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Silicon isotope enrichment in diatoms during nutrient-limited bloomsin a eutrophied river system
Stockholm University, Faculty of Science, Department of Geological Sciences.
Naturhistoriska riksmuseet, Laboratoriet för isotopgeologi .
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Department of Fisheries Oceanography and Marine Ecology, Sea Fisheries Institute, Gdynia, Poland.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We examined the Si isotope fractionation in diatoms by following a massive nutrient limited diatom bloom from a eutrophied natural system. We hypothesized that the Si isotope fractionation should be larger in comparison to observations in less nutrient rich environments. The Oder River, which is a eutrophied river draining the western half of Poland and entering the southern Baltic Sea, shows that a diatom bloom may cause extreme Si isotope fractionation. The rapid nutrient depletion and fast biogenic silica (BSi) increase observed during the spring bloom suggests a Rayleigh behavior for a closed system for dissolved Si (DSi) and BSi in the river at certain time scales. An enrichment factor (ε) of up to -1.6‰ is found based on observations between April and June, 2004. A very high δ30Si value of up to +3.05‰ is measured in diatoms. This is about 2 times higher than previously recorded δ30Si in freshwater diatoms. The Rayleigh model used to predict the δ30Si values of DSi suggests that the initial value before the start of the diatom bloom is close to +2‰. This indicates that there is a biological control of the Si isotope compositions entering the river, probably caused by Si isotope fractionation during uptake of Si in phytoliths. Clearly, eutrophied rivers with enhanced diatom blooms deliver 30Si-enriched DSi and BSi to the coastal ocean, which can be used to trace the biogeochemistry of DSi/BSi in estuaries.

National Category
Geochemistry
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-79186OAI: oai:DiVA.org:su-79186DiVA: diva2:547918
Funder
Swedish Research Council, 2007-4763
Available from: 2012-08-29 Created: 2012-08-29 Last updated: 2012-09-10Bibliographically approved
In thesis
1. Isotope-based reconstruction of the biogeochemical Si cycle: Implications for climate change and human perturbation
Open this publication in new window or tab >>Isotope-based reconstruction of the biogeochemical Si cycle: Implications for climate change and human perturbation
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The global silicon (Si) cycle is of fundamental importance for the global carbon cycle. Diatom growth in the oceans is a major sequestration pathway for carbon on a global scale (often referred to as the biological pump). Patterns of diatoms preserved in marine sediment records can reveal both natural and anthropogenic driven environmental change, which can be used to understand silicon dynamics and climate change. Si isotopes have been shown to have great potential in order to understand the Si cycle by revealing both past and present patterns of dissolved Si (DSi) utilization, primarily when diatoms form their siliceous frustules (noted as biogenic silica, BSi). However, studies using Si isotopes are still scarce and only a few studies exist where stable Si isotopes are used to investigate the biogeochemical Si cycle in aquatic systems. Therefore, this thesis focuses on developing analytical methods for studying BSi and DSi and also provides tools to understand the observed Si isotope distribution, which may help to understand impacts of climate change and human perturbations on marine ecosystems. The Baltic Sea, one of the biggest estuarine systems in the world, was chosen as the study site. BSi samples from a sediment core in Bothnian Bay, the most northern tip of the Baltic Sea, and diatom samples from the Oder River, draining into the southern Baltic Sea were measured and reported in Paper II and III, after establishing a method for Si isotope measurements (Paper I). Si isotope fractionation during diatom production and dissolution was also investigated in a laboratory-controlled experiment (Paper IV) to validate the observations from the field. The major result is that Si isotope signatures in BSi can be used as an historical archive for diatom growth and also related to changes in climate variables. There is isotopic evidence that the Si cycle has been significantly altered in the Baltic Sea catchment by human activities. 

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2012. 20 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 351
Keyword
diatoms, biogenic silica (BSi), dissolved Si (DSi), Si isotope fractionation, the Baltic Sea
National Category
Geochemistry
Research subject
Geochemistry
Identifiers
urn:nbn:se:su:diva-79188 (URN)978-91-7447-559-3 (ISBN)
Public defence
2012-10-12, Ahlmansalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2007-4763
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2012-09-20 Created: 2012-08-29 Last updated: 2013-04-09Bibliographically approved

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