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Cyanobacteria as a trigger for increased primary productivity during sapropel formation in the Baltic Sea: a study of the Ancylus/Litorina transition
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
2007 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 38, no 1, 1-12 p.Article in journal (Refereed) Published
Abstract [en]

A sediment sequence from the Gotland Basin, representing the Ancylus Lake/Litorina Sea transition, was analysed for pigments, stable isotopes (δ13C and δ15N), diatoms and carbon and nitrogen content. The negative correlation between the cyanobacterial specific pigment zeaxanthin and δ15N supports the hypothesis that cyanobacteria in the early Litorina Sea indeed were nitrogen fixers. Their incorporation of nitrogen could have acted as a trigger for eutrophication during the Litorina Sea stage of the Baltic Sea. As cyanobacteria normally flourish in eutrophicated waters, the increasing concentrations of zeaxanthin during early Litorina Sea also corroborate that high primary production was an important part of the formation of organic rich (sapropel) sediments in the Baltic Sea. The first occurrence pre-dates the formation of laminated sediments, but the peaks of both zeaxanthin and organic carbon are within laminated sequences. This implies that the oxygen conditions of the bottom water also play a major role in the formation of sapropel sediments.

Place, publisher, year, edition, pages
2007. Vol. 38, no 1, 1-12 p.
Keyword [en]
Sapropels - Baltic Sea - Primary production - Cyanobacteria - Pigments - Zeaxanthin
URN: urn:nbn:se:su:diva-25827DOI: 10.1007/s10933-006-9055-0ISI: 000247530100001OAI: diva2:200608
Part of urn:nbn:se:su:diva-895Available from: 2006-03-02 Created: 2006-03-02 Last updated: 2010-07-27Bibliographically approved
In thesis
1. Environmental and climatic changes in the Baltic Sea and the eastern Mediterranean Sea: as recorded by pigments and isotopes in sediments
Open this publication in new window or tab >>Environmental and climatic changes in the Baltic Sea and the eastern Mediterranean Sea: as recorded by pigments and isotopes in sediments
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is a study of Holocene sapropels from two semi-enclosed seas; the Baltic Sea and the Mediterranean Sea. Sapropels are sedimentary layers with organic C > 2%. The Baltic Sea and the Mediterranean Sea have a limited water exchange, and despite differences in water depth and salinity, mechanisms for fluxes and preservation of Corg are principally the same. Primary focus is on biomarkers for increased primary productivity and anoxic/euxinic bottom water. Pigments (primarily from cyanobacteria), δ15N, δ13C, N and Corg have been used for studying increased primary productivity. Presence of the pigment isorenieratene from green sulphur bacteria indicates photic zone anoxia. Zn, Mn and δ34S have also been used to identify different scenarios during sapropel formation.

Pigments start to appear at the beginning of both the Baltic Sea sapropel and S1, the Holocene sapropel in the Mediterranean Sea. Cyanobacterial pigments generally increase early in the sapropel, due to fast adaptation to more P-rich conditions. Cyanobacteria are favored by low N/P-ratios and P was probably in excess during the formation of S1 and the Baltic Sea sapropel sediments. Lowering of δ15N and concurrent increase in N in both the Baltic Sea and S1 sapropels is probably caused by cyanobacterial N2-fixation. This most likely increased the N/P-ratio and enhanced overall primary productivity. Both increased primary productivity and enhanced preservation of organic carbon are important mechanisms for sapropel formation. The appearance of isorenieratene in the protosapropel is most likely the result of an environment where even moderate increases in primary productivity could create anoxic conditions. This favours an estuarine water circulation scenario with anoxic bottom waters. δ34S of sulphate and sulphide confirm this scenario, which can be explained by the coexistence of sulphate reducing and sulphur disproportionating bacteria together with phototrophic purple and green sulphur bacteria.

Place, publisher, year, edition, pages
Stockholm: Institutionen för geologi och geokemi, 2006. 33 p.
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 326
National Category
Earth and Related Environmental Sciences
urn:nbn:se:su:diva-895 (URN)91-7155-221-9 (ISBN)
Public defence
2006-03-31, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
Available from: 2006-03-02 Created: 2006-03-02Bibliographically approved

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