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1

ice core  

Microsoft Academic Search

Svalbard ice cores have not yet been fully exploited for studies of climate and environmental conditions. In one recently drilled ice core from Lomonosovfonna we have studied the methanesulphonic acid (MSA) records in relation to temperature and sea ice. During the present climatic conditions MSA appears to be negatively correlated with the sea ice conditions in the Barents Sea, and

Elisabeth Isaksson; Teija Kekonen; John Moore

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.

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, J?rgen 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.

Nation, Nsf S.; Institute, Jim W.

4

Ice Core Secrets  

NSDL National Science Digital Library

In this activity, students will explore the characteristics of ice and explain the influencing factors by using Internet connections to polar field experiences, making their own ice cores and taking a field trip for obtaining a local ice core. The students will practice scientific journaling to document their observations. They will assemble their findings, develop a poster of their ice core and explain their observations. The 'ice is ice' misconception will be dispelled. Students will explain what scientists learn from ice cores and define basic vocabulary associated with ice cores.

Kolb, Sandra

5

Ancient biomolecules from deep ice cores reveal a forested southern Greenland.  

PubMed

It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores, enabling reconstructions of past flora and fauna. We show that high-altitude southern Greenland, currently lying below more than 2 kilometers of ice, was inhabited by a diverse array of conifer trees and insects within the past million years. The results provide 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

2007-07-01

6

Rheological Implications of the Internal Structure and Crystal Fabrics of the West Antarctic Ice Sheet as Revealed by Deep Core Drilling at Byrd Station.  

National Technical Information Service (NTIS)

Crystalline textures and fabrics of ice cores from the 2164-m-thick ice sheet at Byrd Station, Antarctica, reveal the existence of an anisotropic ice sheet. A gradual but persistent increase in the c-axis preferred orientation of the ice crystals was obse...

A. J. Gow T. Williamson

1976-01-01

7

Tree rings and ice cores reveal 14C calibration uncertainties during the Younger Dryas  

Microsoft Academic Search

The Younger Dryas interval during the Last Glacial Termination was an abrupt return to glacial-like conditions punctuating the transition to a warmer, interglacial climate. Despite recent advances in the layer counting of ice-core records of the termination, the timing and length of the Younger Dryas remain controversial. Also, a steep rise in the concentration of atmospheric radiocarbon at the onset

R. Muscheler; B. Kromer; S. Björck; A. Svensson; M. Friedrich; K. F. Kaiser; J. Southon

2008-01-01

8

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.

9

Ice Core Facility  

NASA Astrophysics Data System (ADS)

To support its program of studying ice cores taken from the Greenland, Antarctic and midlatitude ice sheets, the Division of Polar Programs of the National Science Foundation is soliciting proposals for operating its ice core curatorial facility.NSF's current ice core repository is at the State University of New York at Buffalo, where it has been operated under annual contract since 1975. Beginning in Fiscal Year 1991, whoever manages the NSF facility, now to be called the U.S. Ice Core Repository, will do it under a 5-year cooperative agreement.

10

What's An Ice Core?  

NSDL National Science Digital Library

This animation starts with a schematic illustration of glacier growth and then introduces six different methods that researchers use when studying ice cores in order to deduce the climate of the past. The research methods that are briefly introduced are ice layering, pollen, oxygen isotopes, ice crystals and gases trapped inside, and other chemistry.

History, The A.

11

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

12

Ice Core Investigations  

NSDL National Science Digital Library

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 pollution to create a meaningful science learning experience for students.

Krim, Jessica; Brody, Michael

2008-09-01

13

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

14

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

15

Global Ice Core Research  

NSDL National Science Digital Library

This informative site from the US Geological Survey (USGS) covers the latest ice-core research projects from around the world, including sites in Nepal, Norway, and Kyrghyzstan. Authored by researchers at the Global Ice core Research Office, the site contains an overview of the mid-latitude and polar glaciers, isotopic methods in glacial research, and applications to paleoclimatology. Links to maps, figures, and in some cases, full-text articles (HTML) about specific glaciers are available, and the site is peppered with color photos of glacial environments. Links to biographies of the scientists involved in the project, contacts, and other snow and ice sites are also listed.

16

USGS National Ice Core Laboratory  

NSDL National Science Digital Library

This United States Geological Survey site highlights the work of the National Ice Core Laboratory (NICL). It discusses the NICL's role, why ice cores are important to study, how ice cores are drilled and studied, and core drilling locations. These cores are recovered and studied for a variety of scientific investigations, most of which focus on the reconstruction of Earth's climate history. The facility currently houses over 14,000 meters of ice cores from 34 drill sites in Greenland, Antarctica, and high mountain glaciers in the Western United States. There are links for more information and individual core information such as numbers, locations and sizes.

17

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

18

Influence of the westerlies on the precipitation revealed from the isotopic record in Noijin Kangsang ice core on the southern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Many efforts have been made to clarify the climatic significance of stable isotopic variations in ice cores on the southern Tibetan Plateau (TP) through the study of stable isotopes in present precipitation. A 55-m long ice core was drilled close to bedrock from Mt. Noijin Kangsang on the southern TP in summer 2007, dated from 1864 to 2006 AD. A good agreement is shown between ?18O in Noijin Kangsang ice core (NK) and local temperature, indicating that the isotopic record from NK ice core is a reliable temperature trend indicator. Based on the comparison of interannual variations of ?18O in NK ice core and other climatic indicators (monsoon vs. westerlies indicators), the obvious increasing of westerlies moisture is detected on the southern TP. The unusually slow increasing of ?18O in NK ice core from 1980s to present is subjected to the gradually increasing influence of the westerlies and corresponding decreasing influence of the monsoon on the southern TP.

Gao, J.

2012-12-01

19

Ice core drilling at Vostok  

NSF Publications Database

Jane Dionne cc: Chairperson, NSF Committee on Environmental Matters Dr. Eric Saltzman Dr. Jean Jouzel Dr. A.I. Danilov DEEP ICE CORE DRILLING AT VOSTOK STATION, ANTARCTICA: ENVIRONMENTAL ASSESSMENT Summary Statement The deep drilling project at Vostok station Antarctica involves the use of a mixture of kerosene and Freon (CFC-11) as a drilling fluid. During each drill run approximately 30 liters of drill fluid is removed from the hole on the cable, drill, and ice core.

20

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 Niño 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.

Sciencenow, Nova; Domain, Teachers'

21

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.

Center, Byrd P.; University, Ohio S.

22

Ice Core Dating Software for Interactive Dating of Ice Cores  

NASA Astrophysics Data System (ADS)

Scientists involved in ice core dating are well familiar with the problem of identification and recording the depth of annual signals using stable isotopes, glaciochemistry, ECM (electrical conductivity), DEP (dielectric properties) and particle counter data. Traditionally all parameters used for ice core dating were plotted as a function of depth, printed and after years were marked on the paper, converted to depth vs. age time scale. To expedite this tedious and manual process we developed interactive computer software, Ice core Dating (ICD) program. ICD is written in Java programming language, and uses GPL and GPL site licensed graphic libraries. The same 3.5 Mb in size pre-compiled single jar file, that includes all libraries and application code, was successfully tested on WinOS, Mac OSX, Linux, and Solaris operating systems running Java VM version 1.4. We have followed the modular design philosophy in our source code so potential integration with other software modules, data bases and server side distributed computer environments can be easily implemented. We expect to continue development of new suites of tools for easy integration of ice core data with other available time proxies. ICD is thoroughly documented and comes with a technical reference and cookbook that explains the purpose of the software and its many features, and provides examples to help new users quickly become familiar with the operation and philosophy of the software. ICD is available as a free download from the Climate Change Institute web site ( under the terms of GNU GPL public license.

Kurbatov, A. V.; Mayewski, P. A.; Abdul Jawad, B. S.

2005-12-01

23

Ice cores and global change  

Microsoft Academic Search

For scientists interested in global change problems, ice core records provide a unique and invaluable medium for studying the past. These records yield both direct and proxy links to the paleoenvironment over periods potentially as long as hundreds of thousands of years with resolution down to seasonal scale for time-series on the order of hundreds to thousands of years. In

Paul A. Mayewski

1988-01-01

24

A new deep ice core in the Northern Patagonian Icefield reveals a regional cooling in the Southern Andes over the last 120 years  

NASA Astrophysics Data System (ADS)

Several tropical and subtropical ice cores have been extracted along the Andes of South America over the last decades. In Antarctica, numerous ice core studies have been completed. In order to close the gap between tropical and polar environments in this unique 8000-km long ice core records transect, a deep ice core (122m) has been extracted in 2007 from the San Valentin glacier (3747m, 47 degrees S, 73 degrees W) located in the Northern Patagonian Icefield (Chile). The cold conditions at that site enable us to explore the chemical and isotopic records in terms of climate variations over the last 160 years. We will briefly present the dating of the ice and the local climate specificities. Then, we will focus on the decreasing temperature trend (-0.2 degree C per decade) exhibited by the isotopic composition of the ice over the last century. We will discuss this regional cooling in a context of a warming world regarding: (1) recent temperature reconstructions in Southern South America, (2) the influence of the well-known climate modes in this region (ENSO, PDO and SAM/AAOI), (3) the linkages to tropical climate variability and changes in the Southern Pacific Ocean.

Vimeux, F.; Moreno, I.; De Angelis, M.; Ginot, P.; Magand, O.; Kageyama, M.; Casassa, G.; Risi, C.; Minster, B.; Reutenauer, C.

2012-12-01

25

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.

26

Late Cenozoic oscillations of Antarctic ice sheets revealed by provenance of basement clasts and grain detrital modes in ANDRILL core AND1B  

Microsoft Academic Search

Petrological investigations of the sand fraction and of granule- to cobble-sized clasts in the Plio-Pleistocene sedimentary cycles of the AND-1B drill core at the NW edge of the Ross Ice Shelf (McMurdo Sound) highlight significant down-core modal and compositional variations. These variations provide: (i) direct information about potential source regions during both glacial maxima and minima; and (ii) evidence of

F. M. Talarico; R. M. McKay; R. D. Powell; S. Sandroni; T. Naish

2010-01-01

27

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.

28

Factors controlling nitrate in ice cores: Evidence from the Dome C deep ice core  

Microsoft Academic Search

In order to estimate past changes in atmospheric NOx concentration, nitrate, an oxidation product of NOx, has often been measured in polar ice cores. In the frame of the European Project for Ice Coring in Antarctica (EPICA), a high-resolution nitrate record was obtained by continuous flow analysis (CFA) of a new deep ice core drilled at Dome C. This record

Regine Röthlisberger; Manuel A. Hutterli; Stefan Sommer; Eric W. Wolff; Robert Mulvaney

2000-01-01

29

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.

Ahn, Jinho; Brook, Edward J.

2014-01-01

30

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

31

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

NASA Astrophysics Data System (ADS)

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.

Ahn, Jinho; Brook, Edward J.

2014-04-01

32

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

33

The Icelandic Laki volcanic tephra layer in the Lomonosovfonna ice core, Svalbard  

Microsoft Academic Search

The largest sulphuric acid event revealed in an ice core from the Lomono- sovfonna ice cap, Svalbard, is associated with the densest concentration of microparticles in the ice core at 66.99 m depth. Electron microscope analysis of a volcanic ash particle shows it has the same chemical compo- sition as reported for debris from the eruption of Iceland's Laki fissure

Teija Kekonen; John Moore; Paavo Perämäki; Tñnu Martma

2005-01-01

34

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

35

Biological Ice Core Analysis in Russian Altai  

NASA Astrophysics Data System (ADS)

In July 2003, a 171m long ice core was excavated from top of Belukha glacier (4,200m a. s. l.) in the Russian Altai Mountains. We examined vertical distributions of microorganisms (unicellular green algae, fungal spore, yeast) and pollens for potential use of ice core dating and reconstruction of past climate. Microorganisms have no seasonal variation in pit samples, however 5 genus of pollen (Fir, Spruce, Pine, Birch tree and Mugwort) have seasonality of each dispersed season. Therefore, this ice core can be identified past seasonal layers by pollen distribution. Pollen dating analysis of ice core estimate upper 48m ice core contain 86 years snow and ice, and this dating method well correspond to the 1963 peak in Tritium. This dating analysis is more accurate than other markers (oxygen isotope, dust, chemical concentration and melt percentage). Oxygen isotope trend from 1917 and temperature record of meteorological station near the glacier slightly increased and melt percentage have some anomalies from 1950s show recent temperature rising in this region. Otherwise, microorganisms and pollen have no trend except yeast. Vertical distribution of yeast peaks are well correspond to peaks of melt percentage show that yeast cell can grow in surface snow only in the warm period when liquid water available. In 1970s and 1980s, Nitrate increased and peaked because of anthropogenic emissions. Nitrate is major nutrient of photosynthetic microorganism, however, no clear relationship nitrate between unicellular green algae.

Uetake, J.; Nakazawa, F.; Kohshima, S.; Miyake, T.; Narita, H.; Fujita, K.; Takeuchi, N.; Nakawo, M.

2007-12-01

36

Seasonal precipitation timing and ice core records  

SciTech Connect

This is a commentary on global circulation model experiments of moisture source changes in Greenland, urging caution in how they are applied because they have important implications for paleoclimate reconstruction from ice cores. The work comes from preliminary find is of a ice core (GISP2) of the authors. The authors conclude that at present anomalies in Greenland ice core records should not be interpreted solely in terms of source region variations. The combined use of oxygen 18, D and ionic species in the new Summit, Greenland cores should make it possible to answer empirically some of the questions raised by the GCM experiments as to the interpretation of oxygen 18 records in terms of temperature. 4 refs., 1 fig.

Steig, E.J.; Grootes, P.M.; Stuiver, M. (Univ. of Washington, Seattle, WA (United States))

1994-12-16

37

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

38

Measurements of ethane in Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Ethane is one of the most abundant hydrocarbons in the atmosphere. The major ethane sources are fossil fuel production and use, biofuel combustion, and biomass-burning emissions and the primary loss pathway is via reaction with OH. A paleoatmospheric ethane record would be useful as a tracer of biomass-burning emissions, providing a constraint on past changes in atmospheric methane and methane isotopes. An independent biomass-burning tracer would improve our understanding of the relationship between biomass burning and climate. The mean annual atmospheric ethane level at high southern latitudes is about 230 parts per trillion (ppt), and Antarctic firn air measurements suggest that atmospheric ethane levels in the early 20th century were considerably lower (Aydin et al., 2011). In this study, we present preliminary measurements of ethane (C2H6) in Antarctic ice core samples with gas ages ranging from 0-1900 C.E. Samples were obtained from dry-drilled ice cores from South Pole and Vostok in East Antarctica, and from the West Antarctic Ice Sheet Divide (WAIS-D). Gases were extracted from the ice by melting under vacuum in a glass vessel sealed by indium wire and were analyzed using high resolution GC/MS with isotope dilution. Ethane levels measured in ice core samples were in the range 100-220 ppt, with a mean of 157 ± 45 ppt (n=12). System blanks contribute roughly half the amount of ethane extracted from a 300 g ice core sample. These preliminary data exhibit a temporal trend, with higher ethane levels from 0-900 C.E., followed by a decline, reaching a minimum between 1600-1700 C.E. These trends are consistent with variations in ice core methane isotopes and carbon monoxide isotopes (Ferretti et al., 2005, Wang et al., 2010), which indicate changes in biomass burning emissions over this time period. These preliminary data suggest that Antarctic ice core bubbles contain paleoatmospheric ethane levels. With further improvement of laboratory techniques it appears likely that a paleoatmospheric ethane record can be obtained from polar ice cores.

Verhulst, K. R.; Fosse, E. K.; Aydin, K. M.; Saltzman, E. S.

2011-12-01

39

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

PubMed

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 20(th) 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 19(th) 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 21(st) century. PMID:25068819

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

2014-01-01

40

Scientific Plan for Deep Ice Core Drilling in Central Greenland (GISP 2 - Greenland Ice Sheet Project).  

National Technical Information Service (NTIS)

Ice sheets are natural archival systems that continuously collect and preserve the physical and chemical history of the Earth's atmosphere. Ice cores drilled from the ice sheets offer a practical way to study the layers of ice. Deep ice cores have been dr...

E. Mosley-Thompson A. J. Gow M. M. Herron K. Jezek B. Kamb

1985-01-01

41

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.

Center, National C.; Noaa

42

The methanesulfonic acid (MSA) record in a Svalbard ice core  

Microsoft Academic Search

Svalbard ice cores have not yet been fully exploited for studies of climate and environmental conditions. In one recently drilled ice core from Lomonosovfonna, we have studied the methanesulfonic acid (MSA) records in relation to temperature and sea ice. Under the present climatic conditions, MSA appears to be negatively correlated with the sea-ice conditions in the Barents Sea, and positively

Elisabeth Isaksson; Teija Kekonen; John Moore; Robert Mulvaney

2005-01-01

43

Isotope thermometry in melt-affected ice cores  

Microsoft Academic Search

Summertime melt at ice core sites can lead to enrichment of isotopic valuesIsotopic enrichment results in overestimation of ice core-derived temperaturesCorrection of isotopic enrichment improves temperature estimates

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

2011-01-01

44

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

45

Tropical ice core records: evidence for asynchronous glaciation on Milankovitch  

Microsoft Academic Search

Over the last 28 years ice core records have been systematically recovered from ten high-elevation ice fields, nine of which are located in the low latitudes. Each core has provided new information about the regional climate and environmental change, and together their records challenge existing paradigms about the Earth's climate system. When viewed collectively, these ice core histories provide compelling

LONNIE G. THOMPSON; MARY E. DAVIS; ELLEN MOSLEY-THOMPSON; PING-NAN LIN; KEITH A. HENDERSON

46

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

47

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

48

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

Microsoft Academic Search

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

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

2007-01-01

49

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

Microsoft Academic Search

(1) 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

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

2007-01-01

50

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.

51

Ice Core Recorded Climate changes on the Tibetan Plateau in the past 2000 years  

NASA Astrophysics Data System (ADS)

Climate history on the Tibetan Plateau in the past 2000 years has been profusely studied using various proxies. Ice cores have been drilled on the Plateau since last century, with four cores systematically studied and widely reported as the Dasuopu (in Xixabangma on south Plateau), Guliya (in the west Kunlun Mt. on northwest Plateau), Puruogangri (in central Plateau), and Dunde (in Mt Qilian on north Plateau) ice cores. Different geographical locations of those four ice cores give rise to distinct climate histories, with the Dasuopu ice core representing variance of the Indian monsoon influence, the Guliya and Dunde ice cores representing that of the westerlies, and the Puruogangri ice core representing the interaction of both large-scale circulation systems. Despite different dominative circulation processes, study of modern delta-18O in precipitation suggests a positive correlation between delta-18O and temperature, thus confirming the representativeness of long-term delta-18O in ice cores of paleo-temperature. Each ice core record represents regional temperature variation, while comparison of those records highlight the synchronicity of significant climate events in the past 2000 years, including the Medieval Warm Period, Little Ice Age, and the 20th century warming. Besides, solar isolation is shown as the dominant factor over temperature changes on the Plateau, while variation of ENSO bears significantly on precipitation and snow accumulation on Tibetan glaciers. Recent studies of newly drilled ice cores in southeast Plateau reveals close relationship of temperature with bacteria variability, implying potential effect of global warming on bacteria activity. They also demonstrate significant effect of black carbon on glacial melting, suggesting increased influence of human activities on the southeast Plateau. With the widely distributed ice cores acquired, a composite of ice core records on the Plateau is in urgent need to demonstrate climate variation for the Tibetan Plateau in the past 2000 years, as it will help us better fathom with current climate changes and forecast future effect of climate change in this ecologically fragile region.

Yao, T.; Yao Tandong

2011-12-01

52

Methane - The record in polar ice cores  

Microsoft Academic Search

The results of examination of gas samples extracted from the Dye 3 Greenland ice core have demonstrated that atmospheric CH4 concentrations were much lower than at present 30,000 yr ago, and that a 50% increase in the atmospheric CH4 concentration has occurred during the 15-19th centuries. Gas chromatographic techniques were employed to examine the samples, which were studied at 16

H. Craig; C. C. Chou

1982-01-01

53

Is a periglacial biota responsible for enhanced dielectric response in basal ice from the Greenland Ice Core Project ice core?  

NASA Astrophysics Data System (ADS)

A detailed dielectric profiling (DEP) conductivity profile (??) measured in the 6 m of the basal silty ice sequence from the Greenland Ice Core Project (GRIP) ice core (Summit, Central Greenland) is presented and compared to previous multi-parametric studies. DEP conductivities span the whole glacial-interglacial range observed higher up in the GRIP core (9-25 ?S m-1). Values in the bottom meter of the sequence reach the level of some of the highest peaks from Holocene volcanic layers in the core (33 ?S m-1). On a steady increase of the ?? values down the sequence are superimposed large fluctuations "inphase" with other variables measured in the core such as ?18O, debris content, or gas compositions in CO2 and CH4. Analysis of the type and strength of intercorrelations shows that the controlling variable for the DEP signal must be closely related to the gas content and composition of the ice. Plausible candidates for this causality link are investigated. Enhancing of the ? conductivity by CO2 and CH4 encaged in the ice lattice as gas hydrates is ruled out since these are nonpolar clathrates of structure I, known as having negligible impact on the orientational stability of the water molecules under ac currents. NH4+ is proposed as the best candidate since it has been shown to enhance DEP conductivities by introducing Bjerrum defects in the ice lattice and since it could have been initially present partly as gaseous NH3 in the ice. This proposition is supported by the NH4+ profile in the basal ice sequence. Using calibration curves from higher up in the core, it is shown that ? is in fact fully explained by intracrystalline conductivity of pure ice solely disrupted by ammonium impurities in the ice lattice. The origin of the NH4+ signal is discussed in the light of organic acid profiles (formate, acetate, and oxalate). It appears that the most likely source is local degradation of biological residues, which supports the hypothesis that part of the basal ice was formed locally, in the absence of the present-day ice sheet.

Tison, Jean-Louis; Souchez, Roland; Wolff, Eric W.; Moore, John C.; Legrand, Michel R.; de Angelis, Martine

1998-08-01

54

New Greenland MSA and Na ice core records: reliable proxies for Arctic sea ice changes?  

NASA Astrophysics Data System (ADS)

MSA (methanesulfonic acid, derived from marine biogenic emissions) concentrations in coastal Antarctic ice cores have been suggested to record changes in sea ice extent of the previous winter over recent decades. Using post-1979 satellite-derived sea ice and meteorological data, the reliability of MSA as sea ice proxy has indeed been demonstrated in the Indian Ocean and Bellinghausen Sea sectors, but not in the Weddell Sea one. Recently, it has also been argued that the sea ice surface, not open water, is the dominant source of sea salt (including Na) over the Antarctic continent. Sea salt ice core records may thus provide an alternative to MSA for the reconstruction of past sea ice changes. Using new MSA and Na ice core records from two Greenland sites, we here investigate the potential of those two chemical species as indicators of recent sea ice changes in the Arctic sector.

Pol, Katy; Wolff, Eric; Abram, Nerilie; McConnell, Joseph R.; Mulvaney, Robert; Fleet, Louise

2013-04-01

55

A common and optimized age scale for Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Dating ice cores is a complex problem because 1) there is a age shift between the gas bubbles and the surrounding ice 2) there are many different ice cores which can be synchronized with various proxies and 3) there are many methods to date the ice and the gas bubbles, each with advantages and drawbacks. These methods fall into the following categories: 1) Ice flow (for the ice) and firn densification modelling (for the gas bubbles); 2) Comparison of ice core proxies with insolation variations (so-called orbital tuning methods); 3) Comparison of ice core proxies with other well dated archives; 4) Identification of well-dated horizons, such as tephra layers or geomagnetic anomalies. Recently, an new dating tool has been developped (DATICE, Lemieux-Dudon et al., 2010), to take into account all the different dating information into account and produce a common and optimal chronology for ice cores with estimated confidence intervals. In this talk we will review the different dating information for Antarctic ice cores and show how the DATICE tool can be applied.

Parrenin, F.; Veres, D.; Landais, A.; Bazin, L.; Lemieux-Dudon, B.; Toye Mahamadou Kele, H.; Wolff, E.; Martinerie, P.

2012-04-01

56

Devon island ice cap: core stratigraphy and paleoclimate.  

PubMed

Valuable paleoclimatic information can be gained by studying the distribution of melt layers in deep ice cores. A profile representing the percentage of ice in melt layers in a core drilled from the Devon Island ice cap plotted against both time and depth shows that the ice cap has experienced a period of very warm summers since 1925, following a period of colder summers between about 1600 and 1925. The earlier period was coldest between 1680 and 1730. There is a high correlation between the melt-layer ice percentage and the mass balance of the ice cap. The relation between them suggests that the ice cap mass balance was zero (accumulation equaled ablation) during the colder period but is negative in the present warmer one. There is no firm evidence of a present cooling trend in the summer conditions on the ice cap. A comparison with the melt-layer ice percentage in cores from the other major Canadian Arctic ice caps shows that the variation of summer conditions found for the Devon Island ice cap is representative for all the large ice caps for about 90 percent of the time. There is also a good correlation between melt-layer percentage and summer sea-ice conditions in the archipelago. This suggests that the search for the northwest passage was influenced by changing climate, with the 19th-century peak of the often tragic exploration coinciding with a period of very cold summers. PMID:17733504

Koerner, R M

1977-04-01

57

ENSO Events Recorded in the Guliya Ice Core  

Microsoft Academic Search

Based on the ENSO chronology and climatic information recovered from the Guliya ice core in the Tibetan Plateau, China, the ENSO teleconnection was investigated. The results showed that the negative precipitation anomalies are significantly associated with El Niño years but poorly with negative anomaly of d 18O. Thus, the ice core records can be used as an archive of extremely

Meixue Yang; Tandong Yao; Yuanqing He; L. G. Thompson

2000-01-01

58

Ion fractionation and percolation in ice cores with seasonal melting  

Microsoft Academic Search

We examine the impact that post- depositional change has on ion concentrations in ice cores that suffer limited seasonal melting. We show that the impact in the case of at least one Svalbard ice core is limited to decreasing resolution of signals to about 3 years - a similar accuracy as the best dating can usually provide. We model various

John C. Moore; Aslak Grinsted

59

Glaciochemical records from Naimona’Nyi ice core in the Himalayas  

Microsoft Academic Search

A 6-m ice core was recovered in 2004 from the Naimona’Nyi Glacier, the middle Himalayas. Empirical orthogonal function (EOF)\\u000a analysis on the major ion reveals that EOF1 represents the variations of majority of ions which may be originated from crustal\\u000a aerosols. Comparing the calcium concentrations from the Naimona’Nyi with these from Dasuopu, East Rongbuk and Guliya ice cores,\\u000a it is

Yongqin Liu; Tandong Yao; Lide Tian; Baiqin Xu; Guangjian Wu

2006-01-01

60

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

Microsoft Academic Search

Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai-Tibetan Plateau of China provide a detailed record of Holocene and Wisconsin-Wurm late glacial stage (LGS) climate changes in the subtropics. The records reveal that LGS conditions were apparently colder, wetter, and dustier than Holocene conditions. The LGS part of the cores is characterized by more negative

L. G. Thompson; E. Mosley-Thompson; M. E. Davis; J. F. Bolzan; J. Dai; T. Yao; N. Gundestrup; X. Wu; L. Klein; Z. Xie

1989-01-01

61

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

62

Ice-core record of atmospheric methane over the past 160,000 years  

Microsoft Academic Search

Methane measurements along the Vostok ice core are reported which reveal strong variations of past CH4 concentrations in the 350-650 ppbv range, well below the present atmospheric conditions. These variations are well-correlated with climate change deduced from the isotopic composition of the Vostok ice core. Spectral analysis of the record indicates periodicities close to those of orbital variations. These CH4

J. Chappellaz; J. M. Barnola; D. Raynaud; C. Lorius; Y. S. Korotkevich

1990-01-01

63

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

64

Challenging an ice-core paleothermometer  

SciTech Connect

The temperature-depth profile near Earth`s surface has long been recognized as an inventory of environmental history. In 1864 for example, Lord Kelvin used such a profile to argue that the age of Earth`s crust since a presumed molten {open_quotes}birth{close_quotes} was inconsistent with prevailing notions of geologic time. (1) Kelvin`s age estimate turned out to be low because it did not account for radio-active heating within rocks and mantle connection which were discovered after the time of Kelvin`s analysis. Nevertheless, an important lesson is appreciated from Kelvin`s work (2): Environmental history (such as annual average surface air temperature) produces a unique effect on near-surface Earth temperatures. This article discusses the possible inaccuracy of previous deductions of surface temperature history from ice-core oxygen-isotope stratigraphy. The analysis and solution to the paleothermometry problem is presented. 9 refs., 1 fig.

MacAyeal, D. [Univ. of Chicago, IL (United States)

1995-10-20

65

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

66

1500-year record of tropical precipitation in ice cores from the Quelccaya ice cap, Peru  

Microsoft Academic Search

Two ice cores, covering 1500 years of climatic information, from the summit (5670 meters) of the tropical Quelccaya ice cap, in the Andes of southern Peru, provide information on general environmental conditions including droughts, volcanic activity, moisture sources, temperature, and glacier net balance. The net balance record reconstructed from these cores reflects major precipitation trends for the southern Andes of

L. G. Thompson; E. Mosley-Thompson; J. F. Bolzan; B. R. Koci

1985-01-01

67

Continuous flow analysis of labile iron in ice-cores.  

PubMed

The important active and passive role of mineral dust aerosol in the climate and the global carbon cycle over the last glacial/interglacial cycles has been recognized. However, little data on the most important aeolian dust-derived biological micronutrient, iron (Fe), has so far been available from ice-cores from Greenland or Antarctica. Furthermore, Fe deposition reconstructions derived from the palaeoproxies particulate dust and calcium differ significantly from the Fe flux data available. The ability to measure high temporal resolution Fe data in polar ice-cores is crucial for the study of the timing and magnitude of relationships between geochemical events and biological responses in the open ocean. This work adapts an existing flow injection analysis (FIA) methodology for low-level trace Fe determinations with an existing glaciochemical analysis system, continuous flow analysis (CFA) of ice-cores. Fe-induced oxidation of N,N'-dimethyl-p-pheylenediamine (DPD) is used to quantify the biologically more important and easily leachable Fe fraction released in a controlled digestion step at pH ~1.0. The developed method was successfully applied to the determination of labile Fe in ice-core samples collected from the Antarctic Byrd ice-core and the Greenland Ice-Core Project (GRIP) ice-core. PMID:23594184

Hiscock, William T; Fischer, Hubertus; Bigler, Matthias; Gfeller, Gideon; Leuenberger, Daiana; Mini, Olivia

2013-05-01

68

AVHRR imagery reveals Antarctic ice dynamics  

NASA Technical Reports Server (NTRS)

A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf.

Bindschadler, Robert A.; Vornberger, Patricia L.

1990-01-01

69

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

70

Where to find 1.5 million yr old ice for the IPICS "Oldest Ice" ice core  

NASA Astrophysics Data System (ADS)

The recovery of a 1.5 Myr long ice core from Antarctica represents a keystone to our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we show that such old ice is most likely to exist in the plateau area of the East Antarctic Ice Sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions 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, we strongly argue for significantly reduced ice thickness to avoid bottom melting, while at the same time maximizing the resolution and the distance of such old ice to the bedrock. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than 2500 m would be required to find 1.5 Myr old ice. However, the final choice is strongly dependent on the local geothermal heat flux, which is largely unknown for the EAIS and has to be determined beforehand. In addition, the detailed bedrock topography and ice flow history for candidates of an Oldest Ice ice coring site has to be reconstructed. Finally, we argue strongly for rapid access drilling before any full deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Fischer, H.; Severinghaus, J.; Brook, E.; Wolff, E.; Albert, M.; Alemany, O.; Arthern, R.; Bentley, C.; Blankenship, D.; Chappellaz, J.; Creyts, T.; Dahl-Jensen, D.; Dinn, M.; Frezzotti, M.; Fujita, S.; Gallee, H.; Hindmarsh, R.; Hudspeth, D.; Jugie, G.; Kawamura, K.; Lipenkov, V.; Miller, H.; Mulvaney, R.; Pattyn, F.; Ritz, C.; Schwander, J.; Steinhage, D.; van Ommen, T.; Wilhelms, F.

2013-05-01

71

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

72

A tentative chronology for the EPICA Dome Concordia ice core  

Microsoft Academic Search

A tentative age scale (EDC1) for the last 45 kyr is established for the new 788-m EPICA Dome C ice core using a simple ice flow model. The age of volcanic eruptions, the end of the Younger Dryas event, and the estimated depth and age of elevated 10Be, about 41 kyr ago were used to calibrate the model parameters. The

Jakob Schwander; Jean Jouzel; Claus U. Hammer; Jean-Robert Petit; Roberto Udisti; Eric Wolff

2001-01-01

73

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

74

Quantification of Dead-ice Melting in Ice-Cored Moraines at the High-Arctic Glacier Holmströmbreen, Svalbard  

NASA Astrophysics Data System (ADS)

An extensive dead-ice area has developed at the stagnant snout of the Holmströmbreen glacier on Svalbard following its Little Ice Age maximum. Dead-ice appears mainly as ice-cored moraines, ice-cored eskers and ice- cored kames. The most common dead-ice landform is sediment gravity flows on ice-cored slopes surrounding a large ice-walled, moraine-dammed lake. The lake finally receives the sediment from the resedimentation processes. Dead-ice melting is described and quantified through field studies and analyses of high-resolution, multi-temporal aerial photographs and satellite imagery. Field measurements of backwasting of ice-cored slopes indicate short-term melting rates of c. 9.2 cm/day. Long-term downwasting rates indicate a surface lowering of ice-cored moraines of c. 0.9 m/yr from 1984-2004. Different measures for dead-ice melting are assessed in relation to the temperature record from Svalbard since the termination of the Little Ice Age. The most prominent impact of dead-ice melting is the evolution of the ice-walled lake with an area increasing near-exponentially over the last 40 years. As long as backwasting and mass movement processes prevent build-up of an insulating debris-cover and expose ice-cores to melting, the de-icing continues even though the area is characterized by continuous permafrost.

