Evolution of Depositional Environments in Response to the Holocene Sea-Level Change in the Lower Delta Plain of Nakdong River Delta, Korea

The Nakdong River delta, located in southeastern Korea, preserves thick and wide sediments, which are suitable for the high-resolution study of the evolution of depositional environments in the lower delta plain area. This study traces the Holocene evolution of the Nakdong River delta using deep drill core (ND-3; 46.60 m thick) sediments from the present delta plain. Sedimentary units of the sediments were classified based on grain size compositions and sedimentary structures: (A) alluvial zone, (B) estuarine zone, (C) shallow marine, (D) prodelta, (E) delta front, and (F) delta plain. The weathered sediment, paleosol, was observed at 43.16 m below the surface. There is an unconformity (43.10 m) to separate a Pleistocene sediment layer in the lowermost part differentiating from a Holocene sediment layer in the upper part of the core. The shallow marine sedimentary unit (32.20~23.50 m), in which grain size decreases upward is overlain by the prodelta unit (23.50~15.10 m), which consists of fine-grained sediments and relatively homogeneous sedimentary facies. The boundary between the delta front unit (15.10~8.00 m) and the delta plain unit (8.00~0.00 m) appears to lie at 8.0 m, and the variation in grain size is different; coarsening upward in the delta front unit and fining upward in the delta front unit, respectively. These sediments are characterized by a lot of sand–mud couplets and mica flakes aligned along with cross-stratification, which may be deposited in relatively high-energy environments. Until 13 cal ka BP, the sea level was 70 m below the present level and the drilling site might be located onshore. At 10 cal ka BP, the sea level was located 50 m below the present level and the drilling site might be moved to an estuarine environment. From 8 to 6 cal ka BP, a transgression phase occurred as a result of coastline invasion by the rapid rise of the sea level. Thus, the drilling site was drowned in a shallow marine environment. After 6 cal ka BP, the sea level reached the present level, and, since then, progradation might begin to form, primarily by more sediment input. After this period, the progradation phase continues as the sediments have advanced and the delta grows.

Extending and understanding the South West Western Australian rainfall record using a snowfall reconstruction from Law Dome, East Antarctica

South West Western Australia (SWWA) has experienced a prolonged reduction in rainfall in recent decades, with associated reductions in regional water supply and residential and agricultural impacts. The cause of the reduction has been widely considered but remains unclear. The relatively short length of the instrumental record limits long-term investigation. A previous proxy-based study used a statistically negative correlation between SWWA rainfall and snowfall from the Dome Summit South (DSS) ice core drilling site, Law Dome, East Antarctica, and concluded that the anomaly of recent decades is unprecedented over the ∼ 750-year period of the study (1250–2004 CE). Here, we extend the snow accumulation record to cover the period from 22 BCE to 2015 CE and derive a rainfall reconstruction over this extended period. This extended record confirms that the recent anomaly is unique in the period since 1250 CE and unusual over the full ∼ 2000-year period, with just two other earlier droughts of similar duration and intensity. The reconstruction shows that SWWA rainfall started to decrease around 1971 CE. Ensembles of climate model simulations are used to investigate the potential roles of natural variability and external climate drivers in explaining changes in SWWA rainfall. We find that anthropogenic greenhouse gases are likely to have contributed towards the SWWA rainfall drying trend after 1971 CE. However, natural variability may also have played a role in determining the timing and magnitude of the reduction in rainfall.

Significant mass loss in the accumulation area of the Adamello glacier indicated by the chronology of a 46 m ice core

Dating glaciers is an arduous yet essential task in ice core studies, which becomes even more challenging when the glacier is experiencing mass loss in the accumulation zone as result of climate warming, leading to an older ice surface of unknown age. In this context, we dated a 46 m deep ice core from the Central Italian Alps retrieved in 2016 from the Adamello glacier in the locality Pian di Neve (3100 m a.s.l.). Here we present a timescale for the core obtained by integrating results from the analyses of the radionuclides 210Pb and 137Cs with annual layer counting derived from pollen and refractory black carbon concentrations. Our results clearly indicate that the surface of the glacier is older than the drilling date of 2016 by about 20 years and that the 46 m ice core reaches back to around 1944. For the period of 1995–2016 the mass balance at the drilling site (former accumulation zone) decreased on average of about 1 m w.e. a−1 compared to the period 1963–1986. Despite the severe mass loss affecting this glacier even in the former accumulation zone, we show that it is possible to obtain a reliable timescale for such a temperate glacier using black carbon and pollen seasonality in combination with radionuclides 210Pb and 137Cs. Our results are therefore very encouraging and open new perspectives on the potential of such glaciers as informative palaeoarchives.

