H. Anschütz

Antarctic-wide array of high-resolution ice core records reveals pervasive lead pollution began in 1889 and persists today

Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 – beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20th century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19th century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21st century.

An 860 km surface mass-balance profile on the East Antarctic plateau derived by GPR

Abstract Snow accumulation and its variability on the East Antarctic plateau are poorly understood due to sparse and regionally confined measurements. We present a 5.3 GHz (C-band) ground-penetrating radar (GPR) profile with a total length of 860 km recovered during the joint Norwegian–US International Polar Year traverse 2007/08. Mean surface mass balance (SMB) over the last 200 years was derived from the GPR data by identifying the volcanic deposition of the Tambora eruption in 1815. It varies between 9.1 and 37.7 kg m−2 a−1 over the profile, with a mean of 23.7 kg m−2 a−1 and a standard deviation of 4.7 kg m−2 a−1. The 200 year SMB estimated is significantly lower than most of the SMB estimates over shorter time periods in this region. This can be partly explained by a SMB minimum in the vicinity of the ice divide. However, it is more likely that a recent increase in SMB observed by several studies is largely responsible for the observed discrepancy.

Recent climate tendencies on an East Antarctic ice shelf inferred from a shallow firn core network

Nearly three decades of stable isotope ratios and surface mass balance (SMB) data from eight shallow firn cores retrieved at Fimbul Ice Shelf, East Antarctica, in the Austral summers 2009–2011 have been investigated. An additional longer core drilled in 2000/2001 extends the series back to the early eighteenth century. Isotope ratios and SMB from the stacked record of all cores were also related to instrumental temperature data from Neumayer Station on Ekström Ice Shelf. Since the second half of the twentieth century, the SMB shows a statistically significant negative trend, whereas the δ18O of the cores shows a significant positive trend. No trend is found in air temperature at the nearest suitable weather station, Neumayer (available since 1981). This does not correspond to the statistically significant positive trend in Southern Annular Mode (SAM) index, which is usually associated with a cooling of East Antarctica. SAM index and SMB are negatively correlated, which might be explained by a decrease in meridional exchange of energy and moisture leading to lower precipitation amounts. Future monitoring of climate change on the sensitive Antarctic ice shelves is necessary to assess its consequences for sea level change. Key Points Mass balance and stable oxygen isotope ratios from shallow firn cores Decreasing trend in surface mass balance, no trend in stable isotopes Negative correlation between SAM and SMB

Surface mass balance and stable oxygen isotope ratios from shallow firn cores on Fimbulisen, East Antarctica

Abstract The mass balance of Antarctica is one of the crucial factors for determining sea-level change in a warming climate. The marginal zones of the continent, namely the ice shelves, are most sensitive to climate change. During the 2009/10 austral summer an extensive glaciological field campaign was carried out on Fimbulisen, an ice shelf in East Antarctica, to investigate its recent surface mass balance. Shallow (10–18 m) firn cores were drilled and accumulation rates and stable-isotope ratios determined. For firn-core dating, two different methods were compared: (1) seasonal variations of stable oxygen isotope ratios (δ18O), and (2) dielectric profiling, including using the volcanic eruptions of Pinatubo, Philippines (1991), and El Chichόn, Mexico (1982), as time markers. The mean annual accumulation for the period 1992–2009 ranges from 298 to 349 mmw.e. a–1. The interannual variability at the drilling sites is >30%. Accumulation rates show a weak decreasing trend during the past 20–30 years, which is statistically significant only for one of the cores. Stable-isotope ratios were compared to the snowfall temperature of Neumayer station. Neither the temperatures nor the δ18O values show any trend for the investigated time period.

Towards Using AEM for Sensitive Clay Mapping - A Case Study from Norway

An AEM survey has been carried out supporting a highway construction project in Norway in order to obtain information about possible sensitive clay (leached marine clay, also called quick clay). In addition, an ERT profile was acquired along a flight line in an area where geotechnical boreholes indicate a layer of sensitive clay. AEM and ERT data agree very well, indicating only small changes in electrical resistivity throughout the sediment layer. The AEM data show more structures than ERT, demonstrating that resolution and accuracy of AEM are high enough to resolve subtle changes in resistivity charecterizing different clay units. Based on our results, AEM can be used to target zones of possible sensitive clay which can subsequently be investigated in more detail through geotechnical analyses like boreholes and sampling. Thus, using AEM to design the geotechnical program has the potential to provide significant cost reductions for similar projects.