Schomacker, A.; Kjaer, K. H.

2007-12-01

75

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

76

Ice core drilling at McMurdo Dome  

NSF Publications Database

Title : Ice core drilling at McMurdo Dome Type : Antarctic EAM NSF Org: OD / OPP Date : July 28, 1993 File : opp93111 NATIONAL SCIENCE FOUNDATION OFFICE OF POLAR PROGRAMS OFFICE OF THE ENVIRONMENT 202/357-7766 MEMORANDUM Date: July 28, 1993 From: Acting Environmental Officer Subject: Initial Environmental Evaluation (Ice Core Drilling at McMurdo Dome, Antarctica Environmental Impact Assessment and Finding) To: Office Director, Polar Programs Manager, Polar Operations Health and Safety Officer...

77

Uncertainties in climate reconstructions from ice core isotopic data  

NASA Astrophysics Data System (ADS)

Ice cores provide information on temporal variability in stable water isotopes, and often the goal is to utilize these isotopes to reconstruct climate variability over a larger region. However, it is important to quantify the uncertainties associated with the assumption that a given ice core is representative of that larger region. Stacking multiple ice core records can help minimize the uncertainties, but how many cores are necessary? A suite of fifteen firn cores were drilled within a 17,389 km^2 area in the central West Antarctic Ice Sheet, and analyzed for ?18O and ?D. Here, we assess how many cores are actually necessary to confidently represent the region of interest, assuming the full stack of all fifteen cores is representative of the regional average isotopic variability. We statistically compare records of varying numbers of cores to the stacked record of all cores, removing two cores step-wise from the isotopic stack. As might be expected, a greater number of cores included in the stacked record yield a tighter spread in correlation coefficients with the full stacked record. However, lower numbers of cores included in the stacked average, while they have a larger spread in correlation coefficients, contain many combinations of cores with extremely high correlations with the full stack. Indeed, as few as four stacked cores can correlate as highly with the stack of fifteen cores as combinations of ten to twelve cores. Surprisingly, the spatial distribution of the chosen cores to include in the stacked average is not necessarily a good predictor for how well they will correlate with the regional average. One goal of this study is to determine the minimum number of cores necessary to capture the regional average isotopic variability, and a method for selecting the optimal sites to drill the cores. The results of this study will also be used to quantify the uncertainties associated with climate reconstructions from isotopic data. In addition, we will test the methods developed here with suites of ice cores from other regions to determine how applicable the methods are for other areas of the Antarctic Ice Sheet.

Meadows, M. K.; Rupper, S.; Williams, J.; Carpenter, M.

2013-12-01

78

On the gas-ice depth difference (?depth) along the EPICA Dome C ice core  

NASA Astrophysics Data System (ADS)

We compare a variety of methods for estimating the gas/ice depth offset (?depth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, ?depth can be estimated combining a firn densification with an ice flow model. Observations allow direct and indirect estimate of ?depth. (2) The diffusive column height can be estimated from ?15N and converted to ?depth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The bipolar seesaw antiphase relationship is generally supported by the ice-gas cross synchronisation between EDC and the GRIP, EDML and TALDICE ice cores, which provide support for method 4. Applying the bipolar seesaw hypothesis to the deeper section of the EDC core confirms that the ice flow is complex and can help improving our reconstruction of the thinning function and thus of the EDC age scale. We confirm that method 1 overestimates the glacial ?depth at EDC and we suggested that it is due to an overestimation of the glacial Close Off Depth by the firn densification model. In contrast we find that the glaciological models probably underestimate the ?depth during termination II. Finally, we show that method 2 based on 15N data produces for the last deglaciation a ?depth estimate which is in good agreement with methods 3 and 4.

Parrenin, F.; Barker, S.; Blunier, T.; Chappellaz, J.; Jouzel, J.; Landais, A.; Masson-Delmotte, V.; Schwander, J.; Veres, D.

2012-04-01

79

Chemical signals of past climate and environment from polar ice cores and firn air.  

PubMed

Chemical and isotopic records obtained from polar ice cores have provided some of the most iconic datasets in Earth system science. Here, I discuss how the different records are formed in the ice sheets, emphasising in particular the contrast between chemistry held in the snow/ice phase, and that which is trapped in air bubbles. Air diffusing slowly through the upper firn layers of the ice sheet can also be sampled in large volumes to give more recent historical information on atmospheric composition. The chemical and geophysical issues that have to be solved to interpret ice core data in terms of atmospheric composition and emission changes are also highlighted. Ice cores and firn air have provided particularly strong evidence about recent changes (last few decades to centuries), including otherwise inaccessible data on increases in compounds that are active as greenhouse gases or as agents of stratospheric depletion. On longer timescales (up to 800,000 years in Antarctica), ice cores reveal major changes in biogeochemical cycling, which acted as feedbacks on the very major changes in climate between glacial and interglacial periods. PMID:22930179

Wolff, Eric W

2012-10-01

80

Is sea salt in ice cores a proxy of past sea ice extent?  

NASA Astrophysics Data System (ADS)

A number of marine, coastal and ice core proxies have been used to try to assess the past extent of sea ice. Sea salt has been proposed as a proxy for past ice extent, at least in the Southern Ocean. The idea is that the sea ice surface itself holds a source of sea salt, that is stronger than the source from the open ocean it replaces. That a sea ice source exists is apparent from observations of the ratio of sulphate to sodium in coastal aerosol and snow samples. While the idea behind using sea salt as a proxy is attractive, and leads to sensible inferences, many doubts remain. Firstly the exact nature of the source remains uncertain, and secondly it is not clear if ice extent, as opposed to changes in atmospheric transport and lifetime, would dominate variability in the ice core record of sea salt. Here we use a model of atmospheric transport and chemistry (p-TOMCAT) to assess the consequences of a sea ice source, focussing particularly on a source that has been proposed to arise from the sublimation of salty blowing snow. We will briefly report some new observations from a winter cruise, that will allow us to comment on the likelihood that blowing snow does pose a significant source. We will then present results from the model (implemented using existing parameters). The model has been run with seasonally and interannually varying sea ice extent and meteorology for the Antarctic, tracking, at different ice core sites, the concentration that arises from the open ocean and sea ice sources. We have already shown that the model, after tuning, is able to reproduce the magnitude and seasonal cycle of sea salt at a range of sites globally. By varying each component separately we explore which factors (sea ice presence, wind speed at source, transporting winds) and which source regions control the delivery of sea salt to sites in Antarctica. Such work suggests that sea salt cannot be used as a sea ice proxy on interannual timescales, but may be suitable on longer timescales. By employing much larger sea ice extents, such as at the last glacial maximum (LGM), we find a strong increase in concentration at ice core sites when ice extent increases. The increase in modelled sea salt concentration tails off sharply as ice approaches the LGM extent, so that the sensitivity of the proxy is greater at lower ice extents, for example in interglacials. We will discuss the implications of this work for the proposed use of sea salt as a sea ice proxy.

Levine, James; Wolff, Eric; Frey, Markus; Jenkins, Hazel; Jones, Anna; Yang, Xin

2014-05-01

81

Discoveries Within the Ice: Plans of the Ice Coring and Drilling Science Community  

NASA Astrophysics Data System (ADS)

The search for answers to questions about our changing climate creates an urgent need to discover the clues to the past 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 availability of appropriate drills, drilling expertise, and innovations in drilling technology, the Ice Drilling Program Office (IDPO) and its partner, the Ice Drilling Design and Operations group (IDDO), collectively known as IDPO/IDDO, work with the science community to articulate integrated research, technological planning and delivery. This presentation highlights science goals articulated in the IDPO Long Range Science Plan, which lays out the scientific goals and future directions of the multidisciplinary research community and international partners. The science fits into four broad categories: Climate; Ice Dynamics and History; the Sub-ice Environment; and Ice as a Scientific Observatory. A companion plan, the IDDO Long Range Drilling Technology Plan, discusses details of the drills and new development driven by the Long Range Science Plan. The ice drilling technology described in the Long Range Drilling Technology Plan spans from the use of the multi-ton Deep Ice Sheet Coring (DISC) drill for deep drilling projects such as the West Antarctic Ice Sheet Divide, in Antarctica, to shallow drilling endeavors using hand augers, and beyond to identification of new drilling tools not yet in existence.

Albert, M. R.; Bentley, C. R.; Twickler, M.; Idpo/Iddo

2010-12-01

82

Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core  

NASA Astrophysics Data System (ADS)

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position 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, we strongly suggest significantly reduced ice thickness to avoid bottom melting. 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 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Fischer, H.; Severinghaus, J.; Brook, E.; Wolff, E.; Albert, M.; Alemany, O.; Arthern, R.; Bentley, C.; Blankenship, D.; Chappellaz, J.; Creyts, T.; Dahl-Jensen, D.; Dinn, M.; Frezzotti, M.; Fujita, S.; Gallee, H.; Hindmarsh, R.; Hudspeth, D.; Jugie, G.; Kawamura, K.; Lipenkov, V.; Miller, H.; Mulvaney, R.; Parrenin, F.; Pattyn, F.; Ritz, C.; Schwander, J.; Steinhage, D.; van Ommen, T.; Wilhelms, F.

2013-11-01

83

Spatial and Temporal Characteristics of the Little Ice Age: The Antarctic Ice Core Record.  

National Technical Information Service (NTIS)

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 tem...

E. Mosley-Thompson L. G. Thompson

1992-01-01

84

Bayesian Glaciological Modelling to quantify uncertainties in ice core chronologies  

NASA Astrophysics Data System (ADS)

Valuable information about the environment and climate of the past is preserved in ice cores which are drilled through ice sheets in polar and alpine regions. A pivotal part of interpreting the information held within the cores is to build ice core chronologies i.e. to relate time to depth. Existing dating methods can be categorised as follows: (1) layer counting using the seasonality in signals, (2) glaciological modelling describing processes such as snow accumulation and plastic deformation of ice, (3) comparison with other dated records, or (4) any combination of these. Conventionally, implementation of these approaches does not use statistical methods. In order to quantify dating uncertainties, in this paper we develop the approach of category (2) further. First, the sources of uncertainty involved in glaciological models are formalised. Feeding these into a statistical framework, that we call Bayesian Glaciological Modelling (BGM), allows us to demonstrate the effect that uncertainty in the glaciological model has on the chronology. BGM may also include additional information to constrain the resulting chronology, for example from layer counting or other dated records such as traces from volcanic eruptions. Our case study involves applying BGM to date an Antarctic ice core (a Dyer plateau core). Working through this example allows us to emphasise the importance of properly assessing uncertain elements in order to arrive at accurate chronologies, including valid dating uncertainties. Valid dating uncertainties, in turn, facilitate the interpretation of environmental and climatic conditions at the location of the ice core as well as the comparison and development of ice core chronologies from different locations.

Klauenberg, Katy; Blackwell, Paul G.; Buck, Caitlin E.; Mulvaney, Robert; Röthlisberger, Regine; Wolff, Eric W.

2011-10-01

85

Rapid changes in ice core gas records - Part 1: On the accuracy of methane synchronisation of ice cores  

NASA Astrophysics Data System (ADS)

Methane synchronisation is a concept to align ice core records during rapid climate changes of the Dansgaard/Oeschger (D/O) events onto a common age scale. However, atmospheric gases are recorded in ice cores with a log-normal-shaped age distribution probability density function, whose exact shape depends mainly on the accumulation rate on the drilling site. This age distribution effectively shifts the mid-transition points of rapid changes in CH4 measured in situ in ice by about 58% of the width of the age distribution with respect to the atmospheric signal. A minimum dating uncertainty, or artefact, in the CH4 synchronisation is therefore embedded in the concept itself, which was not accounted for in previous error estimates. This synchronisation artefact between Greenland and Antarctic ice cores is for GRIP and Byrd less than 40 years, well within the dating uncertainty of CH4, and therefore does not calls the overall concept of the bipolar seesaw into question. However, if the EPICA Dome C ice core is aligned via CH4 to NGRIP this synchronisation artefact is in the most recent unified ice core age scale (Lemieux-Dudon et al., 2010) for LGM climate conditions of the order of three centuries and might need consideration in future gas chronologies.

Köhler, P.

2010-08-01

86

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

87

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

88

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

89

Climate instability during the last interglacial period recorded in the GRIP ice core  

Microsoft Academic Search

Isotope and chemical analyses of the GRIP ice core from Summit, central Greenland, reveal that climate in Greenland during the last interglacial period was characterized by a series of severe cold periods, which began extremely rapidly and lasted from decades to centuries. As the last interglacial seems to have been slightly warmer than the present one, its unstable climate raises

J. M. Barnola; J. Beer; T. Blunier; J. Chappellaz; H. B. Clausen; D. Dahl-Jensen; W. Dansgaard; M. de Angelis; R. J. Delmas

1993-01-01

90

Instruments and Methods Towards radiocarbon dating of ice cores  

Microsoft Academic Search

A recently developed dating method for glacier ice, based on the analysis of radiocarbon in carbonaceous aerosol particles, is thoroughly investigated. We discuss the potential of this method to achieve a reliable dating using examples from a mid- and a low-latitude ice core. Two series of samples from Colle Gnifetti (4450 m a.s.l., Swiss Alps) and Nevado Illimani (6300 m

M. SIGL; T. M. JENK; T. KELLERHALS; S. SZIDAT; H. W. GAGGELER

2009-01-01

91

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

92

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.

Joyce, Christopher

93

Interpolation methods for Antarctic ice-core timescales: application to Byrd, Siple Dome and Law Dome ice cores  

NASA Astrophysics Data System (ADS)

Antarctic ice cores have often been dated by matching distinctive features of atmospheric methane to those detected in annually dated ice cores from Greenland. Establishing the timescale between these tie-point ages requires interpolation. While the uncertainty at tie points is relatively well described, uncertainty of the interpolation is not. Here we assess the accuracy of three interpolation schemes using data from the WAIS Divide ice core in West Antarctica; we compare the interpolation methods with the annually resolved timescale for the past 30 kyr. Linear interpolation yields large age errors (up to 380 years) between tie points, abrupt changes in duration of climate events at tie points, and an age bias. Interpolations based on the smoothest accumulation rate (ACCUM) or the smoothest annual-layer thickness (ALT) yield timescales that more closely agree with the annually resolved timescale and do not have abrupt changes in duration at tie points. We use ALT to assess the uncertainty in existing timescales for the past 30 kyr from Byrd, Siple Dome, and Law Dome. These ice-core timescales were developed with methods similar to linear interpolation. Maximum age differences exceed 1000 years for Byrd and Siple Dome, and 500 years for Law Dome. For the glacial-interglacial transition (21 to 12 kyr), the existing timescales are, on average, older than ALT by 40 years for Byrd, 240 years for Siple Dome, and 150 years for Law Dome. Because interpolation uncertainty is often not considered, age uncertainties for ice-core records are often underestimated.

Fudge, T. J.; Waddington, E. D.; Conway, H.; Lundin, J. M. D.; Taylor, K.

2014-06-01

94

Interpolation methods for Antarctic ice-core timescales: application to Byrd, Siple Dome and Law Dome ice cores  

NASA Astrophysics Data System (ADS)

Antarctic ice cores have often been dated by matching distinctive features of atmospheric methane to those detected in annually dated ice cores from Greenland. Establishing the timescale between these tie-point ages requires interpolation. While the uncertainty at tie points is relatively well described, uncertainty of the interpolation is not. Here we assess the accuracy of three interpolation schemes using data from the WAIS Divide ice core in West Antarctica; we compare the interpolation methods with the annually resolved timescale for the past 30 kyr. Linear interpolation yields large age errors (up to 380 yr) between tie points, abrupt changes in duration at tie points, and an age bias. Interpolation based on the smoothest accumulation rate (ACCUM) or the smoothest annual-layer thickness (ALT) yield timescales that more closely agree with the annually resolved timescale and do not have abrupt changes in duration at the tie points. We use ALT to assess the uncertainty in existing timescales for the past 30 kyr from Byrd, Siple Dome, and Law Dome. These ice-core timescales were developed with methods similar to linear interpolation. Maximum age differences exceed 1000 yr for Byrd and Siple Dome, and 500 yr for Law Dome. For the glacial-interglacial transition (21 to 12 kyr), the existing timescales are, on average, older than ALT by 40 yr for Byrd, 240 yr for Siple Dome, and 150 yr for Law Dome. Because interpolation uncertainty is often not considered, age uncertainties for ice-core records are often underestimated.

Fudge, T. J.; Waddington, E. D.; Conway, H.; Lundin, J. M. D.; Taylor, K.

2014-01-01

95

A 275 year ice-core record from Akademii Nauk ice cap, Severnaya Zemlya, Russian Arctic  

Microsoft Academic Search

Between 1999 and 2001, a 724 m long ice core was drilled on Akademii Nauk, the largest glacier on Severnaya Zemlya, Russian Arctic. The drilling site is located near the summit. The core is characterized by high melt-layer content. The melt layers are caused by melting and even by rain during the summer. We present high-resolution data of density, electrical

Diedrich Fritzsche; Rainer Schütt; Hanno Meyer; Heinz Miller; Frank Wilhelms; Thomas Opel; Lev M. Savatyugin

2005-01-01

96

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

97

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

98

High-resolution radar mapping of internal layers at the North Greenland Ice Core Project  

NASA Astrophysics Data System (ADS)

Existing accumulation maps with reported errors of about 20% are determined from sparsely distributed ice cores and pits. A more accurate accumulation rate might be obtained by generating continuous profiles of dated layers from high-resolution radar mapping of near-surface internal layers in the ice sheet (isochrones). To generate such profiles we designed and developed an ultrawideband radar for high-resolution mapping of internal layers in the top 200 m of ice and tested it at the North Greenland Ice Core Project drill site. Reflection profiles of 2- and 10-km length reveal horizons that we correlate with electrical conductivity measurement (ECM) recordings. Our results show that the radar-determined depth of internal layers is within ±2 m of that in an ice core collected at a nearby location. Preliminary frequency analyses of layer reflections reveal that the reflections are strongest at the 500-1000 MHz frequency range. Long-term accumulation rate computed from radar data is within 5% of that obtained from snow pits.

Kanagaratnam, P.; Gogineni, S. P.; Gundestrup, Niels; Larsen, Lars

2001-12-01

99

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

100

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

101

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

102

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

103

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

104

Continuous analysis of phosphate in a Greenland shallow ice core  

Microsoft Academic Search

Phosphate is an important and sometimes limiting nutrient for primary production in the oceans. Because of deforestation and the use of phosphate as a fertilizer changes in the phosphate cycle have occurred over the last centuries. On longer time scales, sea level changes are thought to have also caused changes in the phosphate cycle. Analyzing phosphate concentrations in ice cores

Helle Astrid Kjær; Anders Svensson; Matthias Bigler; Paul Vallelonga; Ernesto Kettner; Dorthe Dahl-Jensen

2010-01-01

105

Antarctic temperatures over the past two centuries from ice cores  

Microsoft Academic Search

We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high-resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti-phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental

David P. Schneider; Eric J. Steig; Tas D. van Ommen; Daniel A. Dixon; Paul A. Mayewski; Julie M. Jones; Cecilia M. Bitz

2006-01-01

106

Antarctic Temperatures Over the Past Two Centuries from Ice Cores  

Microsoft Academic Search

We present a reconstruction of Antarctic mean surface temperatures over the past two centuries based on water stable isotope records from high-resolution, precisely dated ice cores. Both instrumental and reconstructed temperatures indicate large interannual to decadal scale variability, with the dominant pattern being anti-phase anomalies between the main Antarctic continent and the Antarctic Peninsula region. Comparative analysis of the instrumental

David P. Schneider; Eric J. Steig; Tas D. van Ommen; Daniel A. Dixon; Paul Andrew Mayewski; Julie M. Jones; Cecilia M. Bitz

2006-01-01

107

An Automated Method for Annual Layer Counting in Ice Cores  

NASA Astrophysics Data System (ADS)

The Greenland ice cores provide a wealth of data on past changes in climate, and have - compared to most other paleoclimatic archives - the potential to be dated very accurately by annual layer counting. An effort of manually doing annual layer counting using multiple chemical components has resulted in the Greenland Ice Core Chronology (GICC05), common to several Greenland deep ice cores. The oldest part of the chronology is based on data from the NGRIP ice core, which has a particularly fine yearly data resolution with depth. However, due to the increased thinning of annual layers with depth, the annual layers in most components are no longer recognizable in the ice core for depths below 2430m, corresponding to an age of 60 ka. At this depth, only the annual layering in the visual stratigraphy is still intact, but due to a high noise-level in these data, it is difficult manually to do annual layer counting only using this data record. In this study, an automated method has been developed, which takes into account the underlying statistical properties of the visual stratigraphy data sequence, and hereby is able to detect layers otherwise unrecovered. The data sequence is modeled using a Hidden Markov Model (HMM), with algorithms otherwise mainly applied to speech recognition. Preliminary studies are promising, and even crude implementations of the method agree to within 90% of the GICC05 counting. Due to more noise in the visual stratigraphy data during warm periods, the method is likely to give better results in cold periods than during warm. However, as the annual layers are thicker during warm periods, it seems to be possible to use other parameters than the visual stratigraphy for counting annual layers during these. Using the combined data, it should therefore be possible to develop a high-resolution timescale for the NGRIP ice core extending back to at least 90 ka. In the future, a similar approach might be used for a general multi-parameter annual layer counting of ice cores and other paleoclimatic records which display annual layering.

Winstrup, M.; Svensson, A.

2010-12-01

108

Environmental signals in a highly resolved ice core from James Ross Island, Antarctica  

Microsoft Academic Search

Assessing the environmental signals in the James Ross Island ice coreExamining accumulation, isotopic and chemical signals in the ice coreThis research is a foundation for interpreting the Holocene palaeoclimate record

Nerilie J. Abram; Robert Mulvaney; Carol Arrowsmith

2011-01-01

109

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

110

Holocene-Late pleistocene climatic ice core records for Qinghai-Tibetan plateau  

SciTech Connect

Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai-Tibetan Plateau of China provide a detailed record of Holocene and Wisconsin-Wuerm late glacial stage (LGS) climate changes in the subtropics. The records reveal that LGS conditions were apparently colder, wetter, and dustier than Holocene conditions. The LGS part of the cores is characterized by more negative {delta}{sup 18}O ratios, increased dust content, decreased soluble aerosol concentrations, and reduced ice crystal sizes than the Holocene part. These changes occurred rapidly {approximately} 10,000 years ago. In addition, the last 60 years were apparently one of the warmest periods in the entire record, equalling levels of the Holocene maximum between 6000 and 8000 years ago.

Thompson, L.G.; Mosley-Thompson, E.; Davis, M.E.; Bolzan, J.F.; Dai, J.; Klien, L. (Ohio State Univ., Columbus (USA)); Yao, T.; Wu, X.; Xie, Z. (Lanzhou Institute of Glaciology and Geocryology (China)); Gundestrup, N. (Univ. of Copenhagen (Denmark))

1989-10-27

111

Holocene--late pleistocene climatic ice core records from qinghai-tibetan plateau.  

PubMed

Three ice cores to bedrock from the Dunde ice cap on the north-central Qinghai-Tibetan Plateau of China provide a detailed record of Holocene and Wisconsin-Würm late glacial stage (LGS) climate changes in the subtropics. The records reveal that LGS conditions were apparently colder, wetter, and dustier than Holocene conditions. The LGS part of the cores is characterized by more negative delta(18)O ratios, increased dust content, decreased soluble aerosol concentrations, and reduced ice crystal sizes than the Holocene part. These changes occurred rapidly approximately 10,000 years ago. In addition, the last 60 years were apparently one of the warmest periods in the entire record, equalling levels of the Holocene maximum between 6000 and 8000 years ago. PMID:17788697

Thompson, L G; Mosley-Thompson, E; Davis, M E; Bolzan, J F; Dai, J; Klein, L; Yao, T; Wu, X; Xie, Z; Gundestrup, N

1989-10-27

112

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

113

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

114

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

115

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

116

Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.  

PubMed

New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf. PMID:17779616

Zotikov, I A; Zagorodnov, V S; Raikovsky, J V

1980-03-28

117

Using Radar Layer Data and AN Inverse Ice Flow Model to Constrain the Vostok Ice Core Age-Depth Relationship  

Microsoft Academic Search

Dating of the ice in the Vostok core has been by a combination of ice-flow modelling and the matching of isotopic variation to data from other sites. We present an inverse ice flow model that uses radar layer (isochronic data from near Vostok) to compute the age-depth distribution. We use an optimal method to invert for accumulation rate and melting

R. C. Hindmarsh; M. J. Siegert

2002-01-01

118

The Greenland Summit Ice Cores CD-ROM  

NSDL National Science Digital Library

The Greenland Ice Core Project collected data to investigate the paleoclimate record for the Northern Hemisphere. This data was collected and made available on a CD-ROM, which is now available for downloading from the National Oceanic and Atmospheric Administration's National Geophysical Data Center site. The contents of the CD-ROM include an overview of the project and the data. The website also features two search engines: citation & data, and information.

Program., National G.

1997-01-01

119

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

120

Penny ice cap cores, baffin island, canada, and the wisconsinan foxe dome connection: two states of hudson bay ice cover  

PubMed

Ice cores from Penny Ice Cap, Baffin Island, Canada, provide continuous Holocene records of oxygen isotopic composition (delta18O, proxy for temperature) and atmospheric impurities. A time scale was established with the use of altered seasonal variations, some volcanic horizons, and the age for the end of the Wisconsin ice age determined from the GRIP and GISP2 ice cores. There is pre-Holocene ice near the bed. The change in delta18O since the last glacial maximum (LGM) is at least 12.5 per mil, compared with an expected value of 7 per mil, suggesting that LGM ice originated at the much higher elevations of the then existing Foxe Dome and Foxe Ridge of the Laurentide Ice Sheet. The LGM delta18O values suggest thick ice frozen to the bed of Hudson Bay. PMID:9445472

Fisher; Koerner; Bourgeois; Zielinski; Wake; Hammer; Clausen; Gundestrup; Johnsen; Goto-Azuma; Hondoh; Blake; Gerasimoff

1998-01-30

121

Accumulation Reconstruction from a 270 Year Ice Core Retrieved from the Gorshkov Crater Glacier, Ushkovsky Ice Cap, Kamchatka  

Microsoft Academic Search

An ice core of 211.7 m length was retrieved in June 1998 from the Gorshkov crater glacier on the top of Ushkovsky volcano (3903 m), situated in the central part of Kamchatka Peninsula. It is the first ice core drilled in Eastern Siberia, or the western part of the North Pacific region, respectively. Past accumulation rates are reconstructed by using

R. Greve; T. Sato; T. Shiraiwa; T. Zwinger; H. Seddik

2009-01-01

122

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

123

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

124

Combined transmission and reflection optical microscopy of ice core sections  

NASA Astrophysics Data System (ADS)

Microstructure analysis of ice cores is vital to understand the processes controlling the flow of ice on the microscale. To quantify the microstructural variability (and thus occurring processes) on centimeter, meter and kilometer scale along deep polar ice cores, a large number of sections has to be analyzed. In the last decade, two different methods have been applied: On the one hand, transmission optical microscopy of thin sections between crossed polarizers yields information on the distribution of crystal c-axes. On the other hand, reflection optical microscopy of polished and controlled sublimated section surfaces allows to characterize the high resolution properties of a single grain boundary, e.g. its length, shape or curvature. Based on a polar and an alpine ice core we applied both methods to the same set of sections. This enables us to combine all information on crystal orientation and (sub-)grain boundaries. In this contribution we introduce the method of combined transmission-polarization and reflection microscopy as well as an image processing framework for processing and matching both image types [1]. The information content of both analysis methods is limited and influenced by different types of artifacts. It is exemplary shown how the combination allows to compensate for deficiencies of one method. The gray values in images of the grain boundaries on polished ice core sections are influenced by the duration of surface sublimation and the energy/misorientation of the grain boundaries in the section. By combining these gray values with the misorientation obtained from the corresponding thin section imaged between crossed polarizers we try to validate the information content of gray values on the basis of large data sets. This approach is compared to X-ray Laue diffraction measurements (yielding full crystallographic orientation) which validated the sensitivity of the surface sublimation method [2]. As microscopy in transmission mode acquires volume information and microscopy in reflection mode gains information on the surface, an "optimal" matching of both images contains displacements of grain boundary sites. We try to quantify this inaccuracy which can also be interpreted as orientation of the grain boundary surface in 3D. [1] T. Binder et al., 2013, Journal of Microscopy, in review [2] I. Weikusat et al., 2011, Journal of Glaciology, 57, 111-120

Binder, Tobias; Weikusat, Ilka; Kerst, Thomas; Eichler, Jan; Svensson, Anders; Bohleber, Pascal; Garbe, Christoph; Kipfstuhl, Sepp

2013-04-01

125

Atmospheric impacts and ice core imprints of a methane pulse from clathrates  

NASA Astrophysics Data System (ADS)

In relation to Arctic warming, the possible occurrence of methane hydrate degassing events has attracted an increasing interest in recent years. We evaluate the atmospheric impact of rapid and massive emissions of methane and how they are imprinted in ice core records, by combining for the first time models of atmospheric chemistry and trace gas transport in firn. Different emission characteristics as well as climatic conditions (present, pre-industrial, glacial) are considered. The ? isotopic signatures characterizing stable isotopologues of methane DCH3 and 13CH4 are also analysed. Our results suggest little effect of clathrate degassing on the main methane oxidant: OH radicals. Due to the relatively short atmospheric lifetime of methane, the simulated clathrate-induced perturbations last for less than a century. This time scale is comparable to or shorter than the duration of air bubble closure in polar ice sheets. As a consequence, rapid methane perturbations in the atmosphere are strongly smoothed in ice core records. This smoothing mostly depends on the snow accumulation rate at the site of ice core drilling. We propose a methodology to identify a potential clathrate degassing event in ice core records. Continuous CH4 records from high accumulation rate sites could allow to decipher short time scale events. ?D of CH4 should reveal a typical "lying S" shape at high accumulation rate sites, reflecting the combined effects of the clathrate source signature (negative excursion) and subsequent OH fractionation in the atmosphere (positive excursion). The amplitude ratio of the negative and positive ?D swings recorded in Greenland and Antarctica under similar accumulation rate conditions could also indicate the latitude of a clathrate degassing event.

Bock, Josué; Martinerie, Patricia; Witrant, Emmanuel; Chappellaz, Jérôme

2012-10-01

126

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

127

The Late Holocene Atmospheric Methane Budget Reconstructed from Ice Cores  

NASA Astrophysics Data System (ADS)

In this thesis I used a newly developed methane measurement line to make high-resolution, high-precision measurements of methane during the late Holocene (2800 years BP to present). This new measurement line is capable of an analytical precision of < 3 ppb using ˜120 g samples. The reduced sample size requirements as well as automation of a significant portion of the analysis process have enabled me to make >1500 discrete ice core methane measurements and construct the highest resolution records of methane available over the late Holocene. I first used a shallow ice core from WAIS Divide (WDC05A) to produce a 1000 year long methane record with a ˜9 year temporal resolution. This record confirmed the existence of multidecadal scale variations that were first observed in the Law Dome, Antarctica ice core. I then explored a range of paleoclimate archives for possible mechanistic connections with methane concentrations on multidecadal timescales. In addition, I present a detailed description of the analytical methods used to obtain high-precision measurements of methane including the effects of solubility and a new chronology for the WDC05A ice core. I found that, in general, the correlations with paleoclimate proxies for temperature and precipitation were low over a range of geographic regions. Of these, the highest correlations were found from 1400-1600 C.E. during the onset of the Little Ice Age and with a drought index in the headwater region of the major East Asian rivers. Large population losses in Asia and the Americas are also coincident with methane concentration decreases indicating that anthropogenic activities may have been impacting multidecadal scale methane variability. In the second component I extended the WAIS Divide record back to 2800 years B.P. and also measured methane from GISP2D over this time interval. These records allowed me to examine the methane Inter-Polar Difference (IPD) which is created by greater northern hemispheric sources. The IPD provides an important constraint on changes in the latitudinal distribution of sources. We used this constraint and an 8-box global methane chemical transport model to examine the Early Anthropogenic Hypothesis which posits that humans began influencing climate thousands of years ago by increasing greenhouse gas emissions and preventing the onset of the next ice age. I found that most of the increase in methane sources over this time came from tropical regions with a smaller contribution coming from the extratropical northern hemisphere. Based on previous modeling estimates of natural methane source changes, I found that the increase in the southern hemisphere tropical methane emissions was likely natural and that the northern hemispheric increase in methane emissions was likely due to anthropogenic activities. These results also provide new constraints on the total magnitude of pre-industrial anthropogenic methane emissions, which I found to be between the high and low estimates that have been previously published in the literature. For the final component of my thesis I assembled a coalition of scientists to investigate the effects of layering on the process of air enclosure in ice at WAIS Divide. Air bubbles are trapped in ice 60-100m below the surface of an ice sheet as snow compacts into solid ice in a region that is known as the Lock-In Zone (LIZ). The details of this process are not known and in the absence of direct measurements previous researchers have assumed it to be a smooth process. This project utilized high-resolution methane and air content measurements as well as density of ice, delta15N of N2, and bubble number density measurements to show that air entrapment is affected by high frequency (mm scale) layering in the density of ice within the LIZ. I show that previous parameterizations of the bubble closure process in firn models have not accounted for this variability and present a new parameterization which does. This has implications for interpreting rapid changes in trace gases measured in ice cores since variable bubble closure wi

Mitchell, Logan E.

