Silicic Acid Concentrations Research Articles

Geothermal Geology Characteristic and Origin Analysis of Shilin Basin in Yunnan Province

based on geothermal anomalies and geothermal wells of Shilin basin, the structure of geothermal reservoirs, geothermal geological characteristics and hydrochemistry of thermal groundwater are examined. Geothermal reservoir of the geothermal field is Proterozoic Sinian dolomite and dolomitic limestone. Characteristic of geothermal water runoff and geothermal field are controlled by Jiuxiang fracture and Niutoushan ancient mainland. The drillings data shows that the temperature gradient is 1.5-4.8°C/100m. Deep circulation is the main origin of geothermal water. The chemical type of geothermal water is HCO3-Ca, and high silicic acid content. The geothermal water supply is limited from the hydrogeological conditions; we should control the development and utilization.

Silicic acid supplied to coastal diatom communities influences cellular silicification and the potential export of carbon

Microcosm experiments were conducted along the Washington and Oregon coasts in May 2009, May 2010, and July 2010 to determine whether variation in the supply of silicic acid from the Columbia River could influence the silicification and sinking potential of coastal diatom blooms. The chlorophyll a concentration increased similarly in communities incubated with added nitrate or both nitrate and silicic acid, indicating that growth was limited by nitrate availability. Communities that grew in the treatment with added silicic acid and nitrate were more silicified than communities in the treatment with only nitrate added. No difference in community composition was detected between these treatments in three out of four experiments. Isolates of Minutocellus, Cylindrotheca, Thalassiosira, and Odontella were obtained from the microcosm experiment conducted in May 2010 and were maintained in the laboratory in 20 µmol L−1 silicic acid. All four diatom isolates contained ∼ 2.5 times more silica per cell when silicic acid concentration in the media was increased to 80 µmol L−1. The intensity of a fluorescent cellular stain of newly precipitated silica (2‐(4‐pyridyl)‐5{[4‐dimethylaminoethyl‐aminocarbamoyl)‐methoxy]phenyl}oxazole) strongly correlated with silica content among species, but was a less sensitive indicator of changing silicification within a single species. Changes in silicification were not correlated with changes in the transcript abundance of silicic acid transporters. Sinking rates increased roughly 2‐fold for cells that contained ∼ 2.5 times more silica. Variation in silicic acid supply alters the silicification of nitrate‐fueled coastal diatom blooms and the potential sink of carbon from coastal zones.

Major contribution of diatom resting spores to vertical flux in the sub-polar North Atlantic

The mass sinking of phytoplankton cells following blooms is an important source of carbon to the ocean's interior, with some species contributing more to the flux of particulate organic carbon (POC) than others. During the 2008 North Atlantic Bloom Experiment in the Iceland Basin, we examined plankton community composition from surface waters and from sediment traps at depths down to 750m. Samples collected with neutrally buoyant Lagrangian sediment traps captured a major flux event. Diatoms comprised ≥99% of cell flux into the sediment traps, with vegetative cells and resting spores of the genus Chaetoceros contributing 50–95% of cell flux. Resting spores of one species, identified as Chaetoceros aff. diadema, were dominant, comprising 35–92% of cell flux. The flux of resting spores ranged from 2 to 63mgCm−2day−1 and was significantly correlated with POC flux (p=0.003). Over the course of 10 days, the flux of resting spores increased by 26 fold, suggesting that the cells sank en masse, possibly in aggregates. In contrast, vegetative cells of C. aff. diadema sampled from surface waters during the period preceding the flux event generally comprised <1% of the diatom community and never exceeded 5.2%. Resting spores of C. aff. diadema were rarely observed in surface waters but their concentrations increased with depth (to 200m) below the mixed layer. This increase in resting spore abundance, coupled with increased dissolved silicic acid concentrations at depth, suggest that the morphological changes associated with spore formation may have occurred in the mesopelagic zone, while cells were sinking. The values of variable fluorescence (Fv/Fm) measured on sediment trap material dominated by resting spores were among the highest values measured in the study area at any depth. This, in combination with the rapid germination of resting spores in ship-board incubations, suggests that vegetative cells were not physiologically stressed during spore formation. The degradation-resistant, heavily silicified resting spore valves explain the high relative contribution of C. aff. diadema resting spores to total plankton carbon at depth. These data emphasize the ephemeral nature of organic carbon flux events in the open ocean and highlight how non-dominant species and transient life stages can contribute more to carbon flux than their more abundant counterparts.

