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1

Science Nation: Ice Core Secrets Could Reveal Answers to Global Warming  

NSDL National Science Digital Library

At the Stable Isotope Lab in Boulder, Colo., geoscientists work primarily with one raw material: ancient ice, in the form of ice cores. The ice cores come from Greenland and Antarctica. The information extracted from this ice could play a critical role in understanding and preparing for any imminent changes to our planet from global warming. Recent analysis of Greenland ice cores, a National Science Foundation (NSF)-supported project, has revealed some important clues about rapid climate changes near the end of the last ice age, about 11,700 years ago.

2

Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland  

PubMed Central

One of the major difficulties in paleontology is the acquisition of fossil data from the 10% of Earth’s terrestrial surface that is covered by thick glaciers and ice sheets. Here we reveal that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores and allow reconstructions of past flora and fauna. We show that high altitude southern Greenland, currently lying below more than two kilometers of ice, was once inhabited by a diverse array of conifer trees and insects that may date back more than 450 thousand years. The results provide the first direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections. PMID:17615355

Willerslev, Eske; Cappellini, Enrico; Boomsma, Wouter; Nielsen, Rasmus; Hebsgaard, Martin B.; Brand, Tina B.; Hofreiter, Michael; Bunce, Michael; Poinar, Hendrik N.; Dahl-Jensen, Dorthe; Johnsen, Sigfus; Steffensen, Jørgen Peder; Bennike, Ole; Schwenninger, Jean-Luc; Nathan, Roger; Armitage, Simon; de Hoog, Cees-Jan; Alfimov, Vasily; Christl, Marcus; Beer, Juerg; Muscheler, Raimund; Barker, Joel; Sharp, Martin; Penkman, Kirsty E.H.; Haile, James; Taberlet, Pierre; Gilbert, M. Thomas P.; Casoli, Antonella; Campani, Elisa; Collins, Matthew J.

2009-01-01

3

Science Nation: Ice Core Secrets Could Reveal Answers to Global Warming  

NSDL National Science Digital Library

This video features research conducted at University of Colorado's Institute of Arctic and Alpine Research, which studies isotopes of hydrogen trapped in ice cores to understand climate changes in the past.

NSF Science Nation

4

The GRIP Ice Coring Effort  

NSDL National Science Digital Library

This NOAA website provides a summary of the Greenland Ice Core Project, which resulted in a 3029 m long ice core drilled in Central Greenland from 1989 to 1992. The core reveals information on past environmental and climatic changes that are stored in the ice. Isotopic studies and various atmospheric constituents in the core have revealed a detailed record of climatic variations that span more than 100,000 years. The final report from the project may be downloaded as either a Word or ASCII file.

5

An Antarctic ice core reveals atmospheric CO2 variations over the past few centuries  

NASA Astrophysics Data System (ADS)

Information is obtained concerning the variation of background CO2 concentrations over the centuries, through analysis of atmospheric air trapped in bubbles inside a 2-3-m-long ice core. The ice core was drilled in East Antarctica in 1980-1981, and the atmospheric air in the bubbles was analyzed using gas chromatography. It is found that the background CO2 level could have been as low as 260 p.p.m.v. (parts per million by volume) before the major anthropogenic effects of fossile fuel consumption became significant in the 19th century. It is suggested that the 'preindustrial' CO2 level was not constant over the few hundred years preceding the nineteenth century.

Raynaud, D.; Barnola, J. M.

1985-05-01

6

Making an Ice Core.  

ERIC Educational Resources Information Center

Explains an activity in which students construct a simulated ice core. Materials required include only a freezer, food coloring, a bottle, and water. This hands-on exercise demonstrates how a glacier is formed, how ice cores are studied, and the nature of precision and accuracy in measurement. Suitable for grades three through eight. (Author/PVD)

Kopaska-Merkel, David C.

1995-01-01

7

Ice Core Investigations  

ERIC Educational Resources Information Center

What can glaciers tell us about volcanoes and atmospheric conditions? How does this information relate to our understanding of climate change? Ice Core Investigations is an original and innovative activity that explores these types of questions. It brings together popular science issues such as research, climate change, ice core drilling, and air…

Krim, Jessica; Brody, Michael

2008-01-01

8

Dust deposition events in Caucasus Mountains as revealed by shallow ice cores from Mt Elbrus  

NASA Astrophysics Data System (ADS)

Dust aerosol transported to the high mountains and is deposited and stored in snow pack and glacier ice. Present and past records of dust stored in glaciers provide valuable information on frequency of deposition events, source regions and atmospheric pathways of mineral dust. The Caucasus Mountains, located between the Black and the Caspian seas is a glacierized region affected by deposition of desert dust from the Middle East and Sahara. In this study, a combination of ice core analysis, remote sensing and air mass trajectory modelling was used to identify the source regions of dust deposited on the glaciers of Mt Elbrus in the central Greater Caucasus and to characterize atmospheric pathways of dust with high temporal and spatial resolution. Shallow ice cores were extracted at Mt Elbrus in 2009 and 2012. Dust deposition events, recorded as brown layers in the snow, firn and ice were dated to the precision on months using oxygen and deuterium isotopic analyses. Examination of the local meteorological and NCEP/NCAR reanalysis data and application of HYSPLIT atmospheric trajectory model enabled dating dust deposition events with a precision of days, identification of potential source regions of desert dust and its pathways in the atmosphere. Examination of red-blue green infrared composite imagery from Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) on board the Meteosat Second Generation (MSG) satellite enabled further provenancing of desert dust with high temporal (hours) and spatial (c. 100 km) resolution. Seventeen dust layers deposited between May 2009 and July 2012 were detected in the shallow cores. The source regions of the desert dust transported to Mt Elbrus were primarily located in the Middle East, in particular in eastern Syria and in the Syrian Desert at the border between Saudi Arabia, Iraq and Jordan. Northern Sahara, the foothills of the Djebel Akhdar Mountains in eastern Libya and the border region between Libya and Algeria were other important sources of desert dust. Fifteen dust deposition events occurred between March and June and two events occurred in October. The relatively high frequency of dust deposition events on Mt Elbrus may be due to the prolonged 2007-2010 drought in the Middle East resulting in more frequent activation of dust sources. Particle size and shape distributions were analysed for each dust sample using scanning electron microscope (SEM). The volume median diameter of dust particles from dust samples ranged from 3 to 13 microns. Particles with diameter of 1-10 microns accounted for 90±3% of the analysed samples. Detailed characterization of desert dust pathways from the Middle East and Sahara to the Caucasus leads to better understanding of pathways of desert dust in the atmosphere and highlights the importance of the Elbrus deep ice cores for the reconstruction of past environmental conditions in the south-eastern Europe and the Middle East in the future. This study is supported by the Marie Curie FP7-PEOPLE-2010-IIF project DIOGENES; Royal Soc JP100-235; RFBR N 1105-00304-a.

Kutuzov, Stanislav; Shahgedanova, Maria; Kemp, Sarah; Lavrentiev, Ivan; Mikhalenko, Vladimir; Popov, Gregory

2013-04-01

9

Decapitation of high-altitude glaciers on the Tibetan Plateau revealed by ice core tritium and mercury records  

NASA Astrophysics Data System (ADS)

Two ice cores were retrieved from high elevations (~ 5800 m a.s.l.) at Mt. Nyainqentanglha and Mt. Geladaindong in the southern to inland Tibetan Plateau. The combined analysis of tritium (3H), 210Pb, mercury tracers, along with other chemical records, revealed that the two coring sites had not received net ice accumulation since at least the 1950s and 1980s, respectively, implying an annual ice loss rate of more than several hundred millimeter water equivalent over these periods. Both mass balance modeling at the sites and in situ data from nearby glaciers confirmed a continuously negative mass balance (or mass loss) in the region due to the dramatic warming in the last decades. Along with a recent report on Naimona'nyi Glacier in the Himalaya, the findings suggest that glacier decapitation (i.e., the loss of the accumulation zone) is a wide-spread phenomenon from the southern to inland Tibetan Plateau even at the summit regions. This raises concerns over the rapid rate of glacier ice loss and associated changes in surface glacier runoff, water availability, and sea levels.

Kang, S. C.; Wang, F. Y.; Morgenstern, U.; Zhang, Y. L.; Grigholm, B.; Kaspari, S.; Schwikowski, M.; Ren, J. W.; Yao, T. D.; Qin, D. H.; Mayewski, P. A.

2015-01-01

10

Consistently dated records from three Greenland ice cores reveal regional millennial-scale isotope gradients with possible Heinrich Event imprint  

NASA Astrophysics Data System (ADS)

We here present records from the NGRIP, GRIP and GISP2 ice cores tied to the same chronology for the past 104 ka at an unprecedented time resolution. The three ice cores have been linked by matching distinct peaks in volcanic proxy records and other impurity records from the three ice cores, assuming that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. In total there are more than 900 identified marker horizons between the three cores including previously published match points, of which we introduce a minor revision. Our matching is independently confirmed by new and existing volcanic ash layers (tephra). The depth-depth relationship from the detailed matching is used to transfer the most recent and widely used Greenland ice core chronology, the GICC05modelext timescale, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new unpublished gas data. A comparison of the GICC05modelext and the former GISP2 timescale reveals major discrepancies in short time intervals during the glacial section. We detect a pronounced change in the relative annual layer thickness between the two Summit sites and NGRIP across the Last Glacial termination and early-to-mid Holocene, which can be explained by a relative accumulation increase at NGRIP compared to the Summit region as response to the onset of the Holocene and the climatic optimum. Between stadials and interstadials we infer that the accumulation contrast typically was nearly 10% greater at Summit compared to at NGRIP. The ?18O temperature-proxy records from NGRIP, GRIP and GISP2 are generally very similar and display a synchronous behavior at climate transitions, but the ?18O differences between Summit and NGRIP is slowly changing over the last glacial-interglacial cycle superimposed by abrupt millennial-to centennial scale anomalies. We suggest that the latitudinal ?18O gradient during the glacial is result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias at Summit, and 3) enhanced Raleigh distillation process due to and increased source-to-site distance, and we conclude that this is governed by North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) at orbital timescales, while changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. We assert that ?18O difference maxima can be linked to Heinrich Events, which is associated with southwards expansion of polar waters and low SSTs in the North Atlantic, and ths propose a direct link between the marine realm and the Greenland ice core records. The work presented is under review for publication in Quaternary Science Reviews. Author team: I.K. Seierstad, P. Abbott, M. Bigler, T. Blunier, A. Bourne, E. Brook, S.L. Buchardt, C. Buizert, H.B. Clausen, E. Cook, D. Dahl-Jensen, S.Davies, M. Guillevic, S.J. Johnsen, D.S. Pedersen, T.J. Popp, S.O. Rasmussen, J. Severinghaus, A. Svensson, B.M. Vinther (deceased).

Seierstad, Inger K.; Rasmussen, Sune O.

2014-05-01

11

Ice Core Exercise  

NSDL National Science Digital Library

Students access the ice core data archived at Lamont-Doherty Geological Observatory. They select a core (Greenland, Antarctica, Quelcaya), pose a working hypothesis regarding the data, import the data in an Excel-readable format, and examine the data to determine correlations between variables and cause/effect as recorded in leads and lags. They generate a written and graphical analysis of the data and, in the next lab period, discuss the similarities and differences among their group outputs in terms of demonstrated correlations, assumptions required, effects of latitude, and any other item that arises.

William Locke

12

The onset of Neoglaciation 6000 years ago in western Mongolia revealed by an ice core from the Tsambagarav mountain range  

NASA Astrophysics Data System (ADS)

Glacier highstands since the Last Glacial Maximum are well documented for many regions, but little is known about glacier fluctuations and lowstands during the Holocene. This is because the traces of minimum extents are difficult to identify and at many places are still ice covered, limiting the access to sample material. Here we report a new approach to assess minimal glacier extent, using a 72-m long surface-to-bedrock ice core drilled on Khukh Nuru Uul, a glacier in the Tsambagarav mountain range of the Mongolian Altai (4130 m asl, 48°39.338'N, 90°50.826'E). The small ice cap has low ice temperatures and flat bedrock topography at the drill site. This indicates minimal lateral glacier flow and thereby preserved climate signals. The upper two-thirds of the ice core contain 200 years of climate information with annual resolution, whereas the lower third is subject to strong thinning of the annual layers with a basal ice age of approximately 6000 years before present (BP). We interpret the basal ice age as indicative of ice-free conditions in the Tsambagarav mountain range at 4100 m asl prior to 6000 years BP. This age marks the onset of the Neoglaciation and the end of the Holocene Climate Optimum. The ice-free conditions allow for adjusting the Equilibrium Line Altitude (ELA) and derive the glacier extent in the Mongolian Altai during the Holocene Climate Optimum. Based on the ELA-shift, we conclude that most of the glaciers are not remnants of the Last Glacial Maximum but were formed during the second part of the Holocene. The ice core derived accumulation reconstruction suggests important changes in the precipitation pattern over the last 6000 years. During formation of the glacier, more humid conditions than presently prevailed followed by a long dry period from 5000 years BP until 250 years ago. Present conditions are more humid than during the past millennia. This is consistent with precipitation evolution derived from lake sediment studies in the Altai.

Herren, Pierre-Alain; Eichler, Anja; Machguth, Horst; Papina, Tatyana; Tobler, Leonhard; Zapf, Alexander; Schwikowski, Margit

2013-06-01

13

Vostok Ice Core: Excel (Mac or PC)  

NSDL National Science Digital Library

Students use Excel to graph and analyze Vostok ice core data (160,000 years of Ice core data from Vostok Station). Data includes ice age, ice depth, carbon dioxide, methane, dust, and deuterium isotope relative abundance.

Professor Stephanie Pfirman, Barnard College. Based on data of J. Chapellaz, Laboratoire de Glaciologie et Geophysique de l'Environment, Grenoble. Archived at: Lamont-Dohert Earth Observatory (more info) . Starting Point page organized by R.M. MacKay.

14

Little ice age clearly recorded in northern Greenland ice cores  

Microsoft Academic Search

Four ice cores drilled in the little investigated area of northern and northeastern Greenland were evaluated for their isotopic (delta18O) and chemical content. From these rather uniform records a stable isotope temperature time series covering the last 500 years has been deduced, which reveals distinct climate cooling during the 17th and the first half of the 19th century. Timing of

H. Fischer; M. Werner; D. Wagenbach; M. Schwager; T. Thorsteinnson; F. Wilhelms; J. Kipfstuhl; S. Sommer

1998-01-01

15

Tropical Ice Cores Measure Climate  

NSDL National Science Digital Library

This video profiles glaciologist Lonnie Thompson and his research into tropical mountain glaciers as a way to understand climate history. Beginning in the 1970s, Thompson recognized that tropical ice cores contain information relating to tropical climate phenomena, including El NiÃo events and monsoons. These phenomena are not archived in ice from polar regions. Thompson explains that his archive of ice cores is full of clues that, taken together with records collected from around the world, can help scientists create a timeline that tells Earth's climate story.

NOVA scienceNOW

16

Evidence of Historical Supernovae in Ice Cores  

NASA Astrophysics Data System (ADS)

Within the framework of the U.S. Greenland Ice Core Science Project (GISP2), an ice core, known as the GISP H-Core, was collected in June, 1992 adjacent to the GISP2 summit drill site. The project scientists, Gisela A.M. Dreschhoff and Edward J. Zeller, were interested in dating solar proton events with volcanic eruptions. The GISP2-H 122-meter firn and ice core is a record of 415 years of liquid electrical conductivity (LEC) and nitrate concentrations, spanning the years 1992 at the surface through 1577 at the bottom. At the National Ice Core Laboratory in Denver, Colorado, the core (beneath the 12-meter firn) was sliced into 1.5 cm sections and analyzed. The resulting data set consisted of 7,776 individual analyses. The ultrahigh resolution sampling technique resulted in a time resolution of one week near the surface and one month at depth. The liquid electrical conductivity (LEC) sequence contains signals from a number of known volcanic eruptions and provides a dating system at specific locations along the core. The terrestrial and solar background nitrate records show seasonal and annual variations, respectively. However, major nitrate anomalies within the record do not correspond to any known terrestrial or solar events. There is evidence that these nitrate anomalies could be a record of supernovae events. Cosmic X-rays ionize atmospheric nitrogen, producing excess nitrate that is then deposited in the Polar Regions. The GISP2-H ice core has revealed nitrate anomalies at the times of the Tycho and Kepler supernovae. The Cassiopeia A supernova event may be documented in the core as well. We have developed a classroom activity for high school and college students, in which they examine several lines of evidence in the Greenland ice core, discriminating among nearby and mid-latitude volcanic activity, solar proton events, and supernovae. Students infer the date of the Cassiopeia A supernova.

Young, Donna

2011-05-01

17

Crystal size variations in Eemian-age ice from the GRIP ice core, Central Greenland  

Microsoft Academic Search

Continuous measurements of ice crystal size have been carried out on an 80 m sequence between 2790 and 2870 m depth in the GRIP ice core from Central Greenland. The ice in this interval is at present considered to orginate from the Eemian interglacial period. The record reveals that the crystal size in ice older than 100,000 yr is highly

Thorsteinn Thorsteinsson; Josef Kipfstuhl; Hajo Eicken; Sigfus J. Johnsen; Katrin Fuhrer

1995-01-01

18

Ice Core Paleoclimatology Research Group  

NSDL National Science Digital Library

This site, hosted by Ohio State University, contributes to our understanding of the complex interactions within the Earth's coupled climate system through the collection and study of a global array of ice cores. These acquisitions provides high resolution climatic and environmental histories that will include ice core histories from Africa, Antarctica, Bolivia, China, Greenland, Peru, Russia and the United States. The project makes it possible to study processes linking the Polar Regions to the lower latitudes where human activities are most intense. These ice core records contribute prominently to the Earth's paleoclimate record, the ultimate yardstick against which the significance of present and projected anthropogenic effects will be assessed. Images, data sets, publications and research projects are linked to the home page.

Byrd Polar Research Center

19

Vostok Ice Core Lab Activity  

NSDL National Science Digital Library

This site from Columbia provides a lab activity that introduces students to Vostok ice core data. Students will examine the changes of temperature, carbon dioxide, methane, and dust as a function of depth and age in order to answer questions about conditions during the last glacial maximum and glacial/interglacial changes.

Department of Earth and Environmental Sciences

20

Irregular glacial interstadials recorded in a new Greenland ice core  

Microsoft Academic Search

Profiles of O-18\\/O-16 ratios along three previous deep Greenland ice cores seemed to reveal irregular but well-defined episodes of relatively mild climate conditions (interstadials) during the mid and late parts of the last glaciation. Results are presented from a new deep ice core drilled at the summit of the Greenland ice sheet, where the depositional environment and the flow pattern

S. J. Johnsen; H. B. Clausen; W. Dansgaard; K. Fuhrer; N. Gundestrup; C. U. Hammer; P. Iversen; J. Jouzel; B. Stauffer; J. P. Steffensen

1992-01-01

21

Paleo Slide Set: Polar Ice Cores  

NSDL National Science Digital Library

This slide show describes scientists' travels to the ends of the earth to study climate variability. Included in this set are color photos of the Greenland Ice Sheet and the Antarctic Ice Sheet, in addition to a comprehensive text for each slide. Examine ice cores, visit science camps, and understand the importance of these two enormous ice sheets. Maps and graphical representations of ice core data along with ice core methodology and long term glacial/interglacial climatic reconstructions are also included. This set can also be used as an educational tool for studying current issues in glaciology, global warming, the greenhouse effect, and global climate variability.

22

CO2 in the Ice Core Record  

NSDL National Science Digital Library

This video segment, from the 'Earth: The Operators' Manual' featuring climate expert Richard Alley, shows how ice cores stored at the National Ice Core Lab provide evidence that ancient ice contains records of Earth's past climate - specifically carbon dioxide and temperature.

Geoff Haines-Stiles Productions

23

Ice-core records of atmospheric sulphur  

PubMed Central

Sulphate and methanesulphonate (MSA), the two major sulphur species trapped in polar ice, have been extensivelyh studied in Antarctic and Greenland ice cores spanning the last centuries, as well as the entire last climatic cycle. Data from the cores are used to investigate the past contribution of volcanic and biogenic emissions to the natural sulphur budget in high latitude regions of both Hemispheres. Sulphate concentrations in polar ice very often increased during one or two years after large volcanic eruptions. Sulphate records show that fossil fuel combustion has enhanced sulphate concentrations in Greenland snow by a factor of 4 since the beginning of this century, and that no similar trend has occurred in Antarctica. At present, sulphate in Antarctic snow is mainly marine and biogenic in origin and the rate of dimethyl sulphide (DMS) emissions may have been enhanced during pst developments of El Niño Southern Oscillations (ENSO). Marine biota and non-eruptive volcanic emissions represent the two main contributors to the natural high northern latitude sulphur budget. Whele these two sources have contributed equally to the natural sulphur budget of Greenland ice over the last 9000 years BP, non-eruptive volcanic emissions largely dominated the budget at the beginning of the Holocene. A general negative correlation is observed between surcace air temperatures of the Northern Hemisphere and Greenland snow MSA concentrations over the last two centuries. Positive sea-ice anomalies also seem to strengthen DMS emissions. A steady decrease of MSA is observed in Greenland snow layers deposited since 1945, which may either be related to decreasing DMS emissions from marine biota at high northern latitudes or a changing yield of MSA from DMS oxidation driven by modification of the oxidative capacity of the atmosphere in these regions. Slightly reduced MSA concentrations are obvserved in Greenland glacial ice with respect to interglacial levels. In contrast, sulphate and calcium levels are strongly enhanced during the ice age compared to the present day. These long-term variations in Greenland cores are opposite in sign to those revealed by Antarctic ice cores. Such a difference suggests that climate changes led to a quite different sulphur cycle response in the two Hemispheres.

Legrand, M.

1997-01-01

24

Paleo Slide Set: Low Latitude Ice Cores  

NSDL National Science Digital Library

This slide show depicts scientists' travels to the far reaches of the earth to study climate variability of the tropics and subtropics. Included in this set are color photos of the Quelccaya Ice Cap in Peru and the Dunde Ice Cap in China, in addition to a comprehensive text. Visit ice core camps, view collections of ice cores, and understand the climatic importance of these two ice caps. Many graphic representations of ice core data are included along with ice core methodology, and climatic reconstruction with annual resolution from the Andes and the Himalayas. This set can be used as an educational tool for studying current issues in glaciology, paleoclimatology, and climate variability of the tropics and subtropics. Each photograph can be enlarged for better viewing.

25

Siple Dome ice reveals two modes of millennial CO2 change during the last ice age  

PubMed Central

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

Ahn, Jinho; Brook, Edward J.

2014-01-01

26

Siple Dome ice reveals two modes of millennial CO2 change during the last ice age.  

PubMed

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

Ahn, Jinho; Brook, Edward J

2014-01-01

27

THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS  

SciTech Connect

Ices regulate much of the chemistry during star formation and account for up to 80% of the available oxygen and carbon. In this paper, we use the Spitzer c2d Legacy ice survey, complimented with data sets on ices in cloud cores and high-mass protostars, to determine standard ice abundances and to present a coherent picture of the evolution of ices during low- and high-mass star formation. The median ice composition H{sub 2}O:CO:CO{sub 2}:CH{sub 3}OH:NH{sub 3}:CH{sub 4}:XCN is 100:29:29:3:5:5:0.3 and 100:13:13:4:5:2:0.6 toward low- and high-mass protostars, respectively, and 100:31:38:4:-:-:- in cloud cores. In the low-mass sample, the ice abundances with respect to H{sub 2}O of CH{sub 4}, NH{sub 3}, and the component of CO{sub 2} mixed with H{sub 2}O typically vary by <25%, indicative of co-formation with H{sub 2}O. In contrast, some CO and CO{sub 2} ice components, XCN, and CH{sub 3}OH vary by factors 2-10 between the lower and upper quartile. The XCN band correlates with CO, consistent with its OCN{sup -} identification. The origin(s) of the different levels of ice abundance variations are constrained by comparing ice inventories toward different types of protostars and background stars, through ice mapping, analysis of cloud-to-cloud variations, and ice (anti-)correlations. Based on the analysis, the first ice formation phase is driven by hydrogenation of atoms, which results in an H{sub 2}O-dominated ice. At later prestellar times, CO freezes out and variations in CO freezeout levels and the subsequent CO-based chemistry can explain most of the observed ice abundance variations. The last important ice evolution stage is thermal and UV processing around protostars, resulting in CO desorption, ice segregation, and the formation of complex organic molecules. The distribution of cometary ice abundances is consistent with the idea that most cometary ices have a protostellar origin.

Oeberg, Karin I. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02139 (United States); Boogert, A. C. Adwin [IPAC, NASA Herschel Science Center, California Institute of Technology, Pasadena, CA 91125 (United States); Pontoppidan, Klaus M. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Van den Broek, Saskia; Van Dishoeck, Ewine F. [Leiden Observatory, Leiden University, 2300 RA Leiden (Netherlands); Bottinelli, Sandrine [Centre d'Etude Spatiale des Rayonnements (CESR), CNRS-UMR 5187, 31028 Toulouse Cedex 4 (France); Blake, Geoffrey A. [California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA 91125 (United States); Evans, Neal J. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States)

2011-10-20

28

Color Reveals Translucent Seasonal Ice  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Figure 1

In a region near the south pole of Mars translucent carbon dioxide ice covers the ground seasonally. For the first time we can 'see' the translucent ice by the affect it has on the appearance of the surface below.

Dark fans of dust (figure 1) from the surface drape over the top of the seasonal ice. The surface would be the same color as the dust except that the seasonal ice affecting its appearance. Bright bluish streaks are frost that has re-crystallized from the atmosphere.

Sunlight can penetrate through the seasonal layer of translucent ice to warm the ground below. That causes the seasonal ice layer to sublime (evaporate) from the bottom rather than the top.

Observation Geometry Image PSP_002942_0935 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 13-Mar-2007. The complete image is centered at -86.4 degrees latitude, 99.2 degrees East longitude. The range to the target site was 245.4 km (153.4 miles). At this distance the image scale is 49.1 cm/pixel (with 2 x 2 binning) so objects 147 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel . The image was taken at a local Mars time of 06:41 PM and the scene is illuminated from the west with a solar incidence angle of 82 degrees, thus the sun was about 8 degrees above the horizon. At a solar longitude of 199.6 degrees, the season on Mars is Northern Autumn.

2007-01-01

29

Coordinated Ocean-ice Reference Experiments (COREs)  

NASA Astrophysics Data System (ADS)

Coordinated Ocean-ice Reference Experiments (COREs) are presented as a tool to explore the behaviour of global ocean-ice models under forcing from a common atmospheric dataset. We highlight issues arising when designing coupled global ocean and sea ice experiments, such as difficulties formulating a consistent forcing methodology and experimental protocol. Particular focus is given to the hydrological forcing, the details of which are key to realizing simulations with stable meridional overturning circulations. The atmospheric forcing from [Large, W., Yeager, S., 2004. Diurnal to decadal global forcing for ocean and sea-ice models: the data sets and flux climatologies. NCAR Technical Note: NCAR/TN-460+STR. CGD Division of the National Center for Atmospheric Research] was developed for coupled-ocean and sea ice models. We found it to be suitable for our purposes, even though its evaluation originally focussed more on the ocean than on the sea-ice. Simulations with this atmospheric forcing are presented from seven global ocean-ice models using the CORE-I design (repeating annual cycle of atmospheric forcing for 500 years). These simulations test the hypothesis that global ocean-ice models run under the same atmospheric state produce qualitatively similar simulations. The validity of this hypothesis is shown to depend on the chosen diagnostic. The CORE simulations provide feedback to the fidelity of the atmospheric forcing and model configuration, with identification of biases promoting avenues for forcing dataset and/or model development.

Griffies, Stephen M.; Biastoch, Arne; Böning, Claus; Bryan, Frank; Danabasoglu, Gokhan; Chassignet, Eric P.; England, Matthew H.; Gerdes, Rüdiger; Haak, Helmuth; Hallberg, Robert W.; Hazeleger, Wilco; Jungclaus, Johann; Large, William G.; Madec, Gurvan; Pirani, Anna; Samuels, Bonita L.; Scheinert, Markus; Gupta, Alex Sen; Severijns, Camiel A.; Simmons, Harper L.; Treguier, Anne Marie; Winton, Mike; Yeager, Stephen; Yin, Jianjun

30

A New Paradigm for Ice Core Drilling  

NASA Astrophysics Data System (ADS)

The search for answers to questions about the changing climate has created an urgent need to discover past climate signatures archived in glaciers and ice sheets, and to understand current ice sheet behavior. Recognizing that U.S. scientific productivity in this area depends upon a mechanism for ensuring continuity and international cooperation in ice coring and drilling efforts, along with the availability of appropriate drills, drilling expertise, and innovations in drilling technology, the U.S. National Science Foundation (NSF) has established the Ice Drilling Program Office (IDPO) and its partner, the Ice Drilling Design and Operations group (IDDO), together known as IDPO/IDDO (Figure 1). This approach to integrated research and technology planning and delivery replaces the prior approach to drilling, which involved a series of NSF contracts with the Polar Ice Coring Office (PICO) and Ice Coring and Drilling Services (ICDS). This contracting approach lacked integrated planning. Previously, NSF had no way to forecast what science the community would propose—it would get compelling climate proposals that needed ice cores for data, but in many cases no existing drill could retrieve the core needed in the proposal. Constructing the needed drill—a process that takes years—forced science objectives to be put on hold. Now the science community is able to give feedback on its needs to IDPO/IDDO continually, allowing those who develop drilling technology to begin designing and constructing drills that scientists will need for the science proposals that they will submit years in the future. As such, IDPO/IDDO represents a new paradigm for integrated science and science support.

Albert, Mary; Bentley, Charles; Twickler, Mark

2010-09-01

31

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

NASA Astrophysics Data System (ADS)

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.

McConnell, J. R.; Maselli, O. J.; Sigl, M.; Vallelonga, P.; Neumann, T.; Anschütz, H.; Bales, R. C.; Curran, M. A. J.; Das, S. B.; Edwards, R.; Kipfstuhl, S.; Layman, L.; Thomas, E. R.

2014-07-01

32

Using ice cores from the East Antarctic Ice Sheet, scientists have been able to study  

E-print Network

, though, if the world outside were always white and snowy, every day of the year. This is true for Earth's ice sheets. Ice sheets are huge areas of permanent ice. There are only three ice sheets on Earth what the Earth was like in the past. To do this, they remove ice cores from the ice sheets. In order

33

NOAA Paleoclimatology Program - Vostok Ice Core Data  

NSDL National Science Digital Library

This site from the World Data Center for Paleoclimatology features links to data from the Vostok Ice Core, with information on the concentration of various gases, ions, and elements available from trapped gas bubbles. Data has also been used to develop Earth temperature histories extending over 400,000 years.

National Climatic Data Center

34

Fabric measurement along the NEEM ice core, Greenland, and comparison with GRIP and NGRIP ice cores.  

NASA Astrophysics Data System (ADS)

Fabric (distribution of crystallographic orientations) profile along the full NEEM ice core, Greenland, is presented in this work. Data were measured in the field by an Automatic Ice Texture Analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening is observed at the Holocene to Wisconsin climatic transition. A similar strengthening, toward an anisotropic single maximum-type fabric, has been observed in several ice cores from Greenland and Antarctica, and can be attributed to a positive feedback between changes in ice viscosity at the climatic transition, and the impact of a shear component of stress. Centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the folding hypothesis used for a climatic reconstruction by Dahl-Jensen and co authors (2013). Comparison is made to two others ice cores drilled along the same ridge; the GRIP ice core drilled at the summit of the ice sheet, and the NorthGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. The fabric profile clearly reflects the increase in shear deformation when moving NW along the ridge from GRIP to NorthGRIP and NEEM. The difference in fabric profiles between NEEM and NorthGRIP also evidences a stronger lateral extension associated with a sharper ridge at NorthGRIP. References: Dahl-Jensen, D. and 120 co-authors. Eemian interglacial reconstructed from a Greenland folded ice core, Nature, 493, 489-493, 2013.

Montagnat, Maurine; Azuma, Nobuhiko; Dahl Jensen, Dorthe; Eichler, Jan; Fujita, Shuji; Gillet-Chaulet, Fabien; Kipfstuhl, Sepp; Samyn, Denis; Svensson, Anders; Weikusat, Ilka

2014-05-01

35

Dissolved Chemical Ions in an Ice Core of Grigoriev Ice Cap, Kyrgyz Tien Shan  

NASA Astrophysics Data System (ADS)

Snow and ice of glaciers contain various chemical ions supplied through the atmosphere and preserve them for a long period of time. Thus, analysis of soluble ions in glaciers is important to reveal material circulation and climate change in the cryosphere. Many glaciers are distributed over the mountains of the Central Asia. Chemical analysis of ice cores recovered from there play an important role to understand the atmosphere and material circulation peculiar to the Eurasian Continent. In this study, we analyzed the concentration of major ions in the ice core drilled on Grigoriev Ice Cap, Kyrgys Tien Shan, located in the northwestern part of Central Asia. We aim to understand material circulation in this area based on the chemical records. Then, we have attempted to reconstruct the environmental change of Central Asia, combining the chronology, hydrogen and oxygen stable isotope ratio, and density of dust in the ice core analyzed by prior researches. In this study, we used 2,176 samples of a snow pit and ice core from the surface to bed (86.87 m total length) on the top of Grigoriev Ice Cap (4,660 m high), Kyrgys Tien Shan in September, 2007. Samples were cut every 1-5 cm and scraped thinly, and transported frozen to Chiba University, Japan. After that, we dispensed those for various experiments, and analyzed the concentration of major ions using ion chromatography. By the way, it is estimated that the date of the bottom of this ice core is approximately 12,000 years ago by prior researches. The concentration of major ions dissolved in the ice core of Grigoriev Ice Cap revealed that Ca is the most dominant species in the measured ions and it accounted for more than 50 % (Eq ratio) of the mean of the entire core. This suggests that CaCO3 included in mineral dust derived from deserts around Tien Shan strongly influence the chemical composition of the Ice Cap. In addition, this composition is similar to those of Urumqi No.1 Glacier (Tien Shan), Mustagh Ata Glacier (Pamir) and Chongce Ice Cap (Kunlun) located around Taklamakan Desert. Therefore, material coming from the desert is a major source of the chemical component of the glacier. The major ions profile in the core revealed that Ca showed more number of peaks compared with other ions. This may be due to seasonal variation in Ca supply. In contrast, other ions showed only some significant peaks in the core. These peaks are probably due to specific events of unusual atmospheric circulation or emission of materials. The ion proportions at Ca peak are divided into seven categories: Type 1 is composed mainly of Cl/SO4/Na, Type 2 is Cl/Na, Type 3 is SO4, Type 4 is Mg, Type 5 is SO4/Mg, Type 6 is Ca, and Type 7 is Ca/Mg. Especially, it is revealed that Type 6 is relatively frequent with upper-middle parts, Type 1 is middle-lower parts, and Type 4 is bottom parts of the core. This suggests that the major ions supplied at the time of events changed by the times from 12,000 years ago to the present. In recent 1,000 years, concentrations of Cl/SO4/Na/Ca tend to decrease after the 1930s. This suggests that melting of the snow and leaching of the chemical ions are promoted by a rise temperature in recent.

SHUN, A.; Takeuchi, N.; Sera, S.; Fujita, K.; Okamoto, S.; Naoki, K.; Aizen, V. B.

2012-12-01

36

Biological proxies recorded in a Belukha ice core, Russian Altai  

NASA Astrophysics Data System (ADS)

Different biological proxies such as pollen, cysts, and diatoms were identified and quantified in the upper part of a Belukha ice core from the Russian Altai. The ice core from the Belukha glacier collected in 2001 (4062 m a.s.l., 49°48' N, 86° 34' E) was analyzed with annual resolution in the period 1964-2000. We used daily data of the frequency of synoptic patterns observed in the Northern Hemisphere along with daily data of precipitation to identify the main modern sources of biological proxies deposited at the Belukha glacier. Our analyses revealed that main sources of diatoms in the Belukha ice core are water bodies of the Aral, Caspian, and North Kazakhstan basins. Coniferous trees pollen originated from the taiga forest of the boreal zone of West Siberia and pollen of hardwoods and herbs from steppe and forest steppe vegetation in the Northern Altai and East Kazakhstan. Cysts of algae and spores of inferior plants were transported from local water bodies and forests. The identified source regions of the biological species are supported by back trajectory analyses and are in good agreement with emission source regions of the trace species in the ice core.

Papina, T.; Blyacharchyuk, T.; Eichler, A.; Malygina, N.; Mitrofanova, E.; Schwikowski, M.

2013-05-01

37

Fabric measurement along the NEEM ice core, Greenland, and comparison with GRIP and NGRIP ice cores  

NASA Astrophysics Data System (ADS)

Fabric (distribution of crystallographic orientations) profile along the full NEEM ice core, Greenland, is presented in this work. Data were measured in the field by an Automatic Ice Texture Analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening is observed at the Holocene to Wisconsin climatic transition. A similar strengthening, toward an anisotropic single maximum-type fabric, has been observed in several ice cores from Greenland and Antarctica, and can be attributed to a positive feedback between changes in ice viscosity at the climatic transition, and the impact of a shear component of stress. Centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the folding hypothesis used for a climatic reconstruction by Dahl-Jensen et al. (2013). Comparison is made to two others ice cores drilled along the same ridge; the GRIP ice core drilled at the summit of the ice sheet, and the NorthGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. The fabric profile clearly reflects the increase in shear deformation when moving NW along the ridge from GRIP to NorthGRIP and NEEM. The difference in fabric profiles between NEEM and NorthGRIP also evidences a stronger lateral extension associated with a sharper ridge at NorthGRIP.

Montagnat, M.; Azuma, N.; Dahl-Jensen, D.; Eichler, J.; Fujita, S.; Gillet-Chaulet, F.; Kipfstuhl, S.; Samyn, D.; Svensson, A.; Weikusat, I.

2014-01-01

38

Fabric along the NEEM ice core, Greenland, and its comparison with GRIP and NGRIP ice cores  

NASA Astrophysics Data System (ADS)

Fabric (distribution of crystallographic orientations) along the full NEEM ice core, Greenland was measured in the field by an automatic ice texture analyzer every 10 m, from 33 m down to 2461 m depth. The fabric evolves from a slightly anisotropic fabric at the top, toward a strong single maximum at about 2300 m, which is typical of a deformation pattern mostly driven by uniaxial compression and simple shearing. A sharp increase in the fabric strengthening rate is observed at the Holocene to Wisconsin (HW) climatic transition. From a simple model we estimate that this depth is located at a transition from a state dominated by vertical compression to a state dominated by vertical shear. Comparisons are made to two others ice cores drilled along the same ridge; the GRIP ice core, drilled at the summit of the ice sheet, and the NGRIP ice core, drilled 325 km to the NNW of the summit along the ridge, and 365 km upstream from NEEM. This comparison tends to demonstrate that the ice viscosity change with the HW climatic transition must be associated with the shear-dominated state to induce the abrupt fabric strengthening observed at NEEM. This comparison therefore reflects the increasing role of shear deformation on the coring site when moving NW along the ridge from GRIP to NGRIP and NEEM. The difference in fabric profiles between NEEM and NGRIP also evidences a stronger lateral extension associated with a sharper ridge at NGRIP. Further along the core, centimeter scale abrupt texture (fabric and microstructure) variations are observed in the bottom part of the core. Their positions are in good agreement with the observed folding layers in Dahl-Jensen et al. (2013).

Montagnat, M.; Azuma, N.; Dahl-Jensen, D.; Eichler, J.; Fujita, S.; Gillet-Chaulet, F.; Kipfstuhl, S.; Samyn, D.; Svensson, A.; Weikusat, I.

2014-07-01

39

Exploring Paleoclimatology using Vostok Ice Core Data  

NSDL National Science Digital Library

This guide for instructors provides information on how to use data from ice cores in the classroom. The data consist of atmospheric gas percentages, such as CO2, in fossil air bubbles trapped in ice cores taken at the Vostok research station near the center of the Antarctic ice sheet. The data provides an historic record of atmospheric gas composition, which scientists use as a baseline to evaluate the effects of human activity. Classroom topics include methods for reconstructing past climates; ice ages and glacial cycles; the use isotopic data to determine temperature or age; and global warming. Students will learn to use the data to make graphs illustrating atmospheric changes over time; use math to process data to determine relationships between temperature and CO2 levels; compare data from independent experiments; and use proxy data to create visual representations of glacial cycles. Links are provided to download the data, and to a web-based application (WebMapper) that allows students to create graphs. There are also links to scientific references and educational resources that use this dataset, and to online resources with related information.

40

A Continuous IC Glaciochemical Record of the last Glacial Period from the NGRIP Ice Core  

NASA Astrophysics Data System (ADS)

Comprehensive chemical analysis of aerosol components over the time period from 100,000 to 10,000 years before present was performed on the NGRIP ice core. In line with high-resolution chemical flow analysis, a continuous sampling of ice core melt water was performed at 55 cm resolution for ion chromatographic (IC) analysis of soluble ions. These records provide a unique potential for detailed investigations of conditions for source load and transport of aerosol during the last glacial period. A comparison with GISP2 IC record shows a good agreement between the two ice core records, but with generally higher concentrations in the NGRIP ice core. A more detailed comparison between the two ice core ion records reveals strong regional differences in source contributions and transport paths for sea salt and dust aerosol over Greenland during the glacial period, indicating a different transport pattern for aerosol over Greenland during the last glacial period.

Siggaard-Andersen, M.; Hansson, M.; Fischer, H.; Bigler, M.; Roethlisberger, R.; Goto-Azuma, K.; Steffensen, J.; Ruth, U.; Andersen, K. K.; Clausen, H. B.; Jonsell, U.

2005-12-01

41

High resolution record of paleoclimate since the Little Ice Age from the Tibetan ice cores  

Microsoft Academic Search

Climate changes during the Little Ice Age were studied based on oxygen isotope values (?18O) measured from ice cores recovered on, and nearby, the Qinghai-Tibetan Plateau. Three cold periods have been identified and are supported by three widely existing moraine ridges formed during the Little Ice Age. Importantly, the amplitude of the three cold periods differ in the cores studied.

Tandong Yao; Yafeng Shi; L. G. Thompson

1997-01-01

42

Sources of backscatter at 5.3 GHz from a superimposed ice and firn area revealed by multi-frequency GPR and cores  

E-print Network

-frequency GPR and cores Kirsty LANGLEY,1* Pascal LACROIX,2 Svein-Erik HAMRAN,1 Ola BRANDT3{ 1 University of Oslo are important for proper interpretation of satellite data. Ground-penetrating radar (GPR) is a common tool of penetration), the GPR time window is subdivided to give backscatter at different depths. GPR instruments

Paris-Sud XI, Université de

43

Chlorophyll a in Antarctic sea ice from historical ice core data  

NASA Astrophysics Data System (ADS)

Sea ice core chlorophyll a data are used to describe the seasonal, regional and vertical distribution of algal biomass in Southern Ocean pack ice. The Antarctic Sea Ice Processes and Climate - Biology (ASPeCt - Bio) circumpolar dataset consists of 1300 ice cores collected during 32 cruises over a period of 25 years. The analyses show that integrated sea ice chlorophyll a peaks in early spring and late austral summer, which is consistent with theories on light and nutrient limitation. The results indicate that on a circum-Antarctic scale, surface, internal and bottom sea ice layers contribute equally to integrated biomass, but vertical distribution shows distinct differences among six regions around the continent. The vertical distribution of sea ice algal biomass depends on sea ice thickness, with surface communities most commonly associated with thin ice (<0.4 m), and ice of moderate thickness (0.4-1.0 m) having the highest probability of forming bottom communities.

Meiners, K. M.; Vancoppenolle, M.; Thanassekos, S.; Dieckmann, G. S.; Thomas, D. N.; Tison, J.-L.; Arrigo, K. R.; Garrison, D. L.; McMinn, A.; Lannuzel, D.; van der Merwe, P.; Swadling, K. M.; Smith, W. O., Jr.; Melnikov, I.; Raymond, B.

2012-11-01

44

Ice core evidence for an explosive tropical volcanic eruption 6 years preceding Tambora  

Microsoft Academic Search

High-resolution analyses of ice cores from Antarctica and Greenland reveal an explosive volcanic eruption in the tropics in A.D. 1809 which is not reflected in the historical record. A comparison in the same ice cores of the sulfate flux from the A.D. 1809 eruption to that from the Tambora eruption (A.D. 1815) indicates a near-equatorial location and a magnitude roughly

Jihong Dai; Ellen Mosley-Thompson; Lonnie G. Thompson

1991-01-01

45

Consistently dated records from the Greenland GRIP, GISP2 and NGRIP ice cores for the past 104 ka reveal regional millennial-scale ?18O gradients with possible Heinrich event imprint  

NASA Astrophysics Data System (ADS)

We present a synchronization of the NGRIP, GRIP and GISP2 ice cores onto a master chronology extending back to 104 ka before present, providing a consistent chronological framework for these three Greenland records. The synchronization aligns distinct peaks in volcanic proxy records and other impurity records (chemo-stratigraphic matching) and assumes that these layers of elevated impurity content represent the same, instantaneous event in the past at all three sites. More than 900 marker horizons between the three cores have been identified and our matching is independently confirmed by 24 new and previously identified volcanic ash (tephra) tie-points. Using the reference horizons, we transfer the widely used Greenland ice-core chronology, GICC05modelext, to the two Summit cores, GRIP and GISP2. Furthermore, we provide gas chronologies for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new gas data (CH4 concentration and ?15N of N2). We infer that the accumulation contrast between the stadial and interstadial phases of the glacial period was ?10% greater at Summit compared to at NGRIP. The ?18O temperature-proxy records from NGRIP, GRIP, and GISP2 are generally very similar and display synchronous behaviour at climate transitions. The ?18O differences between Summit and NGRIP, however, changed slowly over the Last Glacial-Interglacial cycle and also underwent abrupt millennial-to-centennial-scale variations. We suggest that this observed latitudinal ?18O gradient in Greenland during the glacial period is the result of 1) relatively higher degree of precipitation with a Pacific signature at NGRIP, 2) increased summer bias in precipitation at Summit, and 3) enhanced Rayleigh distillation due to an increased source-to-site distance and a potentially larger source-to-site temperature gradient. We propose that these processes are governed by changes in the North American Ice Sheet (NAIS) volume and North Atlantic sea-ice extent and/or sea-surface temperatures (SST) on orbital timescales, and that changing sea-ice extent and SSTs are the driving mechanisms on shorter timescales. Finally, we observe that maxima in the Summit-NGRIP ?18O difference are roughly coincident with prominent Heinrich events. This suggests that the climatic reorganization that takes place during stadials with Heinrich events, possibly driven by a southward expansion of sea ice and low SSTs in the North Atlantic, are recorded in the ice-core records.

Seierstad, Inger K.; Abbott, Peter M.; Bigler, Matthias; Blunier, Thomas; Bourne, Anna J.; Brook, Edward; Buchardt, Susanne L.; Buizert, Christo; Clausen, Henrik B.; Cook, Eliza; Dahl-Jensen, Dorthe; Davies, Siwan M.; Guillevic, Myriam; Johnsen, Sigfús J.; Pedersen, Desirée S.; Popp, Trevor J.; Rasmussen, Sune O.; Severinghaus, Jeffrey P.; Svensson, Anders; Vinther, Bo M.

2014-12-01

46

On the nature of the dirty ice at the bottom of the GISP2 ice core  

NASA Astrophysics Data System (ADS)

We present data on the triple Ar isotope composition in trapped gas from clean, stratigraphically disturbed ice between 2800 and 3040 m depth in the GISP2 ice core, and from basal dirty ice from 3040 to 3053 m depth. We also present data for the abundance and isotopic composition of O 2 and N 2, and abundance of Ar, in the basal dirty ice. The Ar/N 2 ratio of dirty basal ice, the heavy isotope enrichment (reflecting gravitational fractionation), and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier, which comprises most of the ice in the dirty bottom layer. O 2 is partly to completely depleted in basal ice, reflecting active metabolism. The gravitationally corrected ratio of 40Ar/ 38Ar, which decreases with age in the global atmosphere, is compatible with an age of 100-250 ka for clean disturbed ice. In basal ice, 40Ar is present in excess due to injection of radiogenic 40Ar produced in the underlying continental crust. The weak depth gradient of 40Ar in the dirty basal ice, and the distribution of dirt, indicate mixing within the basal ice, while various published lines of evidence indicate mixing within the overlying clean, disturbed ice. Excess CH 4, which reaches thousands of ppm in basal dirty ice at GRIP, is virtually absent in overlying clean disturbed ice, demonstrating that mixing of dirty basal ice into the overlying clean ice, if it occurs at all, is very slow. Order-of-magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow. The dirty ice appears to consist of two or more basal components in addition to clean glacial ice. A small amount of soil or permafrost, plus preglacial snow, lake or ground ice could explain the observations.

Bender, Michael L.; Burgess, Edward; Alley, Richard B.; Barnett, Bruce; Clow, Gary D.

2010-11-01

47

On the nature of the dirty ice at the bottom of the GISP2 ice core  

USGS Publications Warehouse

We present data on the triple Ar isotope composition in trapped gas from clean, stratigraphically disturbed ice between 2800 and 3040m depth in the GISP2 ice core, and from basal dirty ice from 3040 to 3053m depth. We also present data for the abundance and isotopic composition of O2 and N2, and abundance of Ar, in the basal dirty ice. The Ar/N2 ratio of dirty basal ice, the heavy isotope enrichment (reflecting gravitational fractionation), and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier, which comprises most of the ice in the dirty bottom layer. O2 is partly to completely depleted in basal ice, reflecting active metabolism. The gravitationally corrected ratio of 40Ar/38Ar, which decreases with age in the global atmosphere, is compatible with an age of 100-250ka for clean disturbed ice. In basal ice, 40Ar is present in excess due to injection of radiogenic 40Ar produced in the underlying continental crust. The weak depth gradient of 40Ar in the dirty basal ice, and the distribution of dirt, indicate mixing within the basal ice, while various published lines of evidence indicate mixing within the overlying clean, disturbed ice. Excess CH4, which reaches thousands of ppm in basal dirty ice at GRIP, is virtually absent in overlying clean disturbed ice, demonstrating that mixing of dirty basal ice into the overlying clean ice, if it occurs at all, is very slow. Order-of-magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow. The dirty ice appears to consist of two or more basal components in addition to clean glacial ice. A small amount of soil or permafrost, plus preglacial snow, lake or ground ice could explain the observations.

Bender, Michael L.; Burgess, Edward; Alley, Richard B.; Barnett, Bruce; Clow, Gary D.

2010-01-01

48

Ice core records as sea ice proxies: An evaluation from the Weddell Sea region of Antarctica  

NASA Astrophysics Data System (ADS)

Ice core records of methanesulfonic acid (MSA) from three sites around the Weddell Sea are investigated for their potential as sea ice proxies. It is found that the amount of MSA reaching the ice core sites decreases following years of increased winter sea ice in the Weddell Sea; opposite to the expected relationship if MSA is to be used as a sea ice proxy. It is also shown that this negative MSA-sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the Weddell Sea has on MSA production area and transport distance. A historical record of sea ice from the northern Weddell Sea shows that the negative relationship between MSA and winter sea ice exists over interannual (˜7-year period) and multidecadal (˜20-year period) timescales. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the Weddell Sea, which act to synergistically increase sea ice extent (SIE) while decreasing MSA delivery to the ice core sites. Hence our findings show that in some locations atmospheric transport strength, rather than sea ice conditions, is the dominant factor that determines the MSA signal preserved in near-coastal ice cores. A cautious approach is thus required in using ice core MSA for reconstructing past sea ice conditions, including the need for networks of ice core records and multiproxy studies to assess the significance of past MSA changes at different locations around Antarctica.

Abram, Nerilie J.; Mulvaney, Robert; Wolff, Eric W.; Mudelsee, Manfred

2007-08-01

49

Microparticle Concentration Variations Linked with Climatic Change: Evidence from Polar Ice Cores  

Microsoft Academic Search

The microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation. The ratio of the average particle concentration in the late glacial strata to that in the Holocene strata is 6\\/1 for the core from Dome C, Antarctica, 3\\/1 for

L. G. Thompson; E. Mosley-Thompson

1981-01-01

50

Snow algae in an ice core drilled on Grigoriev Ice cap in the Kyrgyz Tien Shen Mountains  

NASA Astrophysics Data System (ADS)

Snow algae are photosynthetic microorganisms and are living on the surfase of glaciers. They grow on melting surface from spring to summer and their biomass and community structure are changed with physical and chemical conditions on glaciers. Ice cores drilled from glaciers also contain snow algae that grew in the past. Studying biomass and community structure of snow algae in ice cores could reveal the temporal variation in snow algae in the past, and also environmental conditions relating propagation of snow algae. In this study, we anlalyzed snow algae preserved in an ice core of Grigoriev Ice cap located in eastern Kyrgyzstan of the central Asia, and to describe their temporal variations for the last 200 years. The ice core drilling was carried out on September in 2007 on the Grigoriev Ice cap in the Kyrgyz Tien Shen Mountains. A 87 m long ice core from the surface to the bedrock was recovered at the top of the ice cap. The core was horizontally cut every 5 cm (total 1212 samples). The samples were melted and preserved as a 3% formalin solution. After the sample water was filtered through a hydrophilized PTFE membrane filter, observed by microscope. Snow algae in the sample water were counting. The algal biomass was represented by the cell number per unit water volume. Here, we showed the results between the surface to the 64 m in depth. We also analyzed the snow algal communities on the surface of the ice cap collected from five different sites from the top down to the terminus. Microscopy revealed that the ice core contained three taxa of filamentous cyanobacteria, an unicellular cyanobacterium, and two green algae. They were also found on the ice or snow surface of the i Ice cap. The quantitative analyses of the algae in the part of upper 64 m deep of the ice core samples revealed that the algal biomass varied significantly and showed many peaks. Furthermore, the biomass profile differed among the taxa. The filamentous cyanobacterium varied from 0.0 to 4.6 x 103?m3 mL-1 (mean: 56?m3 mL-1 ), the unicellular cyanobacterium varied from 0.0 to 3.0 x 104?m3 mL-1 (mean: 1.2 x 103?m3 mL-1 ), and Green algae varied from 0.0 to 2.3 x 104?m3 mL-1 (mean: 2.2 x 103?m3 mL-1 ). Based on the dating by pollen grains, the 64 m core covers 237 years. The results suggest that the snow algae did not grow every year on the top of the ice cap, and their biomass and community structure varied greatly from year to year. The total biomass after the 1960s was significantly higher than those before the 1950s. This suggested suggests that the surface conditions changed more favorable to the growth of algae in the 1960s. Annal variation of the algal biomass was found to be significantly correlated with air temperature at the nearest observing station from Grigoriev the iIce cap and hydrogen stable isotope (?D) in the ice core. The results suggest that the algal growth is more preferable in warmer year.

Honda, M.; Takeuchi, N.; Sera, S.; Fujita, K.; Okamoto, S.; Naoki, K.; Aizen, V. B.

2012-12-01

51

Ice Core Borehole Sonic Logging at GISP2 and GRIP, Greenland, and Siple Dome, Antarctica  

Microsoft Academic Search

Studies of ice cores yield important information about the history of ice sheets and past climates. Interpretation of paleoclimate records from ice cores depends on understanding the ice sheet flow to determine depth-age relationships and whether the ice has been affected by folding. The alignment of crystals in ice, called fabric, is an important factor in understanding ice sheet flow

G. W. Lamorey

2002-01-01

52

The microstructure of polar ice. Part I: Highlights from ice core research  

NASA Astrophysics Data System (ADS)

Polar ice sheets play a fundamental role in Earth's climate system, by interacting actively and passively with the environment. Active interactions include the creeping flow of ice and its effects on polar geomorphology, global sea level, ocean and atmospheric circulation, and so on. Passive interactions are mainly established by the formation of climate records within the ice, in form of air bubbles, dust particles, salt microinclusions and other derivatives of airborne impurities buried by recurrent snowfalls. For a half-century scientists have been drilling deep ice cores in Antarctica and Greenland for studying such records, which can go back to around a million years. Experience shows, however, that the ice-sheet flow generally disrupts the stratigraphy of the bottom part of deep ice cores, destroying the integrity of the oldest records. For all these reasons glaciologists have been studying the microstructure of polar ice cores for decades, in order to understand the genesis and fate of ice-core climate records, as well as to learn more about the physical properties of polar ice, aiming at better climate-record interpretations and ever more precise models of ice-sheet dynamics. In this Part I we review the main difficulties and advances in deep ice core drilling in Antarctica and Greenland, together with the major contributions of deep ice coring to the research on natural ice microstructures. In particular, we discuss in detail the microstructural findings from Camp Century, Byrd, Dye 3, GRIP, GISP2, NorthGRIP, Vostok, Dome C, EDML, and Dome Fuji, besides commenting also on the earlier results of some pioneering ventures, like the Jungfraujoch Expedition and the Norwegian-British-Swedish Antarctic Expedition, among others. In the companion Part II of this work (Faria et al., 2014), the review proceeds with a survey of the state-of-the-art understanding of natural ice microstructures and some exciting prospects in this field of research.

Faria, Sérgio H.; Weikusat, Ilka; Azuma, Nobuhiko

2014-04-01

53

Tributaries of West Antarctic Ice Streams Revealed by RADARSAT Interferometry.  

PubMed

Interferometric RADARSAT data are used to map ice motion in the source areas of four West Antarctic ice streams. The data reveal that tributaries, coincident with subglacial valleys, provide a spatially extensive transition between slow inland flow and rapid ice stream flow and that adjacent ice streams draw from shared source regions. Two tributaries flow into the stagnant ice stream C, creating an extensive region that is thickening at an average rate of 0.49 meters per year. This is one of the largest rates of thickening ever reported in Antarctica. PMID:10514370

Joughin; Gray; Bindschadler; Price; Morse; Hulbe; Mattar; Werner

1999-10-01

54

Ice Core Records of Past Climate: Thunder, Lightning and a Key to the Future?  

