Fei-Jan Lin

Factors controlling the solubilities of trace metals from non-remote aerosols deposited to the sea surface by the ‘dry’ deposition mode

Abstract Previous studies have shown that when non-remote marine aerosols are delivered to the sea surface by the ‘dry’ deposition mode some trace metals (e.g. Cu, Zn and Pb) are more soluble from urban-rich than from crust-rich aerosols, but that others (e.g. Mn and Cd) are significantly soluble from both aerosol types. These solubility variations are not directly related to the enrichment of the metals with respect to the crustal source and an attempt was therefore made to explain them within a speciation-mediated ‘potential environmental mobility” framework, in which metals in exchangeable associations are the most mobile in aqueous media. The results showed that there is a well-developed relationship between the extent to which a trace metal is soluble in seawater and the extent to which it is held in exchangeable associations in non-remote marine aerosols. Thus, Cu, Zn and Pb are more soluble from urban-rich than from crust-rich aerosols because they are more exchangeable in character in the urban-rich types. In contrast, Mn and Cd are significantly soluble from both crust-rich and urban-rich aerosols because they are signifcantly exchangeable in character in both aerosol types. However, there is not a 1:1 relationship between the extent to which all trace metals are exchangeable in character and the extent to which they are soluble in seawater. For example, in one urban-rich aerosol the average ratios between the percentage of the total metal which is soluble in seawater and the percentage which is in exchangeable associations are 0.93 for Zn but only 0.63 for Pb. As a result, only about 65% of the ‘potentially environmentally mobile’ anthropogenic Pb delivered to the oceans via non-remote urban-rich marine aerosols will enter the dissolved trace metal pool, compared with about 90% of the anthropogenic Zn. In seawater, crustal aerosols can act as re-scavenging substrates for dissolved Zn and Pb released from urban-rich aerosols. In contrast, the dissolved Mn and Cd released from urban-rich aerosols is not re-scavenged by crustal aerosols. After their deposition to the sea surface urban-rich aerosols can therefore act as sources for dissolved Zn, Pb, Mn and Cd to the mixed layer. In contrast, whereas crust-rich aerosols are still sources of dissolved Mn and Cd, they can act as sinks for dissolved Zn and Pb in the oceanic mixed layer. The trace metal ‘seawater solubility-exchangeable speciation’ relationship derived in the present paper can be applied directly to coastal seas and to non-remote ocean regions, such as the North Sea and the Arabian Sea; however, for some trace metals, e.g. Fe and Pb, aerosol solubility characteristics may be different in remote open-ocean regions.

Organic carbon and nitrogen contents and their isotopic compositions in surficial sediments from the East China Sea shelf and the southern Okinawa Trough

Abstract The southern Okinawa Trough has been noted as an important depocenter for the particulate organic matter from the East China Sea shelf. In order to determine the major sources of sedimentary organic matter in the southern Okinawa Trough, we analyzed surficial sediments from the East China Sea shelf and the southern Okinawa Trough for organic carbon and nitrogen contents and their isotopic compositions in the decarbonated fraction. Distributions of total organic carbon content, δ13Corg and nitrogen content all show a similar spatial pattern, resembling the distribution of fine-grained sediments. The coastal belt of elevated organic carbon content extends southward from the Changjiang mouth and veers offshore towards the southern Okinawa Trough just north of Taiwan, implying a pathway for channeling fine-grained sediments from the inner shelf to the depocenter. This distribution pattern is consistent with the shelf circulation. The isotope compositions (δ13Corg, δ15N) of sediments from the southern Okinawa Trough fall between those of riverine particulate organic matter and the mid-outer shelf sediments, but overlap with those of the inner shelf sediments. In addition, the previously reported δ13Corg values of sinking particles collected by sediment traps in the southern Okinawa Trough are also close to those of the inner shelf sediments, especially during high-flux conditions. Therefore, the isotopic evidence strongly supports the notion that a major fraction of the sedimentary organic matter in the southern Okinawa Trough may originate from the inner shelf.