Problems relating to operation of geothermal power stations stemming from the presence of admixtures in the geothermal heat carrier

The effects the specific features of chemical composition and the thermophysical properties of geothermal heat carrier have on the metal erosion-corrosion processes and on the formation of deposits during operation of a geothermal power station are analyzed. Methods for preventing the formation of deposits and making the geothermal power station equipment more resistant to erosion and corrosion are considered. Results from calculation and experimental investigations aimed at studying how the concentration of silicic acid and other admixtures vary in the working loop and turbine flow path at the Verkhne-Mutnovsk geothermal power station are presented. The possibility of using surface-active inhibitors to prevent the formation of deposits and erosion-corrosion processes in the geothermal power station equipment is demonstrated.

The use of siliceous baths for the treatment of the patients presenting with arterial hypertension

This article is focused on the benefits of drug-free therapeutic technologies, such as the use of artificial general siliceous baths for the treatment of patients with arterial hypertension. This approach results in the anti-hypertensive effect simultaneous with the correction of lipid metabolism and lipid peroxidation. The positive changes due to the specific action of silicic acid were much more pronounced than those induced by the hydrostatic water pressure or water temperature known to be the main factors producing the therapeutic effect in fresh-water baths. General siliceous baths with the silicic acid concentration of 50-100 mg/I are recommended for the treatment of patients presenting with grade I-II arterial hypertension (stage II-III) and high risk of development of cardiovascular complications associated with coronary heart disease. One of the advantages of the proposed modality is it does not only produce the hypotensive effect but also exerts specific influence on lipid metabolism.

Opening the gateways for diatoms primes Earth for Antarctic glaciation

The abrupt onset of Antarctic glaciation during the Eocene–Oligocene Transition (∼33.7Ma, Oi1) is linked to declining atmospheric pCO2 levels, yet the mechanisms that forced pCO2 decline remain elusive. Biogenic silicon cycling is inextricably linked to both long and short term carbon cycling through the diatoms, siliceous walled autotrophs which today account for up to 40% of primary production. It is hypothesised that during the Late Eocene a sharp rise in diatom abundance could have contributed to pCO2 drawdown and global cooling by increasing the proportion of organic carbon buried in marine sediment. Diatom and sponge silicon isotope ratios (δ30Si) are here combined for the first time to reconstruct the late Eocene–early Oligocene ocean silicon cycle and provide new insight into the role of diatom productivity in Antarctic glaciation. At ODP site 1090 in the Southern Ocean, a 0.6‰ rise in diatom δ30Si through the late Eocene documents increasing diatom silicic acid utilisation with high, near modern values attained by the earliest Oligocene. A concomitant 1.5‰ decline in sponge δ30Si at ODP site 689 on the Maud Rise tracks an approximate doubling of intermediate depth silicic acid concentration in the high southern latitudes. Intermediate depth silicic acid concentration peaked at ∼31.5Ma, coincident with the final establishment of a deepwater pathway through the Tasman Gateway and Drake Passage. These results suggest that upwelling intensification related to the spin-up of a circum-Antarctic current may have driven late Eocene diatom proliferation. Organic carbon burial associated with higher diatom abundance and export provides a mechanism that can account for pCO2 drawdown not only at, but also prior to, Antarctic glaciation as required by a pCO2 ‘threshold’ mechanism for ice sheet growth.

Intrusion of coastal waters into the pelagic eastern Mediterranean: in situ and satellite-based characterization

Abstract. A combined dataset of near-real-time multi-satellite observations and in situ measurements from a high-resolution survey is used for characterizing physical-biogeochemical properties of a patch stretching from the coast to the open sea in the Levantine Basin (LB) of the eastern Mediterranean (EM). Spatial analysis of the combined dataset indicates that the patch is a semi-enclosed system, bounded within the mixed layer and separated from ambient waters by transport barriers induced by horizontal stirring. As such, the patch is characterized by physical-biogeochemical properties that significantly differ from those of the waters surrounding it, with lower salinity and higher temperatures, concentrations of silicic acid and chlorophyll a, and abundance of Synechococcus and picoeukaryote cells. Based on estimates of patch dimensions (∼40 km width and ∼25 m depth) and propagation speed (∼0.09 m s−1), the volume flux associated with the patch is found to be on the order of 0.1 Sv. Our observations suggest that horizontal stirring by surface currents is likely to have an important impact on the ultra-oligotrophic Levantine Basin ecosystem, through (1) transport of nutrients and coastally derived material, and (2) formation of local, dynamically isolated niches. In addition, this work provides a satellite-based framework for planning and executing high-resolution sampling strategies in the interface between the coast and the open sea.