NASA Astrophysics Data System (ADS)

This talk will present an overview of ice core climate records. Ice cores record not only the basic climate (temperature and precipitation amount) at the ice core site, but also the composition of the atmosphere, both gases and dust, as well as a number of proxies that reflect conditions outside of the ice sheet, including ocean conditions and sea ice extents. Accumulation rates determine the temporal resolution of the information, with low accumulation sites yielding records approaching 1,000,000 years in length, and high accumulation records yielding year-by-year information about environmental change for tens of thousands of years. Highlights of ice core contributions to our understanding of past climates will be discussed, including: the remarkably tight relationship between CO2 and climate over the past several hundred thousand years, the flickering nature of climate during glacial periods, the synchronous changes in climate between the hemispheres on Milankovitch time scales and the asynchronous climate between the hemispheres on, millennial time scales, and the unstable and quantum nature of climate as reflected by abrupt climate changes. This last example has direct bearing on future climate change, as the ice core record reveals that abrupt climate changes are very large as much as 10 degrees C change in man annual temperature in less than a human lifetime, as well as very fast atmospheric pressure patterns controlling winds and snowfall rates appear to have shifted in a few years or less, and those shifts were effectively permanent on the time scale of human interest.

White, J. W. C.

2003-04-01

55

West Antarctic Ice-core Records of Sea-Ice Variability: A Neural Network Perspective  

NASA Astrophysics Data System (ADS)

Full understanding of Antarctic sea-ice variability is hindered by limited detailed records beyond the satellite era. Ice-core records from the adjacent continental ice sheet offer a possible solution to this problem. Here we apply new tools from the field of artificial neural networks (ANNs) to reconstruct centennial-scale records of West Antarctic sea-ice variability using a suite of recent ice-core datasets and the satellite-based record of sea ice. Antarctic ice cores are known to record aspects of sea-ice variability (e.g., sea ice-edge and sulfate content). However, the field has yet to fully exploit all of the available ice-core data, and the nonlinear properties therein, to develop robust ice core-sea ice calibrations that can be used to build detailed spatial histories of sea ice. Self-organizing maps (SOMs) and ANNs offer a solution to this problem. With SOMs, we develop sets of representative patterns from our multivariate datasets that, for example, simplify the representation of chemistry data from multiple ice core sites. These patterns let us replace a multidimensional coordinate in data space (e.g., chemistry at all sites at time t) with a 2-d coordinate in “SOM space”. Patterns also classify the input dataset and identify times where particular conditions exist in the data. ANNs allow us to nonlinearly relate a set of predictors to a set of targets, e.g., ice-core chemistry to sea-ice extent. With a well-trained ANN, sea ice conditions outside the satellite era may be developed from extended ice-core datasets. A significant challenge to this approach (as well as any other calibration) is the limited overlap between the ice-core and satellite-based sea ice records. SOM analysis of monthly sea-ice-edge data produces a set of generalized patterns concisely capturing both spatial and temporal variability in this climate variable, e.g., identifying the multiple spatial patterns that correspond to “greatest extent conditions”. By tracking the most common patterns for each month, the annual cycling of expansion and contraction is readily visualized, including variability in the rate of change in extent at different times of the year, e.g., retreat in January is faster than November. Eighteen West Antarctic sites (e.g., Siple Dome, CWA, USITASE) provide extensive glaciochemical data for this work. Preliminary SOM analyses of these data (for the period 1870-1994) readily show the spatial variability of this region. For example, the patterns of high Na+ values focus on sites in the region ~77-79 °S, 115-125 °W (~250 km north of Byrd). Additional analyses will help to identify the best ice-core predictors of sea-ice variability. Further analysis of these sea-ice and ice-core datasets will bring additional insights and the development of long-term West Antarctic sea-ice reconstructions.

Reusch, D. B.

2009-12-01

56

Statistical extraction of volcanic sulphate from nonpolar ice cores  

NASA Astrophysics Data System (ADS)

Ice cores from outside the Greenland and Antarctic ice sheets are difficult to date because of seasonal melting and multiple sources (terrestrial, marine, biogenic and anthropogenic) of sulfates deposited onto the ice. Here we present a method of volcanic sulfate extraction that relies on fitting sulfate profiles to other ion species measured along the cores in moving windows in log space. We verify the method with a well dated section of the Belukha ice core from central Eurasia. There are excellent matches to volcanoes in the preindustrial, and clear extraction of volcanic peaks in the post-1940 period when a simple method based on calcium as a proxy for terrestrial sulfate fails due to anthropogenic sulfate deposition. We then attempt to use the same statistical scheme to locate volcanic sulfate horizons within three ice cores from Svalbard and a core from Mount Everest. Volcanic sulfate is <5% of the sulfate budget in every core, and differences in eruption signals extracted reflect the large differences in environment between western, northern and central regions of Svalbard. The Lomonosovfonna and Vestfonna cores span about the last 1000 years, with good extraction of volcanic signals, while Holtedahlfonna which extends to about AD1700 appears to lack a clear record. The Mount Everest core allows clean volcanic signal extraction and the core extends back to about AD700, slightly older than a previous flow model has suggested. The method may thus be used to extract historical volcanic records from a more diverse geographical range than hitherto.

Moore, J. C.; Beaudon, E.; Kang, Shichang; Divine, D.; Isaksson, E.; Pohjola, V. A.; van de Wal, R. S. W.

2012-02-01

57

Black carbon concentration in a Greenland Dye-3 ice core  

SciTech Connect

We have determined the black carbon concentration in Greenland Dye-3 ice core samples covering the time period from about 3380 to 100 years before present. The average concentration found is 1.53 microg of black carbon per 1 kg of ice. We have found significantly lower black carbon concentrations during the time period from 750 to 100 years before present connected possibly with the Little Ice Age and corresponding changes in atmospheric general circulation patterns and black carbon sources. 18 refs.

Chylek, P.; Johnson, B.; Wu, Hong (Dalhousie Univ., Halifax (Canada))

1992-10-01

58

Greenland ice core evidence of the 79 AD Vesuvius eruption  

NASA Astrophysics Data System (ADS)

Volcanic tephra are independent age horizons and can synchronize strata of various paleoclimate records including ice and sediment cores. The Holocene section of the Greenland Ice Core Project (GRIP) ice core is dated by multi-parameter annual layer counting, and contains peaks in acidity, SO42- and microparticle concentrations at a depth of 429.1 to 429.3 m, which have not previously been definitively ascribed to a volcanic eruption. Here, we identify tephra particles and determine that volcanic shards extracted from a depth of 429.3 m in the GRIP ice core are likely due to the 79 AD Vesuvius eruption. The chemical composition of the tephra particles is consistent with the K-phonolitic composition of the Vesuvius juvenile ejecta and differs from the chemical composition of other major eruptions (? VEI 4) between 50-100 AD.

Barbante, C.; Kehrwald, N. M.; Marianelli, P.; Vinther, B. M.; Steffensen, J. P.; Cozzi, G.; Hammer, C. U.; Clausen, H. B.; Siggaard-Andersen, M.-L.

2013-06-01

59

North Atlantic Deep Water Formation: Information from Ice Cores  

NASA Technical Reports Server (NTRS)

The main results of measurements of the CO2 concentration of air occluded in natural ice during periods of climatic change are presented, as well as other measured ice core parameters. Elements of an interpretation of the data in terms of mechanisms of changing environmental systems are briefly discussed.

Oeschger, H.

1984-01-01

60

Dating of two nearby ice cores from the Illimani, Bolivia  

Microsoft Academic Search

In order to establish a chronology of two nearby ice cores from a glacier at Illimani (6438 m), Bolivia, a broad dating approach is presented here, which in particular makes use of the fast, simple, and nearly nondestructive electrical conductivity method (ECM) that provides a highly resolved record. Thus, ECM is suited for counting annual layers in the ice, especially

S. Knüsel; P. Ginot; U. Schotterer; M. Schwikowski; H. W. Gäggeler; B. Francou; J. R. Petit; J. C. Simões; J. D. Taupin

2003-01-01

61

IceCore: A Web Portal for Workflow Execution  

NASA Astrophysics Data System (ADS)

The large amount of data, complexity of data analysis software and increasing need of computing power are challenges for traditional desktop oriented data analysis. IceCore is a prototype web portal for executing scientific workflows in a workflow engine and for controlling administrative tasks of workflow execution and resources. IceCore is a scalable system that can be used as a common interface for workflows distributed in multiple workflow engine servers and for managing distributed databases.

Maisala, S.; Oittinen, T.; Takala, T.; Solin, O.; Huovelin, J.

2012-09-01

62

Late Holocene fire activity recorded in a Greenland ice core  

NASA Astrophysics Data System (ADS)

The pyrolysis compounds from the thermal decomposition of cellulose during burning events are the dominant smoke tracers in continental airsheds. Important compounds from biomass burning include monosaccharide anhydrides (MAs). Levoglucosan is a MA produced by combusing cellulose at a temperatures of 300°C or greater. Ice cores contain these specific molecular markers and other pyrochemical evidence that provides much-needed information on the role of fire in regions with no existing data of past fire activity. Here, we use atmospheric and snow levoglucosan concentrations to trace fire emissions from a boreal forest fire source in the Canadian Shield through transport and deposition at Summit, Greenland (72°35'N 38°25' W, 3048 masl). Atmospheric and surface samples suggest that levoglucosan in snow can record biomass burning events up to 1000s of kilometers away. Levoglucosan does degrade by interacting with hydroxyl radicals in the atmosphere, but it is emitted in large quantities, allowing the use as a biomass burning tracer. These quantified atmospheric biomass burning emissions and associated parallel oxalate and levoglucosan peaks in snow pit samples validates levoglucosan as a proxy for past biomass burning in snow records and by extension in ice cores. The temporal and spatial resolution of chemical markers in ice cores matches the core in which they are measured. The spatial resolution of chemical markers in ice cores depends on the core location where low-latitude ice cores primarily reflect regional climate parameters, and polar ice cores integrate hemispheric signals. We present levoglucosan flux, and hence past fire activity, measured during the late Holocene in the NEEM, Greenland (77°27' N; 51°3'W, 2454 masl) ice core. We compare the NEEM results with multiple major Northern Hemisphere climate and cultural parameters.

Zennaro, P.; Barbante, C.; Kehrwald, N.; Zangrando, R.; Gambaro, A.; Gabrieli, J.

2012-04-01

63

Raman spectroscopy on ice cores from Greenland and Antarctica  

NASA Astrophysics Data System (ADS)

Ice cores are invaluable archives for the reconstruction of the climatic history of the earth. Besides the analysis of various climatic processes from isotopes and chemical signatures they offer the unique possibility of directly extracting the past atmosphere from gaseous inclusions in the ice. Many aspects of the formation and alterations of these inclusions, e.g. the entrapment of air at the firn-ice-transition, the formation of crystalline gas hydrates (clathrates) from the bubbles or the structural relaxation during storage of the cores, need to be better understood to enable reliable interpretations of the obtained data. Modern micro Raman spectroscopy is an excellent tool to obtain high-quality data for all of these aspects. It has been productively used for phase identification of solid inclusions [1], investigation of air clathrates [2] and high-resolution measurements of N2/O2 mixing ratios inside individual air bubbles [3,4]. Detailed examples of the various uses of Raman spectroscopy will be presented along with practical information about the techniques required to obtain high-quality spectra. Retrieval and interpretation of quantitative data from the spectra will be explained. Future possibilities for advanced uses of Raman spectroscopy for ice core research will be discussed. [1] T. Sakurai et al., 2009, Direct observation of salts as micro-inclusions in the Greenland GRIP ice core. Journal of Glaciology, 55, 777-783. [2] F. Pauer et al., 1995, Raman spectroscopic study of nitrogen/oxygen ratio in natural ice clathrates in the GRIP ice core. Geophysical Research Letters, 22, 969-971. [3] T. Ikeda-Fukazawa et al., 2001, Variation in N2/O2 ratio of occluded air in Dome Fuji antarctic ice. Journal of Geophysical Research, 106, 17799-17810. [4] C. Weikusat et al., Raman spectroscopy of gaseous inclusions in EDML ice core: First results - microbubbles. Journal of Glaciology, accepted.

Weikusat, C.; Kipfstuhl, S.

2012-04-01

64

The isotopic composition of methane in polar ice cores  

NASA Technical Reports Server (NTRS)

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that: (1) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (2) that the carbon-13 to carbon-12 ratio of atmospheric CH4 in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent C-13H4 enrichment, although other factors may also contribute.

Craig, H.; Chou, C. C.; Welhan, J. A.; Stevens, C. M.; Engelkemeir, A.

1988-01-01

65

Post-coring entrapment of modern air in some shallow ice cores collected near the firn-ice transition: evidence from CFC12 measurements in Antarctic firn air and ice cores  

Microsoft Academic Search

In this study, we report measurements of CFC-12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and

M. Aydin; S. A. Montzka; M. O. Battle; M. B. Williams; W. J. de Bruyn; J. H. Butler; K. R. Verhulst; C. Tatum; B. K. Gun; D. A. Plotkin; B. D. Hall; E. S. Saltzman

2010-01-01

66

Ice deformation in the vicinity of the ice-core site at Taylor Dome, Antarctica, and a derived accumulation rate history  

E-print Network

Ice deformation in the vicinity of the ice-core site at Taylor Dome, Antarctica, and a derived@ess.washington.edu ABSTRACT. Knowledge of ice flow and strain rate in the vicinity of the Taylor Dome (East Antarctica) ice-core site enhances interpretation of the paleoclimate information from the ice core. We measured surface ice

Rasmussen, L.A.

67

Greenland ice core evidence of the 79 AD Vesuvius eruption  

NASA Astrophysics Data System (ADS)

Volcanic tephra are indepenent age horizons and can synchronize strata of various paleoclimate records including ice and sediment cores. Before such paleoclimate records can be synchronized, it is essential to first confidently identify individual independent marker horizons. The Greenland Ice Core Project (GRIP) ice core from Central Greenland is often used as a "golden spike" to synchronize Northern Hemisphere paleoclimte records. The Holocene section of the GRIP ice core is dated by multi-parameter annual layer counting, and contains peaks in acidity, SO42- and microparticle concentrations at a depth of 428.4 to 429.6 m, which have not previously been definitively ascribed to a volcanic eruption. Here, we identify tephra particles and determine that volcanic shards extracted from a depth of 429.2 m in the GRIP ice core are likely due to the 79 AD Vesuvius eruption. The chemical compositon of the tephra particles is consistent with the K-phonolitic composition of the Vesuvius juvinile ejecta and differs from the chemical composition of other major eruptions (?VEI 4) between 50-100 AD.

Barbante, C.; Kehrwald, N. M.; Marianelli, P.; Vinther, B. M.; Steffensen, J. P.; Cozzi, G.; Hammer, C. U.; Clausen, H. B.; Siggaard-Andersen, M.-L.

2012-11-01

68

Be climate fingerprints during the Eemian in the NEEM ice core, Greenland  

E-print Network

10 Be climate fingerprints during the Eemian in the NEEM ice core, Greenland Anna Sturevik-Storm1 to stratigraphic disturbances in the ice. The new Greenland deep ice core from the NEEM site (77.456N, 51.066W rilling in North Greenland, through the North Greenland Eemian Ice Coring project (NEEM, 2007

Usoskin, Ilya G.

69

Statistical analysis of the atmospheric sulfate history recorded in Greenland ice cores  

Microsoft Academic Search

The Greenland Ice Sheet contains exceptionally valuable chemical and physical histories that allow reconstruction of paleoclimatic and paleoenvironmental conditions, particularly for the Northern Hemisphere. The chemical analyses of five multi-century long ice cores from the PARCA and Summit collections have yielded a high resolution volcanic aerosol history, which complements volcanic histories extracted from other Greenland ice cores. A detailed ice-core

Lijia Wei

2008-01-01

70

Recent Retreat of Wilkins Ice Shelf Reveals New Insights in Ice Shelf Breakup Mechanisms  

Microsoft Academic Search

The disintegration of various ice shelves on the Antarctic Peninsula has demonstrated their vulnerability and impacts on tributary glaciers. A satellite image of Wilkins Ice Shelf (WIS) from July of 2007 reveals the formation of a large new double fracture, accompanied by numerous small fractures. We show that bending stresses induced by buoyancy forces were responsible for fracture formation. On

Matthias Braun; Angelika Humbert

2009-01-01

71

Seismic anisotropy in ice: numerical modelling, ice core measurements and in-situ observations  

NASA Astrophysics Data System (ADS)

The stress distribution and style of flow in ice produces elastic and rheological anisotropy, which informs ice flow modelling as to how ice masses respond to external changes such as global warming. Here observations of shear wave splitting from three-component icequake seismograms are used to characterise ice anisotropy in the Rutford ice stream, West Antarctica. Over 110 high quality measurements are made on 41 events recorded at five stations temporarily deployed near the ice stream grounding line. The magnitude of the splitting ranges from 2ms to 80ms and suggest a maximum of 6% shear wave splitting. The fast shear wave polarisation direction is roughly perpendicular to the ice flow direction. Motivated by these observations, we consider mechanisms for seismic anisotropy in ice using numerical modelling of the development of crystal preferred orientation of ice and measurement of crystal alignment in an ice core using electron back-scattered diffraction (EBSD). These results suggest transitions in the style of anisotropy both with depth and laterally within an ice stream. Seismic anisotropy is developed with increasing hydrostatic pressure producing a VTI fabric with a vertical alignment of c-axes (so-called cluster fabric). However, convergence in the ice flow and along-flow extension leads to girdles of c-axes (and an HTI fabric). Based on the Rutford shear-wave splitting observations we can rule out a cluster fabric as the sole cause of anisotropy - an HTI component is needed, which may be due extension in the direction of flow forming a girdle fabric or the alignment of cracks or ice-films in the plane perpendicular to the flow direction. Cumulatively, our observations suggest a combination of anisotropy mechanisms are at play in deforming ice sheets. We discuss seismic measurements that can be made to better discriminate between plausible mechanisms for our shear-wave splitting observations and how these different mechanisms may in turn alter ice flow and glacial response to external changes.

Kendall, J. M.; Baird, A. F.; Walker, A.; Wookey, J. M.; Lloyd, G. E.; Stuart, G. W.; Harland, S.; Obbard, R. W.; Smith, A.; Brisbourne, A.

2013-12-01

72

Dual Hemisphere Abrupt Climate Change Analysis from Greenland and Antarctic Ice Cores  

NASA Astrophysics Data System (ADS)

During the last glacial period, Greenland ice cores reveal 25 quasi-cyclical abrupt warmings occurring roughly every ~1-3 ka, known as Dansgaard-Oeschger (D-O) events. In some Antarctica ice cores, these events appear as more symmetrical and dampened out-of-phase signals, known as Antarctic Isotope Maxima (AIM) events. D-O and AIM events occurred concurrently with major reorganizations in the global land-ocean-atmosphere system, but it is unclear in which hemisphere the trigger causing the reorganizations resides. We utilize ice core records from a north-south transect of Greenland (NEEM, NGRIP, and GISP2) and West Antarctica (WAIS Divide) to study the speed, timing and magnitude of D-O and AIM events during the last glaciation with temporal resolution of years in both hemispheres. Our data set includes the first dual hemisphere high-resolution Continuous Flow Analysis (CFA) measurements of ?D, ?18O and deuterium excess from the NEEM and WAIS Divide ice cores, and traditional mass spec measurements from the GISP2 and NGRIP ice cores. Water isotope data will be combined with chemistry and dust data to form a robust temporal image of past climate forcings and climate change.

Jones, T. R.; White, J. W.; Vaughn, B. H.; Popp, T. J.; Steig, E. J.; Markle, B. R.

2012-12-01

73

A first chronology for the NEEM ice core  

NASA Astrophysics Data System (ADS)

A stratigraphy-based chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core has been derived by transferring the annual layer counted Greenland Ice Core Chronology 2005 (GICC05) from the NGRIP core to the NEEM core using 787 match points of mainly volcanic origin identified in the Electrical Conductivity Measurement (ECM) and Dielectrical Profiling (DEP) records. Tephra horizons found in both the NEEM and NGRIP ice cores are used to test the matching based on ECM and DEP and provide additional horizons used for the time scale transfer. A thinning function reflecting the accumulated strain along the core has been determined using a Dansgaard-Johnsen flow model and an isotope-dependent accumulation rate parameterization. Flow parameters are determined from Monte Carlo analysis constrained by the observed depth-age horizons. In order to construct a chronology for the gas phase, the ice age-gas age difference (?age) has been reconstructed using a coupled firn densification-heat diffusion model. Temperature and accumulation inputs to the ?age model, initially derived from the water isotope proxies, have been adjusted to optimize the fit to timing constraints from ?15N of nitrogen and high-resolution methane data during the abrupt onsets of interstadials. The ice and gas chronologies and the corresponding thinning function represent the first chronology for the NEEM core, and based on both the flow and firn modelling results, the accumulation history for the NEEM site has been reconstructed, providing the necessary basis for further analysis of the records from NEEM.

Rasmussen, S. O.; Abbott, P.; Blunier, T.; Bourne, A.; Brook, E.; Buchardt, S. L.; Buizert, C.; Chappellaz, J.; Clausen, H. B.; Cook, E.; Dahl-Jensen, D.; Davies, S.; Guillevic, M.; Kipfstuhl, S.; Laepple, T.; Seierstad, I. K.; Severinghaus, J. P.; Steffensen, J. P.; Stowasser, C.; Svensson, A.; Vallelonga, P.; Vinther, B. M.; Wilhelms, F.; Winstrup, M.

2013-05-01

74

Influence of the Tungurahua eruption on the ice core records of Chimborazo, Ecuador  

NASA Astrophysics Data System (ADS)

The comparison of two shallow ice cores recovered in 1999 and 2000 from the same place on the Chimborazo summit glacier revealed the influence of the coincident Tungurahua volcanic eruption on their stable isotope and chemical records. The surface snow melting and water percolation induced from the ash deposition caused a preferential elution and re-localization of certain ionic species, while the stable isotope records were not affected. Additionally, the comparison of the ionic amount and some selected ion ratios preserved along the ice core column reports under which processes the chemical species are introduced in the snow pack, as snow flake condensation nuclei, by atmospheric scavenging or by dry deposition. This preliminary study is essential for the interpretation of the deep Chimborazo ice core, or for other sites where surrounding volcanic activity influences the glaciochemical records.

Ginot, P.; Schotterer, U.; Stichler, W.; Godoi, M. A.; Francou, B.; Schwikowski, M.

2010-12-01

75

Physical and structural properties of the Greenland Ice Sheet Project 2 ice core: A review  

NASA Astrophysics Data System (ADS)

Substantial data sets have been collected on the relaxation characteristics, density, grain size, c axis fabrics, and ultrasonic velocities of the Greenland Ice Sheet Project 2 (GISP2) core to its contact with bedrock at 3053.4 m. Changes in all these properties paralleled closely those found in cores from Byrd Station, Antarctica, and Dye 3, Greenland. Density increased progressively with depth to a maximum of 0.921 Mg/m3 at about 1400 m, at which depth the ice became bubble free. Below about 2000 m, in situ densities began to decrease in response to increasing ice sheet temperatures. Since drilling, much of the ice core has undergone significant volume expansion (relaxation) due to microcracking and the exsolving of enclathratized gases, especially in the brittle ice zone between 650 and 1400 m. Grain size increased linearly to about 1000 m, thereafter remaining fairly constant until the Younger Dryas event at 1678 m where a twofold to threefold decrease in grain size occurred. These grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical, including a small increase in c axis concentration across the Younger Dryas/Holocene boundary. Increased dust levels in the Wisconsin ice have contributed to the maintenance of a fine-grained texture which, with its strong vertical c axis fabric, persisted to nearly 3000 m. However, beginning at about 2800 m, layers of coarse-grained ice intermixed with the much finer-grained matrix ice are observed. Below 3000 m the ice became very coarse grained. This change, attributed to annealing recrystallization at elevated temperatures in the ice sheet, was accompanied by a dispersed or ring-like redistribution of the c axes about the vertical. Ultrasonic measurements of vertical and horizontal P wave velocities made at 10-m intervals along the entire length of the GISP2 core fully confirmed the results of the crystallo-optical observations. A return to fine-grained ice coincided with the first appearance of brown, silty ice 13 m above bedrock. Bedrock material consisted of 48 cm of till, including boulders and cobbles, overlying gray biotite granite comprising the true bedrock. There is evidence that disturbed structure in the GISP2 cores begins little more than 70% of the way through the ice sheet. This disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10% of the ice sheet.

Gow, A. J.; Meese, D. A.; Alley, R. B.; Fitzpatrick, J. J.; Anandakrishnan, S.; Woods, G. A.; Elder, B. C.

1997-11-01

76

Pre-cometary ice composition from hot core chemistry.  

PubMed

Pre-cometary ice located around star-forming regions contains molecules that are pre-biotic compounds or pre-biotic precursors. Molecular line surveys of hot cores provide information on the composition of the ice since it sublimates near these sites. We have combined a hydrostatic hot core model with a complex network of chemical reactions to calculate the time-dependent abundances of molecules, ions, and radicals. The model considers the interaction between the ice and gas phase. It is applied to the Orion hot core where high-mass star formation occurs, and to the solar-mass binary protostar system IRAS 16293-2422. Our calculations show that at the end of the hot core phase both star-forming sites produce the same prebiotic CN-bearing molecules. However, in the Orion hot core these molecules are formed in larger abundances. A comparison of the calculated values with the abundances derived from the observed line data requires a chemically unprocessed molecular cloud as the initial state of hot core evolution. Thus, it appears that these objects are formed at a much younger cloud stage than previously thought. This implies that the ice phase of the young clouds does not contain CN-bearing molecules in large abundances before the hot core has been formed. The pre-biotic molecules synthesized in hot cores cause a chemical enrichment in the gas phase and in the pre-cometary ice. This enrichment is thought to be an important extraterrestrial aspect of the formation of life on Earth and elsewhere. PMID:16225436

Tornow, Carmen; Kührt, Ekkehard; Motschmann, Uwe

2005-10-01

77

Shifted Ice Cap Unexpectedly Reveals Life  

NSDL National Science Digital Library

Beginning on January 31, 2002, a huge section of the Larsen Ice Shelf in Antarctica broke off and floated away. Scientists used a robotic vehicle to look at what was under the shelf and have discovered huge mats of bacteria as well as clams surrounding a mud volcano vent. This vent is a cold seep, a rare phenomenon (and the first found in the Antarctic) where methane gas bubbles up from under the seabed. The methane gas reacts with seawater to produce sulfide, upon which the bacteria mats feed. The clams are thought to have bacteria in their gills, turning sulfide into food. This audio clip is 3 minutes and 15 seconds in length.

Christopher Joyce

78

The Water Cycle: O-18 and Ice Cores  

NSDL National Science Digital Library

This module introduces students to the use of proxy data as a way to determine past climate. Students will get an overview of proxy sources, with an emphasis on how the ratio of oxygen isotopes in ice cores is used to uncover information about paleoclimates. Students will work with raw ice core oxygen-18 and temperature data from Greenland (1829-1970) using Excel to create charts which will allow them to analyze data and draw conclusions about the connection between oxygen-18 levels and temperature. This module also includes a video, demonstration, formative assessment worksheet and graphing activity.

2011-08-01

79

Continuous flow analysis of total organic carbon in polar ice cores.  

PubMed

Ice cores are a widely used archive to reconstruct past changes of the climate system. This is done by measuring the concentration of substances in the ice and in the air of bubbles enclosed in ice. Some species pertaining to the carbon cycle (e.g., CO2, CH4) are routinely measured. However, information about the organic fraction of the impurities in polar ice is still very limited. Therefore, we developed a new method to determine the content of total organic carbon (TOC) in ice cores using a continuous flow analysis (CFA) system. The method is based on photochemical oxidation of TOC and the electrolytic quantification of the CO2 produced during oxidation. The TOC instrument features a limit of detection of 2 ppbC and a response time of 60 s at a sample flow rate of 0.7 mL/min and a linear measurement range of 2-4000 ppbC. First measurements on the ice core from Talos Dome, Antarctica, reveal TOC concentrations varying between 80 and 360 ppbC in the 20 m section presented. PMID:19031899

Federer, Urs; Kaufmann, Patrik R; Hutterli, Manuel A; Schüpbach, Simon; Stocker, Thomas F

2008-11-01

80

Holocene climate variability from ice core records in the Ross Sea area (East Antarctica)  

NASA Astrophysics Data System (ADS)

Past polar climate variability can be documented at high resolution thanks to ice core records, which have revealed significant Holocene variations in Antarctica. Paleotemperature reconstructions from Antarctic ice cores are mainly based on ?18O (?D) records, a proxy for local, precipitation-weighted atmospheric temperatures. Here, we present a new climate record spanning the past 12,000 years resulting from high resolution (10 cm) stable isotope analyses of the ice core drilled at Talos Dome (TD) in East Antarctica from 2003 to 2007 in the framework of the TALDICE (TALos Dome Ice CorE) project. Talos Dome (72°49'S, 159°11'E; 2315 m; -41°C) is an ice dome on the edge of the East Antarctic plateau, where moisture is mainly advected from the Indian and western Pacific sectors of the Southern Ocean. Pacific moisture arriving at TD has been transported above the Ross Sea, where extensive presence of sea ice also occurs during summer. High-resolution ?18O data have been measured using both IRMS and CRDS techniques on 10 cm samples, leading to a mean time resolution of two years. The long-term trend of the TALDICE ?18O profile shows characteristic features already observed in other ice cores from the East Antarctic plateau. Following the approach of Pol et al. (2011), high frequency climate variability has been investigated using a 3000-year running standard deviation on the de-trended record. The results are compared to the same analysis performed on the nearby Taylor Dome ice core ?18O data, which is the single East Antarctic ice core showing a strong Holocene decreasing trend. Despite these trend differences, both sites share common features regarding changes in variance. We also investigate changes in deuterium excess, a proxy reflecting changes in moisture source conditions. Both deuterium excess records show a two-step increasing trend in the first part of the Holocene. Taylor Dome deuterium excess however depicts an enhanced variability since about 7000 years BP. A wavelet analysis shows a change in isotopic variability patterns at 6-7000 years BP at both sites, suggesting changes in regional climate variability attributed to the opening of the Ross Sea area after the deglaciation. Pol K. et al. (2011). Links between MIS 11 millennial to sub-millennial climate variability and long term trends as revealed by new high resolution EPICA Dome C deuterium data - A comparison with the Holocene. Clim. Past, 7, 437-450.

Braida, Martina; Stenni, Barbara; Masson-Delmotte, Valerie; Pol, Katy; Selmo, Enricomaria; Mezgec, Karin

2014-05-01

81

Where might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records?  

E-print Network

Mountain Range by dating glacial erratics and ice-cored moraines. They concluded that the elevationWhere might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records? S.L. Bradley a, , M. Siddall a , G.A. Milne b , V. Masson-Delmotte c , E. Wolff d

Siddall, Mark

82

Climatic Changes on Tibetan Plateau Based on Ice Core Records  

NASA Astrophysics Data System (ADS)

Climatic changes have been reconstructed for the Tibetan Plateau based on ice core records. The Guliya ice core on the Tibetan Plateau presents climatic changes in the past 100,000 years, thus is comparative with that from Vostok ice core in Antarctica and GISP2 record in Arctic. These three records share an important common feature, i.e., our climate is not stable. It is also evident that the major patterns of climatic changes are similar on the earth. Why does climatic change over the earth follow a same pattern? It might be attributed to solar radiation. We found that the cold periods correspond to low insolation periods, and warm periods to high insolation periods. We found abrupt climatic change in the ice core climatic records, which presented dramatic temperature variation of as much as 10 °C in 50 or 60 years. Our major challenge in the study of both climate and environment is that greenhouse gases such as CO2, CH4 are possibly amplifying global warming, though at what degree remains unclear. One of the ways to understand the role of greenhouse gases is to reconstruct the past greenhouse gases recorded in ice. In 1997, we drilled an ice core from 7100 m a.s.l. in the Himalayas to reconstruct methane record. Based on the record, we found seasonal cycles in methane variation. In particular, the methane concentration is high in summer, suggestiing active methane emission from wet land in summer. Based on the seasonal cycle, we can reconstruct the methane fluctuation history in the past 500 years. The most prominent feature of the methane record in the Himalayan ice core is the abrupt increase since 1850 A.D.. This is closely related to the industrial revolution worldwide. We can also observe sudden decrease in methane concentration during the World War I and World War II. It implies that the industrial revolution has dominated the atmospheric greenhouse gas emission for about 100 years. Besides, the average methane concentration in the Himalayan ice core is higher than that in polar regions, indicating that the low latitude wet land is a major natural source of atmospheric methane.

Yao, T.

2008-12-01

83

Post-coring entrapment of modern air in polar ice cores collected near the firn-ice transition: evidence from CFC12 measurements in Antarctic firn air and shallow ice cores  

Microsoft Academic Search

In this study, we report the first measurements of CFC-12 (CCl2F2) in air extracted from shallow ice cores along with firn air CFC-12 measurements from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice

M. Aydin; S. A. Montzka; M. O. Battle; M. B. Williams; W. de Bruyn; J. H. Butler; K. R. Verhulst; C. Tatum; B. K. Gun; D. A. Plotkin; B. D. Hall; E. S. Saltzman

2010-01-01

84

Post-coring entrapment of modern air in some shallow ice cores collected near the firn-ice transition: evidence from CFC12 measurements in Antarctic firn air and ice cores  

Microsoft Academic Search

In this study, we report measurements of CFC- 12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are con- sistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice

M. Aydin; S. A. Montzka; M. O. Battle; M. B. Williams; W. J. De Bruyn; J. H. Butler; K. R. Verhulst; C. Tatum; B. K. Gun; D. A. Plotkin; B. D. Hall; E. S. Saltzman

2010-01-01

85

An automated approach for annual layer counting in ice cores  

NASA Astrophysics Data System (ADS)

The temporal resolution of some ice cores is sufficient to preserve seasonal information in the ice core record. In such cases, annual layer counting represents one of the most accurate methods to produce a chronology for the core. Yet, manual layer counting is a tedious and sometimes ambiguous job. As reliable layer recognition becomes more difficult, a manual approach increasingly relies on human interpretation of the available data. Thus, much may be gained by an automated and therefore objective approach for annual layer identification in ice cores. We have developed a novel method for automated annual layer counting in ice cores, which relies on Bayesian statistics. It uses algorithms from the statistical framework of Hidden Markov Models (HMM), originally developed for use in machine speech recognition. The strength of this layer detection algorithm lies in the way it is able to imitate the manual procedures for annual layer counting, while being based on purely objective criteria for annual layer identification. With this methodology, it is possible to determine the most likely position of multiple layer boundaries in an entire section of ice core data at once. It provides a probabilistic uncertainty estimate of the resulting layer count, hence ensuring a proper treatment of ambiguous layer boundaries in the data. Furthermore multiple data series can be incorporated to be used at once, hence allowing for a full multi-parameter annual layer counting method similar to a manual approach. In this study, the automated layer counting algorithm has been applied to data from the NGRIP ice core, Greenland. The NGRIP ice core has very high temporal resolution with depth, and hence the potential to be dated by annual layer counting far back in time. In previous studies [Andersen et al., 2006; Svensson et al., 2008], manual layer counting has been carried out back to 60 kyr BP. A comparison between the counted annual layers based on the two approaches will be presented and their differences discussed. Within the estimated uncertainties, the two methodologies agree. This shows the potential for a fully automated annual layer counting method to be operational for data sections where the annual layering is unknown.

Winstrup, M.; Svensson, A.; Rasmussen, S. O.; Winther, O.; Steig, E.; Axelrod, A.

2012-04-01

86

A first chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core  

NASA Astrophysics Data System (ADS)

A stratigraphy-based chronology for the North Greenland Eemian Ice Drilling (NEEM) ice core has been derived by transferring the annual layer counted Greenland Ice Core Chronology 2005 (GICC05) and its model extension (GICC05modelext) from the NGRIP core to the NEEM core using 787 match points of mainly volcanic origin identified in the electrical conductivity measurement (ECM) and dielectrical profiling (DEP) records. Tephra horizons found in both the NEEM and NGRIP ice cores are used to test the matching based on ECM and DEP and provide five additional horizons used for the timescale transfer. A thinning function reflecting the accumulated strain along the core has been determined using a Dansgaard-Johnsen flow model and an isotope-dependent accumulation rate parameterization. Flow parameters are determined from Monte Carlo analysis constrained by the observed depth-age horizons. In order to construct a chronology for the gas phase, the ice age-gas age difference (?age) has been reconstructed using a coupled firn densification-heat diffusion model. Temperature and accumulation inputs to the ?age model, initially derived from the water isotope proxies, have been adjusted to optimize the fit to timing constraints from ?15N of nitrogen and high-resolution methane data during the abrupt onset of Greenland interstadials. The ice and gas chronologies and the corresponding thinning function represent the first chronology for the NEEM core, named GICC05modelext-NEEM-1. Based on both the flow and firn modelling results, the accumulation history for the NEEM site has been reconstructed. Together, the timescale and accumulation reconstruction provide the necessary basis for further analysis of the records from NEEM.

Rasmussen, S. O.; Abbott, P. M.; Blunier, T.; Bourne, A. J.; Brook, E.; Buchardt, S. L.; Buizert, C.; Chappellaz, J.; Clausen, H. B.; Cook, E.; Dahl-Jensen, D.; Davies, S. M.; Guillevic, M.; Kipfstuhl, S.; Laepple, T.; Seierstad, I. K.; Severinghaus, J. P.; Steffensen, J. P.; Stowasser, C.; Svensson, A.; Vallelonga, P.; Vinther, B. M.; Wilhelms, F.; Winstrup, M.

2013-12-01

87

High Resolution Continuous Flow Analysis System for Polar Ice Cores  

NASA Astrophysics Data System (ADS)

In the last decades, Continuous Flow Analysis (CFA) technology for ice core analyses has been developed to reconstruct the past changes of the climate system 1), 2). Compared with traditional analyses of discrete samples, a CFA system offers much faster and higher depth resolution analyses. It also generates a decontaminated sample stream without time-consuming sample processing procedure by using the inner area of an ice-core sample.. The CFA system that we have been developing is currently able to continuously measure stable water isotopes 3) and electrolytic conductivity, as well as to collect discrete samples for the both inner and outer areas with variable depth resolutions. Chemistry analyses4) and methane-gas analysis 5) are planned to be added using the continuous water stream system 5). In order to optimize the resolution of the current system with minimal sample volumes necessary for different analyses, our CFA system typically melts an ice core at 1.6 cm/min. Instead of using a wire position encoder with typical 1mm positioning resolution 6), we decided to use a high-accuracy CCD Laser displacement sensor (LKG-G505, Keyence). At the 1.6 cm/min melt rate, the positioning resolution was increased to 0.27mm. Also, the mixing volume that occurs in our open split debubbler is regulated using its weight. The overflow pumping rate is smoothly PID controlled to maintain the weight as low as possible, while keeping a safety buffer of water to avoid air bubbles downstream. To evaluate the system's depth-resolution, we will present the preliminary data of electrolytic conductivity obtained by melting 12 bags of the North Greenland Eemian Ice Drilling (NEEM) ice core. The samples correspond to different climate intervals (Greenland Stadial 21, 22, Greenland Stadial 5, Greenland Interstadial 5, Greenland Interstadial 7, Greenland Stadial 8). We will present results for the Greenland Stadial -8, whose depths and ages are between 1723.7 and 1724.8 meters, and 35.520 to 35.636 kyr b2k 7), respectively. The results show the conductivity measured upstream and downstream of the debubbler. We will calculate the depth resolution of our system and compare it with earlier studies. 1) Bigler at al, "Optimization of High-Resolution Continuous Flow Analysis For Transient Climate Signals in Ice Cores". Environ. Sci. Technol. 2011, 45, 4483-4489 2) Kaufmann et al, "An Improved Continuous Flow Analysis System for High Resolution Field Measurements on Ice Cores". Environmental Environ. Sci. Technol. 2008, 42, 8044-8050 3) Gkinis, V., T. J. Popp, S. J. Johnsen and T, Blunier, 2010: A continuous stream flash evaporator for the calibration of an IR cavity ring down spectrometer for the isotopic analysis of water. Isotopes in Environmental and Health Studies, 46(4), 463-475. 4) McConnell et al, "Continuous ice-core chemical analyses using inductively coupled plasma mass spectrometry. Environ. Sci. Technol. 2002, 36, 7-11 5) Rhodes et al, "Continuous methane measurements from a late Holocene Greenland ice core : Atmospheric and in-situ signals" Earth and Planetary Science Letters. 2013, 368, 9-19 6) Breton et al, "Quantifying Signal Dispersion in a Hybrid Ice Core Melting System". Environ. Sci. Technol. 2012, 46, 11922-11928 7) Rasmussen et al, " A first chronology for the NEEM ice core". Climate of the Past. 2013, 9, 2967--3013

Dallmayr, Remi; Azuma, Kumiko; Yamada, Hironobu; Kjær, Helle Astrid; Vallelonga, Paul; Azuma, Nobuhiko; Takata, Morimasa

2014-05-01

88

Ice properties revealed by an OPTV log of the full length of the NEEM deep ice borehole, Greenland  

NASA Astrophysics Data System (ADS)

Deployment of a digital optical televiewer (OPTV) in the NEEM deep ice borehole, Greenland, has resulted in an optical log of the entire ~2.5 km hole. The log reveals a variety of ice properties. The presence of regularly-repeated layering, interpreted to be annual, can be seen intermittently to a depth of ~1,600 m, allowing the construction of an age-depth curve. In addition, numerous dust layers are visible throughout the log, many of which are either incomplete or dipping, allowing comparison with, and (for the first time) orientation of, ice core sections. Debris inclusions also appear throughout the log with the basal zone showing a high volume of debris commonly occurring as scattered debris inclusions and large (33-55 cm), dipping (dip 20-36cm, dip direction 148-213°) layers. The log shows large-scale variations in returned luminosity, controlled by corresponding variations in the light transmissivity of the ice bounding the borehole. These include a gradual decrease in luminosity to a depth of ~1,700 m where the ice type changes. Analysis of these changes in sections where annual layering is not clearly visible may be used to complement annual layer counting in the construction of a continuous age-depth curve.

Malone, Terry; Hubbard, Bryn

2013-04-01

89

Ice shelf history inferred from sub-ice shelf sediment cores  

NASA Astrophysics Data System (ADS)

Sediment cores recovered after the break-up of the Larsen-B Ice Shelf show that it had been stable throughout the Holocene (past 11,500 years). This result led to the suggestion that recent ice shelf retreat on the Antarctic Peninsula (AP) was unprecedented, on Holocene timescales, and that we have entered a period of unparalleled climatic change. However, this is not a feature common to other AP ice shelves so far studied. There is evidence that ice shelves on the west (George VI Ice Shelf (GVI-IS)) and northeast of the AP (e.g., Larsen-A/Prince Gustav Ice Shelves) have behaved differently. For example, retreat of the Prince Gustav Channel Ice Shelf during the mid-Holocene (c. 5000-2000 years BP) has been attributed to a well-documented period of atmospheric warming whilst work on GVI-IS demonstrated that ice shelf retreat immediately followed a period of early Holocene warmth detected in ice cores as well as a rapid influx of warmer surface waters over the AP continental shelf. These studies indicate that both atmospheric and oceanic warming are key features of previous retreats of different AP ice shelves during the Holocene, they also highlight an emerging geographical pattern in the history of ice shelf collapse. On the east side of the AP the Larsen B Ice Shelf has been stable throughout the Holocene, whilst ice shelves studied further north (Larsen A Ice Shelf and Prince Gustav Channel Ice Shelf) and on the west of the AP (GVI-IS) have broken up before in the Holocene. It has been suggested that ice shelves on the west coast are pre-disposed to melting (thinning) by warm Circumpolar Deep Water, which is largely absent from such shallow depths in the Weddell gyre. Alternatively, ice shelf thickness has been proposed as a key factor in ice shelf collapse (simply, thicker ice shelves are more stable) and may explain the long-term stability of the Larsen B Ice Shelf which is thought to have remained relatively thick following deglaciation of the ice sheet after the LGM. Here we present a new dataset of sub-ice shelf sediment samples collected during the 2011/12 field season from two sites on the Larsen C Ice Shelf, one in the south and one in the north and one site on southern GVI-IS. Sediments were recovered using a simple hammer assisted gravity corer, which proved to be enormously effective and simple to deploy. In total, 11.60m of sediment was recovered with a maximum penetration of 2.90m. Our new sedimentological datasets will offer a long-term perspective on the Larsen-C Shelf (thinning/evidence for past retreat) and provide new insight into the controls and spatial pattern of past ice shelf retreats on the AP.

Smith, James; Nicholls, Keith; Makinson, Keith; Hodgson, Dominic; Venables, Emily; Anker, Paul; Hillenbrand, Claus-Dieter

2013-04-01

90

Ice Cube Observed PeV Neutrinos from AGN Cores  

E-print Network

I show that the high energy neutrino flux predicted to arise from AGN cores can explain the PeV neutrinos detected by Ice Cube without conflicting with the constraints from the observed extragalactic cosmic ray and gamma-ray backgrounds.

Floyd W. Stecker

2013-08-05

91

Eight glacial cycles from an Antarctic ice core  

Microsoft Academic Search

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine

J. Oerlemans

2004-01-01

92

Dating of two nearby ice cores from the Illimani, Bolivia  

NASA Astrophysics Data System (ADS)

In order to establish a chronology of two nearby ice cores from a glacier at Illimani (6438 m), Bolivia, a broad dating approach is presented here, which in particular makes use of the fast, simple, and nearly nondestructive electrical conductivity method (ECM) that provides a highly resolved record. Thus, ECM is suited for counting annual layers in the ice, especially for ice cores extracted from high-mountain glaciers with a fast layer thinning. Furthermore, ECM can be used for detecting volcanic signals. Annual signals in the ECM record of the Illimani ice core were identified using the 1964 A.D. tritium reference horizon and were counted along 125 m or 90% of the core, representing the time period from 1200 ± 240 A.D. (estimated accumulated error) to 1999 A.D. The resulting age-depth relationship was supported by counting annual peaks in the microparticle record as well as by nuclear dating using the decay of 210Pb. The identification of volcanic signals originating from eruptions such as Pinatubo (1991 A.D.), El Chichón (1982 A.D.), Agung (1963 A.D.), Krakatoa (1883 A.D.), Tambora (1815 A.D.), and the Unknown 1258 A.D. significantly reduced the uncertainty of annual layer counting (ALC) to ±2 years in the vicinity of these events.

Knüsel, S.; Ginot, P.; Schotterer, U.; Schwikowski, M.; GäGgeler, H. W.; Francou, B.; Petit, J. R.; Simões, J. C.; Taupin, J. D.

2003-03-01

93

Earth's Climate History from Glaciers and Ice Cores  

NASA Astrophysics Data System (ADS)

Glaciers serve both as recorders and early indicators of climate change. Over the past 35 years our research team has recovered climatic and environmental histories from ice cores drilled in both Polar Regions and from low to mid-latitude, high-elevation ice fields. Those ice core --derived proxy records extending back 25,000 years have made it possible to compare glacial stage conditions in the Tropics with those in the Polar Regions. High-resolution records of 18°O (in part a temperature proxy) demonstrate that the current warming at high elevations in the mid- to lower latitudes is unprecedented for the last two millennia, although at many sites the early Holocene was warmer than today. Remarkable similarities between changes in the highland and coastal cultures of Peru and regional climate variability, especially precipitation, imply a strong connection between prehistoric human activities and regional climate. Ice cores retrieved from shrinking glaciers around the world confirm their continuous existence for periods ranging from hundreds to thousands of years, suggesting that current climatological conditions in those regions today are different from those under which these ice fields originated and have been sustained. The ongoing widespread melting of high-elevation glaciers and ice caps, particularly in low to middle latitudes, provides strong evidence that a large-scale, pervasive and, in some cases, rapid change in Earth's climate system is underway. Observations of glacier shrinkage during the 20th and 21st century girdle the globe from the South American Andes, the Himalayas, Kilimanjaro (Tanzania, Africa) and glaciers near Puncak Jaya, Indonesia (New Guinea). The history and fate of these ice caps, told through the adventure, beauty and the scientific evidence from some of world's most remote mountain tops, provide a global perspective for contemporary climate.

Thompson, Lonnie

2013-03-01

94

Apollo Rock Reveals Moon Had Molten Core | Universe Additional Resources  

E-print Network

Apollo Rock Reveals Moon Had Molten Core | Universe Today Subscribe Podcast Home Additional Apollo Rock Reveals Moon Had Molten Core Written by Nancy Atkinson If you're new here, you may want to subscribe to my RSS feed. Thanks for visiting! Apollo Rock Reveals Moon Had Molten Core | Universe Today

Weiss, Benjamin P.

95

IceChrono v1: a probabilistic model to compute a common and optimal chronology for several ice cores  

NASA Astrophysics Data System (ADS)

Polar ice cores provides exceptional archives of past environmental conditions. Dating ice and air bubbles/hydrates in ice cores is complicated since it involves different dating methods: modeling of the sedimentation process (accumulation of snow at surface, densification of snow into ice with air trapping and ice flow), use of dated horizons by comparison to other well dated targets (other dated paleo-archives or calculated variations of Earth's orbital parameters), use of dated depth intervals, use of ?depth information (depth shift between synchronous events in the ice matrix and its air/hydrate content), use of stratigraphic links in between ice cores (ice-ice, air-air or mix ice-air links). Here I propose IceChrono v1, a new probabilistic model to combine these different kinds of chronological information to obtain a common and optimized chronology for several ice cores, as well as its confidence interval. It is based on the inversion of three quantities: the surface accumulation rate, the Lock-In Depth (LID) of air bubbles and the vertical thinning function. IceChrono is similar in scope to the Datice model, but has differences on the mathematical, numerical and programming point of views. I apply IceChrono on two dating experiments. The first one is similar to the AICC2012 experiment and I find similar results than Datice within a few centuries, which is a confirmation of both IceChrono and Datice codes. The second experiment involves only the Berkner ice core in Antarctica and I produce the first dating of this ice core. IceChrono v1 is freely available under the GPL v3 open source license.

Parrenin, F.

2014-10-01

96

Biological proxies recorded in a Belukha ice core, Russian Altai  

NASA Astrophysics Data System (ADS)

Different biological proxies such as pollen, cysts, and diatoms were identified and quantified in the upper part of a Belukha ice core from the Russian Altai. The ice core from the Belukha glacier collected in 2001 (4062 m a.s.l., 49°48' N, 86°34' E) was analyzed with annual resolution in the period 1964-2000. Daily data of the frequency of synoptic patterns observed in the Northern Hemisphere along with daily data of precipitation have been used to identify the predominant atmospheric circulations (elementary circulating mechanisms, or ECMs) generating the entry of biological proxies on the glacier surface. It was shown that the high-resolution records of diatoms, cysts, spores, and plant pollen in the Belukha ice core are the biological proxies for the changes in the structure of precipitation in the Altai region since these records can reflect changes in the contribution of different atmospheric circulation to annual or seasonal precipitation. The joint consideration of the transport ability of the biological species and the data of precipitation allowed us to determine the main modern sources of biological proxies deposited at the Belukha glacier. The main sources of diatoms in the Belukha ice core are water bodies of the Aral, Caspian, and northern Kazakhstan basins; coniferous tree pollen originated from the taiga forest of the boreal zone of western Siberia; pollen of deciduous trees and herbs from steppe and forest-steppe vegetation in the northern Altai and eastern Kazakhstan; and cysts and spores of plants were transported from local water bodies and forests. The identified source regions of the biological species are supported by back trajectory analyses and are in good agreement with emission source regions of the trace elements in the ice core.

Papina, T.; Blyakharchuk, T.; Eichler, A.; Malygina, N.; Mitrofanova, E.; Schwikowski, M.

2013-10-01

97

Spatial and Temporal Variability of Volcanic Deposition on Antarctic ice Sheet by Comparing EPICA-Dome C and other Ice-core Sulfate Records  

NASA Astrophysics Data System (ADS)

The Holocene volcanic record, as recorded in the Antarctic ice sheet, has been reconstructed by using the sulfate record of the EDC96 ice core, drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA). The number of volcanic signatures recovered in the EDC96 ice core during the Holocene is 95, with a mean value of 7.9 events per millennium. The distribution of the volcanic frequencies per millennium is here compared with data from other Antarctic ice cores, showing that the last 2000 years were characterized by an enhanced volcanism. The comparison of the volcanic flux profiles in several Antarctic cores reveals a good agreement in the dating of the signatures recorded in the last millennium, but the fit among the volcanic events becomes more and more poor going back in time. Volcanic fluxes show a large variability for isochronous signatures in different Antarctic cores during the last millennium. A flux normalization procedure, obtained by dividing the flux of each event by the Tambora (1815) flux in the same core, was used to compare the intensity of the signatures recorded in different locations. In addition, the standard deviations associated with the ratios of isochronous signatures at different sites show the highest variability in the 1100-1500 A.D. period. This result was interpreted in terms of changes in regional atmospheric transport and linked to climatic changes that occurred during the last millennium.

Castellano, E.; Becagli, S.; Hansson, M.; Petit, J.; Rampino, M. R.; Severi, M.; Steffensen, J.; Traversi, R.; Udisti, R.

2004-05-01

98

Ice Core Evidence to support a Paleo Global Moonsoon  

NASA Astrophysics Data System (ADS)

The notion that many of the monsoon regions are teleconnected over long timescales has gained traction recently. Numerous high resolution climate records from speleothem coral sites, high accumulation rate deep sea sediments, and ice cores tend to support the general notion of a global paleo-monsoon system that appears to be driven by changes in the latitudinal distribution of incident radiation. In particular, the atmospheric CH4 record from ice cores has been shown to follow tropical insolation variations with a strong precession index. High CH4 levels occur during periods of elevated summer insolation presumably related to enhanced tropical emissions from a growth in the areal extent of wetlands and elevated summer temperatures. Here we present a new ultra-high resolution atmospheric CH4 record from the recently completed WAIS divide Antarctic ice core (79S, 112W). Using a new automated CH4 analytical system, we have measured 2632 discrete samples throughout the entire core. The vast majority of the samples were taken from the glacial portion of the core (N=1706) with gas ages between 20 and 68ka, corresponding to roughly one sample every 30 years. Comparisons between our new CH4 record, the isotopic temperature record from the NGRIP ice core in Greenland, and various speleothem d18O records illustrates rather convincingly that all three proxies are responding to the same forcing. The phasing between the abrupt climatic events in all three records is not easily deciphered due to uncertainties in the independent timescales. However, the amazing covariation between these three proxy records is most easily explained by invoking strong teleconnections within the global hydrologic cycle that are paced by changes in incident radiation.

Sowers, T. A.

2013-05-01

99

Coring to the West Antarctic ice sheet bed with a new Deep Ice Sheet Coring (DISC) drill  

NASA Astrophysics Data System (ADS)

As a contribution to IPY 2007-2008, the U.S. ice core research community, supported by the National Science Foundation, plans to core through the West Antarctic ice sheet (WAIS) at the ice-flow divide between the Ross Sea and Amundsen Sea drainage systems. The aim is to develop a unique series of interrelated climatic, ice-dynamic, and biologic records focused on understanding interactions among global earth systems. There will be approximately 15 separate but synergistic projects to analyze the ice and interpret the records. The most significant expected outcome of the WAIS Divide program will be climate records for the last ~40,000 years with an annually resolved chronology (through layer counting), comparable to the records from central Greenland. The data will also extend, at lower temporal resolution, to approximately 100,000 BP. These records will permit comparison of environmental conditions between the northern and southern hemispheres, and study of greenhouse gas concentrations in the paleoatmosphere, with unprecedented detail. To accomplish the coring, an innovative new Deep Ice Sheet Coring (DISC) drill is being built at the University of Wisconsin. The modular design of the bore-hole assembly (sonde) provides high flexibility for producing a 122 mm diameter ice core to depths of 4,000 m with maximum core lengths of 4 m. The DISC drill has a rotating outer barrel that can be used with or without an inner barrel designed to improve core recovery in brittle ice. Separate and independent motors for the drill and pump allow cutter speeds from 0 to 150 rpm and pump rates from 0 to 140 gpm. The high pumping rate should alleviate problems drilling in warm ice near the bed; it also helps make tripping speeds several times faster than with the old US drill. Other innovations include vibration and acoustic sensors for monitoring the drilling process, a segmented core barrel to avoid the formerly persistent problem of bent core barrels, and a high-speed data acquisition system, which allows the real-time monitoring of 30 parameters for operational and scientific use. Data are transmitted from the sonde to the surface through optical fibers contained in the drill cable, which also provides power to the sonde. The entire drilling process utilizes a user-friendly "expert" control system. Quick connectors allow for fast core removal and sonde servicing. The drill tower is a tilting tower utilizing modular truss construction for flexibility and portability. We expect higher quality cores than produced by the old drill, because of a straighter barrel, the independently controlled drill and pump motors, and better monitoring and control of the drilling process. The drill is scheduled for testing in Greenland in the summer of 2006 and for first drilling at the WAIS Divide site late in the 2006-07 austral field season.

Bentley, C. R.; Taylor, K. C.; Shturmakov, A. J.; Mason, W. P.; Emmel, G. R.; Lebar, D. A.

2005-05-01

100

Bipolar ice core records of millennial scale climate variability : an overview of recent findings (Invited)  

NASA Astrophysics Data System (ADS)

Greenland and Antarctic ice cores offer high resolution records of the imprints of millennial scale climate variability on polar climate, aerosol deposition, and atmospheric composition (Wolff et al, QSR, 2010). Improved chronologies and spatial coverage provide new data against which the mechanisms involved in millennial variability and simulated by climate models can be tested. We will first discuss the bipolar sequence of events based on the new AICC2012 chronology, during the last climatic cycle (Veres et al, Clim. Past, 2013; Bazin et al, Clim. Past, 2013). The matrix of ice cores allows to investigate regional differences in the cross-Greenland fingerprints of Dansgaard-Oeschger events (Guillevic et al, Clim. Past, 2013) and the circum-Antarctic signature of their Antarctic Isotopic Maxima counterpart (Buiron et al, QSR, 2012). While Heinrich events have long remained difficult to identify in ice core records, a step change in atmospheric CO2 concentrations has been identified during Heinrich 4 (Ahn et al, GRL, 2012), challenging the gradual CO2 emissions expected from the classical bipolar see-saw explanation. High resolution Antarctic data also reveal centennial to millennial variability during interglacial periods and glacial inceptions which bears similarities with glacial Antarctic Isotopic Maxima, questioning the source and amplifiers of glacial millennial variability. New investigations of the magnitude and recurrence of millennial variability based on multiple long Antarctic ice core records are expected to provide further hints on the interplay between mean climatic states and this millennial variability.

