Bettina Wiegand

Glacial–interglacial cycles in Sr and Nd isotopic composition of Arctic marine sediments triggered by the Svalbard/Barents Sea ice sheet

Sr and Nd isotopic compositions of Arctic marine sediments characterize changes of sediment source regions and trace shelf–ocean particle pathways during glacial–interglacial transitions in the eastern Arctic Ocean. In the 140-ka sedimentary record of a marine core from Yermak Plateau, north of Svalbard, 87Sr/86Sr ratios and eNd values vary between 0.717 and 0.740 and −9.3 and −14.9, respectively. Sr and Nd isotopic composition both change characteristically during glacial–interglacial cycles and are correlated with the extension of the Svalbard/Barents Sea ice sheet (SBIS). The downcore variation in Sr and Nd isotopic composition indicates climatically induced changes in sediment provenance from two isotopically distinct end-members: (1) Eurasian shelf sediments as a distal source; and (2) Svalbard bedrock as a proximal source that coincide with a change in transport mechanism from sea ice to glacial ice. During glacier advance from Svalbard and intensified glacial bedrock erosion, eNd values decrease gradually to a minimum value of −14.9 due to increased input of crystalline Svalbard bedrock material. During glacial maxima, the SBIS covered the entire Barents Sea shelf and supplied increasing amounts of Eurasian shelf material to the Arctic Ocean as ice rafted detritus (IRD). eNd values in glacial sediments reach maximum values that are comparable to the average value of modern Eurasian shelf and sea ice sediments (eNd=−10.3). This confirms ice rafting as a major sediment transport mechanism for Eurasian shelf sediments into the Arctic Ocean and trace a sediment origin from the Kara Sea/Laptev Sea shelf area. After the decay of the shelf-based SBIS, the glacial shelf sediment spikes during glacial terminations I (eNd=−10.6) and II (eNd=−10.1) eNd values rapidly decrease to values of −12.5 typical for interglacial averages. The downcore Sr isotopic composition is anticorrelated to the Nd isotopic composition, but may be also influenced by grain-size effects. In contrast, the Nd isotopic composition in clay- to silt-size fractions of one bulk sediment sample is similar to within 0.3–0.8 eNd units and seems to be a grain-size independent provenance tracer.

87Sr/86Sr-Verhältnisse als Tracer für geochemische Prozesse in einem Lockergesteinsaquifer (Liebenau, NW-Deutschland)

Grundwasser aus den quartaren Lockersedimenten im Einzugsgebiet des Wasserwerkes Liebenau II (NW-Deutschland) sind durch heterogene Verteilungen der gelosten Inhaltsstoffe charakterisiert. Zur Bestimmung der Herkunft der Losungskomponenten und zur Ermittlung von Grundwasserflieswegen wurden Sr-Isotopenuntersuchungen an Grundwassern, Niederschlagswassern und Sedimentproben durchgefuhrt. Die 87Sr/86Sr-Verhaltnisse der Grundwasser liegen im Bereich von 0.708 bis 0.719 und ermoglichen eine Unterscheidung von vier Grundwasserhorizonten. Unterschiede in den 87Sr/86Sr-Verhaltnissen resultieren aus verschiedenen Quellen des gelosten Strontiums im Grundwasser. Diese sind gepragt durch die Mineralverwitterung, die Niederschlage und anthropogene Eintrage. Fur den oberflachennahen Grundwasserbereich sind Einflusse aus den Niederschlagen und vermutlich aus der landwirtschaftlichen Dungung durch niedrige 87Sr/86Sr-Verhaltnisse zwischen 0.710 und 0.713 indiziert. Mit zunehmender Tiefe dominieren Verwitterungsprozesse die Grundwasserchemie. Uber das 87Sr/86Sr-Verhaltnis kann zwischen Silikat- und Karbonatauflosung unterschieden werden. Im mittleren Grundwasserhorizont bestatigen hohe 87Sr/86Sr-Verhaltnisse zwischen 0.713 und 0.719 und Sattigungsindices < –3.5 fur Calcit den Einfluss verwitternder Silikate. Niedrige 87Sr/86Sr-Verhaltnisse von 0.708 bis 0.709 bei gleichzeitig hohem Sattigungsgrad fur Calcit sind auf die Auflosung von Karbonatmineralen in den tiefen Grundwassern zuruckzufuhren. 87Sr/ 86Sr Ratios as a Tracer for Geochemical Processes in an Unconsolidated Sediment Aquifer (Liebenau, NW-Germany) Groundwater of the Quaternary unconsolidated sediments in the catchment area of the waterworks of Liebenau II (NW-Germany) is characterized by heterogeneous distributions of dissolved constituents. In order to determine sources of solutes and to estimate flowpaths, Sr isotope analyses were carried out on groundwater, precipitation, and soil samples. 87Sr/86Sr ratios of the groundwater samples vary between 0.708 and 0.719 and allow to discriminate four groundwater levels. The near-surface groundwater level is characterized by low 87Sr/86Sr ratios in the range of 0.7099 and 0.7130. At greater depths 87Sr/86Sr ratios increase up to a value of 0.7187 in the intermediate groundwater level. Deep groundwaters which can be divided into two levels exhibit a remarkable decrease of 87Sr/86Sr ratios. Groundwater of deep level I shows Sr isotope ratios between 0.7118 and 0.7128, whereas deep level II shows 87Sr/86Sr ratios of 0.7082 to 0.7087. Differences in the 87Sr/86Sr ratios are the result of varying sources of dissolved strontium in the groundwater. These encompass mineral weathering, precipitation, and anthropogenic inputs. Low 87Sr/86Sr ratios of 0.710 to 0.713 indicate the influence of precipitation and probably fertilizers on the near-surface groundwaters. At greater depths, groundwater chemistry is dominated by weathering processes. Due to significant differences in the 87Sr/86Sr ratios the dissolution of silicate minerals can be distinguished from the dissolution of carbonate minerals. For the intermediate groundwater level a dominant influence of silicate weathering is confirmed by radiogenic 87Sr/86Sr ratios between 0.713 and 0.719 and saturation indices < –3.5 for calcite. In contrast, low 87Sr/86Sr ratios of 0.708 to 0.709 indicate dissolution of carbonate minerals in the deep groundwater, where saturation for calcite is observed.

