Frank, Martin
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Frank, Martin
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Frank, Martin
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Frank, M.
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mfrank@geomar.de
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Item-typ:Veröffentlichung, Recordings of cosmogenic beryllium in marine sediments during the Laschamps geomagnetic dipole low: implications for synchronization of paleo archives and geomagnetic field reconstructions(2025-07-22); ; Adolphi, FlorianCosmogenic beryllium (10Be) is produced in the Earth’s atmosphere during the nuclear cascade initiated by the collision of galactic cosmic rays with the nuclei of atmospheric atoms. The production rate of 10Be is therefore globally influenced by the solar and geomagnetic fields. It exhibits both a latitudinal and an altitudinal gradient, with the highest production rate in the polar stratosphere and the lowest in the equatorial troposphere. 10Be is removed from the atmosphere, primarily through wet deposition, and is globally recorded in various paleo archives, such as ice or sediment cores. Given the correlation between the 10Be production rate and Earth’s magnetic shielding and solar activity, 10Be is a valuable tool for the reconstruction of both in the past. Additionally, the global modulation of its production rate renders 10Be an effective synchronization tool for diverse paleo archives. Yet, additional factors may also affect the recorded production rate signal. Recent atmospheric mixing models suggest a latitude-dependent influence of geomagnetic field variations on 10Be records. Consequently, depending on the selected record, the global 10Be production rate change may be either over- or underestimated. In marine sediments, several other influences must be accounted for, including the residence time of beryllium in the water column, changes in sedimentation rates or scavenging efficiency, benthic fluxes of beryllium, bioturbation, and potential sediment re-deposition. Additionally, especially for synchronization purposes, it is imperative to measure marine sediment cores with the highest possible resolution. To begin with, a beryllium purification protocol for measuring 10Be with accelerator mass spectrometry (AMS) was developed. This protocol ensures high sample throughput at a low cost while simultaneously yielding samples that perform well in the AMS. This method employs precipitation reactions and utilizes only standard laboratory materials and equipment. A comparative analysis of this method was conducted against an established protocol based on hydroxide precipitations and column chromatography. Although the method resulted in slightly lower sample purity and yield, this did not adversely affect the AMS measurement. In contrast to the established method, the approach is significantly more cost-effective and enables a two- to threefold increase in sample throughput. To gain a better understanding of the various influences on the recorded 10 Be signal, several marine sediment cores were analyzed. To assess influences on the 10Be recording in marine sediments, three cores were analyzed for their 10Be/9Be ratios during the Laschamps geomagnetic dipole low (∼ 41 ka BP). Although all cores are influenced by the Antarctic Circumpolar Current (ACC) and exhibit high sedimentation rates, differing depositional conditions and influences are present. A rapid and distinct increase in the 10Be/9Be ratios by 50 – 80 percent was observed in all cores during the Laschamps event, which corresponds with changes in the respective paleomagnetic inclinations. However, when compared to 10Be data from ice cores, it was found that all sediment cores were influenced to varying extents by oceanic residence times of 10Be. The short oceanic residence time of beryllium at core PS67/197-1 is consistent with published data for the region, while the longer one of core PS75/054-1 suggests that at least a portion of the scavenged beryllium originates from the pelagic Pacific. In core PS97/085-3, indications of a temporary increase in terrigenous influence were observed. Other sedimentary processes did not significantly affect the 10Be/9Be ratios of the cores. Despite the attenuation effects of residence time and the variable terrigenous influence observed in core PS97/085-3, it was found that the 10Be/9Be ratios are fundamentally suitable for synchronizing different regions and archives. The latitude-dependent distribution of 10Be deposition was investigated by comparing published 10Be sediment data and ice core records during the Laschamps event with the data in this thesis. Variations in 10Be deposition during the Laschamps event were examined in relation to latitude and compared with modeled 10Be deposition rate changes derived from different geomagnetic field reconstructions (LSMOD.2, GGFSS70, Black Sea, GLOPIS-75), in conjunction