The influence of surface structure on H4SiO4 sorption and oligomerization on goethite surfaces: An XPS study using goethites differing in morphology

Two important weathering products are solution phase silicic acid (H4SiO4) and the iron oxides. The chemistry of H4SiO4 on iron oxide surfaces is a complex mix of sorption and polymerization and this affects many iron oxide properties. For example the presence of H4SiO4 directs goethite growth to shorter and fatter needles which implies different H4SiO4 chemistry on different goethite faces and the purpose of this paper is to directly explore this and related phenomena. Isotherms and the Si 2s X-ray photoelectron spectra were measured for H4SiO4 on three goethite samples having different morphologies. Both the shape of the isotherms and the shifts in the Si 2s binding energies (BE) indicated different H4SiO4 chemistry on acicular crystalline goethite compared to previously reported behavior on ≈2nm sized disordered particles of ferrihydrite. The H4SiO4 isotherm on acicular goethites had a plateau for silicic acid concentrations (Si(sol)) between 0.01 and 0.3mM but the isotherm increases steeply for Si(sol)>0.3mM. The Si 2s BE for acicular goethites indicated monomeric sorption occurring at Si(sol)<0.3mM but then the BE increases for Si(sol)>0.3mM indicating the onset of H4SiO4 polymerization as also indicated by the increase in isotherm slope. The data are consistent with a model where monomers sorb on both the (110) and (021) faces (Pbnm space group) but at Si(sol) over ≈0.3mM polymers form only on the (021) face. The arrangement of monomer sorption sites on the acicular goethite (021) face acts as a template for H4SiO4 polymerization. This would explain why the onset of polymerization occurs quite distinctly on the acicular goethite surface compared with that previously observed on ferrihydrite where there is a gradual increase in the significance of polymerization across the H4SiO4 isotherm.

Effect of Solution Aging Time on Stability of Colorimetric Assay for Degradation Rate Evaluation of Porous Si in Artificial Cerebrospinal Fluid

In order to evaluate the degradation rate of porous Si in artificial cerebrospinal fluid and obtain more accurate results, the effect of solution aging time on the stability of the ammonium molybdate colorimetric assay was investigated. Following the protocol of the colorimetric assay, the blue colored solutions with various silicic acid concentrations were prepared and then aged for different time periods up to 7 h. On the basis of linear regression analyses, the absorbance value of the blue colored solution was directly proportional to the silicic acid concentration. Moreover, the optimal aging time span of the solution maintained until 7 h, depending on the stability of the solution.

Quantification Method of Size Distribution of Polysilicic Acid in Supersaturated Silicic Acid Solution

In order to estimate the absolute size distribution of polysilicic acid particles in geothermal waters, the distribution coefficient (K(av)) of gel permeation chromatography (GPC) for polysilicic acid particles and the hydrodynamic radius for the same polysilicic acid particles from Dynamic Light Scattering (DLS) are combined to quantify the particle size. From the combination, a quantitative relationship between the K(av) from GPC and the hydrodynamic radius for polysilicic acid from DLS was built up. Using this relationship, the change in particle size of polysilicic acid formed during the polymerization of silicic acid at pH 8 and 9 (initial silicic acid concentration: 800 ppm as SiO2) was examined. The result showed that polysilicic acid grew to 500 and 1000 nm by 5 h at pH 9 and 8, respectively. It was found that aluminum affects the growth of polysilicic acid particles, and that the effect depends on the pH. The proposed method in this study has been proved to be valid to measure the size of polysilicic acid during the polymerization of silicic acid in solutions with relatively low silicic acid concentration, such as geothermal water.