Masson-Delmotte, V.; Landais, A.

2013-12-01

101

Beryllium-10 in the Taylor Dome ice core: Applications to Antarctic glaciology and paleoclimatology  

SciTech Connect

An ice core was drilled at Taylor dome, East Antarctica, reaching to bedrock at 554 meters. Oxygen-isotope measurements reveal climatic fluctuations through the last interglacial period. To facilitate comparison of the Taylor Dome paleoclimate record with geologic data and results from other deep ice cores, several glaciological issues need to be addressed. In particular, accumulation data are necessary as input for numerical ice-flow-models, for determining the flux of chemical constituents from measured concentrations, and for calculation of the offset in age between ice and trapped air in the core. The analysis of cosmogenic beryllium-10 provides a geochemical method for constraining the accumulation-rate history at Taylor Dome. High-resolution measurements were made in shallow firn cores and snow pits to determine the relationship among beryllium-10 concentrations, wet and dry deposition mechanisms, and snow-accumulation rates. Comparison between theoretical and measured variations in deposition over the last 75 years constrains the relationship between beryllium-10 deposition and global average production rates. The results indicate that variations in geomagnetically-modulated production-rate do not strongly influence beryllium-10 deposition at Taylor Dome. Although solar modulation of production rate is important for time scales of years to centuries, snow-accumulation rate is the dominant control on ice-core beryllium-10 concentrations for longer periods. Results show that the Taylor Dome core can be used to provide new constraints on regional climate over the last 130,000 years, complementing the terrestrial and marine geological record from the Dry Valley, Transantarctic Mountains and western Ross Sea.

Steig, E.J.

1996-12-31

102

Toward unified ice core chronologies with the DatIce tool  

NASA Astrophysics Data System (ADS)

Antarctic and Greenland ice cores provide a means to study the phase relationships of climate changes in both hemispheres. They also enable to study the timing between climate, and greenhouse gases or orbital forcings. One key step for such studies is to improve the absolute and relative precisions of ice core age scales (for ice and trapped gas), and beyond that, to try to reach the best consistency between chronologies of paleo records of any kind. The DatIce tool is designed to increase the consistency between pre-existing (also called background) core chronologies. It formulates a variational inverse problem which aims at correcting three key quantities that uniquely define the core age scales: the accumulation rate, the total thinning function, and the close-off depth. For that purpose, it integrates paleo data constraints of many types among which age markers (with for instance documented volcanoes eruptions), and stratigraphic links (with for instance abrupt changes in methane concentration). A cost function is built that enables to calculate new chronologies by making a trade-off between all the constraints (background chronologies and paleo data). The method presented in Lemieux-Dudon et al (2010) has already been applied simultaneously to EPICA EDML and EDC, Vostok and NGRIP. Currently, on going works are conducted at LSCE Saclay and LGGE Grenoble laboratories to construct unified Antarctic chronologies by applying the DatIce tool with new ice cores and new sets of paleo measurements. We here present the DatIce tool, the underlying methodology, and its potential applications. We further show some improvements that have been made recently. We especially adress the issue related to the calibration of the error of pre-existing core chronologies. They are inputs that may have a strong impact on the results. However these uncertainties are uneasy to analyze, since prior chronologies are most of the time assessed on the basis of glaciological models (firn densification and ice flow models) which still face large uncertainties (forcing fields, model parameters, mechanic and physic formulation). For that reason, we chose to calibrate errors by applying consistency diagnostics, a classical method in data assimilation (Desrozier et al, 2009).

Toye Mahamadou Kele, H.; Lemieux-Dudon, B.; Blayo, E.

2012-04-01

103

Glaciochemical records from a Mt. Everest ice core: relationship to atmospheric circulation over Asia  

Microsoft Academic Search

Glaciochemical records recovered from an 80.4m ice core in the East Rongbuk (ER) Glacier (elevation: 6450m) on the northern slope of Mt. Everest provide a reconstructing of past climate for the period AD 1846–1997. Empirical orthogonal function (EOF) analysis on the eight major ion (SO42?, Mg2+, Ca2+, Na+, Cl?, NH4+, K+, and NO3?) time-series reveals inter-species relations and common structure

S. Kang; P. A. Mayewski; D. Qin; Y. Yan; S. Hou; D. Zhang; J. Ren; K. Kruetz

2002-01-01

104

Climatological significance of an ice core net-accumulation record at Mt. Qomolangma (Everest)  

Microsoft Academic Search

An ice core record at Mt. Qomolangma (Everest) since 1954 reveals a sharp decline in net-accumulation in the 1960s, and the\\u000a annual net-accumulation during the 1970s to the beginning of the 1990s is only half of that at the end of the 1950s. The decreased\\u000a net-accumulation is coincident with glacier retreat, which is associated with recent temperature increase in the

Shugui Hou; Dahe Qin; C. P. Wake; P. A. Mayewski; Jiawen Ren; Qinzhao Yang

2000-01-01

105

Critical Fracture Toughness Measurements of an Antarctic Ice Core  

NASA Astrophysics Data System (ADS)

Fracture toughness is a material parameter describing the resistance of a pre-existing defect in a body to further crack extension. The fracture toughness of glacial ice as a function of density is important for modeling efforts aspire to predict calving behavior. In the presented experiments this fracture toughness is measured using an ice core from Kohnen Station, Dronning Maud Land, Antarctica. The samples were sawed in an ice lab at the Alfred Wegener Institute in Bremerhaven at -20°C and had the dimensions of standard test samples with thickness 14 mm, width 28 mm and length 126 mm. The samples originate from a depth of 94.6 m to 96 m. The grain size of the samples was also identified. The grain size was found to be rather uniform. The critical fracture toughness is determined in a four-point bending approach using single edge V-notch beam samples. The initial notch length was around 2.5 mm and was prepared using a drilling machine. The experimental setup was designed at the Institute of Materials Science at Darmstadt. In this setup the force increases linearly, until the maximum force is reached, where the specific sample fractures. This procedure was done in an ice lab with a temperature of -15°C. The equations to calculate the fracture toughness for pure bending are derived from an elastic stress analysis and are given as a standard test method to detect the fracture toughness. An X-ray computer tomography (CT scanner) was used to determine the ice core densities. The tests cover densities from 843 kg m-3 to 871 kg m-3. Thereby the influence of the fracture toughness on the density was analyzed and compared to previous investigations of this material parameter. Finally the dependence of the measured toughness on thickness, width, and position in the core cross-section was investigated.

Christmann, Julia; Müller, Ralf; Webber, Kyle; Isaia, Daniel; Schader, Florian; Kippstuhl, Sepp; Freitag, Johannes; Humbert, Angelika

2014-05-01

106

Temperature reconstruction for the Tibetan Plateau in the past 2ka years from ice cores and human documentary record  

NASA Astrophysics Data System (ADS)

Temperature variation in the past 2000 years on the plateau is reconstructed from Puruogangri ice core d18O, and compared before compositing with other three ice core records as the Dunde ice core (northeast Plateau), Guliya ice core (northwest Plateau) and Dasuopu ice core (south Plateau). The comparison reveals the synchroneity of large-scale climate events, and the composition highlights the warming in the 7th century and 12-13th centuries, and the cold in the 19th century. We searched for historical documentary about Tibet since A.D. 620, extracting record of human activities and social development directly determined or indirectly influenced by climate, and categorizing it into five aspects as basic resources, economic development, military strength, national coherence, and cultural and religious development, to quantify Tibetan development till A.D. 1900. Curve based upon the sum of the five aspects shows Tibetan national strength variation in the past 2000 years. The composited ice core record and Tibetan national strength variation shows consistency, especially during the Songtsen Gampo reign, medieval warm period and the 19th century cold period, thus suggesting the dominative role of climate change in Tibetan civilization before modern ages, as well as proposing the potential application of historical record in paleoclimate reconstruction on the Tibetan Plateau.

Yang, X.

2011-12-01

107

MIF in Volcanic Sulfate: Preliminary Results From Greenland Ice Cores  

NASA Astrophysics Data System (ADS)

Sulfur dioxide from natural and anthropogenic sources is oxidized in the atmosphere to form sulfuric acid aerosols. These aerosols contribute to acid rain, global climate variations, and are a health hazard to humans. Sulfuric acid aerosols in the stratosphere may also affect ozone levels. Volcanic eruptions are a natural source of sulfur dioxide, but depending on the height of the eruption plume, an eruption can be either tropospheric or stratospheric. It has been found in Antarctic ice cores that sulfate from a stratospheric eruption contains sulfur-33 MIF anomaly, while there is no anomaly when sulfur dioxide is oxidized in the troposphere. The unique sulfur MIF signature for stratospheric eruptions could be a valuable tool to identify large, climate-impacting stratospheric eruptions in ice core records. Modeling studies suggest that the main cause of this sulfur MIF is photochemical reactions induced by high-energy UV light below 310 nm. This is consistent with the Antarctica ice core results that the sulfur anomaly is found only in eruptions that emitted sulfur dioxide directly into the stratosphere, where substantial UV radiation is available. In this work, volcanic sulfate from a few volcanic eruptions has been extracted from a number of Greenland ice cores and analyzed for sulfur anomaly. For the first time, MIF anomaly has been found in the sulfate of a known stratospheric eruption (the 1815 Tambora eruption) preserved in the Northern Hemisphere. These latest data show that the pattern of sulfur anomaly evolution during the deposition of volcanic sulfate is similar at both polar regions. This provides further evidence that sulfur MIF anomaly is generated by photochemical reactions and dynamic processes in the global stratosphere.

Lanciki, A. L.; Cole-Dai, J.; Savarino, J.; Thiemens, M.

2008-12-01

108

Spatial and temporal characteristics of the Little Ice Age: The Antarctic ice-core record  

SciTech Connect

Recently, ice core records from both hemispheres, in conjunction with other proxy records (e.g., tree rings, speleothems and corals), have shown that the Little Ice Age (LIA) was spatially extensive, extending to the Antarctic. This paper examines the temporal and spatial characteristics of the dust and delta 18O information from Antarctic ice cores. Substantial differences exist in the records. For example, a 550-year record of delta 18O and dust concentrations from Siple Station, Antarctica suggests that, less dusty conditions prevailed from A.D. 1600 to 1830. Alternately, dust and delta 18O data from South Pole Station indicate that opposite conditions (e.g., cooler and more dusty) were prevalent during the LIA. Three additional Antarctic delta 18O records are integrated with the Siple and South Pole histories for a more comprehensive picture of LIA conditions. The records provide additional support for the LIA temperature opposition between the Antarctic Peninsula region and East Antarctica. In addition, periods of strongest LIA cooling are not temporally synchronous over East Antarctica. These strong regional differences demonstrate that a suite of spatially distributed, high resolution ice core records will be necessary to characterize the LIA in Antarctica.

Mosley-Thompson, E.; Thompson, L.G.

1992-03-01

109

A shallow ice core re-drilled on the Dunde Ice Cap, western China: recent changes in the Asian high mountains  

Microsoft Academic Search

A 51 m deep ice core was re-drilled on the Dunde Ice Cap of western China in 2002, 15 years after the previous ice core drilling in 1987. Dating by seasonal variations in delta18O and particle concentration showed that this 51 m deep ice core covered approximately the last 150 years. The stratigraphy and density showed that more than 90%

Nozomu Takeuchi; Takayuki Miyake; Fumio Nakazawa; Hideki Narita; Koji Fujita; Akiko Sakai; Masayoshi Nakawo; Yoshiyuki Fujii; Keqin Duan; Tandong Yao

2009-01-01

110

A new high altitude paleoclimate record from the first ice core drilled in the eastern European Alps: preliminary results  

NASA Astrophysics Data System (ADS)

Low latitude ice cores offer unique and detailed paleoclimate information from high elevations. Multiple proxies synchronized within the same ice medium offer the possibility to precisely link past climate variations to changes in the surrounding ecosystems and human activities, providing a unique paleo-geographic perspective of the Earth system. However, as most of the accessible low latitude drilling sites have already been exploited and as glaciers are melting worldwide, it is difficult to identify ice fields that contain novel and intact ice core records. We drilled the first ice cores to bedrock in the eastern European Alps during autumn 2011. These cores were extracted from the Alto dell'Ortles glacier (3859 m, South Tyrol, Italy) and their length was up to 75 m. The firn-ice transition was found at ~30 m depth. Below the temperate firn portion, cold ice layers sitting on frozen bedrock still exist and represent remnants from the colder climate before ~1980 AD. Analysis of beta emissions and tritium indicate the well-known 1963 peak (originating from radioactive nuclear fallout) to be at 41 m depth. Together with a measured density profile, this allows us to estimate an average accumulation rate of ~ 850 mm of water equivalent per year during the last 50 years. This confirms this drilling site as one with the lowest snow accumulation rate in the Alps, potentially containing older ice than most of the other Alpine glaciers. Preliminary analyses reveal that the deep and cold ice layers of this glacier preserve clearly distinguishable annual variations in stable isotopes, dust and major ions that can be precisely dated. Alto dell'Ortles is the first low-accumulation alpine drilling site where both winter and summer layers can be clearly identified. Application of a conventional flow model and preliminary annual layer counting suggest that the high altitude records contained in these ice cores may span at least several centuries.

Gabrielli, P.; Barbante, C.; Carturan, L.; Davis, M. E.; Dalla Fontana, G.; Dinale, R.; Dragà, G.; Gabrieli, J.; Kehrwald, N. M.; Mair, V.; Mikhalenko, V.; Oeggl, K.; Schotterer, U.; Seppi, R.; Thompson, L. G.; Tonidandel, D.

2012-12-01

111

An ice core record of net snow accumulation and seasonal snow chemistry at Mt. Waddington, southwest British Columbia, Canada  

NASA Astrophysics Data System (ADS)

We recovered a 141 m ice core from Combatant Col (51.39°N, 125.22°W, 3000 m asl) on the flank of Mt. Waddington, southern Coast Mountains, British Columbia, Canada. Aerosols and other impurities in the ice show unambiguous seasonal variations, allowing for annual dating of the core. Clustered melt layers, originating from summer surface heating, also aid in the dating of the core. Seasonality in water stable isotopes is preserved throughout the record, showing little evidence of diffusion at depth, and serves as an independent verification of the timescale. The annual signal of deuterium excess is especially well preserved. The record of lead deposition in the core agrees with those of ice cores from Mt. Logan and from Greenland, with a sharp drop-off in concentration in the 1970s and early 1980s, further validating the timescales. Despite significant summertime melt at this mid-latitude site, these data collectively reveal a continuous and annually resolved 36-year record of snow accumulation. We derived an accumulation time series from the Mt. Waddington ice core, after correcting for ice flow. Years of anomalously high or low snow accumulation in the core correspond with extremes in precipitation data and geopotential height anomalies from reanalysis data that make physical sense. Specifically, anomalously high accumulation years at Mt. Waddington correlate with years where "Pineapple Express" atmospheric river events bring large amounts of moisture from the tropical Pacific to western North America. The Mt. Waddington accumulation record thus reflects regional-scale climate. These results demonstrate the potential of ice core records from temperate glaciers to provide meaningful paleoclimate information. A longer core to bedrock (250-300 m) at the Mt. Waddington site could yield ice with an age of several hundred to 1000 years.

Neff, P. D.; Steig, E. J.; Clark, D. H.; McConnell, J. R.; Pettit, E. C.; Menounos, B.

2011-12-01

112

Simulation of the dynamical history of the northwestern Greenland ice sheet with a nested model for interpretation of the NEEM ice core record  

NASA Astrophysics Data System (ADS)

Accurate interpretation of proxy climatic records from deep ice cores requires the separation of the climatic signal from non-climatic components (biases). Non-climatic biases arise from elevation changes of the ice sheet, advection of higher upstream ice, and from latitudinal contrasts in isotopical composition of the ice. This separation requires detailed mathematical modeling of the ice-flow history around the drill site. We employ a 3-D nested ice-dynamic model for the reconstruction of the ice flow in the area between the NEEM and the NGRIP drill sites in northwestern Greenland during the last two glacial-interglacial cycles. The model consists of a low-resolution time-dependent shallow-ice-approximation model responsible for the simulation of the ice-sheet evolution and of an embedded diagnostic LMLa-type higher-order model on a 400×400 km domain. The modeled present-day surface velocity field is in good agreement with satellite and GPS measurements. The ice chronology and non-climatic biases are calculated by means of a Lagrangian backtracing procedure. An attempt to reproduce the correct depth of the ?18O maximum in the NEEM ice core gives a mismatch between the modeled chronology and the GICC05/ss09 chronology below ~1200 m depth. Conversely, the GICC05/ss09 chronology locates the ?18O maximum ~150 higher than its actual position in the core. This discrepancy can be explained by stratigraphical disturbances in the lower part of the Greenland ice sheet between NEEM and NGRIP drill sites as revealed by radio echo-sounding. For this reason, we limit model-based estimates of the ice chronology and non-climatic biases for the NEEM ice core to ~87% of relative depth. In terms of time it means that prior to ca. 108 kyr BP the non-climatic biases can only be estimated approximately. Our estimate shows that the measured contrast between the present and the Eemian ?18O must be increased by about 1.5‰.

Rybak, O.; Fürst, J.; Huybrechts, P.

2012-04-01

113

Physical properties, crystalline textures and c-axis fabrics of the Siple Dome (Antarctica) ice core  

Microsoft Academic Search

The quality of the ice core from Siple Dome, West Antarctica, varied widely, with significant fracturing below 400 m. Bubbly ice persisted to the ice-rock interface at 1004 m and constituted the brittle zone. The core has undergone minimal relaxation and has remained brittle and prone to fracturing more than 5 years after it was drilled. This behavior is attributed

Anthony J. Gow; Debra Meese

2007-01-01

114

Multi-proxy fingerprint of Heinrich event 4 in Greenland ice core records  

NASA Astrophysics Data System (ADS)

Glacial climate was characterised by two types of abrupt events. Greenland ice cores record Dansgaard-Oeschger events, marked by abrupt warming in-between cold, stadial phases. Six of these stadials coincide with major Heinrich events (HE), identified from ice-rafted debris (IRD) and large excursions in carbon and oxygen stable isotopic ratios in North Atlantic deep sea sediments, documenting major ice sheet collapse events. This finding has led to the paradigm that glacial cold events are induced by the response of the Atlantic Meridional Overturning Circulation to such massive freshwater inputs, supported by sensitivity studies conducted with climate models of various complexities. This mechanism could however never be confirmed or infirmed because the exact timing of Heinrich events and associated low latitude hydrological cycle changes with respect to Greenland stadials has so far remained elusive. Here, we provide the first multi-proxy fingerprint of H4 within Stadial 9 in Greenland ice cores through ice and air proxies of low latitude climate and water cycle changes. Our new dataset demonstrates that Stadial 9 consists of three phases, characterised first by Greenland cooling during 550 ± 60 years (as shown by markers of Greenland temperature ?18O and ?15N), followed by the fingerprint of Heinrich Event 4 as identified from several proxy records (abrupt decrease in 17O excess and Greenland methane sulfonic acid (MSA), increase in CO2 and methane mixing ratio, heavier ? D-CH4 and ?18Oatm), lasting 740 ± 60 years, itself ending approximately 390 ± 50 years prior to abrupt Greenland warming. Preliminary investigations on GS-13 encompassing H5, based on the ice core proxies ?18O, MSA, ?18Oatm, CH4 and CO2 data also reveal a 3 phase structure, as well as the same sequence of events. The decoupling between stable cold Greenland temperature and low latitude HE imprints provides new targets for benchmarking climate model simulations and testing mechanisms associated with millennial variability.

Guillevic, M.; Bazin, L.; Landais, A.; Stowasser, C.; Masson-Delmotte, V.; Blunier, T.; Eynaud, F.; Falourd, S.; Michel, E.; Minster, B.; Popp, T.; Prié, F.; Vinther, B. M.

2014-03-01

115

Chemical compositions of soluble aerosols around the last termination in the NEEM (Greenland) ice core  

NASA Astrophysics Data System (ADS)

The polar ice cores provide us with reconstruction of past atmospheric aerosols. Atmospheric aerosols such as dust and sea salt in both Arctic and Antarctic ice cores are well discussed by using the proxy of ion concentration/flux. Recently, studies on the chemical compositions of soluble aerosols in the ice cores have been carried out. The chemical compositions and transition of soluble aerosols in the Dome Fuji (Antarctica) has been revealed, however, there are few studies on those of soluble aerosols in Greenland ice cores. Using ice sublimation method #1, we analyzed the chemical compositions of soluble aerosols around the last termination in the NEEM (Greenland) ice core. A total of 43 samples were distributed from NEEM ice core section from 1280 to 1580 m. Soluble aerosols were extracted from the samples by sublimation system. Constituent elements and diameter of each non-volatile particle were measured by scanning electron micro scope (SEM) and energy dispersive X-ray spectroscopy (EDS). By using a method in our recent paper #2, we assumed that particles containing Ca and S are calcium sulfate and particles containing Na and S are sodium sulfate. We divided around the last termination into 4 stages by focusing on the temperature; Holocene, Younger Dryas (YD), Bølling-Allerød (B-A) and Last Glacial Period (LGP), and compared the mass ratio of sulfate and chloride aerosols in each stage. During the cold stage in YD and LGP, calcium sulfate accounted large percentage of soluble aerosols. On the other hand, during the warm stage in Holocene and B-A, sodium sulfate accounted large percentage of soluble aerosols. These relationships between chemical composition and temperature are probably related to non sea salt (nss)-calcium ion concentration. We will discuss the relationship between nss-calcium ion concentration and chemical compositions of soluble aerosols in the presentation. References #1 Iizuka et al., J. Glaciol., 55(191), 58-64, 2009. #2 Iizuka, Y. et al. J. Geophys. Res. 117, D04308, 2012.

Oyabu, Ikumi; Iizuka, Yoshinori; Karlin, Torbjorn; Fukui, Manabu; Hondoh, Takeo; Hansson, Margareta

2013-04-01

116

Reconstruction of interannual Antarctic climate variability from ice cores  

NASA Astrophysics Data System (ADS)

Antarctica represents a significant gap in efforts to achieve reliable reconstructions of interannual to century-scale climate variability. A reliable reconstruction of Antarctic climate on these timescales requires obtaining precisely dated ice cores at high temporal resolution, and with sufficient spatial coverage to adequately capture large-scale climate variability. Ice cores retrieved by the International TransAntarctic Scientific Expedition (ITASE) program are a major step towards this goal. As part of US ITASE, ice cores were obtained from twenty-three sites that are widely distributed across the West Antarctic Ice Sheet, providing continuous records of snow chemistry covering at least 200 years. These cores have been dated at better-than-annual resolution, primarily though the identification of summer peaks in non-sea-salt sulfate (nss-SO{4}). Validation of the timescales was achieved through independent identification of other seasonal variations and marker horizons. Dating precision to within 1-2 months is demonstrated by the occurrence of spring-time nitrate peaks ~3 months before the nss-SO{4} maxima, by the identification of distinct mid-winter warming in some years in both instrumental temperature records and stable isotope ratios, and by the timing of hydrogen peroxide maxima. Dating accuracy to within ±1 one year is demonstrated by volcanic marker horizons, Tambora (1815-1816) being the most prominent. Additional validation of the ±1 year accuracy is provided by the tracing of isochronal layers from site to site using high-frequency ice penetrating radar observations. Reconstruction of climate variability from the ice core data is achieved in three stages. First, satellite-derived anomalies are used to define characteristic patterns of Antarctic temperature variability by conventional EOF analysis; this provides approximately 20 years of monthly data. Using instrumental weather station data (largely from the Antarctic coastline)] as predictor variables, we obtain a reconstruction of the principal components of Antarctic temperatures, with coverage over the entire continent back to 1961. Finally, the resulting 40+ years of spatiotemporal variations in Antarctic temperatures are used as a calibration target for the ice core data. Our current reconstruction uses five stable isotope records from West Antarctica, plus data from Talos Dome and Law Dome. The results show an overall warming of Antarctica since at least the early 1960s, but with cooling in the summer months. Preliminary results also suggest overall warming since the mid 1800s, with significant multi-decadal scale variations. These results, if further validated, will have important implications for the interpretation of recent observed trends in the Southern Annular Mode/Antarctic Oscillation. Major contributors to this work, in addition to this listed authors, include D. Dixon, G. Hamilton, S. Kaspari, A. Kurbatov, P. Mayewski, B. Spikes (University of Maine), M. Albert, S. Arcone, A. Gow, D. Meese (CRREL), C. Shuman (NASA/Goddard), M. Frey (University of Arizona), M. Wumkes (Glacier Data) and T. van Ommen (Antarctic CRC).

Steig, E. J.; Schneider, D. P.

2004-05-01

117

Shallow seafloor glacial features reveal ice streaming and re-advance of the last British Ice Sheet, offshore eastern Scotland and north-eastern England, UK  

NASA Astrophysics Data System (ADS)

Multibeam echosounder datasets have been combined with high-resolution topographic digital surface models (NEXTMap), 2D seismic reflection profiles and shallow cores to reveal strong evidence for onshore-offshore palaeo-ice streaming in eastern Scotland and north-eastern England, UK. The study area includes the catchments of the previously proposed, but only partly mapped, Strathmore, Forth-Tay, and Tweed palaeo-ice streams. Long suspected to terminate offshore, the full flow path and dimensions of this palaeo-ice stream system can now be reconstructed with some certainty using these new data. The ice sheet glacial landsystem is extremely well preserved on the seabed with four main types of subglacial and ice marginal morphology present: 1) highly elongate flow-parallel ridges and grooves strongly suggestive of ice streaming; 2) shorter-elongation flow aligned drumlins and crag and tails indicative of fast-flowing and persistent ice-sheet flow configurations; 3) large arcuate moraine ridges marking frontal stillstands or readvances of the ice sheet margin; and 4) tunnel valleys and deeply incised meltwater channels probably associated with retreat phases of the British Ice Sheet (BIS) following Last Glacial Maximum. The mapped bedforms indicate that fast-flowing corridors (palaeo-ice streams) existed within the last BIS emanating from the central belt of Scotland and northeast England. This new geomorphological evidence shows that these ice streams extended at least 60km offshore and probably accelerated across the transition from bedrock-dominated onshore terrain to till- dominated North Sea Basin. Of particular note is the observation that the Forth-Tay ice stream diverged, forming two glaciologically separate streams running parallel to the present-day coastline. Evidence shows that the southerly arm of this palaeo-ice stream overprinted the Tweed palaeo-ice stream which is contrary to the previously proposed trajectory. Spatial and morphological relationships between the landforms within this glacial landsystem allow inferences about ice sheet history and behaviour to be reconstructed. Most notably, elongate streamlined bedforms superimposed on conspicuous moraine ridges indicate that an extensive advance of palaeo-ice streams took place into the North Sea Basin during overall ice sheet retreat.

Stewart, H. A.; Bradwell, T.

2013-12-01

118

Tropical Ice Core Records: Evidence for Asynchronous Glaciation on Milankovitch Time Scales  

NASA Astrophysics Data System (ADS)

Ice core records are available from selected high altitude, low and mid-latitude ice caps. Comparisons are made among the histories from the Tibetan Plateau, the tropical Andes of South America, and Kilimanjaro in East Africa. Three of these records (Guliya in China, Huascarán in Peru, and Sajama in Bolivia) contain ice deposited during the Last Glacial Stage (LGS). The oxygen isotopic ratios (? 18O) of this ice suggest significant tropical cooling ( ~5° C). Comparison of a global array of cores reveals large-scale similarities as well as important regional differences. The ? 18O shift from Early Holocene to LGM is 5.4‰ on Sajama, 6.3‰ on Huascarán, ~5.3‰ in central Greenland, 6.6‰ at Byrd Station in Antarctica and 5.4‰ at Vostok also in Antarctica. These records all show similar isotopic depletion, reflecting significant global cooling at the Late Glacial Maximum (LGM). As continental ice sheets form only in high latitudes (>40° ), those regions have provided most of the evidence for the pulsing of Quaternary glaciations. In low latitudes, glaciers are restricted to the high mountains and only recently have enough long tropical ice core histories become available to investigate the timing of glaciations there. Long ice cores recovered to bedrock at 7 high-altitude (>5300 m) sites on three continents are investigated for synchroneity of their glaciation histories. The cores from Huascarán in Peru at 9° S and Sajama in Bolivia at 18° S contain continuous records back into the LGS. Both glaciers clearly survived the early Holocene warm period (9 to 6 ka B.P.), but neither contains a long record of glacial stage climate back to the previous interglacial. Rather, the published records from Huascarán and Sajama extend back ~19 kyr and 25 kyr, respectively. Hence, both mountaintops, among the highest in South America, appear to have been ice free during a time considered significantly colder than the Holocene. The records from Dasuopu (28° N) and Puruogangri (34° N) suggest that the ice present today in the Himalayas and central Tibet formed during the time of greatest summer monsoon activity less than 10 kyr B.P. The younger basal ages for the Dasuopu and Puruogangri cores, coupled with the basal ages in the Andean ice caps, suggests an interesting scenario for the formation of permanent ice fields on these high elevation, low latitude mountains. Moving from 18° S to 9° S to 28° - 34° N, the ice fields appear to have successively younger basal ages (e.g., 25, 19 and ~8 kyr B.P.). Specifically, it is proposed that a northward migration of `the age of glacier formation' occurred as the axis of Intertropical Convergence Zone (ITCZ), the major moisture supply, moved northward. At present, the average latitude of the ITCZ is ~5° N. This narrow band of intense upward water vapor flux determines the position of wet/dry climatic zones over a large portion of the tropics; therefore, any long-term change in its mean position could lead to asynchronous glacier formation/starvation. In fact, the precession cycle reached its Southern Hemisphere maximum about 23 kyr B.P. and its Northern Hemisphere maximum about 11 kyr. This is remarkably consistent with the latitudinal pattern of glacier formation proposed here. This precessional migration provides a powerful working hypothesis for investigating tropical climate records. The nature of this relationship has major implications for understanding the processes controlling global climate.

Thompson, L. G.

2001-12-01

119

Optimisation of glaciological parameters for ice core chronology by implementing counted layers between identified depth levels  

NASA Astrophysics Data System (ADS)

A~recent coherent chronology has been built for 4 Antarctic ice cores and the NorthGRIP (NGRIP) Greenland ice core (Antarctic Ice Core Chronology 2012, AICC2012) using a bayesian approach for ice core dating (Datice). When building the AICC2012 chronology, and in order to prevent any confusion with official ice cores chronology, it has been imposed that the AICC2012 chronology for NGRIP should respect exactly the GICC05 chronology based on layer counting. However, such a strong tuning did not satisfy the hypothesis of independence of background parameters and observations for the NGRIP core as required by Datice. We present here the implementation in Datice of a new type of markers that is better suited to constraints deduced from layer counting: the markers of age-difference. Using this type of markers for NGRIP in a 5 cores dating exercise with Datice, we have performed several sensitivity tests and show that the new ice core chronologies obtained with these new markers do not differ by more than 400 years from AICC2012 for Antarctic ice cores and by more than 130 years from GICC05 for NGRIP over the last 60 000 years. With this new parameterization, the accumulation rate and lock-in depth associated with NGRIP are more coherent with independent estimates than those obtained in AICC2012. While these new chronologies should not be used yet as new ice core chronologies, the improved methodology presented here should be considered in the next coherent ice core dating exercise.

Bazin, L.; Lemieux-Dudon, B.; Landais, A.; Guillevic, M.; Kindler, P.; Parrenin, F.; Martinerie, P.

2014-08-01

120

Ice Core Evidence of Regionalization of Holocene Climate in the Circum-Arctic Region  

NASA Astrophysics Data System (ADS)

Comparison of high resolution Holocene glaciochemical ice core records recovered from the Penny Ice Cap, Baffin Island with those from Summit, Greenland reveal distinct differences that can be related to different source regions and/or transport distances. These records can therefore be used to investigate different aspects of the Arctic climate system. For example, the Penny sea-salt sodium records shows an overall decrease during the Little Ice Age due to an increase in sea ice extent in the nearby source regions in Baffin Bay and Davis Strait, while the GISP2 record shows an overall increase in sea-salt sodium related to an intensification of atmospheric circulation during cold periods. A new high resolution five thousand year glaciochemical record has been developed from the Devon Ice Cap in the eastern Canadian Arctic and is compared and contrasted with the Penny and Summit records. In addition to considerable decadal and century scale variability and a decrease in sea-salt concentrations during the Little Ice Age, the Devon and Penny sea-salt records also show a long-term decrease since the mid-Holocene, suggesting a long-term regional increase in sea ice extent. We also investigate dust deposition and recent anthropogenic signals at the three sites. We conclude that glaciochemical records developed from small ice caps throughout the circum-Arctic region provide valuable measures of regional-scale paleoenvironmental change that are critical for our understanding of the climate change in the region over the mid to late Holocene.

Wake, C. P.; Zielinski, G. A.

2001-12-01

121

Recent mechanical weakening of the Arctic sea ice cover as revealed from larger inertial oscillations  

E-print Network

, such expected evolution of the sea ice mechanical response should enhance sea ice fracturing, deformation is however difficult. Internal ice stress mea- surements [Richter-Menge and Elder, 1998; Richter-Menge et alRecent mechanical weakening of the Arctic sea ice cover as revealed from larger inertial

Paris-Sud XI, Université de

122

Statistical analysis of the atmospheric sulfate history recorded in Greenland ice cores  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet contains exceptionally valuable chemical and physical histories that allow reconstruction of paleoclimatic and paleoenvironmental conditions, particularly for the Northern Hemisphere. The chemical analyses of five multi-century long ice cores from the PARCA and Summit collections have yielded a high resolution volcanic aerosol history, which complements volcanic histories extracted from other Greenland ice cores. A detailed ice-core volcanic index has been constructed and provides an improved estimate of the stratospheric sulfate burden which is an important input for models assessing the climatic impacts of volcanic eruptions. Additionally, these cores made it possible to confirm the timing of the arrival of the ash and aerosols from Laki over Greenland. This time-stratigraphic horizon is an essential dating tool for high northern latitude ice cores, including those from Greenland. The spatial characteristics of the sulfate aerosol deposition associated with specific eruptions provide information about the transport processes and the mechanisms dominating local deposition. Examination of the sulfate deposited from two eruptions, the 1783-84 A.D. Laki and the 1815 A.D. Tambora eruptions, reveals that precipitation over the southeastern coastal regions in 1783 may have been suppressed by a regional cooling associated with Laki. This also suggests that Laki aerosols were likely deposited primarily by dry deposition. In contrast, the sulfate deposition from Tambora is more spatially homogeneous, suggesting primarily stratospheric transport and deposition primarily via wet processes. To quantify the impact of geographical factors on the deposition of volcanic sulfate over Greenland, a category explanatory variable analysis was conducted. The results indicate that the location of ice cores relative to north/south or east/west side of ice divide strongly affects EXS deposition, but the elevation of the core site is relatively unimportant. Since 1850, the EXS flux extracted from Greenland ice cores has increased dramatically primarily as a result of anthropogenic sulfur emissions. To quantify this human impact as well as the effect of accumulation, a linear mixed model was applied. The results indicate that for every Gg increase in the annual NH sulfur emissions, there is a 0.0013% increase in the annual non-volcanic excess sulfate flux. The impact of accumulation on sulfate deposition varies over Greenland, likely as a function of the dominant local depositional mechanisms. The linear slopes of accumulation versus sulfate were found to group naturally by the regional accumulation. The differences among the slopes likely reflect the regional strength of the role of dry deposition. Additionally, local sources as well as the stochastic nature of depositional and post-depositional processes may also affect the sulfate flux deposition on the ice sheet. Thus, it will be valuable to reconstruct the histories of other chemical constituents that contribute to the sulfate flux, such as those from marine biota and biomass burning. Also, close examination of the depositional processes, such as continuous observations of the near surface and sulfate concentrations in fresh snow, may provide valuable information to improve our understanding of the relationship between the atmospheric sulfate background concentrations and the non-volcanic EXS flux deposited and preserved in the Greenland Ice Sheet.

Wei, Lijia

123

Fire in Ice: Glacial-Interglacial biomass burning in the NEEM ice core  

NASA Astrophysics Data System (ADS)

Earth is an intrinsically flammable planet. Fire is a key Earth system process with a crucial role in biogeochemical cycles, affecting carbon cycle mechanisms, land-surface properties, atmospheric chemistry, aerosols and human activities. However, human activities may have also altered biomass burning for thousands of years, thus influencing the climate system. We analyse the specific marker levoglucosan to reconstruct past fire events in ice cores. Levoglucosan (1,6-anhydro-?-D-glucopyranose) is an organic compound that can be only released during the pyrolysis of cellulose at temperatures > 300°C. Levoglucosan is a major fire product in the fine fraction of woody vegetation combustion, can be transported over regional to global distances, and is deposited on the Greenland ice sheet. The NEEM, Greenland ice core (77 27'N, 51 3'W, 2454 masl) documents past fire activity changes from the present back to the penultimate interglacial, the Eemian. Here we present a fire activity reconstruction from both North American and Eurasian sources over the last 120,000 yrs based on levoglucosan signatures in the NEEM ice core. Biomass burning significantly increased over the boreal Northern Hemisphere since the last glacial, resulting in a maximum between 1.5 and 3.5 kyr BP yet decreasing from ~2 kyr BP until the present. Major climate parameters alone cannot explain the observed trend and thus it is not possible to rule out the hypothesis of early anthropogenic influences on fire activity. Over millennial timescales, temperature influences Arctic ice sheet extension and vegetation distribution at Northern Hemisphere high latitudes and may have altered the distance between NEEM and available fuel loads. During the last Glacial, the combination of dry and cold climate conditions, together with low boreal insolation and decreased atmospheric carbon dioxide levels may have also limited the production of available biomass. Diminished boreal forest extension and the southward shift of taiga may have reduced the levoglucosan flux over Greenland during the Glacial, thus limiting the biomass burning signatures in the glacial NEEM section. Eemian biomass burning would be expected to be greater than that of the last Glacial due to incresed temperatures and the lack of continental ice sheets. However, NEEM Eemian levoglucosan concentrations are unexpectedly low, and are lower than any other climate period including the last Glacial. We propose that microbial activity in melting ice layers is a potential explanation for the low observed Eemian levoglucosan values.

Zennaro, Piero; Kehrwald, Natalie; Zangrando, Roberta; Gambaro, Andrea; Barbante, Carlo

2014-05-01

124

Recent Increases in Snow Accumulation and Decreases in Sea-Ice Concentration Recorded in a Coastal NW Greenland Ice Core  

NASA Astrophysics Data System (ADS)

A significant rise in summer temperatures over the past several decades has led to widespread retreat of the Greenland Ice Sheet (GIS) margin and surrounding sea ice. Recent observations from geodetic stations and GRACE show that ice mass loss progressed from South Greenland up to Northwest Greenland by 2005 (Khan et al., 2010). Observations from meteorological stations at the U.S. Thule Air Force Base, remote sensing platforms, and climate reanalyses indicate a 3.5C mean annual warming in the Thule region and a 44% decrease in summer (JJAS) sea-ice concentrations in Baffin Bay from 1980-2010. Mean annual precipitation near Thule increased by 12% over this interval, with the majority of the increase occurring in fall (SON). To improve projections of future ice loss and sea-level rise in a warming climate, we are currently developing multi-proxy records (lake sediment cores, ice cores, glacial geologic data, glaciological models) of Holocene climate variability and cryospheric response in NW Greenland, with a focus on past warm periods. As part of our efforts to develop a millennial-length ice core paleoclimate record from the Thule region, we collected and analyzed snow pit samples and short firn cores (up to 20 m) from the coastal region of the GIS (2Barrel site; 76.9317 N, 63.1467 W) and the summit of North Ice Cap (76.938 N, 67.671 W) in 2011 and 2012, respectively. The 2Barrel ice core was sampled using a continuous ice core melting system at Dartmouth, and subsequently analyzed for major anion and trace element concentrations and stable water isotope ratios. Here we show that the 2Barrel ice core spanning 1990-2010 records a 25% increase in mean annual snow accumulation, and is positively correlated (r = 0.52, p<0.01) with ERA-Interim precipitation. The 2Barrel annual sea-salt Na concentration is strongly correlated (r = 0.5-0.8, p<0.05) with summer and fall sea-ice concentrations in northern Baffin Bay near Thule (Figure 1). We hypothesize that the positive correlation represents a significant Na contribution from frost flowers growing on fall frazil ice. Ongoing analyses will evaluate the relationship between MSA concentrations and sea ice extent. Our results show that a deep ice core collected from this dynamic and climate-sensitive region of NW Greenland would produce a valuable record of late Holocene climate and sea ice extent.

Osterberg, E. C.; Thompson, J. T.; Wong, G. J.; Hawley, R. L.; Kelly, M. A.; Lutz, E.; Howley, J.; Ferris, D. G.

2013-12-01

125

Reevaluation of the reconstruction of summer temperatures from melt features in Belukha ice cores, Siberian Altai  

Microsoft Academic Search

In a previous study, past summer temperatures were reconstructed from melt features in the Belukha ice core, Siberian Altai. We evaluated the climatic representativeness of net accumulation and melt features by comparing two Belukha ice cores retrieved at neighboring sites by different institutions and dated by different methods. Melt features in both cores showed a significant correlation, but the trends

Sachiko Okamoto; Koji Fujita; Hideki Narita; Jun Uetake; Nozomu Takeuchi; Takayuki Miyake; Fumio Nakazawa; Vladimir B. Aizen; Stanislav A. Nikitin; Masayoshi Nakawo

2011-01-01

126

Ice cores and SeaRISE: What we do (and don't) know  

NASA Technical Reports Server (NTRS)

Ice core analyses are needed in SeaRISE to learn what the West Antarctic ice sheet and other marine ice sheets were like in the past, what climate changes led to their present states, and how they behave. The major results of interest to SeaRISE from previous ice core analyses in West Antarctic are that the end of the last ice age caused temperature and accumulation rate increases in inland regions, leading to ice sheet thickening followed by thinning to the present.

Alley, Richard B.

1991-01-01

127

Sea salt as an ice core proxy for past sea ice extent: A process-based model study  

NASA Astrophysics Data System (ADS)

Sea ice is a reflection of, and a feedback on, the Earth's climate. We explore here, using a global atmospheric chemistry-transport model, the use of sea salt in Antarctic ice cores to obtain continuous long-term, regionally integrated records of past sea ice extent, synchronous with ice core records of climate. The model includes the production, transport, and deposition of sea salt aerosol from the open ocean and "blowing snow" on sea ice. Under current climate conditions, we find that meteorology, not sea ice extent, is the dominant control on the atmospheric concentration of sea salt reaching coastal and continental Antarctic sites on interannual timescales. However, through a series of idealized sensitivity experiments, we demonstrate that sea salt has potential as a proxy for larger changes in sea ice extent (e.g., glacial-interglacial). Treating much of the sea ice under glacial conditions as a source of salty blowing snow, we demonstrate that the increase in sea ice extent alone (without changing the meteorology) could drive, for instance, a 68% increase in atmospheric sea salt concentration at the site of the Dome C ice core, which exhibits an approximate twofold glacial increase in sea salt flux. We also show how the sensitivity of this potential proxy decreases toward glacial sea ice extent—the basis of an explanation previously proposed for the lag observed between changes in sea salt flux and ?D (an ice core proxy for air temperature) at glacial terminations. The data thereby permit simultaneous changes in sea ice extent and climate.

Levine, J. G.; Yang, X.; Jones, A. E.; Wolff, E. W.

2014-05-01

128

High-resolution acidity in Antarctic ice cores over the past two millennium  

NASA Astrophysics Data System (ADS)

Ice core acidity is a proxy for acid deposition and atmospheric acidity, where pH controls many chemical reactions. It is also a valuable indicator of changes within global geochemical cycles, since it reflects changes in the concentration of any of the contributing acid or base species. A novel technique for continuous, high-depth-resolution measurements of pH and acidity in ice core samples has been developed and applied to the array of ice cores collected during the Norwegian-US Scientific Traverse of East Antarctica. The technique provides both high resolution accuracy and efficiency that cannot be found with the existing techniques of electrical conductivity measurement (ECM) and Gran titration. Comparison of the acidity measurement with the major ion chemistry reveals the individual acid and base species that are contributing to the acidity. Spatial trends in the acidity across East Antarctica and temporal trends over the last ~2000 years are discussed, along with trends in the concentrations of each of the acid and base species. Changes in the concentration of acid and base species are interpreted in the context of global geochemical cycling and climate variability.

Pasteris, D.; McConnell, J. R.; Edwards, R.; Banta, J. R.

2009-12-01

129

Fire in ice: two millennia of boreal forest fire history from the Greenland NEEM ice core  

NASA Astrophysics Data System (ADS)

Biomass burning is a major source of greenhouse gases and influences regional to global climate. Pre-industrial fire-history records from black carbon, charcoal and other proxies provide baseline estimates of biomass burning at local to global scales spanning millennia, and are thus useful to examine the role of fire in the carbon cycle and climate system. Here we use the specific biomarker levoglucosan together with black carbon and ammonium concentrations from the North Greenland Eemian (NEEM) ice cores (77.49° N, 51.2° W; 2480 m a.s.l) over the past 2000 years to infer changes in boreal fire activity. Increases in boreal fire activity over the periods 1000-1300 CE and decreases during 700-900 CE coincide with high-latitude NH temperature changes. Levoglucosan concentrations in the NEEM ice cores peak between 1500 and 1700 CE, and most levoglucosan spikes coincide with the most extensive central and northern Asian droughts of the past millennium. Many of these multi-annual droughts are caused by Asian monsoon failures, thus suggesting a connection between low- and high-latitude climate processes. North America is a primary source of biomass burning aerosols due to its relative proximity to the Greenland Ice Cap. During major fire events, however, isotopic analyses of dust, back trajectories and links with levoglucosan peaks and regional drought reconstructions suggest that Siberia is also an important source of pyrogenic aerosols to Greenland.

Zennaro, P.; Kehrwald, N.; McConnell, J. R.; Schüpbach, S.; Maselli, O. J.; Marlon, J.; Vallelonga, P.; Leuenberger, D.; Zangrando, R.; Spolaor, A.; Borrotti, M.; Barbaro, E.; Gambaro, A.; Barbante, C.

2014-10-01

130

Carbonyl sulfide during the late Holocene from measurements in Antarctic ice cores (Invited)  

NASA Astrophysics Data System (ADS)

Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere with a global average mixing ratio of about 500 parts per trillion (ppt) and a lifetime of 3 years. It is produced by a variety of natural and anthropogenic sources. Oceans are the largest source, emitting COS and precursors carbon disulfide and dimethyl sulfide. The most important removal process of COS is uptake by terrestrial plants during photosynthesis. Interest in the atmospheric variability of COS is primarily due to its potential value as a proxy for changes in gross primary productivity of the land biosphere. Ice core COS records may provide the long term observational basis needed to explore climate driven changes in terrestrial productivity and the resulting impacts, for example, on atmospheric CO2 levels. Previous measurements in a South Pole ice core established the preindustrial COS levels at ~30% of the modern atmosphere and revealed that atmospheric COS increased at an average rate of 1.8 ppt per 100 years over the last 2,000 years [Aydin et al., 2008]. We have since measured COS in 5 additional ice cores from 4 different sites in Antarctica. These measurements display a site-dependent downcore decline in COS, apparently driven by in situ hydrolysis. The reaction is strongly temperature dependent, with the hydrolysis lifetimes (e-folding) ranging from thousands to hundreds of thousands of years. We implement a novel technique that uses ice and heat flow models to predict temperature histories for the ice core samples from different sites and correct for the COS lost to in situ hydrolysis assuming first order kinetics. The 'corrected' COS records confirm the trend observed previously in the COS record from the South Pole ice core. The new, longer record suggests the slow increase in atmospheric COS may have started about 5,000 years ago and continued for 4,500 years until levels stabilized about 500 years ago. Atmospheric CO2 was also rising during this time period, suggesting the atmospheric levels of both trace gases might have changed as a response to a long-term decline in terrestrial productivity during the late Holocene.

Aydin, M.; Fudge, T. J.; Verhulst, K. R.; Waddington, E. D.; Saltzman, E. S.

2013-12-01

131

Expression and Characterization of an Ice Binding Protein from a Bacterium Isolated at a Depth of 3,519 Meters in the Vostok Ice Core, Antarctica  

NASA Astrophysics Data System (ADS)

The cryopreservation of microorganisms in ancient glacial ice is possible if lethal levels of macromolecular damage are not incurred and cellular integrity is not compromised via intracellular ice formation or recrystallization. There are numerous examples of cold-adapted species that prevent or limit ice crystal growth by producing ice-binding proteins (IBP). Previously, a bacterium (isolate 3519-10; Flavobacteriaceae family) recovered from a depth of 3,519 meters below the surface in the Vostok ice core was shown to produce and secrete an IBP that inhibits the recrystallization of ice. To explore the phenotypic advantage that IBPs confer to ice-entrapped cells, experiments were designed to examine the expression of 3519-10's IBP gene and protein at different temperatures, assess the effect of the IBP on bacterial viability in ice, and determine how the IBP influences the physical structure of the ice. Total RNA isolated from aerobic cultures grown at temperatures between 4C to 25C and analyzed by reverse transcription-PCR indicated constitutive expression of the IBP gene. Additionally, SDS-PAGE analysis of 3519-10's extracellular proteins revealed a polypeptide corresponding to the predicted size of the 54 kDa IBP at all temperatures tested. The total extracellular protein fraction was subsequently used in assays with Escherichia coli to examine the effect of the IBP on bacterial survival in warm ice (-5C) and after freeze-thaw cycling. In the presence of 100 ?g mL-1 of extracellular protein from 3519-10, the survival of E. coli was increased by greater than 100-fold; however, the survival of E. coli suspensions containing the same concentration of bovine serum albumin was not significantly different than controls (p<0.05). Microscopic analysis of ice formed in the presence of the IBP indicated that in a mm^2 field of view, there were 5 times as many crystals as in ice formed in the presence of washed 3519-10 cells and non-IBP producing bacteria, and 10 times as many crystals as in particle-free deionized water. Presumably, the effect that the IBP has on bacterial viability and ice crystal structure is due to its activity as an inhibitor of ice recrystallization. Although a myriad of molecular adaptations are likely to play a role in bacterial persistence under frozen conditions, the ability of 3519-10's IBP to control ice crystal structure may provide one explanation for its successful survival deep within the Antarctic ice sheet for thousands of years.

Christner, B. C.; Achberger, A.; Brox, T. I.; Skidmore, M. L.

2011-12-01

132

Caldicellulosiruptor Core and Pangenomes Reveal Determinants for  

SciTech Connect

Extremely thermophilic bacteria of the genus Caldicellulosiruptor utilize carbohydrate components of plant cell walls, including cellulose and hemicellulose, facilitated by a diverse set of glycoside hydrolases (GHs). From a biofuel perspective, this capability is crucial for deconstruction of plant biomass into fermentable sugars. While all species from the genus grow on xylan and acidpretreated switchgrass, growth on crystalline cellulose is variable. The basis for this variability was examined using microbiological, genomic, and proteomic analyses of eight globally diverse Caldicellulosiruptor species. The open Caldicellulosiruptor pangenome (4,009 open reading frames [ORFs]) encodes 106 GHs, representing 43 GH families, but only 26 GHs from 17 families are included in the core (noncellulosic) genome (1,543 ORFs). Differentiating the strongly cellulolytic Caldicellulosiruptor species from the others is a specific genomic locus that encodes multidomain cellulases from GH families 9 and 48, which are associated with cellulose-binding modules. This locus also encodes a novel adhesin associated with type IV pili, which was identified in the exoproteome bound to crystalline cellulose. Taking into account the core genomes, pangenomes, and individual genomes, the ancestral Caldicellulosiruptor was likely cellulolytic and evolved, in some cases, into species that lost the ability to degrade crystalline cellulose while maintaining the capacity to hydrolyze amorphous cellulose and hemicellulose.

Blumer-Schuette, Sara E. [North Carolina State University; Giannone, Richard J [ORNL; Zurawski, Jeffrey V [North Carolina State University; Ozdemir, Inci [North Carolina State University; Ma, Qin [University of Georgia, Athens, GA; Yin, Yanbin [University of Georgia, Athens, GA; Xu, Ying [University of Georgia, Athens, GA; Kataeva, Irena [University of Georgia, Athens, GA; Poole, Farris [University of Georgia, Athens, GA; Adams, Michael W. W. [University of Georgia, Athens, GA; Hamilton-Brehm, Scott [ORNL; Elkins, James G [ORNL; Larimer, Frank W [ORNL; Land, Miriam L [ORNL; Hauser, Loren John [ORNL; Cottingham, Robert W [ORNL; Hettich, Robert {Bob} L [ORNL; Kelly, Robert M [North Carolina State University

2012-01-01

133

Seismic wave propagation in anisotropic ice - Part 1: Elasticity tensor and derived quantities from ice-core properties  

NASA Astrophysics Data System (ADS)

A preferred orientation of the anisotropic ice crystals influences the viscosity of the ice bulk and the dynamic behaviour of glaciers and ice sheets. Knowledge about the distribution of crystal anisotropy is mainly provided by crystal orientation fabric (COF) data from ice cores. However, the developed anisotropic fabric influences not only the flow behaviour of ice but also the propagation of seismic waves. Two effects are important: (i) sudden changes in COF lead to englacial reflections, and (ii) the anisotropic fabric induces an angle dependency on the seismic velocities and, thus, recorded travel times. A framework is presented here to connect COF data from ice cores with the elasticity tensor to determine seismic velocities and reflection coefficients for cone and girdle fabrics. We connect the microscopic anisotropy of the crystals with the macroscopic anisotropy of the ice mass, observable with seismic methods. Elasticity tensors for different fabrics are calculated and used to investigate the influence of the anisotropic ice fabric on seismic velocities and reflection coefficients, englacially as well as for the ice-bed contact. Hence, it is possible to remotely determine the bulk ice anisotropy.

Diez, A.; Eisen, O.

2015-02-01

134

Volcanic forcing of climate over the past 1500 years: An improved ice-core-based index for climate models  

Microsoft Academic Search

This dissertation has investigated one of the most important natural causes of climate change, volcanic eruptions, by developing an ice core-based volcanic forcing index, using 54 ice core records from both the Arctic and Antarctica. The extensive collection of ice core data reduces errors inherent in reconstructions based on a single or small number of cores. This enables us to

Chaochao Gao; Alan Robock; Caspar Ammann

2008-01-01

135

Study of the texture and fabric in the Taylor Dome ice core.  

NASA Astrophysics Data System (ADS)

A fully automated digital instrument for fabric analysis developed by Hansen and Wilen (2000) increases the quality and the quantity of c-axis fabric data from ice cores. The new data permit different mechanical and physical process in the ice cores to be studied statistically. Software tools are applied to analyze the textures and the fabrics in vertical and horizontal samples from Taylor Dome ice cores in the range 0 to 600 meters. The results show that the grain size increases with depth until the Holocene- Wisconsin boundary. The grain size distributions are very similar among all samples in the Taylor Dome ice core and the evolution of grain size in this depth range is consistent with the normal grain growth process. The samples exhibit correlation among nearest neighbors but their values are lower than the correlation in the GISP2 ice core, implying that polygonization and recrystallization are not particularly active, possibly because the temperature of the ice cores is lower than - 40oC (Alley, 1998). Hence, the results suggest that grain growth is the dominant mechanism to change the size of the grains. The samples exhibit a distinct band in the Schmidt Plot indicative of the stress state in the ice. On average, the maximum elongation direction of the crystal grains is oriented perpendicular to the band in the plot. The results from Taylor Dome are compared with other ice cores in order to understand the different mechanical processes in the ice.

di Prinzio, C. L.; Hurley, S.; Wilen, L.; Alley, R.; Matt Spencer, M.; Fitzpatrick, J.

2003-12-01

136

Using Real Data from Ice Cores and Salt Cores to Interpret Paleoclimate  

NSDL National Science Digital Library

To prepare for this exercise, students do background reading (from journal articles selected by instructor) and participate in classroom lectures about various types of qualitative and quantitative paleoclimate data (including rock/sed. type, stable isotopes, and fluid inclusions). Then, they are given the assignment and asked to complete it on their own (or in groups of two). The assignment consists of four paleotemperature curves. One curve is from the Vostok ice core of Antarctica and another represents the GRIP ice core from Greeenland (Jouzel et al., 1987, 1993; Chapellaz et al., 1997). Two halite cores, one from Death Valley and one from Chile, are also represented (Lowenstein et al., 1998, 1999; Hein, 2000). Students answer written questions that ask them to identify coldest and warmest times in the past 150,000 years, that ask them if cores can be correlated, that ask them if they can distinguish local, regional, and global warming and cooling trends. They are also asked how to better resolve paleoclimate data from this time period. The final questions ask students how confident they would feel about using this data to make paleoclimate predictions into the future. After the students have completed in turned in their assignment, we have a class discussion about the exercise, using the questions to guide us. This discussion can be supplemented with predictions from climate models and explanations of different types of paleoclimate data.

