Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900: approaches and challenges

Matthias Moros; Thorbjørn J. Andersen; Detlef Schulz-Bull; Katharina Häusler; Dennis Bunke; Ian Snowball; Aarno Kotilainen; Lovisa Zillén; Jørn B. Jensen; Karoline Kabel; Ines Hand; Thomas Leipe; Bryan C. Lougheed; Bernd Wagner; Helge W. Arz

doi:10.1111/bor.12193

Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900: approaches and challenges

Matthias Moros, Thorbjørn J. Andersen, Detlef Schulz-Bull, Katharina Häusler, Dennis Bunke, Ian Snowball, Aarno Kotilainen, Lovisa Zillén, Jørn B. Jensen, Karoline Kabel, Ines Hand, Thomas Leipe, Bryan C. Lougheed, Bernd Wagner, Helge W. Arz

Earth and Climate

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Reconstructions of environmental changes at sub-decadal to decadal resolution based on central Baltic Sea sediments rely on accurate and precise high-resolution sediment depth/age relationships. A model chronology for Baltic Sea sediments is presented here based on established historical records of anthropogenic radionuclides (¹³⁷Cs/²⁴¹Am/bomb¹⁴C), polychlorinated biphenyls (PCBs), lead (Pb) and stable lead isotope (^206/207Pb ratios), and radionuclide ²¹⁰Pb and ¹⁴C decay dating methods. Marker horizons consisting of chemical precipitates formed by documented Major Baltic Inflow (MBIs) events and an extended diatom bloom period were also integrated into the model. The main time markers in Baltic Sea sediments that formed during the last 120 years were the following: (i) the deepest observation of ²¹⁰Pb_unsupp. (marking the ²¹⁰Pb dating horizon) and departure of Hg from natural background levels at c. AD 1900; (ii) first detectable presence of PCBs at AD 1935; (iii) radionuclide production (i.e. ²⁴¹Am) due to nuclear weapons testing between AD 1954 and AD 1975, with a peak in AD 1963; (iv) maximum heavy metal and PCB concentrations in the AD 1960s/1970s; (v) the Chernobyl nuclear accident in AD 1986 as a sharp ¹³⁷Cs increase; (vi) exceptionally strong diatom blooms with a massive diatom layer found in the Eastern Gotland Basin in AD 1988–1990; and (vii) characteristic manganese-carbonate layers in the deeper central basins formed by MBIs in AD 1993 and AD 2003. A precise and accurate sediment depth/age relationship can only be achieved in restricted areas of the Baltic Sea where continuous sedimentation has prevailed and there has been limited postdepositional disturbance. We demonstrate that parallel Hg and ¹³⁷Cs measurements can be used to assess the quality of sediment sequences for high-resolution environmental reconstructions. We show examples of sediment profiles that conform to the historical record, and examples from Western Baltic Sea areas where it appears to be impossible to establish accurate geochronologies.

Original language	English
Pages (from-to)	129-142
Number of pages	14
Journal	Boreas
Volume	46
Issue number	1
DOIs	https://doi.org/10.1111/bor.12193
Publication status	Published - 1 Jan 2017

Funding

We thank the captains and the technical and scientific crews on board RV ?Maria S. Merian?, RV ?Meteor?, RV ?Aranda?, RV ?Prof. Albrecht Penck?, RV ?Poseidon? and RV ?Elisabeth Mann Borgese? for their technical assistance in obtaining the cores during the numerous cruises. We acknowledge Sascha Plewe, Ines Scherf, Claas Mellis and Steffi Bednarczyk for technical and laboratory help. We thank the two reviewers, John Boyle and Kay-Christian Emeis, for their constructive and very helpful comments, which greatly improved the manuscript and Jan A. Piotrowski for editorial handling. This study forms part of the INFLOW (The Holocene Saline Water Inflow Changes into the Baltic Sea) project and received funding from the European Community's 7th Framework Programme (FP/2007-2013) BONUS+ under grant agreement 217246.

Funders	Funder number
European Community's 7th Framework Programme
Sascha Plewe
Seventh Framework Programme	217246

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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Moros, M., Andersen, T. J., Schulz-Bull, D., Häusler, K., Bunke, D., Snowball, I., Kotilainen, A., Zillén, L., Jensen, J. B., Kabel, K., Hand, I., Leipe, T., Lougheed, B. C., Wagner, B., & Arz, H. W. (2017). Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900: approaches and challenges. Boreas, 46(1), 129-142. https://doi.org/10.1111/bor.12193

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abstract = "Reconstructions of environmental changes at sub-decadal to decadal resolution based on central Baltic Sea sediments rely on accurate and precise high-resolution sediment depth/age relationships. A model chronology for Baltic Sea sediments is presented here based on established historical records of anthropogenic radionuclides (137Cs/241Am/bomb14C), polychlorinated biphenyls (PCBs), lead (Pb) and stable lead isotope (206/207Pb ratios), and radionuclide 210Pb and 14C decay dating methods. Marker horizons consisting of chemical precipitates formed by documented Major Baltic Inflow (MBIs) events and an extended diatom bloom period were also integrated into the model. The main time markers in Baltic Sea sediments that formed during the last 120 years were the following: (i) the deepest observation of 210Pbunsupp. (marking the 210Pb dating horizon) and departure of Hg from natural background levels at c. AD 1900; (ii) first detectable presence of PCBs at AD 1935; (iii) radionuclide production (i.e. 241Am) due to nuclear weapons testing between AD 1954 and AD 1975, with a peak in AD 1963; (iv) maximum heavy metal and PCB concentrations in the AD 1960s/1970s; (v) the Chernobyl nuclear accident in AD 1986 as a sharp 137Cs increase; (vi) exceptionally strong diatom blooms with a massive diatom layer found in the Eastern Gotland Basin in AD 1988–1990; and (vii) characteristic manganese-carbonate layers in the deeper central basins formed by MBIs in AD 1993 and AD 2003. A precise and accurate sediment depth/age relationship can only be achieved in restricted areas of the Baltic Sea where continuous sedimentation has prevailed and there has been limited postdepositional disturbance. We demonstrate that parallel Hg and 137Cs measurements can be used to assess the quality of sediment sequences for high-resolution environmental reconstructions. We show examples of sediment profiles that conform to the historical record, and examples from Western Baltic Sea areas where it appears to be impossible to establish accurate geochronologies.",

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AU - Moros, Matthias

AU - Andersen, Thorbjørn J.

AU - Schulz-Bull, Detlef

AU - Häusler, Katharina

AU - Bunke, Dennis

AU - Snowball, Ian

AU - Kotilainen, Aarno

AU - Zillén, Lovisa

AU - Jensen, Jørn B.

AU - Kabel, Karoline

AU - Hand, Ines

AU - Leipe, Thomas

AU - Lougheed, Bryan C.

AU - Wagner, Bernd

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Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900: approaches and challenges

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