Biogenic Silicate Research Articles

Biogenic silicate glass-ceramics: Physical, dielectric, and electrical properties

Biogenic silicate glass-ceramics were synthesized from the rice husk and eggshell powder (ESP) using the melt-quench method. The crystallite size (0.351–0.370 nm) increased and the bandgap (3.43–3.15 eV) decreased as the ESP concentration increased from 10 to 20 wt%. The higher dielectric constant at lower frequency range is attributed to the accumulation of charge carriers at the grain boundaries. Beyond ≥350 °C, the maximum dielectric loss was observed due to hopping of charge carriers between Ca2+ and Si4+. The impedance decreased from 8 × 106 to 2 × 102 with respect to the frequency (1 × 103 to 1 × 105 Hz). After the kink temperature (495 °C), the activation energy was observed to be increased from 0.73 to 0.74eV for ESP = 10 wt% and from 0.76 to 0.78 eV for ESP = 20 wt%. The study of silicate glass-ceramics suggests major applications in the field infrared heating elements and optoelectronics.

Seasonal flux patterns and carbon transport from low-oxygen eddies at the Cape Verde Ocean Observatory: lessons learned from a time series sediment trap study (2009–2016)

Abstract. Mesoscale eddies are abundant in the eastern tropical North Atlantic and act as oases for phytoplankton growth due to local enrichment of nutrients in otherwise oligotrophic waters. It is not clear whether these eddies can efficiently transfer organic carbon and other flux components to depth and if they are important for the marine carbon budget. Due to their transient and regionally restricted nature, measurements of eddies' contribution to bathypelagic particle flux are difficult to obtain. Rare observations of export flux associated with low-oxygen eddies have suggested efficient export from the surface to the deep ocean, indicating that organic carbon flux attenuation might be low. Here we report on particle flux dynamics north of the Cabo Verde islands at the oligotrophic Cape Verde Ocean Observatory (CVOO; approx. 17∘35′ N, 24∘15′ W). The CVOO site is located in the preferred pathways of highly productive eddies that ultimately originate from the Mauritanian upwelling region. Between 2009 and 2016, we collected biogenic and lithogenic particle fluxes with sediment traps moored at ca. 1 and 3 km water depths at the CVOO site. From concurrent hydrography and oxygen observations, we confirm earlier findings that highly productive eddies are characterized by colder and less saline waters and a low-oxygen signal as well. Overall, we observed quite consistent seasonal flux patterns during the passage of highly productive eddies in the winters of 2010, 2012 and 2016. We found flux increases at 3 km depth during October–November when the eddies approached CVOO and distinct flux peaks during February–March, clearly exceeding low oligotrophic background fluxes during winter 2011 and showing an enhanced particle flux seasonality. During spring, we observed a stepwise flux decrease leading to summer flux minima. The flux pattern of biogenic silicate (BSi) showed a stronger seasonality compared to organic carbon. Additionally, the deep fluxes of total mass showed an unusually higher seasonality compared to the 1 km traps. We assume that BSi and organic carbon/lithogenic material had different sources within the eddies. BSi-rich particles may originate at the eddy boundaries where large diatom aggregates are formed due to strong shear and turbulence, resulting in gravitational settling and, additionally, in an active local downward transport. Organic carbon associated with lithogenic material is assumed to originate from the interior of eddies or from mixed sources, both constituting smaller, dust-ballasted particles. Our findings suggest that the regularly passing highly productive eddies at CVOO repeatedly release characteristic flux signals to the bathypelagic zone during winter–spring seasons that are far above the oligotrophic background fluxes and sequester higher organic carbon than during oligotrophic settings. However, the reasons for a lower carbon flux attenuation below eddies remain elusive.

