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)
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
Earth and Related Environmental Sciences
IdentifiersURN: urn:nbn:se:su:diva-895ISBN: 91-7155-221-9OAI: oai:DiVA.org:su-895DiVA: diva2:200611
2006-03-31, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00
Bernasconi, Stefano, Professor
Hallberg, Rolf, Professor emeritusRouth, Joyanto, Docent
List of papers