Kathy Benison

137

Ice Core Reconnaissance in Siberian Altai for Mid-Latitudes Paleo-Climatic and Environmental Reconstruction  

NASA Astrophysics Data System (ADS)

Investigations in Siberian Altai permits to expand our scope from Tibet, Himalayas, Tien Shan and Pamir to the area located at the northeastern edge of the Central Asia Mountain System. Altai forms a natural barrier to the northern and western air masses and therefore affords an opportunity to develop modern paleo-climate records relating to the westerly jet stream, the Siberian High and Pacific monsoon. Moreover, Altai alpine snowice accumulation areas are appropriative for studying air pollution dynamics at the center of Eurasia, eastward from the major Former USSR air pollutants in Kazakhstan, South Siberia and Ural Mountains. During the last century Altai Mountains became extremely contaminated region by heavy metal mining, metallurgy, nuclear test in Semipalatinsk polygon and Baikonur rocket site. Our first field reconnaissance on the West Belukha snow/firn plateau at the Central Altai was carried out in July 2001. Dispute of the large Alatai Mountains glaciation, the West Belukha Plateau (49o48' N, 86o32'E, 4000-4100 m a.s.l.) is only one suitable snow accumulation site in Altai to recover ice-core paleo-climatic and environmental records that is not affected by meltwater percolation. The objective of our first reconnaissance was to find an appropriate deep drilling site by radio-echo sounding survey, to recover shallow ice-core, to identify the annual snow accumulation rate, major ions, heavy metals, radio nuclides and oxygen isotopes level distribution. During 6 days of work on the Plateau, a 22 m shallow firn/ice core has been recovered by PICO hand auger at elevation 4050 m where the results of radio-echo sounding suggests about 150 m ice thickness. In addition to the firn/ice core recovery, five 2.5 meter snow pits were sampled for physical statigraphy, major ions, trace element, and heavy metals analysis to assess spatial variability of the environmental impact in this region. Four automatic snow gauges were installed near proposed deep ice coring site for year around records. The seasonal accumulation at the drilling site was ranged from 250 to 300 ?? with density of 0.34 - 0.40 g cm-3. The ice-core stratigraphy analysis has shown that accumulation area seems to lie in the cold infiltration-recrystallization zone. Geochemical analysis of the shallow ice core, snow pit samples collecting during the 2001 field research will be discussed along with meteorological and synoptic data collected at the nearest to Belukha Plateau Akkem, (2050 m) and Kara -Tyurek (3600 ?) stations. A preliminary result has revealed that variability of elementary synoptic processes over the region impact on the amount of precipitation. North Atlantic Oscillation and West Pacific Oscillation indices have inverse associations with average amount of precipitation in Siberia where Altai is located. >http://www.icess.ucsb.edu/%7eaizen/aizen.html

Aizen, V.; Aizen, E.; Kreutz, K.; Nikitin, S.; Fujita, K.; Cecil, D.

2001-12-01

138

Bacterial study of Vostok drilling fluid: the tool to make ice core finding confident  

Microsoft Academic Search

Decontamination of Vostok ice core is a critical issue in molecular biology studies. Core surface contains a film of hardly removable 'dirty' drilling fluid representing a mixture of polyhydrocarbons (PHC) including polyaromatic hydrocarbons (PAH) and freon. To make ice microbial finding more confident the original Vostok drilling fluid sampled from different depths (110m - 3600m) was analyzed for bacterial content

I. A. Alekhina; J. R. Petit; V. V. Lukin; S. A. Bulat

2003-01-01

139

A 300 yr ice-core black carbon record from Queen Maud Land, East Antarctic  

Microsoft Academic Search

Black carbon aerosols (BC), from Southern Hemisphere biomass burning and fossil fuel combustion are deposited to the Antarctic ice cap recording a history of BC over the remote Southern Hemisphere. Here we present a 300 yr ice-core BC record from Queen Maud Land, East Antarctica spanning calendar years 1706 to 1997. The 30.3 m core was drilled in 2007 at

M. M. Bisiaux; R. Edwards; J. R. McConnell; H. Anschuetz

2009-01-01

140

Grain size, concentrations, and fluxes of dust particles in ice cores from the Tibetan Plateau  

NASA Astrophysics Data System (ADS)

We provide the grain size, concentrations, and fluxes of dust particles (1-30 um diameter) in several shallow ice cores recovered from the northern (Dunde), western (Muztagata), central (Tanggula), and southern (Dasuopu and Everest) parts of the Tibetan Plateau over the past few decades. Our results reveal that whether the volume distribution fits the log-normal function or not largely depends on the dust concentration and the specific dust-storm event but is independent of physiographical location and season. Only high-concentration samples obey the log-normal distribution in volume and higher concentration leads to a better lognormal fitting. The log-normal distribution, with mode sizes ranging from 3 to 16 um, was largely attributed to the mid-sized particles between 3 and 15 um, which contribute most (>70%) of the total volume. The volume size distribution characteristics for mineral dust particles from ice cores reveal that the coarse particles might be common in the upper-level troposphere over the Tibetan Plateau, and suggest that the lifetime of silt particles in the atmosphere, especially for the large particles, might still be underestimated in current models. Over the past decades, dust concentrations from the northern and western Tibetan Plateau are 2-10 times higher, and from the central Tibetan Plateau is 5 times higher, respectively, than in the southern part. Dust flux in ice cores is highly dependent on mass concentration, but does not necessarily correlate with accumulation. Dust flux in Dunde (about 798 ug cm-2 a-1) is 10 times higher, and that in Muztagata (342 ug cm-2 a-1) is 4 times higher, respectively, than the dust flux in the central Himalayas (77-103 ug cm-2 a-1). The quantitative assessment of dust flux in ice cores accords with the MODIS aerosol optical depth, and both suggest that the general dust transport route is from northwest to southeast over the Tibetan Plateau. Our results reveal the basic physical properties of upper level tropospheric dust over the Tibetan Plateau, which is useful for the study of the climatic effects on climate.

Wu, G.; Yao, T.; Tian, L.; Xu, B.; Zhang, C.; Zhang, X.

2010-12-01

141

Cruise reveals history of Holocene Larsen Ice Shelf  

Microsoft Academic Search

In May 2000 the U.S. Antarctic Research Vessel Nathaniel B. Palmer braved extensive ice and the frigid temperatures of the Northwest Weddell Sea to penetrate the coastal leads along the Nordenskold Coast (Figures 1-3). The scientific objective of this international endeavor was to understand the natural variability of the Larsen Ice Shelf, the largest of several ice shelves along the

Eugene Domack; Amy Leventer; Robert Gilbert; Stefanie Brachfeld; Scott Ishman; Angelo Camerlenghi; Kathleen Gavahan; David Carlson; Athen Barkoukis

2001-01-01

142

Little Ice Age evidence from a south-central North American ice core, U.S.A.  

USGS Publications Warehouse

In the past, ice-core records from mid-latitude glaciers in alpine areas of the continental United States were considered to be poor candidates for paleoclimate records because of the influence of meltwater on isotopic stratigraphy. To evaluate the existence of reliable paleoclimatic records, a 160-m ice core, containing about 250 yr of record was obtained from Upper Fremont Glacier, at an altitude of 4000 m in the Wind River Range of south-central North America. The ??18O (SMOW) profile from the core shows a -0.95??? shift to lighter values in the interval from 101.8 to 150 m below the surface, corresponding to the latter part of the Little Ice Age (LIA). Numerous high-amplitude oscillations in the section of the core from 101.8 to 150 m cannot be explained by site-specific lateral variability and probably reflect increased seasonality or better preservation of annual signals as a result of prolonged cooler temperatures that existed in this alpine setting. An abrupt decrease in these large amplitude oscillations at the 101.8-m depth suggests a sudden termination of this period of lower temperatures which generally coincides with the termination of the LIA. Three common features in the ??18O profiles between Upper Fremont Glacier and the better dated Quelccaya Ice Cap cores indicate a global paleoclimate linkage, further supporting the first documented occurrence of the LIA in an ice-core record from a temperate glacier in south-central North America.

Naftz, D.L.; Klusman, R.W.; Michel, R.L.; Schuster, P.F.; Ready, M.M.; Taylor, H.E.; Yanosky, T.M.; McConnaughey, E.A.

1996-01-01

143

Climate Variability in the Antarctic Peninsula: Insights from the 2010 Bruce Plateau Ice Core  

NASA Astrophysics Data System (ADS)

A new ice core was drilled to bedrock (448.12 m) in 2010 on the Bruce Plateau (BP) ice field (66.03°S; 64.07°W; 1975.5 masl) in the northern Antarctic Peninsula (AP). This is the second ice core, the 2008 James Ross Island (JRI) core was the first, in the AP to reach bedrock and thereby capture the entire record preserved at the drill site. There are just a handful of multi-century long ice core records from the AP, most extending back less than 500 years. The very high annual mass accumulation on the BP (~1.8 m w.e. from 1900 to 2009 CE) allows precise layer counting back to 1400 CE and with temporal constraints by known volcanic eruptions the record is annually resolved back to 1250 CE. The ?18O of individual samples correlates well with temperature observations at Rothera Station (1977 to 2009) which allows calculation of monthly estimates of mass accumulation. These reveal a late winter/ early spring precipitation maximum which imparts a seasonal bias to the climate signals closely linked to wet deposition (e.g., ?18O, various chemical species). The annually resolved records of ?18O and mass accumulation provide proxy-based histories of temperature and precipitation. Comparison with meteorological observations indicates that the BP ?18O record provides a reliable proxy of mean annual air temperature along the west side of the AP. The resulting ?18O-inferred air temperatures for the last 600 years reveal multi-decadal scale variability with warm conditions during some periods exceeding that of the last few decades. Extracting the annual accumulation history is complicated by layer thinning at depth and to reconstruct annual layer thicknesses a Dansgaard-Johnsen model configured for flank flow was applied. The resulting record indicates that over the last 600 years the average annual mass accumulation (precipitation) rises slightly until ~1800 CE (~2.3 m w.e.) after which it declines to a minimum (~1.5 m w.e.) around 1950 CE. Accumulation then rises rapidly to its current maximum value (~2.6 m w.e.), consistent with several other ice core-derived accumulation records in the AP. The Antarctic Peninsula is characterized by a sharp west to east gradient in both atmospheric and oceanographic conditions that create a marked trans-Peninsula contrast in precipitation and to a lesser extent in winter temperature. Therefore the BP and JRI ice cores offer a unique opportunity to examine the history of regional climate conditions, including the Antarctic Dipole that influences interannual climate variability in the AP. For example, ENSO brings warmer anomalies to the western side and colder anomalies to the eastern side of the AP. These regional (west to east) climate differences are further emphasized by the virtual absence of surface melting at the BP site while a recent acceleration of snow melt is recorded in the JRI core.

Mosley-Thompson, E. S.; Goodwin, B. P.; Sierra, R.; Lin, P.; Miller, D.; Thompson, L. G.; Kenny, D. V.

2013-12-01

144

Recent increase in Ba concentrations as recorded in a South Pole ice core  

NASA Astrophysics Data System (ADS)

Here we present high-resolution (?9.4 samples/year) records of Ba concentrations for the period from 1541 to 1999 A.D. obtained from an ice core recovered at the South Pole (US ITASE-02-6) site. We note a significant increase in Ba concentration (by a factor of ?23) since 1980 A.D. The Ba crustal enrichment factor (EFc) values rise from ?3 before 1980 A.D. to ?32 after 1980 A.D. None of the other measured major and trace elements reveal such significant increases in concentrations and EFc values. Comparison with previously reported Antarctic Ba records suggests that significant increases in Ba concentrations at South Pole since 1980 A.D. are most likely caused by local source pollution. The core was collected in close proximity to Amundsen-Scott South Pole Station; therefore activities at the station, such as diesel fuel burning and intense aircraft activity, most likely caused the observed increase in Ba concentrations and its EFc values in the South Pole ice core record.

Korotkikh, Elena V.; Mayewski, Paul A.; Dixon, Daniel; Kurbatov, Andrei V.; Handley, Michael J.

2014-06-01

145

Technique for continuous high-resolution analysis of trace substances in firn and ice cores  

SciTech Connect

The very successful application of a CFA (Continuous flow analysis) system in the GRIP project (Greenland Ice Core Project) for high-resolution ammonium, calcium, hydrogen peroxide, and formaldehyde measurements along a deep ice core led to further development of this analysis technique. The authors included methods for continuous analysis technique. The authors included methods for continuous analysis of sodium, nitrate, sulfate, and electrolytical conductivity, while the existing methods have been improved. The melting device has been optimized to allow the simultaneous analysis of eight components. Furthermore, a new melter was developed for analyzing firn cores. The system has been used in the frame of the European Project for Ice Coring in Antarctica (EPICA) for in-situ analysis of several firn cores from Dronning Maud Land, Antarctica, and for the new ice core drilled at Dome C, Antarctica.

Roethlisberger, R.; Bigler, M.; Hutterli, M.; Sommer, S.; Stauffer, B.; Junghans, H.G.; Wagenbach, D.

2000-01-15

146

The environmental implications for dust in high-alpine snow and ice cores in Asian mountains  

NASA Astrophysics Data System (ADS)

Dust in ice cores is an excellent proxy for atmospheric dust and can reveal long-term dust history, but the relative contribution from high mountains close to Asian deserts, such as the Tibetan Plateau, remains uncertain. Here we show that dust from high-alpine snow collected from Eastern Tien Shan (Tian Shan), Eastern Pamirs (Muztagata), and Qilian Shan displays a different geochemical composition (e.g. rare earth elements, REEs) to adjacent moraines and neighboring surface soils, but is similar in composition to the upwind remote arid regions. For high-alpine snow dust, the local contribution from moraines and surface soils is minor, with the major source being the Asian deserts. The results have revealed that the snow dust is representative of mid- and upper troposphere dust from Asian deserts, and demonstrates a weak event-based discrepancy but a strong concentration-independent uniformity in composition in the long-term, and confirm the regional environmental implication for the paleo-climatic records from ice cores.

Wu, Guangjian; Zhang, Chenglong; Zhang, Xuelei; Xu, Tianli; Yan, Ni; Gao, Shaopeng

2015-01-01

147

Greenland ice cores tell tales on the extent of the Greenland Ice Sheet during the warm climate Eemian period 130.000 - 115.000 years BP.  

NASA Astrophysics Data System (ADS)

A new Greenland ice core has been drilled. The first results from the NEEM ice core are presented and then combined with the results from the other deep ice cores from the Greenland Ice Sheet. All the ice cores drilled though the Greenland ice sheets have been analyzed and the results show that all the ice cores contain ice from the last interglacial, the Eemian, near the base. Is it thus clear that the Greenland Ice Sheet did exist 124.000 years ago in the previous warm climate period where it was more than 5 deg C warmer over Greenland. The difference between the Eemian and the Holocene stable oxygen isotope values have been combined with an ice sheet flow model constrained by the ice core results and internal radio echo sounding layers to estimate the volume of the Greenland Ice Sheet 124.000 years ago. The results show that South Greenland has not been ice free during the Eemian period and that the sea level contribution from the Greenland Ice Sheet has been 2.0 +-0.5 m.

Dahl-Jensen, D.

2012-12-01

148

Comparison of oxygen isotope records from the GISP2 and GRIP Greenland ice cores  

Microsoft Academic Search

RECENT results1,2 from the Greenland Ice-core Project (GRIP) Summit ice core suggest that the climate in Greenland has been remarkably stable during the Holocene, but was extremely unstable for the time period represented by the rest of the core, spanning the last two glaciations and the intervening Eemian inter-glacial. Here we present the complete oxygen isotope record for the Greenland

P. M. Grootes; M. Stuiver; J. W. C. White; S. Johnsen; J. Jouzel

1993-01-01

149

The 1500m South Pole Ice Core: Recovering a 40 Ka Environmental Record  

NASA Technical Reports Server (NTRS)

Supported by the US National Science Foundation, a new 1500 m, approximately 40 ka old ice core will be recovered from South Pole during the 2014/15 and 2015/16 austral summer seasons using the new US Intermediate Depth Drill. The combination of low temperatures, relatively high accumulation rates and low impurity concentrations at South Pole will yield detailed records of ice chemistry and trace atmospheric gases. The South Pole ice core will provide a climate history record of a unique area of the East Antarctic plateau that is partly influenced by weather systems that cross the West Antarctic ice sheet. The ice at South Pole flows at approximately 10m a(exp-1) and the South Pole ice-core site is a significant distance from an ice divide. Therefore, ice recovered at depth originated progressively farther upstream of the coring site. New ground-penetrating radar collected over the drill site location shows no anthropogenic influence over the past approximately 50 years or upper 15 m. Depth-age scale modeling results show consistent and plausible annual-layer thicknesses and accumulation rate histories, indicating that no significant stratigraphic disturbances exist in the upper 1500m near the ice-core drill site.

Casey, Kimberly Ann; Neumann, Thomas Allen; Fudge, T. J.; Neumann, T. A.; Steig, E. J.; Cavitte, M. G. P.; Blankenship, D. D.

2014-01-01

150

Central Asia Climate Change: Altai, Tien Shan And Pamir Ice Cores Contemporary And Paleo-Reconstruction  

NASA Astrophysics Data System (ADS)

There are some speculations that central Asia (CA) glaciers will disappear in the next two decades or so. The existing climate models predict that a substantial warming will occur in continental interiors, such as CA, both in summer and especially in winter. However, the climate instrumental records barely cover the last 100 years in CA and longer period of proxy data could be recovered only from the high elevation snow glacier ice fields. To evaluate the threshold climatic conditions we analyzed the stable isotopes and chemistry series from 170m surface to bedrock ice core recovered from Belukha ice-cap (4120masl, 49°48’N, 86°33’E) in Siberian Altai (SA). The enriched isotope transition with thermal maximum of about -7.3‰ let us expect that Siberian glaciers survived during the Holocene Climate Optimum with much warmer period than modern (?18O mean of -14.25‰). Two periods of cold snap with ?18O mean of -18.49‰ and depleted to -23.7‰ were found in the ice core records prior to occurrence of thermal maximum. One of them was the Younger Dryas (YD) stadial followed by 8.2 kiloyear event, a cold snap episode with mean of -16.23‰ depleted to -19.4‰, relate to the signs of increased droughts. Rapid changes in d-excess records during transition from cold periods to thermal maximum periods could be associated with changes in atmospheric circulation and transferring from external oceanic moisture sources to internal. Based on developed transfer function, we roughly estimated temperature rise during the thermal maximum. We also analyzed the major ions, their relations and deviations from seawater ratios during different periods of the Siberian glaciation development, degradation, checked the dust input, and strong covariance cold snap period stands out as having much higher dust concentration. The surface to bottom SA ice cores did not contain organic material at the glacier bedrock, because during the thermal maximum and other warm interstadial periods (e.g., Hypsithermal and Medival, Bolling-Allerod (BA)) occurred in the SA, it was significantly dryer and maybe cooler than in the Tien Shan (TS) mountains. The 14C analysis of organic soil obtained from the bottom of ice-core recovered from the Grigoriev Ice-cap, at 4700masl, 41°58’N, 77°55’E The Grigoriev ice-core (1200 km to the South from SA) dated of 10640 14C years, close to the onset of the YD cold period. This result may conclude that glaciers did not exist in the BA period in TS at elevations up to 5000masl because it was significantly warmer. Formation of organic soil requires wet and warm conditions during hundreds/thousands of years thus, much warmer and wet climate rather than arid climate caused the TS glacial recession in the BA period that we did not revealed in the SA. We assume that threshold climate changes occurred prior to YD in the TS (warmer and more wet) and in the SA (much warmer, but dry) was not observed in the Pamir. Differences in prevailing atmospheric circulation, maintaining Pamir glaciers from modern and historical climatic thresholds, occurred in central TS and SA and while the Pamir glaciers might be remnants of the LGM.

Aizen, E.; Aizen, V. B.; Takeuchi, N.; Mayewski, P. A.; Grigholm, B. O.; Fujita, K.; Joswiak, D.

2010-12-01

151

A new 122 mm electromechanical drill for deep ice-sheet coring (DISC): 3. Control, electrical and electronics design  

Microsoft Academic Search

The deep ice-sheet coring (DISC) drill developed by Ice Coring and Drilling Services under contract to the US National Science Foundation is an electromechanical drill designed to take 122 mm ice cores to depths of 4000 m. Electronic, electrical and control systems are major aspects of the DISC drill. The drill sonde, the down-hole portion of the drill system, requires

Nicolai B. Mortensen; Paul J. Sendelbach; Alexander J. Shturmakov

2007-01-01

152

Interplanetary Dust Particles in the EPICA Dronning Maud Land Ice Core  

NASA Astrophysics Data System (ADS)

Polar ice cores and marine sediments provide an archive of the influx of extraterrestrial material in the form of interplanetary dust particles. Interplanetary dust particles are marked by extremely high helium concentrations, and this signal can be used to reconstruct a record of the extraterrestrial Helium-3 flux. Determination of accurate extraterrestrial Helium-3 fluxes from marine sediment cores is limited by the uncertainties in the accumulation rates of marine cores. Ice cores, with their very well known age models and accumulation rates, provide a unique opportunity for accurate and independent estimate of the IDP-related Helium-3 flux. Previous measurements of helium isotopes in samples from the Vostok ice core (Brook et al., GRL, 2000) demonstrated the suitability and potential of ice cores and found Helium-3 fluxes similar to results from marine sediments (e.g. Marcantonio et al., Paleoceanography, 2001). A limiting factor for ice core studies so far has been the access to ice core material and, related to this, the size of the available samples. In order to overcome this limitation, we developed a new extraction method based on filtering dust particles from the "waste water" stream from the melt head of a continuous flow analysis for aerosol chemistry (Roethlisberger et al., 2000). This gives access to bulk samples allowing in principle to analyze a continuous record of Helium-3 accretion and to integrate over longer timescales (500a) thereby improving the particle statistics and thus the over-all precision. We report results of helium isotope measurements of a high-resolution record from the EPICA (European Project for Ice Coring in Antarctica) Dronning Maud Land ice core using 4-5kg samples from 400 to 1100 m depth corresponding to the time period from the LGM to the middle Holocene. We also present a pilot study comparing results from the new sampling technique to measurements on real ice samples.

Winckler, G.; Fischer, H.

2005-12-01

153

The Design and Performance of IceCube DeepCore  

NASA Technical Reports Server (NTRS)

The IceCube neutrino observatory in operation at the South Pole, Antarctica, comprises three distinct components: a large buried array for ultrahigh energy neutrino detection, a surface air shower array, and a new buried component called DeepCore. DeepCore was designed to lower the IceCube neutrino energy threshold by over an order of magnitude, to energies as low as about 10 GeV. DeepCore is situated primarily 2100 m below the surface of the icecap at the South Pole, at the bottom center of the existing IceCube array, and began taking pbysics data in May 2010. Its location takes advantage of the exceptionally clear ice at those depths and allows it to use the surrounding IceCube detector as a highly efficient active veto against the principal background of downward-going muons produced in cosmic-ray air showers. DeepCore has a module density roughly five times higher than that of the standard IceCube array, and uses photomultiplier tubes with a new photocathode featuring a quantum efficiency about 35% higher than standard IceCube PMTs. Taken together, these features of DeepCore will increase IceCube's sensitivity to neutrinos from WIMP dark matter annihilations, atmospheric neutrino oscillations, galactic supernova neutrinos, and point sources of neutrinos in the northern and southern skies. In this paper we describe the design and initial performance of DeepCore.

Stamatikos, M.

2012-01-01

154

Properties of grain boundary networks in the NEEM ice core  

NASA Astrophysics Data System (ADS)

The microstructure along the entire NEEM ice core (North-West Greenland, 2537 m length) drilled in 2008-2011 has been analyzed based on a large data set of sublimation groove images. The sublimated surface of vertical section series (six consecutive 6 x 9 cm2 sections in steps of 20 m - in total about 800 images) have been scanned by a Large Area Scanning Macroscope. In these cross-section images 10-15 ?m wide grain boundary grooves and air bubbles appear dark, whereas the inside of grains appears gray (further developed by [1]). A dedicated method of automatic image analysis has recently been developed to extract and parameterize the grain boundary networks of this set [2]. In contrast to the microstructure obtained from thin sections between crossed polarizers in transmitted light, sublimation groove images in reflected light allow to include small grains (equivalent radius of 65 ?m) in the size distribution. It has become possible to extract continuous curvature values of grain boundaries, an estimate of the lower bound of the stored strain energy and the dislocation density. In this contribution we give an overview on profiles of different calculated parameters related to deformation and recrystallization mechanisms. In older glaciological studies the value of the lower cut-off for grain sizes considered for calculation of a mean grain size has been arbitrary. We suggest to compare different definitions of the lower cut-off in the size. With respect to the important question which processes are dominating the grain size evolution in the late- to middle-Holocene, high sensitivity to the definition of this cut-off has been found [3]. Between 250 m and 1000 m depth the curvature of grain boundaries steadily increases and grains become more irregularly shaped which correlates with increasing pressure of air bubbles. In the NEEM ice core the depth of the transition from air bubbles to clathrate hydrates clearly can be separated from the depth where the transition from Holocene to the last glacial takes place. In this way, we found that the shape of grains is highly influenced by air bubbles, whereas the size of the grains is more sensitive to climatic transitions. [1] S. Kipfstuhl et al., 2006, Journal of Glaciology, 52, 398-406 [2] T. Binder et al., 2013, Journal of Microscopy, in review [3] T. Binder et al., 2013, Proceedings, 5th International Conference on Recrystallization and Grain Growth, in press

Binder, Tobias; Weikusat, Ilka; Freitag, Johannes; Svensson, Anders; Wagenbach, Dietmar; Garbe, Christoph; Kipfstuhl, Sepp

2013-04-01

155

Tree ring effects and ice core acidities clarify the volcanic record of the 1st millennium  

NASA Astrophysics Data System (ADS)

Various attempts have been made to link tree-ring and ice-core records, something vital for the understanding of the environmental response to major volcanic eruptions in the past. Here we demonstrate that, by taking note of the spacing between events, it is possible to clarify linkages between tree-response, as witnessed by frost rings in bristlecone pines from Western North America and volcanic acid deposition in ice cores. The results demonstrate that in the 6th and 7th centuries of the current era, and presumably for all earlier dates, the key European ice chronologies from the North Greenland Ice Core Project, namely Dye3, GRIP, NGRIP and NEEM appear to have been wrongly dated by 7 years, with the ice dates being too old. Similar offsets are observed for the Antarctic Law Dome and West Antarctic Ice Sheet Divide WDC06A ice-core chronologies that have been linked to the Greenland record. Importantly, the results clarify which frost rings in bristlecone pines are related to volcanic activity and which may be the result of other causes. In addition, it is possible to show that ice core researchers have used inappropriate linkages to tree effects to justify their chronology.

Baillie, M. G. L.; McAneney, J.

2014-04-01

156

Photolysis of pyruvic acid in ice: Possible relevance to CO and CO2 ice core record anomalies  

NASA Astrophysics Data System (ADS)

The abnormal spikes detected in some CO and CO2 polar ice core records indicate persistent chemical activity in glacial ice. Since CO and CO2 spikes are correlated, and their amplitudes scale with reported CO/CO2 yields for the photolysis of dissolved natural organic matter, a common photochemical source is implicated. Given that sufficient actinic radiation is constantly generated throughout ice by cosmic muons (Colussi and Hoffmann, 2003), it remains to be shown that the photolyses of typical organic contaminants proceed by similar mechanisms in water and ice. Here we report that the photodecarboxylation of pyruvic acid (PA, an ubiquitous ice contaminant) indeed leads to the same products nearly as efficiently in both media. CO2 is promptly released from frozen PA/H2O films upon illumination and continues to evolve after photolysis. By analogy with our studies in water (Guzmán et al., 2006b), we infer that 3PA* reacts with PA in ice producing CH3C(O)C(O)O· and (CH3? (OH)C(O)OH) radicals. The barrierless decarboxylation, CH3C(O)C(O)O· ? CH3C(O)· + CO2, accounts for prompt CO2 emissions down to ˜140 K. Bimolecular radical reactions subsequently ensue in fluid molecular environments, both in water and ice, leading to metastable intermediates that decarboxylate immediately in water, but protractedly in ice. The overall quantum yield of CO2 production in the ? ~313 nm photolysis of PA in ice at 250 K is ˜60% of that in water at 293 K. The in situ photolysis of natural organic matter is, therefore, a plausible explanation of CO and CO2 ice core record anomalies.

GuzmáN, M. I.; Hoffmann, M. R.; Colussi, A. J.

2007-05-01

157

Insights into the nature of radar attenuation through impure ice from broadband dielectric spectroscopy of polar ice cores  

NASA Astrophysics Data System (ADS)

Water ice is ubiquitous in our solar system and is a key target for planetary radar sounders. A primary unknown in many radar surveys is the energy loss due to conduction (attenuation) within the medium being studied. Electrical conduction through ice is controlled by the mobility, concentration and charge of lattice- and water-soluble impurities. Despite extensive study of the physical and chemical characteristics of lab-frozen and naturally forming ices, several questions have remained as to which impurities can increase conduction and the mechanisms by which this conduction occurs. Here we investigate the role of impurities in electrical conduction using broadband dielectric spectroscopy of terrestrial polar ice cores and report several findings of interest to present and future radar investigations of extraterrestrial ice masses. 1. The dielectric strength of meteoric ice-core samples we studied was often much less than that of pure lab-frozen ice, which suggests that the balance of minority and majority charge carriers in naturally forming ice is much closer to being "crossed-over" than previously realized. 2. Samples with high acid concentrations also have high HF conductivities due to an increase in L-defects caused by chloride, i.e., the ionic defects induced by acid in the lattice partition more chloride into the lattice for charge balance. This behavior explains the larger HF conductivity of acids per unit concentration versus that of chloride and their similar activation energies. 3. The DC conductivity of polar ice is much lower than reported previously from in situ Antarctic field surveys, and is best explained if conduction from acids arises from ionic defects in the ice lattice, rather than through liquid networks. Its conductivity is much less than that of single crystal ice because of the low conductivity of grain boundaries through which charges must migrate. 4. In nearly all the meteoric ice-core samples that we studied, we observed two dielectric relaxations. Their temperature dependencies imply that within most meteoric ices, there are essentially two populations of crystals (pure and salty). Previously, it had been suggested that there was only a single dielectric relaxation at an average "salty" value. 5. Ammonium-rich ice-core and lab-frozen samples have different activation energies than chloride-rich samples and increased conductivities, proving that Bjerrum-D defects formed by ammonium in the ice lattice are indeed mobile. This result supports the conclusions of a previous study of the LF properties of a central Greenland ice core, but is at odds with existing theory. The sum of our results further emphasizes the breadth of the dielectric behavior of polar ice and has greatly expanded our knowledge of the complex role of impurities in determining its dielectric properties. These data will be used to improve radar-attenuation models and predictions of the performance of planetary radars when sounding extraterrestrial ice masses, along with the interpretation of observed echoes.

Stillman, D.; MacGregor, J. A.; Grimm, R. E.

2011-12-01

158

Post-coring entrapment of modern air in polar ice: Evidence from CFC12 measurements in Antarctic firn air and shallow ice cores  

Microsoft Academic Search

This study is a comparison of CFC-12 (CCl2F2) measurements in firn air and ice core samples from three Antarctic sites: South Pole, West Antarctic Ice Sheet Divide (79.46°S, 112.13°W), and Siple Dome (81.65°S, 148.81°W). CFC-12 is a synthetic chlorofluorocarbon manufactured during the mid-late 20th century for use as a refrigerant and an aerosol spray propellant. Its atmospheric history is well

K. M. Aydin; S. A. Montzka; M. O. Battle; M. B. Williams; W. J. de Bruyn; J. H. Butler; K. R. Verhulst; C. Tatum; B. K. Gun; D. A. Plotkin; B. D. Hall; E. S. Saltzman

2009-01-01

159

Arcticibacter eurypsychrophilus sp. nov., isolated from ice core.  

PubMed

A Gram-stain-negative, rod-shaped, non-flagellated bacterium, strain MJ9-5(T), was isolated from ice core of Muji Glacier. Colonies of strain MJ9-5(T) were pink, convex and round on R2A agar. Strain MJ9-5(T) grew between -1 to 25 °C with an optimum growth temperature of 10-15 °C. The strain tolerated 0-1.2 % (w/v) NaCl with an optimum of 1 %. The major cellular fatty acids of strain MJ9-5(T) were iso-C15 : 0, summed feature 3 (C16 : 1?6c and/or C1 6 : 1?7c). The G+C content of the genomic DNA was 38.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain MJ9-5(T) was related to members of the genus Arcticibacter. On the basis of the phenotypic characteristics and phylogenetic analysis, a novel species of this genus, Arcticibacter eurypsychrophilus sp. nov., is proposed. The type strain is MJ9-5(T) (?= KCTC 42008(T)?= JCM 19862(T)). PMID:25410942

Shen, Liang; Liu, Yongqin; Gu, Zhengquan; Yao, Tandong; Xu, Baiqing; Wang, Ninglian; Jiao, Nianzhi; Liu, Hongcan; Zhou, Yuguang

2015-02-01

160

Precipitation pathways for five new ice core sites in Ellsworth Land, West Antarctica  

NASA Astrophysics Data System (ADS)

Ice cores provide a wealth of information about past climate and atmospheric circulation however a good understanding of the precipitation patterns, potential source regions and transport pathways is essential in their interpretation. Here we investigate the precipitation pathways for a transect of five new ice cores drilled in the southern Antarctic Peninsula and Ellsworth Land. We utilize in situ observations from automatic weather stations to confirm that the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis data adequately captures annual and sub-annual variability, with evidence of a slight cold bias in the 2 m temperatures. Back trajectory analysis, from the British Atmospheric Data Centre trajectory service, reveals that warm and snowy years are associated with air masses that originate (5 days before reaching the site) from the Amundsen-Bellingshausen Sea, while cold and dry years are associated with air masses from the Antarctic continent. There is a clear seasonal migration in the trajectories at each site, reflecting the east to west migration of the Amundsen Sea Low, known to have a strong influence on climate in this region.

Thomas, Elizabeth R.; Bracegirdle, Thomas J.

2015-04-01

161

Synoptic climatology reconstruction using ice core data from McCall Glacier, Alaska  

NASA Astrophysics Data System (ADS)

Ice cores have often been used to reconstruct paleoclimate based on proxies contained in the cores. Using an ice core from McCall Glacier, in the eastern Brooks Range of Alaska we attempt to determine relationships between ice core proxies and synoptic weather patterns influencing McCall Glacier. The method of self-organizing maps is used to objectively identify the synoptic patterns that influence Alaska. Results presented in this talk will focus on relationships between ice core proxies and synoptic weather patterns for the past 60 years, when reliable atmospheric reanalysis data is available. The focus will be on the warmest and coldest years observed at the McCall Glacier as represented in the NCEP/NCAR Reanalysis data to separate the synoptic circulation patterns most responsible for these years. An additional focus will be a seasonal analysis to determine if the warmest/coldest years are due primarily to temperatures in the cold or warm season. This relationship will then be extrapolated back in time when reanalysis data are not available to understand changes in synoptic patterns that are responsible for features observed in the ice core. The ultimate goal of this project is to relate climate change observed in northeastern Alaska over the past 250 years to the ice core proxies.

Cassano, E.; Cassano, J. J.; McConnell, J. R.; Nolan, M.

2011-12-01

162

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)  

NASA Astrophysics Data System (ADS)

The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75°37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet.

Vallelonga, P.; Christianson, K.; Alley, R. B.; Anandakrishnan, S.; Christian, J. E. M.; Dahl-Jensen, D.; Gkinis, V.; Holme, C.; Jacobel, R. W.; Karlsson, N. B.; Keisling, B. A.; Kipfstuhl, S.; Kjær, H. A.; Kristensen, M. E. L.; Muto, A.; Peters, L. E.; Popp, T.; Riverman, K. L.; Svensson, A. M.; Tibuleac, C.; Vinther, B. M.; Weng, Y.; Winstrup, M.

2014-07-01

163

A Holocene Ice-Core Pollen Record from Ellesmere Island, Nunavut, Canada  

Microsoft Academic Search

A Holocene record of pollen deposition was obtained from an ice core drilled through the Agassiz Ice Cap. The pollen records long-range atmospheric transport to the ice cap. Pollen concentrations were highest in the early Holocene (?15 grains\\/L), decreased in the mid-Holocene (?6 grains\\/L), and increased in the late Holocene (?9 grains\\/L). In the early Holocene, the higher concentration of

Jocelyne C. Bourgeois; Roy M. Koerner; Konrad Gajewski; David A. Fisher

2000-01-01

164

Recent Climate Change as Documented by Ice Core Evidence, Glacier Retreat, and Borehole Temperatures for the Gregoriev Ice Cap, Central Asia  

Microsoft Academic Search

From 1990 to 2003 five shallow ice cores were recovered from the summit of the Gregoriev Ice Cap (41.98° N; 77.916° E; 4609 m asl) in the Tien Shan, Central Asia. The 1990 ice core was analyzed for stable isotopes, microparticle concentrations, major ions and total Beta-activity. The 2001 and 2003 cores were analyzed for stable isotopes and concentrations of

V. N. Mikhalenko; L. G. Thompson; S. S. Kutuzov; S. M. Arkhipov; O. V. Nagornov; P. Lin

2004-01-01

165

Application of pollen analysis to dating of ice cores from lower-latitude glaciers  

Microsoft Academic Search

Ice cores from temperate regions have long been expected to be useful for understanding local climate trends, but a reliable dating method has proved difficult. Here we show that measurements of pollen using samples with only 10 mL of water can give an accurate measure of the annual ice accumulation. In addition, two major types of pollen allow us to

Fumio Nakazawa; Koji Fujita; Jun Uetake; Mika Kohno; Toshiyuki Fujiki; Serguei M. Arkhipov; Takao Kameda; Keisuke Suzuki; Yoshiyuki Fujii

2004-01-01

166

Visual-Stratigraphic Dating of the GISP2 Ice Core: Basis, Reproducibility, and Application  

NASA Technical Reports Server (NTRS)

Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near-surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in "cloudiness" of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century-length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice-age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by "brittle ice" or many other core-quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.

Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.; Spinelli, G.; Elder, B.

1997-01-01

167

Volcanic eruptions recorded in the Illimani ice core (Bolivia): 1918-1998 and Tambora periods  

Microsoft Academic Search

Acid layers of volcanic origin detected in polar snow and ice layers are commonly used to document past volcanic activity on a global scale or, conversely, to date polar ice cores. Although most cataclysmic eruptions of the last two centuries (Pinatubo, El Chichon, Agung, Krakatoa, Cosiguina, Tambora, etc.) occurred in the tropics, cold tropical glaciers have not been used for

M. de Angelis; J. Simões; H. Bonnaveira; J.-D. Taupin; R. J. Delmas

2003-01-01

168

Volcanic eruptions recorded in the Illimani ice core (Bolivia): 1918–1998 and Tambora periods  

Microsoft Academic Search

Acid layers of volcanic origin detected in polar snow and ice layers are commonly used to document past volcanic activity on a global scale or, conversely, to date po- lar ice cores. Although most cataclysmic eruptions of the last two centuries (Pinatubo, El Chichon, Agung, Krakatoa, Cosiguina, Tambora, etc.) occurred in the tropics, cold tropi- cal glaciers have not been

M. De Angelis; J. Sim; H. Bonnaveira; J.-D. Taupin; R. J. Delmas

2003-01-01

169

Volcanic eruptions recorded in the Illimani ice core (Bolivia): 1918Â 1998 and Tambora periods  

Microsoft Academic Search

Acid layers of volcanic origin detected in polar snow and ice layers are commonly used to document past volcanic activity on a global scale or, conversely, to date polar ice cores. Although most cataclysmic eruptions of the last two centuries (Pinatubo, El Chichon, Agung, Krakatoa, Cosiguina, Tambora, etc.) occurred in the tropics, cold tropical glaciers have not been used for

M. de Angelis; J. Simões; H. Bonnaveira; J.-D. Taupin; R. J. Delmas

2003-01-01

170

Static electrical conductivity as an indicator of the sulfate content of polar ice cores  

Microsoft Academic Search

Past atmospheric sulfate content is probably recorded in polar snow and ice. A simple method based on electrical conductivity measurements on ice cores has been proposed recently to easily detect atmospheric sulfate changes caused by violent volcanic eruptions in the past. We show that this method is particularly useful when used in central polar areas but that its application must

M. Maccagnan; J. M. Barnola; R. Delmas; P. Duval

1981-01-01

171

Carbonyl sulfide hydrolysis in polar ice cores and the feasibility of recovering a paleoatmospheric history  

NASA Astrophysics Data System (ADS)

Carbonyl sulfide (COS) is the most abundant sulfur gas in the atmosphere with a current tropospheric mean level of 484 parts per trillion [Montzka et al., 2007]. The major sources of COS are biomass burning, oceanic emissions of COS, and the atmospheric oxidation of precursor sulfur compounds CS2 and DMS emitted from the oceans and soils. The major losses of atmospheric COS are uptake by vegetation and soil. The uptake of COS by terrestrial vegetation provides a link between the global budget of COS and the carbon cycle. We measured COS in polar ice cores from four Antarctic sites: Taylor Dome, Siple Dome, South Pole, and West Antarctic Ice Sheet Divide. The COS samples ranged in age from 0.2-42 ky BP. There are large differences between the measurements from the various sites during overlapping time periods. COS levels in ice from the warmer sites (Siple Dome and WAIS-D) are considerably lower than those from the colder sites (Taylor Dome and South Pole). This result suggests that the difference reflects COS loss to hydrolysis within the ice core bubbles. The kinetics of COS hydrolysis in aqueous solution have been studied, but there is no information about reaction rates in ice. A 1-dimensional heat and ice flow model was used to determine the temperature history for each ice core sample. Assuming a pseudo-first order Arrhenius rate equation for COS loss in ice, we can correct each ice core sample for post-depositional COS loss. The temperature histories are used with an objective minimization algorithm to determine the optimal kinetic parameters for COS loss to obtain agreement between ice core measurements from different sites. The results indicate that the ice core data from all sites can be reconciled with a single COS atmospheric history. The uncertainty in this history becomes large in warm ice at longer time scales. This study suggests that reconstructing paleoatmospheric COS will require measurements in ice cores from sites with cold surface temperatures and large ice sheet thickness.

Nicewonger, M. R.; Aydin, K. M.; Saltzman, E. S.; Fudge, T. J.; Waddington, E. D.; Verhulst, K. R.

2012-12-01

172

Evidence for general instability of past climate from a 250-kyr ice-core record  

Microsoft Academic Search

A detailed stable-isotope record is presented for the full length of the Greenland Ice-core Project Summit ice core covering the last 250,000 years according to a graduated timescale. It appears that the climatic stability of the Holocene is the exception rather than the rule; the last interglacial is also noted to have lasted longer than is implied by the deep-sea

W. Dansgaard; S. J. Johnsen; H. B. Clausen; D. Dahl-Jensen; N. S. Gundestrup; C. U. Hammer; C. S. Hvidberg; J. P. Steffensen; A. E. Sveinbjornsdottir; J. Jouzel; G. Bond

1993-01-01

173

Improved dating of a mid-fifteenth century volcanic marker in ice cores  

NASA Astrophysics Data System (ADS)

Ice cores are dated with a variety of techniques with varying degrees of accuracy and precision. Recent advances in ice core chemical analysis have enabled high resolution (i.e., sub-annual) measurements that allow many ice cores to be dated with the technique of annual layer counting (ALC). Dating by ALC, when applied to appropriate ice cores, provides accuracy and precision that are not possible with other dating techniques. Two recent ice cores, one from Antarctica and one from Greenland and dated with the ALC technique, yield an 800 year (1200-2007 C.E.) bipolar record of explosive volcanic eruptions. The age uncertainties of volcanic signals in the period of 1400-2007 are no more than ×1 year. A prominent volcanic signal in the 15th century appears in the layers of 1459-1461 of both ice cores, indicating an eruption date of 1458. The mid-15th century eruption of the Kuwae volcano in the tropical Pacific is believed to be the most explosive in the last 700 years and to have impacted global climate. Examination of previous ice core records found 1454-1457 to be the date range of the prominent volcanic signal, presumed to be from the Kuwae eruption, in most Antarctica ice cores. This led to the suggestion that 1452 or 1453 is the probable eruption date for Kuwae. The new bipolar record places 1458×1 as the date of the eruption responsible for the prominent volcanic signal. The date of 1458 appears to be an improvement of the previously suggested date (1452 or 1453) for the eruption responsible for the prominent volcanic signal in the mid-15th century. However, the presence of another, less prominent signal at 1453-1454 in the new bipolar record makes it difficult at this point to attribute either signal to the Kuwae eruption, although current evidence suggests the later (1458) eruption is probably that of Kuwae.

Cole-Dai, J.; Ferris, D. G.; McConnell, J. R.; Sigl, M.; Gao, C.

2013-12-01

174

Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition  

Microsoft Academic Search

Previous studies have used small numbers of ice core records of past volcanism to represent hemispheric or global radiative forcing from volcanic stratospheric aerosols. With the largest-ever assembly of volcanic ice core records and state-of-the-art climate model simulations of volcanic deposition, we now have a unique opportunity to investigate the effects of spatial variations on sulfate deposition and on estimates

Chaochao Gao; Luke Oman; Alan Robock; Georgiy L. Stenchikov

2007-01-01

175

SOLUBILITY OF WATER ICE IN METALLIC HYDROGEN: CONSEQUENCES FOR CORE EROSION IN GAS GIANT PLANETS  

SciTech Connect

Using ab initio simulations we investigate whether water ice is stable in the cores of giant planets, or whether it dissolves into the layer of metallic hydrogen above. By Gibbs free energy calculations we find that for pressures between 10 and 40 Mbar the ice-hydrogen interface is thermodynamically unstable at temperatures above approximately 3000 K, far below the temperature of the core-mantle boundaries in Jupiter and Saturn. This implies that the dissolution of core material into the fluid layers of giant planets is thermodynamically favored, and that further modeling of the extent of core erosion is warranted.

Wilson, H. F.; Militzer, B. [Department of Earth and Planetary Science, University of California, Berkeley, CA 94720 (United States)

2012-01-20

176

Bipolar volcanic events in ice cores and the Toba eruption at 74 ka BP (Invited)  

NASA Astrophysics Data System (ADS)

Acidity spikes in Greenland and Antarctic ice cores are applied as tracers of past volcanic activity. Besides providing information on the timing and magnitude of past eruptions, the acidity spikes are also widely used for synchronization of ice cores. All of the deep Greenland ice cores are thus synchronized throughout the last glacial cycle based on volcanic markers. Volcanic matching of ice cores from the two Hemispheres is much more challenging but it is feasible in periods of favourable conditions. Over the last two millennia, where ice cores are precisely dated, some 50 bipolar volcanic events have thus been identified. In order for an eruption to express a bipolar fingerprint it generally needs to be a low latitude eruption with stratospheric injection. Sometimes tephra is associated with the ice-core acidity spikes, but most often there is no tephra present in the ice. As yet, an unknown eruption occurring in 1259 AD is the only event reported to have deposited tephra in both Greenland and Antarctica. During the last glacial period bipolar volcanic matching is very challenging and very little work has been done, but recent high-resolution ice core records have the potential to provide bipolar ice core matching for some periods. Recently, Greenland and Antarctic ice cores have been linked by acidity spikes in the time window of the most recent eruption (the YTT eruption) of the Indonesian Toba volcano that is situated close to equator in Sumatra. Ash from this Toba event is widespread over large areas in Asia and has been identified as far west as Africa, but no corresponding tephra has been found in polar ice cores despite several attempts. The age of the YTT eruption is well constrained by recent Ar-Ar dating to have occurred some 74 ka ago close to the Marine Isotope Stage 4/5 boundary and close to the onset of the cold Greenland Stadial 20 and the corresponding mild Antarctic Isotopic Maxima 19 and 20. Surprisingly, no single outstanding acidity spike can be associated with the YTT Toba eruption in Greenland or Antarctica. Instead, several large bipolar ice cores acidity spikes are occurring within a couple of centuries at the time of the YTT eruption. To complicate matters, the intensity of those acidity spikes varies greatly from ice core to ice core. At this point, it is therefore impossible to relate the Toba eruption to a single event in the ice cores. Probably there have been several large low-latitude eruptions occurring close to the time of the YTT or the Toba volcano itself had multiple large eruptions within centuries. Bipolar volcanic matching allows for an estimation of the climatic impact of eruptions on a global scale. In the case of Toba, there must have been a global cooling following the enormous eruption, but unfortunately at this depth the resolution of the ice core temperature proxies does not allow for an identification of short term events (<100 yr). A significant warming event in Antarctica following the period associated with the YTT shows, however, that Toba did not initiate a long-term global cooling (>100 yr). At the time of YTT it appears that the inter-hemispheric climate variability is governed by the bipolar seesaw pattern that is active throughout most of the last glacial period. Still, it is intriguing that Toba occurs right at the time when Greenland and much of the northern Hemisphere enters its most extreme cold stadial of the last glacial period.

Svensson, A.

2013-12-01

177

Little ice age evidence from a south-central North American ice core, U.S.A.  

SciTech Connect

In the past, ice-core records from mid-latitude glaciers in alpine areas of the continental United States were considered to be poor candidates for paleoclimate records because of the influence of meltwater on isotopic stratigraphy. To evaluate the existence of reliable paleoclimatic records, a 160-m ice core, containing about 250 yr of record was obtained from Upper Fremont Glacier, at an altitude of 4000 m in the Wind River Range of south-central North America. The {gamma}{sup 18}O (SMOW) profile from the core shows a -0.95{per_thousand} shift to lighter values in the interval from 101.8 to 150 m below the surface, corresponding to the latter part of the Little Ice Age (LIA). Numerous high-amplitude oscillations in the section of the core from 101.8 to 150 m cannot be explained by site-specific lateral variability and probably reflect increased seasonality or better preservation of annual signals as a result of prolonged cooler temperatures that existed in this alpine setting. An abrupt decrease in these large amplitude oscillations at the 101.8-m depth suggests a sudden termination of this period of lower temperatures which generally coincides with the termination of the LIA. Three common features in the {gamma}{sup 18}O profiles between Upper Fremont Glacier and the better dated Quelccaya Ice Cap cores indicate a global paleoclimate linkage, further supporting the first documented occurrence of the LIA in an ice-core record from a temperate glacier in south-central North America.

Naftz, D.L. [Geological Survey, Salt Lake City, UT (United States); Klusman, R.W. [Colorado School of Mines, Golden, CO (United States); Michel, R.L. [Geological Survey, Menlo Park, CA (United States)] [and others

1996-02-01

178

Methyl bromide in pre-industrial air: measurements from an Antarctic ice core  

NASA Astrophysics Data System (ADS)

This paper presents the first ice core measurements of methyl bromide (CH3Br). Samples from a shallow Antarctic ice core (Siple Dome, West Antarctica), with estimated gas dates ranging from 1671 to 1942, were analyzed using GC/MS. The ice core samples gave a mean CH3Br mixing ratio of 5.8 ppt, considerably lower than the modern southern hemispheric mean CH3Br level of 7.9 ppt. These results extend the existing historical record derived from air and Antarctic firn air to about 350 years. Model simulations illustrate that the ice core results are consistent with current estimates of the impact of anthropogenic activity (fumigation, combustion, and biomass burning) on the atmospheric CH3Br burden. A preindustrial scenario assuming no fumigation, no combustion, and a 75 per cent reduction in biomass burning sources, yields agreement with the ice core results. However, there is a significant imbalance between the known CH3Br sources and sinks in the modern atmospheric CH3Br budget, and the ice core data do not resolve the question of whether this imbalance is due to anthropogenic or natural sources.

Saltzman, E. S.; Aydin, M.; de Bruyn, W.; King, D. B.; Yvon-Lewis, S. A.

2003-12-01

179

An ice-core pollen record showing vegetation response to Late-glacial and Holocene climate changes at  

E-print Network

An ice-core pollen record showing vegetation response to Late-glacial and Holocene climate changes the results of pollen analysis performed on an ice core recovered from Nevado Sajama, Bolivia, dated to 25 ka BP. Low pollen concentrations from 25 to 15 ka BP are consistent with the scenario of an expanded ice

Howat, Ian M.

180

Ice-Cored Moraines and Ice Diapirs, Lake Miers, Victoria Land, Antarctica  

Microsoft Academic Search

Lake Miers is covered by a thick ice sheet which is domed over most of its area and thrust into sharp debris-covered ridges around its margin. Ridges result largely from compression generated in the ice raft by freeze and thaw. Apart from a narrow moat in summer the ice round the lake shore is frozen fast to the lake bed.

J. Bradley; D. F. Palmer

1967-01-01

181

High resolution measurements of carbon monoxide along a late Holocene Greenland ice core: evidence for in-situ production  

NASA Astrophysics Data System (ADS)

We present high-resolution measurements of carbon monoxide (CO) concentrations from continuous analysis of a shallow ice core from the North Greenland Eemian Ice Drilling project (NEEM-2011-S1). An Optical Feedback - Cavity Enhanced Absorption Spectrometer (OF-CEAS) was coupled to a continuous melter system during a 4-week laboratory-based measurement campaign. This analytical setup generates highly stable measurements of CO concentrations with an external precision of 7.8 ppbv (1 sigma) based on a comparison of replicate cores. The NEEM-2011-S1 CO record spans 1800 yr and exhibits highly variable concentrations at the scale of annual layers, ranging from 75 to 1327 ppbv. The most recent section of this record (i.e. since 1700 AD) agrees with existing discrete CO measurements from the Eurocore ice core and the deep NEEM firn. However, it is difficult to interpret in terms of atmospheric CO variation due to high frequency, high amplitude spikes in the data. 68% of the elevated CO spikes are observed in ice layers enriched with pyrogenic aerosols. Such aerosols, originating from boreal biomass burning emissions, contain organic compounds, which can be oxidized or photodissociated to produce CO in-situ. We suggest that elevated CO concentration features could present a new integrative proxy for past biomass burning history. Furthermore, the NEEM-2011-S1 record reveals an increase in baseline CO level prior to 1700 AD (129 m depth), with the concentration remaining high even for ice layers depleted in dissolved organic carbon (DOC). Overall, the processes driving in-situ production of CO within the NEEM ice are complex and may involve multiple chemical pathways.

Faïn, X.; Chappellaz, J.; Rhodes, R. H.; Stowasser, C.; Blunier, T.; McConnell, J. R.; Brook, E. J.; Preunkert, S.; Legrand, M.; Desbois, T.; Romanini, D.

2013-05-01

182

Earthquakes and Ice Cores Point to Wet Feet at the NorthGRIP Deep Drill Site  

NASA Astrophysics Data System (ADS)

A seismic broadband station was placed at the NorthGRIP deep drill site (75N, 42W) on the Greenland Ice Cap for the summer 2000. During the 2 month acquisition period 15 earthquakes with sufficient quality for Receiver Function analysis aimed at crust and mantle structure under NorthGRIP were recorded. The models are consistent with the presence of a thin sedimentary layer at the base of the ice. The seismic velocities in the sediments are lower than in the ice, indicating wet sediments. The results from the deep drilling program reveal high basal temperatures at the base of the 3080 m thick ice at NorthGRIP. The measured temperatures and the observed layer thickness' in the ice core indicate that there is basal melting of the order of 5 mm /yr. and that the geothermal heatflow is of the order of 100 mW/m2 (REF), much higher than expected. A detailed radio echo mapping of the bedrock show that NorthGRIP is located in a large, flat-bottomed valley, suggesting that the sediments observed are lacustrine. The thin layer of sediments cannot account for the unexpected high heatflow causing equally unexpected basal melting. The geology is presumed to be Precambrian. Heatflow determined in a similar way at the GRIP deep drill site (73N, 38W) is 51 mW/ m2 (Dahl-Jensen et al, 1998), more in line with expected values. Magnetic anomaly data do not indicate any volcanic structures, which could help explain the high heatflow. Gravity anomaly data show that NorthGRIP is located at the edge of marked gravity discontinuity. The cause of the discontinuity is not known, but "edge effects" could be speculated upon to be the cause of the high heatflow. D. Dahl-Jensen, N. Gundestrup, H. Miller, O. Watanabe, S.J. Johnsen, J.P. Steffensen, H.B. Clausen, A. Svensson, L.B. Larsen in press: The NorthGRIP drilling program. Annals of Glaciology, vol 35 D. Dahl-Jensen, K Mosegaard, N. Grundestrup, G.D. Clow, S.J. Johnson and N. Balling 1998: Past Temperatures Directly from the Greenland Ice Sheet. Science 282 pp 268-271

Dahl-Jensen, D.; Dahl-Jensen, T.; Gundestrup, N. S.

2001-12-01

183

Increase of Atmospheric Methane Recorded in Antarctic Ice Core  

Microsoft Academic Search

Air entrapped in bubbles of cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation. Measurements of the methane concentration in air extracted by two different methods from ice samples from Siple Station in western Antarctica allow the reconstruction of the history of the increase of the atmospheric methane during the past

B. Stauffer; G. Fischer; A. Neftel; H. Oeschger

1985-01-01

184

Recent North West Greenland climate variability documented by NEEM shallow ice cores  

NASA Astrophysics Data System (ADS)

Short water stable isotope records obtained from NEEM ice cores (North West Greenland) have been shown to be sensitive to NW Greenland temperature variations, and sea-ice extent in the Baffin Bay area (Steen-Larsen et al, JGR, 2011), with maximum snowfall deposition during summer, therefore providing information complementary to other Greenland ice core records. At the NEEM deep drilling camp, several snow pits and shallow ice cores have been retrieved and analysed at high resolution (seasonal to annual) for water stable isotopes using mass spectrometry and laser instruments in order to document recent climate variability, complementing and facilitating the interpretation of the long records obtained from the deep ice core which extends back to the last interglacial period (NEEM, Nature, 2013). The different pits and shallow ice core records allow to document the signal to noise ratio and to produce a robust stack back to 1750, and up to 2011. The stack record of annual mean d18O depicts a recent isotopic enrichment in parallel with the Greenland warming inferred from coastal weather stations, and shows that many features of decadal variations are in fact well captured by the low resolution profiles measured along the deep ice core data. Recent variations can therefore be compared to long-term trends and centennial variations of the last Holocene, documented at about 5 year resolution. For the past decades to centuries, the NEEM isotopic records are compared with estimations and simulations of local temperature for different seasons, results from NEEM borehole temperature inversions, d18O records from other Greenland ice cores, large scale modes of variability (NAO and AMO) and with simulations from atmospheric general circulation models equiped with water stable isotopes.

