Environmental changes during isolation processes from the Litorina Sea as reflected by diatoms and geochemical parameters -a case study

Abstract

The aim with the present case study was to detect environmental changes during the isolation of a lake from the Baltic Sea. Elemental and stable-isotope ratios of carbon and nitrogen are presented as well as results of a diatom analysis of a sedimentary sequence from Lake Skären in southeastern Sweden. The dated part of the analysed sequence covers the period c. 8200 to 7000 cal. years BP, i.e., the late Ancylus Lake to early Litorina Sea stages. It is concluded that subtle environmental changes due to uctuations in input of organic material from different sources cannot be detected by diatom analysis alone, but that chemostratigraphy is an important complement to diatom stratigraphy when interpreting the isolation process. We also conclude that, even though d 13 C is highly variable in Baltic Sea sediment, it is most useful in isolation studies for recording the contribution of organic carbon derived from benthic macro-algae and/or terrestrial sources, as a proxy for shore displacement. It is especially valuable in combination with the C/N ratio, which seems to be the most unambiguous parameter. The d 15 N data showed that cyanobacterial blooms in the coastal zone of the early Litorina Sea were probably less pronounced than in the offshore areas of the Baltic Sea. The abrupt increase of Chaetoceros spp. resting spores slightly prior to isolation is interpreted as caused by a eutrophication process during the isolation: it is probably also due to nitrogen de ciency due to denitri cation in the coastal areas.

Assessment of δ13C and C/N ratios in bulk organic matter as palaeosalinity indicators in Holocene and Lateglacial isolation basin sediments, northwest Scotland

“…Chmura and Aharon, 1995;Chivas et al, 2001;Westman and Hedenströ m, 2002;Emeis et al, 2003;Wilson et al, 2004;Mackie et al, 2005;Lamb et al, 2006;Zong et al, 2006). The majority of d 13 C and C/N studies have concentrated on investigating the suitability of this methodology through contemporary analyses and, in general, have limited palaeo-investigations from sediments of Holocene age.…”

Mid-Holocene variability of the East Asian monsoon based on bulk organic δ13C and C/N records from the Pearl River estuary, southern China

“…Application of δ 13 C and C/N analyses of sedimentary organic matter for reconstructing palaeo-environmental changes have been carried out in a range of environments (Lamb et al, 2006), including lagoons (Müller and Mathesius, 1999;Yamamuro, 2000), isolation basins (Chivas et al, 2001;Westman and Hedenström, 2002;Mackie et al, 2007), fjords (Bird et al, 1991;St-Onge and Hillaire-Marcel, 2001;Smittenberg et al, 2004), as well as estuaries (Malamud-Roam et al, 2006;Middelburg et al, 1997;Wilson, et al, 2005;Zong et al, 2006). The advantage of δ 13 C and C/N analysis is that it can be performed on most sediment, as only a small amount of organic carbon (micrograms to milligram) is required for analysis.…”

The Palaeolimnology of Lough Murree, A Brackish Lake in the Burren, Ireland

“…Rock barriers can have both overground and underground hydrological connection to the sea and can isolate lagoons from the sea with falls in sea level and land uplift (Westman and Hedenström 2002;Lamb et al 2006). Physical, chemical and biological sediment proxies from Murree generally suggest an evolution to more freshwater conditions, while a notable change point at c. 40cm sediment depth is evident and may be coincident with the sediment hiatus.…”