scholarly journals Drilling into debris-rich basal ice at the bottom of the NEEM (Greenland) borehole

2014 ◽  
Vol 55 (68) ◽  
pp. 199-206 ◽  
Author(s):  
Trevor J. Popp ◽  
Steffen B. Hansen ◽  
Simon G. Sheldon ◽  
Jakob Schwander ◽  
Jay A. Johnson
Keyword(s):  
Ice Core ◽  
Diamond Cutting ◽  
Additional Material ◽  
Rock Fragments ◽  
Rock Drill ◽  
Climate Reconstructions ◽  
Basal Ice ◽  
Drilling Operations ◽  
Field Season ◽  
Final Closure

AbstractAfter the NEEM (Greenland) deep ice-core drilling was declared terminated with respect to developing stratigraphic climate reconstructions, efforts were turned toward collecting basal ice-sheet debris and, if possible, drilling into the bedrock itself. In 2010, several meters of banded debris-rich ice were obtained under normal ice-drilling operations with the NEEM version of the Hans Tausen (HT) drill, but further penetration was obstructed by a rock in the path of the drill head at 2537.36 m. During short campaigns in 2011 and 2012, attempts were made to penetrate further using various reinforced ice cutters mounted on the HT drill head, tailored to cut through rock. These had some success in penetrating coarse material, but produced severely damaged cutters. Additionally a 51 mm diameter diamond cutting tipped rock drill was adapted to fit the NEEM drill. With this device, several additional meters of core containing subglacial sediments, rocks and rock fragments were collected. With these tools 1.39m of additional material were obtained during the 2011 field season, and 7.1 m during 2012. Subglacial water refreezing into the newly formed borehole hindered further penetration, and the bedrock interface was not reached before final closure of the NEEM Camp.

scholarly journals Site information and initial results from deep ice drilling on Law Dome, Antarctica

1997 ◽  
Vol 43 (143) ◽  
pp. 3-10 ◽  
Author(s):  
V.I. Morgan ◽  
C.W. Wookey ◽  
J. Li ◽  
T.D. van Ommen ◽  
W. Skinner ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Sheet ◽  
High Accumulation ◽  
Ice Flow ◽  
Ice Cap ◽  
Basal Ice ◽  
Inland Ice ◽  
The Last Glacial Maximum ◽  
Initial Results ◽  
The Last Glacial

AbstractThe aim of deep ice drilling on Law Dome, Antarctica, has been to exploit the special characteristics of Law Dome summit, i.e. low temperature and high accumulation near an ice divide, to obtain a high-resolution ice core for climatic/environmental studies of the Holocene and the Last Glacial Maximum (LGM). Drilling was completed in February 1993, when basal ice containing small fragments of rock was reached at a depth of 1196 m. Accurate ice dating, obtained by counting annual layers revealed by fine-detail δ18О, peroxide and electrical-conductivity measurements, is continuous down to 399 m, corresponding to a date of AD 1304. Sulphate concentration measurements, made around depths where conductivity tracing indicates volcanic fallout, allow confirmation of the dating (for Agung in 1963 and Tambora in 1815) or estimates of the eruption date from the ice dating (for the Kuwae, Vanuatu, eruption ~1457). The lower part of the core is dated by extrapolating the layer-counting using a simple model of the ice flow. At the LGM, ice-fabric measurements show a large decrease (250 to 14 mm2) in crystal size and a narrow maximum in c-axis vertically. The main zone of strong single-pole fabrics however, is located higher up in a broad zone around 900 m. Oxygen-isotope (δ18O) measurements show Holocene ice down to 1113 m, the LGM at 1133 m and warm (δ18O) about the same as Holocene) ice near the base of the ice sheet. The LGM/Holocene δ18O shift of 7.0‰, only ~1‰ larger than for Vostok, indicates that Law Dome remained an independent ice cap and was not overridden by the inland ice sheet in the Glacial.

scholarly journals Synchronizing the Greenland ice core and radiocarbon timescales over the Holocene – Bayesian wiggle-matching of cosmogenic radionuclide records

