Schlüter, Michael
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Schlüter, Michael
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Schlüter, Michael
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Item-typ:Veröffentlichung, Erfassung von Porenwasservariationen inWattsedimenten und der Einfluss vonGrundwasseraustritt im Sahlenburger Watt(2009-12-10); ; ; The tidal flat near Sahlenburg is influenced by a confined aquifer. Leakage areas in the aquitard causes an outflow of groundwater (Submarine Groundwater Discarge(SGD)). This is well detectable due to the reduced chloride concentrations in pore water. At the sediment surface the SGD creates so called "sand boils" and "pancake structures"."Sand boils" are focused groundwater outlets with diameters in the centimeter to decimeter range. During the low tide the flow rates are between 0.04 L/min and 1.8 L/min."Pancake structures" are morphologically distinctive sedimentary structures with diameters of up to several meters formed by rising ground water. They show relatively sharp horizontal boundaries in porewater chemistry.Measurements showed that the flow rates vary greatly and are influenced by the tides. Measurements of the pressure in the aquifer show variations of up to 50%. SGD can be confirmed in the whole area by using chloride as inert tracer. Advective and diffusive transport processes are visible. These processes works into and out of the sediment. The determining factors are: convection, hydraulic gradient, tidal and wave-pump processes. Based on the concentration profiles transport modeling is performed. This resulted in diffusive and advective flow through the sediment from 0.01 to 3 L/(m^2*day).The aquifer horizons are different in their properties and components. Different concentrations of chloride, silica, oxygen and nitrate and temperatures were measuered . These indicates recirulation of water and varying pathways.The methane concentrations range from values below the detection limit and 500 mikromol/L. The groundwater itself could not be recognized as a source of methane. The complex structure of the sediment formed methane traps and accumulate great concentrations.Dissertation491 163 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Seasonal variations of Benthic Carbon and Nutrient fluxes in the southern North Sea(2015-01-15); ; ; In shallow water regions, such as the coastal areas of the North Sea, nutrient and carbon cycles are driven by a close coupling of benthic-pelagic processes. Due to shallow water depths, a substantial amount of organic matter which is produced via primary production in surface waters is transferred to the seafloor. Most of the organic matter is degraded within surface sediments and nutrients such as NH4 or PO4 are transported back into the water column, whereas a small amount of organic carbon is buried within the sediment. Consequently, benthic carbon and nutrient fluxes have a direct impact on biological and geological processes such as the availability of nutrients in the water column, nutrient budgets or the storage of carbon within marine sediments. Even though coastal carbon and nutrient cycles are intensively investigated, their seasonal and diurnal variability is poorly understood. The aim of this study was to quantify benthic carbon and nutrient fluxes in the southern North Sea during different seasons. The results are used for carbon and nutrient mass budgets. Furthermore processes which affect carbon and nutrient fluxes over seasonal and diurnal scales were identified. Chapter 2 and 3 present a seasonal study on benthic carbon and nutrient fluxes in the southern North Sea. During five cruises on RV Heincke, carried out in June 2012, August 2012, March 2013, November 2013 and March 2014, carbon and nutrient cycles were studied with the benthic lander NuSObs (Nutrient and Suspension Observatory) and shipboard sampling techniques. Chapter 4 presents laboratory experiments in which the diurnal variability of benthic carbon and nitrate fluxes were studied in light:dark cycles. The first manuscript (chapter 2) presents benthic oxygen and nitrogen fluxes derived from in situ incubations and pore water data. Both oxygen and nitrogen fluxes followed the seasonal cycle with highest fluxes in summer and autumn and lowest fluxes in winter. Detailed investigations of the benthic macrofauna and tracer flux studies showed the importance of faunal induced transport of solutes along the sediment water interface for the benthic oxygen consumption in summer and autumn. Over spatial scales the suspension feeder Ensis directus had a considerable impact on benthic oxygen consumption. Estimated recycling efficiencies of organic bound carbon revealed that most of the carbon (76-93 %) and nitrogen (87-97 %) reaching the seafloor is remineralized within surface sediments. The second manuscript (chapter 3) discusses benthic