128

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

129

Roosevelt Island - a good place for an ice core  

NASA Astrophysics Data System (ADS)

Roosevelt Island, a coastal ice dome in the eastern Ross Sea of West Antarctica, is ideally situated for investigating histories of climate and deglaciation of the region. With ice thickness H=745m, accumulation rate b=0.18m/yr, the characteristic timescale at the divide H/b is ~4kyr. Radar-detected layers (assumed to be isochrones) are arched upward beneath the divide; the pattern of the stack of bumps does not show evidence of divide migration. Matching the depth-profile of bump amplitudes using a 1-D transient ice-flow model indicates that the island has thinned about 300m since the onset of divide-type flow 3-4kyr BP (Conway et al., 1999). A coupled thermo-mechanical model yields similar results for the onset of divide flow and rate of thinning, and also shows that relatively high power rheology (n=4) is necessary to match the observed bump-amplitude distribution (Martin et al., 2006). A depth-age relationship is needed to infer histories of climate and ice dynamics farther back in time (Waddington et al., 2005; Price et al., 2007; Parrenin et al, 2007). RICE (Roosevelt Island Climate Evolution) Project is an international partnership between scientists from New Zealand, USA, Denmark, United Kingdom, Germany, Australia, Italy and China. A primary goal is to drill and date a core from Roosevelt Island. Drilling at the south summit is underway and will be completed during the 2012-13 austral summer. Initial calculations indicate the glacial transition is at about 80% depth; we expect to be able to infer histories of climate and ice dynamics over the past 40kyr. A depth-age relationship will be established from depth profiles of stable isotopes, chemistry, electrical conductivity and gas (methane) chronology. Physical properties (grain size and fabric, dust and volcanic layers) will also be measured. Borehole temperature profiles will be measured after drilling is complete. The spatial pattern of the modern thinning rate is being determined directly from repeat measurements with phase-sensitive radar, and indirectly from continuity (the residual of the sum of the horizontal flux divergence and the accumulation rate). Geophysical inverse methods using ice-flow models of varying complexity will be used to fit all available data at their level of uncertainty to infer histories of ice thickness and climate.

Conway, H.; Bertler, N.; Dahl-Jensen, D.; Hindmarsh, R. C. A.; Pyne, A.; Brook, E.; Waddington, E.; Kipfstuhl, S.; Hawley, R.; Fitzpatrick, J.

2012-04-01

130

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

NASA Astrophysics Data System (ADS)

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

131

Microflora in the basal strata at Antarctic ice core above the Vostok lake.  

PubMed

The microbiological investigations of the Antarctic ice core at the Vostok station become especially important in connection with the discovery of an subglacial lake in this region. This lake is considered by the world-wide scientific community to be an important object for searching for relict forms of life on the Earth and also as a model for solving a number of problems of exobiology--for instance for development of methods to penetrate into underice sea at Europe--Jupiter's satellite. For the first time the Antarctic ice core samples were taken from the horizons which correspond to the basal zone (3534-3541 m) and to the accreation ice zone (3555-3611 m) above the subglacial lake Vostok. As a result of the microbiological investigations it was shown that the total number of microbial cells have been in the same range of quantities as at the upper, younger horizons and varied from 1.3 x 10(2) up to 9.6 x 10(2) cl/ml. Some periodicity in the cell concentration and in their morphological diversity was revealed along the core. The maximal number and the greatest morphological variety were detected at horizons with the depth of 3534, 3555 and 3595 m. A drop in the cell concentration two or three times as much was found in ice layers under each of the above mentioned horizons. The discovered stratification is apparently connected with the periodicity of the lake water interactions with the basal ice layer and obviously depends on the complex natural events which took place in the geological history of our planet. PMID:11803975

Abyzov, S S; Mitskevich, I N; Poglazova, M N; Barkov, N I; Lipenkov, V Y; Bobin, N E; Koudryashov, B B; Pashkevich, V M; Ivanov, M V

2001-01-01

132

A 10 ppmv systematic offset in the EDC CO2 record of the deep part of the ice core  

NASA Astrophysics Data System (ADS)

The EPICA Dome C (EDC) ice core contains the longest continuous ice core time series to date and has allowed reconstructions of atmospheric CO2 concentrations back to 800,000 year BP. Gas measurements from the oldest part of the record between 650,000 and 750,000 years BP revealed significant lower CO2 concentrations on average of about 15 ppmv compared to the expectations from the CO2-temperature relation after 650,000 years BP. We have revisited the EDC CO2 record, in particular for the part older than 650,000 years BP, with CO2 measurements on EDC ice from the ice archive in Antarctica and with measurements using a new sublimation extraction technique. The new measurements show a consistent offset to the original data of up to 10 ppmv in the part before 650,000 years BP calling into question - at least partly - the lower CO2 concentrations found during the 650,000 to 750,000 year BP time window. The new data from different extraction techniques and different parts of the EDC ice core suggest that the ice core part used for the original data, which had been stored in Europe, has changed in such a way that measurements with our standard dry extraction principle result in a systematic offset. The processes responsible for this offset are not known; however, this might be related to fractionation processes between different gases during clathrate formation and relaxation.

Bereiter, Bernhard; Eggleston, Sarah; Schmitt, Jochen; Stocker, Thomas F.; Fischer, Hubertus

2013-04-01

133

Radiocarbon analyses along the EDML ice core in Antarctica  

NASA Astrophysics Data System (ADS)

Samples, 17 in total, from the EDML core drilled at Kohnen station Antarctica are analysed for 14CO and 14CO2 with a dry-extraction technique in combination with accelerator mass spectrometry. Results of the in situ produced 14CO fraction show a very low concentration of in situ produced 14CO. Despite these low levels in carbon monoxide, a significant in situ production is observed in the carbon dioxide fraction. For the first time we found background values for the ice samples which are equal to line blanks. The data set is used to test a model for the production of 14C in the ice matrix, in combination with a degassing as 14CO2 and possibly as 14CO into the air bubbles. Application of the model, for which no independent validation is yet possible, offers the opportunity to use radiocarbon analysis as dating technique for the air bubbles in the ice. Assigning an arbitrary error of 25% to the calculation of the in situ production leads to age estimates, after correction for the in situ production, which are in agreement with age estimates based on a volcanic layer match of EDML to the Dome C timescale in combination with a correction for firn diffusion.

van de Wal, R. S. W.; Meijer, H. A. J.; de Rooij, M.; van der Veen, C.

2007-02-01

134

Dust concentration and flux in ice cores from the Tibetan Plateau over the past few decades  

NASA Astrophysics Data System (ADS)

In this paper, we provide the concentrations and fluxes of dust particles (1-30?m diameter), quantitatively calculated, 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. Dust concentrations from the northern and western Tibetan Plateau are 2-10 times higher, and from the central Tibetan Plateau is five 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?gcm-2a-1) is 10 times higher, and that in Muztagata (342?gcm-2a-1) is four times higher, respectively, than the dust flux in the central Himalayas (77-103?gcm-2a-1). The quantitative assessment of dust flux in ice cores accords with the 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 properties of upper level tropospheric dust over the Tibetan Plateau, which is useful for the study of the climatic effects of this dust.

Wu, Guangjian; Yao, Tandong; Xu, Baiqing; Tian, Lide; Zhang, Chenglong; Zhang, Xuelei

2010-07-01

135

Methane and nitrous oxide in the ice core record.  

PubMed

Polar ice cores contain, in trapped air bubbles, an archive of the concentrations of stable atmospheric gases. Of the major non-CO2 greenhouse gases, methane is measured quite routinely, while nitrous oxide is more challenging, with some artefacts occurring in the ice and so far limited interpretation. In the recent past, the ice cores provide the only direct measure of the changes that have occurred during the industrial period; they show that the current concentration of methane in the atmosphere is far outside the range experienced in the last 650,000 years; nitrous oxide is also elevated above its natural levels. There is controversy about whether changes in the pre-industrial Holocene are natural or anthropogenic in origin. Changes in wetland emissions are generally cited as the main cause of the large glacial-interglacial change in methane. However, changing sinks must also be considered, and the impact of possible newly described sources evaluated. Recent isotopic data appear to finally rule out any major impact of clathrate releases on methane at these time-scales. Any explanation must take into account that, at the rapid Dansgaard-Oeschger warmings of the last glacial period, methane rose by around half its glacial-interglacial range in only a few decades. The recent EPICA Dome C (Antarctica) record shows that methane tracked climate over the last 650,000 years, with lower methane concentrations in glacials than interglacials, and lower concentrations in cooler interglacials than in warmer ones. Nitrous oxide also shows Dansgaard-Oeschger and glacial-interglacial periodicity, but the pattern is less clear. PMID:17513260

Wolff, Eric; Spahni, Renato

2007-07-15

136

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  

Microsoft Academic Search

Measurements of Pb isotope ratios in ice containing sub-pgg?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

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

2009-01-01

137

Coastal ice core evidence for a circum-Antarctic bipolar seesaw during the last deglaciation  

NASA Astrophysics Data System (ADS)

The transition from the last glacial period into the Holocene has a different shape in Antarctica, and the surrounding Southern Ocean, than in Greenland, and more generally in the Northern Hemisphere. Typically, the warming associated with the last deglaciation is relatively steady in Antarctica although interrupted by a return to cold conditions, the Antarctic Cold Reversal before the onset of the Holocene. Instead, it is, in Greenland, characterized by two rapid warmings respectively at the onset of the Bölling-Alleröd and of the Holocene with in-between the Younger-Dryas, a well-marked cold event, which follows the Bölling-Alleröd. Recent studies attempted at explaining the different sequence of events in the two hemispheres through the ocean bi-polar see-saw that explains the competition between deep waters formed in the North Atlantic and in the Southern Ocean. Critical to document the causes and mechanisms involved in this different Greenland / Antarctic behaviour (more generally between North and South) is our ability to define the timing of events between Greenland and Antarctica, which indeed has long been a matter of intense debate. Here we investigate a new 1620 m long ice core drilled at Talos Dome (TD) a peripheral dome of East Antarctica in the framework of the TALDICE (TAlos Dome Ice CorE) project, involving five European nations and led by Italy. TD is located in the Ross Sea sector, about 550 km north of Taylor Dome and 1100 km East from the EPICA Dome C drilling site. The TALDICE coring site (159°11'E 72°49'S; 2315 m; T -41°C; www.taldice.org) is located near the dome summit and is characterised by an annual snow accumulation rate of 80 mm water equivalent. In this study, we present the new oxygen isotope record from the TALDICE ice core with a focus on the time window between 8 and 25 ky. In this work, methane measurements have been used to synchronise TALDICE to NGRIP and EPICA (EDC and EDML) ice cores on GICC05 age scale. The TALDICE and EPICA ice cores, synchronised to GICC05, allows us to confirm the bipolar see-saw between Greenland and Antarctica also from the most distant ice core from the North Atlantic "centre of action" in the Ross Sea sector. This interhemispheric signature is coherent between plateau and coastal sites from the South Atlantic to the Southwest Pacific, providing support that this is a "uniform" feature of millennial-scale climate change in Antarctica. The data presented here reveal synchronous albeit distinct fingerprints of Antarctic Isotopic Maximum in the Indo-Pacific versus Atlantic sectors. This breaks down the hypothesis proposed for Taylor Dome ice core of a synchronous climate change between the two hemispheres during deglaciation in the Ross Sea area. The new ice core chronologies presented here support the hypothesis that the ACR could be a response of MWP1a partially originating from Antarctica.

Stenni, Barbara; Buiron, Daphné; Frezzotti, Massimo

2010-05-01

138

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

Microsoft Academic Search

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

M. I. Guzmán; M. R. Hoffmann; A. J. Colussi

2007-01-01

139

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

140

Pollen, Oxygen Isotope Content and Seasonality in an Ice Core from the Penny Ice Cap, Baffin Island  

Microsoft Academic Search

The results of pollen analyses of 12 ice core samples, covering an eight-year period from 1972 through 1979 from the divide of the Penny Ice Cap, Baffin Island, are reported. The pollen spectra are dominated by long distance transported pollen, especially the conifers Picea and Pinus. Alnus pollen is generally rare. In contrast, pollen spectra from both modern polsters and

SUSAN K. SHORT; GERALD HOLDSWORTH

141

Melting and refreezing beneath Roi Baudouin Ice Shelf (East Antarctica) inferred from radar, GPS, and ice core data  

NASA Astrophysics Data System (ADS)

Ice-penetrating radar profiles across the grounding line of a small ice-rise promontory located within the Roi Baudouin Ice Shelf in the Dronning Maud Land sector of East Antarctica show downward dipping englacial radar-detected reflectors. Model results indicate that this reflector pattern is best fit by including basal melting of at least 15 cm a-1. This rate of melting is low compared with rates observed on larger ice shelves in both West and East Antarctica. Ice cores extracted from a rift system close to the ice-rise promontory show several meters of marine ice accreted beneath the shelf. These observations of low rates of basal melting, and limited distribution of accreted marine ice suggest that either Antarctic surface water may reach the ice shelf base or that circulation beneath the shelf is likely dominated by the production of high salinity shelf water rather than the incursion of circumpolar deep water, implying a weak sub-shelf circulation system here. Many of the ice shelves located along the coast of Dronning Maud Land are, like Roi Baudouin Ice Shelf, characterized by frequent ice rises and promontories. Therefore, it is highly likely that these are also of shallow bathymetry and are subject to similarly weak side-shelf basal melting and refreezing.

Pattyn, F.; Matsuoka, K.; Callens, D.; Conway, H.; Depoorter, M.; Docquier, D.; Hubbard, B.; Samyn, D.; Tison, J. L.

2012-12-01

142

Diffusive equilibration of N2, O2 and CO2 mixing ratios in a 1.5 million years old ice core  

NASA Astrophysics Data System (ADS)

In the framework of the International Partnerships in Ice Core Sciences, one of the most important target is to retrieve an Antarctic ice core that extends over the last 1.5 million years, i.e. an ice core that enters the climate era when glacial-interglacial cycles followed the obliquity cycles of the sun. In such an ice core the annual layers of the oldest ice would be thinned by a factor of about 100 and the climatic information of a 10 000 yr interval would be contained in less than 1m of ice. The gas record in such an Antarctic ice core can potentially reveal the role of greenhouse gas forcing on these 40 000 yr cycles. However, besides the extreme thinning of the annual layers, also the long residence time of the trapped air in the ice and the relatively high ice temperatures near the bedrock favour diffusive exchanges. To investigate the changes in the O2/N2 ratio, as well as the trapped CO2 concentrations, we modelled the diffusive exchange of the trapped gases O2, N2 and CO2 along the vertical axis. Even though the boundary conditions of a potential drilling site are not yet well constrained and the uncertainties in the permeation coefficients of the air constituents in the ice are large, the results suggest that in the oldest ice the precessional variations in the O2/N2 ratio will be damped by 50-100%, whereas CO2 concentration changes associated with glacial-interglacial variations will experience a damping of only 5%. This significant attenuation of the precessional O2/N2 signal in the ice older than 1 Myr will limit the possibility to use the O2/N2 ratio for orbital tuning of the ice core age scale.

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

2013-05-01

143

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

144

Separation of melting and environmental signals in an ice core with seasonal melt  

Microsoft Academic Search

We examine the impact of melt water percolation on the soluble ion chemical record from the Lomonosovfonna ice core. Principle component analysis shows that melting produces only simple changes between bubbly and clear ice facies, due to elution of ions. The data can be naturally split into four groups: pre-industrial, immediately before, and after the end of the Little Ice

John C. Moore; Aslak Grinsted; Teija Kekonen; Veijo Pohjola

2005-01-01

145

Holocene biomass burning recorded in polar and low-latitude ice cores  

NASA Astrophysics Data System (ADS)

Ice cores contain specific molecular markers including levoglucosan (1,6-anhydro-?-D-glucopyranose) and other pyrochemical evidence that provides much-needed information on the role of fire in regions with no existing data of past fire activity. Levoglucosan is a cellulose combustion product produced at burning temperatures of 300°C or greater. We first trace fire emissions from a boreal forest source in the Canadian Shield through transport and deposition at Summit, Greenland. 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 longest temporal resolution extends back approximately eight glacial cycles in the EPICA Dome C ice core, but many ice cores provide high-resolution Holocene records. 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. Here, we compare levoglucosan flux measured during the late Holocene in the Kilimanjaro (3°04.6'S; 37°21.2'E, 5893 masl) and NEEM, Greenland (77°27' N; 51°3'W, 2454 masl) ice cores. We contrast the Holocene results with levoglucosan flux across the past 600,000 years in the EPICA Dome C (75°06'S, 123°21'E, 3233 masl) ice core.

Kehrwald, N. M.; Zennaro, P.; Zangrando, R.; Gabrielli, P.; Thompson, L. G.; Gambaro, A.; Barbante, C.

2011-12-01

146

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

147

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.

Benison, Kathy

148

On high-resolution sampling of short ice cores: Dating and temperature information recovery from Antarctic Peninsula virtual cores  

Microsoft Academic Search

New techniques (CFA) now allow high-resolution ice core analysisA new method to allow interpretation of the new high-resolution core results is presentedThe temperature information that can be recovered from high-resolution cores is quantified

Louise C. Sime; Nicola Lang; Elizabeth R. Thomas; Ailsa K. Benton; Robert Mulvaney

2011-01-01

149

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

150

Wisconsinan and Holocene Climate History from an Ice Core at Taylor Dome, Western Ross Embayment, Antarctica  

Microsoft Academic Search

Geochemical data and geophysical measurements from a 554-m ice-core from Taylor Dome, East Antarctica, pro- vide the basis for climate reconstruction in the western Ross Em- bayment through the entire Wisconsinan and Holocene. In com- parison with ice cores from central East and West Antarctica, Taylor Dome shows greater variance of temperature, snow accu- mulation, and aerosol concentrations, reflecting significant

Eric J. Steig; David L. Morse; Edwin D. Waddington; Minze Stuiver; Pieter M. Grootes; Paul A. Mayewski; Mark S. Twickler; Sallie I. Whitlow

2000-01-01

151

High-resolution ammonium ice core record covering a complete glacial-interglacial cycle  

Microsoft Academic Search

High-resolution ammonium measurements were performed along the Greenland Ice Core Program (GRIP) deep ice core, covering a complete climatic cycle. No overall anthropogenic increase is observed over the last 300 years; however, springtime concentrations have roughly doubled since 1950. Biomass burning is estimated to be a major source for ammonia emissions for preindustrial times. It contributes between 10% to 40%

Katrin Fuhrer; Albrecht Neftel; Martin Anklin; Thomas Staffelbach; Michel Legrand

1996-01-01

152

Ultrasonic Velocity Investigations of Crystal Anisotropy in Deep Ice Cores from Antarctica.  

National Technical Information Service (NTIS)

Ice cores from Byrd Station and Little America V have been used to test an ultrasonic technique for evaluating crystal anisotropy in the Antarctic Ice Sheet. P-wave velocities measured parallel and perpendicular to the vertical axes of cores from the 2164...

H. Kohnen A. J. Gow

1979-01-01

153

Cosmogenic 10Be Depth Profile in top 560 m of West Antarctic Ice Sheet Divide Ice Core  

NASA Astrophysics Data System (ADS)

Concentrations of cosmogenic 10Be in polar ice samples are a function of variations in solar activity, geomagnetic field strength, atmospheric mixing and annual snow accumulation rates. The 10Be depth profile in ice cores also provides independent chronological markers to tie Antarctic to Greenland ice cores and to tie Holocene ice cores to the 14C dendrochronology record. We measured 10Be concentrations in 187 samples from depths of 0-560 m of the main WAIS Divide core, WDC06A. The ice samples are typically 1-2 kg and represent 2-4 m of ice, equivalent to an average temporal resolution of ~12 years, based on the preliminary age-depth scale proposed for the WDC core, (McConnell et al., in prep). Be, Al and Cl were separated using ion exchange chromatography techniques and the 10Be concentrations were measured by accelerator mass spectrometry (AMS) at PRIME lab. The 10Be concentrations range from 8.1 to 19.1 x 10^3 at/g, yielding an average of (13.1±2.1) x 10^3 at/g. Adopting an average snow accumulation rate of 20.9 cm weq/yr, as derived from the age-depth scale, this value corresponds to an average 10Be flux of (2.7±0.5) x 10^5 atoms/yr/cm2. This flux is similar to that of the Holocene part of the Siple Dome (Nishiizumi and Finkel, 2007) and Dome Fuji (Horiuchi et al. 2008) ice cores, but ~30% lower than the value of 4.0 x 10^5 atoms/yr/cm2 for GISP2 (Finkel and Nishiizumi, 1997). The periods of low solar activity, known as Oort, Wolf, Spörer, Maunder and Dalton minima, show ~20% higher 10Be concentrations/fluxes than the periods of average solar activity in the last millennium. The maximum 10Be fluxes during some of these periods of low solar activity are up to ~50% higher than average 10Be fluxes, as seen in other polar ice cores, which makes these peaks suitable as chronologic markers. We will compare the 10Be record in the WAIS Divide ice core with that in other Antarctic as well as Greenland ice cores and with the 14C treering record. Acknowledgment. This work was supported by NSF grants ANT-0538427, 0636815, 0636964 and 0739780. Finkel R. C. and Nishiizumi K. 1997. J. Geophys. Res. 102, 26,699-26,706. Horiuchi K., et al. 2008. Quatern. Geochron. 3, 253-261. Nishiizumi K. and Finkel R. C. 2007. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Welten, K. C.; Woodruff, T. E.; Caffee, M. W.; Edwards, R.; McConnell, J. R.; Bisiaux, M. M.; Nishiizumi, K.

2009-12-01

154

Stable isotope constraints on Holocene carbon cycle changes from an Antarctic ice core.  

PubMed

Reconstructions of atmospheric CO(2) concentrations based on Antarctic ice cores reveal significant changes during the Holocene epoch, but the processes responsible for these changes in CO(2) concentrations have not been unambiguously identified. Distinct characteristics in the carbon isotope signatures of the major carbon reservoirs (ocean, biosphere, sediments and atmosphere) constrain variations in the CO(2) fluxes between those reservoirs. Here we present a highly resolved atmospheric delta(13)C record for the past 11,000 years from measurements on atmospheric CO(2) trapped in an Antarctic ice core. From mass-balance inverse model calculations performed with a simplified carbon cycle model, we show that the decrease in atmospheric CO(2) of about 5 parts per million by volume (p.p.m.v.). The increase in delta(13)C of about 0.25 per thousand during the early Holocene is most probably the result of a combination of carbon uptake of about 290 gigatonnes of carbon by the land biosphere and carbon release from the ocean in response to carbonate compensation of the terrestrial uptake during the termination of the last ice age. The 20 p.p.m.v. increase of atmospheric CO(2) and the small decrease in delta(13)C of about 0.05 per thousand during the later Holocene can mostly be explained by contributions from carbonate compensation of earlier land-biosphere uptake and coral reef formation, with only a minor contribution from a small decrease of the land-biosphere carbon inventory. PMID:19779448

Elsig, Joachim; Schmitt, Jochen; Leuenberger, Daiana; Schneider, Robert; Eyer, Marc; Leuenberger, Markus; Joos, Fortunat; Fischer, Hubertus; Stocker, Thomas F

2009-09-24

155

Black carbon record based on a shallow Himalayan ice core and its climatic implications  

NASA Astrophysics Data System (ADS)

A continuous measurement for black carbon (hereafter "BC") in a 40 m shallow ice core retrieved from the East Rongbuk Glacier (hereafter "ERG") in the northeast saddle of Mt. Qomolangma (Everest) provided the first historical record of BC deposition during the past ~50 yrs in the high Himalyas. Apparent increasing trend (smooth average) of BC concentrations was revealed since the mid-1990s. Seasonal variability of BC concentrations in the ice core indicated higher concentrations in monsoon seasons than those in non-monsoon seasons. Backward air trajectory analysis by the HYSPLIT model indicated that South Asia's BC emissions had significant impacts on the BC deposition in the Mt. Qomolangma (Everest) region. The estimated average atmospheric BC concentration in the region was about 80 ng m-3 during 1951-2001. And it was suggested BC emitted from South Asia could penetrate into the Tibetan Plateau by climbing over the elevated Himalayas. A significant increasing trend of the radiative forcing simulated by the SNICAR model appeared since 1990, which even exceeded 4.5 W m-2 in the summer of 2001. It was suggested that this amplitudes of BC concentrations in the atmosphere over the Himalayas and consequently in the ice in the glaciers could not be neglected when assessing the dual warming effects on glacier melting in the Himalayas.

Ming, J.; Cachier, H.; Xiao, C.; Qin, D.; Kang, S.; Hou, S.; Xu, J.

2008-03-01

156

INTIMATE: Integration of Ice-core Marine and Terrestrial records  

NASA Astrophysics Data System (ADS)

The principal aim of the INTIMATE Project is to synthesize high-resolution ice, terrestrial and marine records spanning the period 60,000 to 8000 years ago (henceforth given as 60-8 ka) to better understand the impact and mechanisms of rapid and extreme climate change, thereby reducing the uncertainty of future predictions. The specific objectives of the INTIMATE Project are to: • lead the development of highly-precise and accurate age-depth models in ice-core, marine, and terrestrial records (including identification and validation of time-stratigraphic marker horizons) over the period 60-8 ka; • promote the development of quantified climate reconstruction methods; • determine the timing, rates of change, spatial variability and climate gradients during key periods at the regional, hemispheric and global level (in collaboration with the INQUA-recognized Australasian INTIMATE Project and future regional INTIMATE projects); • determine the environmental impact of rapid and extreme climate changes in the North Atlantic region (focusing on megafauna and vegetation); and develop climate and environmental reconstructions of change that may be used in climate modeling to better determine the mechanisms of change and how signals are propagated globally. For correlation, precise dating of the records from the different realms is imperative. The development of an event-stratigraphy for the Last Glacial-Interglacial Transition (Björck et al., 1998) provided a template to compare other, independently dated, palaeoclimate records with the high-resolution Greenland oxygen isotope records. The event-stratigraphy has recently been refined and updated to the new NGRIP record using the GICC05 timescale (Lowe et al., 2008), which will be outlined in this paper. References: Björck, S., Walker, M.J.C., Cwynar, L.C., Johnsen, S., Knudsen, K.-L., Lowe, J.J., Wohlfarth, B. and INTIMATE members (1998) An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group, Journal of Quaternary Science 13, 283-292. Lowe, J.J., Rasmussen, S.O., Björck, S., Hoek, W.Z., Steffensen, J.P., Walker, M.J.C., Yu, Z. and INTIMATE group (2008) Precise dating and correlation of events in the North Atlantic region during the Last Termination: a revised protocol recommended by the INTIMATE group. Quaternary Science Reviews, 27, 6-17.

Turney, C. S. M.; Hoek, W. Z.; Intimate Group

2009-04-01

157

Tropical Cyclones and Ice Cores: Developing a Long Term Perspective  

NASA Astrophysics Data System (ADS)

Accurate forecasts of seasonal typhoon activity in the northwestern Pacific are of critical importance to the people living in the densely populated coastal cities of east Asia. The El Niño Southern Oscillation (ENSO) is a key component of these forecasts as past observations indicate that El Niño (La Niña) events are associated with an increase (decrease) in the proportion of typhoons striking Japan, Korea and Taiwan (The Philippines and the South China Sea). The ice core-derived ?18O record from the Quelccaya ice cap (Peru) is strongly correlated (r=0.646, p<0.001, 1856-2003) with sea surface temperatures (SST) in NINO 4, a region of the western equatorial Pacific that is a sensitive recorder of ENSO. Additionally, a direct relationship is observed between ?18O and both the mean longitude of typhoon development (r=0.59, p<.001, 1945-2003) and the number of typhoon days (r=0.59, p<.001, 1945-2003). The typhoon and ice core ?18O records exhibit patterns of decadal-scale variability that closely resemble the longer-term variations in NINO 4 SSTs (decadal NINO 4 SST variability is known as the "Decadal ENSO"). Annual values of ?18O are significantly different (p=.05) between La Niña and El Niño years suggesting that ?18O reflects not only the Decadal ENSO but also the superimposed interannual ENSO variability. ENSO-driven shifts in the SSTs and large-scale atmospheric circulation patterns may provide a physical linkage to explain the observed relationships among ?18O, SSTs and typhoon activity. The effect of the ongoing warming on ENSO is unclear, but any changes in the background frequency or intensity of ENSO events would likely affect the development of typhoons and cyclones in the Pacific as well as hurricanes in the Atlantic. The 1500-year ?18O record from Quelccaya offers a unique opportunity to examine how ENSO-driven hurricane and typhoon activity responded to large-scale climate forcing (changes) in the past and may provide a more complete perspective and better understanding that will be required to evaluate the likely effects under future climate change scenarios

Urmann, D.

2006-12-01

158

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

NASA Astrophysics Data System (ADS)

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 by ribosomal DNA sequencing. Total, 33 clones of 16S ribosomal DNA were recovered from four samples of drilling fluid at 110, 2750, 3400, and 3600m leading to identification of 8 bacterial species. No overlapping was observed even for neighboring samples (3400m and 3600m). At present four major bacteria with the titer more than 103-104 cells per ml (as estimated from PCR results) are identified. Among them we found: unknown representative of Desulfobacteraceae which are able to oxidize sulphates and degrade benzenes (110m); PAH-degrading alpha-proteobacterium Sphingomonas natatoria (3400m); alpha-proteobacterium representing closely-related group of Sphingomonas sp. (e.g., S. aurantiaca) which are able to degrade PAH as well, and human pathogen closely related to Haloanella gallinarum of CFB group (3600m). Four additional species were revealed as single clones and showed relatedness to human pathogens and saprophytes as well as soil bacteria. These bacteria may represent drilling fluid contaminants introduced during its sampling or DNA extraction procedure. Of four major bacteria revealed, one species, Sphingomonas natatoria, has been met by us in the Vostok core from 3607 m depth (AF532054) whereas another Sphingomonas sp. which we refer to as S. aurantiaca was found in Antarctic microbial endolithic community (AF548567), hydrocarbon-containing soil near Scott Base in Antarctica (AF184221) and even isolated from 3593m Vostok accretion ice (AF324199) and Taylor Dome core (AF395031). The source for major human pathogen-related bacteria is rather uncertain indicating that very unusual microbes can be contained in a drilling fluid. All this testifies that kerosene film is indeed hard to remove and everyone should be aware on bacteria introduced with any drilling fluid. Our results demonstrate the necessity to have a drilling fluid data base when studying the microbial contents of ice cores.

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

2003-04-01

159

Toward an integrated ice core chronology using relative and orbital tie-points  

NASA Astrophysics Data System (ADS)

Precise ice cores chronologies are essential to better understand the mechanisms linking climate change to orbital and greenhouse gases concentration forcing. A tool for ice core dating (DATICE [developed by Lemieux-Dudon et al., 2010] permits to generate a common time-scale integrating relative and absolute dating constraints on different ice cores, using an inverse method. Nevertheless, this method has only been applied for a 4-ice cores scenario and for the 0-50 kyr time period. Here, we present the bases for an extension of this work back to 800 ka using (1) a compilation of published and new relative and orbital tie-points obtained from measurements of air trapped in ice cores and (2) an adaptation of the DATICE inputs to 5 ice cores for the last 800 ka. We first present new measurements of ?18Oatm and ?O2/N2 on the Talos Dome and EPICA Dome C (EDC) ice cores with a particular focus on Marine Isotopic Stages (MIS) 5, and 11. Then, we show two tie-points compilations. The first one is based on new and published CH4 and ?18Oatm measurements on 5 ice cores (NorthGRIP, EPICA Dronning Maud Land, EDC, Talos Dome and Vostok) in order to produce a table of relative gas tie-points over the last 400 ka. The second one is based on new and published records of ?O2/N2, ?18Oatm and air content to provide a table of orbital tie-points over the last 800 ka. Finally, we integrate the different dating constraints presented above in the DATICE tool adapted to 5 ice cores to cover the last 800 ka and show how these constraints compare with the established gas chronologies of each ice core.

Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Blunier, T.; Capron, E.; Chappellaz, J.; Fischer, H.; Leuenberger, M.; Lipenkov, V.; Loutre, M.-F.; Martinerie, P.; Parrenin, F.; Prié, F.; Raynaud, D.; Veres, D.; Wolff, E.

2012-04-01

160

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

161

Palynology as an age-control tool for ice cores. First results of PAMOGIS - Pollen Analyses of the Mt. Ortles Glacier Ice Samples  

NASA Astrophysics Data System (ADS)

Glacier ice cores from the mid latitude are capable of retaining essential information on past climate, environmental and human activities on a seasonal/annual time resolution. However, for a correct interpretation of the ice record a good chronological control is essential. Absolute time markers such as 3H peaks and Sahara dust horizons, together with radiometric methods such as 210Pb, radiocarbon from carbonaceous aerosol particles and AMS-dating are commonly used to obtain the age depth model of ice cores. In this frame we present the first pollen-based chronology from the Eastern Alps. Results of pollen analyses performed on a 10 m firn core taken on the top of Alto dell'Ortles Glacier (3905 m a.s.l.) will be discussed. Palynological data are compared and complemented with stable isotopes, major ions and trace elements analyses. Based on the single species flowering periods, our results show that the pollen spectrum presents seasonal and inter-annual variability that enables to distinguish snow accumulated in the three different flowering seasons and winter snow. According to these four components a seasonal and annual chronology was established, proving that the 10 m firn core encompasses four years of snow accumulation and presents a clear seasonal palynological signal. These first results reveal the potential of pollen content of glacier snow and ice as a chronological tool that can contribute to the construction of a robust chronological model with a seasonal to annual resolution. This study is the first step and the base for future research on deeper ice cores on the Alto dell'Ortles Glacier (Ortles project: www.ortles.org).