Spring response to precipitation events using δ18O and δ2H in the Tanour catchment, NW Jordan

ABSTRACT The Tanour spring is one of the several karst springs located in the northern part of Jordan. Water samples from the Tanour spring and precipitation were collected in the area of Ajloun in NW Jordan for the analysis of stable oxygen and hydrogen isotopes to evaluate the spring response to precipitation events. Rainwater and snow samples were collected from different elevations during winters of 2013–2014 and 2014–2015. In addition, spring samples were collected between December 2014 and March 2015. δ18O values in rainwater vary from −3.26 to −17.34 ‰ (average: −7.84 ± 3.23 ‰), while δ2H values range between −4.4 and −110.4 ‰ (average: −35.7 ± 25.0 ‰). Deuterium excess ranges from 17.8 to 34.1 ‰ (average: 27.1 ± 4.0 ‰). The Local Meteoric Water Line for the study area was calculated to be δ2H = 7.66*δ18O + 24.43 (R2 = 0.98). Pre-event spring discharge showed variation in δ18O (range −6.29 to −7.17 ‰; average −6.58 ± 0.19 ‰) and δ2H values (range −28.8 to −32.7 ‰; average: −30.5 ± 1.0 ‰). In contrast, δ18O and δ2H rapidly changed to more negative values during rainfall and snowmelt events and persisted for several days before returning to background values. Spring water temperature, spring discharge, and turbidity followed the trend in isotopic composition during and after the precipitation events. The rapid change in the isotopic composition, spring discharge, water temperature, and turbidity in response to recharge events is related to fast water travel times and low storage capacity in the conduit system of the karst aquifer. Based on the changes in the isotopic composition of spring water after the precipitation events, the water travel time in the aquifer is in the order of 5–11 days.

Fault controlled geochemical properties in Lahendong geothermal reservoir Indonesia