PALEOSTRIPv1.0 – a user-friendly 3D backtracking software to reconstruct paleo-bathymetries

Paleo-bathymetric reconstructions provide boundary conditions to numerical models of ice sheet evolution and ocean circulation that are critical to understanding their evolution through time. The geological community lacks a complex open-source tool that allows for community implementations and strengthens research synergies. To fill this gap, we present PALEOSTRIPv1.0, a MATLAB open-source software designed to perform 1D, 2D, and 3D backtracking of paleo-bathymetries. PALEOSTRIP comes with a graphical user interface (GUI) to facilitate computation of sensitivity tests and to allow the users to switch all the different processes on and off and thus separate the various aspects of backtracking. As such, all physical parameters can be modified from the GUI. It includes 3D flexural isostasy, 1D thermal subsidence, and possibilities to correct for prescribed sea level and dynamical topography changes. In the following, we detail the physics embedded within PALEOSTRIP, and we show its application using a drilling site (1D), a transect (2D), and a map (3D), taking the Ross Sea (Antarctica) as a case study. PALEOSTRIP has been designed to be modular and to allow users to insert their own implementations.

A portable lightweight in situ analysis (LISA) box for ice and snow analysis

There are enormous costs involved in transporting snow and ice samples to home laboratories for “simple” analyses in order to constrain annual layer thicknesses and identify accumulation rates of specific sites. It is well known that depositional noise, incurred from factors such as wind drifts, seasonally biased deposition and melt layers can influence individual snow and firn records and that multiple cores are required to produce statistically robust time series. Thus, at many sites, core samples are measured in the field for densification, but the annual accumulation and the content of chemical impurities are often represented by just one core to reduce transport costs. We have developed a portable “lightweight in situ analysis” (LISA) box for ice, firn and snow analysis that is capable of constraining annual layers through the continuous flow analysis of meltwater conductivity and hydrogen peroxide under field conditions. The box can run using a small gasoline generator and weighs less than 50 kg. The LISA box was tested under field conditions at the East Greenland Ice-core Project (EastGRIP) deep ice core drilling site in northern Greenland. Analysis of the top 2 m of snow from seven sites in northern Greenland allowed the reconstruction of regional snow accumulation patterns for the 2015–2018 period (summer to summer).

Bone drilling with internal gas cooling: Experimental and statistical investigation of the effect of cooling with CO2 on reduction of temperature rise due to drill bit wear

Bone drilling is a major stage in immobilization of the fracture site. During bone drilling operations, the temperature may exceed the allowable limit of 47 °C, causing irrecoverable damages of thermal necrosis and seriously threatening the fracture treatment. One of the parameters affecting the temperature rise of the drilling site is the frequency of applying the drill bit and its extent of wear. The present study attempted to mitigate the effect of drill bit wear on the bone temperature rise through the internal gas cooling method via CO2 and to reduce the risk of incidence of thermal necrosis. To this end, drilling tests were conducted at three rotational speeds 1000, 2000, and 3000 r·min-1 in two states of without cooling and with internal gas cooling by CO2 through an internal coolant carbide drill bit, along with six drill bit states (new, used 10, 20, 30, 40, and 50 times) on a bovine femur bone. The results indicated that in the internal gas cooling state, as the number of drill bit applications increased from the new state to more than 50 times, the temperature of the hole site increased on average by ΔT = 2-3 °C (n = 1000 r·min-1), ΔT = 5-8 °C (n = 2000 r·min-1), and ΔT = 5-7 °C (n = 3000 r·min-1). Furthermore, the internal gas cooling method was able to significantly reduce the effect of the drill bit wear on the temperature rise of the drilling site and to resolve the risk of incidence of thermal necrosis regardless of the process parameters for drilling operations.

Review of Recent Drilling Projects in Unconventional Geothermal Resources at Campi Flegrei Caldera, Cornubian Batholith and Williston Sedimentary Basin

Unconventional geothermal resource development can contribute to increase power generation from renewable energy sources in countries without conventional hydrothermal reservoirs, which are usually associated with magmatic activity and extensional faulting, as well as to expand the generation in those regions where conventional resources are already used. Three recent drilling experiences focused on the characterization of unconventional resources are described and compared: the Campi Flegrei Deep Drilling Project (CFDDP) in Italy, the United Downs Deep Geothermal Power (UDDGP) project in the United Kingdom, and the DEEP Earth Energy Production in Canada. The main aspects of each project are described (geology, drilling, data collection, communication strategies) and compared to discuss challenges encountered at the tree sites considered, including a scientific drilling project (CFDDP) and two industrial ones (UDDGP and DEEP). The first project, at the first stage of pilot hole, although not reaching deep supercritical targets, showed extremely high, very rare thermal gradients even at shallow depths. Although each project has its own history, as well as social and economic context, the lessons learned at each drilling site can be used to further facilitate geothermal energy development.

Theoretical and practical realisation of perspective thermal spallation drilling technology

The article presents the results of theoretical and experimental studies of the conversional use of a rocket engine gas generator to create a device for thermal spallation drilling of solid rocks. The main difference between the studied device and traditional thermal drills is the relatively low temperature of the working fluid. It has been experimentally shown that this level of temperature of the working fluid provides a stable process of thermal spallation of the rock and at the same time a long life of the structure. The developed mathematical apparatus allows to select device parameters for various types of rocks. The concept of a jet drilling rig for drilling blast holes in open pit mines is proposed. This unit is mobile, does not require a heavy basement and preparation of the drilling site; it is charcterized with a high utilization factor and a long service life, and uses widely available components (air, water, kerosene, diesel fuel) as fuel components.