Quantitative salinity reconstructions of the Baltic Sea during the mid-Holocene

详细信息    查看全文

• 作者：Wenxin Ning ; Per S. Andersson ; Anupam Ghosh ; Mansoor Khan and Helena L. Filipsson
• 刊名：Boreas
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：46
• 期：1
• 页码：100-110
• 全文大小：958K
• ISSN：1502-3885

文摘

We reconstructed the past coastal environment of the Baltic Sea from c. 7300 to 3500 cal. a BP, with a focus on sea surface salinity (SSS). To quantitatively determine the SSS, two methods were employed: measurements of ⁸⁷Sr/⁸⁶Sr ratios in mollusc shells (SSS_Sr) and process length variations of dinoflagellate cysts Operculodinium centrocarpum (SSS_pl). The SSS_Sr was ~6–7 between 6800 and 6400 cal. a BP, similar to modern conditions. Between 6000 and 3900 cal. a BP, SSS_Sr was consistently higher, ranging between ~9 and 13. Microfossils sensitive to salinity variations, such as Radiosperma corbiforum and Spiniferites spp., support the SSS_Sr estimate. In comparison with the SSS_Sr, the SSS_pl values were consistently higher, with an average of ~14. We suggest SSSpl tend to overestimate salinity and are not as reliable as SSS_Sr. A multi-proxy approach, including analysis of microfossil, organic carbon content, C/N ratios and grain-size, allowed for a division of the study period into three zones (Zones I–III). Zone I (7300–6400 cal. a BP) is characterized by relatively O. centrocarpum and R. corbiforum concentrations, silt contents and C/N ratios, corresponding to the regional Littorina transgression maximum. Zone II (6400–3900 cal. a BP) is characterized by increased Spiniferites spp. and decreased R. corbiforum abundances, and by lowered C/N ratios and silt contents relative to Zone I. Zone III (3900–3500 cal. a BP) represents the start of the Post-Littorina Sea phase, indicating a shift to the modern Baltic Sea phase with decreased salinity.