Clay Minerals and Detrital Material in Paleocene–Eocene Biogenic Siliceous Rocks (Sw Western Siberia): Implications for Volcanic and Depositional Environment Record

The paper presents the results of a study on clay minerals and detrital material of biosiliceous rocks (Paleocene–Eocene) from three sections in the Transuralian region. The authigenic processes in sediments resulted in the formation of dioctahedral clay minerals (illite, smectite) and insignificant amounts of sulfide phases (pyrite, hydrotroillite). Detrital minerals from the studied diatomites and diatomaceous clays often have a subangular and semi-rounded habit that is evidence of a low degree alteration of the sedimentary material in the provenance areas. The high degree of preservation of the bioclastic debris and the transformation of the limited volcanogenic substratum in clay minerals apparently was possible by initial burial diagenesis. The morphology of kaolinite and illite suggests that these mineral formations were caused by diagenesis with feldspars and smectites as a substrate for their formation. The smectite zone of weathering crust that developed on the adjacent land could have also served as a significant source of smectites entering the sea basin. The association with smectite in aggregates of mixed clayey composition indicates a sequential smectite-to-illite reaction via mixed-layered minerals. Such minerals as amphiboles, pyroxenes, and olivines, semi-stable to transportation and genetically associated with ultramafic rocks, form a significant part of the clastic fraction of the rock, indicating the proximity of provenance areas. This is the evident reason that the provenance areas made of mafic and ultramafic rocks played an essential role.

Freshwater runoff effects on the production of biogenic silicate and chlorophyll-a in western Patagonia archipelago (50–51°S)

Freshwater discharged from the continent to the sea plays an important role in the biogeochemistry and productivity of the coastal ocean. The continental drainage basin characteristics can be a key local factor determining the concentration, proportions and timing of bio-active freshwater solutes discharged into an estuary, and thus could play a “bottom up” role modulating the phytoplankton assemblage attributes. In a period from 2015 to 2017 we characterize the concentration of total alkalinity (AT) and silicic acid (DSi) in continental and estuarine surface waters at both limestone and silicates basins of the Madre de Dios archipelago (ca. 50–51°S and 75.5–75°W). Continental waters had high AT in limestone and low AT in silicate basins causing differences in the specific total alkalinity of estuarine waters. Similarly, while limestone continental water is characterized by very low DSi concentrations (3 ± 3 μM, n = 16) that dilute initial DSi concentrations of sub-Antarctic Surface Water (SAASW) at the mixing zone, continental water from silicate drainage basins (Patagonian Batholith; 53 ± 49 μM, n = 18) acts as a source of DSi to the estuary. Experimental SAASW dilution with two types of native continental water, one supplying high AT – low DSi and another supplying low AT – high DSi to the western central Patagonian Archipelago, resulted in phytoplankton assemblages with different characteristics. While “silicate-water” freshening of SAASW resulted in higher biogenic silicate (bSi) content, “limestone-water” freshening of SAASW resulted in higher levels chlorophyll a allocated in small cells-size range (0.45–2 μm). We suggest that the local variability in the suite of solutes delivered from continental runoff can significantly modulate phytoplankton communities attributes, especially in western Patagonian with interior estuarine waters characterized by extensive channels and fjords, together with extreme precipitation/runoff (>6 m y−1) and sharp contrasts in lithology.

Persistency in Fracture Tendency of Subsurface Biogenic Siliceous Rocks

Persistency in Fracture Tendency of Subsurface Biogenic Siliceous Rocks

Temporal sedimentary record of thallium pollution in an urban lake: An emerging thallium pollution source from copper metallurgy.