silicic acid (Si(OH)4) fluxes which were determined with different sampling techniques including in situ incubations with the benthic lander NuSObs, ex situ incubations and calculated fluxes based on pore water profiles. A comparison of the different sampling techniques shows that in shallow water coastal areas in situ techniques are required for a precise quantification of benthic fluxes. Strong seasonal variations in silicic acid effluxes were measured by in situ and ex situ incubations with highest fluxes in summer and autumn and lowest fluxes in winter. Estimated annual rain rates of biogenic silica (bSi) reaching the seafloor of the southern North Sea are within a range of 1.7 to 2.2 mol bSi m-2 a-1. The third manuscript considers the results of laboratory experiments on diurnal cycling of oxygen and nitrate in a coastal sediment. An oxygen optode (PyroscienceTM) and an optical nitrate sensor (SatlanticTM) were applied to closed microcosm experiments in order to monitor oxygen and nitrate continuously in incubation experiments. A diatom dominated sediment was incubated over 12 hour light:dark shifts. During daylight oxygen was most likely produced by benthic primary producers and during night time consumed by heterotrophs and the oxidation of reduced solutes. The consumption of oxygen was regulated by the presence or absence of benthic macrofauna. Monitoring nitrate continuously with the nitrate sensor revealed that at the onset of light, while sediments and bottom waters were anoxic, a nitrate reducing or assimilating process takes place within surface sediments.Dissertation313 133 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Benthic organic carbon fluxes in the Southern Ocean: Regional differences and links to surface primary production and carbon export(2007-09-27); ; ; Without doubt, global climate change is directly linked to the anthropogenic release of greenhouse gases such as carbon dioxide (CO2) and methane (UN IPCC-Report 2007). Therefore, research efforts to comprehend the global carbon cycle have increased during the last years. In the context of the observed changes, it is of particular interest to decipher the role of the hydro-, bio- and atmospheres and how the different compartments of the earth system are affected by the increase of atmospheric CO2. Due to its huge carbon inventory, the marine carbon cycle represents the most important component in this respect. Numerous findings suggest that the Southern Ocean plays a key role in terms of oceanic CO2 uptake. However, an exact quantification of such fluxes of material is hard to achieve for large areas, not least on account of the inaccessibility of this remote region. In particular, there exist so far only few accurate data for benthic carbon fluxes. The latter can be derived from high resolution pore water oxygen profiles, as one possible method. However the ex situ flux determinations carried out on sediment cores, tend to suffer from temperature and pressure artefacts. Alternatively, oxygen microprofiles can be measured in situ, i.e. at the seafloor. Until now, no such data have been published for the Southern Ocean. During the Antarctic Expedition ANT XXI/4, within the framework of this thesis, in situ and ex situ oxygen profiles were measured and used to derive benthic organic carbon fluxes. Having both types of measurements from the same locations, it was possible to establish a depth-related correction function which was applied subsequently to revise published and additional unpublished carbon fluxes to the seafloor. This resulted in a consistent data base of benthic carbon inputs covering many important sub-regions of the Southern Ocean including the Amundsen and Bellingshausen Seas (southern Pacific), Scotia and Weddell Seas (southern South Atlantic) as well as the Crozet Basin (southern Indian Ocean). Including additional locations on the Antarctic Shelf, there are now 134 new and revised measurement locations, covering almost 180Ã ° of the Southern Ocean, for which benthic organic carbon fluxes and sedimentary oxygen penetration depth values are available.Further, benthic carbon fluxes were empirically related to dominant diatom distributions in surface sediments as well as to long-term remotely sensed chlorophyll-a estimates. The comparison of these results with benthic carbon fluxes of the entire Atlantic Ocean reveals significantly higher export efficiencies for the Southern Ocean than have previously been assumed, especially for the area of the opal belt.Dissertation330 147 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Identification of seafloor provinces - specific applications at the deep-sea HÃ ¥kon Mosby Mud Volcano and the North Sea(2006-03-24); ; ; The identification of distinct provinces is currently an emphasis of marine research geosciences. Typological approaches for the HÃ ¥kon Mosby Mud Volcano and the North