The isotopic signature of particulate organic C and N in bottom ice: Key influencing factors and applications for tracing the fate of ice‐algae in the Arctic Ocean

AbstractThe isotopic, taxonomic, and nutrient dynamics of protist communities at the bottom of first‐year sea ice were studied for a wide range of ice conditions during the spring‐summer transition in the southeast Beaufort Sea. In bottom ice, total protist abundance ranged from 0.07 to 9.94 × 109 cells m–2 and chlorophyll a biomass ranged from 0.33 to 110 mg m–2. Both variables were positively related to the concentrations of nitrate, silicic acid, and phosphate at the ice‐water interface, with r2 values between 0.63 and 0.79. Results showed that the δ13C of sympagic (ice‐associated) particulate organic matter (POM) (–27.1 to –11.4‰) was mainly influenced by ice protist stocks and dissolved inorganic carbon availability. Flagellated cells maintained a low δ13C relative to diatoms. The δ15N of POM (3.9 to 9.4‰) could not be explained by any of the variables considered and showed considerable overlap with the pelagic δ15N‐POM (0.0 to 10.3‰). Detailed analyses of δ13C‐POM through size fractionation and settling experiments along with a short temporal study of the interaction between sympagic and pelagic communities confirmed or demonstrated that (1) the analysis of stable C isotopes is a valuable tool to trace the flow of ice‐derived matter, (2) sympagic POM contributes substantially to suspended pelagic biomass during release episodes, and (3) ice‐grown autotrophic flagellated cells have a strong potential to interact with the pelagic biota in the coastal Arctic Ocean. This study highlights the need to carefully evaluate stable isotope dynamics before assessing food web interactions or the fate of POM in seasonally ice‐covered waters.

INFLUENCE OF PLANT ASSOCIATIONS ON THE SILICON CYCLE IN THE SOIL-PLANT ECOSYSTEM

Soluble Si compounds such as monosilicic and polysilicic acids affect chemicals and physical properties of the soil. The main aim of this study is to evaluate Si cycle in the various soil-plant s ystems via the determination of mobile Si forms in the soi l and of the total content of Si in the plant assoc iations. The concentrations of monosilicic acid, polysilicic acids and acid-extractable Si in unmowed meadow, mowed meadow, birch-aspen forest, spruce wood and agricultural land soil-plant systems, were tested at the soil depths of 0-10, 20-30 and 50-60 cm in a Ru ssian region, south of Moscow. The annual content o f Si within the investigated soil-plant systems was c alculated. Forty to 80 kg ha -1 of Si is annually removed from Grey Forest Soil (Luvisol). The concentration of monosilicic acid in the upper soil horizon depended on the type of plant association and on th e total content of adsorbed Si. The removal of plan t remains from the ecosystems resulted in decreased monosilicilic acid concentration in the upper soil horizon. The ecosystems which utilize annual plant remains increased the content of monosilicilic acid of the surface soil horizon. The concentration of mono silicic acid in the upper soil layer can be used as indicator of the stability of plant association. Th e unmowed meadow and the birch-aspen forest were characterized as ecosystems with accumulative type of Si cycle. The agricultural land, the mowed

Notre expérience dans l’arthroplastie unicompartimentale du genou. Étude réalisée au terme de 21 ans de suivi

Recent work has shown the silicon isotope composition, denoted by δ30Si, of deep-sea sponges reflects the concentration of ambient silicic acid (Si(OH)4) in seawater. However, existing calibrations are based predominantly on living sponges collected from the Southern Ocean. These data cannot, however, be used to determine whether other parameters that correlate with silicic acid in the Southern Ocean, such as temperature and salinity, influence δ30Si of sponges. Furthermore, the published data do not demonstrate whether disaggregated core-top sedimentary spicules preserve the primary δ30Si signal recorded in living sponges. Here, we address both of these issues. We refine and widen the existing calibration by including a global distribution of modern sponges. In addition, we provide the first systematic calibration from spicules picked from core-top sediments that covers sites from different ocean basins. The relationship between Si(OH)4 and δ30Si in sponge spicules is the same in different ocean basins, between specimens that grew in different temperature and salinity conditions. Our core-top data agree well with the modern sponge calibration indicating there are no significant post-depositional effects or early diagenetic overprints. These two new datasets support the assertion that sponge δ30Si can be used as a proxy for silicic acid concentrations in the past.

