| 1. |
- Czymzik, Markus, et al.
(författare)
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Synchronizing the Western Gotland Basin (Baltic Sea) and Lake Kälksjön (central Sweden) sediment records using common cosmogenic radionuclide production variations
- 2024
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Ingår i: Holocene. - 0959-6836.
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Tidskriftsartikel (refereegranskat)abstract
- Multi-archive studies of climate events and archive-specific response times require synchronous time scales. Aligning common variations in the cosmogenic radionuclide production rate via curve fitting methods provides a tool for the continuous synchronization of natural environmental archives down to decadal precision. Based on this approach, we synchronize 10Be records from Western Gotland Basin (WGB, Baltic Sea) and Lake Kälksjön (KKJ, central Sweden) sediments to the 14C production time series from the IntCal20 calibration curve during the Mid-Holocene period ~6400 to 5200 a BP. Before the synchronization, we assess and reduce non-production variability in the 10Be records by using 10Be/9Be ratios and removing common variability with the TOC record from KKJ sediments based on regression analysis. The synchronizations to the IntCal20 14C production time scale suggest decadal to multi-decadal refinements of the WGB and KKJ chronologies. These refinements reduce the previously centennial chronological uncertainties of both archives to about ± 20 (WGB) and ±40 (KKJ) years. Combining proxy time series from the synchronized archives enables us to interpret a period of ventilation in the deep central Baltic Sea basins from ~6250 to 6000 a BP as possibly caused by inter-annual cooling reducing vertical water temperature gradients allowing deep water formation during exceptionally cold winters.
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| 2. |
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| 3. |
- Kämpf, Lucas, et al.
(författare)
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Stable oxygen and carbon isotopes of carbonates in lake sediments as a paleoflood proxy
- 2020
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Ingår i: Geology. - 0091-7613. ; 48:1, s. 3-7
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Tidskriftsartikel (refereegranskat)abstract
- Lake sediments are increasingly explored as reliable paleoflood archives. In addition to established flood proxies including detrital layer thickness, chemical composition, and grain size, we explore stable oxygen and carbon isotope data as paleoflood proxies for lakes in catchments with carbonate bedrock geology. In a case study from Lake Mondsee (Austria), we integrate high-resolution sediment trapping at a proximal and a distal location and stable isotope analyses of varved lake sediments to investigate flood-triggered detrital sediment flux. First, we demonstrate a relation between runoff, detrital sediment flux, and isotope values in the sediment trap record covering the period 2011-2013 CE including 22 events with daily (hourly) peak runoff ranging from 10 (24) m3 s-1 to 79 (110) m3 s-1. The three-to ten-fold lower flood-triggered detrital sediment deposition in the distal trap is well reflected by attenuated peaks in the stable isotope values of trapped sediments. Next, we show that all nine flood-triggered detrital layers deposited in a sediment record from 1988 to 2013 have elevated isotope values compared with endogenic calcite. In addition, even two runoff events that did not cause the deposition of visible detrital layers are distinguished by higher isotope values. Empirical thresholds in the isotope data allow estimation of magnitudes of the majority of floods, although in some cases flood magnitudes are overestimated because local effects can result in too-high isotope values. Hence we present a proof of concept for stable isotopes as reliable tool for reconstructing flood frequency and, although with some limitations, even for flood magnitudes.
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| 4. |
- Nantke, Carla K.M., et al.
(författare)
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Human influence on the continental Si budget during the last 4300 years : δ30Sidiatom in varved lake sediments (Tiefer See, NE Germany)
- 2021
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 258
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Tidskriftsartikel (refereegranskat)abstract
- The continental silicon (Si) cycle, including terrestrial and freshwater ecosystems (lakes, rivers, estuaries), acts as a filter and modulates the amount of Si transported to the oceans. In order to link the variation in the terrestrial Si cycle to aquatic ecosystems, knowledge on changes in vegetation cover, soil disturbance and the impact of human activity are required. This study on varved lake sediments from Tiefer See near Klocksin (TSK) in northeastern Germany investigates Si isotope variations in diatom frustules (δ30Sidiatom) over the last ∼4300 years. δ30Sidiatom values vary between 0.37 and 1.63‰. The isotopic signal measured in centric (mostly planktonic) and pennate (mostly benthic) diatoms shows the same trend through most of the record. A decrease in δ30Sidiatom coinciding with early deforestation between 3900 and 750 a BP in the catchment area, points to an enhanced export of isotopically light dissolved silica (DSi) from adjacent soils to the lake. The burial flux of biogenic silica (BSi) observed in the lake sediments increases with cultivation due to enhanced nutrient supply (N, P and Si) from the watershed and nutrient redistribution caused by wind-driven increased water circulation. When the cultivation intensifies, we observe a shift to higher δ30Sidiatom values that we interpret to reflect a diminished Si soil pool and the preferential removal of the lighter 28Si by crop harvesting. Human activity influences the DSi supply from the catchment and appears to be the primary driver controlling the Si budget in TSK. Our data shows how land use triggers variations in continental Si cycling on centennial timescales and provides important information on the underlying processes.