2016 ◽  
Vol 12 (1) ◽  
pp. 15-30 ◽  
Author(s):  
F. Adolphi ◽  
R. Muscheler
Keyword(s):  
Statistical Approach ◽  
Ice Core ◽  
Ice Cores ◽  
The Holocene ◽  
Counting Error ◽  
Climate Reconstructions ◽  
Uncertainty Measurement ◽  
Uncertainty Estimates ◽  
Paleoclimate Records ◽  
Cosmogenic Radionuclide

Abstract. Investigations of past climate dynamics rely on accurate and precise chronologies of the employed climate reconstructions. The radiocarbon dating calibration curve (IntCal13) and the Greenland ice core chronology (GICC05) represent two of the most widely used chronological frameworks in paleoclimatology of the past  ∼  50 000 years. However, comparisons of climate records anchored on these chronologies are hampered by the precision and accuracy of both timescales. Here we use common variations in the production rates of 14C and 10Be recorded in tree-rings and ice cores, respectively, to assess the differences between both timescales during the Holocene. Compared to earlier work, we employ a novel statistical approach which leads to strongly reduced and yet, more robust, uncertainty estimates. Furthermore, we demonstrate that the inferred timescale differences are robust independent of (i) the applied ice core 10Be records, (ii) assumptions of the mode of 10Be deposition, as well as (iii) carbon cycle effects on 14C, and (iv) in agreement with independent estimates of the timescale differences. Our results imply that the GICC05 counting error is likely underestimated during the most recent 2000 years leading to a dating bias that propagates throughout large parts of the Holocene. Nevertheless, our analysis indicates that the GICC05 counting error is generally a robust uncertainty measurement but care has to be taken when treating it as a nearly Gaussian error distribution. The proposed IntCal13-GICC05 transfer function facilitates the comparison of ice core and radiocarbon dated paleoclimate records at high chronological precision.

scholarly journals Technical innovations and optimizations for intermediate ice-core drilling operations

2014 ◽  
Vol 55 (68) ◽  
pp. 243-252 ◽  
Author(s):  
Jack Triest ◽  
Robert Mulvaney ◽  
Olivier Alemany
Keyword(s):  
Ice Core ◽  
Working Environment ◽  
Column Height ◽  
Drill Fluid ◽  
Drilling Operations ◽  
Remote Sites ◽  
James Ross Island ◽  
Technical Innovations ◽  
Set Up ◽  
Core Storage

AbstractThe British Antarctic Survey, in collaboration with Laboratoire de Glaciologie et Géophysique de l’Environnement, has in recent years successfully drilled to bedrock on three remote sites around the Antarctic Peninsula. Based on the experience from the multi-season project at Berkner Island (948m depth, 2002–05) we optimized the drill set-up to better suit two subsequent single-season projects at James Ross Island (363m depth, 2008) and Fletcher Promontory (654m depth, 2012). The adaptations, as well as the reasons for them, are discussed in detail and include a drill tent set-up without a trench; drilling without a borehole casing with a relatively low fluid column height; and using a shorter drill. These optimizations were aimed at reducing cargo loads and installation time while maintaining good core quality, productivity and a safe working environment. In addition, we introduce a number of innovations, ranging from a new lightweight cable tensioning device and drill-head design to core storage and protection trays. To minimize the environmental impact, all the drill fluid was successfully recovered at both sites and we describe and evaluate this operation.

scholarly journals A search in north Greenland for a new ice-core drill site

1997 ◽  
Vol 43 (144) ◽  
pp. 300-306 ◽  
Author(s):  
D. Dahl-Jensen ◽  
N.S. Gundestrup ◽  
K. Keller ◽  
S.J. Johnsen ◽  
S.P. Gogineni ◽  
...  
Keyword(s):  
Melting Point ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Flow ◽  
Basal Ice ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
North Greenland

AbstractA new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1 at GRIP to 0.19 m ice equivalent year−1 50 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

scholarly journals The Elbrus (Caucasus, Russia) ice core record – Part 1: reconstruction of past anthropogenic sulfur emissions in south-eastern Europe