Thallium (Tl) is an extremely toxic metal with high risk. Sediment samples from a well dated sediment core retrieved from a heavily polluted urban lake were measured to assess the magnitude of Tl pollution and reveal its transfer mechanisms within the lake. The results show that the lake has experienced serious Tl pollution during the past 60 years, owing to a large influx of Tl-bearing wastes mostly from a neighboring copper (Cu) smelter. The Tl contents in the sediment core at different depths generally correlated positively with the production scale of Cu smelting activities in the past. Further mineralogical analysis on the electrostatic precipitator dust from the Cu smelter and highly-polluted samples from the sediment core by electronic microscopy and X-ray diffraction suggested that Tl was primarily bound to quartz and aluminosilicates. Large quantities of Tl were also observed in diatom frustules collected from the sediments, suggesting a potentially significant role of biogenic silicates in the uptake and transfer of Tl in the sediment-water system. The findings indicate a new and emerging pollution source of thallium arising from copper metallurgy activities. The results also highlight the necessity of strengthened monitoring and regulations towards Tl pollution in environmental systems impacted by Cu smelting activities in China and other nations.

Composition and vertical flux of particulate organic matter to the oxygen minimum zone of the central Baltic Sea: impact of a sporadic North Sea inflow

Abstract. Particle sinking is a major form of transport for photosynthetically fixed carbon to below the euphotic zone via the biological carbon pump (BCP). Oxygen (O2) depletion may improve the efficiency of the BCP. However, the mechanisms by which O2 deficiency can enhance particulate organic matter (POM) vertical fluxes are not well understood. Here, we investigate the composition and vertical fluxes of POM in two deep basins of the Baltic Sea (GB: Gotland Basin and LD: Landsort Deep). The two basins showed different O2 regimes resulting from the intrusion of oxygen-rich water from the North Sea that ventilated the water column below 140 m in GB, but not in LD, during the time of sampling. In June 2015, we deployed surface-tethered drifting sediment traps in oxic surface waters (GB: 40 and 60 m; LD: 40 and 55 m), within the oxygen minimum zone (OMZ; GB: 110 m and LD: 110 and 180 m) and at recently oxygenated waters by the North Sea inflow in GB (180 m). The primary objective of this study was to test the hypothesis that the different O2 conditions in the water column of GB and LD affected the composition and vertical flux of sinking particles and caused differences in export efficiency between those two basins. The composition and vertical flux of sinking particles were different in GB and LD. In GB, particulate organic carbon (POC) flux was 18 % lower in the shallowest trap (40 m) than in the deepest sediment trap (at 180 m). Particulate nitrogen (PN) and Coomassie stainable particle (CSP) fluxes decreased with depth, while particulate organic phosphorus (POP), biogenic silicate (BSi), chlorophyll a (Chl a) and transparent exopolymeric particle (TEP) fluxes peaked within the core of the OMZ (110 m); this coincided with the presence of manganese oxide-like (MnOx-like) particles aggregated with organic matter. In LD, vertical fluxes of POC, PN and CSPs decreased by 28 %, 42 % and 56 %, respectively, from the surface to deep waters. POP, BSi and TEP fluxes did not decrease continuously with depth, but they were higher at 110 m. Although we observe a higher vertical flux of POP, BSi and TEPs coinciding with abundant MnOx-like particles at 110 m in both basins, the peak in the vertical flux of POM and MnOx-like particles was much higher in GB than in LD. Sinking particles were remarkably enriched in BSi, indicating that diatoms were preferentially included in sinking aggregates and/or there was an inclusion of lithogenic Si (scavenged into sinking particles) in our analysis. During this study, the POC transfer efficiency (POC flux at 180 m over 40 m) was higher in GB (115 %) than in LD (69 %), suggesting that under anoxic conditions a smaller portion of the POC exported below the euphotic zone was transferred to 180 m than under reoxygenated conditions present in GB. In addition, the vertical fluxes of MnOx-like particles were 2 orders of magnitude higher in GB than LD. Our results suggest that POM aggregates with MnOx-like particles formed after the inflow of oxygen-rich water into GB, and the formation of those MnOx–OM-rich particles may alter the composition and vertical flux of POM, potentially contributing to a higher transfer efficiency of POC in GB. This idea is consistent with observations of fresher and less degraded organic matter in deep waters of GB than LD.