Festi, Daniela; Kofler, Werner; Gabrielli, Paolo; Oeggl, Klaus

2014-05-01

162

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

163

Optimization of high-resolution continuous flow analysis for transient climate signals in ice cores.  

PubMed

Over the past two decades, continuous flow analysis (CFA) systems have been refined and widely used to measure aerosol constituents in polar and alpine ice cores in very high-depth resolution. Here we present a newly designed system consisting of sodium, ammonium, dust particles, and electrolytic meltwater conductivity detection modules. The system is optimized for high-resolution determination of transient signals in thin layers of deep polar ice cores. Based on standard measurements and by comparing sections of early Holocene and glacial ice from Greenland, we find that the new system features a depth resolution in the ice of a few millimeters which is considerably better than other CFA systems. Thus, the new system can resolve ice strata down to 10 mm thickness and has the potential of identifying annual layers in both Greenland and Antarctic ice cores throughout the last glacial cycle. PMID:21504155

Bigler, Matthias; Svensson, Anders; Kettner, Ernesto; Vallelonga, Paul; Nielsen, Maibritt E; Steffensen, Jørgen Peder

2011-05-15

164

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

165

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

166

Proxies and measurement techniques for mineral dust in Antarctic ice cores.  

PubMed

To improve quantitative interpretation of ice core aeolian dust records, a systematic methodological comparison was made. This involved methods for water-insoluble particle counting (Coulter counter and laser-sensing particle detector), soluble ion analysis (ion chromatography and continuous flow analysis), elemental analysis (inductively coupled plasma mass spectroscopy at pH 1 and after full acid digestion), and water-insoluble elemental analysis (proton induced X-ray emission). Antarctic ice core samples covering the last deglaciation from the EPICA Dome C (EDC) and the EPICA Dronning Maud Land (EDML) cores were used. All methods correlate very well among each other, but the ratios of glacial age to Holocene concentrations, which are typically a factor approximately 100, differ between the methods by up to a factor of 2 with insoluble particles showing the largest variability. The recovery of ICP-MS measurements depends on the digestion method and is differentfor different elements and during different climatic periods. EDC and EDML samples have similar dust composition, which suggests a common dust source or a common mixture of sources for the two sites. The analyzed samples further reveal a change of dust composition during the last deglaciation. PMID:18754492

Ruth, Urs; Barbante, Carlo; Bigler, Matthias; Delmonte, Barbara; Fischer, Hubertus; Gabrielli, Paolo; Gaspari, Vania; Kaufmann, Patrik; Lambert, Fabrice; Maggi, Valter; Marino, Federica; Petit, Jean-Robert; Udisti, Roberto; Wagenbach, Dietmar; Wegner, Anna; Wolff, Eric W

2008-08-01

167

Automated Laser-Light Scattering measurements of Impurities, Bubbles, and Imperfections in Ice Cores  

NASA Astrophysics Data System (ADS)

Laser- light scattering (LLS) on polar ice, or on polar ice meltwater, is an accepted method for measuring the concentration of water insoluble aerosol deposits (dust) in the ice. LLS on polar ice can also be used to measure water soluble aerosols, as well as imperfections (air bubbles and cavities) in the ice. LLS was originally proposed by Hammer (1977a, b) as a method for measuring the dust concentration in polar ice meltwater. Ram et al. (1995) later advanced the method and applied it to solid ice, measuring the dust concentration profile along the deep, bubble-free sections of the Greenland Ice Sheet Projetct 2 (GISP2) ice core (Ram et al., 1995, 2000) from central Greenland. In this paper, we will put previous empirical findings (Ram et al., 1995, 2000) on a theoretical footing, and extend the usability of LLS on ice into the realm of the non-transparent, bubbly polar ice. For LLS on clear, bubble-free polar ice, we studied numerically the scattering of light by soluble and insoluble (dust) aerosol particles embedded in the ice to complement previous experimental studies (Ram et al., 2000). For air bubbles in polar ice, we calculated the effects of multiple light scattering using Mie theory and Monte Carlo simulations, and found a method for determining the bubble number size and concentration using LLS on bubbly ice. We also demonstrated that LLS can be used on bubbly ice to measure annual layers rapidly in an objective manner. Hammer, C. U. (1977a), Dating of Greenland ice cores by microparticle concentration analyses., in International Symposium on Isotopes and Impurities in Snow and Ice, pp. 297-301, IAHS publ. no. 118. Hammer, C. U. (1977b), Dust studies on Greenland ice cores, in International Symposium on Isotopes and Impurities in Snow and Ice, pp. 365-370, IAHS publ. no. 118. Ram, M., M. Illing, P. Weber, G. Koenig, and M. Kaplan (1995), Polar ice stratigraphy from laser-light scattering: Scattering from ice, Geophys. Res. Lett., 22(24), 3525-3527. Ram, M., J. Donarummo, M. R. Stolz, and G. Koenig (2000), Calibration of laser-light scattering measurements of dust concentration for Wisconsinan GISP2 ice using instrumental neutron activation analysis of aluminum: Results and discussion, J. Geophys. Res., 105(D20), 24,731--24,738.

Stolz, M. R.; Ram, M.

2004-12-01

168

The design and performance of IceCube DeepCore  

NASA Astrophysics Data System (ADS)

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 physics 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.

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Allen, M. M.; Altmann, D.; Andeen, K.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S. W.; Bay, R.; Bazo Alba, J. L.; Beattie, K.; Beatty, J. J.; Bechet, S.; Becker, J. K.; Becker, K.-H.; Benabderrahmane, M. L.; BenZvi, S.; Berdermann, J.; Berghaus, P.; Berley, D.; Bernardini, E.; Bertrand, D.; Besson, D. Z.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bose, D.; Böser, S.; Botner, O.; Brown, A. M.; Buitink, S.; Caballero-Mora, K. S.; Carson, M.; Chirkin, D.; Christy, B.; Clevermann, F.; Cohen, S.; Colnard, C.; Cowen, D. F.; Cruz Silva, A. H.; D'Agostino, M. V.; Danninger, M.; Daughhetee, J.; Davis, J. C.; De Clercq, C.; Degner, T.; Demirörs, L.; Descamps, F.; Desiati, P.; de Vries-Uiterweerd, G.; DeYoung, T.; Díaz-Vélez, J. C.; Dierckxsens, M.; Dreyer, J.; Dumm, J. P.; Dunkman, M.; Eisch, J.; Ellsworth, R. W.; Engdegård, O.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Fox, B. D.; Franckowiak, A.; Franke, R.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Goodman, J. A.; Góra, D.; Grant, D.; Griesel, T.; Groß, A.; Grullon, S.; Gurtner, M.; Ha, C.; Haj Ismail, A.; Hallgren, A.; Halzen, F.; Han, K.; Hanson, K.; Heinen, D.; Helbing, K.; Hellauer, R.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, B.; Homeier, A.; Hoshina, K.; Huelsnitz, W.; Hülß, J.-P.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Japaridze, G. S.; Johansson, H.; Kampert, K.-H.; Kappes, A.; Karg, T.; Karle, A.; Kenny, P.; Kiryluk, J.; Kislat, F.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Köpke, L.; Koskinen, D. J.; Kowalski, M.; Kowarik, T.; Krasberg, M.; Kroll, G.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Laihem, K.; Landsman, H.; Larson, M. J.; Lauer, R.; Lünemann, J.; Madsen, J.; Marotta, A.; Maruyama, R.; Mase, K.; Matis, H. S.; Meagher, K.; Merck, M.; Mészáros, P.; Meures, T.; Miarecki, S.; Middell, E.; Milke, N.; Miller, J.; Montaruli, T.; Morse, R.; Movit, S. M.; Nahnhauer, R.; Nam, J. W.; Naumann, U.; Nygren, D. R.; Odrowski, S.; Olivas, A.; Olivo, M.; O'Murchadha, A.; Panknin, S.; Paul, L.; Pérez de los Heros, C.; Petrovic, J.; Piegsa, A.; Pieloth, D.; Porrata, R.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Rawlins, K.; Redl, P.; Resconi, E.; Rhode, W.; Ribordy, M.; Richman, M.; Rodrigues, J. P.; Rothmaier, F.; Rott, C.; Ruhe, T.; Rutledge, D.; Ruzybayev, B.; Ryckbosch, D.; Sander, H.-G.; Santander, M.; Sarkar, S.; Schatto, K.; Schmidt, T.; Schönwald, A.; Schukraft, A.; Schultes, A.; Schulz, O.; Schunck, M.; Seckel, D.; Semburg, B.; Seo, S. H.; Sestayo, Y.; Seunarine, S.; Silvestri, A.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Stüer, M.; Sullivan, G. W.; Swillens, Q.; Taavola, H.; Taboada, I.; Tamburro, A.; Tepe, A.; Ter-Antonyan, S.; Tilav, S.; Toale, P. A.; Toscano, S.; Tosi, D.; van Eijndhoven, N.; Vandenbroucke, J.; Van Overloop, A.; van Santen, J.; Vehring, M.; Voge, M.; Walck, C.; Waldenmaier, T.; Wallraff, M.; Walter, M.; Weaver, Ch.; Wendt, C.; Westerhoff, S.; Whitehorn, N.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wischnewski, R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, C.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Zoll, M.

2012-05-01

169

Climate variability features of the last interglacial in the East Antarctic EPICA Dome C ice core  

NASA Astrophysics Data System (ADS)

millennial to submillennial climate variability has been identified during the current interglacial period, past interglacial variability features remain poorly explored because of lacking data at sufficient temporal resolutions. Here we present new deuterium data from the EPICA Dome C ice core, documenting at decadal resolution temperature changes occurring over the East Antarctic plateau during the warmer-than-today last interglacial. Expanding previous evidence of instabilities during the last interglacial, multicentennial subevents are identified and labeled for the first time in a past interglacial context. A variance analysis further reveals two major climatic features. First, an increase in variability is detected prior to the glacial inception, as already observed at the end of Marine Isotopic Stage 11 in the same core. Second, the overall variance level is systematically higher during the last interglacial than during the current one, suggesting that a warmer East Antarctic climate may also be more variable.

Pol, K.; Masson-Delmotte, V.; Cattani, O.; Debret, M.; Falourd, S.; Jouzel, J.; Landais, A.; Minster, B.; Mudelsee, M.; Schulz, M.; Stenni, B.

2014-06-01

170

A Sub-Seasonal Trace Chemical Ice Core Record from Piz Zupo, Swiss Alps  

NASA Astrophysics Data System (ADS)

The NCCR Climate program `Varves, Ice cores, and Tree rings -- Archives with annual resolution (VITA)' aims to compare proxy climate records from trees, lakes, peat bogs and glaciers within the Engadine region, South-East Switzerland. The focus of this work is the ice core component of the VITA project. In March 2002 a 43 m ice core was extracted from the saddle between Piz Zupo and Piz Argient (46o22'6.9''N, 9o55'44.0''E, ˜3900 m asl). High-resolution sampling of the ice core was conducted (sample length 5-8~cm) and the samples analysed by ion chromatography for sodium, ammonium, potassium, magnesium, calcium, fluoride, acetate, formate, methanesulphonate, chloride, nitrate, sulphate and oxalate. Dating of the ice core was performed using the ammonium ion, which shows the most pronounced seasonal variations in Alpine ice cores with elevated levels during spring and summer. Counting these seasonal cycles, the Piz Zupo ice core spans an 11-year period from 1991-2001 with an uncertainty of ±1 year. Here we present a detailed examination of this record including (i) sub-seasonal variations of the chemical species, (ii) comparison of the chemical and meteorological records from the surrounding area, and (iii) identification of Saharan dust events and their spatial variability using various data sources.

Palmer, A. S.; Schwikowski, M.; Gaeggeler, H. W.

2003-04-01

171

Twentieth century sea-ice trends in the Ross Sea from a high-resolution, coastal ice-core record  

NASA Astrophysics Data System (ADS)

present the first proxy record of sea-ice area (SIA) in the Ross Sea, Antarctica, from a 130 year coastal ice-core record. High-resolution deuterium excess data show prevailing stable SIA from the 1880s until the 1950s, a 2-5% reduction from the mid-1950s to the early-1990s, and a 5% increase after 1993. Additional support for this reconstruction is derived from ice-core methanesulphonic acid concentrations and whaling records. While SIA has continued to decline around much of the West Antarctic coastline since the 1950s, concurrent with increasing air and ocean temperatures, the underlying trend is masked in the Ross Sea by a switch to positive SIA anomalies since the early-1990s. This increase is associated with a strengthening of southerly winds and the enhanced northward advection of sea ice.

Sinclair, Kate E.; Bertler, Nancy A. N.; Bowen, Melissa M.; Arrigo, Kevin R.

2014-05-01

172

Temperature Measurements Reveal Accretion Of Ice On Airfoils  

NASA Technical Reports Server (NTRS)

Method of detecting accretion of ice on airfoil based on measurement of difference between temperatures at icing and nonicing locations on airfoil. Release of latent heat of fusion gives rise to characteristic gradient of temperature. Temperatures and difference between them measured by use of contact sensors or remote sensor. Measurements used to trigger alarms and/or deicing equipment.

Hansman, Robert J., Jr.; Dershowitz, Adam Lee

1995-01-01

173

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

174

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

175

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

176

Volcanic Synchronization: Applications and potential for the WAIS Divide ice core  

NASA Astrophysics Data System (ADS)

We present a new, annually dated sulfur record from the WAIS Divide ice core in West Antarctica spanning most of the last 27,000 years, analyzed using high-resolution continuous flow analysis coupled to two mass spectrometers. The high dating accuracy, demonstrated through comparison to independent, annually dated ice core records from NorthGRIP and Law Dome, permitted use of this new ice core record as a reference volcano chronology for Antarctica. Using volcanic time markers, seven new sulfur records from low accumulation ice core sites in East Antarctica (Norwegian US Traverse) covering the last 250 to 2,000 years were synchronized to the WAIS Divide timescale, providing a understanding of the spatial pattern of past climate variability. Changes in past climate forcing, as indicated by ice core records of mineral dust, volcanic aerosols or black carbon - all measured conjointly at high resolution - can thus be addressed on a continental scale and contrasted to temperature histories from Antarctica. We further evaluate the potential of linking the current WAIS Divide timescale to ice core records in East Antarctica (e.g. EPICA Dome C, EPICA Dronning Maud Land, Talos Dome) which had been synchronized to each other using volcanic time markers during the last glacial period. Volcanic synchronization allows investigation of the relative timing of climate events (e.g. abrupt climate changes), with age uncertainties being independent from the uncertainties of the gas-age to ice-age difference inherent in using paleo-gas records for synchronization.

Sigl, M.; McConnell, J. R.; Maselli, O.; Pasteris, D.; Lawrence, R.; Isaksson, E. D.; Anschuetz, H.; Udisti, R.; Severi, M.; Fudge, T. J.

2012-12-01

177

Location of a new ice core site at Talos Dome (East Antarctica)  

Microsoft Academic Search

In the frame of glaciology and palaeoclimate research, Talos Dome (72°48lS; 159°06lE), an ice dome on the East Antarctic plateau, represents the new selected site for a new deep ice core drilling. The increasing interest in this re- gion is due to the fact that the ice accumulation is higher here than in other domes in East Antarctica. A new

Stefano Urbini; Lili Cafarella; Achille Zirizzotti; Cesidio Bianchi; Ignazio Tabacco; Massimo Frezzotti; Ardito Desio; S. Maria

2006-01-01

178

Climate Scientists Dig Deep Into Greenland's Ice  

NSDL National Science Digital Library

This short video, under 6 minutes, explores Greenland Ice Core data that that reveal rapid climate changes that have happened in the past. The video includes scientists discussing their research results and views of Ice core sampling.

179

Siple Dome shallow ice cores: a study in coastal dome microclimatology  

NASA Astrophysics Data System (ADS)

Ice cores at Siple Dome, West Antarctic receive the majority of their precipitation from Pacific Ocean moisture sources. Pacific climate patterns, particularly in response to the El Niño-Southern Oscillation, affect local temperature, atmospheric circulation, snow accumulation, and water isotope signals at Siple Dome. We examined borehole temperatures, accumulation, and water isotopes from a number of shallow ice cores recovered from a 60 km north-south transect of the Dome. The data (with coverage from 1920-1995) reveal a microclimate heavily influenced by ENSO and the location of the Amundsen Sea Low Pressure Area. The Dome Summit and Pacific Flank respond to La Niña conditions by warming, increased isotope ratios, higher deuterium excess, and increased snowfall. The Inland Flank responds to El Niño conditions and cold interior air masses by cooling, decreased isotope ratios, lower deuterium excess, and decreased snowfall. ENSO-type spectral signatures (2-7 yr) are present in all water isotope records, but are not similar in their power structures. A longer 300 yr wavelet analysis record from the Dome Summit shows a late 19th-century climate shift similar to that seen in South Pacific coral isotope records. Our analyses suggest that while an ENSO signal is evident at Siple Dome, the microclimate effect makes climate reconstruction problematic, a conclusion which should be considered at other West Antarctic coastal dome locations.

Jones, T. R.; White, J. W. C.; Popp, T.

2013-05-01

180

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

181

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

182

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

183

Simulating the temperature and precipitation signal in an Alpine ice core  

NASA Astrophysics Data System (ADS)

Accumulation and ?18O data from Alpine ice cores provide information on past temperature and precipitation. However, their correlation with seasonal or annual mean temperature and precipitation at nearby sites is often low. This is partly due to the irregular sampling of the atmosphere by the ice core (i.e. ice cores almost only record precipitation events and not dry periods) and the possible incongruity between annual layers and calendar years. Using daily meteorological data from a nearby station and reanalyses, we replicate the ice core from the Grenzgletscher (Switzerland, 4200 m a.s.l.) on a sample-by-sample basis by calculating precipitation-weighted temperature (PWT) over short intervals. Over the last 15 yr of the ice core record, accumulation and ?18O variations can be well reproduced on a sub-seasonal scale. This allows a wiggle-matching approach for defining quasi-annual layers, resulting in high correlations between measured quasi-annual ?18O and PWT. Further back in time, the agreement deteriorates. Nevertheless, we find significant correlations over the entire length of the record (1938-1993) of ice core ?18O with PWT, but not with annual mean temperature. This is due to the low correlations between PWT and annual mean temperature, a characteristic which in ERA-Interim reanalysis is also found for many other continental mid-to-high-latitude regions. The fact that meteorologically very different years can lead to similar combinations of PWT and accumulation poses limitations to the use of ?18O from Alpine ice cores for temperature reconstructions. Rather than for reconstructing annual mean temperature, ?18O from Alpine ice cores should be used to reconstruct PWT over quasi-annual periods. This variable is reproducible in reanalysis or climate model data and could thus be assimilated into conventional climate models.

Brönnimann, S.; Mariani, I.; Schwikowski, M.; Auchmann, R.; Eichler, A.

2013-08-01

184

Modeling production and climate-related impacts on 10Be concentration in ice cores  

Microsoft Academic Search

The connection between the production of the cosmogenic isotope 10Be and changes in heliomagnetic activity makes ice core 10Be an attractive proxy for studying changes in solar output. However, interpreting 10Be ice core records on centennial timescales is complicated by potential climate-related deposition changes that could obscure the 10Be production signal. By using the Goddard Institute for Space Studies ModelE

Christy V. Field; Gavin A. Schmidt; Dorothy Koch; Colette Salyk

2006-01-01

185

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

186

Two extraterrestrial dust horizons found in the Dome Fuji ice core, East Antarctica  

NASA Astrophysics Data System (ADS)

Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ˜ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 10 6 km 2. Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 10 9 kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-?m to ?m-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 10 9 kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere.

Misawa, Keiji; Kohno, Mika; Tomiyama, Takayuki; Noguchi, Takaaki; Nakamura, Tomoki; Nagao, Keisuke; Mikouchi, Takashi; Nishiizumi, Kunihiko

2010-01-01

187

Massilia yuzhufengensis sp. nov., isolated from an ice core.  

PubMed

A gram-negative, rod-shaped, aerobic, motile bacterium, strain Y1243-1(T), was isolated from an ice core drilled from Yuzhufeng Glacier, Tibetan Plateau, China. Cells had polar flagella. The novel strain shared 94.7-97.6?% 16S rRNA gene sequence similarity with the type strains of species of the genus Massilia. The novel isolate is thus classified in the genus Massilia. The major fatty acids of strain Y1243-1(T) were summed feature 3 (C16?:?1?7c and/or iso-C15?:?0 2-OH) (43.98?%), C16?:?0 (27.86?%), C10?:?0 3-OH (7.10?%), C18?:?0 (6.95?%) and C18?:?1?7c (5.01?%). The predominant isoprenoid quinone was Q-8. The DNA G+C content of strain Y1243-1(T) was 65.7 mol% (Tm). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol and diphosphatidylglycerol. A number of phenotypic characteristics distinguished the novel isolate from the type strains of recognized Massilia species. Furthermore, in DNA-DNA hybridization tests, strain Y1243-1(T) shared 45?% relatedness with its closest phylogenetic relative, Massilia consociata CCUG 58010(T). From the genotypic and phenotypic data, it is evident that strain Y1243-1(T) represents a novel species of the genus Massilia, for which the name Massilia yuzhufengensis sp. nov. is proposed. The type strain is Y1243-1(T) (?=?KACC 16569(T)?=?CGMCC 1.12041(T)). PMID:22798646

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

2013-04-01

188

The 800 year long ion record from the Lomonosovfonna (Svalbard) ice core  

Microsoft Academic Search

We present a high-resolution record of water-soluble ion chemistry from a 121 m ice core spanning about 800 years. The core is well dated to 2\\/3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1\\/3 of the core. This core suffers from modest seasonal melt, and so we present concentration data

Teija Kekonen; John Moore; Paavo Perämäki; Robert Mulvaney; Elisabeth Isaksson; Veijo Pohjola

2005-01-01

189

Annual accumulation for Greenland updated using ice core data developed during 2000-2006 and analysis of daily coastal data  

Microsoft Academic Search

An updated accumulation map was prepared using ice-core and snow-pit data from 250 historical locations on the ice sheet, plus 39 new ice cores strategically placed to fill gaps in the previous accumulation map. In addition data from 26 coastal weather stations were used in the analysis. Daily coastal data were analyzed, gaps filled using interpolation from nearby stations, and

D. Shen; R. Bales; J. McConnell; J. Burkhart; Q. Guo

2007-01-01

190

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

191

Ice-Rafted Detritus as a Climatic Indicator in Antarctic Deep-Sea Cores.  

PubMed

Ice-rafted detritus is readily identified in sediment cores raised from the deep ocean floor around Antarctica. A few cores have reached a depth below which no ice-rafted material is found. This depth is interpreted as indicating the establishment of earliest Pleistocene glaciation in the Southern Hemisphere. It is just below a depth where there is a change in assemblages of Radiolaria which Hays associates with the Pliocene-Pleistocene boundary. The presence of ice-rafted material throughout the upper zone in cores taken south of the Polar Front indicates continuity of glaciation in Antarctica. Further north, near 45 degrees S in the Argentine Basin, zonation of the ice-rafted detritus can be used to delineate glacial stages of the Pleistocene. PMID:17841978

Conolly, J R; Ewing, M

1965-12-31

192

Stratigraphic analysis of an ice core from the Prince of Wales Icefield, Ellesmere Island, Arctic Canada, using digital image analysis: High-resolution density, past summer warmth reconstruction, and melt effect on ice core solid conductivity  

Microsoft Academic Search

High-resolution (1 mm) stratigraphic information was derived from digital image analysis of an ice core from the Prince of Wales (POW) Icefield, Central Ellesmere Island, Canada. Following careful image processing, a profile of ice core transmitted light was derived from the greyscale images and used to reconstruct high-resolution density variations for the unfractured sections of the core. Images were further

Christophe Kinnard; Roy M. Koerner; Christian M. Zdanowicz; David A. Fisher; Jiancheng Zheng; Martin J. Sharp; Lindsey Nicholson; Bernard Lauriol

2008-01-01

193

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

194

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

195

Anthropogenic emissions and combustion products recorded in a Colle Gnifetti ice core  

NASA Astrophysics Data System (ADS)

Ice cores provide direct and highly resolved records of atmospheric parameters that record both climate signals and forcing factors. European Alpine glaciers are located near densely populated and industrialized areas and provide excellent archives of past air pollution. Ice cores to bedrock on Colle Gnifetti, Monte Rosa (45°55'51''N, 07°52'34''E; 4450 m a.s.l.) permit centennial to millennial reconstruction of past regional climate, while snow pit and shallow core studies from the same site allow multiple parameter reconstructions of anthropogenic emissions. Air pollution includes fossil fuel and biomass burning products that influence regional smog and contain trace elements hazardous to human health. Here, we examine a high-resolution suite of anthropogenic and natural emissions (black carbon, levoglucosan, trace elements, heavy metals) and climate proxies (major ions and stable isotopes) in a 12 m Colle Gnifetti ice core to determine seasonal changes in anthropogenic emissions and their interaction with climate parameters. This is the first study to compare black carbon (a fossil fuel and biomass combustion tracer) with levoglucosan (a fire activity biomarker) in a European ice core. The combination of these two proxies can determine changing combustion product sources through time. Our results demonstrate that anthropogenic emissions influence the summer aerosol flux while crustal sources dominate the winter aerosol flux. These ice core chemical data are consistent with observational data and boundary layer dynamics that transport pollutants concentrated in the Po Valley and similar industrial lowland regions to glacier surfaces during the summer.

Gabrieli, J.; Kehrwald, N. M.; Zennaro, P.; Lim, S.; Laj, P.; Barbante, C.

2012-12-01

196

Rapid fluctuations of West Antarctic Ice Sheet during the last deglaciation recorded in the sediment cores from off the Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

Far-field sea-level observations and glacio-hydro-isostatic analyses have indicated that considerable amount of ice was stored in Antarctica during the Last Glacial Maximum (LGM), and has been melted during the last 20 ka (Nakada and Lambeck, 1989; Yokoyama et al., 2001). Particular interest for our study is to reveal behavior of the ice sheet during the 2 major rapid ice melting events during the last deglaciation. One is the post-LGM MWP (Melt Water Pulse) at 19 ka (Yokoyama et al., 2000: Clark et al., 2004) and the other is the MWP1a event (Fairbanks, 1989; Bard et al., 1990). Recent observations and modeling results show that Antarctic ice sheet was melted during the MWP1a (Clark et al., 1995; Bassett, et al., 2005) yet the timing and magnitude of waxing and waning of the Antarctic Ice Sheet is still under debate. Direct evidence of ice melting events in the past could be preserved in the sediment cores as the peaks of the IRD (ice rafted detritus) and we have investigated 11 deep sea cores retrieved around the Antarctic Peninsula. Sediment composition reflects their origin and core top radiocarbon results further confirm the source of the icebergs. Radiocarbon dating on sediments together with the assemblage of radiolaria was used to reconstruct the chronology in the cores. We detected 2 major peaks of the IRD respectively at LGM and about 14 ka among the cores. The first peak is corresponding to the expansion of the ice margin around the Antarctic Peninsula during the LGM whereas the latter may be corresponding to the timing of the MWP1a. Considering our results as well as other previous studies suggested that the Antarctic ice sheet, at least in this region, contributed the rapid rise in global sea-level known as MWP1a.

Yokoyama, Y.; Noumi, M.; Miura, H.; Ohkouchi, N.; Matsuzaki, H.

2005-12-01

197

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

198

Tephrochronological Investigation of Mid- to Late Holocene Acid Signals in Greenland Ice Cores  

NASA Astrophysics Data System (ADS)

Volcanic acidity peaks provide critical reference horizons that enable the linkage of multiple ice cores in Greenland and have aided the construction of the Greenland Ice Core Chronology 2005 (GICC05). The source eruption of these acid layers can only be established though geochemical characterization of associated tephras, a process which then enables the correlation of all sedimentary records containing the same tephra at fixed points in time and, in the case of prehistoric eruptions, a refinement of the age of the volcanic event. Here we present results of a study that examined sub-sections of the Dye-3, GRIP and NGRIP ice cores, the main objectives of which were to isolate tephras in order to: 1) confirm the robustness of the ice core chronology by locating tephras from Katmai AD 1912, Laki AD 1783, Öraefajökull AD 1362, Hekla AD 1104, Eldgjá ~AD 930s, and Vesuvius AD 79; 2) use the ice core chronology to ascertain precise ages for the prehistoric eruptions of Thera ~17th century BC and Hekla 4 ~2300 BC; 3) determine the source of volcanic signals at AD 1259 and ~AD 536, both of which have counterparts in Antarctic ice; and 4) compare the relationship of tephra layers and other volcanic products in the ice. Major element geochemistry of isolated tephras has been characterised using single-shard EPMA. We report the discovery of the Katmai and Öraefajökull tephras in the NGRIP and GRIP cores respectively, confirming the annually-resolved ice core chronology for the last 700 years. The Katmai tephra precedes the peak levels in ECM, Cl- and SO4-- associated with this eruption, with sulphates peaking last. The Öraefajökull tephra is not accompanied by any notable acid signal. Although the remaining targeted events were not found, we identified tephras from 14 other eruptions, including the so-called "AD860B" tephra in NGRIP, a widespread isochron found across NW Europe to which a GICC05 date of AD 847 can now be assigned. Three tephras were present in NGRIP in ice dating to ~1644/1643 BC, ~1641/1639 BC and ~1629/1628 BC, the first two of which are closely comparable in their major element composition with published data from an Aniakchak eruption of similar date. Only the 1641/1639 BC tephra corresponds directly with a rise in ECM and sulphate. The source of the remaining tephras has not yet been established. We examine the implications of our findings for the understanding of volcanic records in ice cores.

Plunkett, G.; Coulter, S.; Pilcher, J. R.; Hall, V. A.; Baillie, M. G.; Steffensen, J.; Vinther, B.; Clausen, H. B.; Johnsen, S. J.

2011-12-01

199

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.

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

2013-01-01

200

Millennial and sub-millennial scale climatic variability over Marine Isotopic Stage 5: insights from polar ice cores (Invited)  

NASA Astrophysics Data System (ADS)

The millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28-60 thousand of years before present, hereafter ka) and characterized by short and frequent Dansgaard-Oeschger (DO) events in Greenland ice cores. Recent and new results obtained on Antarctic (EPICA Dronning Maud Land and EPICA Dome C) and Greenlandic (NorthGRIP) ice cores now allow to precisely describe the rapid variations of temperature at both poles during MIS 5 (73.5-123 ka), a time period spanning the last glacial inception and corresponding to relatively high sea levels. By contrast with the “classical” DO events of MIS 3, we evidence the peculiarities of the MIS 5 DO events. In particular, a sub-millennial scale climatic variability is highlighted over these long MIS 5 DO events, depicted by (i) short-lived and abrupt warming events preceding some Greenland InterStadial (GIS) (precursor-type events) and (ii) abrupt warming events at the end of some GIS (rebound-type events). The occurrence of these secondary events is suggested to be driven by the northern hemisphere summertime insolation at 65°N and influenced by the ice sheet extent. Thanks to a recent timescale synchronisation between Antarctic and Greenland records over MIS 5, the bipolar sequence of climatic events can be established at millennial to sub-millennial timescale. This reveals that the see-saw behavior identified during the glacial MIS 3 is also at play over the warm MIS 5 even at sub-millennial timescales. Finally, we make a focus on the first DO event occurring during the last glacial inception (DO 25). A multi-parametric study performed on the NorthGRIP ice core suggests that this first rapid event is a regional feature likely resulting from the interaction between the orbitally driven sea-ice expansion and the north Atlantic circulation.

Capron, E.; Landais, A.; Chappellaz, J.; Schilt, A.; Buiron, D.; Dahl-Jensen, D.; Fischer, H.; Johnsen, S. J.; Jouzel, J.; Lemieux-Dudon, B.; Leuenberger, M.; Masson-Delmotte, V.; Meyer, H.; Oerter, H.; Stenni, B.; Stocker, T. F.

2010-12-01

201

Ice-core Evidence of Holocene Climatic and Environmental Variations Across Tibet  

NASA Astrophysics Data System (ADS)

Since 1984 The Ohio State University, in collaboration with the Lanzhou Institute of Glaciology and Geocryology and more recently the Institute for Tibetan Plateau Research, has recovered ice cores from a number of ice fields across Tibet. The Guliya ice cap is located in the western Kunlun Mountains while the Dasuopu and Naimona`nyi ice fields are located in the Himalayas to the south. The Puruogangri ice cap is in the Tanggula Mountains that are considered a boundary between the monsoon-dominated southern region and the continental-dominated northern region. All these ice core records are complete, except Naimona`nyi, which was drilled in late 2006. Dasuopu has a high annual accumulation rate (~1 meter water equivalent per year, or w.e. a-1) along with low soluble and insoluble aerosol content and a well-defined seasonal stratigraphy. The Guliya and Puruogangri cores are from more arid regions (0.20 - 0.40 m w.e. a-1), contain high concentrations of mineral dust and ionic species and a less distinct seasonal stratigraphy. The climate of the Tibetan Plateau also varies from west to east. The Guliya ice cap provided the longest ice core record recovered to date, extending through the last glacial cycle. This likely reflects the dominance of the continental westerlies in northwestern Tibet. On the other hand, the Puruogangri, Dasuopu and Naimona`nyi ice core records appear to be much younger and those ice fields may have formed during the Holocene "Optimum" when Northern Hemisphere insolation was high and forced a more active Indian/Asian monsoon circulation. Climate models indicate that sections of High Asia were much warmer in the early Holocene than in the Late Holocene; thus, it is possible that these glaciers did not exist prior to that time. Regional and local variations in climate will be presented, using a combination of stable isotopes, soluble and insoluble aerosol concentrations, and physical stratigraphy. Special emphasis is placed on the last 2000 years when the dating control is more robust. The Holocene records from Dasuopu, Puruogangri and Guliya reflect regional variations in climate, but also display large-scale similarities over decadal and centennial time scales. For example, although the warming trend of the twentieth century is present in all the records, it is more pronounced in the Himalayan ice cores than in those from the Western Kunlun.