The solid state speciation of copper in surface water particulates and oceanic sediments

A sequential leaching technique has been used to characterize the solid state speciation of total copper (∑Cu) among a number of operationally defined host fractions in surface seawater particulates from the Atlantic Ocean, a diagenetically active hemipelagic sediment core from the eastern Mediterranean, a turbidite - rich sediment core from the Madeira Abyssal Plain and a series of 79 Atlantic Ocean surface or near surface sediments. Around 50% of the ∑Cu in the surface water particulates is held in organic associations. When the material is deposited at the sediment surface, following its entry into the down-column carbon flux, the ∑Cu undergoes phase transformations as the organic carriers are destroyed. However, some of the organically associated copper (Cu5) is preserved in the sediments, the amount depending on the diagenetic environment of deposition. The relationship between ∑Cu and organic carbon in an oceanic sediment may be masked, but the partitioning speciation data has shown that good correlations can be found between organic carbon and Cu5. The concentration of Cu5 in Atlantic Ocean surface sediments is highest in hemipelagic (diagenetically active) sediments deposited in the marginal regions, and lowest in open-ocean (less diagenetically active) sediments of the Mid-Atlantic Ridge and ridge flanks. The marginal sediments contain an average of ∼20% of their total Cu in an organic association, with the result that these sediments can act as traps for seawater-derived Cu that would normally be regarded as being ‘reactive’ in the marine environment. To a first approximation, the preservation of Cu5 in the sediments mimics that of primary production in the overlying waters, and so ‘fingerprints’ the operation of the global ocean carbon flux in oceanic deposits. However, the relationship can be perturbed by the off-shelf transport of organic-rich, Cu5-containing, turbidites which can result in the transfer and burial of organic copper host fractions in open-ocean oxic environments.

High wintertime particulate matter pollution over an offshore island (Kinmen) off southeastern China: An overview

Both the Yangtze River Delta (YRD) and the Pearl River Delta (PRD), the two most rapidly developing areas in eastern China, have suffered from serious air pollution, and thus, numerous investigations were devoted to studying these problems. Other areas in eastern China have received less attention despite similar rapid development in their industries and economy. In this study, we analyzed air‐quality data from Kinmen Island (24°27′26′′N, 118°19′36′′E) located off Fujian Province and between the two above‐mentioned deltas. Our results clearly show that the study area is experiencing serious air quality deterioration. Particularly, high levels of suspended particulate matter (PM) were observed during winter, when the northeasterly monsoon prevails. For example, concentrations of wintertime PM10 (particles ≤ 10 mm in diameter) frequently exceeded 100 mg/m3 in the last three years. In addition to the air‐quality data analysis, aerosol samples were collected between 22 November 2007 and 6 March 2008 and subjected to chemical analyses of various species. Our findings show that the three principal PM components include organic, mineral, and sulfate species with moderate to minor fractions of nitrate, sea salt, elemental carbon, and trace metal oxides. The high PM levels observed over the island may be partly attributed to the transport from a mixed‐type industrial area located ∼40 km northeast of Kinmen. Our study could partially fill the air quality data gap between the YRD and PRD regions, and highlight the alarming fact that air pollution has gradually expanded along eastern China’s coastal zone.

Effects of acidic processing, transport history, and dust and sea salt loadings on the dissolution of iron from Asian dust

[1] Aerosol particles collected over the East China Sea (ECS) were analyzed for water-soluble Fe (Fe s ), total Fe (Fe T ), and other chemical species. Eight samples were classified as high Asian dust (HAD) on the basis of total Al concentrations >1500 ng/m 3 . Comparisons with low Asian dust (LAD) samples showed that unlike Fe T or most other substances, the percentage of Fe T soluble in deionized water (%Fe s ) was lower in the HAD samples. The %Fe s in the HAD samples varied with transport pattern and air mass history. As the difference in Fe s concentrations between HAD and LAD is relatively small and HAD occurs several days each year, the supply of Fe s through dry deposition to the surface ocean may be less sporadic than previously thought. Soluble Fe correlated with non-sea-salt sulfate, water-soluble organic carbon, and nitrate, possibly because of an anthropogenic, relatively soluble, form of Fe or enhanced dissolution caused by reactions with anthropogenic acids. Sea salt loadings evidently have a negative effect on %Fe s , presumably due to buffering effects of the salts. Dust concentrations and %Fe s followed an inverse power law relationship with a moderate correlation, suggesting that the %Fe s may be increased by acid processing during transport as dust loadings gradually decrease.

Hemispheric dispersion of radioactive plume laced with fission nuclides from the Fukushima nuclear event

Radioactivities of particulate 131I and 137Cs released from the Fukushima nuclear accident were monitored in a regional aerosol network including two high mountain sites (central Taiwan and Tibetan Plateau). The results were integrated with data measured elsewhere around the world, with special focus on the mid-latitudes. The hemispheric transport of the Fukushima radiation clouds (FRCs) by the westerlies took

The effect of a cyclonic eddy on the distribution of lithogenic particles in the southern East China Sea

18 days, displaying an exponential-like decrease eastward, with a dilution factor of at least five orders of magnitude following a full circuit around the globe. The initial two waves of FRCs may travel at different atitudes: the first one at

Hydrothermal signatures in the southern Okinawa Trough detected by the sequential extraction of settling particles

3–4 km, whereas the second one up to 5 km or more. 131I and 137Cs were fractionated during transport, with 137Cs concentrated in the shallower layer, susceptible to depositional removal, while 131I moving faster and higher. This accident may be exemplified to identify some atmospheric processes on the hemispheric scale.