2019 ◽  
Vol 19 (22) ◽  
pp. 14119-14132 ◽  
Author(s):  
Susanne Preunkert ◽  
Michel Legrand ◽  
Stanislav Kutuzov ◽  
Patrick Ginot ◽  
Vladimir Mikhalenko ◽  
...  
Keyword(s):  
Eastern Europe ◽  
Western Europe ◽  
Ice Core ◽  
Ice Cores ◽  
Fold Increase ◽  
South Eastern ◽  
Basal Ice ◽  
Ice Core Record ◽  
South Eastern Europe ◽  
The 19Th Century

Abstract. This study reports on the glaciochemistry of a deep ice core (182 m long) drilled in 2009 at Mount Elbrus in the Caucasus, Russia. Radiocarbon dating of the particulate organic carbon fraction in the ice suggests that the basal ice dates to 280±400 CE (Common Era). Based on chemical stratigraphy, the upper 168.6 m of the core was dated by counting annual layers. The seasonally resolved chemical records cover the years 1774–2009 CE, thus being useful to reconstruct many aspects of atmospheric pollution in south-eastern Europe from pre-industrial times to the present day. After having examined the extent to which the arrival of large dust plumes originating from the Sahara and Middle East modifies the chemical composition of the Elbrus (ELB) snow and ice layers, we focus on the dust-free sulfur pollution. The ELB dust-free sulfate levels indicate a 6- and 7-fold increase from 1774–1900 to 1980–1995 in winter and summer, respectively. Remaining close to 55±10 ppb during the 19th century, the annual dust-free sulfate levels started to rise at a mean rate of ∼3 ppb per year from 1920 to 1950. The annual increase accelerated between 1950 and 1975 (8 ppb per year), with levels reaching a maximum between 1980 and 1990 (376±10 ppb) and subsequently decreasing to 270±18 ppb at the beginning of the 21st century. Long-term dust-free sulfate trends observed in the ELB ice cores are compared with those previously obtained in Alpine and Altai (Siberia) ice, with the most important differences consisting in a much earlier onset and a more pronounced decrease in the sulfur pollution over the last 3 decades in western Europe than south-eastern Europe and Siberia.

Basal ice formation and deformation in central Greenland: a review of existing and new ice core data

2000 ◽  
Vol 176 (1) ◽  
pp. 13-22 ◽  
Author(s):  
R. Souchez ◽  
G. Vandenschrick ◽  
R. Lorrain ◽  
J.-L. Tison
Keyword(s):  
Ice Core ◽  
Ice Formation ◽  
Core Data ◽  
Basal Ice

scholarly journals Metatranscriptomic and Metagenomic Analysis of Biological Diversity in Subglacial Lake Vostok (Antarctica)

Biology ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 55 ◽  
Author(s):  
Colby Gura ◽  
Scott O. Rogers
Keyword(s):  
Lake Water ◽  
Biological Diversity ◽  
Ice Core ◽  
Biologically Active ◽  
Marine Animal ◽  
Nutrient Sources ◽  
Lake Vostok ◽  
Subglacial Lake ◽  
Basal Ice ◽  
Accretion Ice

A combined metatranscriptomic and metagenomic study of Vostok (Antarctica) ice core sections from glacial, basal, and lake water accretion ice yielded sequences that indicated a wide variety of species and possible conditions at the base of the glacier and in subglacial Lake Vostok. Few organisms were in common among the basal ice and accretion ice samples, suggesting little transmission of viable organisms from the basal ice meltwater into the lake water. Additionally, samples of accretion ice, each of which originated from water in several locations of the shallow embayment, exhibit only small amounts of mixing of species. The western-most portion of the embayment had very low numbers of organisms, likely due to biologically challenging conditions. Increasing numbers of organisms were found progressing from west to east, up to approximately 7 km into the embayment. At that point, the numbers of unique sequences and sequence reads from thermophilic, thermotolerant, psychrophilic, and psychrotolerant organisms increased dramatically, as did sequences from alkaliphilic, alkalitolerant, acidophilic, and acidotolerant sequences. The number of unique and total sequences were positively associated with increases in concentrations of Na+, Ca2+, Mg2+, SO42−, Cl−, total amino acids, and non-purgeable organic carbon. The numbers of unique sequences from organisms reported from soil, sediment, ice, aquatic, marine, animal, and plant (probably pollen) sources also peaked in this region, suggesting that this was the most biologically active region. The confluence of the high numbers of organisms, physiologies, and metabolic capabilities suggests the presence of energy and nutrient sources in the eastern half of the embayment. Data from the main basin suggested a cold oligotrophic environment containing fewer organisms. In addition to bacteria, both the basal ice and accretion ice contained sequences from a diverse assemblage of eukaryotes, as well as from bacteria that are known to be associated with multicellular eukaryotes.