Rock and fluid geochemical data from Lahendong, Indonesia, were analyzed to evaluate the influence of fault zones on reservoir properties. It was found that these properties depend on fault-permeability controlled fluid flow.Results from measurements of spring and well water as well as rocks and their hydraulic properties were combined with hydrochemical numerical modeling. The models show that the geothermal field consists of two geochemically distinct reservoir sections. One section is characterized by acidic water, considerable gas discharge and high geothermal-power productivity—all related to increased fault zone permeability. The other section is characterized by neutral water and lower productivity.Increased fluid flow in the highly fractured and permeable areas enhances chemical reaction rates. This results in strong alteration of their surrounding rocks. Numerical models of reactions between water and rock at Lahendong indicate the main alteration products are clay minerals. A geochemical conceptual model illustrates the relation between geochemistry and permeability and their distribution within the area.Our conceptual model illustrates the relation between geochemistry and fault-zone permeability within the Lahendong area. Further mapping of fault-related permeability would support sustainable energy exploitation by avoiding low-productive wells or the production of highly corroding waters, both there and elsewhere in the world.ZusammenfassungDie Analyse von geochemischen Daten am Standort Lahendong in Indonesien wird in dieser Studie für die Untersuchung des Einflusses von Störungszonen auf Reservoireigenschaften genutzt. Diese Eigenschaften sind von Grundwasserbewegungen in Störungszonen und deren Permeabilitäten abhängig.In unserem Ansatz werden die Ergebnisse von physikochemikalischen Messungen an Brunnen und Quellen, Laboruntersuchungen zur Zusammensetzung von Wasser und Gesteinen und deren hydraulische Eigenschaften mit den Resultaten aus hydrochemischen Simulationen kombiniert. Die Ergebnisse zeigen, dass das geothermische Feld aus zwei geochemisch unterschiedlichen Reservoirbereichen besteht, wovon eins durch saures Wasser, erhöhte Gasaustritte und höhere Produktionsraten charakterisiert ist und das andere durch neutrale Wässer charakterisiert ist. Durch intensive Grundwasserbewegungen und chemische Reaktionen in Störungszonen, weisen Gesteine vor allem in diesen Bereichen starke Alterationserscheinungen auf. Die chemischen Reaktionen zwischen Wasser und Gestein wurden durch numerische Simulationen abgebildet und zeigen, dass durch die Alterationsprozesse vor allem Tonminerale gebildet werden. Ein konzeptionelles Modell stellt den Zusammenhang zwischen geochemischen Eigenschaften und der Permeabilitätsverteilung im Gebiet dar.Unser konzeptionelles Modell erklärt den Zusammenhang zwischen Geochemie und Permeabilitäten in Störungszonen in Lahendong. Die Untersuchung von Permeabilitätsverteilungen in geothermischen Reservoiren ist wichtig für eine nachhaltige Nutzung und verhindert das Bohren an unproduktiven Standorten, sowie die Förderung von sauren, aggressiven Wässern in Lahendong und vergleichbaren Standorten.

Geochemical/hydrochemical evaluation of the geothermal potential of the Lamongan volcanic field (Eastern Java, Indonesia)

Magmatic settings involving active volcanism are potential locations for economic geothermal systems due to the occurrence of high temperature and steam pressures. Indonesia, located along active plate margins, hosts more than 100 volcanoes and, therefore, belongs to the regions with the greatest geothermal potential worldwide. However, tropical conditions and steep terrain reduce the spectrum of applicable exploration methods, in particular in remote areas. In a case study from the Lamongan volcanic field in East Java, we combine field-based data on the regional structural geology, elemental and isotopic composition of thermal waters, and the mineralogical and geochemical signatures of volcanic rocks in exploring hidden geothermal systems. Results suggest infiltration of groundwater at the volcanoes and faults. After infiltration, water is heated and reacts with rocks before rising to the surface. The existence of a potential heat source is petrologically and geophysically constrained to be an active shallow mafic-magma chamber, but its occurrence is not properly reflected in the composition of the collected warmed spring waters that are predominantly meteoric in origin. In conclusion, spring temperature and hydrochemistry alone may not always correctly reflect the deep geothermal potential of an area.

Groundwater vulnerability assessment for the karst aquifer of Tanour and Rasoun springs catchment area (NW-Jordan) using COP and EPIK intrinsic methods

Groundwater vulnerability maps were constructed for the surface water catchment area of Tanour and Rasoun spring (north-west of Jordan) using the COP and EPIK intrinsic groundwater vulnerability assessment methods. Tanour and Rasoun springs are the main water resources for domestic purposes within the study area. A detailed geological survey was carried out, and data of lithology, karst features, precipitation, vegetation and soil cover, etc. were gathered from various sources for the catchment area in order to determine the required parameters for each method. ArcGIS software was used for map preparation. In the resulting COP vulnerability map, spatial distribution of groundwater vulnerability is as follows: (1) high (37%), (2) moderate (34.8%), (3) low (20.1%), and (4) very low (8.1%). In the EPIK vulnerability map, only two out of four vulnerability classes characterize the catchment area: very high vulnerable areas (38.4%) and moderately vulnerable areas (61.6%). Due to limited soil thickness, the low vulnerability class is absent within the catchment. The high percentage of very high to moderately vulnerable areas displayed by both the COP and EPIK vulnerability assessment methods are reflected by different pollution events in Tanour and Rasoun karst springs especially during the winter season. The high sensitivity of the aquifer to pollution can be explained by different factors such as: thin or absent soil cover, the high development of the epikarst and karst network, and the lithology and confining conditions of the aquifer.