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Environmental and climatic changes in the Baltic Sea and the eastern Mediterranean Sea: as recorded by pigments and isotopes in sediments
Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
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.
Series
Meddelanden från Stockholms universitets institution för geologi och geokemi, ISSN 1101-1599 ; 326
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-895ISBN: 91-7155-221-9 (print)OAI: oai:DiVA.org:su-895DiVA: diva2:200611
Public defence
2006-03-31, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
Opponent
Supervisors
Available from: 2006-03-02 Created: 2006-03-02Bibliographically approved
List of papers
1. Probable causes for cyanobacterial expansion in the Baltic Sea: role of anoxia and phosphorus retention
Open this publication in new window or tab >>Probable causes for cyanobacterial expansion in the Baltic Sea: role of anoxia and phosphorus retention
2003 In: Estuaries, ISSN 0160-8347, Vol. 26, no 3, 680-689 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25826 (URN)
Note
Part of urn:nbn:se:su:diva-895Available from: 2006-03-02 Created: 2006-03-02Bibliographically approved
2. Cyanobacteria as a trigger for increased primary productivity during sapropel formation in the Baltic Sea: a study of the Ancylus/Litorina transition
Open this publication in new window or tab >>Cyanobacteria as a trigger for increased primary productivity during sapropel formation in the Baltic Sea: a study of the Ancylus/Litorina transition
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.

Keyword
Sapropels - Baltic Sea - Primary production - Cyanobacteria - Pigments - Zeaxanthin
Identifiers
urn:nbn:se:su:diva-25827 (URN)10.1007/s10933-006-9055-0 (DOI)000247530100001 ()
Note
Part of urn:nbn:se:su:diva-895Available from: 2006-03-02 Created: 2006-03-02 Last updated: 2010-07-27Bibliographically approved
3. Phytoplankton pigments and δ15N in the eastern Mediterranean sapropel S1 and comparisons with the Holocene sapropel from the Baltic Sea
Open this publication in new window or tab >>Phytoplankton pigments and δ15N in the eastern Mediterranean sapropel S1 and comparisons with the Holocene sapropel from the Baltic Sea
(English)In: Marine Geology, ISSN 0025-3227, E-ISSN 1872-6151Article in journal (Refereed) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-25828 (URN)
Available from: 2006-03-02 Created: 2006-03-02 Last updated: 2013-07-09Bibliographically approved
4. Sapropel S1 formation from proxy signals: biomarkers and sulphur isotopes
Open this publication in new window or tab >>Sapropel S1 formation from proxy signals: biomarkers and sulphur isotopes
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25829 (URN)
Note
Part of urn:nbn:se:su:diva-895Available from: 2006-03-02 Created: 2006-03-02 Last updated: 2010-01-13Bibliographically approved

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