scholarly journals Bottom Topography and Internal Layers in East Dronning Maud Land, East Antarctica, from 179 MHz Radio Echo-Sounding

1987 ◽  
Vol 9 ◽  
pp. 221-224 ◽  
Author(s):  
Minoru Yoshida ◽  
Kazunobu Yamashita ◽  
Shinji Mae
Keyword(s):  
Cross Sections ◽  
Flow Line ◽  
Bottom Topography ◽  
Ice Core ◽  
Ice Sheet ◽  
Internal Layers ◽  
Radio Echo Sounding ◽  
Dronning Maud Land ◽  
Field Season ◽  
Echo Sounding

Extensive echo-sounding was carried out in east Dronning Maud Land during the 1984 field season. A 179 MHz radar with separate transmitting and receiving antennae was used and the echoes were recorded by a digital system to detect minute reflections. The results gave cross-sections of the ice sheet along traverse routes from lat. 69 °S. to 75°S, Detailed observations on the ground at Mizuho station showed that there was elliptical polarization in the internally reflected echoes when two antennae, kept in parallel with each other, were rotated horizontally. The internal echoes were most clearly distinguished when the antenna azimuth was oriented perpendicular to the flow line of the ice sheet. The internal echoes with a high reflection coefficient were detected at depths of 500–700 m and 1000–1500 m at Mizuho station. Since a distinct internal echo at a depth of 500 m coincides with a 5 cm thick volcanic ash-laden ice layer found in the 700 m ice core taken near the observation site, these echoes may correspond to the acidic ice layers formed by past volcanic events in east Dronning Maud Land.

scholarly journals A search in north Greenland for a new ice-core drill site

1997 ◽  
Vol 43 (144) ◽  
pp. 300-306 ◽  
Author(s):  
D. Dahl-Jensen ◽  
N.S. Gundestrup ◽  
K. Keller ◽  
S.J. Johnsen ◽  
S.P. Gogineni ◽  
...  
Keyword(s):  
Melting Point ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Flow ◽  
Basal Ice ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
North Greenland

AbstractA new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1at GRIP to 0.19 m ice equivalent year−150 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

scholarly journals Results From The Amery Ice Shelf Project

1982 ◽  
Vol 3 ◽  
pp. 36-41 ◽  
Author(s):  
W. F. Budd ◽  
M. J. Corry ◽  
T. H. Jacka
Keyword(s):  
High Strain ◽  
Ice Core ◽  
Snow Accumulation ◽  
Ice Thickness ◽  
Surface Slope ◽  
Ice Shelf ◽  
Substantial Growth ◽  
Basal Ice ◽  
Amery Ice Shelf ◽  
Comprehensive Study

The major results from a comprehensive study of the Amery Ice Shelf are presented, following the work of a wintering expedition in 1968 and supplemented by further measurements during the summer seasons of 1969 to 1971. The Programme included ice-core drilling, oversnow surveys for ice movement and optical levelling, ice-thickness sounding, and measurements of snow accumulation. The new data obtained provide the basis for a more accurate assessment of the mass balance and dynamics of the ice shelf than was possible from the earlier surveys. The results indicate a substantial growth of basal ice under the ice shelf inland where the ice thickness is greater than 450 m. Further towards the ice front the high strain thinning is approximately balanced by the horizontal ice advection. The velocity distribution over the ice shelf is primarily governed by a substantial surface slope towards the ice front and high restraining shear stress along the sides.

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