Thallium occurrence and partitioning in soils and sediments affected by mining activities in Madrid province (Spain)

Thallium (Tl) and its compounds are toxic to biota even at low concentrations but little is known about Tl concentration and speciation in soils. An understanding of the source, mobility, and dispersion of Tl is necessary to evaluate the environmental impact of Tl pollution cases. In this paper, we examine the Tl source and dispersion in two areas affected by abandoned mine facilities whose residues remain dumped on-site affecting to soils and sediments of natural water courses near Madrid city (Spain). Total Tl contents and partitioning in soil solid phases as determined by means of a sequential extraction procedure were also examined in soils along the riverbeds of an ephemeral and a permanent streams collecting water runoff and drainage from the mines wastes. Lastly, electronic microscopy and cathodoluminescence probe are used as a suitable technique for Tl elemental detection on thallium-bearing phases. Tl was found mainly bound to quartz and alumino-phyllosilicates in both rocks and examined soils. Besides, Tl was also frequently found associated to organic particles and diatom frustules in all samples from both mine scenarios. These biogenic silicates may regulate the transfer of Tl into the soil-water system.

Bar-built estuary as a buffer for riverine silicate discharge to the coastal ocean

River discharge is a primary source of silicates to the ocean. In this study, we show that a bar-built estuary can buffer this silicate input, which may influence the onset of the diatom spring bloom and have a leveling effect on coastal diatom production dynamics. Primary production in the northeastern Gulf of Mexico is strongly affected by the outflow of nutrient-rich water from the Apalachicola River that enters into the Apalachicola Bay. We compared the seasonal dynamics of dissolved silicate (DSi), dissolvable particulate biogenic silicate (BSi), and the total of dissolved and dissolvable silicate (DSi+BSi) in the water column and pore water at two sandy sublittoral sites located in Apalachicola Bay and the adjacent coastal Gulf of Mexico in order to determine the influence of the Bay on silicate transfer to the coastal Gulf. The one-year time series measurements in the Bay water column showed that DSi was strongly influenced by the riverine outflow, while the DSi concentrations in the nearby coastal Gulf water followed a different trend and appeared to be dominated by biological processes. The temporal changes in pore water DSi, BSi, and DSi+BSi were similar at both study sites suggesting that larger scale processes, i.e., increased sediment flushing by increased wave action in winter, controlled these changes. The sediments acted as a continuous source of DSi to the overlying water, and when the river discharge was lower during early winter, the magnitude of area-integrated DSi flux from the Bay sediments was similar to the riverine DSi input to the Bay. The Bay sediments thus functioned as a significant source of DSi for the Bay and the adjacent Gulf at the onset of the diatom spring bloom and before Apalachicola River discharge reached maximum discharge in late winter/early spring.