with the atmospheric mixing model GEOS-Chem. It was found that the results align well with the atmospheric mixing model, which postulates incomplete mixing of 10 Be in the atmosphere before deposition, revealing a lower amplitude of deposition at higher latitudes compared to lower ones. Furthermore, the global deposition rate change during the Laschamps event was estimated, yielding a value that supports the geomagnetic field model LSMOD.2, while indicating that the production rate change derived from GLOPIS-75 may be overestimated. Overall, the gap between geomagnetic field models and atmospheric transport models of 10Be, as well as data-based reconstructions, was narrowed by this study. Notably, it was demonstrated that the global 10Be production rate increased by 117 – 133 percent during the Laschamps event. Although this figure exceeds previous estimates derived from ice core data, it remains insufficient to fully reconstruct the production rate changes of 14C based on 14C measurements.Dissertation38 47 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, 230Th and 231Pa – tracers for particle fluxes and deep water circulation in the Central Arctic Ocean(2021-06-14); ; ; The currently ongoing climate change can be ascribed without exaggerating as one the most important topics and threats for humanity. Understanding its mechanisms and consequences is an important step to target and manage arising problems, which accompany a rapidly warming climate. The oceans play a crucial role in the Earth’s climate controlling and response mechanism. Its physical and biological carbon pump systems are crucial regulators for the atmospheric CO2 content. Biological primary production is an important part of the Oceans CO2 uptake capability. Some trace elements are important (micro-) nutrients in oceanic primary production. Therefore it is important to investigate and understand the reaction of those elements to changing environmental conditions. Particle fluxes and ocean circulation contribute to their distribution in the water column. 230Th and 231Pa are suitable tracers for both particle fluxes and deep water circulation. Their well-known sources and production ratio, as well as their fractionation by particle fluxes and deep water circulation, enables their use as tracers. Their water column distribution serves as an indicator for recent environmental changes, while their sedimentary 231Pa/230Th activity ratio is used as a paleoceanographic tool. Therefore 230Th and 231Pa are standard parameters of GEOTRACES, an international programme with the goal to improve understanding of the cycling of trace elements and their isotopes in the Ocean. Different areas of the World’s Ocean react in different velocities and intensities to climate change. The Arctic Ocean is the most sensitive one to climate change. Climate change related consequences are already visible, e.g. the retreat and thinning of sea ice. Other consequences, like increasing particle fluxes and changing particle composition, as well as potentially changing circulation patterns and ventilation times are less obvious. It is expected that climate change will cause significant changes on the Arctic Oceans’ primary production and particle input. The consequences of these changes are not well understood and known. Therefore it is important to investigate changes in particle fluxes and composition, already in an initial stage of these changes. 230Th and 231Pa are valuable tools to gain insights into changes, which will potentially influence the global climate in the near future. In order to derive information about trace element cycling from 230Th and 231Pa in a changing Arctic Ocean, it is therefore crucial to investigate and understand the processes that control the distribution and concentrations of 230Th and 231Pa in the Arctic Ocean. To achieve this, a time series of this tracer pair, consisting of data from 1991, 2007 and 2015, was created to investigate the temporal development of 230Th and 231Pa over the past three decades. This new time series revealed quite variable 230Th and 231Pa inventories, indicating changing removal processes, caused by changing environmental conditions. This thesis consists of three first author manuscripts that are either published or in preparation for submission to international peer-reviewed journals. Additionally, two co-author manuscripts, published in international peer-reviewed journals, are part of this thesis. This section assigns the role of each manuscript, presented in this thesis, in the context of the general introduction. Changes in scavenging behaviour of 230Th need not necessarily have to be related to a changing climate. Hydrothermal activity and submarine volcanic eruptions at the ultra-slow spreading Gakkel Ridge caused a significant reduction of dissolved 230Th in only eight years in the deep Nansen Basin, contributing to sporadically increased removal and sedimentation rates of 