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Climate Dependent Diatom Production is Preserved in Biogenic Si Isotope Signatures
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). Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
Stockholm University, Stockholm Resilience Centre, Baltic Nest Institute.
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2011 (English)In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, no 11, 3491-3499 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study was to reconstruct diatom production in the subarctic northern tip of the Baltic Sea, Bothnian Bay, based on down-core analysis of Si isotopes in biogenic silica (BSi). Dating of the sediment showed that the samples covered the period 1820 to 2000. The sediment core record can be divided into two periods, an unperturbed period from 1820 to 1950 and a second period affected by human activities (from 1950 to 2000). This has been observed elsewhere in the Baltic Sea. The shift in the sediment core record after 1950 is likely caused by large scale damming of rivers. Diatom production was inferred from the Si isotope composition which ranged between δ30Si −0.18‰ and +0.58‰ in BSi, and assuming fractionation patterns due to the Raleigh distillation, the production was shown to be correlated with air and water temperature, which in turn were correlated with the mixed layer (ML) depth. The sedimentary record showed that the deeper ML depth observed in colder years resulted in less production of diatoms. Pelagic investigations in the 1990's have clearly shown that diatom production in the Baltic Sea is controlled by the ML depth. Especially after cold winters and deep water mixing, diatom production was limited and dissolved silicate (DSi) concentrations were not depleted in the water column after the spring bloom. Our method corroborates these findings and offers a new method to estimate diatom production over much longer periods of time in diatom dominated aquatic systems, i.e. a large part of the world's ocean and coastal seas.

Place, publisher, year, edition, pages
2011. Vol. 8, no 11, 3491-3499 p.
National Category
Geosciences, Multidisciplinary Geochemistry Climate Research
Research subject
Geochemistry
Identifiers
URN: urn:nbn:se:su:diva-65184DOI: 10.5194/bg-8-3491-2011ISI: 000298132200024OAI: oai:DiVA.org:su-65184DiVA: diva2:461572
Funder
Swedish Research Council, 2007-4763
Available from: 2011-12-05 Created: 2011-12-05 Last updated: 2017-12-08Bibliographically 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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