| 1. |
- Grasse, Patricia, et al.
(author)
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GEOTRACES inter-calibration of the stable silicon isotope composition of dissolved silicic acid in seawater
- 2017
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In: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 32:3, s. 562-578
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Journal article (peer-reviewed)abstract
- The first inter-calibration study of the stable silicon isotope composition of dissolved silicic acid in seawater, delta Si-30(OH)(4), is presented as a contribution to the international GEOTRACES program. Eleven laboratories from seven countries analyzed two seawater samples from the North Pacific subtropical gyre (Station ALOHA) collected at 300 m and at 1000 m water depth. Sampling depths were chosen to obtain samples with a relatively low (9 mmol L-1, 300 m) and a relatively high (113 mmol L-1, 1000 m) silicic acid concentration as sample preparation differs for low- and highconcentration samples. Data for the 1000 m water sample were not normally distributed so the median is used to represent the central tendency for the two samples. Median delta Si-30(OH)(4) values of +1.66& for the low-concentration sample and +1.25& for the high-concentration sample were obtained. Agreement among laboratories is overall considered very good; however, small but statistically significant differences among the mean isotope values obtained by different laboratories were detected, likely reflecting inter-laboratory differences in chemical preparation including pre-concentration and purification methods together with different volumes of seawater analyzed, and the use of different mass spectrometers including the Neptune MC-ICP-MS (Thermo Fisher (TM), Germany), the Nu Plasma MC-ICP-MS (Nu Instruments (TM), Wrexham, UK), and the Finnigan (TM) (now Thermo Fisher (TM), Germany) MAT 252 IRMS. Future studies analyzing delta Si-30(OH)(4) in seawater should also analyze and report values for these same two reference waters in order to facilitate comparison of data generated among and within laboratories over time.
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| 2. |
- Hassellöv, Martin, 1970, et al.
(author)
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Application of cross-flow ultrafiltration for the determination of colloidal abundances in suboxic ferrous-rich ground waters.
- 2007
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In: The Science of the total environment. - : Elsevier BV. - 0048-9697. ; 372:2-3, s. 636-44
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Journal article (peer-reviewed)abstract
- A suboxic groundwater from a sandy coastal aquifer was sampled using a new air free, large volume sampling method. Subsequent processing for size fractionation was completed with a modified cross-flow ultrafiltration (CFF) system equipped with a 1 kDa CFF membrane. By purging the CFF system with nitrogen, no oxygen was able to reach the sample. With this optimization, the sample was processed with higher than 90% recovery in terms of both iron and phosphate. Only about 4% of iron and 20% of phosphate in the filtered (0.2 microm) groundwater sample was found to be in colloidal form in the groundwater. In contrast, if no care was taken to maintain the suboxic environment of the original sample, iron was rapidly and completely oxidized and subsequently adsorbed to the CFF membrane. Other elements, such as phosphorus, were also lost to the CFF membrane to a substantial degree, and the mechanism is most likely coprecipitation with iron oxides. This study thus strongly supports the importance of maintaining ambient redox conditions during sampling and fractionation, especially for the determinations of colloid abundances in groundwater.
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| 3. |
- Zhang, Zhouling, et al.
(author)
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Impact of human disturbance on the biogeochemical silicon cycle in a coastal sea revealed by silicon isotopes
- 2020
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 65:3, s. 515-528
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Journal article (peer-reviewed)abstract
- Biogeochemical silicon (Si) cycling in coastal systems is highly influenced by anthropogenic perturbations in recent decades. Here, we present a systematic study on the distribution of stable Si isotopes of dissolved silicate (delta Si-30(DSi)) in a highly eutrophic coastal system, the Baltic Sea. Besides the well-known processes, diatom production and dissolution regulating delta Si-30(DSi) values in the water column, we combined field data with a box model to examine the role of human disturbances on Si cycling in the Baltic Sea. Results reveal that (1) damming led to increased delta Si-30(DSi) values in water but had little impacts on their vertical distribution; (2) decrease in saltwater inflow due to enhanced thermal stratification had negligible impacts on the delta Si-30(DSi) distribution. An atypical vertical distribution of delta Si-30(DSi) with higher values in deep water (1.57-1.95 parts per thousand) relative to those in surface water (1.24-1.68 parts per thousand) was observed in the central basin. Model results suggest the role of enhanced biogenic silica (BSi) deposition and subsequently regenerated dissolved silicate (DSi) flux from sediments. Specifically, eutrophication enhances diatom production, resulting in elevated exports of highly fractionated BSi to deep water and sediments. In situ sedimentary geochemical processes, such as authigenic clay formation, further fractionate Si isotopes and increase pore-water delta Si-30(DSi) values, which then leads to pore-water DSi flux carrying higher delta Si-30(DSi) compositions into deep water. Our findings provide new quantitative information on how the isotope-based Si cycle responds to human perturbations in coastal seas and shed lights on shifts of Si export to open ocean.
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