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

TY - JOUR

T1 - Towards an event stratigraphy for Baltic Sea sediments deposited since AD 1900

T2 - approaches and challenges

AU - Moros, Matthias

AU - Andersen, Thorbjørn Joest

AU - Schulz-Bull, Detlef

AU - Häusler, Katharina

AU - Bunke, Dennis

AU - Snowball, Ian

AU - Kotilainen, Aarno

AU - Zillén, Lovisa

AU - Jensen, Jørn Bo

AU - Kabel, Karoline

AU - Hand, Ines

AU - Leipe, Thomas

AU - Lougheed, Bryan C.

AU - Wagner, Bernd

AU - Arz, Helge W.

PY - 2017

Y1 - 2017

N2 - 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.

AB - 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.

U2 - 10.1111/bor.12193

DO - 10.1111/bor.12193

M3 - Journal article

AN - SCOPUS:84997051888

SN - 0300-9483

VL - 46

SP - 129

EP - 142

JO - Boreas

JF - Boreas

IS - 1

ER -