Masson-Delmotte, Valérie; Steen-Larsen, Hans-Christian; Popp, Trevor; Vinther, Bo; Oerter, Hans; Ortega, Pablo; White, Jim; Orsi, Anais; Falourd, Sonia; Minster, Benedicte; Jouzel, Jean; Landais, Amaelle; Risi, Camille; Werner, Martin; Swingedouw, Didier; Fettweis, Xavier; Gallée, Hubert; Sveinbjornsdottir, Arny; Gudlaugsdottir, Hera; Box, Jason

2014-05-01

185

Fire in ice: two millennia of Northern Hemisphere fire history from the Greenland NEEM ice core  

NASA Astrophysics Data System (ADS)

Biomass burning is a major source of greenhouse gases and influences regional to global climate. Pre-industrial fire-history records from black carbon, charcoal and other proxies provide baseline estimates of biomass burning at local to global scales, but there remains a need for broad-scale fire proxies that span millennia in order to understand the role of fire in the carbon cycle and climate system. We use the specific biomarker levoglucosan, and multi-source black carbon and ammonium concentrations to reconstruct fire activity from the North Greenland Eemian (NEEM) ice cores (77.49° N; 51.2° W, 2480 m a.s.l.) over the past 2000 years. Increases in boreal fire activity (1000-1300 CE and 1500-1700 CE) over multi-decadal timescales coincide with the most extensive central and northern Asian droughts of the past two millennia. The NEEM biomass burning tracers coincide with temperature changes throughout much of the past 2000 years except for during the extreme droughts, when precipitation changes are the dominant factor. Many of these multi-annual droughts are caused by monsoon failures, thus suggesting a connection between low and high latitude climate processes. North America is a primary source of biomass burning aerosols due to its relative proximity to the NEEM camp. During major fire events, however, isotopic analyses of dust, back-trajectories and links with levoglucosan peaks and regional drought reconstructions suggest that Siberia is also an important source of pyrogenic aerosols to Greenland.

Zennaro, P.; Kehrwald, N.; McConnell, J. R.; Schüpbach, S.; Maselli, O.; Marlon, J.; Vallelonga, P.; Leuenberger, D.; Zangrando, R.; Spolaor, A.; Borrotti, M.; Barbaro, E.; Gambaro, A.; Barbante, C.

2014-02-01

186

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)  

NASA Astrophysics Data System (ADS)

The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75° 37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607-2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that a deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice-lithosphere interactions of the Greenland Ice Sheet.

Vallelonga, P.; Christianson, K.; Alley, R. B.; Anandakrishnan, S.; Christian, J. E. M.; Dahl-Jensen, D.; Gkinis, V.; Holme, C.; Jacobel, R. W.; Karlsson, N.; Keisling, B. A.; Kipfstuhl, S.; Kjær, H. A.; Kristensen, M. E. L.; Muto, A.; Peters, L. E.; Popp, T.; Riverman, K. L.; Svensson, A. M.; Tibuleac, C.; Vinther, B. M.; Weng, Y.; Winstrup, M.

2014-01-01

187

Integrated tephrochronology of the West Antarctic region-Implications for a potential tephra record in the West Antarctic Ice Sheet (WAIS) Divide Ice Core  

E-print Network

record in the West Antarctic Ice Sheet (WAIS) Divide Ice Core N.W. Dunbar,1 W.C. McIntosh,1 A.V. Kurbatov and Mt. Takahe A number of volcanoes protrude through the West Antarctic Ice Sheet (Le the last 500,000 years . Mt. Takahe, a flat-topped stratovolcano, has produced a number of recent trachytic

Dunbar, Nelia W.

188

Continuous methane measurements from a late Holocene Greenland ice core: Atmospheric and in-situ signals  

NASA Astrophysics Data System (ADS)

Ancient air trapped inside bubbles in ice cores can now be analysed for methane concentration utilising a laser spectrometer coupled to a continuous melter system. We present a new ultra-high resolution record of atmospheric methane variability over the last 1800 yr obtained from continuous analysis of a shallow ice core from the North Greenland Eemian project (NEEM-2011-S1) during a 4-week laboratory-based measurement campaign. Our record faithfully replicates the form and amplitudes of multi-decadal oscillations previously observed in other ice cores and demonstrates the detailed depth resolution (5.3 cm), rapid acquisition time (30 m day-1) and good long-term reproducibility (2.6%, 2?) of the continuous measurement technique. In addition, we report the detection of high frequency ice core methane signals of non-atmospheric origin. Firstly, measurements of air from the firn-ice transition region and an interval of ice core dating from 1546-1560 AD (gas age) resolve apparently quasi-annual scale methane oscillations. Traditional gas chromatography measurements on discrete ice samples confirm these signals and indicate peak-to-peak amplitudes of ca. 22 parts per billion (ppb). We hypothesise that these oscillations result from staggered bubble close-off between seasonal layers of contrasting density during time periods of sustained multi-year atmospheric methane change. Secondly, we report the detection of abrupt (20-100 cm depth interval), high amplitude (35-80 ppb excess) methane spikes in the NEEM ice that are reproduced by discrete measurements. We show for the first time that methane spikes present in thin and infrequent layers in polar, glacial ice are accompanied by elevated concentrations of carbon- and nitrogen-based chemical impurities, and suggest that biological in-situ production may be responsible.

Rhodes, Rachael H.; Faïn, Xavier; Stowasser, Christopher; Blunier, Thomas; Chappellaz, Jérôme; McConnell, Joseph R.; Romanini, Daniele; Mitchell, Logan E.; Brook, Edward J.

2013-04-01

189

Eurasian Arctic climate over the past two millennia as recorded in the Akademii Nauk ice core (Severnaya Zemlya, Russian Arctic)  

NASA Astrophysics Data System (ADS)

In the context of the ongoing and future strong warming of the Arctic detailed knowledge of past climate changes in particular on a regional scale is crucial. An ice core drilled on the Akademii Nauk (AN) ice cap (Severnaya Zemlya, 80.52° N, 94.82° E) at a relatively low altitude of about 750 m a.s.l. has shown to provide high-resolution climate proxy data from the Central Russian Arctic, although the ice cap is affected by melt-water infiltration. Here for the first time, we present ?18O and major ion records for the last about two millennia. The age-depth relationship of the core is based on annual layer counting and volcanic reference layers for cross-checking (Bezymianny 1956, Katmai 1912, Laki 1783, unknown volcano 1259, Eldgja 934). The multi-annual AN ?18O data are highly correlated to instrumental temperature data from the Western Eurasian Arctic (e.g. Vardø/Northern Norway) and thus provide a valuable near-surface temperature proxy for this region, also underlined by the good coincidence with the Austfonna (Svalbard) ice core ?18O data. The long-term decrease of AN ?18O data does not solely reflect climate cooling but probably also a growing of AN ice cap. AN ?18O record reveal major temperature changes over the last centuries, e.g. the absolute minimum around 1800 and the exceptional warming to a maximum in early 20th century (Early Twentieth Century Warming - ETCW), representing the temperature maximum of the record. By comparison with meteorological data it can be shown that a double-peak structure of the ETCW is a peculiarity of the Barents and Kara Sea region. Neither a pronounced Medieval Climate Anomaly nor a Little Ice Age could be identified. In contrast, AN ice-core records show evidence for several abrupt warming and cooling events such as in the 15th and 16th centuries. These abrupt changes might be analogous to the ETCW and probably caused by shifts in the atmospheric circulation patterns and accompanied sea-ice feedbacks in the Barents and Kara seas region that highlight the role of the internal variability of the Arctic climate system.

Fritzsche, D.; Opel, T.; Meyer, H.

2012-04-01

190

A novel method for the detection of acidity in ice cores  

NASA Astrophysics Data System (ADS)

The pH of polar ice is important for the stability and mobility of impurities in ice cores and can be strongly influenced by volcanic eruptions or anthropogenic emissions. We present a simple optical method for continuous determination of acidity in ice cores based on the absorption spectroscopy of two common pH-indicator dyes, bromophenol blue and chlorophenol red. The method does not require calibration with CO2 and is simpler than existing continuous flow analysis (CFA) methods for pH determination in ice cores, offering a 10-90% peak response time of 45s and a combined uncertainty of 9%. The method has been applied to sections of Greenland firn and Antarctic ice and compared to standard techniques such as Electrical Conductivity Measurements (ECM), conducted on the solid ice, and electrolytic conductivity of melted ice samples. The acidity as detected in the Greenland NEGIS firn core (75.38N, 35.56W), show an increasing trend up to the 1970's that can be explained by deposition of anthropogenic SO42- and NOX. The seasonal variability show highest acidity in winter (1900-1950 AD), but shifts towards spring for the period 1950-2000 AD. Conductivity and pH are found to be highly correlated in the Greenland NEGIS firn core with all signals greater than 3? variability being related to either volcanic eruptions or forest fire activity. The method is ideal for finding the volcanic spikes in the firn than conventional ECM and DEP, which require density corrections in firn. In contrast to the NEGIS site, the Antarctic Roosevelt Island ice core (79.36S, 161.71W) features an anti-correlation between conductivity and pH, most likely due to the influence of marine salts.

Kjær, Helle Astrid; Vallelonga, Paul; Svensson, Anders

2014-05-01

191

Aerial photographs reveal late-20th-century dynamic ice loss in northwestern Greenland.  

PubMed

Global warming is predicted to have a profound impact on the Greenland Ice Sheet and its contribution to global sea-level rise. Recent mass loss in the northwest of Greenland has been substantial. Using aerial photographs, we produced digital elevation models and extended the time record of recent observed marginal dynamic thinning back to the mid-1980s. We reveal two independent dynamic ice loss events on the northwestern Greenland Ice Sheet margin: from 1985 to 1993 and 2005 to 2010, which were separated by limited mass changes. Our results suggest that the ice mass changes in this sector were primarily caused by short-lived dynamic ice loss events rather than changes in the surface mass balance. This finding challenges predictions about the future response of the Greenland Ice Sheet to increasing global temperatures. PMID:22859486

Kjær, Kurt H; Khan, Shfaqat A; Korsgaard, Niels J; Wahr, John; Bamber, Jonathan L; Hurkmans, Ruud; van den Broeke, Michiel; Timm, Lars H; Kjeldsen, Kristian K; Bjørk, Anders A; Larsen, Nicolaj K; Jørgensen, Lars Tyge; Færch-Jensen, Anders; Willerslev, Eske

2012-08-01

192

Influence of regional precipitation patterns on stable isotopes in ice cores from the central Himalayas  

NASA Astrophysics Data System (ADS)

Several ice cores have been recovered from the Dasuopu (DSP) Glacier and the East Rongbuk (ER) Glacier in the central Himalayas since the 1990s. Although the distance between the DSP and the ER ice core drilling sites is only ~ 125 km, the stable isotopic record (?18O or ?D) of the DSP core is interpreted in previous studies as a temperature proxy, while the ER core is interpreted as a precipitation proxy. Thus, the climatological significance of the stable isotopic records of these Himalayan ice cores remains a subject of debate. Based on analysis of regional precipitation patterns over the region, we find that remarkable discrepancy in precipitation seasonality between the two sites may account for their disparate isotopic interpretations. At the ER core site, the Indian summer monsoon (ISM) precipitation is dominating due to topographic blocking of the moisture from westerlies by the high ridges of Mt. Qomolangma (Everest), which results in a negative correlation between the ER ?18O or ?D record and precipitation amount along the southern slope of the central Himalayas in response to the "amount effect". At the DSP core site, in comparison with the ISM precipitation, the wintertime precipitation associated with the westerlies is likely more important owing to its local favorable topographic conditions for interacting with the western disturbances. Therefore, the DSP stable isotopic record may be primarily controlled by the westerlies. Our results have important implications for interpreting the stable isotopic ice core records recovered from different climatological regimes of the Himalayas.

Pang, H.; Hou, S.; Kaspari, S.; Mayewski, P. A.

2014-02-01

193

Annually resolved southern hemisphere volcanic history from two Antarctic ice cores  

Microsoft Academic Search

The continuous sulfate analysis of two Antarctic ice cores, one from the Antarctic Peninsula region and one from West Antarctica, provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century. The dating is accurate within +\\/-3 years due to the high rate of snow accumulation at both core sites and the small sample sizes

Jihong Cole-Dai; Ellen Mosley-Thompson; Lonnie G. Thompson

1997-01-01

194

27 m of lake ice on an Antarctic lake reveals past hydrologic variability  

NASA Astrophysics Data System (ADS)

Lake Vida, located in Victoria Valley, is one of the largest lakes in the McMurdo Dry Valleys. Unlike other lakes in the region, the surface ice extends at least 27 m, which has created an extreme and unique habitat by isolating a liquid-brine with salinity of 195 g L-1. Below 21 m, the ice is marked by well-sorted sand layers up to 20 cm thick, within a matrix of salty ice. From ice chemistry, isotopic abundances of 18O and 2H, ground penetrating radar profiles, and mineralogy, we conclude that the entire 27 m of ice formed from surface runoff, and the sediment layers represent the accumulation of fluvial and aeolian deposits. Radiocarbon and optically stimulated luminescence dating limit the maximum age of the lower ice to 6300 14C yr BP. As the ice cover ablated downwards during periods of low surface inflow, progressive accumulation of sediment layers insulated and preserved the ice and brine beneath; analogous to the processes that preserve shallow ground ice. The repetition of these sediment layers reveals climatic variability in Victoria Valley during the mid- to late Holocene. Lake Vida is an excellent Mars analog for understanding the preservation of subsurface brine, ice and sediment in a cold desert environment.

Dugan, H. A.; Doran, P. T.; Wagner, B.; Kenig, F.; Fritsen, C. H.; Arcone, S.; Kuhn, E.; Ostrom, N. E.; Warnock, J.; Murray, A. E.

2014-07-01

195

Ice-cored drumlins at the surge-type glacier Brúarjökull, Iceland: a transitional-state landform  

NASA Astrophysics Data System (ADS)

This paper presents data on a glacial landform that, to our knowledge, has not previously been described in the literature: the ice-cored drumlin. The study area is the forefield of the surge-type glacier Brúarjökull at the northeastern margin of the Vatnajökull ice cap, East Iceland. Based on sedimentological field investigations and aerial photograph interpretation, a qualitative model for the formation of ice-cored drumlins is proposed. The drumlin core consists of stagnant glacier ice from a previous advance and bubbly ice formed by snowdrifts, which were incorporated during the most recent advance - the 1963-64 surge. This advance deposited a mantle of basal till and streamlined the ice-cored moraines. Till deformation and deposition on the drumlin ice-core is facilitated by a substratum of low-permeability ice-cored moraines.In the present climate, the ice-core is subject to melting and the drumlin landform will degrade. The ongoing melting of the core and re-sedimentation of the till cover cause the originally streamlined subglacial landform to develop into a patch of hummocky moraine surrounded by a basal till sheet. Thus, ice-cored drumlins are a transitional-state landform in the surging glacier landsystem at Brúarjökull rather than a final landform.

Schomacker, Anders; Krüger, Johannes; Kjær, Kurt H.

2006-01-01

196

Sensitivity of IceCube-DeepCore to neutralino dark matter in the MSSM-25  

SciTech Connect

We analyse the sensitivity of IceCube-DeepCore to annihilation of neutralino dark matter in the solar core, generated within a 25 parameter version of the minimally supersymmetric standard model (MSSM-25). We explore the 25-dimensional parameter space using scanning methods based on importance sampling and using DarkSUSY 5.0.6 to calculate observables. Our scans produced a database of 6.02 million parameter space points with neutralino dark matter consistent with the relic density implied by WMAP 7-year data, as well as with accelerator searches. We performed a model exclusion analysis upon these points using the expected capabilities of the IceCube-DeepCore Neutrino Telescope. We show that IceCube-DeepCore will be sensitive to a number of models that are not accessible to direct detection experiments such as SIMPLE, COUPP and XENON100, indirect detection using Fermi-LAT observations of dwarf spheroidal galaxies, nor to current LHC searches.

Silverwood, Hamish; Adams, Jenni; Brown, Anthony M [Department of Physics and Astronomy, University of Canterbury, Christchurch 8140 (New Zealand); Scott, Pat [Department of Physics, McGill University, Montréal QC H2W2L8 (Canada); Danninger, Matthias; Savage, Christopher; Edsjö, Joakim; Hultqvist, Klas, E-mail: h.g.m.silverwood@uva.nl, E-mail: patscott@physics.mcgill.ca, E-mail: danning@fysik.su.se, E-mail: savage@physics.utah.edu, E-mail: edsjo@fysik.su.se, E-mail: jenni.adams@canterbury.ac.nz, E-mail: anthony.brown@canterbury.ac.nz, E-mail: klas.hultqvist@fysik.su.se [Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, SE-10691 Stockholm (Sweden)

2013-03-01

197

Straospheric loading and otpical depth estimates of explosive volcanism over the last 2100 years derived from the Greenland Ice Sheet Project 2 ice core  

Microsoft Academic Search

The high-resolution and lengthy records of volcanic aersol deposition in ice cores allow assessment of the atmospheric impact of different styles and magnitudes of past eruptions and the impact of volcanism during periods of varied climatic conditions. The 2100-year long volcanic SO2-4 time series in the Greenland Ice Sheet Project 2 (GISP2) ice core was used to calculate the mass

Gregory A. Zielinski

1995-01-01

198

In Situ Production of Methyl Chloride in Siple Dome and WAIS Divide Ice Cores from Antarctica  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) is a naturally-occurring halocarbon with a global mean abundance of 550 pmol mol-1 and a lifetime of about 1 year. It constitutes about 16% of the total chlorine burden in the stratosphere. The sources of methyl chloride are mainly natural and include tropical vegetation, oceans and biomass burning. Oxidation with the hydroxyl radical is the primary removal mechanism with additional loss via microbial degradation in soils and in the oceans. Previous measurements suggest ice cores from cold Antarctic sites (Dome Fuji, South Pole, Taylor Dome) preserve a record of atmospheric CH3Cl variability during the Holocene (Saito et al., 2007; Williams et al., 2007; Verhulst et al., in review). However, measurements at Siple Dome displayed evidence of in situ enhancement (Saltzman et al., 2009). This study involves new CH3Cl measurements in 117 ice core samples from the West Antarctic Ice Sheet Divide (WAIS-D) 06A ice core. Measurements from the Holocene are compared with earlier CH3Cl measurements from Taylor Dome and Siple Dome. In Late Holocene ice (5-0 ky BP), the WAIS-D and Siple Dome show evidence of in situ CH3Cl enrichment. The mean level and scatter are both larger than in Taylor Dome ice of the same age. The in situ enrichment is not time or depth-dependent. Interestingly, for most of the Early Holocene (11-5 ky BP), Siple Dome and WAIS-D exhibit less scatter and are closer to the Taylor Dome ice core data. In situ CH3Cl production may be purely chemical or involve biological reactions. Here, we investigate whether the excess CH3Cl in the Siple Dome and the WAIS-D ice cores can be explained by differences in ice chemistry between the various Antarctic sites. The results of this research will help establish the causes of CH3Cl production in ice cores and provide a basis to assess the possibility of studying long-term atmospheric CH3Cl variability using ice core data.

Frausto-Vicencio, I.; Verhulst, K. R.; Aydin, M.; Saltzman, E. S.

2013-12-01

199

Physical properties, crystalline textures and c-axis fabrics of the Siple Dome (Antarctica) ice core  

NASA Astrophysics Data System (ADS)

The quality of the ice core from Siple Dome, West Antarctica, varied widely, with significant fracturing below 400 m. Bubbly ice persisted to the ice-rock interface at 1004 m and constituted the brittle zone. The core has undergone minimal relaxation and has remained brittle and prone to fracturing more than 5 years after it was drilled. This behavior is attributed to unrelieved stresses from Kamb and Bindschadler Ice Streams (former Ice Streams C and D) flanking the dome. Melt layers were identified sporadically throughout the core, as were inclined layers tilted at angles that occasionally exceeded 10°. Structurally, the ice was characterized by extensive recrystallization including grain-size changes from 0.074 cm2 at 59 m to >50 cm2 at 992 m, and major transitions in c-axis fabrics. Unusual fabrics included vertical c-axis clusters superimposed on vertical girdles that may reflect vertical compression acting in conjunction with horizontal tension. The sudden appearance of a shear-type fabric at 700-800 m appears closely linked to the occurrence of abundant tephra particles embedded in the ice. The occurrence of dispersed sediment in the bottom 2 m is attributed to freeze-on of basal meltwater.

Gow, Anthony J.; Meese, Debra

200

Lagrangian analysis of ICESat altimetry reveals patterns of ice shelf basal melting  

NASA Astrophysics Data System (ADS)

Iceberg calving and ice shelf basal melting are normal mass-loss processes that over time roughly balance the outflow of ice from the Antarctic Ice Sheet. Most basal melting is thus compensated by ice advection and is not detected by the traditional methods of analyzing surface elevation changes in a fixed geographic coordinate system (Eulerian). Here we present a new method that derive elevation changes in a "Lagrangian" sense from repeat-track ICESat laser altimetry, where specific locations are followed on the advancing ice shelf surface. We use a published ice shelf velocity field to correct for ice advection between consecutive repeats, and then convert the Lagrangian dh/dt estimates into ice thickness changes based on a model of the firn layer. In some locations, the derived ice thickness changes are much larger the Eulerian approach. The Lagrangian approach reduces the noise level of the derived ice thickness changes and reveals clear spatial patterns that we interpret as variations in basal melting. For the largest Antarctic ice shelves (Ross and Filchner-Ronne), we find that the Lagrangian thinning rates increase progressively towards the fronts, which is consistent with oceanographic models that suggest higher basal melt rates in the frontal zone. There are few examples of localized Lagrangian thickening, suggesting that basal melting is likely dominating over basal freezing in the interior of most ice shelves. Combined with data on surface mass balance and firn compaction, our Lagrangian approach can provide new insights into the magnitude and extent of basal melting, as well as being an important validation for models of ice-ocean interaction.

Moholdt, G.; Fricker, H. A.; Padman, L.

2012-12-01

201

Tree ring effects and ice core acidities clarify the volcanic record of the first millennium  

NASA Astrophysics Data System (ADS)

In 2012 Plummer et al., in presenting the volcanic chronology of the Antarctic Law Dome ice core, chose to list connections to acid layers in other ice cores and also possible chronological coincidences between ice acid dates and the precise dates of frost damage, and/or reduced growth in North American bristlecone pines. We disagree with the chronological links indicated by Plummer et al. for the period before AD 700, and in this paper we show that a case can be made that better linkages between ice acid and tree ring effects occur for this period if the ice chronologies are systematically moved forward by around 7 years, consistent with a hypothesis published by Baillie in 2008. In the paper we seek to explore the proposition that frost damage rings in North American bristlecone pines are a very useful indicator of the dates of certain large explosive volcanic eruptions; the dating of major eruptions being critical for any clear understanding of volcanic forcing. This paper cannot prove that there is an error in the Greenland Ice Core Chronology 2005 (GICC05), and in equivalent ice chronologies from the Antarctic, however, it does provide a coherent argument for an apparent ice dating offset. If the suggested offset were to prove correct it would be necessary to locate where the error occurs in the ice chronologies and in this regard the dating of the increasingly controversial Icelandic Eldgjá eruption in the AD 930s, and the China/Korean Millennium eruption which occurs some 7 years after Eldgjá, may well be critical. In addition, if the offset were to be substantiated it would have implications for the alleged identification of tephra at 429.3 m in the Greenland GRIP core, currently attributed to the Italian volcano Vesuvius and used as a critical zero error point in the GICC05 chronology.

Baillie, M. G. L.; McAneney, J.

2015-01-01

202

Microbial Analyses of Ancient Ice Core Sections from Greenland and Antarctica  

PubMed Central

Ice deposited in Greenland and Antarctica entraps viable and nonviable microbes, as well as biomolecules, that become temporal atmospheric records. Five sections (estimated to be 500, 10,500, 57,000, 105,000 and 157,000 years before present, ybp) from the GISP2D (Greenland) ice core, three sections (500, 30,000 and 70,000 ybp) from the Byrd ice core, and four sections from the Vostok 5G (Antarctica) ice core (10,500, 57,000, 105,000 and 105,000 ybp) were studied by scanning electron microscopy, cultivation and rRNA gene sequencing. Bacterial and fungal isolates were recovered from 10 of the 12 sections. The highest numbers of isolates were found in ice core sections that were deposited during times of low atmospheric CO2, low global temperatures and low levels of atmospheric dust. Two of the sections (GISP2D at 10,500 and 157,000 ybp) also were examined using metagenomic/metatranscriptomic methods. These results indicated that sequences from microbes common to arid and saline soils were deposited in the ice during a time of low temperature, low atmospheric CO2 and high dust levels. Members of Firmicutes and Cyanobacteria were the most prevalent bacteria, while Rhodotorula species were the most common eukaryotic representatives. Isolates of Bacillus, Rhodotorula, Alternaria and members of the Davidiellaceae were isolated from both Greenland and Antarctica sections of the same age, although the sequences differed between the two polar regions. PMID:24832659

Knowlton, Caitlin; Veerapaneni, Ram; D’Elia, Tom; Rogers, Scott O.

2013-01-01

203

The Antarctic Ice.  

ERIC Educational Resources Information Center

The International Antarctic Glaciological Project has collected information on the East Antarctic ice sheet since 1969. Analysis of ice cores revealed climatic history, and radar soundings helped map bedrock of the continent. Computer models of the ice sheet and its changes over time will aid in predicting the future. (DH)

Radok, Uwe

1985-01-01

204

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.  

PubMed

We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ? y(-1), equivalent to 0.68 mm ? y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers. PMID:25512537

Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

2014-12-30

205

Post-coring entrapment of modern air in polar ice: Evidence from CFC-12 measurements in Antarctic firn air and shallow ice cores  

NASA Astrophysics Data System (ADS)

This study is a comparison of CFC-12 (CCl2F2) measurements in firn air and ice core samples from three Antarctic sites: South Pole, West Antarctic Ice Sheet Divide (79.46°S, 112.13°W), and Siple Dome (81.65°S, 148.81°W). CFC-12 is a synthetic chlorofluorocarbon manufactured during the mid-late 20th century for use as a refrigerant and an aerosol spray propellant. Its atmospheric history is well established with agreement among instrumental time series measurements and industry-reported production data [Walker et al., 2000], the distribution of dissolved CFC-12 in the oceans [e.g. Weiss et al., 1985], and firn air measurements [Butler et al., 1999]. The atmospheric history indicates that there was no measureable CFC-12 in the atmosphere prior to the 1940’s. The firn air CFC-12 profiles are consistent with the known atmospheric history of this gas. In contrast, the air in ice core samples collected near the close-off depth exhibit anomalously high CFC-12 levels. We propose that this is due to entrapment of modern air in open pores that close after drilling, resulting in elevated CFC-12 mixing ratios. These results demonstrate how the composition of air trapped in shallow ice cores can be altered during the post-drilling period through purely physical processes. Comparison of firn air and ice core bubble composition is one of the commonly used tools for studying the bubble close-off process. The post-drilling entrapment process detected in this study represents a potential complication for such investigations.

Aydin, K. M.; Montzka, S. A.; Battle, M. O.; Williams, M. B.; de Bruyn, W. J.; Butler, J. H.; Verhulst, K. R.; Tatum, C.; Gun, B. K.; Plotkin, D. A.; Hall, B. D.; Saltzman, E. S.

2009-12-01

206

Offshore Extent of the Iceland Ice Cap During the Last Glacial Maximum Inferred from Multibeam Bathymetric Data and Sediment Cores.  

NASA Astrophysics Data System (ADS)

The insular margin of Iceland is incised by several major troughs, which mark the pathways of outlet glaciers during the last glaciations. Multibeam bathymetric data have revealed features of glacial erosion and sedimentation pertinent to the extent of the Iceland ice cap during the Last Glacial Maximum. Marginal moraines have been identified at the southern, western and northwestern edge of the insular margin. Furthermore, glacial erosion and sedimentation along the Kolbeinsey Ridge, North Iceland, indicates that the Iceland ice cap extended beyond 67°30'N. The ridge axis is made up of various types of seamounts, crater rows and hummocky ridges whereas older seamounts have been sculptured into roche moutonnées by glacial erosion. The far extent of the ice cap to the north is also supported by sediment studies on cores that have been retrieved from the troughs on the northern and northwestern part of the insular margin. Numerous smaller moraines exist closer to land marking stepwise retreat of the ice cap during deglacial times. Such moraines have been identified at 400-500 m depth within a 3-6 km wide, U-shaped valley along the western margin of the Kolbeinsey ridge (at 66°55'N) and within many of the costal fjords. Many of the offshore features resemble those known from land, such as streamlined bedrock features elongated in the regional direction of ice flow, eskers and subglacial meltwater channels together with erosional channels possibly formed by jökulhlaups. Extensive number of ice plough marks are revealed on bank areas and landslides on the marginal slope. Fluted surfaces and subglacially formed meltwater channels suggest formation underneath fast flowing, warm-based ice streams. These newly identified glacial features reveal new information on the spatial extent, dynamics and retreat of the Iceland ice cap during the last glaciation and deglaciation. Eustatic and isostatic contributions can be predicted from models of ice sheets and mantle rheology, which varies across the divergent plate boundary. Continuing study will focus on spatial and temporal variability of the combined effect of glaciation and isostacy as well as tectonic movements.

Helgadottir, G.; Brandsdottir, B.; Geirsdottir, A.; Björnsson, H.

2005-12-01

207

Methyl bromide in preindustrial air: Measurements from an Antarctic ice core  

NASA Astrophysics Data System (ADS)

This paper presents the first ice core measurements of methyl bromide (CH3Br). Samples from a shallow Antarctic ice core (Siple Dome, West Antarctica), ranging in mean gas dates from 1671 to 1942, had a mean CH3Br mixing ratio of 5.8 ppt. These results extend the existing historical record derived from air and Antarctic firn air to about 350 years before present. Model simulations illustrate that the ice core results are consistent with estimates of the impact of anthropogenic activity (fumigation, combustion, and biomass burning) on the atmospheric CH3Br burden, given the large current uncertainties in the modern atmospheric CH3Br budget. A preindustrial scenario assuming no fumigation, no combustion, and a 75% reduction in biomass-burning sources yields a Southern Hemisphere mean mixing ratio of 5.8 ppt, in good agreement with the ice core results. There is a significant imbalance between the known CH3Br sources and sinks in the modern atmospheric CH3Br budget. The ice core data do not sufficiently constrain the model to determine how much of the "unknown source" was present in the preindustrial budget. The results do indicate that most of the southern hemispheric component of this "unknown source" is not anthropogenic.

Saltzman, Eric S.; Aydin, Murat; de Bruyn, Warren J.; King, Daniel B.; Yvon-Lewis, Shari A.

2004-03-01

208

Modeling the configuration of the Greenland ice sheet during the Last Interglacial constrained by ice core data  

NASA Astrophysics Data System (ADS)

The Last Interglacial (LIG or Eemian) between ca. 130 and 115 ky BP is probably the best analogue for future climate warming for which increasingly better proxy data are becoming available. The volume of the Greenland ice sheet (GIS) during this period is of particular interest to better assess how much and how fast sea-level can rise in a future Earth undergoing gradual climatic warming. Sea-level during the LIG is inferred to have been 6-9 meter higher than today, but the contribution of the GIS remains unclear. Various ice-sheet modeling studies have come up with a very broad range of the LIG volume loss by the GIS to between 1 and 6 m of equivalent sea-level rise. This wide range is explained by the sensitivity of GIS models to the imposed climatic conditions and to poor knowledge of the LIG climate itself in terms of the magnitude and precise timing of the maximum warming, as well as in terms of spatial and annual patterns. Using a three-dimensional thermomechanical ice-sheet model, we produced an ensemble of possible LIG configurations by varying only three key parameters for temperature, precipitation rate, and surface melting within realistic bounds. The outcome of the numerical experiments is a variety of glaciologically consistent GIS geometries corresponding to a wide range of possible "climates", thereby avoiding the complications of having to prescribe the details of the LIG climate itself. For instance, uncertainty in the magnitude of the warming (8±4 ?C) has a dramatic influence on the results. To constrain the ensemble of GIS geometries, we used data inferred from 5 Greenland ice cores including NEEM, such as the presence or absence of LIG ice, borehole temperature and isotopic composition. Lagrangian backtracing of particles was used to establish ice-core chronologies and to take into account biases introduced by horizontal advection, systematic latitudinal contrast and local elevation changes. Comparison of model-generated ice-core characteristics with the observed data enabled to narrow down the ensemble to a bound on the GIS contribution to the LIG sea-level rise of between 2.7 and 3.1 m. This indicates that a substantial share of the LIG sea-level rise must have originated from the Antarctic ice sheet.

Rybak, Oleg; Huybrechts, Philippe

2013-04-01

209

A chemical pacemaker to refine chronology for the deep East Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Dating of the deep East Antarctic ice core spanning more than 100,000 years of climate records is challenging but benefited recently from iterative and complementary approaches. As a principle, ice core dating relies on ice flow modelling (thinning function of ice layer) as well as on the (modelled) estimate of the past snow accumulation rate. The inverse method allows integration of various dated horizons from other records assuming the physical properties of the ice (its deformation) remain within realistic boundaries. The modelled ice chronology is generally constrained by few dated horizons (volcanic, 10Be peaks from solar or from magnetic inversion related events…) and/or by orbital tuning process (temperature proxy, 18O of air bubbles…). Due to the scarcity of absolute dating, the use of orbital tuning from ice proxies may serve as a test of the modelled ice age. As a prerequisite, the proxy should not already be used to constrain the modelled chronology. Also, to prevent gas-age/ice age uncertainties, a preference should be given to a proxy associated to the ice instead to the air bubbles. Also, the physical link with the insolation should be rather direct, and a preference given to proxies sensitive to precession band (20kyr) instead obliquity band (41kyr). The continental dust and marine sodium records were so far not used to constrain the modelled chronology of EPICA and Vostok ice core. The dust and marine sodium appear firstly correlated to patterns of temperature and therefore to the hydrological cycle which influences at the same time the source emissions (for dust), the atmospheric cleansing and the deposition onto the ice sheet. Once the overall temperature effects is compensated, the residual signal for dust and sodium concentrations over the last 400 ky from EPICA Dome C and Vostok records display strong precession oscillations for both sites. Interestingly, the sodium residuals appear to increase with austral summer insolation while the dust residuals decrease, and remaining out of phase. Such behaviour could be understood by a positive effect of insolation on sodium emission (strengthening of spring cyclonic activity…) and negative effect on dust sources (reduction of Patagonian dust emission by strengthening of Southern American monsoon…). This dual behaviour which needs to be determined, allows combination of sodium and dust residuals providing a "chemical pacemaker" dominated by precession which could be used to refine the modelled chronology. A test was done on the EDC3 modelled age of the Epica Dome C deep ice core which covers the last 800ky.

Petit, J. R.; Parrenin, F.; Delmonte, B.

2012-04-01

210

Direct linking of Greenland and Antarctic ice cores at the Toba eruption (74 ka BP)  

NASA Astrophysics Data System (ADS)

The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia, where it constitutes a major time marker close to the Marine Isotope Stage 4/5 boundary. As yet, no tephra associated with Toba has been identified in Greenland or Antarctic ice cores. Based on new accurate dating of Toba tephra and on accurately dated European stalagmites, the Toba event is known to occur between the onsets of Greenland interstadials (GI) 19 and 20. Furthermore, the existing linking of Greenland and Antarctic ice cores by gas records and by the bipolar seesaw hypothesis suggests that the Antarctic counterpart is situated between Antarctic Isotope Maxima (AIM) 19 and 20. In this work we suggest a direct synchronization of Greenland (NGRIP) and Antarctic (EDML) ice cores at the Toba eruption based on matching of a pattern of bipolar volcanic spikes. Annual layer counting between volcanic spikes in both cores allows for a unique match. We first demonstrate this bipolar matching technique at the already synchronized Laschamp geomagnetic excursion (41 ka BP) before we apply it to the suggested Toba interval. The Toba synchronization pattern covers some 2000 yr in GI-20 and AIM-19/20 and includes nine acidity peaks that are recognized in both ice cores. The suggested bipolar Toba synchronization has decadal precision. It thus allows a determination of the exact phasing of inter-hemispheric climate in a time interval of poorly constrained ice core records, and it allows for a discussion of the climatic impact of the Toba eruption in a global perspective. The bipolar linking gives no support for a long-term global cooling caused by the Toba eruption as Antarctica experiences a major warming shortly after the event. Furthermore, our bipolar match provides a way to place palaeo-environmental records other than ice cores into a precise climatic context.

Svensson, A.; Bigler, M.; Blunier, T.; Clausen, H. B.; Dahl-Jensen, D.; Fischer, H.; Fujita, S.; Goto-Azuma, K.; Johnsen, S. J.; Kawamura, K.; Kipfstuhl, S.; Kohno, M.; Parrenin, F.; Popp, T.; Rasmussen, S. O.; Schwander, J.; Seierstad, I.; Severi, M.; Steffensen, J. P.; Udisti, R.; Uemura, R.; Vallelonga, P.; Vinther, B. M.; Wegner, A.; Wilhelms, F.; Winstrup, M.

2013-03-01

211

Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition  

NASA Astrophysics Data System (ADS)

Previous studies have used small numbers of ice core records of past volcanism to represent hemispheric or global radiative forcing from volcanic stratospheric aerosols. With the largest-ever assembly of volcanic ice core records and state-of-the-art climate model simulations of volcanic deposition, we now have a unique opportunity to investigate the effects of spatial variations on sulfate deposition and on estimates of atmospheric loading. We have combined 44 ice core records, 25 from the Arctic and 19 from Antarctica, and Goddard Institute for Space Studies ModelE simulations to study the spatial distribution of volcanic sulfate aerosols in the polar ice sheets. We extracted volcanic deposition signals by applying a high-pass loess filter to the time series and examining peaks that exceed twice the 31-year running median absolute deviation. Our results suggest that the distribution of volcanic sulfate aerosol follows the general precipitation pattern in both regions, indicating the important role precipitation has played in affecting the deposition pattern of volcanic aerosols. We found a similar distribution pattern for sulfate aerosols from the 1783-1784 Laki and 1815 Tambora eruptions, as well as for the total ? activity after the 1952-1954 low-latitude Northern Hemisphere and 1961-1962 high-latitude Northern Hemisphere atmospheric nuclear weapon tests. This confirms the previous assumption that the transport and deposition of nuclear bomb test debris resemble those of volcanic aerosols. We compare three techniques for estimating stratospheric aerosol loading from ice core data: radioactive deposition from nuclear bomb tests, Pinatubo sulfate deposition in eight Antarctic ice cores, and climate model simulations of volcanic sulfate transport and deposition following the 1783 Laki, 1815 Tambora, 1912 Katmai, and 1991 Pinatubo eruptions. By applying the above calibration factors to the 44 ice core records, we have estimated the stratospheric sulfate aerosol loadings for the largest volcanic eruptions during the last millennium. These loadings agree fairly well with estimates based on radiation, petrology, and model simulations. We also estimate the relative magnitude of sulfate deposition compared with the mean for Greenland and Antarctica for each ice core record, which provides a guideline to evaluate the stratospheric volcanic sulfate aerosol loading calculated from a single or a few ice core records.

Gao, Chaochao; Oman, Luke; Robock, Alan; Stenchikov, Georgiy L.

2007-05-01

212

Mineral Dust Elemental Composition Over the Last 220 Kyr from the EPICA-Dome C ice core (East Antarctica)  

NASA Astrophysics Data System (ADS)

Mineral windblown aerosol (dust) represents a small fraction of the total mass of atmospheric aerosols. However, it may play an important role in climate and, in turn, it is itself sensitive to climatic changes. The investigation of the temporal variability of dust flux as well as the changes of its mineralogical composition within different climatic periods offers a unique way of assessing the source-related environmental changes, the variation in atmospheric circulation, and the potential influence of dust on biogeochemical cycles, for several key elements (such as Si and Fe). The mineral composition of dust found in ice cores is still poorly known, because few techniques are able to provide information on the chemical composition of the insoluble aerosol fraction, because of the very low mass of dust usually present in polar ice samples. Total volume of mineral content is provided by Coulter Counter measurements, and the dust record shows higher dust input during glacial periods than during interglacials (Delmonte et al., 2004). Sr and Nd isotopic tracers for identification of dust provenance to East Antarctica suggest southern South America as the dominant common source for dust in glacial periods of the late Pleistocene (Delmonte et al., 2004), whereas dust provenance during interglacials periods is still highly uncertain. Elemental composition of mineral dust from the Dome C ice core (75° 06' S, 123° 21' E) drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA) is presented, showing measurements obtained by the Proton Induced X-ray Emission (PIXE) technique applied on insoluble atmospheric dust in ice cores. Within this work, substantial improvements to the experimental set-up and data processing have been made, compared to previously presented works on the first 2200 m of the EDC ice core, corresponding to about 220 kyr of climatic history (Marino et al., 2004; Ghermandi et al., 2003). The PIXE technique, based on X-ray spectrometry, allows direct measurements on filters of the insoluble dust fraction without sample pre-treatment, with analytical detection limits less than 1 ppb. The minimum required mass density of sample material on the filter is about 0.1 microg cm-2. Improvements made here allowed us to obtain accurate records of 8 major and minor crustal elements (Si, Al, Fe, Ti, K, Ca, Mg, Na). The data for these 8 elements, as well as their proportions as oxides, are shown for different climatic periods. Because O, Si, Al, Fe, Ti, K, Ca, Mg, Na are the principal constituents (99.90 %) of the Earth's Continental Crust, a comparison with literature data can reveal changes in relative elemental abundances, and hence variable composition of dust under different climatic conditions.

Marino, F.; Maggi, V.; Delmonte, B.; Ghermandi, G.; Petit, J.; Hinkley, T. K.

2004-12-01

213

Holocene-Late Pleistocene Climatic Ice Core Records from Qinghai-Tibetan Plateau  

E-print Network

. XIE Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai- Tibetan Plateau ofChina temperature is -7.3°C. The glacier is 140 m thick and the underlying bedrock topography is flat. About 0.4 m samples that were melted in closed containers by passive solar L. G. Thompson, E. Mosle-Thompson, M. E

Howat, Ian M.

214

New Ice-Core Evidence Challenges the 1620s BCage for the Santorini (Minoan) Eruption  

Microsoft Academic Search

Determining a reliable calendrical age of the Santorini (Minoan) eruption is necessary to place the impact of the eruption into its proper context within Bronze Age society in the Aegean region. The high-resolution record of the deposition of volcanically produced acids on polar ice sheets, as available in the SO42?time series from ice cores (a direct signal), and the high-resolution

Gregory A. Zielinski; Mark S. Germani

1998-01-01

215

Influence of regional precipitation patterns on stable isotopes in ice cores from the central Himalayas  

NASA Astrophysics Data System (ADS)

Several ice cores have been recovered from the Dasuopu Glacier and the East Rongbuk (ER) Glacier in the central Himalayas since the 1990s. Although the distance between the ER and the Dasuopu ice core drilling sites is only ∼125 km, the stable isotopic record (?18O or ?D) of the ER core is interpreted as a precipitation proxy while the Dasuopu core as a temperature proxy. Thus, the climatological significance of the stable isotopic records of these Himalayan ice cores remains a subject of debate. Based on analysis of regional precipitation patterns over the region, we find that the different interpretations of the Dasuopu and Everest isotopic records may not be contradictive. The north-south and west-east seesaws of the Indian Summer Monsoon (ISM) precipitation are primarily responsible for precipitation falling at the ER site, which results in a negative correlation between the ER ?18O or ?D record and precipitation amount along the southern slope of the central Himalayas, corresponding to the "amount effect". In addition to the ISM precipitation, non-summer monsoonal precipitation associated with winter westerlies also significantly contributes to precipitation falling at the Dasuopu site, which may cause a positive correlation between the Dasuopu stable isotopic record and temperature, in response to the "temperature effect". Our results have important implications for interpreting the stable isotopic ice core records recovered from different climatological regimes of the Himalayas.

Pang, H.; Hou, S.; Kaspari, S.; Mayewski, P. A.

2013-05-01

216

30-Year Satellite Record Reveals Accelerated Arctic Sea Ice Loss, Antarctic Sea Ice Trend Reversal  

NASA Technical Reports Server (NTRS)

Arctic sea ice extent decreased by 0.30 plus or minus 0.03 x 10(exp 6) square kilometers per decade from 1972 through 2002, but decreased by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per decade from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast to the Arctic, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased, with an overall 30-year trend of -0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent observed in the early 1970's.

Cavalieri, Donald J.; Parkinson, C. L.; Vinnikov, K. Y.

2003-01-01

217

A centrifugal ice microtome for measurements of atmospheric CO2 on air trapped in polar ice cores  

NASA Astrophysics Data System (ADS)

For atmospheric CO2 reconstructions using ice cores, the technique to release the trapped air from the ice samples is crucial for the precision and accuracy of the measurements. We present here a new dry extraction technique in combination with a new gas analytical system that together show significant improvements with respect to current systems. Ice samples (3-15 g) are pulverized using a novel Centrifugal Ice Microtome (CIM) by shaving the ice in a cooled vacuum chamber (-27 °C) in which no friction occurs due to the use of magnetic bearings. Both, the shaving principle of the CIM and the use of magnetic bearings have not been applied so far in this field. Shaving the ice samples produces finer ice powder and releases a minimum of 90% of the trapped air compared to 50%-70% when needle crushing is employed. In addition, the friction-free motion with an optimized design to reduce contaminations of the inner surfaces of the device result in a reduced system offset of about 2.0 ppmv compared to 4.9ppmv. The gas analytical part shows a factor two higher precision than our corresponding part of the previous system and all processes except the loading and cleaning of the CIM now run automatically. Compared to our previous system the new system shows a 3 times better measurement reproducibility of about 1.1 ppmv (1?) which is similar to the best reproducibility of other systems applied in this field. With this high reproducibility, replicate measurements are not required anymore for most prospective measurement campaigns resulting in a possible output of 12-20 measurements per day compared to a maximum of 6 with other systems.

Bereiter, B.; Stocker, T. F.; Fischer, H.

2012-10-01

218

A centrifugal ice microtome for measurements of atmospheric CO2 on air trapped in polar ice cores  

NASA Astrophysics Data System (ADS)

For atmospheric CO2 reconstructions using ice cores, the technique to release the trapped air from the ice samples is essential for the precision and accuracy of the measurements. We present here a new dry extraction technique in combination with a new gas analytical system that together show significant improvements with respect to current systems. Ice samples (3-15 g) are pulverised using a novel centrifugal ice microtome (CIM) by shaving the ice in a cooled vacuum chamber (-27 °C) in which no friction occurs due to the use of magnetic bearings. Both, the shaving principle of the CIM and the use of magnetic bearings have not been applied so far in this field. Shaving the ice samples produces finer ice powder and releases a minimum of 90% of the trapped air compared to 50%-70% when needle crushing is employed. In addition, the friction-free motion with an optimized design to reduce contaminations of the inner surfaces of the device result in a reduced system offset of about 2.0 ppmv compared to 4.9 ppmv. The gas analytical part shows a higher precision than the corresponding part of our previous system by a factor of two, and all processes except the loading and cleaning of the CIM now run automatically. Compared to our previous system, the complete system shows a 3 times better measurement reproducibility of about 1.1 ppmv (1 ?) which is similar to the best reproducibility of other systems applied in this field. With this high reproducibility, no replicate measurements are required anymore for most future measurement campaigns resulting in a possible output of 12-20 measurements per day compared to a maximum of 6 with other systems.

Bereiter, B.; Stocker, T. F.; Fischer, H.

2013-02-01

219

Temperature and precipitation signal in two Alpine ice cores over the period 1961-2001  

NASA Astrophysics Data System (ADS)

Water stable isotope ratios and net snow accumulation in ice cores are commonly interpreted as temperature or precipitation proxies. However, only in a few cases has a direct calibration with instrumental data been attempted. In this study we took advantage of the dense network of observations in the European Alpine region to rigorously test the relationship of the annual and seasonal resolved proxy data from two highly resolved ice cores with local temperature and precipitation. We focused on the time period 1961-2001 with the highest amount and quality of meteorological data and the minimal uncertainty in ice core dating (±1 year). The two ice cores were retrieved from the Fiescherhorn glacier (northern Alps, 3900 m a.s.l.), and Grenzgletscher (southern Alps, 4200 m a.s.l.). A parallel core from the Fiescherhorn glacier allowed assessing the reproducibility of the ice core proxy data. Due to the orographic barrier, the two flanks of the Alpine chain are affected by distinct patterns of precipitation. The different location of the two glaciers therefore offers a unique opportunity to test whether such a specific setting is reflected in the proxy data. On a seasonal scale a high fraction of ?18O variability was explained by the seasonal cycle of temperature (~60% for the ice cores, ~70% for the nearby stations of the Global Network of Isotopes in Precipitation - GNIP). When the seasonality is removed, the correlations decrease for all sites, indicating that factors other than temperature such as changing moisture sources and/or precipitation regimes affect the isotopic signal on this timescale. Post-depositional phenomena may additionally modify the ice core data. On an annual scale, the ?18O/temperature relationship was significant at the Fiescherhorn, whereas for Grenzgletscher this was the case only when weighting the temperature with precipitation. In both cases the fraction of interannual temperature variability explained was ~20%, comparable to the values obtained from the GNIP stations data. Consistently with previous studies, we found an altitude effect for the ?18O of -0.17‰/100 m for an extended elevation range combining data of the two ice core sites and four GNIP stations. Significant correlations between net accumulation and precipitation were observed for Grenzgletscher during the entire period of investigation, whereas for Fiescherhorn this was the case only for the less recent period (1961-1977). Local phenomena, probably related to wind, seem to partly disturb the Fiescherhorn accumulation record. Spatial correlation analysis shows the two glaciers to be influenced by different precipitation regimes, with the Grenzgletscher reflecting the characteristic precipitation regime south of the Alps and the Fiescherhorn accumulation showing a pattern more closely linked to northern Alpine stations.

Mariani, I.; Eichler, A.; Jenk, T. M.; Brönnimann, S.; Auchmann, R.; Leuenberger, M. C.; Schwikowski, M.

2014-06-01

220

Dating a tropical ice core by time-frequency analysis of ion concentration depth profiles  

NASA Astrophysics Data System (ADS)

Ice core dating is a key parameter for the interpretation of the ice archives. However, the relationship between ice depth and ice age generally cannot be easily established and requires the combination of numerous investigations and/or modelling efforts. This paper presents a new approach to ice core dating based on time-frequency analysis of chemical profiles at a site where seasonal patterns may be significantly distorted by sporadic events of regional importance, specifically at the summit area of Nevado Illimani (6350 m a.s.l.), located in the eastern Bolivian Andes (16°37' S, 67°46' W). We used ion concentration depth profiles collected along a 100 m deep ice core. The results of Fourier time-frequency and wavelet transforms were first compared. Both methods were applied to a nitrate concentration depth profile. The resulting chronologies were checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points. With this first experiment, we demonstrated the efficiency of Fourier time-frequency analysis when tracking the nitrate natural variability. In addition, we were able to show spectrum aliasing due to under-sampling below 70 m. In this article, we propose a method of de-aliasing which significantly improves the core dating in comparison with annual layer manual counting. Fourier time-frequency analysis was applied to concentration depth profiles of seven other ions, providing information on the suitability of each of them for the dating of tropical Andean ice cores.

Gay, M.; De Angelis, M.; Lacoume, J.-L.

2014-09-01

221

Time-trends in the pattern of ocean-atmosphere exchange in an ice core from the Weddell Sea sector of Antarctica  

NASA Astrophysics Data System (ADS)

The east coast of the Antarctic Peninsula is strongly influenced by air masses that have traversed the Weddell Sea zone. A continuous record of annual-average values for ?18O, ?D, Cl- and non sea-salt SO42- in snowfall deposited since 1795, has been obtained on an ice core drilled on Dolleman Island (70°35.2'S, 60°55.5'W). Chemical changes along the ice core seem to be linked to changes in the concentration of the ice cover in the marginal ice zone. In the period since 1956, these variations appear to be coupled to the atmospheric circulation, as indexed by the atmospheric pressure gradient across the marginal ice zone. The largest anomaly in the 200-year sequence occurs in the period 1820-1880, during the final stages of the Little Ice Age. Exceptionally high concentrations of Cl-, low concentrations of biologically-derived sulphate, and high deuterium excess suggest that at this time there was a dense, compacted marginal ice zone with cyclones tracking more frequently than normal across ocean areas to the north of the ice edge. During the past century, there has been a marked decrease in deuterium excess of about 4‰, which implies that there has been a progressively increasing contribution to precipitation from moisture sources at lower temperature, probably from within the marginal ice zone. The implication is that there may have been significant weakening of the ice cover in this zone during the past century, despite satellite evidence which reveals no significant change in the position of the ice edge, at least since 1973.

Peel, D. A.; Mulvaney, R.

1992-09-01

222

Ice Core Contributions To Global Change Research: Past Successes and Future Directions  

NSDL National Science Digital Library

The U.S. ice coring community has, in concert with its international partners, made remarkable strides to advance in the understanding of global change. This document was assembled by the Ice Core Working Group (ICWG), and provides a synthesis of the global change lessons learned thus far, and the requirements and plans for solving new global change questions utilizing future ice coring activities. Sections on lessons learned include: the greenhouse/gas relationship, rapid climate change events, natural climate variability during the Holocene, extreme events (volcanoes and biomass burning), recent climate change as a precursor to modern climate, hindcasting instruments, anthropogenic impact on atmospheric chemistry, and human response to climate change as deduced from the paleorecord.

223

A method for analysis of vanillic acid in polar ice cores  

NASA Astrophysics Data System (ADS)

Biomass burning generates a wide range of organic compounds that are transported via aerosols to the polar ice sheets. Vanillic acid is a product of conifer lignin combustion, which has previously been observed in laboratory and ambient biomass burning aerosols. In this study a method was developed for analysis of vanillic acid in melted polar ice core samples. Vanillic acid was chromatographically separated using reversed-phase liquid chromatography (HPLC) and detected using electrospray ionization-triple quadrupole mass spectrometry (ESI-MS/MS). Using a 100 ?L injection loop and analysis time of 4 min, we obtained a detection limit of 77 ppt (parts per trillion by mass) and an analytical precision of ±10%. Measurements of vanillic acid in Arctic ice core samples from the Siberian Akademii Nauk core are shown as an example application of the method.

Grieman, M. M.; Greaves, J.; Saltzman, E. S.

2015-02-01

224

A 300 years environmental and climate archive for western Spitsbergen from Holtedahlfonna ice core  

NASA Astrophysics Data System (ADS)

An ice core extracted from Holtedahlfonna ice cap, the most extensive in western Spitsbergen, was analyzed for major ions and spans the period 1700-2005. The leading EOF component is correlated with an indicator of summer melt (log ([Na+]/[Mg2+])) from 1850 and shows that almost 50% of the variance can be attributed to seasonal melting since the beginning of the industrial revolution. Percolation or diffusion disturbs the annual stratigraphy allowing paleoclimate interpretation of the chemical record only at decadal resolution. The Holtedahlfonna ?18O value is less negative than that in the more easterly Lomonosovfonna ice core suggesting that moist air masses originate from a closer source most likely the Greenland Sea. During the Little Ice Age lower methansulfonic acid (MSA) concentration and MSA non-sea salt sulfate fraction is consistent with the Greenland Sea as the main source for biogenic ions in the ice core. Ammonium concentrations rise from 1880, which may result from the warming of the Greenland Sea or from zonal differences in atmospheric pollution transport over Svalbard. During winter neutralized aerosols are trapped within the tropospheric inversion layer which is usually weaker over open seas than over sea ice placing Holtedahlfonna within the inversion more frequently than Lomonosovfonna.

Beaudon, Emilie; Moore, John; Martma, Tõnu; Pohjola, Veijo; Van de Wal, Roderik; Kohler, Jack; Isaksson, Elisabeth

2013-04-01

225

A 300 years of environmental and climate archive for western Spitsbergen from Holtedahlfonna ice core  

NASA Astrophysics Data System (ADS)

An ice core extracted from Holtedahlfonna ice cap, the most extensive in western Spitsbergen, was analyzed for major ions and spans the period 1700-2005. The leading EOF component is correlated with an indicator of summer melt (log ([Na+]/[Mg2+])) from 1850 and shows that almost 50% of the variance can be attributed to seasonal melting since the beginning of the industrial revolution. Percolation or diffusion disturbs the annual stratigraphy allowing paleoclimate interpretation of the chemical record only at decadal resolution. The Holtedahlfonna ?18O value is less negative than that in the more easterly Lomonosovfonna ice core suggesting that moist air masses originate from a closer source most likely the Greenland Sea. During the Little Ice Age lower methansulfonic acid (MSA) concentration and MSA non-sea salt sulfate fraction is consistent with the Greenland Sea as the main source for biogenic ions in the ice core. Ammonium concentrations rise from 1880, which may result from the warming of the Greenland Sea or from zonal differences in atmospheric pollution transport over Svalbard. During winter neutralized aerosols are trapped within the tropospheric inversion layer which is usually weaker over open seas than over sea ice placing Holtedahlfonna within the inversion more frequently than Lomonosovfonna.

Beaudon, E.; Moore, J. C.; Pohjola, V. A.; Martma, T.; Van de Wal, R.; Kohler, J.; Isaksson, E. D.

2012-12-01

226

Application of composite flow laws to grain size distributions derived from polar ice cores  

NASA Astrophysics Data System (ADS)

Apart from evaluating the crystallographic orientation, focus of microstructural analysis of natural ice during the last decades has been to create depth-profiles of mean grain size. Several ice flow models incorporated mean grain size as a variable. Although such a mean value may coincide well with the size of a large proportion of the grains, smaller/larger grains are effectively ignored. These smaller/larger grains, however, may affect the ice flow modeling. Variability in grain size is observed on centimeter, meter and kilometer scale along deep polar ice cores. Composite flow laws allow considering the effect of this variability on rheology, by weighing the contribution of grain-size-sensitive (GSS, diffusion/grain boundary sliding) and grain-size-insensitive (GSI, dislocation) creep mechanisms taking the full grain size distribution into account [1]. Extraction of hundreds of grain size distributions for different depths along an ice core has become relatively easy by automatic image processing techniques [2]. The shallow ice approximation is widely adopted in ice sheet modeling and approaches the full-Stokes solution for small ratios of vertical to horizontal characteristic dimensions. In this approximation shear stress in the vertical plain dominates the strain. This assumption is not applicable at ice divides or dome structures, where most deep ice core drilling sites are located. Within the upper two thirds of the ice column longitudinal stresses are not negligible and ice deformation is dominated by vertical strain. The Dansgaard-Johnsen model [3] predicts a dominating, constant vertical strain rate for the upper two thirds of the ice sheet, whereas in the lower ice column vertical shear becomes the main driver for ice deformation. We derived vertical strain rates from the upper NEEM ice core (North-West Greenland) and compared them to classical estimates of strain rates at the NEEM site. Assuming intervals of constant accumulation rates, we found a variation of vertical strain rates by a factor 2-3 in the upper ice column. We discuss the current applicability of composite flow laws to grain size distributions extracted from ice cores drilled at sites where the flow direction rotates by 90 degrees with depth (i.e. ice divide). An interesting finding is that a transition to a glacial period in future would be associated with a decrease in vertical strain rate (due to a reduced accumulation rate) and an increase of the frequency of small grains (due to an enhanced impurity content). Composite flow laws assign an enhanced contribution of GSS creep to this transition. It is currently unclear which factor would have a greater influence. [1] Herwegh et al., 2005, J. Struct. Geol., 27, 503-521 [2] T. Binder et al., 2013, J. Microsc., 250, 130-141 [3] W. Dansgaard & S.J. Johnsen, 1969, J. Glaciol., 8, 215-223

Binder, Tobias; de Bresser, Hans; Jansen, Daniela; Weikusat, Ilka; Garbe, Christoph; Kipfstuhl, Sepp

2014-05-01

227

Chronology of Pu isotopes and 236U in an Arctic ice core.  