Sea combining geological, biological and chemical properties are accomplished by geostatistical, multivariate statistical, and GIS techniques. Besides scientific needs seafloor provinces support management decisions related to upcoming economic use of the seafloor and bear up to model spatio-temporal connections and changes of coastal regions.Submarine mud volcanoes are considered as source locations for methane indicated by unique communities as Beggiatoa and pogonophorans. They signify graduated CH4 consumption of microbial consortia (sulphate-reducing bacteria and anaerobic methane-oxidising archaea). The quantification of the habitat areas identified by indicator kriging is thus important for understanding the global methane cycle.Kriging methods were also applied for selected parameters for the North Sea creating surface maps from measured data as an assumption for multivariate statistics like Classification and Regression Trees.Dissertation212 154 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Distribution and fate of methane released from submarine sources - Results of measurements using an improved in situ mass spectrometer(1980-02-12); ; ; Methane (CH4) is the most frequent organic compound in the atmosphere and its influence on the global climate is subject of currently conducted scientific discussion. Despite its limited content in the atmosphere (1787 ppbv in 2003), it contributes to ~15 % of the global warming as a result of its 20 to 40 times higher global warming potential compared to carbon dioxide (CO2) on a 100 year timescale. One source of atmospheric methane is the release of biogenic and/or thermogenic CH4 from the oceans seafloor, which is currently one of the research priorities of the marine geosciences. These submarine sources are characterized by rising gas bubbles or diffusive methane flux into the water column. It is estimated that these point sources release a total of ~30 Tg CH4 per year into the ocean, and after its biological oxidation or dissolving in the water, ~10 Tg CH4 are released into the atmosphere per year. Additionally, due to the warming of the oceans, an increasing release of methane can be expected as a result of the melting of permafrost and gas hydrates. Steep gradients over very short distances (< 20 m) and high time-based variability (few hours) are known from dissolved methane concentrations in the water column above these submarine CH4 sources. Due to the limited number of samples taken by conventional ex situ methods, an accurate quantification of the methane distribution could hardly be estimated. Nevertheless, one objective of the present thesis was the detailed spatial representation of the dissolved CH4 in the water column originates from submarine seeps as well as the study of relevant pathways such as vertical or horizontal transport, dilution and its microbial oxidation. Therefore, the first part of the dissertation deals with the optimization and establishment of a novel underwater mass spectrometer (UWMS, Inspectr200-200, Applied Microsystems Limited ) designed for inline, real time and in situ sampling in high frequency. Analysis and evaluation of several thousand samples per day take place in one step, so that one obtains the measurement result in situ and, unlike using conventional methods, without delay, and thus the sampling strategies can be adapted to the existing environment. Additionally, through the use of this novel analytical tool, potential sources of errors that occur during sampling or transport to the laboratories are eliminated. In order to be able to use the potential of this mass spectrometer for scientific research questions, it was necessary to optimize the detection limit for the trace gases that were to be determined. For this purpose, a Stirling cooler was applied, which serves as a trapping system for water vapour and thus leads to optimized conditions for the analysis. Within the framework of this thesis two gas ebullition areas were studied in detail. While one, which is located in the continental shelf northwest of Spitsbergen, is in the center of scientific attention, the gas ebullition area that was studied in the North Sea has not yet been examined until now with regard to the methane release into the water column and its subsequent pathways. With the help of the optimized mass spectrometer it became possible for the first time to obtain distribution patterns of dissolved CH4 in the water column in high resolution. With respect to the geochemical functionality of these increasingly important methane sources, the research conducted in this dissertation contribute to improve our knowledge of the entry of CH4 into the water column as well as its fate. Therefore, the applied novel technique can contribute to revolutionize our understanding of the behavior of seep plumes as suggested by Judd and Hovland (2007).Dissertation336 119