Diatom silicon isotopes as a proxy for silicic acid utilisation: A Southern Ocean core top calibration

Despite a growing body of work that uses diatom δ30Si to reconstruct past changes in silicic acid utilisation, few studies have focused on calibrating core top data with modern oceanographic conditions. In this study, a microfiltration technique is used to divide Southern Ocean core top silica into narrow size ranges, separating components such as radiolaria, sponge spicules and clay minerals from diatoms. Silicon isotope analysis of these components demonstrates that inclusion of small amounts of non-diatom material can significantly offset the measured from the true diatom δ30Si. Once the correct size fraction is selected (generally 2–20μm), diatom δ30Si shows a strong negative correlation with surface water silicic acid concentration (R2=0.92), highly supportive of the qualitative use of diatom δ30Si as a proxy for silicic acid utilisation. The core top diatom δ30Si matches well with mixed layer filtered diatom δ30Si from published in situ studies, suggesting little to no effect of either dissolution on export through the water column, or early diagenesis, on diatom δ30Si in sediments from the Southern Ocean. However, the core top diatom δ30Si shows a poor fit to simple Rayleigh or steady state models of the Southern Ocean when a single source term is used. The data can instead be described by these models only when variations in the initial conditions of upwelled silicic acid concentration and δ30Si are taken into account, a caveat which may introduce some error into quantitative reconstructions of past silicic acid utilisation from diatom δ30Si.

Influence of a flood event on salinity and nutrients in the Changshan Archipelago area (Northern Yellow Sea)

River discharge can deliver nutrients to the coastal zone and change the hydrologic properties of the water column. Soon after a flash flood from the Yalu River (Northeast China) in August 2010, we investigated the salinity and nutrient concentrations, as well as other environmental conditions in the Changshan Archipelago area, located approximately 100 km west of the river mouth in the northern Yellow Sea. Diluted water was mainly observed in the upper layers shallower than 15 m, with surface salinity between 18.13 and 30.44 in the eastern study area and between 28.16 and 29.72 in the western area. Surface salinity showed a significant negative correlation with concentrations of dissolved nutrients (P < 0.05), but not with that of Chlorophyll-a (Chl-a), dissolved oxygen (DO), particulate materials or pH. The average concentrations of nitrite, nitrate, and silicic acid decreased from the surface layer to bottom layer and were significantly higher in the east area than in the west area (P < 0.05). In contrast, average ammonium and phosphate concentrations were highest in the bottom layer of both areas, with no significant spatial differences. DO varied between 6.06 and 8.25 mg L-1 in the surface layer, and was significantly higher in the eastern area than in the western area in the surface and middle layers. Chl-a concentration was constantly below 4.09 mu g L-1. Our work demonstrated the strong influences of Yalu River on proportions of various nutrient components in the Changshan Archipelago area. Silicic acid and total inorganic nitrogen levels were significantly elevated comparing to phosphate in the eastern area. Such changes can potentially induce phosphate limit to phytoplankton growth.

Removal and Recovery of Silica Source from Geothermal Water Recycling System by Calcium Nitrate and Sodium Hydroxide

In order to elucidate the possibility of removal of silicic acid from geothermal water, the calcium nitrate and sodium hydroxide as removing agent was investigated under various conditions. The initial concentration of silicic acid in geothermal water was 412 ppm as Si. The concentration of silicic acid decreased rapidly when the removing agent was added. Precipitation reaction for silicic acid reached equilibrium within 30 minutes and was independent of pH. The removing rate of silicic acid increased with increasing the pH of solution. The high concentration of silicic acid in geothermal water was perfectly removed by addition of calcium nitrate with molar ratio of Ca/Si over 2.1 at pH12. XRD pattern showed that the component of precipitation was calcium silicate hydrate Ca2SiO4・nH2O (CSH).

Diatom dynamics in a long-lived mesoscale eddy in the northeast subarctic Pacific Ocean