Helicopter Electromagnetic Scanning as a First Step in Regional Quick Clay Mapping

Identification of sediment types and in particular delineation of leached, possibly sensitive marine clays is of crucial importance for geotechnical design of infrastructure projects in Norway. Since leached clays normally have a lower salt content than intact marine clays, the electrical resistivity is consequently higher, and thus clay characterization may be based on data from high-resolution airborne electromagnetics (AEM) collected from helicopter. However, the resistivity difference between leached and unleached clays is small compared to the transition to bedrock and may furthermore vary locally. Therefore, indication of leached clays based on resistivity data has so far been done by manual interpretation. Here, we present a new procedure to calculate the likelihood of possible sensitive clays directly from AEM data. Geotechnical ground investigations are used to locally determine the expected resistivity of sensitive clay. The computation results are compared with well-known quick clay zones. The procedure is not intended as a simple solution to delineate quick clay, but to evaluate an area’s likelihood of sensitive clays that can be used as a cost-saving tool to efficiently place geotechnical investigations.

From Manual to Automatic AEM Bedrock Mapping

ABSTRACT An extensive airborne electromagnetic (AEM) survey was carried out in Norway with the primary purpose to obtain information of depth to bedrock in areas with little or no prior geotechnical knowledge. We present different approaches to extract a bedrock model from the high-resolution time-domain AEM data, including both automated and manual procedures. It was found that in the area of investigation a user-driven approach of manual bedrock picking was the most suitable, taking into account the strongest vertical resistivity gradient and geological information as additional information. A semi-automatic, statistical method, called Localized Smart Interpretation (LSI), is also presented and discussed. This method, while not included in the original bedrock model for the entire area, showed promising results while using less time compared to the fully manual approach. It is recommended that LSI be considered in future projects of similar scope.

ERT INVERSION INDUSTRY STANDARD VERSUS CUTTING EDGE DEVELOPMENTS, TIME FOR A CHANGE?

ERT (Electrical Resistivity Tomography) is a versatile and widely used method in terms of applications for surface geophysics. For processing and inverting resistivity data engineering geophysics consultancies around the globe largely use the software package Res2Dinv as an industry standard. On the other hand, universities and other research groups have made numerous attempts towards different and maybe better solutions to derive an earth model from resistivity data. We have investigated the variability of ERT results based on three different inversion packages and based on datasets with ground truth information. Here we present two of our studied cases. Our work illustrates advantages and shortcomings of academic, semi-academic and commercial software to the user and interpreter. As one may expect, there is no clear winner or loser, yet the results indicate the potential benefit for interpretation when different results from the same dataset are combined to one geological model with minimum uncertainty.

Black Shale Mapping by AEM for Geotechnical Applications

Airborne Electromagnetics (AEM) has been used to map the extent of environmentally harmful black shale in two geotechnical projects in Norway, supported by electrical resistivity ground surveys and laboratory measurements. The work demonstrates that resistivity is a suitable parameter for both mapping and characterizing black shales, since their high sulfide content in general means a more harmful shale and in addition gives very low resistivity (0.1-1 Ωm). Various interpretation procedures to define a black shale volume have been explored, and some of the data show vertical resolution sufficient for geotechnical applications.

Case study of crosshole GPR tomography for grouting distribution in rock fractures

The Nordic method for tunnelling consists of drill and blast, pre-grouting and rock support adapted to the geologic conditions. Extensive use of pre-grouting is normally applied to limit water leakage. The injection is stopped at a predetermined pressure or total volume of injected grout (Stille, 2015). However, little is known about the dissemination of the grout within the host rock. The aim of this project is to better understand the grouting distribution in the fractures. The research is associated with the research program True Improvement in Grouting High pressure Technology for tunnelling (TIGHT) funded by the Norwegian research council. The objective of TIGHT is to increase understanding and subsequently implement efficient grouting control in tunnelling. The ultimate purpose is to reduce material consumption and time spent for grouting. Geophysical instrumentation was developed to carry a crosshole Ground Penetration Radar (GPR) investigation in a pre-grouted tunnel wall. The GPR tomography results have been compared to the data recorded in the drilled cores. Preliminary results indicate that crosshole GPR can provide valuable information on the distribution of fractures filled with grout or filled with water.