Harald Biester

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Lead (Pb) isotope fingerprints in marine sediments are frequently used as tracers of natural or anthropogenic Pb sources. This assumes that Pb isotope ratios are not altered within the water column or sediments. Recent studies suggest reverse scavenging of Pb isotopes by biogenic particles during sinking through the water column, but it remains unclear if and how this affects the Pb isotope signal in deep sea sediments. This study examines Pb isotope records (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb) in pelagic sediments of a highly productive area in the South Atlantic Ocean and their relation to primary productivity as reflected by the silicon (Si) and total organic carbon (TOC) contents. Three cores were extracted at three different stations northwest and southeast of South Georgia and at different water depths (St9: 3796 m, St15: 8066 m, and St16: 5002 m). Downcore Pb and total organic carbon concentrations ranged from 4 to 12 µg g^-1 and from 0.17 to 0.89 % respectively, with highest Pb concentrations in the core taken at the deepest water depth. Lead isotope signatures reflected Patagonian dust as the major Pb source. Lead isotope ratios in the sediment cores were generally larger than those of dissolved Pb in the water phase observed in previous studies, indicating a separation between Pb isotope pools in the water column. Distinct variations in Pb isotope ratios correlated with the content of Si and TOC, indicating an influence of primary productivity on Pb scavenging in the water column. Correlations of Pb concentrations and isotope ratios with TOC content were most pronounced at the deepest sampling station, but were less distinct at other stations presumably due to dilution by biogenic Si. Besides implications on the biogeochemical Pb marine cycle, our findings question the use of Pb isotope signatures in deep sea sediments for source tracing. Future studies combining water phase, particulate matter and sediment Pb isotope analyses should address how signatures of Pb isotope ratios are altered in the water phase during sinking and investigate fractionation processes during Pb burial in deep sea sediments.

Stomatal uptake of mercury (Hg) by trees and litterfall are the major pathways of atmospheric Hg to the terrestrial environment. However, underlying processes and controlling factors of Hg accumulation in tree rings which have been used in numerous studies to reconstruct historical atmospheric Hg concentrations at polluted sites are poorly understood. Especially the role of changing climatic conditions such as rising temperature and frequent drought events compared to local Hg contamination levels have been widely ignored. We investigated tree rings of oaks at a former Hg mining site and an unpolluted reference site and compared the oak tree-ring records with tree rings of Douglas fir from unpolluted sites, all located in western Germany. Our data indicates that the overall Hg accumulation in trees is determined by local Hg loads in soil, but did not follow the historical record of atmospheric Hg pollution. In contrast, the long-term evolution of tree-ring Hg concentrations can statistically be attributed to changing hydroclimatic conditions. We suggest that different physiological heat adaption strategies of the investigated oaks are likely to lead to continuously increasing tree-ring Hg concentration with rising temperature and precipitation rates during the past century, whereas the investigated Douglas fir trees show a strongly declining trend in Hg load in the same period. Our findings indicate that climate conditions appear to overwrite changes in atmospheric Hg and may alter the Hg accumulation in different forest types and likely the related transfer of atmospheric Hg to the soil through litterfall.

Methylated mercury (MeHg), including dimethylmercury and monomethylmercury (MMHg), is a pollutant of concern because it biomagnifies in marine biota. The formation of MeHg in the oceans, specifically at highly productive regions and at high oxygen levels, remains elusive. We investigated dissolved and particulate total (THg) and MeHg in the water column and sediments at six stations in a highly productive area of the Southern Atlantic Ocean. Total MeHg concentrations and proportions of THg in seawater were higher (50%–73%) at eutrophic stations. We found that the distribution of MeHg in the mixed layer is strongly controlled by the biological pump. Concentrations of THg and MMHg were highest in particles within the chlorophyll maximum, suggesting THg and MMHg scavenging or assimilation by phytoplankton and an oxic pathway of MMHg formation. Particle breakdown and respiration appeared to increase dissolved MeHg concentrations and MMHg concentrations in small particles (2–51 μm) at greater depths. MMHg concentrations in the sediments were consistently lower than in particles from the mixed layer, indicating MMHg release during particle sinking and that deep‐sea sediments are unlikely to be an important source of MeHg in the water phase. Our study identifies productive marine areas as hotspots of MeHg formation and suggests increasing Hg methylation with increasing ocean eutrophication and may amplify biomagnification in marine food webs.

