Mercury in Baltic Sea sediments—Natural background and anthropogenic impact

Andersen

Schulz–Bull

et al. 2016

Self Cite

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 ( 137 Cs/ 241 Am/bomb 14 C), polychlorinated biphenyls (PCBs), lead (Pb) and stable lead isotope ( 206/207 Pb ratios), and radionuclide 210 Pb and 14 C 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 210 Pb unsupp. (marking the 210 Pb 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. 241 Am) 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 137 Cs 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 137 Cs 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.

Section: Pollutant Concentrationsmentioning

confidence: 99%

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

Andersen

Schulz–Bull

et al. 2016

Self Cite

“…The 137 Cs record shows slightly increasing values between approximately 58.5 and 40 cm core depth ( Fig. 2A) and mark the onset of accumulation of material affected by the beginning of industrialization at c. AD 1900 (Leipe et al 2013;Moros et al this issue). Accordingly, sediments of this depth interval accumulated during the nuclear weapon tests period.…”

Section: Chronostratigraphy and Sedimentation Ratesmentioning

confidence: 90%

“…Accordingly, sediments of this depth interval accumulated during the nuclear weapon tests period. from c. AD 1950s to the AD 1970s (Leipe et al 2013;Moros et al this issue). Davis et al 1984), and (ii) generally high sedimentation rates strongly diluting the 137 Cs signal (see discussion below).…”

Section: Chronostratigraphy and Sedimentation Ratesmentioning

confidence: 97%

See 1 more Smart Citation

Mid‐ to late Holocene environmental separation of the northern and central Baltic Sea basins in response to differential land uplift

Häusler

Wacker

et al. 2016

Self Cite

The Littorina Sea stage (past c. 7000 years) development of the northern, and its interactions with the central Baltic Sea have been influenced by spatially different but in the north very strong glacio‐isostatic uplift. Here we investigate the impact of the isostatic readjustment on the northern Baltic Sea environment and on the water exchange with the central Baltic Sea using geochemical and microfossil records from well‐dated sediment cores of the Bothnian Sea/Bay that are compared to sedimentary records of the Gotland Basin and Landsort Deep. Benthic foraminifera and manganese carbonate layers in the sediments from northern Baltic Sea sub‐basins imply oxic marine intrusions from c. 7.0 cal. ka BP. Related water‐column stratification together with enhanced primary productivity caused oxygen‐depleted bottom waters and deposition of organic‐rich laminated sediments during the Holocene Thermal Maximum. Comparable sedimentary/geochemical records in early Littorina Sea sediments of e.g. the eastern Gotland Basin therefore imply a low impact of isostatic uplift on the northern Baltic Sea environment. A climate‐controlled decline in hypoxia induced a gradual deposition of rather homogenous sediments in the central and northern Baltic Sea during the mid‐Littorina Sea stage. Progressive isostatic uplift caused a diverging environmental development in both basins during the mid‐ to late Littorina Sea stage. The Åland sill shoaled markedly allowing only strong inflows to enter the northern Baltic Sea as late as 2.3 cal. ka BP. The restricted deep‐water exchange with the central Baltic Sea probably resulted in a pronounced freshening and oxic bottom waters. This, together with an uplift‐related sediment re‐deposition induced accumulation of rather homogenous sediments throughout the remaining Littorina Sea stage. By contrast, a climate‐controlled depositional environment in the central Baltic Sea during this time caused the formation of homogeneous sediments during cold phases and laminated sediments during warm phases.

“…Anthropogenic mercury analysis was performed at the Leibniz Institute for Baltic Sea Research using a DMA-80 Analyzer from MLS Company and a sample weight varying between 20 and 100 mg. Data were calibrated against CRM (BCR) 142R certified reference material and the SRM 2709 soil standard using five concentration steps covering a range from 5 to 500 ng Hg. For further analytical information and details regarding quality assurance see Leipe et al (2013).…”

Section: Methodsmentioning

confidence: 99%

Late Holocene palaeoproductivity changes: a multi‐proxy study in the Norwegian Trench and the Skagerrak, North Sea

Asteman

Risebrobakken

et al. 2017

Self Cite

To detect climatic linkages between the Baltic Sea, the Skagerrak and the Nordic Seas, we present multi‐proxy reconstructions covering the last 4500 years from three sediment cores taken in the Skagerrak and along the SW Norwegian margin. Foraminiferal assemblages at all three sites show a distinct change at c. 1700 years BP, associated with a transition from absence and rare occurrence of Brizalina skagerrakensis during c. 4500–2300 years BP to its subsequent abundance increase, suggesting a stronger influence of nutrient‐rich water‐masses during the last c. 1700 years. Increased nutrient availability, which probably stimulated higher primary productivity, is further supported by an increase in diatoms, total organic carbon and benthic foraminiferal species indicative of high productivity and carbon fluxes during the last c. 1700 years as compared to c. 4500–2300 years BP. The amplitude of the B. skagerrakensis signal is largest in the central Skagerrak and gradually becomes smaller towards the Norwegian Sea suggesting that the dominant source of the nutrient‐rich water was the brackish outflow from the Baltic Sea. The generally lower abundances of planktonic foraminifera since c. 1700 years BP support the hypothesis of less saline surface water conditions in the Skagerrak. These results agree with other studies, which suggest a stronger Baltic outflow over the last 1700 years coinciding with a general cooling, increased wintertime westerlies bringing more winter precipitation to northern Europe, increased river runoff and higher frequency of floods. The increase in outflow also occurs during deposition of laminated sediments in the deep Baltic Sea. Leakage of dissolved inorganic phosphorus from anoxic sediments, as well as enhanced erosion due to deforestation in combination with higher runoff from Norway, coastal upwelling and more vigorous frontal dynamics may all have contributed to higher nutrient availability within the adjacent Skagerrak during the last 1700 years BP as compared to c. 4500–2300 years BP, when low productivity prevailed in the study area.