Thompson, L. G.; Davis, M. E.; Yao, T.; Kehrwald, N.; Lin, P.

2007-12-01

202

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

203

High-resolution, continuous method for measurement of acidity in ice cores.  

PubMed

The acid content of ice core samples provides information regarding the history of volcanism, biogenic activity, windblown dust, forest fires, and pollution-induced acid rain. A continuous ice core analysis allows for collection of high-resolution data in a very efficient manner, but this technique has not been readily applied to the measurement of pH and acidity in ice cores. The difficulty arises because the sample is highly undersaturated with respect to carbon dioxide (CO(2)) immediately after melting, making it difficult to maintain stable concentrations of dissolved carbon dioxide and carbonic acid (H(2)CO(3)). Here, we present a solution to this problem in the form of a small flow-through bubbling chamber that is supplied with a known concentration of CO(2). The bubbling action allows for quick equilibration while the small size of the chamber limits sample mixing in order to maintain high resolution. Thorough error analysis provides a measurement uncertainty of ±0.20 ?M or ±5% of the acidity value, whichever is greater, and the T95 signal response time is determined to be 1.25 min. The performance of the technique is further evaluated with data from a 63-year ice core from northwest Greenland for which all major ion species were also measured. The measured acidity closely matches the acidity derived from a charge balance calculation, indicating that all of the analytes were measured accurately. The performance specifications that we provide are applicable to ice cores with low concentrations of alkaline dust (<500 ppb), which includes the vast majority of ice cores that are collected. To date, the method has not been evaluated with samples containing high alkaline dust concentrations, such as Greenland cores from the last glacial period, where measurement could be made difficult by memory effects as particles coat the internal surfaces of the sample stream. PMID:22148513

Pasteris, Daniel R; McConnell, Joseph R; Edwards, Ross

2012-02-01

204

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

NASA Astrophysics Data System (ADS)

The Toba eruption that occurred some 74 kyr 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 from Malaysia 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 kyr 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. Furthermore, our bipolar match provides a way to place paleo-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.

2012-11-01

205

Sulphate profile in EPICA-DML ice core (Kohnen Station East Antarctica) by Fast Ion Chromatography.  

NASA Astrophysics Data System (ADS)

Kohnen Station (Dronning Maud Land - Atlantic sector of Antarctica) is one of the two drilling sites, the other being located at Dome C, chosen in the framework of EPICA project. Unlike Dome C ice core (EDC), where the low accumulation rate allowed recovering climatic and environmental data covering more than 800.000 years, the Kohnen Station ice core (EDML) is expected to provide paleo-data related to the last two glacial/interglacial cycles, due to the higher accumulation rate. On the other hand, the thicker annual accumulation rate grants a stratigraphy with higher temporal detail, providing more accurate information about fast climatic variations super-imposed to the major cycles. Moreover, EDML is expected to be influenced by Atlantic Ocean, then potentially able to give information about variations in the North Atlantic Deep Water and its relationship with global climate change. In order to temporally set the EDML paleo-records and allow a reliable synchronization with paleo-data memorised in Greenland and Antarctica ice cores, an accurate dating of the ice core is fundamental. The high accumulation rate and relative closeness to the sea drives toward the use of marine biogenic substances, irreversibly fixed in the snow layers as seasonal markers. Non-sea-salt sulphate coming from atmospheric oxidation of dimethylsulphide emitted by phytoplanktonic activity seems to be useful to this purpose. Since at Kohnen Station nss-sulphate is the dominant contribute to the sulphate budget, high-resolution sulphate profile could be used for a stratigraphic dating (summer maxima). An improvement of the FIC method, successfully used for in field measurement on EDC ice core, was performed. The method was applied to ice core processing at Bremerhaven (D) in June 2002 (113 to 449 m depth), giving a continuous sulphate record at 1.0 cm ice resolution, with a melting rate of 4.0 cm/min. The measured standard deviation is lower than 5.0 % and the detection limit is 4.0 ug/l. The data elaboration is in progress but preliminary results related to selected ice core sections seem to confirm a seasonal trend able to allow a reliable annual layer counting. Abrupt sulphate peaks, related to volcanic eruptions, superimposed to the seasonal trend, provide depth horizons for an absolute dating by knowing the event date or by comparing the same volcanic signatures recorded in already dated ice cores.

Severi, M.; Becagli, S.; Benassai, S.; Castellano, E.; Migliori, A.; Udisti, R.

2003-04-01

206

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

NASA Astrophysics Data System (ADS)

Glaciochemical records recovered from an 80.4 m ice core in the East Rongbuk (ER) Glacier (elevation: 6450 m) 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 (SO 42-, Mg 2+, Ca 2+, Na +, Cl -, NH 4+, K +, and NO 3-) time-series reveals inter-species relations and common structure within the ER glaciochemical data. The first two EOF series (EOF1-ions and EOF2-ions) are compared with instrumental data of sea level pressure (SLP) to demonstrate that the EOF-ions series display strong connections to winter (January) and summer (July) SLP over the Mongolian region. The positive relationship between EOF1-ions and the Mongolian High (MongHi) series suggests that enhanced winter MongHi strengthens the transport of dust aerosols southward from arid regions over central Asia to Mt. Everest. The close correspondence between EOF2-ions and the summer Mongolian Low (MongLow) indicates that the deeper MongLow, which is related to the stronger Indian Monsoon, contributes to a decrease in summer dust aerosols. Therefore, the ER ice core record comprises two assemblages of crustal species, each transported from different source regions during different seasons. EOF1-ions represents the majority of the crustal species and is related to winter atmospheric circulation patterns. These species are mainly transported from arid regions of central Asia during the winter dry season. EOF2-ions represents crustal species transported by summer atmospheric circulation from local/regional sources in the northern and southern Himalayas.

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

207

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

208

Application of Ground Penetrating Radar and Geodetics to the Selection of an Ice Core Drill Site on the Kahiltna Glacier of Mount McKinley, Alaska  

NASA Astrophysics Data System (ADS)

Interest in global climate change continues to fuel the search for more sources of quality paleo-climate information in hopes of accurately reconstructing and predicting past and future climates respectively. Ice core records from the Arctic and Antarctic have provided some of the most reliable data for paleo-climate modeling however, the validity of these data and models rely heavily on a number of assumptions regarding ice stratigraphy and glacier structure. Unfortunately, many Arctic valley glaciers are unsuitable for ice core drilling because they exhibit significant melt, ice flow, deformation, and dipping stratigraphy due to their thermal regime and confined flow boundary conditions. Other valley glaciers do exhibit stable accumulation basins with conditions suitable for ice core drilling, however these sites need to be validated through a variety of geophysical and glacio-chemical techniques. A thorough assessment of local meteorological data, snow chemistry, ice flow dynamics, glacier structure, and stratigraphy prior to ice core drilling in a valley glacier is important to determine if the site meets the proper criteria. A glacio-chemical and geophysical reconnaissance of the Kahiltna Glacier on Mount McKinley, Alaska, was performed in 2008 and 2009 to search for an appropriate deep ice core drill location in Central Alaska. Surface velocity measurements from a rapid static GPS survey were coupled with approximately 10 km of 100 MHz GPR profiles to determine surface and subsurface glacier structure and dynamics at a promising drill site near Kahiltna Pass (3078 masl). The GPR profiles reveal a pocket of ice east of Kahiltna Pass with horizontal stratigraphy and 300 meters of ice; based on local accumulation rates and ice flow modeling, this depth of ice likely represents 500 +/- years of climate record. Preliminary geodetic data suggest low velocities (less the 0.1 m/day) at the potential drill site and velocities up to 0.45 m/day 7 km down slope of the drill site. These velocities are comparable to previous velocity measurements recorded on the Kahiltna Glacier. Stratigtraphic complexities do exist in the upper Kahiltna Glacier region; interpretation of these features and their relevance to local ice flow and drill site selection will be discussed.

Campbell, S. W.; Kreutz, K. J.; Wake, C. P.; Osterberg, E. C.; Arcone, S. A.; Volkening, K.; Lurie, M.

2009-12-01

209

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

210

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.

1998-05-01

211

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

212

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

213

Automated ice-core layer-counting with strong univariate signals  

NASA Astrophysics Data System (ADS)

We present an automated method for determining the annual layer chronology of an ice-core with a strong annual signal, utilising the hydrogen peroxide record from an Antarctic Peninsula ice-core as a test signal on which to count annual cycles. The signal is de-trended and normalised before being split into sections with a deterministic cycle count and those that need more attention. Possible reconstructions for the uncertain sections are determined and a method for assigning probability measures to each reconstruction is discussed. These methods could be adapted for use on much longer datasets, thereby reducing manual effort and providing a robust methodology.

Wheatley, J. J.; Blackwell, P. G.; Abram, N. J.; McConnell, J. R.; Thomas, E. R.; Wolff, E. W.

2012-07-01

214

Global ice-core research: Understanding and applying environmental records of the past  

USGS Publications Warehouse

Environmental changes are of major concern at low- or mid-latitude regions of our Earth simply because this is where 80 to 90 percent of the world’s human population live. Ice cores collected from isolated polar regions are, at best, proxy indicators of low- and mid-latitude environmental changes. Because polar icecore research is limiting in this sense, ice cores from low- and mid-latitude glaciers are being used to study past environmental changes in order to better understand and predict future environmental changes that may affect the populated regions of the world.

Cecil, L. DeWayne; Green, Jaromy R.; Naftz, David L.

2000-01-01

215

Ice-core record of oceanic emissions of dimethylsulphide during the last climate cycle  

NASA Astrophysics Data System (ADS)

Depth profiles along the Vostok ice core of methanesulfonate and non-seasalt sulfate are presented which provide the first historical record of biogenic sulfur emissions from the Southern Hemisphere oceans over a complete glacial-interglacial cycle. Those measurements confirm and extend some previous observations made on a very limited data set from the Dome C ice core in Antarctica, which indicated increased oceanic emissions of dimethylsulfide during the later stages of the glacial period, compared with the present day. The observed glacial-interglacial variations in methanesulfonate and non-seasalt sulfate confirm that the ocean-atmosphere sulfur cycle is extremely sensitive to climate change.

Legrand, M.; Feniet-Saigne, C.; Saltzman, E. S.; Germain, C.; Barkov, N. I.

1991-03-01

216

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

217

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

218

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

219

Automated ice-core layer-counting with strong univariate signals  

NASA Astrophysics Data System (ADS)

We present an automated process for determining the annual layer chronology of an ice-core with a strong annual signal, utilising the hydrogen peroxide record from an Antarctic Peninsula ice-core as a test signal on which to count annual cycles and explain the methods. The signal is de-trended and normalised before being split into sections with a deterministic cycle count and those that need more attention. Possible reconstructions for the uncertain sections are determined which could be used as a visual aid for manual counting, and a simple method for assigning probability measures to each reconstruction is discussed. The robustness of this process is explored by applying it to versions of two different chemistry signals from the same stretch of the NGRIP (North Greenland Ice Core Project) ice-core, which shows more variation in annual layer thickness, with and without thinning to mimic poorer quality data. An adapted version of these methods is applied to the more challenging non-sea-salt sulphur signal from the same Antarctic Peninsula core from which the hydrogen peroxide signal was taken. These methods could readily be adapted for use on much longer datasets, thereby reducing manual effort and providing a robust automated layer-counting methodology.

Wheatley, J. J.; Blackwell, P. G.; Abram, N. J.; McConnell, J. R.; Thomas, E. R.; Wolff, E. W.

2012-11-01

220

Nitrate and chloride in Antarctic ice cores - postdepositional effects and the preservation of atmospheric signals (Invited)  

NASA Astrophysics Data System (ADS)

Continuous nitrate and chloride measurements have been made from an array of ice cores located in interior Dronning Maud Land that cover the last 2000 years. The average snow accumulation rates at the ice core sites range from 2.7 to 10 cm weq yr-1, which has enabled the study of how accumulation rate affects the preservation and diffusion of nitrate and chloride in the snow. High-resolution dating of the ice cores by tie-point matching with the WAIS Divide ice core has allowed the effects of temporal changes in accumulation rate to also be observed. Results show a strong linear dependence of nitrate concentration on site-average accumulation rate, suggesting that fresh snow concentrations and reemission rates of nitrate from the snowpack are homogenous across the study area. Bulk chloride to sodium ratios over scales greater than 1 m are close to bulk sea salt composition at all of the sites, suggesting that little net gain or loss of volatile chloride has occurred. However, the chloride signal is heavily diffused relative to sodium and the extent of diffusion does not increase with depth in the ice cores, suggesting that it is a near-surface phenomenon. Possible mechanisms behind the observed chloride diffusion pattern will be discussed. Lastly, a sustained decline in nitrate concentration occurred during the Little Ice Age (LIA, 1500-1900 C.E.), but the high-resolution snow accumulation records show that it is not caused by a decrease in accumulation rate during that time. The nitrate record is highly correlated with published methane isotope data from Antarctica (?13CH4), suggesting that the decline during the LIA was caused by a decrease in a biomass burning nitrate source. Average nitrate concentration versus site-average inverse accumulation rate Composite time series of nitrate (thick black line), ?13CH4 (thin red line with diamonds), and black carbon (dashed black line).

Pasteris, D.; McConnell, J. R.; Edwards, R.; Isaksson, E. D.; Albert, M. R.

2013-12-01

221

Isotope thermometry in melt-affected ice cores  

Microsoft Academic Search

A statistically significant relationship is observed between stable water isotopes (delta18O) 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

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

2011-01-01

222

The accumulations of solids beyond the primordial Jupiter and Saturn to form the ice-giant cores  

NASA Astrophysics Data System (ADS)

We study the dynamics of small bodies in the dissipating solar nebula during the era when Jupiter and Saturn were already formed and occupied mutual 3:2 mean-motion resonance. The study is done in the course to reveal the eventual sites of accumulation of material in the proto-planetary disk. Such an accumulation could significantly enhance the formation of the ice-giant cores. Actually, we found that the resonant action of Jupiter and Saturn in combination with the gas drag of the dissipating solar nebula may create two maxima in the distribution of solid material beyond Saturn, if the prevailing amount of the solids is concentrated in kilometer-sized or smaller bodies. Specifically, the distribution is then peaked at about ˜ 11 and ˜ 16.5 AU. A higher amount of solid material is in smaller bodies, the higher peaks occur. We suspect that the two maxima correspond to just two existing ice giants, Uranus and Neptune.

Jakubík, M.; Neslušan, L.

2014-04-01

223

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

224

Climate Variability in West Antarctica Derived from Marine Aerosol Species from ITASE Firn/Ice Cores  

NASA Astrophysics Data System (ADS)

Marine aerosol species (sodium, chloride, magnesium, sulfate) from 13 high-resolution ice cores covering the last approximately 200 years from the Pine Island-Thwaites and Ross drainage systems and the South Pole are used to examine climate variability in West Antarctica. The large-scale spatial distribution of the ice cores improves characterization of the source regions and pathways of marine aerosols into West Antarctica. The Ross Sea is the dominant source region for marine aerosols in the study area, and the dominant pathway is across the Ross Ice Shelf. Factors contributing to the amount of marine aerosols transported inland are strength and positioning of low pressure systems, sea-ice extent, and wind strength. Associations of the sodium time-series with sea level pressure are investigated using the National Centers for Environmental Prediction (NCEP) data reanalysis, the Southern Oscillation Index (SOI), and Trans-Polar Index (TPI). Sea-ice associations are explored by correlating sea-ice extent with the marine aerosol time-series, and wind strength is investigated using a circumpolar vortex index and the NCEP meridional and zonal wind fields. The associations demonstrate that West Antarctic climate is extremely dynamic, with regional differences in the mechanisms driving marine aerosol variability.

Kaspari, S. D.; Mayewski, P. A.; Dixon, D. A.; Sneed, S. B.

2003-12-01

225

Bed topography under Greenland outlet glaciers revealed by Operation IceBridge data and mass conservation  

NASA Astrophysics Data System (ADS)

Detailed maps of bed elevation and ice thickness are essential to many glaciological applications, including ice sheet numerical models. These maps are typically obtained using airborne radar-sounding profiler data interpolated onto regular grids using geostatistical techniques, such as kriging. While this approach provides continuous maps of bedrock elevation, it generates products that are not consistent with ice flow dynamics and are impractical for high-resolution ice flow simulations. Here, we first analyze radar-sounding data from a dense survey of Russell Glacier, in central-west Greenland, collected in 2010 and 2011 by NASA's Operation IceBridge. We compare gridded maps of bed elevation obtained using (1) radar tomography, (2) ordinary kriging and (3) mass conversation. Radar tomography eliminates radar-sounding profiler errors caused by off-nadir bed reflections to yield reference bed elevations. Ordinary kriging yields a standard error of 50 m at 500 m resolution, but with model artifacts in between tracks and flux divergence errors larger than 200 m/yr, which confound ice sheet flow models. Mass conservation optimally combines radar-sounding profiler data with independently gridded ice velocity data to lower the standard error to 30 m and flux divergence errors smaller than 1 m/yr. More importantly, mass conservation uniquely reveals complex structural features in bed elevation, e.g. valleys, ridges, bumps and hollows, that play a central role in channelizing ice flow toward the ice sheet margin. We then apply this technique to other outlet glaciers along the west coast of Greenland. The application of the mass conservation method to the entire ice sheet periphery, combined with radar tomography, promises to be transformative in our knowledge of basal topography in coastal Greenland, especially for the modeling of its outlet glaciers. This work was performed at the University of California Irvine and the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration, Cryospheric Sciences Program, grant NNX12AB86G.ed topography (m) of Russell Glacier inferred using the mass conservation method at 400 m resolution. The dashed white line defines the limits of the model domain. NASA Operation IceBridge (OIB) flight tracks are indicated as lines. Surface elevation is from Howat et al. 2012 (in prep.), including on ice-free zone. Note the agreement between ice-free and ice-covered elevations.

Morlighem, M.; Rignot, E. J.; Mouginot, J.; Seroussi, H. L.; Larour, E. Y.

2012-12-01

226

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

NASA Astrophysics Data System (ADS)

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

227

Greenland ice reveals imprint of the Early Cenozoic passage of the Iceland mantle plume  

NASA Astrophysics Data System (ADS)

Modelling and observation of ice sheet basal conditions suggests that elevated values of geothermal heat flow (GHF) result in enhanced basal melting. For the Greenland Ice Sheet (GIS), radar soundings and deep ice core measurements indicate unexpectedly high local values of GHF in areas where thick and stable Early Proterozoic lithosphere suggests they should be low. Rapid basal ice melt and accelerated ice flow, linked to abnormal GHF, indicate that regional heat flow patterns strongly influence the present-day thermodynamic state of the GIS and may affect its evolution in the future. Using a coupled model of climate-driven GIS and lithosphere, constrained by a wide range of interdisciplinary data, we detect a laterally continuous west-to-east area of high GHF in central-northern Greenland. The area of elevated heat flow closely coincides with a west-to-east negative anomaly in seismic velocity, which recent high-resolution tomography models tie to the present-day location of the Iceland mantle plume. Plate paleoreconstructions and analysis of magmatism in eastern and western Greenland suggest passage of the Greenland lithosphere over a mantle plume between around 80 and 35 Ma. Independent evidence under the GIS for magmatism along the putative mantle plume track comes from local gravity anomalies, igneous rock fragments recovered from the bedrock beneath the deep ice core GISP2, and radar sounding evidence of a caldera-like bedrock structure under the central GIS. We argue that long-lived, non-stationary effects of the mantle plume still affect the thermal state of the present-day Greenland lithosphere and are the origin of rapid basal ice melting over vast areas of central and northern Greenland.

Rogozhina, I.; Petrunin, A. G.; Vaughan, A. P.; Kaban, M. K.; Mulvaney, R.; Steinberger, B. M.; Koulakov, I.; Thomas, M.; Johnson, J. V.

2013-12-01

228

Geomagnetic paleointensity and environmental record from Labrador Sea core MD95-2024: global marine sediment and ice core chronostratigraphy for the last 110 kyr  

Microsoft Academic Search

Piston core MD95-2024 from the Labrador Rise provides a continuous record of rapidly deposited detrital layers denoting Laurentide ice sheet (LIS) instability. The core also provides a high-resolution record of geomagnetic paleointensity, that is consistent with, but at higher temporal resolution than previous Labrador Sea records. Correlation to the Greenland Summit ice cores (GRIP\\/GISP2) is achieved by assuming that Labrador

J. S. Stoner; J. E. T. Channell; C. Hillaire-Marcel; C. Kissel

2000-01-01

229

Ice core record of the C-13\\/C-12 ratio of atmospheric CO2 in the past two centuries  

Microsoft Academic Search

CO2 released into the atmosphere by human activity is depleted in C-13 relative to C-12. The delta C-13 of CO2 separated from air trapped in bubbles in ice samples from an ice core taken at Siple Station in Antarctica has been measured. The isotopic results, together with the CO2 record from the same ice core, yield information on the sources

H. Friedli; H. Loetscher; H. Oeschger; U. Siegenthaler; B. Stauffer

1986-01-01

230

The pH value and electrical conductivity of atmospheric environment from ice cores in the Tianshan Mountains  

Microsoft Academic Search

Electrical Conductivity Measurement (ECM) from ice core is a representative index for atmospheric environmental change. The\\u000a pH value and ECM from three shallow ice cores (each 3.85 m, 231 ice samples total) on Glacier No.1 at the headwater of Urumqi\\u000a River, Glacier No.48 in Kuitun area, and Miaoergou Glacier in Hami area in the eastern Tianshan Mountains, western China,\\u000a were

Zhiwen Dong; Mingjun Zhang; Zhongqin Li; Feiteng Wang; Wenbin Wang

2009-01-01

231

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

232

Warm climate isotopic simulations: what do we learn about interglacial signals in Greenland ice cores?  

NASA Astrophysics Data System (ADS)

Measurements of Last Interglacial stable water isotopes in ice cores show that central Greenland ?18O increased by at least 3‰ compared to present day. Attempting to quantify the Greenland interglacial temperature change from these ice core measurements rests on our ability to interpret the stable water isotope content of Greenland snow. Current orbitally driven interglacial simulations do not show ?18O or temperature rises of the correct magnitude, leading to difficulty in using only these experiments to inform our understanding of higher interglacial ?18O. Here, analysis of greenhouse gas warmed simulations from two isotope-enabled general circulation models, in conjunction with a set of Last Interglacial sea surface observations, indicates a possible explanation for the interglacial ?18O rise. A reduction in the winter time sea ice concentration around the northern half of Greenland, together with an increase in sea surface temperatures over the same region, is found to be sufficient to drive a >3‰ interglacial enrichment in central Greenland snow. Warm climate ?18O and ?D in precipitation falling on Greenland are shown to be strongly influenced by local sea surface condition changes: local sea surface warming and a shrunken sea ice extent increase the proportion of water vapour from local (isotopically enriched) sources, compared to that from distal (isotopically depleted) sources. Precipitation intermittency changes, under warmer conditions, leads to geographical variability in the ?18O against temperature gradients across Greenland. Little sea surface warming around the northern areas of Greenland leads to low ?18O against temperature gradients (0.1-0.3‰ per °C), whilst large sea surface warmings in these regions leads to higher gradients (0.3-0.7‰ per °C). These gradients imply a wide possible range of present day to interglacial temperature increases (4 to >10 °C). Thus, we find that uncertainty about local interglacial sea surface conditions, rather than precipitation intermittency changes, may lead to the largest uncertainties in interpreting temperature from Greenland ice cores. We find that interglacial sea surface change observational records are currently insufficient to enable discrimination between these different ?18O against temperature gradients. In conclusion, further information on interglacial sea surface temperatures and sea ice changes around northern Greenland should indicate whether +5 °C during the Last Interglacial is sufficient to drive the observed ice core ?18O increase, or whether a larger temperature increases or ice sheet changes are also required to explain the ice core observations.

Sime, Louise C.; Risi, Camille; Tindall, Julia C.; Sjolte, Jesper; Wolff, Eric W.; Masson-Delmotte, Valérie; Capron, Emilie

2013-05-01

233

Extreme accumulation on Patagonian ice fields revealed by high-resolution regional climate modeling  

NASA Astrophysics Data System (ADS)

Gravimetric observations and differential DEM's indicate that the Patagonian ice fields are currently thinning and retreating. Little is known, however, on the mechanisms that drive this ice mass loss. In particular, surface mass balance (SMB) of the ice fields is poorly constrained, because the wet southern Andes climate complicates performing in-situ measurements. Instead, regional climate modeling may provide the first, independent estimate of the ice field's SMB. Here we present results from a high-resolution (5.5 km) regional atmospheric climate and multi-layer snow model (RACMO2), forced by ERA-Interim atmospheric and ocean surface fields (1979-2013). The model is evaluated using existing weather stations, precipitation gauges, and available glacier firn cores. Our results confirm the occurrence of extremely high accumulation on the higher portions of both ice fields (10-35 m w.e. of snow per year). Precipitation is abundant throughout the entire year, and driven by quasi-continuous atmospheric westerlies, in combination with significant orographic forcing. On the other hand, we find strong ablation on the outlet glacier tongues, although these are only partly resolved by the model grid. Integrated over the ice fields, we find no significant recent trend in the SMB.

Lenaerts, J.; van Wessem, M.; van den Broeke, M. R.; van Ulft, L.; van Meijgaard, E.; Schaefer, M.; Van De Berg, W.

2013-12-01

234

Comparison of analytical results for chloride, sulfate and nitrate obtained from adjacent ice core samples by two ion chromatographic methods.  

PubMed

The anions chloride, sulfate and nitrate in nearly 500 pairs of ice core samples from the same depth were determined in a 121 m long ice core from Svalbard. The analyses were performed separately using an ion chromatograph with Dionex AS9 and AS15 columns with Na(2)CO(3) and NaOH eluents. Results showed a small (5-6 microg l(-1)) but statistically significant difference in mean concentrations for chloride and sulfate but not for nitrate. 2% of the data indicate real differences in concentrations across the ice core. Despite these differences ion information in ice core layers are comparable for ice core paleoclimate and environmental studies even though analyses are made using two different procedures. PMID:14760459

Kekonen, T; Perämäki, P; Moore, J C

2004-02-01

235

Ice Core Data of Atmospheric Carbon Monoxide Over Antarctica During The Last 170 Years  

NASA Astrophysics Data System (ADS)

The importance and interest for reconstructing past CO concentrations arises from its significant role on the chemistry of the troposphere. As the major sink for hydroxyl radicals (OH), carbon monoxide is considered to regulate the oxidative capacity of the atmosphere. CO also has a close link with methane which is a main source of CO especially in Southern Hemisphere. Past atmospheric CO concentration will help better understand past trend of the atmospheric oxidative capacity. Past isotopic data of CO will assist in determining the various sources and sinks in the past and their historic relative magnitudes. However, little information about past CO is reported due to the difficulties of measuring atmospheric CO in the ppbv range. Our study on CO in Antarctic ice cores helps determine the past trend of atmospheric oxidative capacity and relationship between CO and methane. In this study, we present both the isotopic data and concentration measurements of atmospheric CO in D47 ice cores. Ice core samples were prepared based on wet extraction method in LGGE, France. Measurements were made with a cryogenic vacuum extraction system and continuous-flow isotopic ratio mass spectrometer (CF-IRMS) in Stony Brook University, NY. 12 D47 ice core samples have been measured for both CO mixing ratio and isotopic ratios. The range of the depth is from 69m to 109m, corresponding to a range of gas age from 1829 AD to 1941 AD. It is found that CO level in the above gas age range is around 55-60ppbv and doesn't change much during this time frame. d13C (VPDB) of CO is around -28 per mil and no apparent trend of d13C is found. More isotope data are needed to show us a clear trend, especially for ice cores extending back to pre-industrial time. As for d18O, our data show very heavier d18O values. Usually high d18O values indicate foreign CO, but due to the relatively constant CO mixing ratio, this possibility can be eliminated. If there is no foreign CO, there may be some unexpected processes such as isotope exchange between oxygen in CO and oxygen in other compounds in ice, some growth process and loss process at the same time which we don't know. Or the worst is that CO in ice is corrupted in an unpredictable way. Testing with other Antarctic ice cores will help us figure this out.

Wang, Z.; Mak, J.; Chappellaz, J.

2008-12-01

236

Retrieving a Common Accumulation Record From Greenland Ice Cores for the Past 1800 Years  

NASA Astrophysics Data System (ADS)

In the accumulation zone of the Greenland ice sheet the annual accumulation rate may be identified through identification of the annual cycle in the isotopic climate signal and other seasonally varying parameters. On an annual basis the accumulation rate in different Greenland ice cores is highly variable, and the degree of correlation between the accumulation series from different ice cores is low. When using multiyear averages of the different accumulation records the correlation however increases significantly. A statistical model has been developed estimating the common climate signal in the different records through optimization of the signal to noise variance ratio. A common Greenland accumulation record with five years resolution for the past 1800 years has been extracted. The record establishes a climatic record which points to a possible cause for the disappearance of the Norse settlements in Greenland.

Andersen, K. K.; Ditlevsen, P. D.; Rasmussen, S. O.; Clausen, H. B.; Johnsen, S. J.

2005-12-01

237

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

238

Understanding the Causes of Climate Change: Ice Cores, the International Polar Year, and Beyond  

Microsoft Academic Search

The polar regions have a large influence on the earth's climate, and they contain records of how and why climate has changed in the past. In order to understand how climate might change in the future, and to determine the extent to which climate is changing now, we need to understand how polar regions influence climate. The international ice core

K. Taylor; E. Wolff; J. Jouzel; J. Severinghaus; P. Mayewski

2003-01-01

239

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

240

Atmospheric pollution of a remote area of Tianshan Mountain: Ice core record  

Microsoft Academic Search

The influence of anthropogenic pollution on the region of Tianshan Mountain, a remote area in arid central Asia, has been debated in the recent years. An ice core, covering the past 43 years, retrieved from Glacier 1 at Urumqi River head in the east Tianshan, northwest China, was analyzed to examine the problem. CH3COO? (acetate) and HCOO? (formate), the chief

Xinqing Lee; Dahe Qin; Guibin Jiang; Keqing Duan; Hui Zhou

2003-01-01

241

Atmospheric pollution of a remote area of Tianshan Mountain: Ice core record  

Microsoft Academic Search

The influence of anthropogenic pollution on the region of Tianshan Mountain, a remote area in arid central Asia, has been debated in the recent years. An ice core, covering the past 43 years, retrieved from Glacier 1 at Urumqi River head in the east Tianshan, northwest China, was analyzed to examine the problem. CH3COO- (acetate) and HCOO- (formate), the chief

Xinqing Lee; Dahe Qin; Guibin Jiang; Keqing Duan; Hui Zhou

2003-01-01

242

Wind-Driven Sublimation Impact on Surface Mass Balance and Ice Core Interpretation in East Antarctica  

Microsoft Academic Search

Temporal and spatial variability of snow accumulation are input parameters in mass balance studies. They are key issues of paleoclimatic reconstructions from ice cores. As part of the International TransAntarctic Scientific Expedition and of the Franco-Italian Concordia Station collaboration, field survey along traverses and spot research at selected sites have been performed over the East and NE Dome C drainage

M. Frezzotti

2004-01-01

243

The GISP ice core record of volcanism since 7000 B.C.  

SciTech Connect

Two technical comments are presented on an article by Zielinski concerning the GISP ice core record of volcanic activity in 7000 BC, including a detailed record of the volcanic contribution to sulfate concentrations. The authors describe concerns about (1) correct C14 dating for known eruptions correlated to calendar years and (2) the need for unambiguous volcanic source identifications. 24 refs., 1 tab.

Fiedel, S.J. [Enserch Environmental Corp., Lyndhurst, NJ (United States)

1995-01-13

244

Influence of North Atlantic Oscillation on anthropogenic transport recorded in northwest Greenland ice cores  

Microsoft Academic Search

Nitrate records from six Greenland ice cores covering the period 1789 to 1995 show a significant correlation in concentration for averaging periods greater than 10 years, as well as an approximately 60% increase in average concentration during the last 75 years. Annual nitrate fluxes contain low-frequency trends driven primarily by changes in concentration, while higher-frequency variability is driven by changes

John F. Burkhart; Roger C. Bales; Joseph R. McConnell; Manuel A. Hutterli

2006-01-01

245

The EDC3 chronology for the EPICA Dome C ice core  

Microsoft Academic Search

The EPICA (European Project for Ice Coring in Antarctica) Dome C drilling in East Antarctica has now been completed to a depth of 3260 m, at only a few meters above bedrock. Here we present the new EDC3 chronology, which is based on the use of 1) a snow accumulation and mechanical flow model, and 2) a set of independent

F. Parrenin; J.-M. Barnola; J. Beer; T. Blunier; E. Castellano; J. Chappellaz; G. Dreyfus; H. Fischer; S. Fujita; J. Jouzel; K. Kawamura; B. Lemieux-Dudon; L. Loulergue; V. Masson-Delmotte; B. Narcisi; J.-R. Petit; G. Raisbeck; D. Raynaud; U. Ruth; J. Schwander; M. Severi; R. Spahni; J. P. Steffensen; A. Svensson; R. Udisti; C. Waelbroeck; E. Wolff

2007-01-01

246

Pliocene Antarctic sea-ice reconstruction based on the diatom record the ANDRILL 1B core  

Microsoft Academic Search

The ANtarctic DRILLing Program's AND-1B core, comprising 13 interglacial diatomaceous sections spanning the early Pliocene to the early Pleistocene, provides a largely complete record of Pliocene climate and sea-ice conditions in the Ross Sea. As primary producers, diatoms are directly influenced by surface water conditions, thus fossil assemblages provide a high quality proxy for past surface waters. The modern diatom

R. P. Scherer; C. M. Sjunneskog; D. Winter; C. Riesselman

2010-01-01

247

Continental biogenic species in the Greenland Ice Core Project ice core: Tracing back the biomass history of the North American continent  

NASA Astrophysics Data System (ADS)

Ammonium, nitrate, and organic acid records from the Greenland Ice Core Project deep ice core are discussed. All species have a continental biogenic source that is situated predominantly on the North American continent for species deposited in Summit, central Greenland. The record therefore can be used to trace back the biomass history of the North American continent. Difficulty in the interpretation of these records arises from their unknown transfer behavior in a more alkaline atmosphere, which characterizes glacial time periods compared to interglacial stadials. This may have implications not only for weak acids such as formate and acetate, but also possibly for the transport and incorporation of HNO3 into aerosols, whereas ammonium is probably not affected by the alkalinity change of the atmosphere. Our approach is to compare samples with similar H+ concentrations throughout the record. From the records we infer several significant fluctuations in the extent of the Laurentide Ice Sheet during the last glaciation. We find evidence against the occurrence of an extensive Younger Dryas event in North America.