Stomatal uptake of mercury (Hg) by trees is the major pathway of atmospheric Hg to the terrestrial environment and most studies have suggested that Hg concentrations in tree rings are determined primarily by gaseous elemental mercury (GEM) concentrations in the atmosphere. Most studies on tree-ring Hg records were aiming to reconstruct historical atmospheric Hg emissions at polluted sites. However, the role of changing climate such as rising temperature and frequent drought events on tree-ring Hg concentrations has been rarely addressed. We show that the overall Hg load in tree rings in oaks and Douglas fir from contaminated and uncontaminated sites in Germany has been strongly determined by local atmospheric Hg emissions, but its long-term evolution has been largely determined by hydroclimate and did not follow the trend of GEM emissions in Europe. Due to different physiological heat adaption strategies Central European oaks show continuously increasing tree-ring Hg concentration with rising temperature and precipitation rates during the past century, whereas coniferous trees show a strongly declining trend in Hg concentration in the same period, which was also observed at other sites within the Northern Hemisphere. Our findings indicate that besides atmospheric Hg concentrations, climate change alters the Hg accumulation in different forest types and most likely the related transfer of atmospheric Hg to the soil.

Stomatal uptake of mercury (Hg) by trees is the major pathway of atmospheric Hg to the terrestrial environment and most studies have suggested that Hg concentrations in tree rings are determined primarily by gaseous elemental mercury (GEM) concentrations in the atmosphere. Most studies on tree-ring Hg records were aiming to reconstruct historical atmospheric Hg emissions at polluted sites. However, the role of changing climate such as rising temperature and frequent drought events on tree-ring Hg concentrations has been rarely addressed. We show that the overall Hg load in tree rings in oaks and Douglas fir from contaminated and uncontaminated sites in Germany has been strongly determined by local atmospheric Hg emissions, but its long-term evolution has been largely determined by hydroclimate and did not follow the trend of GEM emissions in Europe. Due to different physiological heat adaption strategies Central European oaks show continuously increasing tree-ring Hg concentration with rising temperature and precipitation rates during the past century, whereas coniferous trees show a strongly declining trend in Hg concentration in the same period, which was also observed at other sites within the Northern Hemisphere. Our findings indicate that besides atmospheric Hg concentrations, climate change alters the Hg accumulation in different forest types and most likely the related transfer of atmospheric Hg to the soil.

Stomatal uptake of mercury (Hg) by trees is the major pathway of atmospheric Hg to the terrestrial environment and most studies have suggested that Hg concentrations in tree rings are determined primarily by gaseous elemental mercury (GEM) concentrations in the atmosphere. Most studies on tree-ring Hg records were aiming to reconstruct historical atmospheric Hg emissions at polluted sites. However, the role of changing climate such as rising temperature and frequent drought events on tree-ring Hg concentrations has been rarely addressed. We show that the overall Hg load in tree rings in oaks and Douglas fir from contaminated and uncontaminated sites in Germany has been strongly determined by local atmospheric Hg emissions, but its long-term evolution has been largely determined by hydroclimate and did not follow the trend of GEM emissions in Europe. Due to different physiological heat adaption strategies Central European oaks show continuously increasing tree-ring Hg concentration with rising temperature and precipitation rates during the past century, whereas coniferous trees show a strongly declining trend in Hg concentration in the same period, which was also observed at other sites within the Northern Hemisphere. Our findings indicate that besides atmospheric Hg concentrations, climate change alters the Hg accumulation in different forest types and most likely the related transfer of atmospheric Hg to the soil.

Methylated mercury (MeHg), including dimethylmercury and monomethylmercury (MMHg), is a pollutant of concern because it biomagnifies in marine biota. The formation of MeHg in the oceans, specifically at highly productive regions and at high oxygen levels, remain elusive. Most existing studies have analysed the distribution of total Hg (THg) and MeHg in the water column in oligotrophic areas and have focussed on dissolved Hg species, while insights into THg and MMHg in marine particles are scarce. We investigated dissolved and particulate THg and MeHg in the water column and sediments at six stations in a highly productive area of the Southern Atlantic Ocean. Total MeHg concentrations in seawater and proportions were higher (50–73 %) at eutrophic stations. We found that the distribution of MeHg in the mixed layer is strongly controlled by the biological pump. Concentrations of THg and MMHg were highest in particles within the chlorophyll maximum with high oxygen levels, suggesting THg and MMHg scavenging or assimilation by phytoplankton and an oxic pathway of MMHg formation. At greater depth, particle breakdown and respiration appeared to increase dissolved MeHg concentrations and MMHg concentrations in small particles (2–53 µm). MMHg concentrations in the sediments were lower than in particles from the mixed layer, indicating that deep-sea sediments are unlikely an important source of MeHg in the water phase. Our study identifies productive marine areas as hotspots of MeHg formation, but further studies are needed to disentangle Hg methylation pathways under oxic conditions.