达里诺尔湖沉积物中无机碳的形态组成

Sediments play an important role in carbon cycle as the important sources and sinks of carbon.The role of sediments in the carbon cycle is closely related to the forms and distribution of inorganic carbon in the sediments.The forms of inorganic carbon have different capacity in the carbon cycle and recycle.Forms and changes of inorganic carbon in the sediments were essential for the fluxes and processes of carbon across the water-sediment interface.The study of inorganic carbon forms is the basis and premise for discussing their contribution to carbon cycling.In this wok,the sequential extraction method was employed to extract inorganic carbon forms in sediments from Dali Lake.The form distribution characters of inorganic carbon in surface sediments and sediment cores were studied.The correlations between inorganic carbon and physical-chemistry characteristics such as total organic carbon(TOC),total nitrogen(TN),total phosphorus(TP) and biogenic silicate(BSi) were discussed in sediment cores.The results showed that the dominant form of inorganic carbon was NH2OH·HCl form both in surface sediment and sediment cores;The content of NH2OH·HCl form in sediments ranges from 6.26 to 17.51 mg/g,with mean content of 14.02 mg/g,accounted for 82.77% of the total inorganic carbon in the sediments.The contents of inorganic carbon forms in surface sediment are rank as: NH2OH·HCl form HCl form NaCl form NH3·H2O form NaOH form.In terms of the horizontal characteristics,the central area was the high value area of inorganic carbon form,the east and north area were the low value area in the lake.Water depth and inorganic carbon present a good positive correlation(R2=0.86,P0.01).The correlationship and the horizontal characteristics of inorganic carbon implied that the terrigenous material which were carried by inflowing rivers have dilute effect on sediments.The supersaturation coefficients of Calcium carbonate in different year in Dali Lake are far greater than 1(31.59IAP/Ksp166.92).The calculation results showed that calcium carbonate was supersaturation in the lake and implied that the aquatic environmental conditions were beneficial to authigenic carbonate precipitation in Dali Lake.In sediment cores,the content of NH2OH·HCl form ranges from 5.29 to 21.72 mg/g,with mean content of 12.90 mg/g,accounted for 82.21% of the total inorganic carbon in the sediments.The contents of NH2OH·HCl form in sediment cores of DLNE-3 and DLNE-5 are obviously higher than DLNE-8 and DLNE-10.The former lied in deep water area are weakly affected by the dilution effect of terrigenous input,which is beneficial to authigenic carbonate precipitation.The latter lied in shallow water area are strongly affected by the dilution effect of terrigenous input,which is not helpful for authigenic carbonate precipitation.The correlations between inorganic carbon and nitrogen,phosphorus,biogenic silicate in the sediments implied that nutrients rising can promote the formation of calcium carbonate supersaturation.In addition,the physical and chemical properties changes in aquatic environment caused by photosynthesis was one of the important factors leading to precipitation of carbonate.

Influence of sea squirt (Halocynthia roretzi) aquaculture on benthic–pelagic coupling in coastal waters: A study of the South Sea in Korea

The influence of sea squirt aquaculture on benthic–pelagic coupling was evaluated in semi-enclosed Korean coastal waters with an in situ benthic chamber and results show for the first time that suspended sea squirt cultures play an important role in benthic–pelagic coupling in the coastal zone. Measurements of primary production, vertical particulate fluxes, and benthic fluxes were made at two stations, a sea squirt ( Halocynthia roretzi ) farm (SSF) and an area of organic-matter-enriched sediment in Jinhae Bay. The vertical material fluxes of organic carbon, nitrogen, and biogenic silicate (BSi) were significantly higher at SSF than in Jinhae Bay, indicating massive biodeposits in the surface sediments at SSF. The organic carbon oxidation rates (C ox ) were estimated after correction for CaCO 3 dissolution. The average C ox at SSF (204 mmol C m −2 d −1 ) was significantly higher than that in the organic-enriched Jinhae Bay sediment (77 mmol C m −2 d −1 ). The organic carbon burial fluxes were determined using vertical profiles of organic carbon of up to 30 cm and the sedimentation rate calculated from the excess 210 Pb distribution. At both stations, ∼95% of the settled organic carbon was oxidized and only ∼5% was buried in the deep sediment layer. The benthic fluxes of dissolved inorganic nitrogen and phosphate at SSF were 2–12 times higher than in Jinhae Bay, corresponding to 85%, and 270%, respectively, of the requirements for primary production.