Fuhrer, Katrin; Legrand, Michel

1997-11-01

248

Isotopic (?18O, ?D and deuterium excess) records from the TALDICE ice core (East Antarctica) (Invited)  

NASA Astrophysics Data System (ADS)

Paleotemperature reconstructions from Antarctic ice cores rely mainly on ?D and ?18O records and the main key factors controlling the observed distribution of ?D and ?18O in Antarctic surface snow are mainly related to the condensation temperature of the precipitation and the origin of moisture. The deuterium excess, d = ?D - 8*?18O, contains information about climate conditions prevailing in the source regions of precipitation and can be used as an integrated tracer of past hydrological cycle changes. In the framework of the TALos Dome Ice CorE (TALDICE) project, a deep ice core (1620 m) has been drilled at Talos Dome, a peripheral dome of East Antarctica facing the Ross Sea, about 550 km north of Taylor Dome and 1100 km East from the EPICA Dome C drilling site. The TALDICE coring site (159°11'E 72°49'S; 2315 m; T -41°C; www.taldice.org) is located near the dome summit and is characterised by an annual snow accumulation rate of 80 mm water equivalent. Backtrajectory analyses suggest that Talos Dome is mainly influenced by air masses arriving both from the Pacific (Ross Sea) and Indian Ocean sectors. A preliminary dating based on an ice flow model and an inverse method suggests for the upper 1580 m an age of about 300,000 years BP. The full TALDICE ?18O record obtained from the bag samples as well as ?D and deuterium excess data are presented here. The ?18O and ?D measurements were carried out in Italy and France on a continuous basis of 1 m. These new records will be compared to the ones obtained from the EDC ice core as well as with other East Antarctic ice core records. In particular, we will focus on the whole isotopic profiles, in good agreement with other inland deep ice cores, and on the last deglaciation, showing climatic changes at Talos Dome in phase with the Antarctic plateau and suggesting that the bipolar see saw with Greenland temperature is also valid for this new coastal site facing the Ross Sea sector.

Stenni, B.; Buiron, D.; Masson-Delmotte, V.; Bonazza, M.; Braida, M.; Chappellaz, J.; Frezzotti, M.; Falourd, S.; Minster, B.; Selmo, E.

2010-12-01

249

Stable isotope records from Dronning Maud Land: Results from the EPICA ice core and the pre-site survey cores  

NASA Astrophysics Data System (ADS)

The European Project for Ice Coring in Antarctica (EPICA) focuses on the drilling of two deep ice cores, the first at Dome Concordia in the Indian/Pacific sector, and the second in Dronning Maud Land in the Atlantic sector of Antarctica. We focus on Dronning Maud Land and the isotope records from ice cores drilled there. The pre-site survey cores sampled the ice archive up to the 150 m depth and document the climate history in the last 2000 years in this part of Antarctica. The drilling of the main core EDML (EPICA Dronning Maud Land) started in the 2001/2002 season at Kohnen station (75 00 S, 0 04 E, 2882 m a.s.l.) and reached in that season the 450 m depth and recovered approx. 7000 year old ice. Generally, the stable isotope profiles (18O, 2H) are characterized by Holocene stable climate and show only low variability. But, in the last 4000 years (based on a preliminary time scale) the d18O values decrease continuously by about 0.6 %o, and the deuterium excess values increase in the same time by about 0.5 %o. Both trends could indicate climate cooling in this part of Antarctica. The correlation between the 2H and the deuterium excess profile (d = d2H - 8 d18O) are different for the low and high frequency part of the isotope profiles. On the one hand, high-pass filtered d profiles are positively correlated. This correlation is probably caused by diffusion processes, which affect the 18O and 2H profiles in a different way and force the d profile to vary in phase with the 2H profile. This post-depositional effect can also be seen in sub-annually resolved profiles from snow-pit samples. On the other hand, the correlation between the low-pass filtered profiles is negative. This could indicate both, changes in the build-up of the snow cover or temperature fluctuations. Unambiguous are the findings at a site in the southernmost part of the area under investigation of the pre-site survey. There the changes of the stable isotope profiles are not induced by temperature, but by the seasonality in the snow cover. This is indicated by contemporaneous changes of the deuterium excess values and accumulation rates.

Oerter, H.; Graf, W.; Meyer, H.; Wilhelms, F.

2003-04-01

250

Time-scale synchronization among EDC, EDML and TD ice cores (Antarctica) by volcanic stratigraphies.  

NASA Astrophysics Data System (ADS)

In the framework of the TALDICE project (TALos Dome Ice CorE), a deep ice core has been drilled on a peripheral dome of East Antarctica. The perforation at Talos Dome (159°11' E 72°49'S 2315 m a.s.l.) reached 1620 m during the 2007-2008 austral summer, covering a period of about 250 kyr. A reliable high-resolution synchronisation of the TD volcanic stratigraphy with the well dated EPICA DC and EPICA DML ice cores is a basic tool for the construction of a reliable timescale and will be a powerful tool to discover whether related climatic events in different sectors of the Antarctic continent occurred at the same time or if there was an offset for the same event in different sites. In this optic, a FIC (Fast Ion Chromatography) system (coupled to a CFA - Continuous Flow Analysis setup) was used to reconstruct the paleo-volcanic record at this site as was already done for the two EPICA cores with very high resolution (ranging from less than 1 to about 3.5 cm per sample). Here we report the results of the synchronisation among the TD and the EDC and EDML ice-cores via individuation of synchronous volcanic events for the last 40 kyr. Several isochronous volcanic events were identified by the comparison of the volcanic stratigraphies and these signatures will be an helpful tool in carrying on a fine-tuning of the pure glaciological model of the TD timescale. Low resolution accumulation rates at TD site for the last deglaciation were then derived from the comparison of couples of volcanic events using the EDC3 agescale. These accumulation rates were then compared to those derived via glaciological modelling showing a very good agreement. This kind of volcanic synchronisation was already carried out for the two EPICA ice cores and for the Vostok and EPICA-DC cores. Once this comparison will be fully available, it will be possible to synchronize these 4 archives and to extend the peak to peak comparison to other Antarctic ice cores. Furthermore the comparison of several paleorecords of volcanic eruptions will be a powerful tool to point out whether the volcanic events involved the whole Antarctic continent or were just regional scale phenomena.

Severi, Mirko; Becagli, Silvia; Castellano, Emiliano; Manganelli, Desirè; Traversi, Rita; Udisti, Roberto

2010-05-01

251

Radioactive fallouts as temporal makers for glacier ice cores dating  

NASA Astrophysics Data System (ADS)

In this paper, we intend to show how analytical methods used in nuclear physics, as gamma spectroscopy, are powerful tools for the dating of environmental archives. Specifically, we will show how events related to the release in the environment of great amount of radioactive isotopes ( e.g., atmospheric nuclear test explosions) can be used as temporal markers in alpine glaciers. The radio-isotope selected for the dating of ice carrots is 137Cs , because of its chemical and nuclear properties. The radioactive measurements have been conducted using a low-background high-purity germanium detector. The sensitivity for the prepared samples is 10mBq/kg. We will illustrate how dating curves (date versus depth of the sample) can be considered as an absolute calibrator for all the other chemical dating methods used on glacier samples analyses.

Clemenza, M.; Cucciati, G.; Maggi, V.; Pattavina, L.; Previtali, E.

2012-06-01

252

The Carrington event not observed in most ice core nitrate records  

NASA Astrophysics Data System (ADS)

The Carrington Event of 1859 is considered to be among the largest space weather events of the last 150 years. We show that only one out of 14 well-resolved ice core records from Greenland and Antarctica has a nitrate spike dated to 1859. No sharp spikes are observed in the Antarctic cores studied here. In Greenland numerous spikes are observed in the 40 years surrounding 1859, but where other chemistry was measured, all large spikes have the unequivocal signal, including co-located spikes in ammonium, formate, black carbon and vanillic acid, of biomass burning plumes. It seems certain that most spikes in an earlier core, including that claimed for 1859, are also due to biomass burning plumes, and not to solar energetic particle (SEP) events. We conclude that an event as large as the Carrington Event did not leave an observable, widespread imprint in nitrate in polar ice. Nitrate spikes cannot be used to derive the statistics of SEPs.

Wolff, E. W.; Bigler, M.; Curran, M. A. J.; Dibb, J. E.; Frey, M. M.; Legrand, M.; McConnell, J. R.

2012-04-01

253

Physics Potential of the IceCube DeepCore detector  

NASA Astrophysics Data System (ADS)

The recent commissioning of the full DeepCore sub-array, a low-energy extension of the IceCube neutrino observatory, offers opportunities for neutrino physics in the energy region of 10 GeV to 1 TeV. The improved energy reach, use of the surrounding IceCube detector as an active veto and immense size of DeepCore will produce one of the largest all-sky neutrino datasets ever acquired. DeepCore will provide sensitivity to neutrinos from possible neutralino dark matter annihilations in the Earth, Sun and galactic center, down to neutralino masses in the region of ˜ 50 GeV. Tens of thousands of atmospheric neutrinos will be detected annually after oscillating over a baseline of up to one Earth diameter, opening the possibilities for muon neutrino disappearance and tau neutrino appearance measurements.

Koskinen, D. J.; IceCube Collaboration

2012-08-01

254

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

255

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

256

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

257

Sulfur Isotope Composition of Volcanic Sulfate in Polar Ice Cores (Invited)  

NASA Astrophysics Data System (ADS)

Explosive volcanic eruptions often emit copious amounts of sulfur gases into the atmosphere. Similar to that of anthropogenic aerosols, volcanic aerosols can influence climate by altering the atmosphere's radiative properties. Traces of sulfate aerosols from past explosive eruptions are preserved in the snow strata of polar ice sheets and can be retrieved with ice cores. We have been measuring sulfur isotope composition of volcanic sulfate in Antarctica and Greenland ice cores to investigate the kinetics of atmospheric oxidation chemistry and to determine the climatic impact of the eruptions. We have found that the chemical conversion process of volcanic sulfur dioxide into sulfuric acid and sulfate aerosols in the stratosphere proceeds through oxidation reaction pathways different from those for sulfur dioxide in the troposphere. Recent laboratory experiments and modeling efforts by other investigators support the hypothesis that short wavelength ultra-violet radiation above the stratospheric ozone layer plays a key role in the chemical conversion or oxidation and can cause mass independent fractionation (MIF) of sulfur isotopes (33S, 34S, 36S). The discovery of the sulfur MIF isotope signatures in the volcanic sulfate offers a unique and dependable way to distinguish the signals of large, stratospheric eruptions in the ice core volcanic records from those of eruptions with little or no climate impact. Identification of the climate-impacting eruptions helps to improve our understanding of the volcano-climate connection.

Cole-Dai, J.; Savarino, J.; Thiemens, M. H.

2011-12-01

258

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

259

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

260

The total air content in the NGRIP ice core from 120 to 10 kyr BP.  

NASA Astrophysics Data System (ADS)

With a melt-refreezing technique we measured the concentration of methane (CH4) and nitrous oxide (N2O) of the enclosed air along the ice core of the North Greenland Ice Core Project (NGRIP). A valuable byproduct of those measurements is an estimation of the total air content (TAC). The total air content depends, among others, on altitude, surface temperature, close off depth and insolation parameters. Due to unknown temperatures in some parts of the measuring system, our TAC raw data have been calibrated to additional measurements with an uncertainty of 0.5 ml/kg. Here we present a large dataset of 2323 new TAC data points from NGRIP. Our results cover the time interval from 120 to 10 kyr BP (3082 to 1481 m depth) and the TAC values vary between 75 to 105 ml/kg at standard temperature and pressure (STP). We compare the data to other available proxies such as dust and ?18O, measured on the ice core, and to the summer insolation at the core location. We find the insolation to be imprinted in the TAC record, supporting previous TAC studies. Interestingly, for some of the millennial scale variations known as Dansgaard Oeschger (DO) events, a corresponding signal in the TAC can be observed. Our analysis will provide further information on potential drivers of TAC changes.

Eicher, Olivier; Baumgartner, Matthias; Schilt, Adrian; Schmitt, Jochen; Stocker, Thomas; Fischer, Hubertus

2014-05-01

261

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.

Schneider, David P.; Steig, Eric J.

2008-01-01

262

Properties of grain boundary networks in the NEEM ice core analyzed by combined transmission and reflection optical microscopy  

NASA Astrophysics Data System (ADS)

Microstructure analysis of ice cores is vital to understand the processes controlling the flow of ice on the microscale. To quantify the microstructural variability (and thus occurring processes) on centimeter, meter and kilometer scale along deep polar ice cores, a large number of sections has to be analyzed. In the last decade, two different methods have been applied: On the one hand, transmission optical microscopy of thin sections between crossed polarizers yields information on the distribution of crystal c-axes. On the other hand, reflection optical microscopy of polished and controlled sublimated section surfaces allows to characterize the high resolution properties of a single grain boundary, e.g. its length, shape or curvature (further developed by [1]). Along the entire NEEM ice core (North-West Greenland, 2537 m length) drilled in 2008-2011 we applied both methods to the same set of vertical sections. The data set comprises series of six consecutive 6 x 9 cm2 sections in steps of 20 m - in total about 800 images. A dedicated method for automatic processing and matching both image types has recently been developed [2]. The high resolution properties of the grain boundary network are analyzed. Furthermore, the automatic assignment of c-axis misorientations to visible sublimation grooves enables us to quantify the degree of similarity between the microstructure revealed by both analysis techniques. The reliability to extract grain boundaries from both image types as well as the appearance of sublimation groove patterns exhibiting low misorientations is investigated. X-ray Laue diffraction measurements (yielding full crystallographic orientation) have validated the sensitivity of the surface sublimation method for sub-grain boundaries [3]. We introduce an approach for automatic extraction of sub-grain structures from sublimation grooves. A systematic analysis of sub-grain boundary densities indicates a possible influence of high impurity contents (amongst others visible in ice-penetrating radar measurements) on the generation of sub-grain boundaries. [1] S. Kipfstuhl et al., 2006, Journal of Glaciology, 52, 398-406 [2] T. Binder et al., 2013, Journal of Microscopy, 250, 130-141 [3] I. Weikusat et al., 2011, Journal of Glaciology, 57, 111-120

Binder, Tobias; Weikusat, Ilka; Garbe, Christoph; Svensson, Anders; Kipfstuhl, Sepp

2014-05-01

263

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

264

10Be evidence for the Matuyama-Brunhes geomagnetic reversal in the EPICA Dome C ice core.  

PubMed

An ice core drilled at Dome C, Antarctica, is the oldest ice core so far retrieved. On the basis of ice flow modelling and a comparison between the deuterium signal in the ice with climate records from marine sediment cores, the ice at a depth of 3,190 m in the Dome C core is believed to have been deposited around 800,000 years ago, offering a rare opportunity to study climatic and environmental conditions over this time period. However, an independent determination of this age is important because the deuterium profile below a depth of 3,190 m depth does not show the expected correlation with the marine record. Here we present evidence for enhanced 10Be deposition in the ice at 3,160-3,170 m, which we interpret as a result of the low dipole field strength during the Matuyama-Brunhes geomagnetic reversal, which occurred about 780,000 years ago. If correct, this provides a crucial tie point between ice cores, marine cores and a radiometric timescale. PMID:17080088

Raisbeck, G M; Yiou, F; Cattani, O; Jouzel, J

2006-11-01

265

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

266

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

267

Ice-volcano interactions during the 2010 Eyjafjallajökull eruption, as revealed by airborne imaging radar  

NASA Astrophysics Data System (ADS)

During the eruption of the ice-covered Eyjafjallajökull volcano, a series of images from an airborne Synthetic Aperture Radar (SAR) were obtained by the Icelandic Coast Guard. Cloud obscured the summit from view during the first three days of the eruption, making the weather-independent SAR a valuable monitoring resource. Radar images revealed the development of ice cauldrons in a 200 m thick ice cover within the summit caldera, as well as the formation of cauldrons to the immediate south of the caldera. Additionally, radar images were used to document the subglacial and supraglacial passage of floodwater to the north and south of the eruption site. The eruption breached the ice surface about four hours after its onset at about 01:30 UTC on 14 April 2010. The first SAR images, obtained between 08:55 and 10:42 UTC, show signs of limited supraglacial drainage from the eruption site. Floodwater began to drain from the ice cap almost 5.5 h after the beginning of the eruption, implying storage of meltwater at the eruption site due to initially constricted subglacial drainage from the caldera. Heat transfer rates from magma to ice during early stages of cauldron formation were about 1 MW m-2 in the radial direction and about 4 MW m-2 vertically. Meltwater release was characterized by accumulation and drainage with most of the volcanic material in the ice cauldrons being drained in hyperconcentrated floods. After the third day of the eruption, meltwater generation at the eruption site diminished due to an insulating lag of tephra.

Magnússon, E.; Gudmundsson, M. T.; Roberts, M. J.; Sigurã°Sson, G.; HöSkuldsson, F.; Oddsson, B.

2012-07-01

268

Retrieving a common accumulation record from Greenland ice cores for the past 1800 years  

NASA Astrophysics Data System (ADS)

In the accumulation zone of the Greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations. On an annual basis the accumulation rate in different Greenland ice cores is highly variable, and the degree of correlation between accumulation series from different ice cores is low. However, when using multiyear averages of the different accumulation records, the correlation increases significantly. A statistical model has been developed to estimate the common climate signal in the different accumulation records through optimization of the ratio between the variance of the common signal and of the residual. Using this model, a common Greenland accumulation record for the past 1800 years has been extracted. The record shows significant 11.9 years periodicity. A sharp transition to very dry conditions is found just before A.D. 1200, and very dry conditions during the 13th century together with dry and cold spells during the 14th century may have put extra strain on the Norse population in Greenland and may have contributed to their extinction. Accumulation rates gradually decrease from a distinct maximum in A.D. 1394 to very dry conditions in the late 17th century and thus reflect the Little Ice Age.

Andersen, K. K.; Ditlevsen, P. D.; Rasmussen, S. O.; Clausen, H. B.; Vinther, B. M.; Johnsen, S. J.; Steffensen, J. P.

2006-08-01

269

Two-hundred-year record of biogenic sulfur in a south Greenland ice core (20D)  

NASA Astrophysics Data System (ADS)

The concentration of methanesulfonic acid (MSA) was determined in a shallow south central Greenland ice core (20D). This study provides a high-resolution record of the DMS-derived biogenic sulfur in Greenland precipitation over the past 200 years. The mean concentration of MSA is 3.30 ppb (? = 2.38 ppb, n = 1134). The general trend of MSA is an increase from 3.01 to 4.10 ppb between 1767 and 1900, followed by a steady decrease to 2.34 ppb at the present time. This trend is in marked contrast to that of non-sea-salt sulfate (nss SO42-), which increases dramatically after 1900 due to the input of anthropogenic sulfur. The MSA fraction ((MSA/(MSA + nss SO42-))* 100) ranges from a mean of 15% in preindustrial ice to less than 5% in recent ice. These MSA fractions suggest that approximately 15 to 40% of the sulfur in recent Greenland ice is of biological origin. It is suggested that there is a significant low-latitude component to the biogenic sulfur in the core and that variations in the MSA fraction reflect changes in the relative strengths of low- and high-latitude inputs. The data show no evidence for a strong dependence of dimethyl sulfide (DMS) emissions on sea surface temperature during the last century. There is also no indication that the yield of MSA from DMS oxidation has been altered by increased NOx levels over the North Atlantic during this period.

Whung, P.-Y.; Saltzman, E. S.; Spencer, M. J.; Mayewski, P. A.; Gundestrup, N.

1994-01-01

270

Multifractal detrended fluctuation analysis of the ? 18 O record of NGRIP ice core  

NASA Astrophysics Data System (ADS)

The multifractal properties and scaling behaviors of the long-term and recent 2000-year ? 18 O records of NGRIP ice core are investigated by the multifractal detrended fluctuation analysis method. The generalized Hurst exponents, multifractal scaling exponents, and singularity spectrums of two ? 18 O records are derived to verify the multifractiality of two records. And the multifractal behaviors of two records are obviously different, which may reflect the climate change of the recent 2000-year time is quite different from one of the long-term time. In addition, the probability distribution analysis of two ? 18 O records is presented to manifest the different multifractality between two ? 18 O records of NGRIP ice core. Our results will be helpful to research the climate change.

Shao, Zhi-Gang; Wang, Hui-Hui

2014-01-01

271

Gas Hydrate-Sediment Morphologies Revealed by Pressure Core Analysis  

NASA Astrophysics Data System (ADS)

Analysis of HYACINTH pressure cores collected on IODP Expedition 311 and NGHP Expedition 1 showed gas hydrate layers, lenses, and veins contained in fine-grained sediments as well as gas hydrate contained in coarse-grained layers. Pressure cores were recovered from sediments on the Cascadia Margin off the North American West Coast and in the Krishna-Godavari Basin in the Western Bay of Bengal in water depths of 800- 1400 meters. Recovered cores were transferred to laboratory chambers without loss of pressure and nondestructive measurements were made at in situ pressures and controlled temperatures. Gamma density, P-wave velocity, and X-ray images showed evidence of grain-displacing and pore-filling gas hydrate in the cores. Data highlights include X-ray images of fine-grained sediment cores showing wispy subvertical veins of gas hydrate and P-wave velocity excursions corresponding to grain-displacing layers and pore-filling layers of gas hydrate. Most cores were subjected to controlled depressurization experiments, where expelled gas was collected, analyzed for composition, and used to calculate gas hydrate saturation within the core. Selected cores were stored under pressure for postcruise analysis and subsampling.

Holland, M.; Schultheiss, P.; Roberts, J.; Druce, M.

2006-12-01

272

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

273

A 110,000Yr Record of Explosive Volcanism from the GISP2 (Greenland) Ice Core  

Microsoft Academic Search

The time series of volcanically produced sulfate from the GISP2 ice core is used to develop a continuous record of explosive volcanism over the past 110,000 yr. We identified ?850 volcanic signals (700 of these from 110,000 to 9000 yr ago) with sulfate concentrations greater than that associated with historical eruptions from either equatorial or mid-latitude regions that are known

Gregory A. Zielinski; Paul A. Mayewski; L. David Meeker; S. Whitlow; Mark S. Twickler

1996-01-01

274

The ice-core record - Climate sensitivity and future greenhouse warming  

Microsoft Academic Search

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

C. Lorius; D. Raynaud; J. Jouzel; J. Hansen; H. Le Treut

1990-01-01

275

Model-based constraints on interpreting 20th century trends in ice core 10Be  

Microsoft Academic Search

Beryllium-10 ice-core records are useful for understanding solar magnetic field changes over time, and in particular over the 20th century, during which there are a variety of relevant observations. However, differences between 10Be snow concentration records from different locations complicate the process of developing a coherent understanding of changes in cosmogenic isotope production. We use the Goddard Institute for Space

Christy V. Field; Gavin A. Schmidt

2009-01-01

276

A 800year record of nitrate from the Lomonosovfonna ice core, Svalbard  

Microsoft Academic Search

Detailed chemical analysis of the122m, relatively high-altitude and low- melt Lomonosovfonna ice core provides the best-dated record of nitrate from Svalbard. A very significant non-linear trend present in the record shows: (a) a rise in concentrations from the12th to the mid-16th century, (b) reasonably stable concentrations until the mid- 19th century, (c) a rise in concentrations into the 20th century,

Teija KEKONEN; John C. MOORE; Robert MULVANEY; Elisabeth ISAKSSON; Veijo POHJOLA

277

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

278

Twentieth Century Increase of Atmospheric Ammonia Recorded in Mt. Everest Ice Core  

Microsoft Academic Search

An NH4+ record covering the period AD1846-1997 was reconstructed using an 80.4 m ice core from East Rongbuk Glacier on Mt. Everest. Variations in NH4+ are characterized by a dramatic increase since the 1950s. The highest NH4+ concentrations occur in the 1980s. They are about two-fold more than those in the first half of 20th century. EOF analysis on the

S. Kang; P. A. Mayewski; Y. Yan; D. Qin

2001-01-01

279

Chemical compositions of soluble particles around the Termination 1 in the Dome Fuji ice core  

NASA Astrophysics Data System (ADS)

Micro sized particles preserved in Antarctic ice cores are useful proxies for reconstructing past climate and environmental changes. The recent studies on chemical compounds of the particles by using the Dome Fuji ice core showed that sulfate salts were main soluble particles, and chemical compositions of primary sulfate salt were calcium sulfate during the glacial maximum and sodium sulfate during the Holocene #1. However, it is still unknown that how chemical compositions of sulfate particles have changed on millennial time scale. In this study, we focused on sulfate salts and sea salts (precursor of sulfate salts) and measured constituent element of non-volatile particles in the Dome Fuji ice core around the Termination 1(9-25 kyr BP). A total of 48 samples were distributed from Dome Fuji ice core section from 298.900m to 582.590m (Holocene to Last Glacial Maximum: LGM, 9-25 kyr BP), with a time resolution of about 320 year. Non-volatile particles were extracted from the samples by sublimation system #2. 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 #3, we made a classification of non-volatile particles into insoluble dust, soluble sulfate salts and soluble chloride salts. Also we assumed that particles containing Ca and S are calcium sulfate, particles containing Na and S are sodium sulfate and particles containing Na and Cl are sodium chloride. We found several fluctuations of calcium sulfate, sodium sulfate, and sodium chloride around the Termination 1, and these fluctuations are associated with changes in terrestrial as well as marine environments. Main sulfate salts changed from calcium sulfate to sodium sulfate after 16.5 kyr BP. A plausible explanation is that sulfuric acid in atmosphere became to react with sodium chloride instead of dusts (calcium carbonate) after 16.5 kyr BP, because atmospheric dust concentrations decreased to Holocene level around 16.5 kyr BP #4. Mass ratio of sodium sulfate+ sodium chloride (soluble sodium salt) to total particles showed 3 peaks at 16.5, 13 and 10 kyr BP. These peak ages were consistent with those of sea ice expansion in southern Atlantic Ocean which was reconstructed from the diatoms abundance of sea ice indicator in a marine sediment core #5. Therefore the mass fraction of the sodium salt probably reflects the sea ice expansion in southern Atlantic Ocean. #1 Ohno, H., M. Igarashi and T. Hondoh, Characteristics of salt inclusions in polar ice from Dome Fuji, East Antarctica, Geophysical Research Letters, 33, L08501, doi: 10.1029/2006GL025774, 2006. #2 Iizuka, Y. and 6 others, Constituent elements of insoluble and non-volatile particles during the Last Glacial Maximum exhibited in the Dome Fuji (Antarctica) ice core, J. Glaciol., 55(191),58-64, 2009. #3 Iizuka, Y. and 9 others, The rates of sea salt sulfatization in the atmosphere and surface snow of inland Antarctica. J. Geophys. Res. In press #4 Delmas, R.J. and 6 others, Linking Antarctic glaciochemical records to past climatic conditions, Mem. Natl Inst. Polar Res., Special Issue 57, 105-120, 2003. #5 Bianchi, C., R. Gersonde, Climate evolution at the last deglaciation: the role of the Southern Ocean. Earth Planet. Sci. Lett., 228, 407-424, 2004.

Oyabu, I.; Iizuka, Y.; Sakurai, T.; Suzuki, T.; Miyake, T.; Hirabayashi, M.; Motoyama, H.; Hondoh, T.

2012-04-01

280

A brief history of ice core science over the last 50 yr  

NASA Astrophysics Data System (ADS)

For about 50 yr, ice cores have provided a wealth of information about past climatic and environmental changes. Ice cores from Greenland, Antarctica and other glacier-covered regions now encompass a variety of time scales. However, the longer time scales (e.g. at least back to the Last Glacial period) are covered by deep ice cores, the number of which is still very limited: seven from Greenland, with only one providing an undisturbed record of a part of the last interglacial period, and a dozen from Antarctica, with the longest record covering the last 800 000 yr. This article aims to summarize this successful adventure initiated by a few pioneers and their teams and to review key scientific results by focusing on climate (in particular water isotopes) and climate-related (e.g. greenhouse gases) reconstructions. Future research is well taken into account by the four projects defined by IPICS. However, it remains a challenge to get an intact record of the Last Interglacial in Greenland and to extend the Antarctic record through the mid-Pleistocene transition, if possible back to 1.5 Ma.

Jouzel, J.

2013-11-01

281

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

282

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

PubMed Central

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 10Be and 14C 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 10Be ice core records from Greenland and Antarctica with the global 14C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution 10Be 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.

Steinhilber, Friedhelm; Beer, Jurg; Brunner, Irene; Christl, Marcus; Fischer, Hubertus; Heikkila, Ulla; Kubik, Peter W.; Mann, Mathias; McCracken, Ken G.; Miller, Heinrich; Miyahara, Hiroko; Oerter, Hans

2012-01-01

283

Recent and past dust concentrations and fluxes from a developing array of Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Continental dust is an important component of climate forcing, both because of its interaction with incoming solar and outgoing long wave radiation and because of its impact on albedo when deposited on bright surfaces such as fresh snow. Continental dust may also play an important role in ocean fertilization and carbon sequestration. Because the lifetime of dust aerosol in the atmosphere is only on the order of days to weeks, spatial and temporal variability in concentrations and fluxes is high and understanding of recent and long term changes is limited. Here we present and discuss detailed continuous, high depth resolution measurements of a range of dust proxies in a developing array of Antarctic ice cores. Included are traditional proxies such as non-sea-salt (nss) calcium and insoluble particle number and size distribution as well as less traditional proxies such as aluminum, vanadium, manganese, rare earth elements, and nss uranium which together provide important insights into how dust sources and transport may have changed in the past. The array includes a number of new shallow ice core records from East and West Antarctica spanning recent centuries to millennia, as well as Last Glacial Maximum to early Holocene records from the deep WAIS Divide and Taylor Glacier Horizontal ice cores.

McConnell, J. R.; Anschütz, H.; Baggenstos, D.; Das, S. B.; Isaksson, E. D.; Lawrence, R.; Layman, L.; Maselli, O.; Severinghaus, J. P.; Sigl, M.; Petit, J. R.; Grente, B.

2012-12-01

284

Impact of climate fluctuations on deposition of DDT and hexachlorocyclohexane in mountain glaciers: evidence from ice core records.  

PubMed

How do climate fluctuations affect DDT and hexachlorocyclohexane (HCH) distribution in the global scale? In this study, the interactions between climate variations and depositions of DDT and HCH in ice cores from Mt. Everest (the Tibetan Plateau), Mt. Muztagata (the eastern Pamirs) and the Rocky Mountains were investigated. All data regarding DDT/HCH deposition were obtained from the published results. Concentrations of DDT and HCH in an ice core from Mt. Everest were associated with the El Nino-Southern Oscillation. Concentrations of DDT in an ice core from Mt. Muztagata were significantly correlated with the Siberia High pattern. Concentrations of HCH in an ice core from Snow Dome of the Rocky Mountains responded to the North Atlantic Oscillation. These associations suggested that there are some linkages between climate variations and the global distribution of persistent organic pollutants. PMID:19775787

Wang, Xiaoping; Gong, Ping; Zhang, Qianggong; Yao, Tandong

2010-02-01

285

Pliocene Antarctic sea-ice reconstruction based on the diatom record the ANDRILL 1B core  

NASA Astrophysics Data System (ADS)

The ANtarctic DRILLing Program’s AND-1B core, comprising 13 interglacial diatomaceous sections spanning the early Pliocene to the early Pleistocene, provides a largely complete record of Pliocene climate and sea-ice conditions in the Ross Sea. As primary producers, diatoms are directly influenced by surface water conditions, thus fossil assemblages provide a high quality proxy for past surface waters. The modern diatom flora of the Southern Ocean reflects the strong zonal system characterized by a seasonal sea-ice zone (SSIZ), a permanent open ocean zone (POOZ), and a subantarctic zone (SAZ), each with a distinct water column and sedimentary diatom assemblage. The stratigraphic distribution of these assemblages in the AND-1B core provides a history of changing sea surface temperature (SST) and sea-ice conditions through the Pliocene and early Pleistocene. In the early to mid-Pliocene section (4.6-3.3 Ma) the SSIZ is only represented by a few percent, including during glacial stages. This contrasts with the >80% present in the modern western Ross Sea. The SAZ is well represented during this interval in the core, along with the POOZ assemblage, despite the high latitude and proximity to the coastline. This assemblage indicates minimal sea-ice during the summer photoperiod at this latitude. The SSIZ assemblage is present but remains minor during the latter part of the mid-Pliocene (3.3-3.0 Ma). The diatom assemblage suggests surface water stratification, possibly indicating persistent polynya conditions. This period is followed by an interval characterized by both a slight increase in sea-ice and in subantarctic species, which we interpret as reflecting stronger seasonal SST variability compared to prior periods. The sea-ice assemblage and specific sea-ice indicator species increase slightly through the late Pliocene (2.0 Ma) and early Pleistocene (1.07 Ma) but never approach the abundance observed in the modern Ross Sea. These results show that the seasonal sea-ice belt that characterizes the modern Southern Ocean did not develop until the mid or late Pleistocene. The AND-1B diatom record suggests summer SST of up to 4-5° C with slightly colder conditions that remained above freezing (-1.8° C) during the mid-Pliocene and late Pliocene. The subantarctic assemblage is represented by only a few species, which suggests that SSTs never reached temperatures above 8°. The co-occurrence of species from SSIZ, POOZ and SAZ in certain intervals suggests that the zonal system was weaker than that of the modern Southern Ocean. With SST above the freezing point for extended periods of time during the interglacial Pliocene and early Pleistocene (MIS-31), it follows that marine and coastal ice sheets and ice shelves were reduced as well, corroborating recent modeling results. Coastal oceanographic conditions reflected in the AND-1B core indicate that throughout the Pliocene ocean circulation and bottom-water formation were significantly different than today.