PubMed

In the present work, state of the art isotopic fingerprinting techniques are applied to an Arctic ice core in order to quantify deposition of U and Pu, and to identify possible tropospheric transport of debris from former Soviet Union test sites Semipalatinsk (Central Asia) and Novaya Zemlya (Arctic Ocean). An ice core chronology of (236)U, (239)Pu, and (240)Pu concentrations, and atom ratios, measured by accelerator mass spectrometry in a 28.6m deep ice core from the Austfonna glacier at Nordaustlandet, Svalbard is presented. The ice core chronology corresponds to the period 1949 to 1999. The main sources of Pu and (236)U contamination in the Arctic were the atmospheric nuclear detonations in the period 1945 to 1980, as global fallout, and tropospheric fallout from the former Soviet Union test sites Novaya Zemlya and Semipalatinsk. Activity concentrations of (239+240)Pu ranged from 0.008 to 0.254 mBq cm(-2) and (236)U from 0.0039 to 0.053 ?Bq cm(-2). Concentrations varied in concordance with (137)Cs concentrations in the same ice core. In contrast to previous published results, the concentrations of Pu and (236)U were found to be higher at depths corresponding to the pre-moratorium period (1949 to 1959) than to the post-moratorium period (1961 and 1962). The (240)Pu/(239)Pu ratio ranged from 0.15 to 0.19, and (236)U/(239)Pu ranged from 0.18 to 1.4. The Pu atom ratios ranged within the limits of global fallout in the most intensive period of nuclear atmospheric testing (1952 to 1962). To the best knowledge of the authors the present work is the first publication on biogeochemical cycles with respect to (236)U concentrations and (236)U/(239)Pu atom ratios in the Arctic and in ice cores. PMID:23770554

Wendel, C C; Oughton, D H; Lind, O C; Skipperud, L; Fifield, L K; Isaksson, E; Tims, S G; Salbu, B

2013-09-01

228

First Measurements of Osmium Concentration and Isotopic Composition in a Summit, Greenland Ice Core  

NASA Astrophysics Data System (ADS)

Osmium (Os) is one of the rarer elements in the environment and therefore one of the most difficult to accurately measure, but its isotopically distinctive crustal, mantle-derived, and extra-terrestrial sources make it a valuable geochemical tracer. Recent state-of-the-art analyses of precipitation, river water, and ocean water samples from around the world have revealed elevated concentrations of Os with a characteristically low (unradiogenic) Os isotopic signature (187Os/188Os). This unusual low Os isotopic signal has been interpreted as evidence for widespread Os pollution due to the smelting of Platinum Group Element (PGE) sulfide ores for use in automobile catalytic converters. However, an environmental time series of Os concentrations and isotopic composition spanning the pre-industrial to modern era has not previously been developed to evaluate changes in atmospheric Os sources through time. Here we present the first measurements of Os concentration and isotopic composition (to our knowledge) in a 100 m-long ice core collected from Summit, Greenland, spanning from ca. 1700 to 2010 AD. Due to the extremely low Os concentrations in snow (10-15 g/g), these analyses have only recently become possible with advances in Thermal Ionization Mass Spectrometry (TIMS) and ultra-clean analytical procedures. Initial results indicate that the 187Os/188Os of Greenland snow was unradiogenic (187Os/188Os = 0.13-0.15) for at least several periods over the past 300 years, including both pre-anthropogenic and modern times. Os concentrations in the Summit ice core are relatively high (11-52 pg/kg) compared to previously measured precipitation in North America, Europe, Asia and Antarctic sea ice (0.35-23 pg/kg). The low (unradiogenic) isotopic composition are consistent with extraterrestrial (cosmic dust and meteorites; 187Os/188Os = 0.13) and possibly volcanic (187Os/188Os = 0.15-0.6) Os sources, although the Os isotopic composition of volcanic emissions is poorly constrained. Crustal dust, with a radiogenic isotopic value of 1.26, is clearly not a major source for Os in Greenland snow. Additional analyses of trace element concentration and Os isotopic composition will be discussed in the context of constraining the relative contributions of extraterrestrial, volcanic, aeolian, and anthropogenic Os sources to Greenland snow through time.

Osterberg, E. C.; Sharma, M.; Hawley, R. L.; Courville, Z.

2010-12-01

229

Relationship between large-scale circulation and ice core proxy data from the McCall Glacier, Alaska  

NASA Astrophysics Data System (ADS)

Ice cores have often been used to reconstruct paleoclimate based on proxies contained in the cores. Using an ice core from McCall Glacier, in the eastern Brooks Range of Alaska, we attempt to determine relationships between ice core proxies and synoptic weather patterns influencing McCall Glacier. The method of self-organizing maps is used to objectively identify the synoptic patterns that influence Alaska. Results presented in this talk will focus on relationships between ice core proxies and synoptic weather patterns for the past 50 years, when reliable atmospheric reanalysis data are available. The focus will be on annual accumulation and lead concentration from an ice core recovered from the McCall Glacier.

Cassano, E.; Cassano, J. J.; McConnell, J. R.; Nolan, M.

2013-12-01

230

Detailed history of atmospheric trace elements from the Quelccaya ice core (Southern Peru) during the last 1200 years  

NASA Astrophysics Data System (ADS)

The recent increase in trace element concentrations, for example Cr, Cu, Zn, Ag, Pb, Bi, and U, in polar snow and ice has provided compelling evidence of a hemispheric change in atmospheric composition since the nineteenth century. This change has been concomitant with the expansion of the Industrial Revolution and points towards an anthropogenic source of trace elements in the atmosphere. There are very few low latitude trace element ice core records and these are believed to be sensitive to perturbations of regional significance. To date, these records have not been used to document a preindustrial anthropogenic impact on atmospheric composition at low latitudes. Ice cores retrieved from the tropical Andes are particularly interesting because they have the potential to reveal detailed information about the evolution and environmental consequences of mineral exploitation related to the Pre Inca Civilizations, the Inca Empire (1438-1533 AD) and the subsequent Spanish invasion and dominance (1532-1833 AD). The chemical record preserved in the ice of the Quelccaya ice cap (southern Peruvian Andes) offers the exceptional opportunity to geochemically constrain the composition of the tropical atmosphere at high resolution over the last ~1200 years. Quantification of twenty trace elements (Ag, Al, As, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb, Sb, Sn, Ti, Tl, U, V, and Zn) was performed by ICP-SFMS over 105 m of the Quelccaya North Dome core (5600 m asl, 128.57 m) by analyzing 2450 samples. This provides the first atmospheric trace element record in South America spanning continuously and at high resolution for the time period between 1990 and 790 AD. Ag, As, Bi, Cd, Cr, Co, Cu, Mn, Mo, Sb, Sn, Pb and Zn show increases in concentration and crustal enrichment factor starting at different times between 1450 and 1550 AD, in concomitance with the expansions of the Inca Empire and, subsequently, the Spanish Empire well before the inception of the Industrial Revolution. This indicates that there have been additional anthropogenic sources that have impacted the South American atmosphere during the past ~550 years. Furthermore, As, Bi and Pb record shows, the two most significant increases have occurred in the 20th century, one beginning in ~1905 AD and peaking in the 1920s and the second beginning in ~1955 AD and peaking in the 1970s. Comparison with other trace element records from Greenland and Antarctica reveals concomitant peaks of different amplitude in Pb concentration and crustal enrichment factor, possibly pointing to an unexpected larger than regional scale significance for the Quelccaya ice core record during the last century. In conclusion, the Quelccaya ice core indicates that societal and industrial development influenced the atmospheric composition in South America, from different large scale sources, during the last ~550 years. This is the first time that a low latitude ice core record has been used to reconstruct pre-industrial anthropogenic forcing on the atmosphere.

Uglietti, C.; Gabrielli, P.; Thompson, L. G.

2013-12-01

231

High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice cores  

E-print Network

High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice of diverse vascular plant- derived biomarkers in high-altitude ice cores, Geophys. Res. Lett., 36, L13501-volatile organic compounds derived from burned and fresh vascular plant sources and preserved in high- altitude ice

Howat, Ian M.

232

Modeling englacial attenuation using ice-core data for radar sounding of basal conditions  

NASA Astrophysics Data System (ADS)

Observation of the radar reflectivity of ice-sheet beds is a primary tool for discriminating wet from frozen beds, and for finding subglacial lakes. However, uncertainty in englacial radar attenuation and its spatial variation introduces corresponding uncertainty in estimates of basal reflectivity. Radio-frequency ice-sheet attenuation is dependent on the impurity (acidity and salinity) and temperature profiles in the ice column that is being probed. Modeling englacial radar attenuation using modeled temperature profiles and assumed, depth-averaged impurity concentrations reduces such uncertainties only modestly. Here we develop a physical attenuation model based on ice-core chemistry and temperature data that can be used, in conjunction with ice flow modeling, to estimate englacial attenuation over wide areas around an ice core (e.g., Vostok). We test the model initially at Siple Dome, West Antarctica, where both ice-core and independent radar attenuation data are available for comparison. The modeled depth-averaged attenuation rate there is 32 dB km-1, which lies between values of 26 dB km-1 and 35 dB km-1 measured at Siple Dome [Winebrenner et al., Ann. Glaciol. 37, 226-232, 2003]. A synthesis of experimental conductivity data shows that uncertainty in computed attenuation rates depends on uncertainties in conductivity parameterizations, which increase with increasing impurity concentrations and decreasing temperature. When the ice temperature is below about -15°C, fine-depth-scale impurity variations (mostly acid) control the attenuation rate; above -15°C, the higher temperature controls the attenuation rate more strongly, as the attenuation increases with temperature following an Arrhenius relationship.

MacGregor, J. A.; Winebrenner, D. P.; Matsuoka, K.; Conway, H.; Mayewski, P. A.; Clow, G.

2005-12-01

233

Chemical compounds of past soluble aerosols preserved in the NEEM and Dome Fuji ice cores  

NASA Astrophysics Data System (ADS)

We will present a study on chemical compounds of past soluble aerosols preserved in the NEEM and Dome Fuji (DF) ice cores. We have developed a new method, called the 'ice sublimation method', for detecting large amounts of aerosol particles in polar ice cores #1. The elemental components of detected single particles were measured by SEM-EDS, and then chemical compounds of each single particle are obtained such as insoluble dust, soluble sulfate salts, and soluble chloride salts. We have applied this sublimation method to the NEEM and DF ice cores in order to compare chemical compounds of past aerosols during Holocene and Last Glacial Maximum (LGM) in Arctic and Antarctic regions. The results showed that the primary soluble aerosols are sodium sulfate during Holocene #2, and sodium sulfate, calcium sulfate and sodium chloride during LGM #1 in the DF ice core. On the other hand, soluble aerosols in NEEM core is more chloride rich (less sulfate) than that of the DF core. The chloride rich aerosols in NEEM ice core indicate that sea salt in Arctic atmosphere is likely to survive against oxidation from nitric and sulfuric acid. During LGM in the NEEM core, there are many particles of 1) coexistence of dust, sulfate salt, and chloride salt, and of 2) calcium chloride. The coexistence is a result of both sulfate and chloride salts formation on/in dust by attached from hydrochloric and sulfuric acid. Calcium chloride is secondary aerosol, and is probably formed by chemical reaction in atmosphere of calcium carbonate and hydrochloric acid. Hydrochloric acid is also a reacted product from sea salt and strong acid (nitric and sulfuric acid). The existence of these particles implies that multiple chemical reactions occurred in the Arctic atmosphere during LGM. #1: Iizuka et al., 2009 Constituent elements of insoluble and non-volatile particles during the Last Glacial Maximum of the Dome Fuji ice core. J. Glaciol., 55, 552-562. #2: Iizuka et al., 2012 The rates of sea salt sulfatization in the atmosphere and surface snow of inland Antarctica. J. Geophys. Res. In press

Iizuka, Y.; Hansson, M.; Oyabu, I.; Karlin, T.; Goto-Azuma, K.

2012-04-01

234

Volcanic forcing of climate over the past 1500 years: An improved ice core-based index for climate models  

Microsoft Academic Search

Understanding natural causes of climate change is vital to evaluate the relative impacts of human pollution and land surface modification on climate. We have investigated one of the most important natural causes of climate change, volcanic eruptions, by using 54 ice core records from both the Arctic and Antarctica. Our recently collected suite of ice core data, more than double

Chaochao Gao; Alan Robock; Caspar Ammann

2008-01-01

235

Air fractionation in plate-like inclusions within the EPICA-DML deep ice core  

NASA Astrophysics Data System (ADS)

On ice samples from the ice core recovered in the frame of the European Project for Ice Coring in Antarctica at the deep drilling site in Dronning Maud Land (75°00S; 00°04E) micro-Raman spectrochemical analysis was applied to typical relaxation features appearing after the extraction of an ice core. Essentially, these relaxation microinclusions are little planar polygonal cavities possessing hexagonal symmetry i.e. thin negative crystals lying on the basal plane of the hosting ice crystallite. Usually named plate-like inclusions, PLIs, they tend to change their aspect ratio becoming in general rounder, thicker or thinner depending on the equilibrium established between the structure-composition of the ice and the minute environmental temperature-pressure conditions around a specific PLI, but still preserving a very large aspect ratio (typically 20:1). Muguruma and others (1966) and Mae (1968) have reported studies on plate hexagonal voids, i.e. PLIs, produced (only) in tensile deformation tests of natural and artificial single ice crystals while the first report of PLIs in Antarctic ice cores was presented by Gow (1971). In spite of these early studies and the abundance of PLIs in stored ice core samples, extended investigations of these relaxation features are scarce. We present the results of the first successful study of the chemical composition of PLIs using microfocus Raman spectroscopy (Nedelcu and others, in press). We observe that the relaxation features contain mainly O2 and N2 in their interior, with N2/O2 ratios smaller than 3.7 (the nowadays atmospheric air N2/O2 ratio), indicating a general oxygen enrichment that is not so different from O2 enrichments reported in other investigations on polar ice samples (Nakahara and others, 1988, Ikeda and others, 1999). These results seem to lend support to the current hypothesis that O2 diffuses faster than N2 through the ice matrix (Ikeda-Fukazawa and others, 2001, 2005; Severinghaus and Battle, 2006). More than this, they suggest that the diffusion of chemical traces in the ice matrix may not be negligible, at least locally, on a timescale of few years. These results could be important for the interpretation of ice-core paleoclimate records. Muguruma, J., S. Mae and A. Higashi, 1966. Void formation by non-basal glide in ice single crystals, Philos. Mag., 13(123), 625-629. Mae, S., 1968. Void formation during non-basal glide in ice single crystals under tension, Philos. Mag., 18(151), 101-114. Gow, A. J., 1971. Relaxation of ice in deep drill cores from Antarctica, J. Glaciol., 76(11), 2533-2541. Nedelcu, A. F., S. H. Faria and W. F. Kuhs, in press. Raman spectra of plate-like inclusions in the EPICA-DML ice core. J. Glaciol., 55(189) Nakahara, J., Y. Shigesato, A. Higashi, T. Hondoh and C.C. Langway, 1988. Raman spectra of natural clathrates in deep ice cores, Philos. Mag. B, 57(3), 421-430. Ikeda, T., H. Fukazawa, S. Mae, L. Pepin, P. Duval, B. Champagnon, V. Y. Lipenkov and T. Hondoh, 1999. Extreme fractionation of gases caused by formation of clathrate hydrates in Vostok Antarctic ice, Geophys. Res. Lett., 26(1), 91-94. Ikeda-Fukazawa, T., T. Hondoh, T. Fukumura, H. Fukazawa and S. Mae, 2001. Variation in N2/O2 ratio of occluded air in Dome Fuji antarctic ice, J. Geophys. Res., 106(D16), 17799-17810. Ikeda-Fukazawa, T., K. Fukumizu, K. Kawamura, S. Aoki, T. Nakazawa and T. Hondoh, 2005. Effects of molecular diffusion on trapped gas composition in polar ice cores, Earth Planet.Sci.Lett.,229(3-4),183-192. Severinghaus, J. P., and M. O. Battle, 2006. Fractionation of gases in polar ice during bubble close-off: new constraints from firn air, Ne, Kr and Xe observations, Earth Planet. Sci. Lett., 244(1-2), 474-500.

Nedelcu, A.; Faria, S. H.; Kipfstuhl, S.; Schmidt, B.; Kuhs, W. F.

2009-04-01

236

Investigating the preservation of nitrate isotopic composition in a tropical ice core from the Quelccaya Ice Cap, Peru  

NASA Astrophysics Data System (ADS)

The nitrogen and oxygen isotopic composition of nitrate in ice cores offers unique potential for examining reactive nitrogen oxide (NOx) budgets and oxidation chemistry of past atmospheres. A low-latitude record is of particular interest given that the dominant natural sources of NOx and production of hydroxyl radical are most prevalent in the tropics. Any interpretation of nitrate in ice cores, however, must first consider that nitrate in snow is vulnerable to postdepositional loss and isotopic alteration. We report and assess the integrity of nitrate-?15N, -?18O, and -?17O in a 30 m ice core from a high-elevation site in the central Andes. Clear seasonality in ?15N, ?18O, and nitrate concentration exists throughout most of the record and cannot be explained by photolysis or evaporation based on our current understanding of these processes. In contrast, nitrate in the upper ~12 m of the core and in a snowpit shows very different behavior. This may reflect alteration facilitated by recent melting at the surface. The relationships between ?15N, ?18O, ?17O, and concentration in the unaltered sections can be interpreted in terms of mixing of nitrate from discrete sources. Transport effects and an englacial contribution from nitrification cannot be ruled out at this time, but the observed isotopic compositions are consistent with expected signatures of known NOx sources and atmospheric oxidation pathways. Specifically, nitrate deposited during the wet season reflects biogenic soil emissions and hydroxyl/peroxy radical chemistry in the Amazon, while dry season deposition reflects a lightning source and ozone chemistry at higher levels in the troposphere.

Buffen, Aron M.; Hastings, Meredith G.; Thompson, Lonnie G.; Mosley-Thompson, Ellen

2014-03-01

237

Phylogenetic analysis of anaerobic psychrophilic enrichment cultures obtained from a greenland glacier ice core  

NASA Technical Reports Server (NTRS)

The examination of microorganisms in glacial ice cores allows the phylogenetic relationships of organisms frozen for thousands of years to be compared with those of current isolates. We developed a method for aseptically sampling a sediment-containing portion of a Greenland ice core that had remained at -9 degrees C for over 100,000 years. Epifluorescence microscopy and flow cytometry results showed that the ice sample contained over 6 x 10(7) cells/ml. Anaerobic enrichment cultures inoculated with melted ice were grown and maintained at -2 degrees C. Genomic DNA extracted from these enrichments was used for the PCR amplification of 16S rRNA genes with bacterial and archaeal primers and the preparation of clone libraries. Approximately 60 bacterial inserts were screened by restriction endonuclease analysis and grouped into 27 unique restriction fragment length polymorphism types, and 24 representative sequences were compared phylogenetically. Diverse sequences representing major phylogenetic groups including alpha, beta, and gamma Proteobacteria as well as relatives of the Thermus, Bacteroides, Eubacterium, and Clostridium groups were found. Sixteen clone sequences were closely related to those from known organisms, with four possibly representing new species. Seven sequences may reflect new genera and were most closely related to sequences obtained only by PCR amplification. One sequence was over 12% distant from its closest relative and may represent a novel order or family. These results show that phylogenetically diverse microorganisms have remained viable within the Greenland ice core for at least 100,000 years.

Sheridan, Peter P.; Miteva, Vanya I.; Brenchley, Jean E.

2003-01-01

238

Synchronizing the North American Varve Chronology with Greenland ice core records using meteoric 10Be flux  

NASA Astrophysics Data System (ADS)

The North American Varve Chronology (NAVC) is a floating 5700-year sequence of glacial lake varves deposited in the Connecticut River Valley of the northeast US ~18,000-12,500 years ago. The NAVC is an annually resolved record of regional climate and ice-marginal processes at 40-45° N latitude, near the margin of the retreating Laurentide Ice Sheet (LIS). NAVC deposition occurred at the same time as rapid and abrupt Arctic and North Atlantic climate changes that took place during the last deglaciation. An age estimate for the NAVC based on radiocarbon dated plant macrofossils in individual varves implies a relationship between ice-marginal events recorded by the NAVC and climate events recorded in Greenland ice cores. For example, the retreat rate of the LIS up the Connecticut River Valley increased during the Bolling warming in Greenland, a readvance of the LIS margin took place during the Older Dryas cold period, and a correlation between an outburst flood from glacial Lake Iroquois and the Intra-Allerod Cold Period supports the hypothesis that the flood affected North Atlantic thermohaline circulation. On the other hand, a doubling of the ice-margin retreat rate recorded by the NAVC around 16,000 years ago coincides with a relatively cold period in Greenland. Our goal is to investigate the precise time relationship between these events by synchronizing the NAVC with the Greenland ice core time scale using atmospherically-produced 10Be. Existing 10Be flux records, including those from Greenland ice cores, exhibit solar variability on a range of time scales. Because this variability is globally synchronous, a 10Be flux record for the NAVC can, in principle, be used to align NAVC and ice core timescales. We are generating such a record at present. First, we are analyzing short varve sections at high temporal resolution to evaluate the magnitude of solar variability signals; a single section analyzed so far displays interannual variability with a period consistent with the 11-year solar cycle. Second, we are investigating seasonal variability in 10Be concentrations in individual varves to learn about 10Be transport and deposition in proglacial lakes. Third, we will generate a long record of 10Be concentrations at decadal resolution for comparison with similar ice core records.

DeJong, B.; Balco, G.; Ridge, J. C.; Rood, D. H.; Bierman, P. R.

2012-12-01

239

Kelp genes reveal effects of subantarctic sea ice during the Last Glacial Maximum.  

PubMed

The end of the Last Glacial Maximum (LGM) dramatically reshaped temperate ecosystems, with many species moving poleward as temperatures rose and ice receded. Whereas reinvading terrestrial taxa tracked melting glaciers, marine biota recolonized ocean habitats freed by retreating sea ice. The extent of sea ice in the Southern Hemisphere during the LGM has, however, yet to be fully resolved, with most palaeogeographic studies suggesting only minimal or patchy ice cover in subantarctic waters. Here, through population genetic analyses of the widespread Southern Bull Kelp (Durvillaea antarctica), we present evidence for persistent ice scour affecting subantarctic islands during the LGM. Using mitochondrial and chloroplast genetic markers (COI; rbcL) to genetically characterize some 300 kelp samples from 45 Southern Ocean localities, we reveal a remarkable pattern of recent recolonization in the subantarctic. Specifically, in contrast to the marked phylogeographic structure observed across coastal New Zealand and Chile (10- to 100-km scales), subantarctic samples show striking genetic homogeneity over vast distances (10,000-km scales), with a single widespread haplotype observed for each marker. From these results, we suggest that sea ice expanded further and ice scour during the LGM impacted shallow-water subantarctic marine ecosystems more extensively than previously suggested. PMID:19204277

Fraser, Ceridwen I; Nikula, Raisa; Spencer, Hamish G; Waters, Jonathan M

2009-03-01

240

Kelp genes reveal effects of subantarctic sea ice during the Last Glacial Maximum  

PubMed Central

The end of the Last Glacial Maximum (LGM) dramatically reshaped temperate ecosystems, with many species moving poleward as temperatures rose and ice receded. Whereas reinvading terrestrial taxa tracked melting glaciers, marine biota recolonized ocean habitats freed by retreating sea ice. The extent of sea ice in the Southern Hemisphere during the LGM has, however, yet to be fully resolved, with most palaeogeographic studies suggesting only minimal or patchy ice cover in subantarctic waters. Here, through population genetic analyses of the widespread Southern Bull Kelp (Durvillaea antarctica), we present evidence for persistent ice scour affecting subantarctic islands during the LGM. Using mitochondrial and chloroplast genetic markers (COI; rbcL) to genetically characterize some 300 kelp samples from 45 Southern Ocean localities, we reveal a remarkable pattern of recent recolonization in the subantarctic. Specifically, in contrast to the marked phylogeographic structure observed across coastal New Zealand and Chile (10- to 100-km scales), subantarctic samples show striking genetic homogeneity over vast distances (10,000-km scales), with a single widespread haplotype observed for each marker. From these results, we suggest that sea ice expanded further and ice scour during the LGM impacted shallow-water subantarctic marine ecosystems more extensively than previously suggested. PMID:19204277

Fraser, Ceridwen I.; Nikula, Raisa; Spencer, Hamish G.; Waters, Jonathan M.

2009-01-01

241

Design and Calibration of a High-Precision Density Gauge for Firn and Ice Cores  

NASA Astrophysics Data System (ADS)

The Maine Automated Density Gauge Experiment (MADGE) is a field deployable gamma-ray density gauging instrument designed to provide high resolution (3.3 mm) and high precision (±0.004 g cm-3) density profiles of polar firn and ice cores at a typical throughput of 1.5 m h-1. The resulting density profiles are important in ice sheet mass balance and paleoclimate studies, as well as the modeling electromagnetic wave propagation in firn and ice for remote sensing and ground penetrating radar applications. This study describes the design (optimal gamma-ray energy selection, measurement uncertainty analysis, dead-time corrections) and calibration (mass-attenuation coefficient and absolute density calibrations) of the instrument, and discusses the results of additional experiments to verify the calculated measurement uncertainty. Data collected from firn cores drilled on the recent 2006-2007 U.S. Internation Trans-Antarctic Scientific Expedition are also shown and discussed.

Breton, Daniel; Hamilton, Gordon

2009-10-01

242

Annually resolved ice core records of tropical climate variability over the past ~1800 years.  

PubMed

Ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics, but they are difficult to recover and few exist. Here, we report annually resolved ice core records from the Quelccaya ice cap (5670 meters above sea level) in Peru that extend back ~1800 years and provide a high-resolution record of climate variability there. Oxygen isotopic ratios (?(18)O) are linked to sea surface temperatures in the tropical eastern Pacific, whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the Intertropical Convergence Zone in the region of the tropical Andes. Quelccaya continues to retreat and thin. Radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia. PMID:23558172

Thompson, L G; Mosley-Thompson, E; Davis, M E; Zagorodnov, V S; Howat, I M; Mikhalenko, V N; Lin, P-N

2013-05-24

243

Time-series analysis of chemical trends in a dated ice core from Antarctica  

SciTech Connect

Polar ice sheets contain valuable information about past atmospheric conditions. Atmospherically produced or transported substances from natural and anthropogenic sources are preserved stratigraphically within the ice layers as a result of both wet and dry deposition mechanisms. Substances deposited include aerosols and gaseous compounds. The analysis of trace elements contained in dated annual snow layers provides a measure of the elemental chemistry content of the atmosphere during the same time interval. The aerosol content of the atmosphere and ice sheets is one of the most important parameters for cloud/radiation interaction processes. Ice cores were obtained from the Byrd Station, West Antarctica, in November, 1989. This study presents results obtained from instrumental neutron activation analysis and ion chromatography on 30 samples over a 20 year period.

Keskin, S.S.; Olmez, I. [Massachusetts Institute of Technology, Cambridge, MA (United States); Langway, C.C. Jr. [State Univ. of New York, Buffalo, NY (United States)

1994-12-31

244

Tephrochronology of the Siple Dome ice core, West Antarctica: correlations and sources  

NASA Astrophysics Data System (ADS)

A total of 24 tephra-bearing volcanic layers have been recognized between 550 and 987 m depth in the Siple Dome A (SDM-A) ice core, in addition to a number already recognized tephra in the upper 550 m ( Dunbar et al., 2003; Kurbatov et al., 2006). The uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of explosive volcanic eruptions and that the layers therefore represent time-stratigraphic markers in the ice core. Despite the very fine grain size of these tephra (mostly less than 20 microns), robust geochemical compositions were determined by electron microprobe analysis. The source volcanoes for these tephra layers are largely found within the Antarctic plate. Statistical geochemical correlations tie nine of the tephra layers to known eruptions from Mt. Berlin, a West Antarctic volcano that has been very active for the past 100,000 years. Previous correlations were made to an eruption of Mt. Takahe, another West Antarctic volcano, and one to Mt. Hudson, located in South America ( Kurbatov et al., 2006). The lowest tephra layer in the ice core, located at 986.21 m depth, is correlated to a source eruption with an age of 118.1 ± 1.3 ka, suggesting a chronological pinning point for the lower ice. An episode of anomalously high volcanic activity in the ice in the SDM-A core between 18 and 35 ka ( Gow and Meese, 2007) appears to be related to eruptive activity of Mt. Berlin volcano. At least some of the tephra layers found in the SDM-A core appear to be the result of very explosive eruptions that spread ash across large parts of West Antarctica, off the West Antarctic coast, as well as also being recognized in East Antarctica ( Basile et al., 2001; Narcisi et al., 2005, 2006). Some of these layers would be expected to should be found in other deep Antarctic ice cores, particularly ones drilled in West Antarctica, providing correlative markers between different cores. The analysis of the tephra layers in the Siple Dome core, along with other Antarctic cores, provides a timing framework for the relatively proximal Antarctic and South American volcanic eruptive events, allowing these to be distinguished from the tropical eruptions that may play a greater role in climate forcing.

Dunbar, Nelia W.; Kurbatov, Andrei V.

2011-06-01

245

10Be climate fingerprints during the Eemian in the NEEM ice core, Greenland  

NASA Astrophysics Data System (ADS)

Several deep Greenland ice cores have been retrieved, however, capturing the Eemian period has been problematic due to stratigraphic disturbances in the ice. The new Greenland deep ice core from the NEEM site (77.45°N, 51.06°W, 2450 m.a.s.l) recovered a relatively complete Eemian record. Here we discuss the cosmogenic 10Be isotope record from this core. The results show Eemian average 10Be concentrations about 0.7 times lower than in the Holocene which suggests a warmer climate and approximately 65-90% higher precipitation in Northern Greenland compared to today. Effects of shorter solar variations on 10Be concentration are smoothed out due to coarse time resolution, but occurrence of a solar maximum at 115.26-115.36 kyr BP is proposed. Relatively high 10Be concentrations are found in the basal ice sections of the core which may originate from the glacial-interglacial transition and relate to a geomagnetic excursion about 200 kyr BP.

Sturevik-Storm, Anna; Aldahan, Ala; Possnert, Göran; Berggren, Ann-Marie; Muscheler, Raimund; Dahl-Jensen, Dorthe; Vinther, Bo M.; Usoskin, Ilya

2014-09-01

246

10Be climate fingerprints during the Eemian in the NEEM ice core, Greenland.  

PubMed

Several deep Greenland ice cores have been retrieved, however, capturing the Eemian period has been problematic due to stratigraphic disturbances in the ice. The new Greenland deep ice core from the NEEM site (77.45 °N, 51.06 °W, 2450 m.a.s.l) recovered a relatively complete Eemian record. Here we discuss the cosmogenic (10)Be isotope record from this core. The results show Eemian average (10)Be concentrations about 0.7 times lower than in the Holocene which suggests a warmer climate and approximately 65-90% higher precipitation in Northern Greenland compared to today. Effects of shorter solar variations on (10)Be concentration are smoothed out due to coarse time resolution, but occurrence of a solar maximum at 115.26-115.36 kyr BP is proposed. Relatively high (10)Be concentrations are found in the basal ice sections of the core which may originate from the glacial-interglacial transition and relate to a geomagnetic excursion about 200 kyr BP. PMID:25266953

Sturevik-Storm, Anna; Aldahan, Ala; Possnert, Göran; Berggren, Ann-Marie; Muscheler, Raimund; Dahl-Jensen, Dorthe; Vinther, Bo M; Usoskin, Ilya

2014-01-01

247

Exploring seasonal accumulation bias in a west central Greenland ice core with observed and reanalyzed data  

E-print Network

Exploring seasonal accumulation bias in a west central Greenland ice core with observed, Department of Geography, The Ohio State University, Columbus, OH, USA ABSTRACT. The seasonality heights and affords a unique opportunity to assess the seasonal distribution of accumulation and test

Howat, Ian M.

248

10Be climate fingerprints during the Eemian in the NEEM ice core, Greenland  

PubMed Central

Several deep Greenland ice cores have been retrieved, however, capturing the Eemian period has been problematic due to stratigraphic disturbances in the ice. The new Greenland deep ice core from the NEEM site (77.45°N, 51.06°W, 2450?m.a.s.l) recovered a relatively complete Eemian record. Here we discuss the cosmogenic 10Be isotope record from this core. The results show Eemian average 10Be concentrations about 0.7 times lower than in the Holocene which suggests a warmer climate and approximately 65–90% higher precipitation in Northern Greenland compared to today. Effects of shorter solar variations on 10Be concentration are smoothed out due to coarse time resolution, but occurrence of a solar maximum at 115.26–115.36?kyr BP is proposed. Relatively high 10Be concentrations are found in the basal ice sections of the core which may originate from the glacial-interglacial transition and relate to a geomagnetic excursion about 200?kyr BP. PMID:25266953

Sturevik-Storm, Anna; Aldahan, Ala; Possnert, Göran; Berggren, Ann-Marie; Muscheler, Raimund; Dahl-Jensen, Dorthe; Vinther, Bo M.; Usoskin, Ilya

2014-01-01

249

PeV Neutrinos Observed by IceCube from Cores of Active Galactic Nuclei  

NASA Technical Reports Server (NTRS)

I show that the high energy neutrino flux predicted to arise from active galactic nuclei cores can explain the PeV neutrinos detected by IceCube without conflicting with the constraints from the observed extragalactic cosmic-ray and gamma-ray backgrounds.

Stecker, Floyd W.

2013-01-01

250

Holocene Climate Variability in Antarctica Based on 11 Ice-Core Isotopic Records  

Microsoft Academic Search

A comparison is made of the Holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east Antarctica (Vostok, Dome B, Plateau Remote, Komsomolskaia, Dome C, Taylor Dome, Dominion Range, D47, KM105, and Law Dome) and west Antarctica (Byrd), with temporal resolution from 20 to 50 yr. The long-term trends possibly reflect local

Valérie Masson; Françoise Vimeux; Jean Jouzel; Vin Morgan; Marc Delmotte; Philippe Ciais; Claus Hammer; Sigfus Johnsen; Vladimir Ya. Lipenkov; E. Mosley-Thompson; Jean-Robert Petit; Eric J. Steig; Michel Stievenard; Rein Vaikmae

2000-01-01

251

An 80-year summer temperature history from the Xiao Dongkemadi ice core in the central Tibetan Plateau and its association with atmospheric circulation  

NASA Astrophysics Data System (ADS)

The climate significance of oxygen isotopes from the central Tibetan Plateau (cTP) ice cores is a debated issue because of large scale atmospheric circulation. A high-resolution ?18O record was recovered from the Xiao Dongkemadi (XD) ice core, which expanded the spatial coverage of ?18O data in this region. Annual average ?18O correlated significantly with nearby MJJAS air temperatures, suggesting the ?18O can be used as a proxy to reconstruct regional climate change. The reconstructed temperature anomaly is related to the regional and global warming trends, and the greater warming amplitude since 1970s is related to the elevation dependency of the warming signal. The close relationship of the warming to variations in glacier mass balances and discharge reveal that recent warming has led to obvious glacier shrinkage and runoff increase. Correlation analysis suggests that monsoon and westerly moisture substantially influence the cTP ice core records, along with an increase in their level of contribution to the XD core accumulation in recent decades, and confirms a teleconnection of regional climate of the cTP ice cores with climate parameters in the Indian and North Atlantic Oceans.

Li, Xiangying; Ding, Yongjian; Yu, Zhongbo; Mika, Sillanpää; Liu, Shiyin; Shangguan, Donghui; Lu, Chengyang

2015-02-01

252

Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation  

NASA Astrophysics Data System (ADS)

The Greenland ?18O ice core record is used as a proxy for Greenland surface air temperatures and to interpret Atlantic Multidecadal Oscillation (AMO) variability. An analysis of annual ?18O data from six Arctic ice cores (five from Greenland and one from Canada's Ellesmere Island) suggests a significant AMO spatial and temporal variability within a recent period of 660 years. A dominant AMO periodicity near 20 years is clearly observed in the southern (Dye3 site) and the central (GISP2, Crete and Milcent) regions of Greenland. This 20-year variability is, however, significantly reduced in the northern (Camp Century and Agassiz Ice Cap) region, likely due to a larger distance from the Atlantic Ocean, and a much lower snow accumulation. A longer time scale AMO component of 45-65 years, which has been seen clearly in the 20th century SST data, is detected only in central Greenland ice cores. We find a significant difference between the AMO cycles during the Little Ice Age (LIA) and the Medieval Warm Period (MWP). The LIA was dominated by a ˜20 year AMO cycle with no other decadal or multidecadal scale variability above the noise level. However, during the preceding MWP the 20 year cycle was replaced by a longer scale cycle centered near a period of 43 years with a further 11.5 year periodicity. An analysis of two coupled atmosphere-ocean general circulation models control runs (UK Met Office HadCM3 and NOAA GFDL CM2.1) agree with the shorter and longer time-scales of Atlantic Meridional Overturning Circulation (AMOC) and temperature fluctuations with periodicities close to those observed. However, the geographic variability of these periodicities indicated by ice core data is not captured in model simulations.

Chylek, Petr; Folland, Chris; Frankcombe, Leela; Dijkstra, Henk; Lesins, Glen; Dubey, Manvendra

2012-05-01

253

A shallow ice core re-drilled on the Dunde Ice Cap, western China: recent changes in the Asian high mountains  

NASA Astrophysics Data System (ADS)

A 51 m deep ice core was re-drilled on the Dunde Ice Cap of western China in 2002, 15 years after the previous ice core drilling in 1987. Dating by seasonal variations in ?18O and particle concentration showed that this 51 m deep ice core covered approximately the last 150 years. The stratigraphy and density showed that more than 90% of the ice core was refrozen ice layers, which comprised less than 5% of the annual accumulation in the older core. This indicates that the ice cap had experienced a more intense melting since 1987, possibly due to climate warming in this region. Mean net accumulation since the last drilling (2002-1987) was 176 mm a-1, which was considerably smaller than that obtained from the 1987 core (390 mm a-1, 1987-1963), indicating a significant decrease of net accumulation on the ice cap in the more recent period. The ?18O record showed an increasing trend in the late 19th century and the highest in the 1950s, which is consistent with the previous core findings. However, there has been no significant increase in ?18O during the last two decades, in contrast to the warming trends suggested by the melt features and other climate records. This discrepancy may be due to the modification of ?18O records by melt water runoff, percolation, and refreezing on the ice cap. Results strongly suggest recent significant mass loss of glaciers in the Asian high mountains and serious shortage of water supply for local people in this arid region in the near future.

Takeuchi, Nozomu; Miyake, Takayuki; Nakazawa, Fumio; Narita, Hideki; Fujita, Koji; Sakai, Akiko; Nakawo, Masayoshi; Fujii, Yoshiyuki; Duan, Keqin; Yao, Tandong

2009-10-01

254

The WAIS Divide deep ice core WD2014 chronology - Part 1: Methane synchronization (68-31 ka BP) and the gas age-ice age difference  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet Divide (WAIS Divide, WD) ice core is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WD gas age-ice age difference (?age) using a combination of firn densification modeling, ice-flow modeling, and a data set of ?15N-N2, a proxy for past firn column thickness. The largest ?age at WD occurs during the Last Glacial Maximum, and is 525 ± 120 years. Internally consistent solutions can be found only when assuming little to no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WD chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu Cave speleothem record. The small ?age at WD provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the "bipolar seesaw".

Buizert, C.; Cuffey, K. M.; Severinghaus, J. P.; Baggenstos, D.; Fudge, T. J.; Steig, E. J.; Markle, B. R.; Winstrup, M.; Rhodes, R. H.; Brook, E. J.; Sowers, T. A.; Clow, G. D.; Cheng, H.; Edwards, R. L.; Sigl, M.; McConnell, J. R.; Taylor, K. C.

2015-02-01

255

Reconstruction of recent climate change in Alaska from the Aurora Peak ice core, central Alaska  

NASA Astrophysics Data System (ADS)

A 180.17 m ice core was drilled at Aurora Peak in the central part of the Alaska Range, Alaska, in 2008 to allow reconstruction of centennial-scale climate change in the northern North Pacific. The 10 m depth temperature in the borehole was -2.2 °C, which corresponded to the annual mean air temperature at the drilling site. In this ice core, there were many melt-refreeze layers due to high temperature and/or strong insolation during summer seasons. We analyzed stable hydrogen isotopes (?D) and chemical species in the ice core. The ice core age was determined by annual counts of ?D and seasonal cycles of Na+, and we used reference horizons of tritium peaks in 1963 and 1964, major volcanic eruptions of Mount Spurr in 1992 and Mount Katmai in 1912, and a large forest fire in 2004 as age controls. Here, we show that the chronology of the Aurora Peak ice core from 95.61 m to the top corresponds to the period from 1900 to the summer season of 2008, with a dating error of ± 3 years. We estimated that the mean accumulation rate from 1997 to 2007 (except for 2004) was 2.04 m w.eq. yr-1. Our results suggest that temporal variations in ?D and annual accumulation rates are strongly related to shifts in the Pacific Decadal Oscillation index (PDOI). The remarkable increase in annual precipitation since the 1970s has likely been the result of enhanced storm activity associated with shifts in the PDOI during winter in the Gulf of Alaska.

Tsushima, A.; Matoba, S.; Shiraiwa, T.; Okamoto, S.; Sasaki, H.; Solie, D. J.; Yoshikawa, K.

2015-02-01

256

Reconstruction of recent climate change in Alaska from the Aurora Peak ice core, central Alaska  

NASA Astrophysics Data System (ADS)

A 180.17 m ice core was drilled at Aurora Peak in the central part of the Alaska Range, Alaska, in 2008 to allow reconstruction of centennial-scale climate change in the northern North Pacific. The 10 m-depth temperature in the borehole was -2.2 °C, which corresponded to annual mean air temperature at the drilling site. In this ice core, there were many melt-refrozen layers due to high temperature and/or strong insolation during summer seasons. We analyzed stable hydrogen isotopes (?D) and chemical species in the ice core. The ice core age was determined by annual counts of ?D and seasonal cycles of Na+, and we used reference horizons of tritium peaks in 1963 and 1964, major volcanic eruptions of Mount Spurr in 1992 and Mount Katmai in 1912, and a large forest fire in 2004 as age controls. Here, we show that the chronology of the Aurora Peak ice core from 95.61 m w.eq. to the top corresponds to the period from 1900 to the summer season of 2008, with a dating error of ±3 years. We estimated that the mean accumulation rate from 1997 to 2007 (except for 2004) was 1.88 m w.eq per year. Our results suggest that temporal variation in ?D and annual accumulation rates are strongly related to shifts in the Pacific Decadal Oscillation index (PDOI). The remarkable increase in annual precipitation since the 1970s has likely been the result of enhanced storm activity associated with shifts in the PDOI during winter in the Gulf of Alaska.

Tsushima, A.; Matoba, S.; Shiraiwa, T.; Okamoto, S.; Sasaki, H.; Solie, D. J.; Yoshikawa, K.

2014-04-01

257

A chemical pacemaker to refine chronology for the deep East Antarctic ice cores  

NASA Astrophysics Data System (ADS)

A current dating approach of ice core records of the deep East Antarctic ice cores relies on ice flow modelling (thinning function of ice layer) as well as on the estimate of the snow accumulation rate. By the use of inverse method, the modelled ice chronology is generally constrained by few dated horizons (volcanic, 10Be peaks from solar or from magnetic inversion related events…) and/or by orbital tuning process (temperature proxy, 18O of air bubbles…). In absence of absolute dating the orbital tuning from new data or proxies is attractive and may serve as a test of the modelled ice age. In this respect a proxy showing orbital frequencies is adequate if: i) it was not already used to constrain the modelled chronology, ii) it reflects properties of the ice rather than properties of the gas (to prevent gas-age/ice age uncertainties), iii) its physical link with insolation must be rather direct, iv) the precession band (20kyr) which supplies more tie points than the obliquity band (41kyr) should dominate. The continental dust and marine sodium records were so far not used to constrain the modelled chronology. The dust and marine sodium appear firstly correlated to patterns of temperature and therefore to the hydrologic cycle which influences at the same time the source emissions (for dust), the atmospheric cleansing and the deposition onto the ice sheet. Once the overall temperature effects is compensate by best fit functions, the residual signal for dust and sodium concentrations over the last 400 ky from Epica Dome C and Vostok records display strong precession oscillations for both sites. Interestingly, the sodium residuals appear to increase with austral summer insolation while the dust residuals decrease remaining out of phase. Such behaviour could be understood by a positive effect of insolation on sodium emission (strengthening of spring cyclonic activity…) and negative effect on dust sources (reduction of Patagonian dust emission by strengthening of Southern American monsoon…). This dual behaviour which need to be determined, allows combination of sodium and dust residuals providing a "chemical pacemaker" dominated by precession which could be used to refine the modelled chronology. A test was done on the EDC3 modelled age of the Epica Dome C deep ice core which covers the last 800ky.

Petit, J. R.; Delmonte, B.; Lemieux-Dudon, B.; Parrenin, F.

2009-04-01

258

Continuous online field deployable high precision and high resolution water isotope analysis from ice cores  

NASA Astrophysics Data System (ADS)

One of the most important features of ice cores as climate and atmospheric paleoarchives is their potential for high temporal resolution. The measurement of chemical impurities in ice cores that fully exploits this high resolution has become standard with the advent of Continuous Flow Analysis (CFA) from continuously melted ice core segments, often performed in the field. Meanwhile, the measurement of water stable isotopic composition (deuterium and oxygen-18) continues, for the most part, to be performed offline via discrete sampling with traditional mass spectroscopy. These offline procedures are time consuming, expensive, and do not fully exploit the temporal resolution available in the ice core. Here we describe a new method and the first results for the determination of water isotopic content measured from a continuous melted rod with a commercially available near-infrared cavity ring down spectrometer (CRDS; http://www.picarro.com/) coupled to a CFA system both in the field on the Greenland ice sheet and in the laboratory. For the measurement of water isotopes a carefully controlled fraction of the CFA melt stream is evaporated directly into the laser cavity for simultaneous analysis of both deuterium and oxygen-18 content. The details of the system have been tested with a deployment to the North Greenland Eemian Ice Drilling (NEEM) coupled to the University of Bern CFA system and in the laboratory with NGRIP ice coupled to the University of Copenhagen CFA system. The results show that the system already produces the highest interpretable resolution records that are comparable or somewhat less precise than traditional mass spectroscopy discrete sample methods. The enormous potential of the system is being realized in the density and resolution of the produced records in connection with other highly resolved series (e.g. chemical impurities), and also in the efficiency by which the records can be produced. Among other things, time series from this type of analysis will benefit ice core dating via layer counting of deconvoluted isotopic series. High resolution paleo-temperature reconstructions based on the calculation of the differential diffusion rates of the two heavy isotopologues of water vapor in firn, via the study of their spectral properties, can also benefit from the enhanced resolution of the measured time series.

Gkinis, Vasileios; Popp, Trevor; Johnsen, Sigfus; Blunier, Thomas; Stowasser, Christopher; Kettner, Ernesto

2010-05-01

259

An ultra-clean technique for accurately analysing Pb isotopes and heavy metals at high spatial resolution in ice cores with sub-pg g(-1) Pb concentrations.  

PubMed

Measurements of Pb isotope ratios in ice containing sub-pg g(-1) concentrations are easily compromised by contamination, particularly where limited sample is available. Improved techniques are essential if Antarctic ice cores are to be analysed with sufficient spatial resolution to reveal seasonal variations due to climate. This was achieved here by using stainless steel chisels and saws and strict protocols in an ultra-clean cold room to decontaminate and section ice cores. Artificial ice cores, prepared from high purity water were used to develop and refine the procedures and quantify blanks. Ba and In, two other important elements present at pg g(-1) and fg g(-1) concentrations in Polar ice, were also measured. The final blank amounted to 0.2+/-0.2 pg of Pb with (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios of 1.16+/-0.12 and 2.35+/-0.16, respectively, 1.5+/-0.4 pg of Ba and 0.6+/-2.0 fg of In, most of which probably originates from abrasion of the steel saws by the ice. The procedure was demonstrated on a Holocene Antarctic ice core section and was shown to contribute blanks of only approximately 5%, approximately 14% and approximately 0.8% to monthly resolved samples with respective Pb, Ba and In concentrations of 0.12 pg g(-1), 0.3 pg g(-1) and 2.3 fg g(-1). Uncertainties in the Pb isotopic ratio measurements were degraded by only approximately 0.2%. PMID:19185125

Burn, Laurie J; Rosman, Kevin J R; Candelone, Jean-Pierre; Vallelonga, Paul; Burton, Graeme R; Smith, Andrew M; Morgan, Vin I; Barbante, Carlo; Hong, Sungmin; Boutron, Claude F

2009-02-23

260

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

PubMed Central

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 ?18O 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

Schlosser, E; Anschütz, H; Divine, D; Martma, T; Sinisalo, A; Altnau, S; Isaksson, E

2014-01-01

261

A new Himalayan ice core CH4 record: possible hints at the preindustrial latitudinal gradient  

NASA Astrophysics Data System (ADS)

Two ice cores recovered from the Himalayan East Rongbuk (ER) Glacier on the northeast saddle of Mt. Qomolangma (Everest) (28°01' N, 86°58' E, 6518 m above sea level) give access to a tentative record of past Himalayan atmospheric mixing ratio of CH4 spanning the past 1200 yr. The major part of the record is affected by artifacts probably due to in situ production. After selecting what may represent the true atmospheric mixing ratio, an average of 749 ± 25 ppbv of CH4 is estimated for the late preindustrial Holocene, which is ~ 36 ± 17 (~ 73 ± 18) ppbv higher than the atmospheric levels recorded in the Greenland (Antarctic) ice cores. A comparison of these new data with model simulations of the CH4 latitudinal gradient suggests either that the models do not get a correct balance between high and low latitude CH4 sources, or that the filtered CH4 profile from the ER cores remains biased by small artifacts.

Hou, S.; Chappellaz, J.; Raynaud, D.; Masson-Delmotte, V.; Jouzel, J.; Bousquet, P.; Hauglustaine, D.

2013-11-01

262

Chronological refinement of an ice core record at Upper Fremont Glacier in south central North America  

NASA Astrophysics Data System (ADS)

The potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized. Although excellent paleoclimatic records exist for the polar regions, paleoclimatic ice core records are not common from midlatitude locations. An ice core removed from the Upper Fremont Glacier in Wyoming provides evidence for abrupt climate change during the mid-1800s. Volcanic events (Krakatau and Tambora) identified from electrical conductivity measurements (ECM) and isotopic and chemical data from the Upper Fremont Glacier were reexamined to confirm and refine previous chronological estimates of the ice core. At a depth of 152 m the refined age-depth profile shows good agreement (1736±10 A.D.) with the 14C age date (1729±95 A.D.). The ?18O profile of the Upper Fremont Glacier (UFG) ice core indicates a change in climate known as the Little Ice Age (LIA). However, the sampling interval for ?18O is sufficiently large (20 cm) such that it is difficult to pinpoint the LIA termination on the basis of ?18O data alone. Other research has shown that changes in the ?18O variance are generally coincident with changes in ECM variance. The ECM data set contains over 125,000 data points at a resolution of 1 data point per millimeter of ice core. A 999-point running average of the ECM data set and results from ƒ tests indicates that the variance of the ECM data decreases significantly at about 108 m. At this depth, the age-depth profile predicts an age of 1845 A.D. Results indicate the termination of the LIA was abrupt with a major climatic shift to warmer temperatures around 1845 A.D. and continuing to present day. Prediction limits (error bars) calculated for the profile ages are ±10 years (90% confidence level). Thus a conservative estimate for the time taken to complete the LIA climatic shift to present-day climate is about 10 years, suggesting the LIA termination in alpine regions of central North America may have occurred on a relatively short (decadal) timescale.

Schuster, Paul F.; White, David E.; Naftz, David L.; Cecil, L. Dewayne

2000-02-01

263

Chronological refinement of an ice core record at Upper Fremont Glacier in south central North America  

USGS Publications Warehouse

The potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized. Although excellent paleoclimatic records exist for the polar regions, paleoclimatic ice core records are not common from midlatitude locations. An ice core removed from the Upper Fremont Glacier in Wyoming provides evidence for abrupt climate change during the mid-1800s. Volcanic events (Krakatau and Tambora) identified from electrical conductivity measurements (ECM) and isotopic and chemical data from the Upper Fremont Glacier were reexamined to confirm and refine previous chronological estimates of the ice core. At a depth of 152 m the refined age-depth profile shows good agreement (1736 ?? 10 A.D.) with the 14C age date (1729 ?? 95 A.D.). The ??18O profile of the Upper Fremont Glacier (UFG) ice core indicates a change in climate known as the Little Ice Age (LIA). However, the sampling interval for ??18O is sufficiently large (20 cm) such that it is difficult to pinpoint the LIA termination on the basis of ??18O data alone. Other research has shown that changes in the ??18O variance are generally coincident with changes in ECM variance. The ECM data set contains over 125,000 data points at a resolution of 1 data point per millimeter of ice core. A 999-point running average of the ECM data set and results from f tests indicates that the variance of the ECM data decreases significantly at about 108 m. At this depth, the age-depth profile predicts an age of 1845 A.D. Results indicate the termination of the LIA was abrupt with a major climatic shift to warmer temperatures around 1845 A.D. and continuing to present day. Prediction limits (error bars) calculated for the profile ages are ??10 years (90% confidence level). Thus a conservative estimate for the time taken to complete the LIA climatic shift to present-day climate is about 10 years, suggesting the LIA termination in alpine regions of central North America may have occurred on a relatively short (decadal) timescale. Copyright 2000 by the American Geophysical Union.

Schuster, P.F.; White, D.E.; Naftz, D.L.; Cecil, L.D.

2000-01-01

264

Chronological refinement of an ice core record at Upper Fremont Glacier in south central North America  

SciTech Connect

The potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized. Although excellent paleoclimatic records exist for the polar regions, paleoclimatic ice core records are not common from midlatitude locations. An ice core removed from the Upper Fremont Glacier in Wyoming provides evidence for abrupt climate change during the mid-1800s. Volcanic events (Krakatau and Tambora) identified from electrical conductivity measurements (ECM) and isotopic and chemical data from the Upper Fremont Glacier were reexamined to confirm and refine previous chronological estimates of the ice core. At a depth of 152 m the refined age-depth profile shows good agreement (1736{+-}10 A.D.) with the {sup 14}C age date (1729{+-}95 A.D.). The {delta}{sup 18}O profile of the Upper Fremont Glacier (UFG) ice core indicates a change in climate known as the Little Ice Age (LIA). However, the sampling interval for {delta}{sup 18}O is sufficiently large (20 cm) such that it is difficult to pinpoint the LIA termination on the basis of {delta}{sup 18}O data alone. Other research has shown that changes in the {delta}{sup 18}O variance are generally coincident with changes in ECM variance. The ECM data set contains over 125,000 data points at a resolution of 1 data point per millimeter of ice core. A 999-point running average of the ECM data set and results from f tests indicates that the variance of the ECM data decreases significantly at about 108 m. At this depth, the age-depth profile predicts an age of 1845 A.D. Results indicate the termination of the LIA was abrupt with a major climatic shift to warmer temperatures around 1845 A.D. and continuing to present day. Prediction limits (error bars) calculated for the profile ages are {+-}10 years (90% confidence level). Thus a conservative estimate for the time taken to complete the LIA climatic shift to present-day climate is about 10 years, suggesting the LIA termination in alpine regions of central North America may have occurred on a relatively short (decadal) timescale. (c) 2000 American Geophysical Union.

Schuster, Paul F. [U.S. Geological Survey, Water Resources Division, Boulder, Colorado (United States)] [U.S. Geological Survey, Water Resources Division, Boulder, Colorado (United States); White, David E. [Golden Software, Golden, Colorado (United States)] [Golden Software, Golden, Colorado (United States); Naftz, David L. [U.S. Geological Survey, Water Resources Division, Salt Lake City, Utah (United States)] [U.S. Geological Survey, Water Resources Division, Salt Lake City, Utah (United States); Cecil, L. DeWayne [U.S. Geological Survey, Water Resources Division, Idaho Falls, Idaho (United States)] [U.S. Geological Survey, Water Resources Division, Idaho Falls, Idaho (United States)

2000-02-27

265

Volcanic eruptions recorded in the Illimani ice core (Bolivia): 1918Â 1998 and Tambora periods  

NASA Astrophysics Data System (ADS)

Acid layers of volcanic origin detected in polar snow and ice layers are commonly used to document past volcanic activity on a global scale or, conversely, to date polar ice cores. Although most cataclysmic eruptions of the last two centuries (Pinatubo, El Chichon, Agung, Krakatoa, Cosiguina, Tambora, etc.) occurred in the tropics, cold tropical glaciers have not been used for the reconstruction of past volcanism. The glaciochemical study of a 137 m ice core drilled in 1999 close to the summit of Nevado Illimani (Eastern Bolivian Andes, 16°37' S, 67°46' W, 6350 m asl) demonstrates, for the first time, that such eruptions are recorded by both their tropospheric and stratospheric deposits. An 80-year ice sequence (1918-1998) and the Tambora years have been analyzed in detail. In several cases, ash, chloride and fluoride were also detected. The ice records of the Pinatubo (1991), Agung (1963) and Tambora (1815) eruptions are discussed in detail. The potential impact of less important regional eruptions is discussed.

de Angelis, M.; Simões, J.; Bonnaveira, H.; Taupin, J.-D.; Delmas, R. J.