Biogenic silicate accumulation in sediments, Jiazhou Bay

It has been widely recognized that low silicate content in seawater is a major limiting factor to phytoplankton primary production in Jiaozhou Bay. However the reason of Si-limitation remains poorly understood. In the present study we measured the biogenic silicate content and discussed the accumulation of silicate in Jiaozhou Bay sediment. The results show that the biogenic silica content in the sediment of the Jiaozhou Bay is obviously much higher than those in the Yellow Sea and the Bohai Sea. The Bsi:TN ratios and BSi:16P ratios in the sediment are>1 and the OC:BSi ratio in sediment is lower than these of Redfield ratio (106∶16), indicating that the decomposition rate of OC is much higher than that for BSi in similar conditions. Therefore, the majority of the biogenic silicate was buried and thus did not participate in silicate recycling. Silicate accumulation in sediment may explain why Si limits the phytoplankton growth in the Jiaozhou Bay. Comparing the flux of biogenic silicate from sediments with primary production rate, it can be concluded that only 15.5% of biogenic silicate is hydrolyzed during the journey from surface to bottom in seawater, thus approximate 84.5% of biogenic silicate could reach the bottom. The silicate releasing rate from the sediment to seawater is considerably lower than that of sedimentation of biogenic silicate, indicating silicate accumulation in sediment too. In a word, the silicate accumulation in sediment is the key reason of silicate limiting to phytoplankton growth in Jiaozhou Bay.

Relationship between Composition of Settling Particles and Organic Carbon Flux in the Western North Pacific and the Japan Sea

Settling particles play an important role in transporting organic carbon from the surface to the deep ocean. It is known that major components of settling particles are biogenic silicates (opal), biogenic carbonate (CaCO 3 ), lithogenic clays and organic matter. Since each component aggregates and/or takes in organic carbon, all of these components have the ability to transport particulate organic carbon (POC) to the interior of the ocean. In this study, sediment trap experiments were carried out in four areas of the western North Pacific (including a marginal sea). Factors are pro- posed that correlate the composition of settling particles with POC flux. Annual mean organic carbon fluxes at 1 km depth in the western North Pacific Basin, Japan Sea, Hidaka Basin and northern Japan Trench were found to be 14.9, 18.1, 13.0 and 6.6 mg/m 2 /day, respectively. Organic carbon flux in the western North Pacific was greater than that in the Eastern North Pacific (7.4), the Equatorial Pacific (4.2), the Southern Ocean (5.8) and the Eastern North Atlantic (1.8). In the western North Pacific, it was calculated that 52% of POC was carried by opal particles. Opal is known to be a major component even in the Eastern North Pacific and the Southern Ocean, and the opal fluxes in these areas are similar to those in the western North Pacific. However, the organic carbon flux that was carried by opal particles (OC opal flux) in the western North Pacific was greater than that in the Eastern North Pacific and the Southern Ocean. These results indicate that the ability of opal particles to transport POC to the deep ocean in the western North Pacific is greater than that in the other areas.

Bacteriohopanepolyols in hydrothermal vent biogenic silicates

Biogenic silicates from the Taupo Volcanic Zone (North Island, New Zealand) are shown to contain a number of unusual polyfunctionalised bacteriohopanepolyols. Hopanoid fractions isolated from the Rotokawa hot spring (80–82 °C) contained significant amounts of 32,35-anhydrobacteriohopanetetrol and two isomers of a related trihydroxylated compound. The origin of these unusual hopanoid side chains is unclear and they may result either from novel biosynthetic or diagenetic transformation pathways of known biohopanoid precursors such as bacteriohopanetetrol (via cyclisation) or reductive removal of adenine from adenosylhopane.

Glacial to interglacial changes in non-carbonate and carbonate accumulation in the SW Pacific Ocean, New Zealand