Scherer, R. P.; Sjunneskog, C. M.; Winter, D.; Riesselman, C.

2010-12-01

286

Comparison of analytical results for chloride, sulfate and nitrate obtained from adjacent ice core samples by two ion chromatographic methods  

Microsoft Academic Search

The anions chloride, sulfate and nitrate in nearly 500 pairs of ice core samples from the same depth were determined in a 121 m long ice core from Svalbard. The analyses were performed separately using an ion chromatograph with Dionex AS9 and AS15 columns with Na2CO3 and NaOH eluents. Results showed a small (5-6 m gl 21 ) but statistically

T. Kekonen; P. Peramaki; J. C. Moore

2003-01-01

287

High resolution CO2 record over the last 1000 years from the EPICA Kohnen Station ice core  

NASA Astrophysics Data System (ADS)

The concentration of atmospheric CO_2 has been increasing steadily since the beginning of industrialization to its present value of over 370 ppmv. Although the value of 280 ppmv is genarally accepted for the pre-industrial CO_2 concentration, it was not constant during the last millennium. A high resolution record of atmospheric CO_2 concentration from the last millennium is obtained by analysing the air enclosed in the Kohnen Station ice core drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA). The record shows an increase from about 280 ppmv to 284 ppmv between 1000 and 1200 yr A.D. and a fairly continuous decrease to a mean value of about 279 ppmv around 1700 yr A.D. This record is in good agreement with the record obtained from the Law Dome ice core, except between 1600 and 1800 yr A.D. where the values of the Kohnen Station ice core are higher than those from the Law Dome ice core. Possible reasons for this discrepancy and comparisons with previous results from other ice cores are discussed.

Siegenthaler, U.; Monnin, E.; Kawamura, K.; Stauffer, B.; Spahni, R.; Barnola, J.-M.; Stocker, T. F.

2003-04-01

288

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

289

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

290

Spatial heterogeneity of Greenland ice-core dust composition and provenance  

NASA Astrophysics Data System (ADS)

By comparing mineralogical and isotopic (Sr and Nd) composition of mineral dust extracted from Greenland ice-cores and snow deposits with that of fine particles in sediment samples from potential source areas (PSA) for Greenland dust, it has been shown that eastern Asia was the source for central Greenland dust during several intervals of the last Glacial period [Biscaye et al., 1997; Svensson et al., 2000], in two intervals of the Holocene [Svensson, 1998], and through the present day [Bory et al., 2002; Bory et al., in press]. Based on transport patterns, it has often been suggested, however, that North American and African dust could reach the Greenland ice cap. Mosher et al. [1993], for instance, claimed to have identified an African source for a dust event at Dye 3 in southern Greenland. Identifying possible non-Asian dust sources to Greenland is important since it would bear on the large temporal variability of ice-core dust concentration, whose causes remain largely unexplained, as well as on the validation of dust transport models. Determining the degree of spatial heterogeneity of Greenland dust composition, and therefore provenance, can be done by analyzing contemporaneous dust samples in as many locations as possible. Here we report on six samples from six Greenland ice-cores, representing several decades of dust deposition each, all expect one within the 17th and 18th century. The six locations (Dye 3, A8-Crete region, Renland, GRIP, NorthGRIP, Hans Tausen) range from 65-82^oN and 27-43^oW. Variations in tracers composition (mineralogical and isotopic) are apparent, particularly between sites located on top of the ice cap and those located around the periphery, reflecting a distribution with altitude of dust sources and transport patterns to the ice-cap. The lower altitude sites are likely to be influenced by proximal dust sources. These results, however, confirm that long-range dust transport from eastern Asia is the main source of dust deposited on all central elevated sites.

Bory, A.; Biscaye, P.; Piotrowski, A.; Steffensen, J. P.

2003-04-01

291

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

292

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

293

Exploitation of chemical profiles by conjugate variable analysis: application to the dating of a tropical ice core (Nevado Illimani, Bolivia)  

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 age can generally not be easily established and requires to combine a large number of investigations and/or modeling effort. This paper presents a new approach of ice core dating based on conjugate variable (depth and spatial frequency) analysis of chemical profiles. The relationship between the depth of a given ice layer and the date it was deposited is determined using ion concentration depth profiles obtained along a one hundred-meters deep ice core recovered in the summit area of the Nevado Illimani (6350 m a.s.l.), located in the Eastern Bolivian Andes (16°37' S, 67°46' W). The results of Fourier conjugate analysis and wavelet tranforms are first compared. Both methods are applied to nitrate concentration depth profile. The resulting chronologies are checked by comparison with the multi-proxy year-by-year dating published by de Angelis et al. (2003) and with volcanic tie points, demonstrating the efficiency of Fourier conjugate analysis when tracking the natural variability of chemical proxies. The Fourier conjugate analysis is then applied to concentration depth profiles of seven other ions thus providing information on the suitability of each of them for dating studies of tropical Andean ice cores.

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

2013-06-01

294

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

SciTech Connect

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{degree} to 12{degree}C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio {delta}{sup 18}O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5{degree} to 6{degree}C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.

Thompson, L.G.; Henderson, K.A.; Bolzan, J.F. [Ohio State Univ., Columbus, OH (United States)] [and others

1995-07-07

295

Reduction in northward incursions of the South Asian monsoon since ~1400 AD inferred from a Mt. Everest ice core  

NASA Astrophysics Data System (ADS)

A highly resolved Mt. Everest ice core reveals a decrease in marine and increase in continental air masses related to relatively high summer surface pressure over Mongolia, and reduction in northward incursions of the summer South Asian monsoon since ~1400 AD. Previously published proxy records from lower sites south of the Himalayas indicate strengthening of the monsoon since this time. These regional differences are consistent with a south-north seesaw in convective activity in the Asian monsoon region, and reflect a southward shift in the mean summer position of the monsoon trough since ~1400 AD. The change in monsoonal circulation at 1400 AD is synchronous with a reduction in solar irradiance and the onset of the LIA. This demonstrates a hemispheric scale circulation reorganization at this time, and the potential for future large shifts in monsoonal circulation.

Kaspari, S.; Mayewski, P.; Kang, S.; Sneed, S.; Hou, S.; Hooke, R.; Kreutz, K.; Introne, D.; Handley, M.; Maasch, K.; Qin, D.; Ren, J.

2007-08-01

296

Testing Environmental Records From Ice Cores of a Temperate Alpine Glacier  

NASA Astrophysics Data System (ADS)

Low-latitude temperate alpine glaciers are largely overlooked but potentially useful archives of paleoenvironmental data; although smaller and shorter-lived than polar glaciers, their position adjacent to areas of dense population makes these glaciers attractive research targets. The Palisade Glacier is the largest glacier in the Sierra Nevada, and thus most likely to contain a reasonably unaltered physical and chemical record for the region. We collected two ice cores, ~4-m and 6-m long, from the uppermost bench on the glacier in August, 2003. Subsamples of the ice cores were analyzed for stable isotopes (d18O and dD), trace elemental abundance, and mass-accumulation stratigraphy. In addition, we sampled snow pits near the coring site in early July and early August 2003, and late June 2004 to constrain physical and isotopic changes in the snowpack through the summer meltseason. A SNOTEL site in the same drainage basin provides local records of daily precipitation and temperature, approximately 2000 feet below Palisade Glacier Our results suggest that despite recent thinning, the Palisade glacier preserves both isotopic and elemental stratigraphy. Annual layers are most apparent in the trace element concentrations, which indicate the cores preserve 4-5 years of accumulation, probably from the mid-to late1990's. A heavy concentration of the dust at the surface, combined with snow accumulation records from nearby SNOTEL sites, indicate that all snow from the previous 6 years (since winter of 1997/98, the last above-average snow year in the basin) was lost to ablation. Significantly lower visible dust concentrations in the underlying layers indicate that the core site had net accumulation during the preceding 4 years, in agreement with the SNOTEL record. Stable isotopes co-vary in the cores, coincident with the dust stratigraphy. In addition, the dD/d18O ratios closely resemble the trend of the global meteoric water line, suggesting that post-depositional melting and fractionation have been minimal. These results lend further support to previous studies (e.g., Naftz et al., 1993; Steig et al., 1998) that indicate that small temperate glaciers can preserve valuable, if complex, records of past environmental change. Further coring is needed to confirm our results, and to test viability of deeper ice in this or other glaciers.

Gillespie, A. J.; Clark, D. H.; Steig, E. J.; McConnell, J.

2004-12-01

297

A new method for high-resolution methane measurements on polar ice cores using continuous flow analysis.  

PubMed

Methane (CH4) is the second most important anthropogenic greenhouse gas in the atmosphere. Rapid variations of the CH4 concentration, as frequently registered, for example, during the last ice age, have been used as reliable time markers for the definition of a common time scale of polar ice cores. In addition, these variations indicate changes in the sources of methane primarily associated with the presence of wetlands. In order to determine the exact time evolution of such fast concentration changes, CH4 measurements of the highest resolution in the ice core archive are required. Here, we present a new, semicontinuous and field-deployable CH4 detection method, which was incorporated in a continuous flow analysis (CFA) system. In CFA, samples cut along the axis of an ice core are melted at a melt speed of typically 3.5 cm/min. The air from bubbles in the ice core is extracted continuously from the meltwater and forwarded to a gas chromatograph (GC) for high-resolution CH4 measurements. The GC performs a measurement every 3.5 min, hence, a depth resolution of 15 cm is achieved atthe chosen melt rate. An even higher resolution is not necessary due to the low pass filtering of air in ice cores caused by the slow bubble enclosure process and the diffusion of air in firn. Reproducibility of the new method is 3%, thus, for a typical CH4 concentration of 500 ppb during an ice age, this corresponds to an absolute precision of 15 ppb, comparable to traditional analyses on discrete samples. Results of CFA-CH4 measurements on the ice core from Talos Dome (Antarctica) illustrate the much higher temporal resolution of our method compared with established melt-refreeze CH4 measurements and demonstrate the feasibility of the new method. PMID:19708368

Schüpbach, Simon; Federer, Urs; Kaufmann, Patrik R; Hutterli, Manuel A; Buiron, Daphné; Blunier, Thomas; Fischer, Hubertus; Stocker, Thomas F

2009-07-15

298

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

299

Annual accumulation for Greenland updated using ice core data developed during 2000–2006 and analysis of daily coastal meteorological data  

Microsoft Academic Search

An updated accumulation map for Greenland is presented on the basis of 39 new ice core estimates of accumulation, 256 ice sheet estimates from ice cores and snow pits used in previous maps, and reanalysis of time series data from 20 coastal weather stations. The period 1950–2000 is better represented by the data than are earlier periods. Ice-sheet-wide accumulation was

Roger C. Bales; Qinghua Guo; Dayong Shen; Joseph R. McConnell; Guoming Du; John F. Burkhart; Vandy B. Spikes; Edward Hanna; John Cappelen

2009-01-01

300

A Deglacial Record of Carbon Dioxide from the WAIS Divide Ice Core, Antarctica  

NASA Astrophysics Data System (ADS)

Establishing the role of atmospheric CO2 during the last deglaciation has important implications for deciphering the mechanisms associated with the transition from glacial to interglacial states. A precise, high-resolution record of atmospheric CO2 is one essential milestone. Existing Antarctic ice core records have provided insight into both the timing of CO2 changes and likely sources, but lack the temporal resolution to address some important problems. The WAIS Divide ice core has the potential to produce the highest resolution and most well dated CO2 record for the last ~60 ka, due to the high accumulation rate at the site (presently 20 cm/yr). This record will be key for understanding the timing and role of CO2 changes during notable climatic intervals in the past (e.g. Antarctic Cold Reversal, Younger Dryas). Here we present a CO2 record from WAIS Divide, Antarctica for the period 22,000 - 8,000 years BP. Preliminary data at ~200 yr resolution are in general agreement with previous reconstructions of CO2 during the last 20,000 years, and document the same general trends at millennial and longer scales. Additionally, several abrupt changes in both CO2 and CH4 occur synchronously throughout the core, which may provide insight into the mechanisms associated with those shifts. Given the small delta-age and excellent chronologic constraints for the WAIS Divide core, the CO2 record will document variability at the centennial or shorter scale and thus we are currently measuring CO2 at this resolution over critical transitions in the core (i.e. ACR), which we will also present at the meeting.

Marcott, S. A.; Brook, E. J.; Sowers, T.; Kalk, M. K.

2012-04-01

301

A High Resolution Isotopic ice Core Record Covering the Last 800 000 Years.  

NASA Astrophysics Data System (ADS)

The two cores drilled at the Dome C site in East Antarctica (elevation 3233 m, mean annual temperature, - 54.5°C) in the framework of the European Program for Ice Coring in Antarctica, now provide a continuous deuterium profile covering the last 800 ky. Thanks to a recent extension over its last 60 meters, the 3201 m Antarctic climate record now extends back to marine stage 20. Whereas published data (EPICA Community members, 2004) are of low temporal resolution (e.g. 3000 years), we will have at the time of the meeting a much more detailed deuterium profile to present, at least for most of the core. We will first discuss the EPICA profile in view of existing East Antarctic ice core records (Vostok and Dome F) and its temperature interpretation. This comparison will also include the results from the second EPICA core drilled at Kohnen Station in the Atlantic sector of East Antarctica, available at that time. We will then focus on the spectral properties of the 800 ky climate record and on its comparison with marine records. Of particular interest are the change of pacing before and after the MBE (Mid-Brunhes Event) and the timing and duration of stadials, interstadials, and interglacials which will lead us to discuss how the EPICA timescale was derived. Particular attention will be paid to the last glacial cycle, for which the EPICA deuterium record shows counterparts for each of the successive Dansgaard/Oeschger events, both for large and small ones, with possible implications for the seesaw mechanism.

Jouzel, J.; Cattani, O.; Dreyfus, G.; Falourd, S.; Masson-Delmotte, V.; Nouet, J.; Oerter, H.; Johnsen, S.; Parrenin, F.; Stenni, B.

2004-12-01

302

Organic acids: Differences in ice core records between Glacier 1, Tianshan, China and the polar areas  

Microsoft Academic Search

Formate (HCOO?), acetate (CH3COO?), oxalate (C2O42?) and pyruvate ((CO2O42?) are detected in a 14.08-m-long ice core recovered in Glacier 1 at the Urumqi riverhead, Tianshan, China, which is a mid-latitude\\u000a alpine glacier (43°06?N, 86°49?E). the mean concentrations for the four organic acids in recent four decades are (102.8 ±\\u000a 147.3), (392.3±390.8), (6.9 ± 14.8) and (4.2 ± 8.3) ng\\/g, respectively,

Xinqing Li; Dahe Qin; Hui Zhou

2001-01-01

303

Large longitude libration of Mercury reveals a molten core.  

PubMed

Observations of radar speckle patterns tied to the rotation of Mercury establish that the planet occupies a Cassini state with obliquity of 2.11 +/- 0.1 arc minutes. The measurements show that the planet exhibits librations in longitude that are forced at the 88-day orbital period, as predicted by theory. The large amplitude of the oscillations, 35.8 +/- 2 arc seconds, together with the Mariner 10 determination of the gravitational harmonic coefficient C22, indicates that the mantle of Mercury is decoupled from a core that is at least partially molten. PMID:17478713

Margot, J L; Peale, S J; Jurgens, R F; Slade, M A; Holin, I V

2007-05-01

304

Synchronisation of the EDML and EDC ice cores for the last 52 kyr by volcanic signature matching  

NASA Astrophysics Data System (ADS)

A common time scale for the EPICA ice cores from Dome C (EDC) and Dronning Maud Land (EDML) was established. Since EDML core was not drilled on a dome, the development of the EDML1 time scale for the EPICA ice core drilled in Dronning Maud Land was carried on by creating a detailed stratigraphic link between this core and the one drilled at Dome C, dated by a simpler 1D ice-flow model. The synchronisation between the two ice cores was built via the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulfate, which was employed for the last 52 kyr of the record. By evaluating the ratio R of the apparent duration of temporal intervals between couples of isochrones, the depth comparison between the two cores was turned into an estimate of anomalies between the modelled EDC and EDML glaciological age models during the studied period. On average R ranges between 0.8 and 1.2 corresponding to an uncertainty within 20% in the estimate of the time duration in at least one of the two ice cores. Significant deviations of R up to 1.4-1.5 are observed between 18 and 28 kyr BP. At this step our approach is not able to unequivocally find out which of the models is affected by the errors, but assuming the thinning function at both sites and accumulation history at Dome C, which was drilled on a dome, as being correct, this anomaly can be ascribed to a complex spatial accumulation variability (which may be different at present day and in the past) and to upstream ice flow in the area of the EDML core.

Severi, M.; Becagli, S.; Castellano, E.; Morganti, A.; Traversi, R.; Udisti, R.; Ruth, U.; Fischer, H.; Huybrechts, P.; Wolff, E.; Parrenin, F.; Kaufmann, P.; Lambert, F.; Steffensen, J. P.

2007-03-01

305

New constraints on the gas age-ice age difference along the EPICA ice cores, 0-50 kyr  

Microsoft Academic Search

Gas is trapped in polar ice sheets at ~50-120 m below the surface and is therefore younger than the surrounding ice. Firn densification models are used to evaluate this ice age-gas age difference (Deltaage) in the past. However, such models are not well tested on low accumulation and cold sites of the East Antarctic plateau, especially for periods with different

L. Loulergue; F. Parrenin; T. Blunier; J.-M. Barnola; R. Spahni; A. Schilt; G. Raisbeck; J. Chappellaz

2007-01-01

306

Formation of the isotopic composition of snow at the Elbrus highlands (Caucasus) based on ice cores investigations  

NASA Astrophysics Data System (ADS)

The results of the isotopic investigations of several ice cores obtained at the Western Plateau of the Mt. Elbrus (Caucasus) are presented. The isotopic composition of the upper part (60 m) of the deep ice core (182 m) obtained in 2009 is also discussed. According to our estimations this core covers last 400 years. There is distinct seasonal cycle in the isotopic composition record of these cores. High accumulation rate (mean accumulation rate 1450 mm w.e. per year) and precise sampling resolution (20-25 samples for one year cycle) allowed obtaining seasonal values of the isotopic composition and accumulation rate. Dating of the cores was performed based on annual layers counting and was corrected using precisely dated dust layers. Mean year and mean seasonal values of the isotopic composition and accumulation rate were calculated for 33 years (1979-2011). These values were compared with available meteorological records (10 stations) in the region, atmosphere circulation characteristics, back-trajectories calculations and GNIP data. Possible mechanisms of precipitation and ice core isotopic composition in the Caucasus were derived. These results will be used for interpretation of the isotopic composition data from the bottom part of the deep ice core.

Kozachek, Anna

2014-05-01

307

Cross-Spectral Comparison of Dust and Cosmogenic Nuclide Records from Greenland Ice Cores Demonstrate Synchronicity at Millennial Timescales  

NASA Astrophysics Data System (ADS)

Greenland ice core records of dust and cosmogenic nuclides, converted to flux, share a striking resemblance on millennial timescales. However, to date, the significance of the relationship between these two parameters has received little attention. Here, we compare records of 10Be, 36Cl, and dust spanning ~18ky to ~33ky from the GRIP and GISP2 ice cores using cross-spectral analysis. Our findings demonstrate a statistically robust relationship between the cosmogenic nuclide flux and the dust flux, revealing a common mode of in-phase variability with a period of ~1600 years and coincident with the Northern Hemisphere Dansgaard-Oeschger events. Millennial-scale variability in cosmogenic nuclides from Greenland ice cores is commonly attributed to solar variability while variations in Greenland dust concentrations are associated with changes in atmospheric circulation, but why these two processes would co-vary remains unclear. We suggest that circulation could also act as a previously unrecognized control on cosmogenic nuclide fluxes, whereby variable mixing between the troposphere and stratosphere could explain the portion of the observed millennial-scale variability which cannot be explained by solar variability alone. Our proposed mechanism invokes changes in atmospheric mixing due to upper level (troposphere-stratosphere boundary) wind shear, which climate models predict may change during climate changes as a result of baroclinic variability. GCM simulations suggest that changes in baroclinicity between the LGM and present day lead to changes in the upper level jet velocities (500mb), which in turn, affect the vertical wind shear at upper levels (200-300mb). Because dust deposition scales closely with changes in wind velocity and chemical constituent exchange from the stratosphere to the troposphere is largely a function of jet proximal clear air turbulence provoked by instabilities in vertical shear, the Greenland dust and cosmogenic records may be particularly sensitive to atmospheric reorganizations influencing the jet. Therefore, dust deposition and cosmogenic mixing from the stratosphere are intimately coupled as both are affected by changes in climate regimes. Additional work is required to quantify the relationship between wind-shear variability and stratosphere-troposphere exchange, and their effects on atmospheric dust and cosmogenic nuclide deposition.

Balbas, A.; Cuzzone, J. K.; Mix, A. C.; Clark, P. U.

2013-12-01

308

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

309

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

310

Methanesulphonic acid from Talos Dome ice core as a marker of past periodicity of Ross Sea ice extent and southern hemisphere atmospheric circulation mode  

NASA Astrophysics Data System (ADS)

This work contributes to the understanding of variation in methanesulphonic (MSA) concentration in an ice core drilled during the 1996-97 Antarctic Campaign at the coastal plateau site of Talos Dome (East Antarctica) as function of sea ice extent in Ross Sea sector and southern hemisphere atmospheric circulation mode. Unperturbed stratigraphy and high ice thickness make Talos Dome a promising site for deep ice coring, which started in December 2004 and reached a depth of 1619.2 m, which is a few meters above the bedrock, in December 2007. This ice core record is assumed to cover the previous 120 kyr. In preparation of the deep drilling, an 89 m firn core (TD96) was drilled at the dome culmination in November 1996 and, in this work, the results obtained from this firn core are reported. MSA stratigraphy from TD96 core was compared with anomalies of the satellite-measured sea ice extension (1973-1995) in the Ross Sea and Wilkes Land oceanic sector. In spite of the sparseness of sea ice data, the MSA maxima fit with many positive sea ice anomalies in the Ross Sea. This evidence suggests that marine biogenic activity enhanced by large sea ice cover is an important, but not exclusive, factor in controlling MSA concentration in snow precipitation at Talos Dome. Other than source intensity, differences in regional atmospheric transport mechanisms affect the arrival of MSA-rich aerosol at Talos Dome. To clarify the role of transport processes in bringing biogenic aerosol to Talos Dome, a spectral analysis was applied to the MSA, SOI (South Oscillation Index), and SAM (Southern Annular Mode) record. Synchronicity or phase shift between the chemical signature and atmospheric circulation modes were tested. The variations in the MSA profile have a periodicity of 6.9, 4.9, 3.5, and 2.9 years. The 6.9 and 2.9 year periodicities show a strong positive correlation and are synchronous with corresponding SOI periodicity. This variability could be related to an increase in MSA source intensity (by dimethylsulphide from phytoplanktonic activity) linked to the sea ice extension in the Ross Sea area, but also to an increased strength in transport processes. Both of these factors are correlated with La Niña events (SOI positive values). Furthermore, SAM positive values are related to an increased sea ice extension in the Ross Sea sector and show two main periodicities 3.3 and 3.8 years. These periodicities determine the MSA variability at 3.5 years. However, the effect of intensification of the polar vortex and the consequent reduction in transport process intensity, which reduce the delivery of air masses enriched in MSA from oceanic areas to Talos Dome, makes the effect of the SAM on the MSA concentration at Talos Dome less active than the SOI. In this way, snow deposition at the Talos Dome records larger MSA concentration by the combined effects of increased source emissions and more efficient transport processes. The MSA record from Talos Dome can therefore be considered a reliable proxy of sea ice extension when the effect of changes in transport processes in this region of Antarctica is considered. Over the previous 140 years, these conditions occur with a periodicity of 6.9 years.

Becagli, S.; Castellano, E.; Curran, M.; Manganelli, D.; Marino, F.; Morganti, A.; Proposito, M.; Severi, M.; Traversi, R.; Udisti, R.

2009-04-01

311

A Holocene record of atmospheric methyl chloride from Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) is a naturally occurring, ozone-depleting trace gas with an atmospheric lifetime of about a year. The current CH3Cl level over Antarctica is about 530 parts per trillion. Tropical terrestrial emissions are the largest CH3Cl source and reaction with atmospheric OH is the major loss. In this study, we present CH3Cl measurements from the Taylor Dome ice core from East Antarctica. CH3Cl was measured in 62 ice core samples with gas ages covering the past ~70 ky BP. The new Holocene data partially overlaps in time with Late Holocene measurements from South Pole. These two records show reasonable agreement given uncertainties in gas ages, suggesting that both cores contain a record of paleoatmospheric CH3Cl variability. The Taylor Dome ice core shows Early Holocene (~11-10 ky BP) CH3Cl levels of 490-510 ppt, ~5-10% lower than the present day level. CH3Cl levels declined from ~10-7 ky BP to a broad minimum of 440 ppt from ~7-3 ky BP. This period was followed by a 15-20% rise during the Late Holocene (~3-0.5 ky BP), when CH3Cl levels increased to 470-480 ppt. The observed Holocene variations in atmospheric CH3Cl are on the order of 10-20% and are most likely a result of changes in tropical terrestrial emissions, assuming the changes are source-driven. The pattern of CH3Cl variability during the Holocene parallels that of atmospheric methane (CH4) [Brook et al., 2000]. The similar timing and magnitude of changes in the CH3Cl and CH4 records suggests that their variations are due to a common cause. Large-scale changes in tropical hydrology could be responsible for the long-term trends in both trace gases during the Holocene. Alternatively, changes in atmospheric OH may be responsible for the Holocene variability, since reaction with OH is the major loss process for both CH3Cl and CH4.

Verhulst, K. R.; Aydin, K. M.; Saltzman, E. S.

2012-12-01

312

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 L.

313

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

314

Volcanic synchronisation between the EPICA Dome C and Vostok ice cores (Antarctica) 0-145 kyr BP  

NASA Astrophysics Data System (ADS)

This study aims at refining the synchronisation between the EPICA Dome C (EDC) and Vostok ice cores in the time interval 0-145 kyr BP by using the volcanic signatures. 102 common volcanic events were identified by using continuous electrical conductivity (ECM), di-electrical profiling (DEP) and sulfate measurements while trying to minimize the distortion of the glaciological chronologies. This is an update and a continuation of previous works performed over the 0-45 kyr interval that provided 56 tie points to the ice core chronologies (Udisti et al., 2004). This synchronisation will serve to establish Antarctic Ice Core Chronology 2012, the next synchronised Antarctic dating. A change of slope in the EDC-depth/Vostok-depth diagram is probably related to a change of accumulation regime as well as to a change of ice thickness upstream of the Lake Vostok, but we did not invoke any significant temporal change of surface accumulation at EDC relative to Vostok. No significant phase difference is detected between the EDC and Vostok isotopic records, but depth shifts between the Vostok 3G and 5G ice cores prevent from looking at this problem accurately. Three possible candidates for the Toba volcanic super-eruption ~73 kyr ago are suggested in the Vostok and EDC volcanic records. Neither the ECM, DEP nor the sulfate fingerprints for these 3 events are significantly larger than many others in the records.

Parrenin, F.; Petit, J.-R.; Masson-Delmotte, V.; Wolff, E.; Basile-Doelsch, I.; Jouzel, J.; Lipenkov, V.; Rasmussen, S. O.; Schwander, J.; Severi, M.; Udisti, R.; Veres, D.; Vinther, B. M.

2012-06-01

315

Resedimentation of debris on an ice-cored lateral moraine in the high-Arctic (Kongsvegen, Svalbard)  

NASA Astrophysics Data System (ADS)

In ice-cored landform assemblages, the process of resedimentation via sediment-flow is important in determining the morphology and sedimentary facies distribution after the ice core has melted. This paper documents the sediment-flow processes associated with the resedimentation of an ice-cored lateral moraine at Kongsvegen, Svalbard. Decay of the ice-cored lateral moraine is dominated by the development of a sediment-flow fan, which has an 'hour-glass' form in plan. The fan comprises a broad source area on the crest of the lateral moraine separated from the fan surface, composed of tessellated flow lobes, by a narrow ice-floored channel system. The principle sedimentary facies associated with this fan include matrix-supported diamictons, laminated silts and fine sands. The evolution of this fan and the likely end-products after complete deglaciation are discussed, and this paper contributes modern analogue data relevant to the interpretation of the Pleistocene landform and sediment record.

Bennett, Matthew R.; Huddart, David; Glasser, Neil F.; Hambrey, Michael J.

2000-10-01

316

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

317

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

318

Arrival of Sulfate Aerosols from Iceland's Laki Eruption (1783-1784 AD) to the Greenland Ice Sheet: A Critical Ice Core Dating Tool  

NASA Astrophysics Data System (ADS)

The Laki (Iceland) volcanic event was a basaltic flood lava eruption lasting from June 8, 1783 to February 7, 1784. The timing of the arrival of the sulfate aerosols and volcanic fragments to the Greenland Ice Sheet (GIS) remains uncertain, but is important to confirm as the highly conductive sulfate layer has been consistently used as a time stratigraphic marker (1783 AD) in ice cores collected across Greenland. However, in the GISP2 ice core a few glass shards were found within the annual layer lying just below that containing the sulfate aerosols from Laki suggesting that the ash arrived first, in 1783, while the aerosols arrived the following year [Fiacco et al., 1994]. Additional published ice core results have neither confirmed nor refuted this observation. We have taken advantage of the accurately dated, high temporal resolution ice cores collected by PARCA (Program for Arctic Regional Climate Assessment) to (1) determine more precisely the timing of the arrival of Laki's sulfate aerosols and (2) assess the spatial variability of the excess sulfate contributed by Laki to the GIS. Our results indicate that the sulfate emitted from the Laki eruption most likely arrived on the GIS in the late summer or early fall of 1783 AD. This is also supported by contemporary weather logs and official reports of the appearance of Laki haze [Thordarson and Self, 2003]. The flux of Laki sulfate varies significantly over the GIS, largely as a function of the regional annual accumulation rate. Laki sulfate aerosols also arrived as a single pulse in most of the PARCA cores, suggesting that only a small fraction of the gases emitted from Laki reached the stratosphere. References: Fiacco, R.J.,et al., Atmospheric aerosol loading and transport due to the 1783-84 Laki eruption in Iceland, interpreted from ash particles and acidity in the GISP2 ice core, Quat. Res., 42, 231-240, 1994. Thordarson, T, and S. Self, Atmospheric and environmental effects of the 1783-1784 Laki eruption: A review and reassessment, J. Geophy. Res., 108, 4011-4039, 2003.

Wei, L.; Mosley-Thompson, E.

2006-12-01

319

Changes in black carbon deposition to Antarctica from two high-resolution ice core records, 1850-2000 AD  

NASA Astrophysics Data System (ADS)

Refractory black carbon aerosols (rBC) emitted by biomass burning (fires) and fossil fuel combustion, affect global climate and atmospheric chemistry. In the Southern Hemisphere (SH), rBC is transported in the atmosphere from low- and mid-latitudes to Antarctica and deposited to the polar ice sheet preserving a history of emissions and atmospheric transport. Here, we present two high-resolution Antarctic rBC ice core records drilled from the West Antarctic Ice Sheet divide and Law Dome on the periphery of the East Antarctic ice sheet. Separated by ~3500 km, the records span calendar years 1850-2001 and reflect the rBC distribution over the Indian and Pacific ocean sectors of the Southern Ocean. Concentrations of rBC in the ice cores displayed significant variability at annual to decadal time scales, notably in ENSO-QBO and AAO frequency bands. The delay observed between rBC and ENSO variability suggested that ENSO does not directly affect rBC transport, but rather continental hydrology, subsequent fire regimes, and aerosol emissions. From 1850 to 1950, the two ice core records were uncorrelated but were highly correlated from 1950 to 2002 (cross-correlation coefficient at annual resolution: r = 0.54, p < 0.01) due to a common decrease in rBC variability. The decrease in ice-core rBC from the 1950s to late 1980s displays similarities with inventories of SH rBC grass fires and biofuel emissions, which show reduced emission estimates over that period.

Bisiaux, M. M.; Edwards, R.; McConnell, J. R.; Curran, M. A. J.; Van Ommen, T. D.; Smith, A. M.; Neumann, T. A.; Pasteris, D. R.; Penner, J. E.; Taylor, K.