2003-10-01

266

Volcanic eruptions recorded in the Illimani ice core (Bolivia): 1918-1998 and Tambora periods  

NASA Astrophysics Data System (ADS)

Acid layers of volcanic origin detected in polar snow and ice layers are commonly used to document past volcanic activity on a global scale or, conversely, to date polar ice cores. Although most cataclysmic eruptions of the last two centuries (Pinatubo, El Chichon, Agung, Krakatoa, Cosiguina, Tambora, etc.) occurred in the tropics, cold tropical glaciers have not been used for the reconstruction of past volcanism. The glaciochemical study of a 137 m ice core drilled in 1999 close to the summit of Nevado Illimani (Eastern Bolivian Andes, 16°37' S, 67°46' W, 6350 m a.s.l.) demonstrates, for the first time, that such eruptions are recorded by both their tropospheric and stratospheric deposits. An 80-year ice sequence (1918-1998) and the Tambora years have been analyzed in detail. In several cases, ash, chloride and fluoride were also detected. The ice records of the Pinatubo (1991), Agung (1963) and Tambora (1815) eruptions are discussed in detail. Less important eruptions located in the Andes are also recorded and may also disturb background aerosol composition on a regional scale.

de Angelis, M.; Simões, J.; Bonnaveira, H.; Taupin, J.-D.; Delmas, R. J.

2003-05-01

267

Reassessment of Crete (Greenland) ice core acidity/volcanism link to climate change  

SciTech Connect

Previous comparisons of the Crete (Greenland) ice core acidity record with climate variations of the last 1,400 years suggested that changes in volcanism may have significantly influenced climate on this time scale. However, the ice core acidity record consists of volcanically-induced spikes superimposed on a background acidity of nonvolcanic origin that varied significantly in amplitude. Herein the authors produce a record of Crete volcanism based solely on an objective definition of individual volcanic events in the ice core record. There are 92 acidity peaks in the 1,420-year record. Since at least 26% of the post-1,600 eruptions are of local (Icelandic) origin, they estimate a mean recurrence interval of 20.8 years for hemispheric-scale eruptions rich in sulphate. On decadal time scales, volcanism has varied by a factor of three-four over the last 1,400 years. However, the climate-volcanism correlation is considerably less impressive (r = [minus]0.23) than previously concluded (r = [minus]0.52). The good correspondence between volcanism and climate previously reported are due to background acidity levels that show a significant Little Ice Age increase. The background increase may reflect changes in ocean productivity. 24 refs., 5 figs., 1 tab.

Crowley, T.J.; Criste, T.A.; Smith, N.R. (Applied Research Corp., College Station, TX (United States))

1993-02-05

268

A new ice core proxy of continental weathering and its feedback with atmospheric CO2  

NASA Astrophysics Data System (ADS)

The analysis of CO2 and its stable carbon isotopes from ice cores revealed large changes of atmospheric CO2 which are closely related to a reorganisation of the global ocean circulation, marine processes and minor contributions in the terrestrial carbon storage. These components dominate the large CO2 amplitudes during glacial/interglacial terminations. Yet, on longer orbital time scales, CO2 is also modulated by the alkalinity of the ocean system. The net alkalinity influx to the ocean is driven by silicate weathering, which draws down atmospheric CO2 and provides alkalinity in the form of bicarbonate ions. Conversely, alkalinity is lost during coral reef growth and when CaCO3 is buried in marine sediments. On orbital time scales, these fluxes are assumed to be almost balanced as atmospheric CO2 and its climatic effects feed back on the weathering rates providing a negative feedback loop. Besides these basic concepts, little is known about the magnitude of weathering rate fluctuations on orbital time scales. To date, proxies from marine sediments and Fe-Mn crusts that faithfully record the ocean composition over glacial interglacial cycles do not quantify the total weathering fluxes to the ocean but only indicate that the style of weathering or the source area of sediment has changed. Due to large spatial heterogeneity, individual field site measurements do not elucidate global fluxes of weathering products to the ocean and how those might affect atmospheric CO2 concentrations. Here, we use a novel approach using the pptv-level trace gas CF4, which can be analysed in air trapped in ice cores. CF4 is a trace impurity in granites and other plutonic rocks, and during weathering this gas escapes into the atmosphere. In preindustrial times, weathering of granitic rocks was the only natural source of CF4. Because CF4 is inert to destruction processes in the tropo- and stratospheres, its only sink is destruction by UV radiation in the mesosphere. This chemical inertness is responsible for an exceptionally long atmospheric lifetime which is expected to range between 50 kyr and 400 kyr. We developed a vacuum melt-extraction system for ice core samples coupled to a mass spectrometry detector to precisely measure the trace amounts of CF4 found in past atmosphere. During the last 800 kyr, the atmospheric CF4 concentrations varied in a narrow band between 31 ppt and 35 ppt, i.e. only 10-15 % variability, providing a first estimate of the long-term weathering rate fluctuations. On closer inspection, our CF4 record, however, shows a pronounced shift toward higher CF4 levels after 430 kyr (the Mid-Brunhes Event). With the beginning of Marine Isotope stage 11, we find a steep rise in CF4 that probably relates to intense weathering during the first interglacial, where CO2 reached 280 ppm and sea level may have been even higher than today. Further, our record shows that CF4 concentrations, and thus weathering, increases during interglacials and falls during the coldest, glacial phases. This dataset lends support to a strong positive coupling of continental weathering rates during warmer climate conditions at high CO2 levels.

Schmitt, J.; Seth, B.; Köhler, P.; Willenbring, J. K.; Fischer, H.

2012-04-01

269

High resolution ice core records of late Holocene volcanism: Current and future contributions from the Greenland PARCA core  

NASA Astrophysics Data System (ADS)

A suite of spatially distributed, multi-century cores collected since 1995 under NASA's Program for Arctic Regional Climate Assessment (PARCA) provides an excellent archive of volcanic emissions reaching Greenland. As records of equivalent quality from higher accumulation sites in Antarctica become available, their integration will produce a richer, better temporally constrained and more climatologically valuable history of global volcanism. The Greenland PARCA cores have been accurately dated using multiple seasonally varying indicators (?18O, insoluble dust, H202, nitrate, calcium) and the ongoing chemical analyses are providing new volcanic histories that complement the limited records that exist. The first results confirm that the sulfate aerosols from an unidentified pre-Tambora eruption called Unknown: (1) were widely dispersed across the Greenland ice sheet; (2) first arrived in the 1810 A.D. snow fall; and, (3) in 1810 A.D., the first year after the eruption (1809 A.D.), produced concentrations of excess SO42- (EXS) comparable to those deposited in 1816 A.D., the first year after the eruption of Tambora in 1815 A.D. The EXS originating from the eruption of Laki craters or Lakagigar (1783 A.D.) is confined to a single year (1783 A.D.) and varies considerably across the ice sheet, primarily as a function of the local accumulation rate. Future chemical analyses of the PARCA cores promise richly detailed histories of EXS emissions from both known and yet to be identified volcanic eruptions. The high temporal resolution of these ice core records will help resolve timing issues and their broad spatial distribution will provide a more representative estimate of the EXS flux associated with a specific eruption.

Mosley-Thompson, Ellen; Mashiotta, Tracy A.; Thompson, Lonnie G.

270

Assessment of diffusive isotopic fractionation in polar firn, and application to ice core trace gas records  

NASA Astrophysics Data System (ADS)

During rapid variations of the atmospheric mixing ratio of a trace gas, diffusive transport in the porous firn layer atop ice sheets and glaciers alters the isotopic composition of that gas relative to the overlying atmosphere. Records of past atmospheric trace gas isotopic composition from ice cores and firn need to be corrected for this diffusive fractionation artifact. We present a novel, semi-empirical method to accurately estimate the magnitude of the diffusive fractionation in the ice core record. Our method (1) consists of a relatively simple analytical calculation; (2) requires only commonly available ice core data; (3) is not subject to the uncertainties inherent to estimating the accumulation rate, temperature, close-off depth and depth-diffusivity relationship back in time; (4) does not require knowledge of the true atmospheric variations, but uses the smoothed records obtained from ice cores; (5) arguably gives more accurate results than a combined firn densification-firn air transport modeling study would. We apply the method to records of CH4, CO2 and N2O mixing ratios, and we find that the correction is particularly important for ?13C-CH4. We apply the correction to ?13C-CH4 records over the last glacial termination and the 8.2 ka event. In both cases the diffusive signal exceeds the analytical precision of the data, and has a significant impact on the observed isotopic trends. For the 8.2 ka event the corrected data show an isotopic enrichment in ?13C-CH4 for the duration of the event, consistent with reduced wetland emissions.

Buizert, Christo; Sowers, Todd; Blunier, Thomas

2013-01-01

271

A 2680 year volcanic record from the DT-401 East Antarctic ice core  

NASA Astrophysics Data System (ADS)

Volcanic signals recorded in the Antarctic and Greenland ice cores can provide useful information on past explosive volcanism and its impact. In this study, we carried out a continuous sulfate analysis of a 102.65 m East Antarctic ice core (DT-401, dated as 2682 years) and identified 36 extensive volcanic eruption signals using Cole-Dai's method, which gives an average of 1.4 eruptions per century, consistent with the results from the Plateau Remote (PR-B) ice core. When the record is divided into three parts, the latest millennium (1999-1000 A.D.), the middle millennium (999-1 A.D.), and the earliest 682 years (0 A.D. to 682 B.C.), it is found that there were more volcanic eruptions that occurred during the latest millennium (19 eruptions) than during the middle millennium (10 eruptions) of the record and that the intensities of the eruptions in the latest millennium are markedly larger than those in the middle one. There were only seven events recorded in the earliest 682 years, but their intensities were greater, and nearly half of the eruptions had a similar intensity to Tambora's (1815 A.D.), which differs from the PR-B record. It is also found that volcanism and its average accumulation rate were lower during the "Little Ice Age" than during the "Medieval Warm Period." Comparison of volcanic records between DT-401 and other Antarctica ice cores (PR-B, Dome C, DT-263, and Byrd) show that in the East Antarctica area with its lower accumulation rates, postdepositional effects may play an important role in the deposition of the sulfate.

Ren, Jiawen; Li, Chuanjin; Hou, Shugui; Xiao, Cunde; Qin, Dahe; Li, Yuansheng; Ding, Minghu

2010-06-01

272

The GISP2 ice core and snow-atmosphere chemical exchange  

NASA Astrophysics Data System (ADS)

Polar snow and ice are among the most valuable, or perhaps are the most valuable, tools for reconstructing past climatic conditions. Glacial-ice records large changes over time scales ranging from intraannual to glacial-interglacial transitions. Changes in the ice are thought to largely reflect changes in atmospheric chemistry and dynamics resulting from variations in biogeochemical cycling due to climatic, and other, perturbations [Oeschger and Langway, 1989].However, two broad classes of processes, air-to-snow transfer and post-depositional modification, combine to filter and potentially distort atmospheric signals before they can be preserved in the glacial record [Neftel, 1991]. Recognizing the critical need to understand air-snow transfer and postdepositional modifications to unravel the climate information recorded in ice cores, the International Commission on Snow and Ice (ICSI) established a working group on Snow-Atmosphere Chemical Exchange. With support from the National Science Foundation, Division of Polar Programs, the ICSI working group organized a workshop to develop a science plan for a 3- to 5-year research effort focused on exchange processes. The workshop will follow the current Greenland Ice Sheet Project Two (GISP2) drilling effort at Summit, Greenland.

Bales, Roger; Dibb, Jack; Neftel, Albrecht

273

Ice Core Evidence of Past Changes in the Hydrological Cycle of the Tropics and Subtropics  

NASA Astrophysics Data System (ADS)

Ice core records from South America, Africa, the Himalayas and the Tibetan Plateau provide records of past changes in the hydrological cycle over a wide range of latitudes. Ice cores from seven high elevation (>5300 m asl) sites raise questions about the synchroneity of glaciation and the relative importance of temperature and precipitation in governing the growth of permanent ice fields in low latitude mountain ranges. Cores from Huascarán (Peru at 9°S) and Sajama (Bolivia at 18°S) contain continuous records back ~ 19 ka and 25 ka, respectively and thus extend into Late Glacial Stage (LGS). Both glaciers undoubtedly survived the early Holocene warm period (10 to 6 ka B.P.), but neither contains a record of the entire LGS back to the previous interglacial. Thus, both mountains, among the highest in South America, appear to have been ice-free during a time when the Earth was in the grip of a 'global' glaciation. Conversely, the ice core records from the Dasuopu (28°N) and Puruogangri (34°N) glaciers suggest that ice existing today in the Himalayas and central Tibet formed during the early Holocene warm period. Glacier formation/starvation in the tropics and subtropics appears to be controlled by wetter/drier conditions in response to precession-driven changes in solar radiation. These ice core records are combined with more than 120 other paleoclimate to produce a global map of effective moisture changes between the Last Glacial Maximum and the Early Holocene. Changes in the tropical hydrological system over the last 25 ka have been extreme with the global pattern of climate in the Early Holocene being nearly opposite that during the Last Glacial Maximum. For example, the zonal belts in the deep tropics that experienced greater aridity during the LGS attained maximum humidity in the Early Holocene while at the same time the humid subtropical and mid-latitude belts became drier. The symmetry of these changes in moisture about the equator suggests a strong role for the Hadley circulation, and that either its position or its intensity or both were altered as the Earth moved from glacial to interglacial conditions.

Thompson, L. G.; Davis, M. E.; Mosley-Thompson, E. S.; Lin, P.; Mashiotta, T. A.

2002-12-01

274

Isotope thermometry in melt-affected ice cores  

NASA Astrophysics Data System (ADS)

A statistically significant relationship is observed between stable water isotopes (?18O) and melt amounts in a melt-affected firn core (SSummit) taken from the Prince of Wales Icefield, Ellesmere Island, Canada. By contrast, a low-melt firn core taken from a higher-elevation, higher-latitude location on the same icefield shows no relationship between these variables. We interpret this as evidence for meltwater-induced isotopic enrichment at SSummit. A percent melt-based correction slope is applied to isotopic values from SSummit. Uncorrected and corrected temperature records derived from the raw and corrected ?18O values are compared to bias-corrected temperature data from the NCEP Reanalysis. Improvements are observed in the isotopic reconstruction of SSummit annual precipitation-weighted temperatures when we correct for meltwater enrichment, with a reduction from +0.6°C to 0.0°C in the mean annual error and a decrease in root-mean-square error from 1.8°C to 1.6°C. The correction factor appears to overcorrect isotopic modification during high melt years such as 1999, during which SSummit experienced nearly 70% more melt than the average from 1975 to 2000. Excluding 1999 data from the correction analysis results in a slight reduction in mean absolute error from 1.4°C to 1.3°C. These results suggest that melt-induced isotopic modification cannot be corrected in very high melt years.

Moran, T.; Marshall, S. J.; Sharp, M. J.

2011-06-01

275

Recent Increase in Elemental Carbon Concentration and Deposition in a Svalbard Ice Core  

NASA Astrophysics Data System (ADS)

Black carbon (BC) is an aerosol produced by incomplete combustion of biomass and fossil fuels. Due to its strong light absorption it warms the atmosphere. Climate effects of BC are intensified in the Arctic where its deposition on snow and ice decreases surface albedo, causing earlier spring melt and associated feedbacks. Despite the significant role of BC in Arctic climate warming, there is little information on its concentrations and climate effects in the Arctic in time periods preceding direct observational data. Here we present first results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard (European Arctic) glacier (Holtedahlfonna) from 1700 to 2004. The inner part of a 125 m deep ice core was melted, filtered and analyzed for apparent elemental carbon using a thermal optical method. EC concentrations (?g L-1) and the deposition (mg m-2 yr-1) were generally low in the pre-industrial era. Concentrations peaked around 1910 and again around 1950, whereas only the 1910 peak was recorded in the EC deposition, followed by decreasing deposition values. Strikingly, both EC concentration and deposition started to increase rapidly from the 1970s until 2004. This rise is not seen in any thus far published European or Arctic ice core, and it seems to contradict atmospheric BC measurements from the Arctic which indicate decreasing atmospheric BC concentrations since the beginning of the observations at the end of 1980s. However, the magnitude of the measured concentrations is in accordance with previous ice core EC measurements from the European Alps and a BC concentration and deposition peak around 1910 has also been recorded in Greenland ice cores. Work is continuing to disentangle the cause of the increasing EC values in the recent decades suggested by the present ice core. Contribution from any local sources has been ruled out. Back trajectory modeling is carried out to establish the EC source areas. The present results might indicate some long-range transport of EC to Svalbard, since BC emissions have decreased or stayed constant in Europe and North America for the last decades, whereas the emissions from China, India and parts of the former USSR have increased at the same time. Regardless of the cause of the increasing EC values, these results have significant implications to the past radiative transfer at the coring site. This project will continue with modeling of the past EC surface radiative forcing in the Holtedahlfonna area based on the present results.

Ruppel, M.; Isaksson, E. D.; Ström, J.; Svensson, J.; Beaudon, E.; Korhola, A.

2013-12-01

276

Metagenomics Reveals Microbial Community Composition And Function With Depth In Arctic Permafrost Cores  

NASA Astrophysics Data System (ADS)

The Arctic is one of the most climatically sensitive regions on Earth and current surveys show that permafrost degradation is widespread in arctic soils. Biogeochemical feedbacks of permafrost thaw are expected to be dominated by the release of currently stored carbon back into the atmosphere as CO2 and CH4. Understanding the dynamics of C release from permafrost requires assessment of microbial functions from different soil compartments. To this end, as part of the Next Generation Ecosystem Experiment in the Arctic, we collected two replicate permafrost cores (1m and 3m deep) from a transitional polygon near Barrow, AK. At this location, permafrost starts from 0.5m in depth and is characterized by variable ice content and higher pH than surface soils. Prior to sectioning, the cores were CT-scanned to determine the physical heterogeneity throughout the cores. In addition to detailed geochemical characterization, we used Illumina MiSeq technology to sequence 16SrRNA genes throughout the depths of the cores at 1 cm intervals. Selected depths were also chosen for metagenome sequencing of total DNA (including phylogenetic and functional genes) using the Illumina HiSeq platform. The 16S rRNA gene sequence data revealed that the microbial community composition and diversity changed dramatically with depth. The microbial diversity decreased sharply below the first few centimeters of the permafrost and then gradually increased in deeper layers. Based on the metagenome sequence data, the permafrost microbial communities were found to contain members with a large metabolic potential for carbon processing, including pathways for fermentation and methanogenesis. The surface active layers had more representatives of Verrucomicrobia (potential methane oxidizers) whereas the deep permafrost layers were dominated by several different species of Actinobacteria. The latter are known to have a diverse metabolic capability and are able to adapt to stress by entering a dormant yet viable state. In addition, several isolates were obtained from different depths throughout the cores, including methanogens from some of the deeper layers. Together these data present a new view of potential geochemical cycles carried out by microorganisms in permafrost and reveal how community members and functions are distributed with depth.

Jansson, J.; Tas, N.; Wu, Y.; Ulrich, C.; Kneafsey, T. J.; Torn, M. S.; Hubbard, S. S.; Chakraborty, R.; Graham, D. E.; Wullschleger, S. D.

2013-12-01

277

Ice cores record significant 1940s Antarctic warmth related to tropical climate variability  

PubMed Central

Although the 20th Century warming of global climate is well known, climate change in the high-latitude Southern Hemisphere (SH), especially in the first half of the century, remains poorly documented. We present a composite of water stable isotope data from high-resolution ice cores from the West Antarctic Ice Sheet. This record, representative of West Antarctic surface temperature, shows extreme positive anomalies in the 1936–45 decade that are significant in the context of the background 20th Century warming trend. We interpret these anomalies—previously undocumented in the high-latitude SH—as indicative of strong teleconnections in part driven by the major 1939–42 El Niño. These anomalies are coherent with tropical sea-surface temperature, mean SH air temperature, and North Pacific sea-level pressure, underscoring the sensitivity of West Antarctica's climate, and potentially its ice sheet, to large-scale changes in the global climate. PMID:18697932

Schneider, David P.; Steig, Eric J.

2008-01-01

278

Tephra studies on the deep Talos Dome ice core, East Antarctic Plateau  

NASA Astrophysics Data System (ADS)

In the context of the TALDICE (TALos Dome Ice CorE) project conducted by a consortium of five European nations led by Italy, a 1620-m long ice core has been drilled at Talos Dome (72°49'S, 159°11'E; 2315 m; www.taldice.org), on the eastern edge of the East Antarctic plateau during the field seasons 2004-2008. Owing to its relatively high accumulation rate, this near-coastal core preserves a detailed undisturbed paleoclimate record covering the past 250,000 years, back to Marine Isotope Stage (MIS) 7.5. The Talos Dome ice is a significant volcanic ash archive. During core inspection of the TALDICE core, more than 100 macroscopic tephra layers were located and inventoried, with an average tephra frequency one order of magnitude greater than the tephra frequency in deep cores from inland East Antarctic plateau over the last two glacial cycles. TALDICE prominent tephra layers, studied by scanning electron microscopy, Coulter Counter and electron microprobe analysis, display an alkaline geochemical character indicating an origin in nearby volcanoes of the Melbourne Volcanic Province (McMurdo Volcanic Group). Our tephra record helps reconstruct an improved history of explosive eruptions in northern Victoria Land, supplementing the stratigraphic record obtained by outcrop studies and documenting previously unknown temporal trends and specific episodes. Investigations on less prominent tephra horizons are in progress with the aim of complementing the Holocene volcanic record of local visible beds and establishing the detailed tephrostratigraphy for the region. To date about ten discrete ice sections showing anomalously coarse grain size has proved to contain significant concentrations of unreworked volcanic glass. Single shard major element analyses of some invisible volcanic horizons indicate subalkaline compositions, which are incompatible with Antarctic volcanism and suggesting long-distance tephra transport from either South American and/or New Zealand volcanoes. Ongoing comparison between geochemical results and literature data on Holocene tephrostratigraphies of potential source volcanoes will likely suggest correlation of TALDICE invisible tephras with known radiometrically-dated eruptions, with potential implications for ice core timescale and stratigraphic correlations over wide areas.

Narcisi, B.; Petit, J.; Delmonte, B.; Stenni, B.

2011-12-01

279

Continuous and discrete measurements of atmospheric methane from an ice core from Roosevelt Island, East Ross Sea, Antarctica  

NASA Astrophysics Data System (ADS)

A new ice core from Roosevelt Island was drilled for the Roosevelt Island Climate Evolution (RICE) project to establish the history of deglaciation of the Ross Sea through the Holocene. Evidence of glacial retreat in the Ross Sea Embayment shows that deglaciation happened in several stages of rapid collapse and persisted well after the melting of the Northern Hemisphere ice sheets was complete. The ice rise on Roosevelt Island records the timing of the last leap when the West Antarctic Ice Sheet (WAIS) receded past Roosevelt Island. In order to discern the timing of deglaciation, a precise age-depth relationship is required for the RICE ice core. We present a timescale for Roosevelt Island using mixing ratios of methane in air preserved within the ice core measured continuously with a Picarro laser spectrometer as well as in high-resolution with gas chromatography (GC). Discrete data from GC analysis over the top 400m of core replicate both the magnitude and variations from other high-resolution ice core records from WAIS Divide, Law Dome, GISP2 and NEEM S1. Both the continuous and discrete methane records of the RICE core were matched to these established records and provide an accurate and consistent depth-age relationship for the past 3.6kyr. Future work on the 400-750m depth section is expected to extend the RICE chronology to at least the Last Glacial Maximum.

Lee, James; Brook, Ed; Blunier, Thomas; Paul, Vallelonga; Bertler, Nancy

2014-05-01

280

Ice age aerosol content from East Antarctic ice core samples and past wind strength  

Microsoft Academic Search

Isotopic analysis of Antarctic deep cores provides valuable information on the Earth's past climate. Past atmospheric trace element contents of continental, volcanic, marine or other origins can also be reconstructed assuming that the chemical concentrations in the air and in the snow are well correlated1,2. These atmospheric trace element contents, as well as atmospheric gas contents3, are important for climate

Jean-Robert Petit; Martine Briat; Alain Royer

1981-01-01

281

Multilayer Formation and Evaporation of Deuterated Ices in Prestellar and Protostellar Cores  

NASA Astrophysics Data System (ADS)

Extremely large deuteration of several molecules has been observed toward prestellar cores and low-mass protostars for a decade. New observations performed toward low-mass protostars suggest that water presents a lower deuteration in the warm inner gas than in the cold external envelope. We coupled a gas-grain astrochemical model with a one-dimensional model of a collapsing core to properly follow the formation and the deuteration of interstellar ices as well as their subsequent evaporation in the low-mass protostellar envelopes with the aim of interpreting the spatial and temporal evolutions of their deuteration. The astrochemical model follows the formation and the evaporation of ices with a multilayer approach and also includes a state-of-the-art deuterated chemical network by taking the spin states of H2 and light ions into account. Because of their slow formation, interstellar ices are chemically heterogeneous and show an increase of their deuterium fractionation toward the surface. The differentiation of the deuteration in ices induces an evolution of the deuteration within protostellar envelopes. The warm inner region is poorly deuterated because it includes the whole molecular content of ices, while the deuteration predicted in the cold external envelope scales with the highly deuterated surface of ices. We are able to reproduce the observed evolution of water deuteration within protostellar envelopes, but we are still unable to predict the super-high deuteration observed for formaldehyde and methanol. Finally, the extension of this study to the deuteration of complex organics, important for the prebiotic chemistry, shows good agreement with the observations, suggesting that we can use the deuteration to retrace their mechanisms and their moments of formation.

Taquet, Vianney; Charnley, Steven B.; Sipilä, Olli

2014-08-01

282

Depositional phasing of volcanic aerosols in the WAIS Divide ice core over the past 2400 years  

NASA Astrophysics Data System (ADS)

Explosive volcanic events originating in the tropics are an intermittent but significant factor in climate forcing, with the potential to cause global cooling for up to several years. Evidence of prehistoric eruptions in the form of tephra has been documented in sedimentary records throughout the globe, including the polar ice sheets. The chemical record of volcanic aerosols is also found in ice core records. While the record of tropical volcanism observed in Antarctic ice cores (based on sulfate deposition) is consistent regionally, little to no evidence of insoluble aerosols (ash particles) from tropical eruptions has been found. The upper 577 m (2400 years) of the WAIS Divide deep ice core (WDC06A) was melted using the UMaine WAIS Melt Monitor system, which allows accurate mm-scale depth co-registration of electrical conductivity and particle data, with subsequent collection of discrete samples for expanded particle, glaciochemical and geochemical analysis. The concentration and size distribution of microparticles were measured using a flow-through Klotz Abakus laser particle detector, developed by Ruth et al (2002) and calibrated with Coulter-Counter measurements. High-resolution analysis of ice spanning these volcanic intervals indicates that insoluble aerosols consistently arrive sooner than soluble aerosols (i.e., sulfate) at the WAIS Divide site (e.g., the Kuwae, Vanuatu eruption of ~1452 C.E.; Figure 1). We have observed this phasing difference for multiple tropical eruptions, including Agung (1963 C.E.), Krakatau/Tarawera (1886/1883), Tambora (1815), Kuwae (~1452) and Unknown (~1259). This phasing difference, which is on the order of 6-18 months, appears to be related to the eruptive column height and atmospheric transport of material.

Koffman, B. G.; Kreutz, K. J.; Breton, D. J.; Dunbar, N. W.; Kurbatov, A.

2011-12-01

283

Constraining Glacial input of phosphorus to the oceans based on Greenland ice core evidence  

NASA Astrophysics Data System (ADS)

Ice cores provide insight to past environmental conditions and Greenland ice cores can cover continuous records back to the previous interglacial period. Phosphorus is believed to have been the limiting nutrient for the ocean primary production in the past. Not much is known, however, about the atmospheric delivery of phosphorus to the oceans over time. In this study phosphate concentrations have been measured in the North Greenland Eemian Ice Drilling (NEEM) ice core for the period 35.6 to 25.2 kyr b2k. Phosphate was determined continuously in selected ice core sections using a molybdenum blue method and discretely by ion chromatography (IC). 20th century phosphate concentrations have recently been reported for a firn core from the North East Greenland Ice Stream (NEGIS), showing a fairly constant level, with a mean value of 2.7 nM. For the last glacial period, the molybdenum blue method indicated concentrations between 3 and 32 nM, whereas the IC method indicated higher concentrations. The deviation between the methods is strongly correlated (corr=0.9) to the dust content in the sample, suggesting that part of the phosphorus attached to dust particles does not instantly become labile after melting, but slowly (within hours) dissolves in the water. Both methods show higher concentrations during colder periods (stadials). The concentration differences between glacial mild and cold periods correlate positively to the dust variability suggesting that changes are linked to transport, however for very high phosphate loads (last glacial maximum) the relationship between phosphate and dust is weaker, suggesting secondary phosphate sources. We estimate that glacial atmospheric fluxes of phosphorus to the northern Hemisphere high latitude open oceans were 4 to 11 times higher during the glacial period as compared to recent Holocene, with the highest input during the stadials. For the recent century we find that between 4 and 100 % of the dissolved reactive phosphorus has a dust source, and between 4 and 38 % is of biogenic origin. We find no correlation with sea salt and no evidence of recent anthropogenic changes of the phosphate concentration.

Kjær, Helle Astrid; Goto-Azuma, Kumiko; Dallmayr, Remi; Hirabayashi, Motohiro; Vallelonga, Paul; Svensson, Anders

2014-05-01

284

North Pacific Volcanism in Three Ice Cores from Eclipse Icefield, Yukon Territory, Canada  

NASA Astrophysics Data System (ADS)

Prior work has demonstrated that a record of regionally significant volcanic eruptions in the North Pacific is available from Eclipse Icefield, Yukon Territory, Canada. The acquisition of two new cores from Eclipse Icefield during the 2002 field season allows us to extend the record of volcanism by at least five hundred years and assess the variability in volcanic signal preservation using the three ice core records now available from Eclipse Icefield. Non- sea - salt sulfate residuals above a robust spline and empirical orthogonal function (EOF) analysis were used to identify volcanic sulfate signatures. These signals were then matched to the historical record of volcanism to identify eruptions in the Eclipse ice core. At least ten of these identifications have been independently verified by means of tephrochronology, including, for the first time, recovery of tephra from the unknown 1809 eruption seen in both Greenland and Antarctic ice core records. The largest eruptions, such as Katmai 1912 (VEI 6) and Ksudach 1907 (VEI 5), as well as some moderate-sized eruptions (i.e., Redoubt 1989; VEI 3), are consistently recorded in each of the available cores. Meanwhile, other moderate to large eruptions, such as Bezymianny 1956 (VEI 5), are not recorded in any of the cores. Anthropogenic sulfate deposition at Eclipse since about 1950 appears to mask signals from large tropical eruptions such as Pinatubo (1991) and El Chichon (1982), while older tropical eruptions prior to the period of anthropogenic sulfate deposition such as Krakatau (1883), Tambora (1815), and the unknown 1809 eruption are clearly recorded at Eclipse Icefield.

Yalcin, K.; Wake, C. P.; Whitlow, S.; Kreutz, K. J.; Germani, M. S.

2004-05-01

285

30-Year Satellite Record Reveals Contrasting Arctic and Antarctic Decadal Sea Ice Variability  

NASA Technical Reports Server (NTRS)

A 30-year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the Arctic sea ice extent decreased by 0.30+0.03 x 10(exp 6) square kilometers per 10 yr from 1972 through 2002, but by 0.36 plus or minus 0.05 x 10(exp 6) square kilometers per 10yr from 1979 through 2002, indicating an acceleration of 20% in the rate of decrease. In contrast, the Antarctic sea ice extent decreased dramatically over the period 1973-1977, then gradually increased. Over the full 30-year period, the Antarctic ice extent decreased by 0.15 plus or minus 0.08 x 10(exp 6) square kilometers per 10 yr. The trend reversal is attributed to a large positive anomaly in Antarctic sea ice extent in the early 1970's, an anomaly that apparently began in the late 1960's, as observed in early visible and infrared satellite images.

Cavalieri, D. J.; Parkinson, C. L.; Vinnikov, K. Y.

2003-01-01

286

An ice core perspective on the age of the Matuyama–Brunhes boundary  

Microsoft Academic Search

Two intervals of enhanced 10Be flux thought to be associated with periods of low dipole intensity and identified as the Matuyama–Brunhes transition and a precursor event have been observed in the bottom section of the EPICA Dome C ice core. The peaks span 764–776 ka and 788–798 ka on the new EDC3 chronology with a stated absolute age uncertainty of 6 ka (2?).

G. B. Dreyfus; G. M. Raisbeck; F. Parrenin; J. Jouzel; Y. Guyodo; S. Nomade; A. Mazaud

2008-01-01

287

Twentieth century increase of atmospheric ammonia recorded in Mount Everest ice core  

Microsoft Academic Search

An NH4+ record covering the period A.D. 1845-1997 was reconstructed using an 80.4 m ice core from East Rongbuk Glacier at an elevation of 6450 m on the northern slope of Mount Everest. Variations in NH4+ are characterized by a dramatic increase since the 1950s. The highest NH4+ concentrations occur in the 1980s. They are about twofold more than those

Shichang Kang; Paul Andrew Mayewski; Dahe Qin; Yuping Yan; Dongqi Zhang; Shugui Hou; Jiawen Ren

2002-01-01

288

Tephrochronology of the Siple Dome ice core, West Antarctica: correlations and sources  

Microsoft Academic Search

A total of 24 tephra-bearing volcanic layers have been recognized between 550 and 987 m depth in the Siple Dome A (SDM-A) ice core, in addition to a number already recognized tephra in the upper 550 m (Dunbar et al., 2003; Kurbatov et al., 2006). The uniform composition and distinctive morphological of the particles composing these tephra layers suggest deposition as a result of

Nelia W. Dunbar; Andrei V. Kurbatov

2011-01-01

289

Effects of sudden mixing in the solar core on solar neutrinos and ice ages.  

NASA Technical Reports Server (NTRS)

Some numerical experiments with a solar model have been conducted in connection with the hypothesis regarding the effects of mixing in the solar core. Questions concerning a plausible mechanism by which such a mixing could be produced are explored. The variation of solar luminosity throughout the numerical experiments is shown. In connection with a great change in luminosity after a second mixing, it is suggested that the earth is presently undergoing an ice age.

Ezer, D.; Cameron, A. G. W.

1972-01-01

290

Constraining recent lead pollution sources in the North Pacific using ice core stable lead isotopes  

NASA Astrophysics Data System (ADS)

Trends and sources of lead (Pb) aerosol pollution in the North Pacific rim of North America from 1850 to 2001 are investigated using a high-resolution (subannual to annual) ice core record recovered from Eclipse Icefield (3017 masl; St. Elias Mountains, Canada). Beginning in the early 1940s, increasing Pb concentration at Eclipse Icefield occurs coevally with anthropogenic Pb deposition in central Greenland, suggesting that North American Pb pollution may have been in part or wholly responsible in both regions. Isotopic ratios (208Pb/207Pb and 206Pb/207Pb) from 1970 to 2001 confirm that a portion of the Pb deposited at Eclipse Icefield is anthropogenic, and that it represents a variable mixture of East Asian (Chinese and Japanese) emissions transported eastward across the Pacific Ocean and a North American component resulting from transient meridional atmospheric flow. Based on comparison with source material Pb isotope ratios, Chinese and North American coal combustion have likely been the primary sources of Eclipse Icefield Pb over the 1970-2001 time period. The Eclipse Icefield Pb isotope composition also implies that the North Pacific mid-troposphere is not directly impacted by transpolar atmospheric flow from Europe. Annually averaged Pb concentrations in the Eclipse Icefield ice core record show no long-term trend during 1970-2001; however, increasing208Pb/207Pb and decreasing 206Pb/207Pb ratios reflect the progressive East Asian industrialization and increase in Asian pollutant outflow. The post-1970 decrease in North American Pb emissions is likely necessary to explain the Eclipse Icefield Pb concentration time series. When compared with low (lichen) and high (Mt. Logan ice core) elevation Pb data, the Eclipse ice core record suggests a gradual increase in pollutant deposition and stronger trans-Pacific Asian contribution with rising elevation in the mountains of the North Pacific rim.

Gross, B. H.; Kreutz, K. J.; Osterberg, E. C.; McConnell, J. R.; Handley, M.; Wake, C. P.; Yalcin, K.

2012-08-01

291

Late glacial stage and holocene tropical ice core records from Huascaran, Peru  

Microsoft Academic Search

Two ice cores from the col of Huascaran in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Wuerm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8° to 12°C cooler than today, the atmosphere contained

L. G. Thompson; K. A. Henderson; J. F. Bolzan

1995-01-01

292

9,400 years of cosmic radiation and solar activity from ice cores and tree rings.  

PubMed

Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as (10)Be and (14)C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different (10)Be ice core records from Greenland and Antarctica with the global (14)C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution (10)Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate. PMID:22474348

Steinhilber, Friedhelm; Abreu, Jose A; Beer, Jürg; Brunner, Irene; Christl, Marcus; Fischer, Hubertus; Heikkilä, Ulla; Kubik, Peter W; Mann, Mathias; McCracken, Ken G; Miller, Heinrich; Miyahara, Hiroko; Oerter, Hans; Wilhelms, Frank

2012-04-17

293

Relationships between tropical cyclone intensity and satellite based indicators of inner core convection: 85 GHz ice scattering signature and lightning  

E-print Network

ingredients for charge separation, leading to lightning. Various parameters derived from the inner core ice scattering signature are computed for regions encircling hurricanes and typhoons, and observations of lightning activity or inactivity are analyzed...

Cecil, Daniel Joseph

1997-01-01

294

Comparative evaluation of the indigenous microbial diversity vs. drilling fluid contaminants in the NEEM Greenland ice core.  

PubMed

Demonstrating that the detected microbial diversity in nonaseptically drilled deep ice cores is truly indigenous is challenging because of potential contamination with exogenous microbial cells. The NEEM Greenland ice core project provided a first-time opportunity to determine the origin and extent of contamination throughout drilling. We performed multiple parallel cultivation and culture-independent analyses of five decontaminated ice core samples from different depths (100-2051 m), the drilling fluid and its components Estisol and Coasol, and the drilling chips collected during drilling. We created a collection of diverse bacterial and fungal isolates (84 from the drilling fluid and its components, 45 from decontaminated ice, and 66 from drilling chips). Their categorization as contaminants or intrinsic glacial ice microorganisms was based on several criteria, including phylogenetic analyses, genomic fingerprinting, phenotypic characteristics, and presence in drilling fluid, chips, and/or ice. Firmicutes and fungi comprised the dominant group of contaminants among isolates and cloned rRNA genes. Conversely, most Proteobacteria and Actinobacteria originating from the ice were identified as intrinsic. This study provides a database of potential contaminants useful for future studies of NEEM cores and can contribute toward developing standardized protocols for contamination detection and ensuring the authenticity of the microbial diversity in deep glacial ice. PMID:24450335

Miteva, Vanya; Burlingame, Caroline; Sowers, Todd; Brenchley, Jean

2014-08-01

295

Direct chemical analysis of frozen ice cores by UV-laser ablation ICPMS Wolfgang Muller,*a  

E-print Network

Direct chemical analysis of frozen ice cores by UV-laser ablation ICPMS Wolfgang Muller,*a J recrystalli- zation of ice with increasing depth. Using 193 nm excimer laser-ablation ICPMS (UV-LA-ICPMS), we in this study. A custom- built cryo-sample holder is loaded into a standard Laurin two-volume laser-ablation

Royal Holloway, University of London

296

Modified HNO 3 seasonality in volcanic layers of a polar ice core: Snowpack effect or photochemical perturbation?  

Microsoft Academic Search

Using the chemical composition of snow and ice of a central Greenland ice core, we have investigated changes in atmospheric HNO3 chemistry following the large volcanic eruptions of Laki (1783), Tambora (1815) and Katmai (1912). The concentration of several cations and anions, including SO42- and NO3-, were measured using ion chromatography. We found that following those eruptions, the ratio of

Paolo Laj; Julie M. Palais; James E. Gardner; Haraldur Sigurdsson

1993-01-01

297

Simulating ice core 10Be on the glacial-interglacial timescale  

NASA Astrophysics Data System (ADS)

10Be ice core measurements are an important tool for paleoclimate research, e.g., allowing for the reconstruction of past solar activity or changes in the geomagnetic dipole field. However, especially on multi-millennial timescales, the share of production and climate-induced variations of respective 10Be ice core records is still up for debate. Here we present the first quantitative climatological model of the 10Be ice concentration up to the glacial-interglacial timescale. The model approach is composed of (i) a coarse resolution global atmospheric transport model and (ii) a local 10Be air-firn transfer model. Extensive global-scale observational data of short-lived radionuclides as well as new polar 10Be snow-pit measurements are used for model calibration and validation. Being specifically configured for 10Be in polar ice, this tool thus allows for a straightforward investigation of production- and non-production-related modulation of this nuclide. We find that the polar 10Be ice concentration does not immediately record the globally mixed cosmogenic production signal. Using geomagnetic modulation and revised Greenland snow accumulation rate changes as model input, we simulate the observed Greenland Summit (GRIP and GISP2) 10Be ice core records over the last 75 kyr (on the GICC05modelext timescale). We show that our basic model is capable of reproducing the largest portion of the observed 10Be changes. However, model-measurement differences exhibit multi-millennial trends (differences up to 87% in case of normalized to the Holocene records) which call for closer investigation. Focusing on the (12-37) b2k (before the year AD 2000) period, mean model-measurement differences of 30% cannot be attributed to production changes. However, unconsidered climate-induced changes could likely explain the model-measurement mismatch. In fact, the 10Be ice concentration is very sensitive to snow accumulation changes. Here the reconstructed Greenland Summit (GRIP) snow accumulation rate record would require revision of +28% to solely account for the (12-37) b2k model-measurement differences.

Elsässer, C.; Wagenbach, D.; Levin, I.; Stanzick, A.; Christl, M.; Wallner, A.; Kipfstuhl, S.; Seierstad, I. K.; Wershofen, H.; Dibb, J.

2015-02-01

298

An annual layer counted ice-core chronology from EDML, Antarctica, over the termination of the last glacial  

NASA Astrophysics Data System (ADS)

Accurate and consistent timescales for paleoclimate records are crucial for advancing our understanding of the governing mechanisms and inter-hemispheric coupling involved in rapid climate change. For ice cores, very high-resolution chronologies can be established far back in time by identifying and counting annual layers in the ice core records. This is in particular true for the Greenland ice cores, for which the relatively high accumulation rates act to preserve the annual signal to great depths. The Greenland Ice Core Chronology 2005 (GICC05) is based on annual layer counts in data records from multiple Greenland ice cores, and it reaches back to 60 kyr BP. In Antarctica, only few ice core locations have sufficiently high accumulation rates for the annual signal in the ice core data to be maintained back into the last glacial. An annual layer counted timescale (WDC06A-7) reaching back to 30 kyr BP was recently completed for WAIS Divide, West Antarctica. Overall, the timescale is in good agreement with GICC05 within their respective uncertainties. Over the last glacial termination, however, significant discrepancies exist between the two chronologies, which cannot be reconciled within the specified uncertainty of the respective annual layer counts. Here, we present an independent annual layer counted chronology for the EPICA ice core from Dronning Maud Land (EDML), Antarctica, over the termination of the last glacial (10-15 kyr BP). The chronology is based on the annual signal visible in high-resolution impurity records and electrical conductivity measurements (liquid conductivity, DEP). The timescale is constructed using a novel Bayesian framework for multi-parameter annual layer counting in ice core records, which originates from sophisticated speech-recognition algorithms. It provides an objective estimate of the most likely number of layers within a section, as well as a confidence interval judging the uncertainty involved in layer identification. Resulting automated layer counts are validated against manual layer counts over parts of the data section. By use of bipolar volcanic marker horizons, a synchronization of the EDML ice core to GICC05 was recently completed. While the synchronization over the termination of the last glacial is less certain than during the Holocene, it can nevertheless be used for testing the consistency of the annual layer counts from both continents. The obtained EDML chronology is also compared to existing Antarctic ice-core chronologies.

Winstrup, Mai; Vinther, Bo M.; Svensson, Anders M.; Clausen, Henrik B.; Rasmussen, Sune O.; Fudge, Tj; Steig, Eric J.; Wegner, Anna; Kipfstuhl, Sepp

2013-04-01

299

Mount Logan ice core record of tropical and solar influences on Aleutian Low variability: 500-1998 A.D.  

NASA Astrophysics Data System (ADS)

Continuous, high-resolution paleoclimate records from the North Pacific region spanning the past 1500 years are rare; and the behavior of the Aleutian Low (ALow) pressure center, the dominant climatological feature in the Gulf of Alaska, remains poorly constrained. Here we present a continuous, 1500 year long, calibrated proxy record for the strength of the wintertime (December-March) ALow from the Mount Logan summit (PR Col; 5200 m asl) ice core soluble sodium time series. We show that ice core sodium concentrations are statistically correlated with North Pacific sea level pressure and zonal wind speed. Our ALow proxy record reveals a weak ALow from circa 900-1300 A.D. and 1575-1675 A.D., and a comparatively stronger ALow from circa 500-900 A.D., 1300-1575 A.D., and 1675 A.D. to present. The Mount Logan ALow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the El Niño-Southern Oscillation and is consistent with the hypothesis that the Medieval Climate Anomaly was characterized by more persistent La Niña-like conditions while the Little Ice Age was characterized by at least two intervals of more persistent El Niño-like conditions. The Mount Logan ALow proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various time scales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions. However, a step-like increase in ALow strength during the Dalton solar minimum circa 1820 is associated with enhanced Walker circulation. Furthermore, rising CO2 forcing or internal variability may be masking the twentieth century rise in solar irradiance.

Osterberg, Erich C.; Mayewski, Paul A.; Fisher, David A.; Kreutz, Karl J.; Maasch, Kirk A.; Sneed, Sharon B.; Kelsey, Eric

2014-10-01

300

Association between atmospheric circulation patterns and firn-ice core records from the Inilchek glacierized area, central Tien Shan, Asia  

Microsoft Academic Search

Glacioclimatological research in the central Tien Shan was performed in the summers of 1998 and 1999 on the South Inilchek Glacier at 5100–5460 m. A 14.36 m firn-ice core and snow samples were collected and used for stratigraphic, isotopic, and chemical analyses. The firn-ice core and snow records were related to snow pit measurements at an event scale and to

Vladimir B. Aizen; Elena M. Aizen; John M. Melack; Karl J. Kreutz; L. DeWayne Cecil

2004-01-01

301

Past local temperatures obtained from the EDML ice core using differential diffusion  

NASA Astrophysics Data System (ADS)

Since the 1960-s the stable water isotope signal in ice core records has been used as a proxy for palaeotemperatures. However, this direct interpretation of the isotope signal has limitations, as the relationship between the isotope ratio and atmospheric temperature is known to fluctuate both spatially and temporally. One way to circumvent these limitations is the use of diffusion thermometry as pioneered by Johnsen et al (2000). In the firn stage the isotope signal is subject to a smoothing caused by the random movement of water vapour in the pores of the snow. The total amount of diffusion a layer has suffered is measured in terms of the diffusion length. This length is sensitive to changes in firn temperature and the accumulation rate at the site. The diffusion length for Oxygen-18 is higher than that for Deuterium due to a difference in ice-vapour fractionation factors. As these fractionation factors are dependent on the temperature of the firn, the difference in diffusion length can be used to estimate past local temperatures. To apply this differential diffusion method successfully, it is necessary to have high resolution measurements for both Oxygen-18 and Deuterium. We present such measurements for the EDML ice core. In total 400 m of ice was measured with a 5 cm resolution from periods in the mid and early Holocene, the last glacial-interglacial transition and the last glacial period. Application of the differential diffusion method to this dataset shows a decreasing temperature trend during the Holocene and a surface temperature of approximately -55 °C in the interval representing the LGM in the ice (~10 °C colder than present day temperature (not corrected for changes in altitude)). This is, within the error limits, in line with the temperature reconstructed from the stable water isotope proxy itself using the spatial isotope/temperature gradient (EPICA community members, 2006).

van der Wel, G.; Oerter, H.; Meyer, H.; Fischer, H.

2012-04-01

302

High permafrost ice contents in Holocene slope deposits as observed from shallow geophysics and a coring program in Pangnirtung, Nunavut, Canada  

NASA Astrophysics Data System (ADS)

A study of permafrost conditions was undertaken in the Hamlet of Pangnirtung, Nunavut, by the Geological Survey of Canada (GSC) and Université Laval's Centre d'études nordiques (CEN) to support decision makers in their community planning work. The methods used for this project were based on geophysical and geomorphological approaches, including permafrost cores drilled in surficial deposits and ground penetrating radar surveys using a GPR Pulse EKKO 100 extending to the complete community area and to its projected expansion sector. Laboratory analysis allowed a detailed characterization of permafrost in terms of water contents, salinity and grain size. Cryostratigraphic analysis was done via CT-Scan imagery of frozen cores using medical imaging softwares such as Osiris. This non destructive method allows a 3D imaging of the entire core in order to locate the amount of the excess ice, determine the volumetric ice content and also interpret the ice-formation processes that took place during freezing of the permafrost. Our new map of the permafrost conditions in Pangnirtung illustrates that the dominant mapping unit consist of ice-rich colluvial deposits. Aggradationnal ice formed syngenitically with slope sedimentation. Buried soils were found imbedded in this colluvial layer and demonstrates that colluviation associated with overland-flow during snowmelt occurred almost continuously since 7080 cal. BP. In the eastern sector of town, the 1 to 4 meters thick colluviums cover till and a network of ice wedges that were revealed as spaced hyperbolic reflectors on GPR profiles. The colluviums also cover ice-rich marine silt and bedrock in the western sector of the hamlet; marine shells found in a permafrost core yielded a radiocarbon date of 9553 cal. BP which provides a revised age for the local deglaciation and also a revised marine submergence limit. Among the applied methods, shallow drilling in coarse grained permafrost, core recovery and CT-Scan allowed the discovery of the importance of Holocene slope processes on shaping the surface of the terrain and leading to the observed cryostructures and ice contents in the near surface permafrost.

Carbonneau, A.; Allard, M.; L'Hérault, E.; LeBlanc, A.

2011-12-01

303

The WAIS-Divide deep ice core WD2014 chronology - Part 2: Methane synchronization (68-31 ka BP) and the gas age-ice age difference  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice Sheet (WAIS)-Divide ice core (WAIS-D) is a newly drilled, high-accumulation deep ice core that provides Antarctic climate records of the past ∼68 ka at unprecedented temporal resolution. The upper 2850 m (back to 31.2 ka BP) have been dated using annual-layer counting. Here we present a chronology for the deep part of the core (67.8-31.2 ka BP), which is based on stratigraphic matching to annual-layer-counted Greenland ice cores using globally well-mixed atmospheric methane. We calculate the WAIS-D gas age-ice age difference (?age) using a combination of firn densification modeling, ice flow modeling, and a dataset of ?15N-N2, a proxy for past firn column thickness. The largest ?age at WAIS-D occurs during the last glacial maximum, and is 525 ± 100 years. Internally consistent solutions can only be found when assuming little-to-no influence of impurity content on densification rates, contrary to a recently proposed hypothesis. We synchronize the WAIS-D chronology to a linearly scaled version of the layer-counted Greenland Ice Core Chronology (GICC05), which brings the age of Dansgaard-Oeschger (DO) events into agreement with the U/Th absolutely dated Hulu speleothem record. The small ?age at WAIS-D provides valuable opportunities to investigate the timing of atmospheric greenhouse gas variations relative to Antarctic climate, as well as the interhemispheric phasing of the bipolar "seesaw".

Buizert, C.; Cuffey, K. M.; Severinghaus, J. P.; Baggenstos, D.; Fudge, T. J.; Steig, E. J.; Markle, B. R.; Winstrup, M.; Rhodes, R. H.; Brook, E. J.; Sowers, T. A.; Clow, G. D.; Cheng, H.; Edwards, R. L.; Sigl, M.; McConnell, J. R.; Taylor, K. C.

2014-08-01

304

Annually resolved southern hemisphere volcanic history from two Antarctic ice cores  

NASA Astrophysics Data System (ADS)

The continuous sulfate analysis of two Antarctic ice cores, one from the Antarctic Peninsula region and one from West Antarctica, provides an annually resolved proxy history of southern semisphere volcanism since early in the 15th century. The dating is accurate within ±3 years due to the high rate of snow accumulation at both core sites and the small sample sizes used for analysis. The two sulfate records are consistent with each other. A systematic and objective method of separating outstanding sulfate events from the background sulfate flux is proposed and used to identify all volcanic signals. The resulting volcanic chronology covering 1417-1989 A.D. resolves temporal ambiguities about several recently discovered events. A number of previously unknown, moderate eruptions during late 1600s are uncovered in this chronology. The eruption of Tambora (1815) and the recently discovered eruption of Kuwae (1453) in the tropical South Pacific injected the greatest amount of sulfur dioxide into the southern hemisphere stratosphere during the last half millennium. A technique for comparing the magnitude of volcanic events preserved within different ice cores is developed using normalized sulfate flux. For the same eruptions the variability of the volcanic sulfate flux between the cores is within ±20% of the sulfate flux from the Tambora eruption.

Cole-Dai, Jihong; Mosley-Thompson, Ellen; Thompson, Lonnie G.

1997-07-01

305

Physical and chemical characteristics of the Subglacial Lake Whillans sediment cores, Whillans Ice Stream, West Antarctica  

NASA Astrophysics Data System (ADS)

Sediment recovered from Subglacial Lake Whillans (SLW) is well-homogenized, structureless diamict; typical subglacial till. Based on theoretical estimates, the basal ice above SLW should be below the pressure melting point preventing melt-out of debris from basal ice. Therefore, the lake floor diamict likely formed through deformation while the ice stream was grounded at the drill site. Using satellite altimetry, Fricker, et al. (2007) inferred that SLW experiences short (~7 month) discharge events, lowering the ice surface and lake water level by between 1 and 4 m. The lake 'lowstands' are separated by longer periods of gradual recharge, but over the period of a lowstand the ice stream is suspected to touch down and couple with the lake floor, potentially shearing new till into the lake. The lack of sorted sediment or erosional lags indicates water flow during discharge/recharge events has had a low current velocity with quiescent conditions in the lake. The most notable variability in the cores is a uniformly weak, critical porosity horizon extending to ~50 cm depth above more consolidated till. We interpret the weak upper horizon as the product of shear deformation and decreasing effective pressure experienced during the final stages of grounding prior to a lake recharge event (see generally, the undrained plastic bed model of Tulaczyk et al. (2000)). The presence of this weak layer illustrates the importance of hydrology in modulating till rheology and is an example of how subglacial sediments can preserve archives of hydrologic conditions at the glacial bed. Fricker, H.A., T. Scambos, R. Bindschadler and L. Padman. 2007. An active subglacial water system in West Antarctica mapped from space. Science, 315(5818), 1544-1548. Tulaczyk S, Kamb WB, Engelhardt HF. 2000. Basal mechanics of Ice Stream B, West Antarctica. 2. Undrained plastic bed model. J. Geophys. Res. 105:483-94.

Hodson, T. O.; Powell, R. D.

2013-12-01

306

Solving the riddle of interglacial temperatures over the last 1.5 million years with a future IPICS "Oldest Ice" ice core  

NASA Astrophysics Data System (ADS)

The sequence of the last 8 glacial cycles is characterized by irregular 100,000 year cycles in temperature and sea level. In contrast, the time period between 1.5-1.2 million years ago is characterized by more regular cycles with an obliquity periodicity of 41,000 years. Based on a deconvolution of deep ocean temperature and ice volume contributions to benthic ?18O (Elderfield et al., Science, 2012), it is suggested that glacial sea level became progressively lower over the last 1.5 Myr, while glacial deep ocean temperatures were very similar. At the same time many interglacials prior to the Mid Brunhes event showed significantly cooler deep ocean temperatures than the Holocene, while at the same time interglacial ice volume remained essentially the same. In contrast, interglacial sea surface temperatures in the tropics changed little (Herbert et al., Science,2010) and proxy reconstructions of atmospheric CO2 using ?11B in planktic foraminifera (Hönisch et al., Science, 2009) suggest that prior to 900,000 yr before present interglacial CO2 levels did not differ substantially from those over the last 450,000 years. Accordingly, the conundrum arises how interglacials can differ in deep ocean temperature without any obvious change in ice volume or greenhouse gas forcing and what caused the change in cyclicity of glacial interglacial cycles over the Mid Pleistocene Transition. Probably the most important contribution to solve this riddle is the recovery of a 1.5 Myr old ice core from Antarctica, which among others would provide an unambiguous, high-resolution record of the greenhouse gas history over this time period. Accordingly, the international ice core community, as represented by the International Partnership for Ice Core Science (IPICS), has identified such an 'Oldest Ice' ice core as one of the most important scientific targets for the future (http://www.pages.unibe.ch/ipics/white-papers). However, finding stratigraphically undisturbed ice, which covers this time period in Antarctica, is not an easy task. Based on a simple ice and heat flow model and glaciological observations (Fischer et al., Climate of the Past, 2013), we conclude that sites in the vicinity of major domes and saddle positions on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, significantly reduced ice thickness is required to avoid bottom melting. The most critical parameter is the largely unknown geothermal heat flux at the bottom of the ice sheet. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 My old ice. If sites with lower geothermal heat flux can be found, also a higher ice thickness is allowed, alleviating the problem of potential flow disturbances in the bottom-most ice to affect a 1.5 Myr climate record.

Fischer, Hubertus

2014-05-01

307

Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period  

USGS Publications Warehouse

We perform a Monte Carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies in Greenland and East Antarctica determined by continuous core chemistry, together with West Antarctic volcanic ash layers determined by remote optical borehole logging and core assays. We find that the Antarctic record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% (???3??) significance level and that volcanic depositions at the three locations match at levels exceeding 3??, likely indicating that many common horizons represent single eruptive events which dispersed material world wide. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. The striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated. Copyright 2006 by the American Geogphysical Union.

Bay, R.C.; Bramall, N.E.; Price, P.B.; Clow, G.D.; Hawley, R.L.; Udisti, R.; Castellano, E.