Fluxes of carbonate and non-carbonate (terrigenous+biogenic siliceous) sediment, back to a maximum of marine isotope stage (MIS) 6, were determined for 54 cores from off eastern New Zealand. Mass accumulation rates (MARs) were derived using dry bulk densities measured directly from fresh cores or, in the case of dry archived samples, on estimates from a density/carbonate relationship.MARs exhibit wide spatial and temporal variability in response to (i) the location of cores relative to the terrigenous source of New Zealand, current pathways and local oceanographic features, and (ii) palaeoclimatic change. For MIS 1–2, non-carbonate accumulated at a high rate between 27 and 18 ka (calendar years), due to an influx of waterborne and aeolian terrigenous detritus together with localised production of biogenic silica under a northward intrusion of subantarctic waters, and an increase in wind-induced upwelling. By 18–12 ka, non-carbonate MARs reduced as winds ameliorated and sea level rose to confine some of the terrigenous load to the continental shelf. The Holocene transgression was accompanied by warmer sea surface temperatures, the formation of coastal and lacustrine sediment traps, and more widespread terrestrial vegetation. These conditions further reduced the deep oceanic non-carbonate flux to levels about half those of glacial periods.In contrast, carbonate MARs were lower in cold periods, reflecting lower productivity, increased dissolution and, in the case of the generally productive waters of Chatham Rise, to redistribution by bottom currents. However, off central New Zealand, carbonate production was higher on the continental margin, possibly because of enhanced upwelling under the strong wind regime of MIS 2. Such localised effects produced glacial carbonate MARs higher than interglacial MIS 1 values. For the rest of the region, carbonate fluxes increased to an early to middle MIS 1 maximum before generally declining in recent times.

A Comparative Study of Nutrient Behavior along the Salinity Gradient of Tropical and Temperate Estuaries

The differences and similarities between near-pristine estuaries of different latitudinal regions were examined by selecting three tropical systems from North Queensland, Australia (Jardine, Annan, Daintree) and three temperate systems from Scotland, United Kingdom (Inverness, Cromarty, Dornoch Firths) for comparison. Although estuaries from the different regions have a number of unifying features, such as salinity gradients, tidal variations and terrestrial inputs they also have a number of important differences. The most distinct of these is the timing and variability of the major physical forcings on the estuary (e.g., river flow, insolation). The three tropical estuaries were much more episodic than their temperate counterparts, with a much more dynamic salinity structure and more variable riverwater concentrations, so that delivery of material to the estuary is dominated by short-lived flood events. In contrast, seawater concentrations were more stable in the tropical estuaries due to a more constant input of insolation, resulting in year round biological activity. There was biological removal of dissolved inorganic phosphorus in the low salinity region of the tropical Jardine and Daintree estuaries and a low salinity input of nitrate in the tropical Annan estuary most likely due to nitrification in the bottom sediments, and the biological reaction zone in the tropical Annan Estuary was flushed out of the estuarine basin to the edge of the offshore plume during a flood. Similar effects were not seen in the temperate Inverness, Cromarty, and Dornoch Firths. Similarities between estuaries include mid-estuary inputs of ammonium which were seen in both the temperate and tropical estuaries, although they occur under vastly contrasting conditions of low river discharge and periods of flood, respectively. Five of the estuaries show a general increase in dissolved inorganic phosphorus concentrations towards the sea during low flows, reflecting their pristine condition, and all six estuaries had low salinity silicate maxima probably sourced from the dissolution of freshwater biogenic silicate that has been carried seaward, except in the tropical estuaries during the dry season when a benthic source is proposed.

Individual particle analysis of Western Mediterranean sediment cores, Rhône suspended matter and Sahara aerosols — investigation of inputs to the sediments

Individual particle analysis using electron probe X-ray microanalysis was performed on sediment cores from the Gulf of Lions (Western Mediterranean Sea), on atmospheric aerosols sampled in Corsica and originating from Northern Africa, and on Rhône suspended matter. Cluster analysis was done to yield major particle types and kriging spatial analysis was applied to obtain the distributions of the particle types in the sediment surface layers. For three sediment cores, the depth profiles of particle groups were examined. The predominant particle types composing the sediment material in the Gulf of Lions were found to be Si-rich particles (quartz and biogenic silicate), aluminosilicate minerals (illite, kaolinite, chlorite) and Ca-rich particles (aragonite, calcite, high-Mg calcite). During the diagenesis, dissolution and crystallization processes occurred, yielding the substitution of quartz and Si-rich particles by calcium carbonates in deeper sediment layers. Only a small amount of Fe-S-rich (pyrite) particles was found in the analyzed sediments. An evident impact of Rhône derived and offshore eroded material was noticed in the sedimentation area investigated. Yet, the input of Northern Africa aerosols to the sediment vicinity was not so evidently noticeable from these results.