We characterized the diatom flora and determined biogenic silica concentrations within an anticyclonic Haida eddy four times as it drifted westward from the coast of the Queen Charlotte Islands (British Columbia, Canada) into the Alaska Gyre (February 2000–September 2001). For the whole data set (eddy and surrounding waters), diatoms accounted for 6 to 91% of phytoplankton carbon (6–54% total phytoplankton abundance). The proportional contribution of diatoms to phytoplankton carbon within the eddy was higher than in the surroundings inshore of the Transition Zone between coastal and High Nitrate, Low Chlorophyll waters. As the eddy drifted away from the coast and into the Alaska Gyre over the 20-month period, the average biovolume of diatoms decreased by 2–4 times, while in the surroundings a 2-fold increase in average biovolume was observed. The highest diatom abundances were observed in June 2001, when the assemblages were dominated by small colonies of Neodenticula seminae (=Nitzschia cylindroformis) both within the eddy (at the edge and center) and in the surrounding waters. N. seminae lacked the characteristic morphological features of the type species (deck and basal ridges, solid-walled costae) and instead more closely resembled specimens observed for the first time in ∼0.8Ma in the Gulf of St. Lawrence (North Atlantic) in the same year (2001). The corresponding biogenic silica inventories were 10-fold higher in June 2001 compared to the other cruises, yet particulate organic carbon and nitrogen did not increase substantially, potentially indicating a senescing population of diatoms with high Si:C and N. Diatom diversity and evenness indices were lower in June 2001 compared to the other cruises. A combination of high retention, episodic colonization, and significant losses due to sinking or grazing could result in lower diatom abundances but higher diversity observed within the Haida-2000a eddy compared to the surroundings. While silicic acid concentrations may have reached low enough levels to limit diatom growth after an initial spring bloom, levels of this nutrient were not limiting in later observations. Collectively, the data underscore the importance of diatoms in phytoplankton assemblages both close to shore and in High Nitrate, Low Chlorophyll waters.

Silicic acid flux to the ocean from tidal permeable sediments: A modeling study

Sandy sediments of tidal beaches are poor in reactive substances because they are regularly flushed by significant flow caused by tidal forcing. This transport process may significantly affect the flux of reactive solutes to the ocean. A two dimensional model coupling the Richards equation that describes the flow in permeable sediments and the conservation equation of the silicic acid was developed to simulate the evolution of the silicic acid concentration into a variably saturated porous media submitted to tidal forcing. A detailed algorithm of drainage zone under tidal forcing and numerical methods needed to solve it are properly presented. Flux to the ocean has been estimated. The silicic acid concentration displays a permanent lens with low silicic acid concentration at the top of the tidal zone. This lens that results from the tidal forcing, presents weak variations of area during the tidal cycle. Silicic outflux to the ocean increases with increasing beach slope, hydraulic conductivity and tidal range. Simulations reveal that the total silicic acid flux to the ocean from the coastal marine sands can be considered as significant compared to the flux supplied by the rivers. These results may alter the previously published global budget of the silicic acid to the ocean.

Abrupt changes in high-latitude nutrient supply to the Atlantic during the last glacial cycle

The supply of nutrients to the low-latitude thermocline is largely controlled by intermediate depth waters formed at the surface in the high southern latitudes. Silicic acid is an essential macronutrient for diatoms, which are responsible for a significant portion of marine carbon export production. Changes in ocean circulation, such as those observed during the last deglaciation, would influence the nutrient composition of the thermocline and, therefore, the relative abundance of diatoms in the low-latitudes. Here we present the first record of the silicic acid content of the Atlantic over the last glacial cycle. Our results show that at intermediate depths of the South Atlantic the silicic acid concentration was the same at the LGM as it is today, overprinted by high silicic acid pulses that coincided with abrupt changes in ocean and atmospheric circulation during Heinrich Stadials and the Younger Dryas. We suggest these pulses were caused by changes in intermediate water formation resulting from shifts in the subpolar hydrological cycle, with fundamental implications for the nutrient supply to the Atlantic.

The relationship between silicon isotope fractionation in sponges and silicic acid concentration: Modern and core-top studies of biogenic opal

Recent work has shown the silicon isotope composition, denoted by δ30Si, of deep-sea sponges reflects the concentration of ambient silicic acid (Si(OH)4) in seawater. However, existing calibrations are based predominantly on living sponges collected from the Southern Ocean. These data cannot, however, be used to determine whether other parameters that correlate with silicic acid in the Southern Ocean, such as temperature and salinity, influence δ30Si of sponges. Furthermore, the published data do not demonstrate whether disaggregated core-top sedimentary spicules preserve the primary δ30Si signal recorded in living sponges. Here, we address both of these issues. We refine and widen the existing calibration by including a global distribution of modern sponges. In addition, we provide the first systematic calibration from spicules picked from core-top sediments that covers sites from different ocean basins. The relationship between Si(OH)4 and δ30Si in sponge spicules is the same in different ocean basins, between specimens that grew in different temperature and salinity conditions. Our core-top data agree well with the modern sponge calibration indicating there are no significant post-depositional effects or early diagenetic overprints. These two new datasets support the assertion that sponge δ30Si can be used as a proxy for silicic acid concentrations in the past.