230Th. The role of hydrothermal activity in the variation of scavenging behaviour of 230Th in the Eurasian Basin is described in CHAPTER 2 (Valk et al., 2018). Changing environmental conditions caused a significant decrease of dissolved 230Th concentrations in the entire Eurasian Basin between 2007 and 2015. Those changes include elevated particle fluxes at the shelves and margins of the deep basins, specifically the Barents Sea shelf and the Nansen Basin margin. Those increased particle fluxes caused increased scavenging removal of 230Th and to a minor degree of 231Pa, indicating an increasing sink for particle reactive trace elements. Increased scavenging removal of 230Th at the Barents Sea shelf and at the margins of the Nansen Basin caused a drastic decrease of dissolved 230Th in the central Amundsen Basin (CHAPTER 3, Valk et al., 2020). This highlights the increasing importance of shelf-basin interactions in the Arctic Ocean, due to rapidly increasing particle fluxes at the shelves and margins. Even before particle fluxes within the central basins increase, climate change already causes notable changes in trace element distributions and probably in their export to the North Atlantic. This is important for the nutrient availability in the North Atlantic as well as the paleoceanographic application of the 231Pa/230Th sedimentary activity ratio. Distribution and concentrations of dissolved 230Th and 231Pa can change significantly within less than ten years in the central Arctic Ocean. In CHAPTER 4 (Valk et al., in preparation) new budgets for dissolved 230Th and 231Pa, based on a water column data from 1991 over 2007 to 2015, as well as box models, are presented to illustrate scavenging removal and sedimentation patterns for these tracers. The model results are discussed in the context of boundary scavenging of 230Th and 231Pa in the Eurasian Basin and their export to the GIN Seas (Greenland, Iceland and Norwegian Seas). Consequences of the identified removal processes of 230Th and 231Pa from CHAPTER 1 and CHAPTER 2 on the sedimentary 231Pa/230Th activity ratios in the Eurasian Basin, its margins and the GIN Seas are discussed in the context of the paleoceanographic use of these tracers. It is an open question whether 230Th and 231Pa are subject to boundary scavenging in the Arctic Ocean. The study presented in CHAPTER 5 (Gdaniec et al., 2020) investigates the influence of boundary scavenging and shelf-basin interactions on the observed distribution of 230Th and 231Pa in the Arctic Ocean. A modelling approach adapted from Roy-Barman (2009) is used to constrain the scavenging behaviour of 230Th and 231Pa between the Arctic margin and the inner ocean. This study links very well to CHAPTER 3 and CHAPTER 4, giving detailed insight in particulate and dissolved radionuclide data from 2015. The study presented in CHAPTER 6 (Grenier et al., 2019) investigates the temporal 230Th and 231Pa developments in the Amerasian Basin of the Arctic Ocean, based on 230Th and 231Pa time series and therefore links well to CHAPTER 2, CHAPTER 3 and CHAPTER 4 which focus on the Eurasian Basin. The Amerasian Basin time series reveal a large scale decrease in dissolved 230Th and 231Pa concentrations, indicating intensification of scavenging removal, especially in coastal areas. This study illustrates how dissolved 230Th and 231Pa combined with εNd, can give insights into changes in particle fluxes, as well as into the evolution of ocean circulation and mixing. Thus the research presented in this thesis contributes to the understanding of trace element cycling and the tracer application of 230Th and 231Pa in the Arctic Ocean under changing environmental conditions.Dissertation407 165 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Historical Development of Heavy Metal Input into Near-Coastal Areas : Reconstruction, Assessment&Ecological Response(2019-07-18); ; ; Anthropogenic influences on coastal marine ecosystems can date back several centuries or even millennia, however, with severely increasing impacts following the onset of the industrial revolution. Of particular interest is the release of contaminants, such as heavy metals, as they can have adverse effects on marine ecosystems. Monitoring programs record levels of heavy metals in coastal areas in order to assess the current degree of pollution and state of ecosystem health. To quantify the anthropogenic impact, heavy metal contents need to be compared to their naturally occurring background values. Near-coastal sediment cores have the potential to provide high-resolution archives to determine pristine background values, reconstruct the pollution history in sediments and evaluate its ecotoxicological effects. Therefore, this dissertation unravels the pollution history and elucidates natural background values in three study areas, the Firth of Thames (New Zealand), the Helgoland Mud Area (SE North Sea) and the Skagerrak (NE North Sea).Dissertation536 337