Trace metal solid state speciation changes associated with the down-column fluxes of oceanic particulates

Off northeastern Taiwan, the collision between the Kuroshio Current (KC) and the East China Sea (ECS) shelf forms a branch current (Kuroshio Branch Current) on the shelf, and the counterclockwise deflection of the subsurface Kuroshio water annually generates a cyclonic eddy, about 70 km in diameter, over the shelf-slope in summer. In this study, the total suspended matter collected from varying water depths over the eddy during August 1994 has been analyzed for Al, which is used as an indicator element to trace lithogenic particle transport. Simultaneously, the measurements of current field, using the Shipboard Acoustic Doppler Current Profiler, and hydrography have also been conducted on the same cruise during the seawater sampling. These offer an opportunity for direct examination of the relationships between circulation patterns and distributions of lithogenic particles to further establish a transport model for lithogenic particles. However, we must emphasize that this is a representative case for the export of terrigenous suspensions delivered from rivers, although the observation was made only in summer. The spatial distribution of particulate Al (PAI) in the upper water displays an Ω shape with high concentrations of PAI close to the Taiwan coast and around the eddy center. It suggests that Taiwan-derived riverborne particulates are the main source for the lithogenic particles in the upper water of the study area. Moreover, the PAI in the upper water is essentially constrained by the cyclonic eddy, and the entrainment and subsequent accumulation of lithogenic particles occur at the eddy center. The 6 μg/l contour of PAI in the upper water almost matches the western boundary of the main stream and branch of the KC across the ECS shelf-slope, and two concentration provinces of PAI can be identified from this contour: one to the west is larger and variable and the other to the east is smaller and uniform. This indicates that the main stream and branch of the KC may confine terrigenous particles to the inshore area where mixing of the lithogenic particle-rich coastal water and the clearer Kuroshio water occurs and may act as a barrier to the offshore transport of terrigenous particles to regions farther away from the coast, toward the north and east. In this study, a conceptual model for the transport of lithogenic particles in the water of the southern ECS is proposed according to the spatial distributions of PAI. This model suggests that the cyclonic eddy at the turning site of the KC may be the important conduit for the indirect transport of terrigenous particles from the ECS shelf and slope to the southern Okinawa Trough or the Pacific Ocean. This is also a valuable example of the role of the eddy system in regulating the distribution and transport of terrigenous particulates.

Ammonium deficiency caused by heterogeneous reactions during a super Asian dust episode

Sediment trap samples collected over 6 months at two depths within the southern Okinawa Trough (SOT) have been analyzed for phase associations of Al, Fe, Mn and Pb by six-stage sequential extraction (SSSE). The deeper samples are characterized by the presence of hydrothermal constituents (such as Mn and likely Fe and Pb), while shallower samples are representative of background-settling particles originating from laterally transported sediments. These results suggest that the extraction scheme is appropriate for detecting particles affected by hydrothermal emanations. Analytical results show that shallower and deeper samples have similar total Al contents and total Fe contents; by contrast, Mn and Pb are 1.7- and 1.6-fold higher in the deeper samples than in the shallower samples, respectively. Additionally, the two depths have almost the same phase associations for Al and Fe, but largely different phase associations for Mn and Pb. Compositional differences in Mn and Pb between the two depths depend essentially on the relative abundance of the fresh oxide fraction. The observed phase association suggests that Mn anomalies in the deeper samples are derived preferentially from adsorptive oxidation of dissolved hydrothermal Mn onto settling particles and/or incorporation of very fine Mn-enriched hydrothermal precipitates within settling particles. Pb anomalies in the deeper samples imply either a similar hydrothermal origin and/or scavenging of dissolved Pb from ambient water by newly formed oxides/hydroxides. The constant concentration of Mn within the deeper samples may reflect phase equilibrium between dissolved Mn and settling particles. Hydrothermally derived fluxes, defined as the fraction from hydrothermal contributions and/or indirectly by processes related to hydrothermal activities, have been estimated at 7.0F3.1 mg/m 2 /day for Fe, 2.3F1.0 mg/m 2 /day for Mn and 0.07F0.03 mg/m 2 /day for Pb. These fluxes are higher than those found at other hydrothermal systems owing to high loads of settling and suspended particles. D 2003 Elsevier B.V. All rights reserved.