphere and suggested probable sources such as resuspension of top soils, stratospheric aerosols, sea spray of the surface micro-layer, volcanic emission, and bio-volatile 210 Po species from the productive ocean. We have observed excess 210 Po on aerosols in the coastal atmosphere of the Chesapeake and Delaware Bays. On-board measurements in the Chesapeake Bay atmosphere show that the increase of this excess 210 Po is dependent upon wind speed. Simultaneously measured activity ratios of 7 Be/ 210 Pb and 210 Pb/ 222 Rn argue against either higher altitude air or continental soils as the source of this excess. We hypothesize that the excess 210 Po originates mainly from surface waters either by the sea-spray of the surface microlayer, or more likely, by gas exchange. We conclude gas exchange as the mechanism since the polonium excess increases linearly with wind speed over a threshold of 3 m s -1 (mean) similar to other gases (i.e., CO 2 , SF 6 , and DMS). In addition, higher 210 Po excess with lower 222 Rn is observed in on-shore marine air at Lewes, DE. This suggests sea-air exchange of volatile Po along with other bio-volatile species (i.e., DMS, DMSe, and MMHg) in the coastal productive ocean during high wind speeds. DOI: 10.1034/j.1600-0889.2000.00975.x