2006-01-01

308

Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period  

NASA Astrophysics Data System (ADS)

We perform a Monte Carlo pattern recognition analysis of the coincidence between three regional volcanic histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies in Greenland and East Antarctica determined by continuous core chemistry, together with West Antarctic volcanic ash layers determined by remote optical borehole logging and core assays. We find that the Antarctic record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% (˜3?) significance level and that volcanic depositions at the three locations match at levels exceeding 3?, likely indicating that many common horizons represent single eruptive events which dispersed material world wide. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden intensifications of millennial cold periods. The striking agreement between sites implies that the consistency of current timescales obtained by isotopic and glaciological dating methods is better than estimated.

Bay, R. C.; Bramall, N. E.; Price, P. B.; Clow, G. D.; Hawley, R. L.; Udisti, R.; Castellano, E.

2006-06-01

309

Factors affecting the reproducibility of trace element analyses of ice core samples  

NASA Astrophysics Data System (ADS)

Ice cores provide high-resolution records of past atmospheric and environmental conditions. Increasingly, conventional stable isotope and major ion analyses of ice cores are being complimented by determination of ultra-trace levels of trace elements by inductively coupled plasma mass spectrometry (ICP-MS). Typically, these analyses are performed on acidified, melted, ice without removal of particulates by centrifugation or filtration. We have carried out a systematic investigation of the factors influencing the reproducibility of trace element determinations in ice core samples, which can be considered to contain three inorganic chemical components: marine salt, aerosol and mineral dust. The prevalent method of ICP-MS analysis of ice core samples involves analysing acidified samples (typically to 1% HNO3). To mimic these conditions, we undertook systematic leaching experiments on geochemically well-characterised, powdered, rock standards to examine how trace element measurements varied depending on the length of the acidification time, whether samples were frozen after acidification or not, dust lithology and the dust concentration. Four certified standards were leached at a dust concentration of 10 ppm in 1% HNO3 and leachates were sampled at regular time intervals up to a period of several months. The standards encompass a range of lithologies and textures, including basalt (BHVO-2), dolerite (W-2), granite (JG-2) and Fe-Mn oxyhydroxide (Nod P-1) materials. The basalt, dolerite and granite all have silicate mineralogies and showed some similar trace element trends during leaching. For example, the concentration of Al in the leachates increased by between 125% and 280% during the first 12 hr and did not stop rising after 8 weeks of leaching. In contrast, rare earth element and Y concentrations in the leachates became constant after just 2 hr. However, total element recovery differed between lithologies. After 12 hr of acidification the recovery of elements from Na to Mn was less than 10% for basalt and dolerite but was significantly higher for the granite, reaching up to 57% for Mg. For the Nod P-1 standard, nearly all elements reached a constant leachate concentration after 12 hr, but recovery of different elements varied from 3.5% to 80%. These patterns of trace element leaching were similar at different dust concentrations, however, freezing of acidified samples promotes leaching of elements such as Zr and Ti. These results reflect variable and time-dependent leaching of different elements from different mineral constituents in the rock standards which has important implications for ultra-trace element analysis of ice core material: (1) trace element concentrations and ratios will generally not reflect that of the source dust material; (2) trace element concentrations and ratios will vary considerably (more than an order of magnitude) depending on the acidification time; (3) trace element concentrations determined on ice core material containing mineral dust will not be reproducible unless dust is removed prior to acidification and ICP-MS analysis.

Rhodes, R. H.; Baker, J.; Millet, M.; Bertler, N.

2010-12-01

310

10Be of the last interglacial in the NEEM ice core, North Greenland  

NASA Astrophysics Data System (ADS)

We report here on 10Be results from ice saw dust samples covering the depth interval 2200-2500 m and at 2.2 m resolution from the 2540 m deep NEEM ice. The 10Be analyzed depth interval includes the last interglacial ice. After chemical separation, the 10Be was measured using the Uppsala AMS system at a general machine and background correction <15%. Concentration of 10Be varies between 0.7-2.27x104atoms/gice with a mean value of 1.18x104atoms/gice. The mean value seems to be about 25% lower than what has been measured for early Holocene sections in the NEEM ice cores. This feature suggests that either 10Be production was lower during the Eemian period than that in the Holocene or that 10Be concentration was diluted by higher snow accumulation rate. The Eemian period is known to have a warmer climate than the Holocene and that would be associated with higher temperatures and most likely with higher precipitation. Higher precipitation would mean dilution of 10Be concentrations as also indicated by our results. The 10Be data also provide possibility for exploring Cosmic-Solar-Earth interactions that have operated during the Eemian period.

Sturevik Storm, Anna; Possnert, Göran; Aldahan, Ala; Berggren, Ann-Marie; Usoskin, Ilya; Dahl-Jensen, Dorthe

2013-04-01

311

The decrease in Greenland ice-core ?15N of nitrate in the industrial period: influenced by changes in atmospheric acidity?  

NASA Astrophysics Data System (ADS)

Previous study in a central Greenland ice core has revealed a decreasing trend in ?15N of nitrate (?15N (nitrate)) starting as early as 1850 C.E.. Lake sediment cores from North America show a similar trend in ?15N of total nitrogen starting around 1895 C.E.. The decrease in ?15N has been proposed to be due to the increasing deposition of anthropogenically derived (i.e., fossil fuel combustion) nitrate in the industrial period. However, this interpretation is questioned by measurements of ?15N in NOx and atmospheric nitrate. Here, we present new, annually-resolved records of ?15N (nitrate) and major ion concentrations (Cl-, NO3-, SO42-, Na+, NH4+, K+, Mg2+, and Ca2+) obtained from two central Greenland ice cores. The results (Figure 1) indicate that the significant decrease in ?15N is coincident with an increase in acidity (H+ concentration estimated based on ionic balance) beginning around 1895 C.E., which is about 50 years earlier than the start of the increase in nitrate concentration (~1945 C.E.) . This observation suggests that it is likely the acidity change, instead of the input of anthropogenic nitrate, triggered the decrease in ice-core ?15N (nitrate). Atmospheric aerosol acidity influences the partitioning of atmospheric nitrate between its gaseous (HNO3) and particulate (p-NO3-) phases, resulting in a depletion of ?15N in HNO3 relative to p-NO3-. If atmospheric nitrate is transported to central Greenland preferentially in its gaseous form (HNO3), which is an open question, a decrease in ice-core ?15N (nitrate) would be expected with an increase in atmospheric acidity. We will examine the relationships between ?15N (nitrate) and the ice-core records of acidity, and HNO3, to discern the processes from changes in atmospheric acidity to the observed variability in ice core ?15N (nitrate) during the Industrial era.igure 1. The annual NO3- (blue curve), H+ (black curve) concentrations, and annual ?15N (nitrate) (red curve, y-axis is reversely plotted). Gray dots represent the annual data; the curves are plotted from 3-year running averages.

Geng, L.; Cole-Dai, J.; Alexander, B.; Steig, E. J.; Schauer, A. J.; Savarino, J.

2012-12-01

312

Changes in Black Carbon Deposition to Antarctica from Two Ice Core Records, A.D. 1850-2000  

NASA Technical Reports Server (NTRS)

Continuous flow analysis was based on a steady sample flow and in-line detection of BC and other chemical substances as described in McConnell et al. (2007). In the cold room, previously cut one meter ice core sticks of 3x3cm, are melted continuously on a heated melter head specifically designed to eliminate contamination from the atmosphere or by the external parts of the ice. The melted ice from the most inner part of the ice stick is continuously pumped by a peristaltic pump and carried to a clean lab by Teflon lines. The recorded signal is continuous, integrating a sample volume of about 0.05 mL, for which the temporal resolution depends on the speed of melting, ice density and snow accumulation rate at the ice core drilling site. For annual accumulation derived from the WAIS and Law Dome ice cores, we assumed 3.1 cm water equivalent uncertainty in each year's accumulation from short scale spatial variability (glaciological noise) which was determined from several measurements of annual accumulation in multiple parallel ice cores notably from the WAIS Divide ice core site (Banta et al., 2008) and from South Pole site (McConnell et al., 1997; McConnell et al., 2000). Refractory black carbon (rBC) concentrations were determined using the same method as in (Bisiaux et al., 2011) and adapted to continuous flow measurements as described by (McConnell et al., 2007). The technique uses a single particle intracavity laser induced incandescence photometer (SP2, Droplet Measurement Technologies, Boulder, Colorado) coupled to an ultrasonic nebulizer/desolvation (CETAC UT5000) Flow Injection Analysis (FIA). All analyses, sample preparation etc, were performed in a class 100 cleanroom using anti contamination "clean techniques". The samples were not acidified.

Bisiaux, Marion M.; Edward, Ross; McConnell, Joseph R.; Curran, Mark A. J.; VanOmmen, Tas D.; Smith, Andrew M.; Neumann, Thomas A.; Pasteris, Daniel R.; Penner, Joyce E.; Taylor, Kendrick

2012-01-01

313

Identifying and Tracking Individual Updraft Cores using Cluster Analysis: A TWP-ICE case study  

NASA Astrophysics Data System (ADS)

Cumulus parameterizations in GCMs depend strongly on the vertical velocity structures of convective updraft cores, or plumes. There hasn't been an accurate way of identifying these cores. The majority of previous studies treat the updraft as a single grid column entity, thus missing many intrinsic characteristics, e.g., the size, strength and spatial orientation of an individual core, its life cycle, and the time variations of the entrainment/detrainment rates associated with its life cycle. In this study, we attempt to apply an innovative algorithm based on the centroid-based k-means cluster analysis to improve our understanding of convection and its associated updraft cores. Both 3-D Doppler radar retrievals and cloud-resolving model simulations of a TWP-ICE campaign case during the monsoon period will be used to test and improve this algorithm. This will provide for more in-depth comparisons between CRM simulations and observations that were not possible previously using the traditional piecewise analysis with each updraft column. The first step is to identify the strongest cores (maximum velocity >10 m/s), since they are well defined and produce definite answers when the cluster analysis algorithm is applied. The preliminary results show that the radar retrieved updraft cores are smaller in size and with the maximum velocity located uniformly at higher levels compared with model simulations. Overall, the model simulations produce much stronger cores compared with the radar retrievals. Within the model simulations, the bulk microphysical scheme simulation produces stronger cores than the spectral bin microphysical scheme. Planned researches include using high temporal-resolution simulations to further track the life cycle of individual updraft cores and study their characteristics.

Li, X.; Tao, W.; Collis, S. M.; Varble, A.

2013-12-01

314

Isotopic composition of ice cores and meltwater from upper fremont glacier and Galena Creek rock glacier, Wyoming  

USGS Publications Warehouse

Meltwater runoff from glaciers can result from various sources, including recent precipitation and melted glacial ice. Determining the origin of the meltwater from glaciers through isotopic analysis can provide information about such things as the character and distribution of ablation on glaciers. A 9.4 m ice core and meltwater were collected in 1995 and 1996 at the glacigenic Galena Creek rock glacier in Wyoming's Absaroka Mountains. Measurements of chlorine-36 (36Cl), tritium (3H), sulphur-35 (35S), and delta oxygen-18 (??18O) were compared to similar measurements from an ice core taken from the Upper Fremont Glacier in the Wind River Range of Wyoming collected in 1991-95. Meltwater samples from three sites on the rock glacier yielded 36Cl concentrations that ranged from 2.1 ?? 1.0 X 106 to 5.8??0.3 X 106 atoms/l. The ice-core 36Cl concentrations from Galena Creek ranged from 3.4??0.3 X 105 to 1.0??0.1 X 106 atoms/l. Analysis of an ice core from the Upper Fremont Glacier yielded 36Cl concentrations of 1.2??0.2 X 106 and 5.2??0.2 X 106 atoms/l for pre- 1940 ice and between 2 X 106 and 3 X 106 atoms/l for post-1980 ice. Purdue's PRIME Lab analyzed the ice from the Upper Fremont Glacier. The highest concentration of 36Cl in the ice was 77 ?? 2 X 106 atoms/l and was deposited during the peak of atmospheric nuclear weapons testing in the late 1950s. This is an order of magnitude greater than the largest measured concentration from both the Upper Fremont Glacier ice core that was not affected by weapons testing fallout and the ice core collected from the Galena Creek rock glacier. Tritium concentrations from the rock glacier ranged from 9.2??0.6 to 13.2??0.8 tritium units (TU) in the meltwater to -1.3??1.3 TU in the ice core. Concentrations of 3H in the Upper Fremont Glacier ice core ranged from 0 TU in the ice older than 50 years to 6-12 TU in the ice deposited in the last 10 years. The maximum 3H concentration in ice from the Upper Fremont Glacier deposited in the early 1960s during peak weapons testing fallout for this isotope was 360 TU. One meltwater sample from the rock glacier was analyzed for 35S with a measured concentration of 5.4??1.0 millibecquerel per liter (mBeq/l). Modern precipitation in the Rocky Mountains contains 35S from 10 to 40 mBeq/L. The ??18O results in meltwater from the Galena Creek rock glacier (-17.40??0.1 to -17.98??0.1 per mil) are similar to results for modern precipitation in the Rocky Mountains. Comparison of these isotopic concentrations from the two glaciers suggest that the meltwater at the Galena Creek site is composed mostly of melted snow and rain that percolates through the rock debris that covers the glacier. Additionally, this water from the rock debris is much younger (less than two years) than the reported age of about 2000 years for the subsurface ice at the mid-glacier coring site. Thus the meltwater from the Galena Creek rock glacier is composed primarily of melted surface snow and rain water rather than melted glacier ice, supporting previous estimates of slow ablation rates beneath the surface debris of the rock glacier.

DeWayne, Cecil L.; Green, J.R.; Vogt, S.; Michel, R.; Cottrell, G.

1998-01-01

315

Phylogenetic and physiological diversity of microorganisms isolated from a deep greenland glacier ice core  

NASA Technical Reports Server (NTRS)

We studied a sample from the GISP 2 (Greenland Ice Sheet Project) ice core to determine the diversity and survival of microorganisms trapped in the ice at least 120,000 years ago. Previously, we examined the phylogenetic relationships among 16S ribosomal DNA (rDNA) sequences in a clone library obtained by PCR amplification from genomic DNA extracted from anaerobic enrichments. Here we report the isolation of nearly 800 aerobic organisms that were grouped by morphology and amplified rDNA restriction analysis patterns to select isolates for further study. The phylogenetic analyses of 56 representative rDNA sequences showed that the isolates belonged to four major phylogenetic groups: the high-G+C gram-positives, low-G+C gram-positives, Proteobacteria, and the Cytophaga-Flavobacterium-Bacteroides group. The most abundant and diverse isolates were within the high-G+C gram-positive cluster that had not been represented in the clone library. The Jukes-Cantor evolutionary distance matrix results suggested that at least 7 isolates represent new species within characterized genera and that 49 are different strains of known species. The isolates were further categorized based on the isolation conditions, temperature range for growth, enzyme activity, antibiotic resistance, presence of plasmids, and strain-specific genomic variations. A significant observation with implications for the development of novel and more effective cultivation methods was that preliminary incubation in anaerobic and aerobic liquid prior to plating on agar media greatly increased the recovery of CFU from the ice core sample.

Miteva, V. I.; Sheridan, P. P.; Brenchley, J. E.

2004-01-01

316

A new Himalayan ice core CH4 record: possible hints on the preindustrial latitudinal gradient  

NASA Astrophysics Data System (ADS)

Two ice cores recovered from the Himalayan East Rongbuk (ER) Glacier on the northeast saddle of Mt. Qomolangma (Everest) (28° 01' N, 86° 58' E, 6518 m a.s.l.) give access to a tentative record of past Himalayan atmospheric mixing ratio of CH4 spanning the past 1200 yr. The major part of the record is affected by artefacts probably due to in-situ production. After selecting what may represent the true atmospheric mixing ratio, an average of 749 ± 25 ppbv of CH4 is estimated for the late preindustrial Holocene, which is ~ 36 ± 17 (~ 73 ± 18) ppbv higher than the atmospheric levels recorded respectively in Greenland and Antarctic ice cores. A comparison of these new data with model simulations of the CH4 latitudinal gradient suggests either that the models do not get a correct balance between high and low latitude CH4 sources, or that the filtered CH4 profile from the ER cores remains infected by small artefacts.

Hou, S.; Chappellaz, J.; Raynaud, D.; Masson-Delmotte, V.; Jouzel, J.; Bousquet, P.; Hauglustaine, D.

2013-05-01

317

Dating annual layers of a shallow Antarctic ice core with an optical scanner  

NASA Astrophysics Data System (ADS)

This study tests novel methods for automatically identifying annual layers in a shallow Antarctic ice core (WDC05Q) using images that were collected with an optical scanner at the US National Ice Core Laboratory. A new method of optimized variance maximization (OVM) modeled the density-related changes in annual layer thickness directly from image variance. This was done by using multi-objective complex (MOCOM) parameter optimization to drive a low-pass filtering scheme. The OVM-derived changes in annual layer thickness corresponded well with the results of an independent glaciochemical interpretation of the core. Individual annual cycles in image brightness were then identified by using OVM results to apply a depth-varying low-pass filter and fitting a second-order polynomial to a locally detrended neighborhood. The resulting map of annual cycles agreed to within 1% of the overall annual count of the glaciochemical interpretation. Agreement on the presence of specific annual layer features was 96%. It was also shown that the MOCOM parameter optimization could calibrate the image-based results to match directly the date of a specific volcanic marker.

McGwire, Kenneth C.; McConnell, Joseph R.; Alley, Richard B.; Banta, John R.; Hargreaves, Geoffrey M.; Taylor, Kendrick C.

318

Unexpected increase in elemental carbon values over the last 30 years observed in a Svalbard ice core  

NASA Astrophysics Data System (ADS)

Black carbon (BC) is a light-absorbing particle that warms the atmosphere-Earth system. The climate effects of BC are amplified in the Arctic where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125 m deep ice core from Holtedahlfonna glacier (79°8' N, 13°16' E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004. This rise is not seen in Greenland ice cores and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. Several hypotheses, such as changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere, are discussed for the differences between the Svalbard and Greenland ice core records, and the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values in the recent decades, the results have significant implications for the past radiative energy balance at the coring site.

Ruppel, M. M.; Isaksson, E.; Ström, J.; Beaudon, E.; Svensson, J.; Pedersen, C. A.; Korhola, A.

2014-05-01

319

Increase in elemental carbon values between 1970 and 2004 observed in a 300-year ice core from Holtedahlfonna (Svalbard)  

NASA Astrophysics Data System (ADS)

Black carbon (BC) is a light-absorbing particle that warms the atmosphere-Earth system. The climate effects of BC are amplified in the Arctic, where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming, there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125 m deep ice core from Holtedahlfonna glacier (79°8' N, 13°16' E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal-optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004 after a temporary low point around 1970, reaching unprecedented values in the 1990s. This rise is not seen in Greenland ice cores, and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. For example, changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere are discussed for the differences between the Svalbard and Greenland ice core records, as well as the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values between 1970 and 2004, the results have significant implications for the past radiative energy balance at the coring site.

Ruppel, M. M.; Isaksson, I.; Ström, J.; Beaudon, E.; Svensson, J.; Pedersen, C. A.; Korhola, A.

2014-10-01

320

Millennial and Sub-millennial Variability of Total Air Content from the WAIS Divide Ice Core  

NASA Astrophysics Data System (ADS)

The analysis of ancient air bubbles trapped in ice is integral to the reconstruction of climate over the last 800 ka. While mixing ratios of greenhouse gases along with isotopic ratios are being studied in ever increasing resolution, one aspect of the gas record that continues to be understudied is the total air content (TAC) of the trapped bubbles. Published records of TAC are often too low in temporal resolution to adequately capture sub-millennial scale variability. Here we present a high-resolution TAC record (10-50 year sampling resolution) from the WAIS Divide ice core, measured at Oregon State and Penn State Universities. The records cover a variety of climatic conditions over the last 56 ka and show millennial variability of up to 10% and sub-millennial variability between 2.5 and 3.5%. We find that using the pore close off volume parameterization (Delomotte et al., J. Glaciology, 1999, v.45), along with the site temperature derived from isotopes, our TAC record implies unrealistically large changes in surface pressure or elevation. For example, the TAC decreases by ~10% between 19.5ka and 17.3ka, and would imply an elevation increase of nearly 800m. The total accumulation of ice over this period is just 280m (Fudge et al. Nature 2013), making the calculated elevation interpretation implausible. To resolve this discrepancy, we investigate the millennial and sub-millennial variability in our TAC record as a function of changes in firn densification and particularly layering. The firn is the uppermost layer of an ice sheet where snow is compressed into ice, trapping ancient air. Thus firn processes are important for the interpretation of total air content as well as other gas records. We compare our TAC record with proxies for dust, temperature and accumulation to determine how processes other than elevation affect TAC.

Edwards, Jon; Brook, Edward; Fegyveresi, John; Lee, James; Mitchell, Logan; Sowers, Todd; Alley, Richard; McConnell, Joe; Severinghaus, Jeff; Baggenstos, Daniel

2014-05-01

321

The nature of abrupt climate change during the last glacial period from detailed isotopic records from the NGRIP ice core  

NASA Astrophysics Data System (ADS)

Isotopic and chemical impurity records from Greenland ice cores with sub-annual resolution across three fast climate transitions of the last deglacial termination reveal complex patterns of environmental change for the onset of Greenland Interstadial 1 (GI-1 or Bølling), the onset of Greenland Stadial 1 (GS-1 or Younger Dryas), and the onset of the Holocene. In the NGRIP ice core each of these transitions is initiated by a 1-3 year mode shift in deuterium excess, which is a proxy for the Greenland precipitation moisture source. These mode shifts in deuterium excess are decoupled in time from the isotopic (deuterium and oxygen-18) transitions from which they are derived. In general the abrupt isotopic transitions follow the corresponding deuterium excess shifts and span decades rather than years. Similar data from GISP2 confirms the clear deuterium excess mode shifts for transitions from cold states to warm states; however the abrupt deuterium excess transition at the onset of GS-1 is not expressed in a similar way at GISP2. Ironically, it appears that this cooling at the beginning of the Younger Dryas, for which we have theories of the triggering event, is less clearly recorded than warming events, the triggering of which is still poorly understood. Along with other available paleo-data, these results indicate that the sum of an abrupt climate change is composed of multiple responses from different parts of the climate system. These responses can be separated by as little as a single year to a few decades and the collection of these responses result in a variety of abrupt transitions giving each a unique anatomy. Here we expand this type of analysis with new isotope, deuterium excess, and accumulation rate time series from NGRIP across the abrupt transitions associated with several interstadial events of the Last Glacial period (Dansgaard-Oeschger events). Indeed the temporal phasing of deuterium excess and the isotopic content of the ice can vary from one event to the next and emerging patterns may depend on the conditions associated with specific events such as Heinrich Events and ice volume boundary conditions. Together with modeling and chemical impurity data, these patterns will provide clues to the timing and origin of ocean and atmospheric changes that comprise an abrupt climate change. The emerging picture indicates that abrupt climate changes have both a temporal and geographic anatomy that can change from one event to the next in how they are recorded across Greenland.

Popp, T. J.; Svensson, A.; Steffensen, J. P.; Johnsen, S. J.; White, J. W. C.

2009-04-01

322

The ice-core record - Climate sensitivity and future greenhouse warming  

NASA Technical Reports Server (NTRS)

The prediction of future greenhouse-gas-warming depends critically on the sensitivity of earth's climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial-interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.

Lorius, C.; Raynaud, D.; Jouzel, J.; Hansen, J.; Le Treut, H.

1990-01-01

323

The 1452 A.D. Kuwae Eruption Signal Derived from Multiple Ice Core Records: Greatest Eruption over the Past 700 Years  

NASA Astrophysics Data System (ADS)

We combined 20 ice core records, 10 from the Northern Hemisphere and 10 from the Southern Hemisphere to determine the timing and magnitude of the Great Kuwae Eruption in the mid-15th century. The volcanic deposition signals were extracted by applying a high pass loess filter to each time series and examining peaks that exceed twice the 30-yr running median absolute deviation. By accounting for the dating uncertainties associated with each record, these ice core records together reveal a large volcanogenic acid deposition event during 1453-1457 A.D. The results suggest only one major stratospheric injection from the Kuwae eruption and confirm previous findings that the Kuwae eruption took place in 1452, which may serve as a reference to evaluate and improve the dating of ice core records. The average total sulfate deposition from the Kuwae eruption was 103 kg SO4/km2 in Antarctica and 44 kg SO4/km2 in Greenland. By applying the same technique to the other major eruptions of the past 700 yr, our result suggests that the Kuwae eruption was the largest stratospheric sulfate event of that period, probably surpassing the total sulfate deposition of the Tambora eruption of 1815, which produced 65 kg SO4/km2 in Antarctica and 49 SO4/km2 in Greenland.

Gao, C.; Robock, A.; Self, S.; Witter, J.; Steffenson, J.; Clausen, H.; Siggaard-Andersen, M.; Johnsen, S.; Mayewski, P. A.; Ammann, C.

2005-12-01

324

Thallium as a tracer for preindustrial volcanic eruptions in an ice core record from Illimani, Bolivia.  

PubMed

Trace element records from glacier and ice sheet archives provide insights into biogeochemical cycles, atmospheric circulation changes, and anthropogenic pollution history. We present the first continuous high-resolution thallium (Tl) record, derived from an accurately dated ice core from tropical South America, and discuss Tl as a tracer for volcanic eruptions. We identify four prominent Tl peaks and propose that they represent signals from the massive explosive eruptions of the "unknown 1258" A.D. volcano, of Kuwae ( approximately 1450 A.D.), Tambora (1815 A.D.), and Krakatoa (1883 A.D.). The highly resolved record was obtained with an improved setup for the continuous analysis of trace elements in ice with inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The new setup allowed for a stronger initial acidification of the meltwater and shorter tubing length, thereby reducing the risk of memory effects and losses of analytes to the capillary walls. With a comparison of the continuous method to the established conventional decontamination and analysis procedure for discrete samples, we demonstrate the accuracy of the continuous method for Tl analyses. PMID:20050662

Kellerhals, Thomas; Tobler, Leonhard; Brütsch, Sabina; Sigl, Michael; Wacker, Lukas; Gäggeler, Heinz W; Schwikowski, Margit

2010-02-01

325

Ice and Dust in the Quiescent Medium of Isolated Dense Cores  

NASA Astrophysics Data System (ADS)

The relation between ices in the envelopes and disks surrounding young stellar objects (YSOs) and those in the quiescent interstellar medium (ISM) is investigated. For a sample of 31 stars behind isolated dense cores, ground-based and Spitzer spectra and photometry in the 1-25 ?m wavelength range are combined. The baseline for the broad and overlapping ice features is modeled, using calculated spectra of giants, H2O ice and silicates. The adopted extinction curve is derived empirically. Its high resolution allows for the separation of continuum and feature extinction. The extinction between 13 and 25 ?m is ~50% relative to that at 2.2 ?m. The strengths of the 6.0 and 6.85 ?m absorption bands are in line with those of YSOs. Thus, their carriers, which, besides H2O and CH3OH, may include NH+ 4, HCOOH, H2CO, and NH3, are readily formed in the dense core phase, before stars form. The 3.53 ?m C-H stretching mode of solid CH3OH was discovered. The CH3OH/H2O abundance ratios of 5%-12% are larger than upper limits in the Taurus molecular cloud. The initial ice composition, before star formation occurs, therefore depends on the environment. Signs of thermal and energetic processing that were found toward some YSOs are absent in the ices toward background stars. Finally, the peak optical depth of the 9.7 ?m band of silicates relative to the continuum extinction at 2.2 ?m is significantly shallower than in the diffuse ISM. This extends the results of Chiar et al. to a larger sample and higher extinctions. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Boogert, A. C. A.; Huard, T. L.; Cook, A. M.; Chiar, J. E.; Knez, C.; Decin, L.; Blake, G. A.; Tielens, A. G. G. M.; van Dishoeck, E. F.

2011-03-01

326

Natural and Anthropogenic Impacts on the Stable Isotopes of Nitrogen and Oxygen of Ice-Core Nitrate  

NASA Astrophysics Data System (ADS)

The stable isotopes of nitrogen and oxygen of the Ross Ice Drainage System (RIDS) ice-core nitrate were measured in approximately 2-3 year time resolution using a Delta V Isotope Ratio Mass Spectrometer (IRMS). The nitrogen isotope variation (?15N) and the mass-independent fractionation of oxygen (?17O = ?17O - 0.52*?18O) yield a detailed picture of the changes in the global nitrogen cycling and the shift in the oxidation capacity of the atmosphere in response to natural and anthropogenic induced climate change. This is one of the few studies on stable isotopes of ice-core nitrate for time periods prior to the 1800's and will increase our understanding of the oxidation feedbacks of the atmosphere in response to volcanic events, the Little Ice Age, the Maunder Minimum, and anthropogenic emissions in the Southern Hemisphere.

Walters, W.; Michalski, G. M.

2013-12-01

327

Single particle mineralogy of aeolian dust in the East Rongbuk ice core from Mt. Qomolangma (Everest)  

NASA Astrophysics Data System (ADS)

A recent work demonstrated the practical applicability of the combined use of two techniques, attenuated total reflectance FT-IR (ATR-FT-IR) imaging and a quantitative energy-dispersive electron probe X-ray microanalysis, low-Z particle EPMA, for the characterization of individual aerosol particles. These single particle analytical techniques provide complementary information on the physicochemical characteristics of the same individual particles, such as low-Z particle EPMA on morphology and elemental concentrations and the ATR-FT-IR imaging on molecular species, crystal structures, functional groups, and physical states. In this work, this analytical methodology was applied to characterize an insoluble mineral particle sample in the East Rongbuk ice core from Mt. Qomolangma (Everest). On the basis of morphological, X-ray spectral, and ATR-FT-IR spectral data, 140 individual particles were classified into different mineral types, such as SiO2, montmorillonite, montmorillonite + K-feldspar, K-feldspar, Na-feldspar, carbonaceous, FeOx, muscovite, illite, vermiculite, and AlSiO3. In Figure 1, typical X-ray spectrum and ATR-FT-IR spectrum of a particle selected from the ice core sample are shown. This work demonstrates that more detailed physiochemical properties of individual airborne particles can be obtained using this approach than when either the low-Z particle EPMA or ATR-FT-IR imaging technique is used alone.

Hwang, H.; Jung, H.; Eom, H.; Malek, M. A.; Hur, S.; Ro, C.

2011-12-01

328

Human and climate impacts on Holocene fire activity recorded in polar and mountain ice cores  

NASA Astrophysics Data System (ADS)

Fire is one of the major influences of biogeochemical change on local to hemispheric scales through emitting greenhouse gases, altering atmospheric chemistry, and changing primary productivity. Levoglucosan (1,6-anhydro-?-D-glucopyranose) is a specific molecular that can only be produced by cellulose burning at temperatures > 300°C, comprises a major component of smoke plumes, and can be transported across > 1000 km distances. Levoglucosan is deposited on and archived in glaciers over glacial interglacial cycles resulting in pyrochemical evidence for exploring interactions between fire, climate and human activity. Ice core records provide records of past biomass burning from regions of the world with limited paleofire data including polar and low-latitude, high-altitude regions. Here, we present Holocene fire activity records from the NEEM, Greenland (77° 27'N; 51° 3'W; 2454 masl), EPICA Dome C, Antarctica (75° 06'S; 123° 21'E; 3233 masl), Kilimanjaro, Tanzania (3° 05'S, 21.2° E, 5893 masl) and the Muztagh, China (87.17° E; 36.35° N; 5780 masl ice cores. The NEEM ice core reflects boreal fire activity from both North American and Eurasian sources. Temperature is the dominant control of NEEM levoglucosan flux over decadal to millennial time scales, while droughts influence fire activity over sub-decadal timescales. Our results demonstrate the prominence of Siberian fire sources during intense multiannual droughts. Unlike the NEEM core, which incorporates the largest land masses in the world as potential fire sources, EPICA Dome C is located far from any possible fire source. However, EPICA Dome C levoglucosan concentrations are consistently above detection limits and demonstrate a substantial 1000-fold increase in fire activity beginning approximately 800 years ago. This significant and sustained increase coincides with Maori arrival and dispersal in New Zealand augmented by later European arrival in Australia. The EPICA Dome C levoglucosan profile is similar to regional charcoal compilations from New Zealand and southeastern Australia. Evidence from Kilimanjaro demonstrates a major increase in fire activity centered around 800-1000 years ago, corresponding to both increased temperatures and aridity as recorded in regional lake cores. This peak in fire activity is an order of magnitude higher than at any other time in the record including the most recent period. Environmental and anthropological studies suggest that upslope human migrations have occurred in response to the warmer, drier conditions. Kilimanjaro is surrounded by flammable savanna vegetation, yet the Muztagh core is located in an especially arid section of the Tibetan Plateau and consistently contains levoglucosan concentrations that are 100 to 1000 times greater than the mean Kilimanjaro flux. These high concentrations and the lack of available fuel suggest that regional rather than local biomass burning may be the source of the fire products. Biomass burning aerosols are a major component of the South Asian Brown Cloud and may influence the composition and concentration of pyrogenic aerosols across the Tibetan Plateau. The relative impact of human activity versus climate change on Holocene biomass burning varies regionally. Combining ice and sediment core data with model output can help place these regional differences into a global context with implications for a warming climate.

Kehrwald, Natalie; Zennaro, Piero; Kirchgeorg, Torben; Li, Quanlian; Wang, Ninglian; Power, Mitchell; Zangrando, Roberta; Gabrielli, Paolo; Thompson, Lonnie; Gambaro, Andrea; Barbante, Carlo

2014-05-01

329

Detection and Isolation of Ultrasmall Microorganisms from a 120,000YearOld Greenland Glacier Ice Core  

Microsoft Academic Search

The abundant microbial population in a 3,043-m-deep Greenland glacier ice core was dominated by ultra- small cells (<0.1 m3) that may represent intrinsically small organisms or starved, minute forms of normal- sized microbes. In order to examine their diversity and obtain isolates, we enriched for ultrasmall psychro- philes by filtering melted ice through filters with different pore sizes, inoculating anaerobic

Vanya I. Miteva; Jean E. Brenchley

2005-01-01

330

Detection prospects for GeV neutrinos from collisionally heated gamma-ray bursts with IceCube/DeepCore.  

PubMed

Jet reheating via nuclear collisions has recently been proposed as the main mechanism for gamma-ray burst (GRB) emission. In addition to producing the observed gamma rays, collisional heating must generate 10-100 GeV neutrinos, implying a close relation between the neutrino and gamma-ray luminosities. We exploit this theoretical relation to make predictions for possible GRB detections by IceCube + DeepCore. To estimate the expected neutrino signal, we use the largest sample of bursts observed by the Burst and Transient Source Experiment in 1991-2000. GRB neutrinos could have been detected if IceCube + DeepCore operated at that time. Detection of 10-100 GeV neutrinos would have significant implications, shedding light on the composition of GRB jets and their Lorentz factors. This could be an important target in designing future upgrades of the IceCube + DeepCore observatory. PMID:25165903

Bartos, I; Beloborodov, A M; Hurley, K; Márka, S

2013-06-14

331

Chlorine-36 and cesium-137 in ice-core samples from mid-latitude glacial sites in the Northern Hemisphere  

USGS Publications Warehouse

Chlorine-36 (36Cl) concentrations, 36Cl/Cl ratios, and 36Cl fluxes in ice-core samples collected from the Upper Fremont Glacier (UFG) in the Wind River Mountain Range, Wyoming, United States and the Nangpai Gosum Glacier (NGG) in the Himalayan Mountains, Nepal, were determined and compared with published results from the Dye-3 ice-core drilling site on the Greenland Ice Sheet. Cesium-137 (137Cs) concentrations in the NGG also were determined. The background fluxes for 36Cl for each glacial site were similar: (1.6??0.3)??10-2 atoms/cm2 s for the UFG samples, (0.7??0.1)??10-2 atoms/cm2 s for the NGG samples, and (0.4??0.1)??10-2 atoms/cm2 s for the Dye-3 samples. The 36Cl fluxes in ice that was deposited as snow during peak atmospheric nuclear weapon test (1957-1958) were (33??1)??10-2 atoms/cm2 s for the UFG site, (291??3)??10-2 atoms/cm2 s for the NGG site, and (124??5)??10-2 atoms/ cm2 s for the Dye-3 site. A weapon test period 137Cs concentration of 0.79??0.05 Bq/kg in the NGG ice core also was detected in the same section of ice that contained the largest 36Cl concentration. ?? 2000 Elsevier Science B.V. All rights reserved.

Green, J.R.; Cecil, L.D.; Synal, H.-A.; Kreutz, K.J.; Wake, C.P.; Naftz, D.L.; Frape, S.K.

2000-01-01

332

Ice  

NSDL National Science Digital Library

When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.

Harris, Kathryn Louise.

333

In situ production of ethane and propane in dust-rich Greenland ice core samples: is methane also affected?  

NASA Astrophysics Data System (ADS)

The analysis of methane and the stable isotopic composition extracted from ice core samples provides a suite of valuable climatic sensitive parameters like CH4 mixing ratios, d13C(CH4), dD(CH4) and the respective interhemispheric differences of these parameters. Their interpretation as palaeoclimatic proxies relies on the assumption that the measured properties represent true atmospheric concentrations after correction for the well-known diffusive processes in the firn column. Up to now, methane is assumed to be unaffected from in situ production with the exception of melt layers and alpine ice cores which show elevated concentrations. In contrast, other trace gases like CO2 and N2O show in situ production under certain conditions, especially in dust-rich Greenland ice core samples. Also other trace gases which are chemically more related to methane, like the hydrocarbons ethane and propane as well as methyl chloride show pronounced in situ production in some ice cores. To explore the processes leading to situ production for ethane and propane and a possible link to methane it is helpful to measure these parameters simultaneously on a single ice core sample. For this task we present a new online preparation line for extraction and measurement of several trace gas species (isotope ratios and/or mixing ratios) of 150-200 g ice samples. The analytical setup comprises continuous flow-isotope ratio mass spectrometry and a custom-built online pre-concentration system with a vacuum extraction part and a continuous He flow GC line. Our setup allows for analysing isotope ratios of CH4(13C) and N2O (d15N, d18O) as well as their mixing ratios and, additionally, the mixing ratios of ethane, propane and methyl chloride. We measured ice core samples on the NGRIP ice core during, selected time intervals covering DO events, the LGM and, the Bølling/Allerød Younger Dryas. Where possible, we focused on intervals where dust showed its larges variability. In summary, we see a strong in situ production for ethane, propane and methyl chloride related to dust concentrations in Greenland ice. However, methane is likely not affected by this production pathway or the contribution is so small that it is hidden in the atmospheric signal so far. A better sampling strategy focusing with a denser temporal coverage on intervals with variable dust loading could further constrain a possible contribution of methane from in situ production.

Schmitt, J.; Seth, B.; Fischer, H.

2012-04-01

334

Basal Crevasses Reveal a Dynamic Ice-Ocean Interface in an Embayment of the Whillans Ice Stream Grounding Line, West Antarctica  

NASA Astrophysics Data System (ADS)

The transition from limited- or no-slip conditions at the base of grounded ice to free-slip conditions beneath floating ice occurs across the few-kilometers-wide grounding zone of ice sheets. This transition is either an elastic flexural transition from bedrock- to hydrostatically-supported ice (often tidally influenced), or a transition from thicker to thinner ice over a flat bed, or some combination of these processes. In either case, the stress-change in the basal layers of ice can result in brittle deformation that may produce crevassing. Thus the position and morphology of basal crevasses reveal important information about the stress state across the grounding zone. We conducted ground-based radar surveys at two locations of the Whillans Ice Stream grounding zone, one over a subglacial peninsula where the transition to floatation is abrupt, and the second over a subglacial embayment where several dynamic subglacial lakes drain to the ocean, likely resulting in episodic high sediment and water flux across the grounding line. Our surveys indicate a complex pattern of basal crevasses. Some are associated with steeper surface slopes, but others appear to be related to ice flexure across an incised basal channel carrying water and sediment to the ocean. Here we image pairs of crevasses from either side of the channel that produce curious signatures in the radar profiles showing a high degree of symmetry at both shorter and longer arrival times than the nadir bed echo. In other locations, due to the high reflectivity of seawater and the relatively shallow ice thickness, we image many off-nadir crevasses where the radar energy is first reflected from the ice-water interface and then from the crevasse, producing an echo signature with a reversed phase due to the second reflection. In several cases these crevasse echoes appear to mimic the geometry of a sub-ice "wedge" dipping into the sediment, while in reality the radar never penetrates below the basal interface. Our results indicate that basal crevasses offer a rich, but unexploited, dataset for diagnosing stress state and ice/ocean interaction processes across grounding zones and that special care is needed when interpreting subglacial returns in radar data.

Jacobel, Robert; Christianson, Knut; Wood, Adam; DallaSanta, Kevin; Gobel, Rebecca

2014-05-01

335

Utilization of Fluorescent Microspheres and a Green Fluorescent Protein-Marked Strain for Assessment of Microbiological Contamination of Permafrost and Ground Ice Core Samples from the Canadian High Arctic  

PubMed Central

Fluorescent microspheres were applied in a novel fashion during subsurface drilling of permafrost and ground ice in the Canadian High Arctic to monitor the exogenous microbiological contamination of core samples obtained during the drilling process. Prior to each drill run, a concentrated fluorescent microsphere (0.5-?m diameter) solution was applied to the interior surfaces of the drill bit, core catcher, and core tube and allowed to dry. Macroscopic examination in the field demonstrated reliable transfer of the microspheres to core samples, while detailed microscopic examination revealed penetration levels of less than 1 cm from the core exterior. To monitor for microbial contamination during downstream processing of the permafrost and ground ice cores, a Pseudomonas strain expressing the green fluorescent protein (GFP) was painted on the core exterior prior to processing. Contamination of the processed core interiors with the GFP-expressing strain was not detected by culturing the samples or by PCR to detect the gfp marker gene. These methodologies were quick, were easy to apply, and should help to monitor the exogenous microbiological contamination of pristine permafrost and ground ice samples for downstream culture-dependent and culture-independent microbial analyses. PMID:15691963

Juck, D. F.; Whissell, G.; Steven, B.; Pollard, W.; McKay, C. P.; Greer, C. W.; Whyte, L. G.

2005-01-01

336

New high-resolution aerosol proxy data from the Greenland NEEM ice core covering the last 128,000 years  

NASA Astrophysics Data System (ADS)

High-resolution multicomponent continuous flow analysis (CFA) measurements have been performed over the entire depth of the NEEM ice core in three field seasons 2009-2011. Only in the brittle ice section, covering an age of approx. 4,000-8,000 years, continuous measurements could not be performed due to the bad ice quality which hampered such analyses. On all the other ice, continuous records of tracers for sea salt aerosol (sodium), mineral dust aerosol (calcium), inorganic and biogenic nitrogen compounds (nitrate and ammonium), hydrogen peroxide, and electrolytic conductivity were recorded. Data evaluation and quality control of the raw data of the 2.5 km long ice core have recently been finalised, resulting in the final multi-proxy CFA dataset of the NEEM ice core presented here. It covers the last 128,000 years including the entire (stratigraphically folded) Eemian warm period in Greenland. Our chemical CFA measurements are performed in a nominal resolution of 0.5 mm, allowing for the resolution of seasonal cycles over the top 1500 m of the ice core. Thus, seasonality of aerosol tracers can be studied as far back as the early Holocene, and to a certain extent even further back in time. The lower part of the ice core, however, including the last glacial period as well as the Eemian ice section, is subject to such strong thinning of the ice that no unambiguous seasonal cycles can be resolved any more. Nevertheless, long-term glacial-interglacial and stadial-interstadial changes on the one side and the peculiarities of the first Greenland Eemian aerosol record in comparison to the Holocene on the other can be investigated in highest resolution. Here, the new NEEM aerosol proxy records are presented and compared to NGRIP and GRIP CFA records focussed on the early Holocene and last glacial period. Thanks to the particularly high resolution we can furthermore closely investigate the timing and phasing of fast climate transitions such as Termination I and Dansgaard-Oeschger events during the last glacial period.

Schüpbach, Simon; Bigler, Matthias; Gfeller, Gideon; Fischer, Hubertus

2014-05-01

337

Characterizing atmospheric circulation signals in Greenland ice cores: insights from a weather regime approach  

NASA Astrophysics Data System (ADS)

Greenland ice cores offer seasonal to annual records of ?18O, a proxy for precipitation-weighted temperature, over the last few centuries to millennia. Here, we investigate the regional footprints of the North Atlantic weather regimes on Greenland isotope and climate variability, using a compilation of 22 different shallow ice-cores and the atmospheric pressure conditions from the twentieth century reanalysis (20CR). As a first step we have verified that the leading modes of winter and annual ?18O are well correlated with oceanic (Atlantic multidecadal oscillation) and atmospheric [North Atlantic oscillation (NAO)] indices respectively, and also marginally with external forcings, thus confirming earlier studies. The link between weather regimes and Greenland precipitation, precipitation-weighted temperature and ?18O is further explored by using an isotope simulation from the LMDZ-iso model, where the 3-dimensional wind fields are nudged to those of 20CR. In winter, the NAO+ and NAO- regimes in LMDZ-iso produce the largest isotopic changes over the entire Greenland region, with maximum anomalies in the South. Likewise, the Scandinavian blocking and the Atlantic ridge also show remarkable imprints on isotopic composition over the region. To assess the robustness and model dependency of our findings, a second isotope simulation from the isotopic model is also explored. The percentage of Greenland ?18O variance explained by the ensemble of weather regimes is increased by a factor near two in both LMDZ-iso and IsoGSM when compared to the contribution of the NAO index only. Similarly, weather regimes provide a net gain in the ?18O variance explained of similar magnitude for the whole set of ice core records. Greenland ?18O also appears to be locally affected by the low-frequency variations in the centres of action of the weather regimes, with clearer imprints in the LMDZ-iso simulation. This study opens the possibility for reconstructing past changes in the frequencies of occurrence of the weather regimes, which would rely on the sensitive regions identified here, and the use of additional proxies over the North Atlantic region.

Ortega, Pablo; Swingedouw, Didier; Masson-Delmotte, Valérie; Risi, Camille; Vinther, Bo; Yiou, Pascal; Vautard, Robert; Yoshimura, Kei

2014-11-01

338

Can we retrieve a clear paleoclimatic signal from the deeper part of the EPICA Dome C ice core?  

NASA Astrophysics Data System (ADS)

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (?D-?18Oice, ?18Oatm, total air content, CO2, CH4, N2O, dust, high resolution chemistry, ice texture) of the bottom 60 m of the EPICA Dome C ice core from central Antarctica. These bottom layers have been subdivided in two sections: the lower 12 m showing visible solid inclusions (basal ice) and the 48 m above which we refer to as "deep ice". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end-term from a previous/initial ice sheet configuration) can explain the observed bottom ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of allochtone material at the ice-bedrock interface. We also discuss how the proposed mechanism is compatible with the other variables described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the time scale has been considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice.

Tison, J.-L.; de Angelis, M.; Littot, G.; Wolff, E.; Fischer, H.; Hansson, M.; Bigler, M.; Udisti, R.; Wegner, A.; Jouzel, J.; Stenni, B.; Johnsen, S.; Masson-Delmotte, V.; Landais, A.; Lipenkov, V.; Loulergue, L.; Barnola, J.-M.; Petit, J.-R.; Delmonte, B.; Dreyfus, G.; Dahl-Jensen, D.; Durand, G.; Bereiter, B.; Schilt, A.; Spahni, R.; Pol, K.; Lorrain, R.; Souchez, R.; Samyn, D.

2015-01-01

339

The volcanic record of the upper 600 m of the ANDRILL AND-1 drill cores: Evidence of ice-free conditions and local volcanic activity over the  

E-print Network

. The occurrence and nature of the volcanic layers also has implications to ice local conditions, sediment in the core consist of reworked volcanogenic sediments, volcanic clasts and reworked or primary pyroclasticThe volcanic record of the upper 600 m of the ANDRILL AND-1 drill cores: Evidence of ice

Dunbar, Nelia W.

340

Large variability of trace element mass fractions determined by ICP-SFMS in ice core samples from worldwide high altitude glaciers  

E-print Network

Large variability of trace element mass fractions determined by ICP-SFMS in ice core samples from and mass fractions of trace elements in melted acidified ice core samples measured by Inductively Coupled. Twenty trace elements (Ag, Al, As, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb, Sb, Sn, Ti, Tl, U, V and Zn

Howat, Ian M.

341

Evidence for Pacific Climate Regime Shifts as Preserved in a Southeast Alaska Ice Core  

NASA Astrophysics Data System (ADS)

Climate modes emanating from the Pacific sector have far-reaching effects across the globe. The El Niño/Southern Oscillation (ENSO) reflects anomalies in the sea surface temperature and pressure fields over the tropical Pacific, but climate implications from these anomalies extend to monsoon regions of Asia to North America and even Europe. The Pacific Decadal Oscillation (PDO) explains sea surface temperature anomalies in the North Pacific sector and influences the long-term behavior of the ENSO cycle as well as the storm track over North America expressed as the Pacific/North American Pattern (PNA). The impacts of both climate change and drastically reduced Arctic sea ice cover on these teleconnection patterns are poorly understood, and with little knowledge about their past behavior, predicting the changes in these climate modes is extremely difficult. An ice core from the col between Mt. Bona and Mt. Churchill in southeast Alaska provides an opportunity to examine the PDO prior to both the start of instrumental records and the more recent effects of anthropogenic climate change. The Bona-Churchill records of isotopic, dust, and chemical composition are compared to nearby meteorological station and 20th century reanalysis data to evaluate their strength as climate recorders. Climate indices such as the PDO and PNA, along with indices created to describe the strength and position of the Aleutian Low and Siberian High, are incorporated into the analysis to determine if proxy relationships are altered under different climate regimes. Satellite records of sea ice extent within the Sea of Okhotsk and the Bering Sea, when compared to the Bona-Churchill data, show a distinct change in behavior in the mid-1990s possibly in response to the temporary negative shift in the PDO. This behavioral shift is explored and placed into a broader climate context to determine whether similar events have occurred in the past or if this shift is unique to a rapidly warming Arctic.

Porter, S. E.; Mosley-Thompson, E. S.; Thompson, L. G.

2012-12-01

342

Volcanic forcing of climate over the past 1500 years: An improved ice-core-based index for climate models  

NASA Astrophysics Data System (ADS)

This dissertation has investigated one of the most important natural causes of climate change, volcanic eruptions, by developing an ice core-based volcanic forcing index, using 54 ice core records from both the Arctic and Antarctica. The extensive collection of ice core data reduces errors inherent in reconstructions based on a single or small number of cores. This enables us to obtain much higher accuracy in both detection of events and quantification of the radiative effects. We extracted volcanic deposition signals from each ice core record by applying a high-pass loess filter to the time series and examining peaks that exceed twice the 31-yr running median absolute deviation. We then studied the spatial pattern of volcanic sulfate deposition on Greenland and Antarctica, and combined this knowledge with a new understanding of stratospheric transport of volcanic aerosols to produce a forcing index that is a function of month from 501 to 2000 CE, latitude in 10° bands, and height from 9 to 30 km at 0.5 km resolution. This index is the longest and most advanced volcanic forcing index of the type. It eliminates or minimizes many aspects of problems previous reconstruction had with the ice core records. The estimated uncertainty is a significant reduction from the factor of two uncertainty reported in previously constructed volcanic forcing indices. We forced an energy balance climate model with this new volcanic forcing index, together with solar and anthropogenic forcing, to simulate the large scale temperature response. The results agree well with instrumental observations for the past 150 years and the proxy records for the last millennium. Through better characterization of the natural causes of climate change, this new index will lead to improved prediction of anthropogenic impacts on climate. Using 33 ice core records we investigated the 15th century Kuwae eruption. We found it was indeed a single-phase eruption occurred during late 1452 to early 1453 CE and it emitted about 140 Tg of sulfate aerosols into the stratosphere with 2(SH):1(NH) hemispheric partitioning. This finding provides an important reference to evaluate and improve the dating of ice core records.

Gao, Chaochao

343

Climatic implications of the dust measurements from a horizontal ice core sequence in ablation area of Taylor glacier (Antarctica)  

NASA Astrophysics Data System (ADS)

We present a new dust record from a horizontal ice core taken in the ablation zone of Taylor Glacier. The glacier is fed by ice deposited on the northern slope of Taylor Dome and flows in a dry valley region (Antarctica) where the ice surface mostly disappears by sublimation. A series of ice samples have been collected from 202 shallow cores performed every 30cm along an 80m long transect outside from an apparent ice folding. The 7 cm long section was analyzed for the dust size and concentration by using a Coulter counter multisizer IIe, after decontamination of the outer part of the ice by the washing method. The size distribution of the dust samples displays a systematic a mode around 2 microns and the absence of particle larger than 5-7 microns, a property which is similar to dust records from inland sites. This indicates the dust has a long distance transport origin excluding the surrounding dry valleys and denuded mountains area as potential sources. As an implication, we use the dust data to tie our record to the EPICA Dome C timescale. The series in undisturbed (no folding) and encompasses the full deglaciation from ~38 ka to ~15 ka. Comparison with other climate proxies (stable isotope, chemistry, gases …) shows that the Taylor Dome region went through a similar deglacial climatic transition as the rest of Antarctica.

Grente, Benjamin; Petit, Jean Robert; Baggenstos, Daniel; Severinghaus, Jeffrey; McConnell, Joseph; Sigl, Michael; Maselli, Olivia; Bauska, Thomas; Brook, Edward

2013-04-01

344

Implication of azelaic acid in a Greenland Ice Core for oceanic and atmospheric changes in high latitudes  

NASA Astrophysics Data System (ADS)

A Greenland ice core (450 years) has been studied for low molecular weight dicarboxylic acids (C2-C10) using a capillary gas chromatography and mass spectrometer. Their molecular distribution generally showed a predominance of succinic acid (C4) followed by oxalic (C2), malonic (C3), glutaric (C5), adipic (C6), and azelaic (C9) acids. Azelaic acid, that is a specific photochemical reaction product of biogenic unsaturated fatty acids, gave a characteristic historical trend in the ice core; i.e., the concentrations are relatively low during late 16th to 19th century (Little Ice Age) but become very high in late 19th to 20th century (warmer periods) with a large peak in 1940s AD. Lower concentrations of azelaic acid may have been caused by a depressed emission of unsaturated fatty acids from seawater microlayers due to enhanced sea ice coverage during Little Ice Age. Inversely, increased concentrations of azelaic acid in late 19th to 20th century are likely interpreted by an enhanced sea-to-air emission of the precursor unsaturated fatty acids due to a retreat of sea ice and/or by the enhanced production due to a potentially increased oxidizing capability of the atmosphere.

Kawamura, K.; Yokoyama, K.; Fujii, Y.; Watanabe, O.

345

Variations of the CO2 concentration of occluded air and of anions and dust in polar ice cores  

NASA Astrophysics Data System (ADS)

Analysis of impurities entrapped in natural ice is the most promising method for reconstructing the history of atmospheric composition before the period of direct measurement and offers the possibility of extending the record to at least 100,000 years B.P. We report here the present state of work in this field, with special emphasis on atmospheric CO2 concentration. After discussing the mechanism by which atmospheric gases are entrapped in ice, we report CO2 concentrations in ice core samples, up to 100,000 years old, from deep drilling projects in Greenland and the Antarctic. Results from ice deposited during the last 2000 years allow us to estimate the preindustrial atmospheric CO2 level, an important boundary condition for modelling the anthropogenic CO2 increase. Using older samples from a deep ice core drilled at Dye 3, Greenland, we show that the CO2 concentration was 180 to 200 ppmv at the end of the Wisconsin and increased during the transition to the Holocene to values in the 260 to 300 ppmv range. Detailed CO2 measurements on sections of the Wisconsin part of the Dye 3 core which, based on ?18O, were deposited during times of significant climatic variation, show that the ?18O variations were accompanied by simultaneous correlated rapid CO2 variations. Other parameters, including micro-particle concentration and Cl-, NO-3 and SO2-4 concentrations also showed significant variations which correlate with the measured ?18O shifts.

Oeschger, H.; Stauffer, B.; Finkel, R.; Langway, C. C., Jr.

346

Carbon isotope constraints on the deglacial CO? rise from ice cores.  

PubMed

The stable carbon isotope ratio of atmospheric CO(2) (?(13)C(atm)) is a key parameter in deciphering past carbon cycle changes. Here we present ?(13)C(atm) data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in ?(13)C(atm) during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the ?(13)C(atm) evolution. During the Last Glacial Maximum, ?(13)C(atm) and atmospheric CO(2) concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then. PMID:22461496

Schmitt, Jochen; Schneider, Robert; Elsig, Joachim; Leuenberger, Daiana; Lourantou, Anna; Chappellaz, Jérôme; Köhler, Peter; Joos, Fortunat; Stocker, Thomas F; Leuenberger, Markus; Fischer, Hubertus

2012-05-11

347

New ice core evidence for a volcanic cause of the A.D. 536 dust veil  

NASA Astrophysics Data System (ADS)

New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533-534 +/- 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree-ring data to have occurred in A.D. 536. Tree-ring data suggest that this was the most severe and protracted short-term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.

Larsen, L. B.; Vinther, B. M.; Briffa, K. R.; Melvin, T. M.; Clausen, H. B.; Jones, P. D.; Siggaard-Andersen, M.-L.; Hammer, C. U.; Eronen, M.; Grudd, H.; Gunnarson, B. E.; Hantemirov, R. M.; Naurzbaev, M. M.; Nicolussi, K.

2008-02-01

348

Climate varibility during the last 2,000 years: an Eastern European cave ice core perspective  

NASA Astrophysics Data System (ADS)

To place the climate changes we witnessed over the past decades in a longer-term context, an understanding of the climate during the past two millennia is required. This can shed light on helping us decipher both natural and anthropogenic forces acting on the climate system. Here we present an ice core proxy-based on reconstruction of air temperatures over the past 2000 years for east-central Europe, an area with poorly documented climatic studies. Our results suggests that over the past two millennia, the climate shifted back and forth between warmer (0-400 AD and 900-1300 AD) and colder (400-900 AD and 1300-1850 AD) periods, with a higher variability during the Little Ice Age and the Dark Ages Cold Period, than during the intervening warm intervals. The paper will discuss the possible role played by NAO variations and solar influence on the long-term trends and the short-lived climatic fluctuations caused by volcanic eruptions.

Per?oiu, Aurel; Onac, Bogdan P.

2010-05-01