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| 5. |
- Nantke, Carla K.M., et al.
(författare)
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Si cycling in transition zones : a study of Si isotopes and biogenic silica accumulation in the Chesapeake Bay through the Holocene
- 2019
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 146:2, s. 145-170
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Tidskriftsartikel (refereegranskat)abstract
- Si fluxes from the continents to the ocean are a key element of the global Si cycle. Due to the ability of coastal ecosystems to process and retain Si, the ‘coastal filter’ has the potential to alter Si fluxes at a global scale. Coastal zones are diverse systems, sensitive to local environmental changes, where Si cycling is currently poorly understood. Here, we present the first palaeoenvironmental study of estuarine biogenic silica (BSi) fluxes and silicon isotope ratios in diatoms (δ30Sidiatom) using hand-picked diatom frustules in two sediment cores (CBdist and CBprox) from the Chesapeake Bay covering the last 12000 and 8000 years, respectively. Constrained by the well-understood Holocene evolution of the Chesapeake Bay, we interpret variations in Si cycling in the context of local climate, vegetation and land use changes. δ30Sidiatom varies between + 0.8 and + 1.7‰ in both sediment cores. A Si mass balance for the Chesapeake Bay suggests much higher rates of Si retention (~ 90%) within the system than seen in other coastal systems. BSi fluxes for both sediment cores co-vary with periods of sea level rise (between 9500 and 7500 a BP) and enhanced erosion due to deforestation (between 250 and 50 a BP). However, differences in δ30Sidiatom and BSi flux between the sites emphasize the importance of the seawater/freshwater mixing ratios and locally variable Si inputs from the catchment. Further, we interpret variations in δ30Sidiatom and the increase in BSi fluxes observed since European settlement (~ 250 a BP) to reflect a growing human influence on the Si cycle in the Chesapeake Bay. Thereby, land use change, especially deforestation, in the catchment is likely the major mechanism.
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| 6. |
- Nantke, Carla
(författare)
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Reconstructing Si cycling in transition zones during the Holocene using terrestrial and aquatic records
- 2020. - LUNDQUA THESIS
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global biogeochemical cycles and their interactions are an important parts of climate research. Investigations during the last decades emphasize the key role of diatoms – siliceous phytoplankton – in the silicon (Si) cycle as they are important carbon sequesters in both marine and lacustrine environments. Terrestrial Si cycling and especially fluxes across the vegetation-soil interface are highly variable but important for the global Si budget. Shifts from natural vegetation to cultivated soils have been shown to impact the Si cycle in modern soil systems. Coastal zones and lake sediments provide suitable archives to investigate how human land use modified the terrestrial Si cycle in the past.The aim of this PhD project is to further constrain changes in the continental Si budget and link them to environmental factors such as land cultivation, deforestation, and salinity. Our study sites, Chesapeake Bay (East coast of the United States) and Tiefer See (north-eastern Germany) record climate and vegetation changes as well as human settlements during the Holocene. The measurement of biogenic Si (BSi) fluxes and Si isotopes in diatom frustules (30Sidiatom) separated from sediment cores, create a record of terrestrial Si cycling back in time, which then can be linked to the factors mentioned above. Our results show that increasing human activity, especially deforestation and crop harvest impact the terrestrial Si cycle on geologically short time scales (decades-centuries). Changes in dissolved Si inputs from the catchment area dominate the variation in Si cycling in terrestrial freshwater systems; in contrast to marine environments where 30Sidiatom is a proxy for Si utilization. On a local scale, Si inputs can alter the budget of lake within decades. Overall this thesis investigates how climate and human activity influence the so called ‘terrestrial Si loop’ determining the amount of Si delivered to the ocean.
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