The biogeochemical cycling of dissolved Silicate in a Galician Ria

Abstract The annual variation of the dissolved silica contributions to the ria of Vigo and its spatial distributions on the silicate sediment is considered using a box model. During winter, the silicate freshwater flux is high, about 10 mol Si s-l. This mixes with the ria water and is exported to the ocean. During the rest of the year, the most important source of dissolved silicate is the subsurface incoming flux of marine water to the ria which provides from 52% to 65% of the total. In these seasons, the redissolution of biogenic silicate is the second source and causes up to 46% of silicate inputs to the photic zone. The utilisation of dissolved silicate by the diatoms was 1 mol Si s-1, but increased to 11 mol Si s-1 in the event of upwelling. The abundance of silicate in sediments in different parts of the ria of Vigo is a consequence of the cited fluxes. The bottom of the inner middle zone in the ria receives diatoms in spring and summer when no upwelling occurs (from 50 to 120 mg Si m-2 d-1), and silicate is resupended due to sediment stirring during winter. The external mid-zone of the ria is richer in remains of diatoms and opal, there being no resuspension and sedimentation is greater than in other areas during upwelling events (172 mg Si m-2 d-1), as indicated by the relative abundance of Chaetoceros spp. spores.

Particle flux, and composition of sedimenting matter, in the Greenland Sea

Vertical flux of particulate material was recorded with moored sediment traps during 1988/1989 in the Greenland Sea at 72°N, 10°W. This region exhibits pronounced seasonal variability in ice cover. Annual fluxes at 500 m water depth were 22. 79, 8.55, 2.39, 3.81 and 0.51 g m −2 for total flux (dry weight), carbonate particulate biogenic silicate, particulate organic carbon and nitrogen, respectively. Fluxes increased in April, maximum rates of all compounds occurred in May–June, and consistently high total flux rates of around 100 mg m −2d −1 prevailed the summer. The increasing flux of biogenic particles measured in April is indicative of an early onset of algal growth in spring. Small pennate diatoms dominated in the trap collections during April, and were still numerous during the high flux period when Thalassiosira species were the most abundant diatoms. During May–June, up to 22% of the Thalassiosira cells collected were viable-looking cells. The faecal pellet flux increased after the May–June event. Therefore we conclude that the diatoms settled as phytodetritus, most likely in rapidly sinking aggregates. From seasonal nutrient profiles it is concluded that diatoms contribute 25% to new production during spring and 50% on an annual basis. More than 50% of newly produced silicate particles are dissolved above the 500 m horizon. High new production during spring does not lead to a pronounced sedimentation pulse of organic matter during spring but elevated vertical export is observed during the entire growth period.

Exposure Assessment of Smoke and Biogenic Silica Fibers During Sugar Cane Harvesting in Hawaii

Abstract Agricultural burning is a worldwide practice performed to reduce trash and pest infestation after the crops are harvested. Although this function is economically beneficial, the large quantities of smoke potentially expose not only the farm workers but also any surrounding communities. Characterization of this smoke is difficult, and there are few published reports on this topic. Unique to the sugar cane industry is the practice of burning the crop before harvesting. This not only produces smoke but also creates a considerable potential for worker exposure to the ash during the harvesting operations. A previous study had characterized workers' exposures to biogenic silicate fibers during manual harvesting of sugar cane in Florida. In Hawaii, contrary to practice in Florida, all cane is mechanically harvested. An exploratory survey was performed in Hawaii for the purpose of evaluating the feasibility of using gravimetric particulates, organic and elemental carbon, total elemental profiles, polycyc...