2012-05-01

320

A gas extraction system for the measurement of carbon dioxide and carbon isotopes in polar ice cores  

SciTech Connect

Knowledge of the distribution of Carbon 13 in the glacial ocean, atmosphere, and biosphere is important to understanding the causes of glacial/interglacial changes in atmospheric CO[sub 2] levels. Although deep-ocean Carbon 13 values are well-constrained by ocean sediment studies, model-based estimates of changes in the carbon budget for the biosphere and atmosphere vary considerably. Measurement of atmospheric Carbon 13 in CO[sub 2] in ice cores will provide additional constraints on this budget and will also improve estimates of changes in the ocean surface layer Carbon 13. Direct measurement of ancient atmospheric Carbon 13 can be accomplished through polar ice core studies. A gas-extraction line for ice cores has been designed and constructed with particular attention to the specific difficulties of measuring Carbon 13 in CO[sub 2]. The ice is shaved, rather than crushed, to minimize fractionation effects resulting from gas travel through long air-paths in the ice. To minimize the risk of isotopic contamination and fractionation within the vacuum line, CO[sub 2] is separated immediately from the air; the CO[sub 2] concentration is then measured by a simple pressure/volume comparison rather than by gas chromatography or spectroscopy. Measurements from Greenland ice core samples give an average value of 280[plus minus]2 ppM CO[sub 2] for preindustrial samples, demonstrating that the extraction system gives accurate, precise determinations Of CO[sub 2] concentrations. Measurement of [delta][sup 13]C from polar ice samples has not been achieved at this time. However, results on standard air samples demonstrate a precision for [delta][sup 13]C of less than 0.2[per thousand] at the 95% confidence level.

Steig, E.

1992-06-01

321

A gas extraction system for the measurement of carbon dioxide and carbon isotopes in polar ice cores  

SciTech Connect

Knowledge of the distribution of Carbon 13 in the glacial ocean, atmosphere, and biosphere is important to understanding the causes of glacial/interglacial changes in atmospheric CO{sub 2} levels. Although deep-ocean Carbon 13 values are well-constrained by ocean sediment studies, model-based estimates of changes in the carbon budget for the biosphere and atmosphere vary considerably. Measurement of atmospheric Carbon 13 in CO{sub 2} in ice cores will provide additional constraints on this budget and will also improve estimates of changes in the ocean surface layer Carbon 13. Direct measurement of ancient atmospheric Carbon 13 can be accomplished through polar ice core studies. A gas-extraction line for ice cores has been designed and constructed with particular attention to the specific difficulties of measuring Carbon 13 in CO{sub 2}. The ice is shaved, rather than crushed, to minimize fractionation effects resulting from gas travel through long air-paths in the ice. To minimize the risk of isotopic contamination and fractionation within the vacuum line, CO{sub 2} is separated immediately from the air; the CO{sub 2} concentration is then measured by a simple pressure/volume comparison rather than by gas chromatography or spectroscopy. Measurements from Greenland ice core samples give an average value of 280{plus_minus}2 ppM CO{sub 2} for preindustrial samples, demonstrating that the extraction system gives accurate, precise determinations Of CO{sub 2} concentrations. Measurement of {delta}{sup 13}C from polar ice samples has not been achieved at this time. However, results on standard air samples demonstrate a precision for {delta}{sup 13}C of less than 0.2{per_thousand} at the 95% confidence level.

Steig, E.

1992-06-01

322

Stable isotope records for the past 2000 years from ice cores in central Dronning Maud Land, Antarctica  

NASA Astrophysics Data System (ADS)

Ice coring on the plateau of the inland ice of Dronning Maud Land, Antarctica, took place in the period 1998 through 2006. The central ice core is the EDML ice core (75.0017 S, 0.0678 E, 2882 m a.s.l.) drilled adjacent to the German Kohnen station in the frame of the European Project for Ice Coring in Antarctica (EPICA). It covers more than 150 kyrs in time and can serve as a reference core for the complete Holocene, too. In this paper the focus is on the past 2 kyrs of 18-O data. During the EPICA pre-site survey in the 1997/98 field season two ice cores were drilled and analysed reaching back in time approximately 2 kyrs. The core B32 was located 1.6 km west of EDML, the core B33 (75.1670 S, 6.4985 E, 3160 m a.s.l.) approximately 190 km to the east and at a 300 m higher elevation. In the surroundings of Kohnen station in 2004 another 200 m deep core (B34) was drilled, covering more than 2 kyrs of accumulation. It was synchronized with the age scale of EDML by means of DEP measurements. The paper compares the 18-O records, which are converted to temperature with the local isotope-temperature relationship. None of the cores shows an increase of the 18-O content indicating a stable temperature regime during the past 2 kyrs. However, decadal and centennial variations are detectable. Thus, a slight increase of 18-O content in the 20th century can be observed. It peaks around 1985 AD and does not continue afterwards. Some of the cooling periods appear after volcanic eruptions. The cores are used to construct a stacked isotope/ temperature record for central Dronning Maud Land. The work was done in the frame of the ESF PolarCLIMATE joint research project HOLOCLIP, with financial support of the German Ministry of Education and Research (BMBF).

Oerter, H.; Kipfstuhl, S.; Wilhelms, F.

2012-04-01

323

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

2014-02-01

324

Black carbon concentrations and fluxes since the Last Glacial Maximum in Greenland and Antarctic ice cores  

NASA Astrophysics Data System (ADS)

Warming from increased carbon dioxide and other greenhouse gas concentrations is the long-term driver of climate change but short-lived aerosols such as black carbon (BC) and continental dust also are important components of climate forcing. BC and dust aerosols in snow are especially important in the high latitudes because of their strong impact on albedo. With their short lifetimes in the atmosphere, aerosol concentrations and deposition rates are dominated by regional - rather than global - sources and intra- and inter-annual variability is high. Because most dust and BC aerosols in high latitudes originate in lower latitudes, changes in long range transport processes and pathways may dominate over changes in source strength in determining concentrations and deposition rates in the Polar Regions. However, detailed understanding of past and present concentrations, deposition rates, sources, and transport pathways of BC and dust is lacking. Here we present and discuss detailed measurements of BC, dust, and related source tracers in the WAIS Divide and NEEM deep ice cores. Our records at both sites extend from the Last Glacial Maximum to the Early Holocene and also span the last two millennia. Similar measurements in a Taylor Glacier horizontal core and section of GISP2, as well as in a broad array of Greenland and Antarctic cores spanning recent centuries to decades, help elucidate spatial variability within each region during the last glacial to interglacial transition and recent past, respectively.

McConnell, J. R.; Sigl, M.; Baggenstos, D.; Fritzsche, D.; Dahl-Jensen, D.; Das, S. B.; Kreutz, K. J.; Maselli, O.; McGwire, K. C.; Nolan, M.; Opel, T.; Severinghaus, J. P.; Steffensen, J.

2012-12-01

325

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

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-microm 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

2005-02-01

326

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.

Juck, D. F.; Whissell, G.; Steven, B.; Pollard, W.; McKay, C. P.; Greer, C. W.; Whyte, L. G.

2005-01-01

327

Near-edge x-ray absorption fine structures revealed in core ionization photoelectron spectroscopy.  

PubMed

Simultaneous core ionization and core excitation have been observed in the C(2)H(2n) (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K(-2)V) core excited states of the K(-1) molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude. PMID:24093255

Nakano, M; Selles, P; Lablanquie, P; Hikosaka, Y; Penent, F; Shigemasa, E; Ito, K; Carniato, S

2013-09-20

328

Near-Edge X-Ray Absorption Fine Structures Revealed in Core Ionization Photoelectron Spectroscopy  

NASA Astrophysics Data System (ADS)

Simultaneous core ionization and core excitation have been observed in the C2H2n (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K-2V) core excited states of the K-1 molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude.

Nakano, M.; Selles, P.; Lablanquie, P.; Hikosaka, Y.; Penent, F.; Shigemasa, E.; Ito, K.; Carniato, S.

2013-09-01

329

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

330

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

331

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.

332

Assessing post-depositional alteration and the integrity of ice core nitrate-N and -O isotopic records at the Quelccaya Ice Cap, Peru  

NASA Astrophysics Data System (ADS)

Nitrate (NO3-) is a common chemical species found in snow and ice. Both nitrate and its atmospheric precursor NOx (NO and NO2) are of importance to climate, biogeochemistry and the composition of the atmosphere. For instance, nitrate is a critical biological nutrient, while NOx regulates concentrations of ozone (O3) and hydroxyl (OH) and thus influences the chemical and radiative properties of Earth's atmosphere. NOx sources include fossil fuel combustion, biomass burning, soil microbial processes and lightning. Past changes in NOx emissions, tropospheric distributions and consequent effects on the atmosphere, however, are unknown. Interpreting stable nitrogen (?15N) and oxygen (?18O and ?17O) isotope ratios in nitrate preserved in ice cores can address these issues as they contain diagnostic signatures of NOx sources and oxidation processes, respectively. The potential caveat to this is that nitrate can be lost from snow and firn via photolysis (as NOx) and/or volatilization (as nitric acid). Because these processes are isotopically fractionating, it is necessary to determine if, or to what degree, such post-depositional alteration takes place at a given site before an isotopic record from ice core nitrate can be utilized as a paleoenvironmental proxy. This work addresses post-depositional alteration at the Quelccaya Ice Cap (5670 masl) in southeastern Peru in order to assess the integrity of the nitrate record in an 1800-year ice core from the site. This work represents the first of its kind outside the polar regions and is significant in that natural NOx sources and OH production are dominantly located in the Tropics. Additionally, because nitrate and NOx are not uniformly distributed in the troposphere, low-latitude records are needed to bridge ongoing polar work in order to establish a global perspective.

Buffen, A. M.; Hastings, M. G.; Thompson, L. G.; Mosley-Thompson, E. S.

2011-12-01

333

Proposed re-dating of the European ice core chronology by seven years prior to the 7th century AD  

NASA Astrophysics Data System (ADS)

Progress in the study of past climate change requires integration of historical documentation, tree-ring data and ice-core chemistry. Larsen et al. (2008) re-evaluate volcanic acid signals in the Dye-3, GRIP and NGRIP ice cores and identify large eruptions at 529 +/- 2 and 533-534 +/- 2; the latter claimed to cause the `dry fog' of 536-537 and environmental consequences to 550; this conflicts with previous suggestions of a two stage environmental event; one in 536, the second c.540. Understanding the full range of natural hazards requires critical evaluation of the happenings in the mid-6th century. This paper will show that 4 spaced tree-ring responses to extreme environmental conditions in the 6th century can be used to re-locate 4 key ice-acid dates. Moving the ice-core chronology forward 7 years places two large volcanoes in 536 and 541 explaining the extended duration of the 536-550 effects and anchoring the ice chronology.

Baillie, M. G. L.

2008-08-01

334

Southern Ocean simulations in Coordinated Ocean-ice reference experiments phase II (CORE-II)  

NASA Astrophysics Data System (ADS)

The Coordinated Ocean-Ice Reference Experiment (CORE) phase II is an experimental protocol for ocean-ice coupled simulations forced with interannually varying atmospheric data sets for the period 1948-2007. This effort, involving several centers around the world, is coordinated by the CLIVAR Working Group on Ocean Model Development (WGOMD). The hindcast simulations provide a framework for both model evaluation and studying variability and change at seasonal to decadal time scales. Several regional studies are planned and currently underway. We present an intercomparison that focuses on the recent evolution of the Southern Ocean as simulated by the different models. We focus on the mean state and variability of the Antarctic circumpolar current (ACC), the meridional overturning circulation (MOC), as well as water masses and their ventilation. To do this, we consider the evolution of the drivers of these circulations, both wind stress and buoyancy forcing, and of the interior structure of the Southern Ocean. Models of different resolutions are considered, from coarse to eddy-permitting/resolving, and an attempt is made to evaluate the role of mesoscale eddies and their parameterization. Comparison with observational estimates is made when possible. The identification of the strengths and weaknesses of ocean models with respect to the evolution of the Southern Ocean and its global consequences is also a key aim of the study.

Farneti, Riccardo; Core Groups

2013-04-01

335

Background levels of formate and other ions in ice cores from inland Greenland  

NASA Astrophysics Data System (ADS)

Concentration levels of the organic acids HCOO- and CH3SO3(-), inorganic acids NO3(-) and excess SO4(2-) and ammonium were measured in pre-1900 AD ice layers from seven geographically dispersed inland sites in Greenland. Average multiple-year background concentration levels are calculated for each ion at each site from laboratory measurements of continuous core samples representing from 4 to 10 years of snow accumulation (32 to 80 individual measurements) from various time intervals. The HCOO(-) concentration level increases from 6 ng/g in the most northern colder site to 36 ng/g in the most southern warmer site; CH3SO3(-) increases from 0.9 ng/g to 2.8 ng/g; NO3(-) decreases from 83 ng/g to 37 ng/g; excess SO4(2-) decreases from 43 ng/g to 19ng/g, all with variability. The distribution of the NH4(+) ion shows a nearly constant level at about 6 ng/g for all sites except Dye-2 where it reaches 10 ng/g. The deposition patterns for HCOO(-) and NH4(+) on the ice sheet suggest major contributions arrive from sources originating from the southwest of Greenland.

Osada, Kazuo; Langway, Chester C., Jr.

1993-12-01

336

Temperature reconstruction from 10 to 120 kyr b2k from the NGRIP ice core  

NASA Astrophysics Data System (ADS)

In order to reconstruct the temperature of the North Greenland Ice Core Project (NGRIP) site, new measurements of ?15N have been performed covering the time period from the beginning of the Holocene to Dansgaard-Oeschger (DO) event 8. Together with previously measured and mostly published ?15N data, we present for the first time a NGRIP temperature reconstruction for the whole last glacial period from 10 to 120 kyr b2k (thousand years before 2000 AD) including every DO event based on ?15N isotope measurements combined with a firn densification and heat diffusion model. The detected temperature rises at the onset of DO events range from 5 °C (DO 25) up to 16.5 °C (DO 11) with an uncertainty of ±3 °C. To bring measured and modelled data into agreement, we had to reduce the accumulation rate given by the NGRIP ss09sea06bm timescale in some periods by 30 to 35%, especially during the last glacial maximum. A comparison between reconstructed temperature and ?18Oice data confirms that the isotopic composition of the stadial was strongly influenced by seasonality. We evidence an anticorrelation between the variations of the ?18Oice sensitivity to temperature (referred to as ?) and obliquity in agreement with a simple Rayleigh distillation model. Finally, we suggest that ? might be influenced by the Northern Hemisphere ice sheet volume.

Kindler, P.; Guillevic, M.; Baumgartner, M.; Schwander, J.; Landais, A.; Leuenberger, M.; Spahni, R.; Capron, E.; Chappellaz, J.

2014-04-01

337

Volcanic forcing during the Common Era reevaluated based on new ice core evidence  

NASA Astrophysics Data System (ADS)

The attribution of observed temperature trends to external forcings strongly relies on the use of climate model simulations. The history of forcing and global temperatures of the past can be used to constrain projections into the future which are the basis for environmental policy decisions. Climate model simulations of global climate evolution during the past Millennium use reconstructions of volcanic aerosol forcing based on sulfate signals extracted from the polar ice sheets. Beside uncertainties related to the calibration of atmospheric optical depth (AOD), low spatial and temporal coverage of the proxy data and low confidence in the dating are the main sources of uncertainty for existing volcanic forcing indices. Here we reconstruct volcanic sulfate deposition over Antarctica based on a comprehensive array of existing and new ice core records, synchronized to the annually dated WAIS Divide timescale. This reconstruction for the last 2,000 years is unprecedented in robustness, dating accuracy, length and spatial coverage. We find that Antarctic average volcanic sulfate deposition for some of the largest events during the Common Era currently is overestimated by 20 to 30%, while for some other large eruptions values are underestimated by up to 160%. This implies that current volcanic aerosol forcing sets used in climate model simulations have errors of similar magnitude. Combined with a similar detailed reconstruction obtained for the Northern Hemisphere, the Antarctic sulfate record presented here provides the proxy data needed for improvement of volcanic forcing reconstructions that are widely used in climate simulations.

Sigl, M.; McConnell, J. R.; Toohey, M.; Maselli, O. J.; Pasteris, D.; Layman, L.; Isaksson, E. D.; Kawamura, K.; Motizuki, Y.; Edwards, R.; Curran, M. A.; Das, S. B.; Krueger, K.

2013-12-01

338

Glaciochemical investigation of an ice core from Belukha glacier, Siberian Altai  

NASA Astrophysics Data System (ADS)

During summer 2001, a 140 m long ice core was recovered from the Belukha glacier (49°48'26''N, 86°34'43''E, 4062 m a.s.l.) in the Siberian Altai. The englacial temperature of -17°C indicates that this unique glaciochemical record is well preserved and suitable for the reconstruction of air pollution levels in this previously unexplored region. The upper 86 m were dated by 210Pb and cover the period 1862-2001. A lack of strong winter minima was observed in the ?18O record and attributed to the small amount of precipitation during that season and to wind erosion. The ion concentrations are comparable to those observed in Swiss glaciers, except for ammonium and formate, where enhanced concentrations indicate biogenic emissions from Siberian forests. Sulfate, ammonium and nitrate records all show anthropogenic impacts despite the remoteness of this site.

Olivier, Susanne; Schwikowski, Margit; Brütsch, Sabina; Eyrikh, Stella; Gäggeler, Heinz W.; Lüthi, Martin; Papina, Tatyana; Saurer, Matthias; Schotterer, Ulrich; Tobler, Leonhard; Vogel, Edith

2003-10-01

339

A 750 year ice core record of past biogenic emissions from Siberian boreal forests  

NASA Astrophysics Data System (ADS)

Emissions from forests represent an important source of gaseous precursors of aerosols that can significantly alter the regional radiation balance. Long-term records of biogenic emissions are available for Northern America and the Amazon Basin, whereas the historical development of emissions from Siberian forests, comprising about 20% of the world's forested area, is unknown so far. Here we investigate ice core ammonium and formate records for the last 750 years, representing biogenic emissions from boreal Siberian forests in the pre-industrial era. Biogenic emissions were found to be closely related to changes in temperature following variations in solar activity. In addition, anthropogenic emissions have caused a strong increase of the ammonium concentrations and a drop of the formate concentrations in the last 60 years.

Eichler, Anja; Brütsch, Sabina; Olivier, Susanne; Papina, Tatyana; Schwikowski, Margit

2009-09-01

340

Carbon Isotope Constraints on the Deglacial CO2 Rise from Ice Cores  

NASA Astrophysics Data System (ADS)

The stable carbon isotope ratio of atmospheric CO2 (?13Catm) is a key parameter in deciphering past carbon cycle changes. Here we present ?13Catm 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 ?13Catm 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 ?13Catm evolution. During the Last Glacial Maximum, ?13Catm and atmospheric CO2 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.

Schmitt, Jochen; Schneider, Robert; Elsig, Joachim; Leuenberger, Daiana; Lourantou, Anna; Chappellaz, Jérôme; Köhler, Peter; Joos, Fortunat; Stocker, Thomas F.; Leuenberger, Markus; Fischer, Hubertus

2012-05-01

341

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

342

Black Carbon Record from an Eastern Pamir Ice Core and its Biomass Contribution  

NASA Astrophysics Data System (ADS)

Black carbon (BC) and levoglucosan concentrations were measured in an ice core, covering time period 1868-2000 AD, from Mt. Muztagh Ata, east Pamir, to recover temporal trend of BC emission, and contribution of biomass as an energy resource. BC concentration before 1950 AD is 0.37 ng/g on average, increases rapidly afterwards to the maximum value of 2.0 ng/g during 1980s, and then shortly decreases dramatically, which is likely due to the economic collapse of the Former USSR. Levoglucosan concentration presents a similar variation with BC, especially in the recent three decades, and suggests in the source regions biomass burning (including lignite) plays an important role in historical BC emission.

Wang, Mo; Xu, Baiqing; Kaspari, Susan; Gleixner, Gerd

2014-05-01

343

Synchronisation of the EDML and EDC ice cores for the last 52 kyr by volcanic signature matching  

NASA Astrophysics Data System (ADS)

A common time scale for the EPICA ice cores from Dome C (EDC) and Dronning Maud Land (EDML) has been established. Since the EDML core was not drilled on a dome, the development of the EDML1 time scale for the EPICA ice core drilled in Dronning Maud Land was based on the creation of a detailed stratigraphic link between EDML and EDC, which was dated by a simpler 1D ice-flow model. The synchronisation between the two EPICA ice cores was done through the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulfate, which was employed for the last 52 kyr of the record. We estimated the discrepancies between the modelled EDC and EDML glaciological age scales during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. On average R ranges between 0.8 and 1.2 corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. Significant deviations of R up to 1.4-1.5 are observed between 18 and 28 kyr before present (BP), where present is defined as 1950. At this stage our approach does not allow us unequivocally to find out which of the models is affected by errors, but assuming that the thinning function at both sites and accumulation history at Dome C (which was drilled on a dome) are correct, this anomaly can be ascribed to a complex spatial accumulation variability (which may be different in the past compared to the present day) upstream of the EDML core.

Severi, M.; Becagli, S.; Castellano, E.; Morganti, A.; Traversi, R.; Udisti, R.; Ruth, U.; Fischer, H.; Huybrechts, P.; Wolff, E.; Parrenin, F.; Kaufmann, P.; Lambert, F.; Steffensen, J. P.

2007-07-01

344

Climate sensitivity of the century-scale hydrogen peroxide (H2O2) record preserved in 23 ice cores from West Antarctica  

Microsoft Academic Search

We report new century-scale ice core records of hydrogen peroxide (H2O2), a major atmospheric oxidant, from 23 locations across the West Antarctic Ice Sheet (WAIS) and use the spatial variability of (multi-) annual mean H2O2 concentrations in snow and firn to investigate the sensitivity of ice core H2O2 preservation to mean annual temperature and accumulation rate. In agreement with the

Markus M. Frey; Roger C. Bales; Joseph R. McConnell

2006-01-01

345

Validity of the Temperature Reconstruction from Water Isotopes in Ice Cores  

NASA Technical Reports Server (NTRS)

Well-documented present-day distributions of stable water isotopes (HDO and others) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (SD and 51"0) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/ surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh-type distillation models and (particularly over Greenland) general circulation models (GCMS) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present-day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes.

Jouzel, J.; Alley, R. B.; Cuffey, K. M.; Dansgaard, W.; Grootes, P.; Hoffmann, G.; Johnsen, S. J.; Koster, R. D.; Peel, D.; Shuman, C. A.; Stievenard, M.; Stuiver, M.; White, J.

1997-01-01

346

Holocene CO2 Records from the EPICA Dome C and Kohnen Station (DML) Ice Cores.  

NASA Astrophysics Data System (ADS)

The concentration of atmospheric CO_2 has been increasing steadily since the beginning of the industrialization, from 280 parts per million by volume (ppmv) to its present value of over 370 ppmv. By investigating earlier, natural CO_2 variations, we expect to obtain information about feedbacks between the carbon cycle and climate and also the possible impact of the anthropogenic CO_2 on the climate system. Two high resolution records of atmospheric CO_2 concentration were measured at the Kohnen Station and Dome C ice cores, both drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA). The Dome C record shows a decrease of the CO_2 concentration from about 265 ppmv to 260 ppmv between 11 and 7 Ky B.P. (kiloyears before present) followed by an increase to about 280 ppmv at 1 Ky B.P.. The records from Dome C and Kohnen Station, which reach back to 5.5 Ky B.P., are in good agreement, whereas the scatter of the Dome C record seems higher. A comparison with the Taylor Dome record shows differences up to 5 ppmv, especially between 5 and 7 Ky B.P.. It is still not established if this difference is due to artefacts or differences in the timescale. However, based on the good agreement of the Dome C and Kohnen Station records we favour the interpretation that the difference between Dome C and Taylor Dome can be explained by a difference in the timescales up to 1 Ky. Some records suggest a stepwise increase of the CO_2 concentration. The credibility of this interesting feature is discussed.

Monnin, E.; Siegenthaler, U.; Kawamura, K.; Bellier, B.; Barnola, J.-M.; Stauffer, B.; Stocker, T. F.

2003-04-01

347

Ice-core data evidence for a prominent near 20 year time-scale of the Atlantic Multidecadal Oscillation  

Microsoft Academic Search

Using five ice core data sets combined into a single time series, we provide for the first time strong observational evidence for two distinct time scales of Arctic temperature fluctuation that are interpreted as variability associated with the Atlantic Multidecadal Oscillation (AMO). The dominant and the only statistically significant multidecadal signal has a time scale of about 20 years. The

Petr Chylek; Chris K. Folland; Henk A. Dijkstra; Glen Lesins; Manvendra K. Dubey

2011-01-01

348

Glacial to Holocene implications of the new 27000-year dust record from the EPICA Dome C (East Antarctica) ice core  

Microsoft Academic Search

Insoluble dust concentrations and volume-size distributions have been measured for the new 581 m deep Dome C-EPICA ice core (Antarctica). Over the 27000 years spanned by the record, microparticle measurements from 169 levels, to date, confirm evidence of the drastic decrease in bulk concentration from the Last Glacial Maximum (LGM) to the Holocene (interglacial) by a factor of more than

B. Delmonte; J. R. Petit; V. Maggi

2002-01-01

349

Seasonal deuterium excess in a Tien Shan ice core: Influence of moisture transport and recycling in Central Asia  

USGS Publications Warehouse

Stable water isotope (??18O, ??D) data from a high elevation (5100 masl) ice core recovered from the Tien Shan Mountains, Kyrgyzstan, display a seasonal cycle in deuterium excess (d = ??D - 8*??18O) related to changes in the regional hydrologic cycle during 1994-2000. While there is a strong correlation (r2 = 0.98) between ??18O and ??D in the ice core samples, the regression slope (6.9) and mean d value (23.0) are significantly different than the global meteoric water line values. The resulting time-series ice core d profile contains distinct winter maxima and summer minima, with a yearly d amplitude of ???15-20???. Local-scale processes that may affect d values preserved in the ice core are not consistent with the observed seasonal variability. Data from Central Asian monitoring sites in the Global Network of Isotopes in Precipitation (GNIP) have similar seasonal d changes. We suggest that regional-scale hydrological conditions, including seasonal changes in moisture source, transport, and recycling in the Caspian/Aral Sea region, are responsible for the observed spatial and temporal d variability.

Kreutz, K. J.; Wake, C. P.; Aizen, V. B.; DeWayne, Cecil, L.; Synal, H. -A.

2003-01-01

350

An Andean ice-core record of a Middle Holocene mega-drought in North Africa and Asia  

Microsoft Academic Search

An ice core from the Nevado Huascaran col in the Cordillera Blanca of northern Peru contains high-resolution time series of dust concentrations and size distributions since the end of the last glacial stage. A large dust peak, dated ? 4500 years ago, is contemporaneous with a widespread and prolonged drought that apparently extended from North Africa to eastern China, evidence

Mary E. Davis; Lonnie G. Thompson

2006-01-01

351

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

National Technical Information Service (NTIS)

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...

A. M. Smith D. R. Pasteris J. E. Penner J. R. McConnell K. Taylor M. A. J. Curran M. M. Bisiaux R. Edward T. A. Neumann T. D. VanOmmen

2012-01-01

352

Millennial and sub-millennial scale climatic variability over Marine Isotopic Stage 5: insights from polar ice cores (Invited)  

Microsoft Academic Search

The millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28-60 thousand of years before present, hereafter ka) and characterized by short and frequent Dansgaard-Oeschger (DO) events in Greenland ice cores. Recent and new results obtained on Antarctic (EPICA Dronning Maud Land

E. Capron; A. Landais; J. Chappellaz; A. Schilt; D. Buiron; D. Dahl-Jensen; H. Fischer; S. J. Johnsen; J. Jouzel; B. Lemieux-Dudon; M. Leuenberger; V. Masson-Delmotte; H. Meyer; H. Oerter; B. Stenni; T. F. Stocker

2010-01-01

353

Volcanic synchronisation of the EPICA-DC and TALDICE ice cores for the last 42 kyr BP  

NASA Astrophysics Data System (ADS)

The age scale synchronisation between the Talos Dome and the EPICA Dome C ice cores was carried on through the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulphate, which was employed for the last 42 kyr of the record. Using this tight stratigraphic link, we transferred the EDC age scale to the Talos Dome ice core, producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modelled TALDICE-1 age scale and the new scale during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. Except for a very few cases, R ranges between 0.8 and 1.2, corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. At this stage our approach does not allow us to unequivocally identify which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to 200 yr appear in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Thus, we propose for the Talos Dome ice core a new age scale (covering the whole Holocene) obtained by a direct transfer, via our stratigraphic link, from the EDC modelled age scale by Lemieux-Dudon et al. (2010).

Severi, M.; Udisti, R.; Becagli, S.; Stenni, B.; Traversi, R.

2012-03-01

354

Volcanic synchronisation of the EPICA-DC and TALDICE ice cores for the last 42 kyr BP  

NASA Astrophysics Data System (ADS)

An age scale synchronisation between the Talos Dome and the EPICA Dome C ice cores was carried on through the identification of several common volcanic signatures for the last 42 kyr. Using this tight stratigraphic link we transferred the EDC age scale to the Talos Dome ice core producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modeled TALDICE-1 age scale and the new one during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. Except for a very few cases, R ranges between 0.8 and 1.2 corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. At this stage our approach does not allow us unequivocally to find out which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to 200 years appears in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Thus, we propose for the Talos Dome ice core a new age scale (covering the whole Holocene) obtained by a direct transfer, via our stratigraphic link, from the EDC modelled age scale by Lemieux-Dudon et al. (2010).

Severi, M.; Udisti, R.; Becagli, S.; Stenni, B.; Traversi, R.

2012-04-01

355

A 62 ka record from the WAIS Divide ice core with annual resolution to 30 ka (so far)  

NASA Astrophysics Data System (ADS)

Drilling of the West Antarctic Ice Sheet (WAIS) Divide ice core has been completed to a depth of 3400 m, about 60 meters above the bed. We present an annually resolved time scale for the most recent 30ka (to 2800 m) based on electrical conductivity measurements, called "timescale WDC06A-5". Below 2800 m the ice is dated by matching isotopes, methane, and/or dust records to other ice cores. Optical borehole logging provides stratigraphic ties to other cores for the bottom-most 75 m that was drilled in December 2011, and indicates the bottom-most ice has an age of 62 ka. The relatively young ice at depth is likely the result of basal melting. The inferred annual layer thickness of the deep ice is >1 cm, suggesting that annual layer counting throughout the entire core may be possible with continuous flow analysis of the ice core chemistry; however, the annual signal in the electrical measurements fades at about 30 ka. We compare the WDC06A-5 timescale through the glacial-interglacial transition with the Greenland GICC05 and GISP2 timescales via rapid variations in methane. We calculate a preliminary delta-age with: 1) accumulation rate inferred from the annual layer thicknesses and thinning functions computed with a 1-D ice flow model, and 2) surface temperature inferred from the low resolution d18O record and a preliminary borehole temperature profile. The WDC06A-5 timescale agrees with the GICC05 and GISP2 timescales to within decades at the 8.2k event and the ACR termination (Younger Dryas/Preboreal transition, 11.7 ka). This is within the delta-age and correlation uncertainties. At the rapid methane drop at ~12.8 ka, the WDC06A-5 timescale is ~150 years older than GICC05 and ~90 older than GISP2; while at ~14.8 ka, the timescales once again agree within the delta-age and correlation uncertainties. The cause of the age discrepancy at 12.8 ka is unclear. We also compare the WDC06A-5 timescale at Dansgaard-Oeschger events 3 and 4 (~27.5 and 29 ka) to the radiometrically-dated speolethem records from Hulu Cave, China (Larry Edwards and Hai Cheng, personal communication). To make such a comparison, we assume that the rapid variations in methane from the WAIS Divide core are synchronous with the rapid variations in d18O in the speleothem record. We find that the WDC06A-5 timescale is multiple hundreds of years older than the Hulu Cave record. As the GICC05 timescale is younger than the Hulu timescale, this puts the WDC06A-5 timescale even older than the GICC05. The uncertainties in the comparison are large both because of the uncertainty in the synchroneity of the ice core methane and speleothem isotope variations and because of the larger delta-age for the ice core in the glacial period. The timescale for the WAIS Divide core will be revised when the CFA results become available.

Fudge, T. J.; Taylor, K.; McGwire, K.; Brook, E.; Sowers, T.; Steig, E.; White, J.; Vaughn, B.; Bay, R.; McConnell, J.; Waddington, E.; Conway, H.; Clow, G.; Cuffey, K.; Cole-Dai, J.; Ferris, D.; Severinghaus, J.

2012-04-01

356

Dynamics of the late Plio-Pleistocene West Antarctic Ice Sheet documented in subglacial diamictites, AND-1B drill core  

NASA Astrophysics Data System (ADS)

Geologic studies of sediment deposited by glaciers can provide crucial insights into the subglacial environment. We studied muddy diamictites in the ANtarctic geological DRILLing (ANDRILL) AND-1B drill core, acquired from beneath the Ross Ice Shelf in McMurdo Sound, with the aim of identifying paleo-ice stream activity in the Plio-Pleistocene. Glacial advances were identified from glacial surfaces of erosion (GSEs) and subglacial diamictites within three complete sequences were investigated using lithofacies associations, micromorphology, and quartz sand grain microtextures. Whereas conditions in the Late Pliocene resemble the modern Greenland Ice Sheet where fast flowing glaciers lubricated by surface meltwater terminate directly in the sea (interval 201-212 mbsl) conditions in the Late Pleistocene are similar to modern West Antarctic Ice Sheet (WAIS) ice streams (38-49 mbsl). We identify the latter from ductile deformation and high pore-water pressure, which resulted in pervasive rotation and formation of till pellets and low relief, rounded sand grains dominated by abrasion. In the transitional period during the Mid-Pleistocene (55-68 mbsf), a slow moving inland ice sheet deposited tills with brittle deformation, producing lineations and bi-masepic and unistrial plasma fabric, along with high relief, conchoidally fractured quartz grains. Changes in the provenance of gravel to cobble-size clasts support a distant source area of Byrd Glacier for fast-flowing paleo-ice streams and a proximal area between Darwin and Skelton Glaciers for the slow-moving inland ice sheet. This difference in till provenance documents a shift in direction of glacial flow at the core site, which indirectly reflects changes in the size and thickness of the WAIS. Hence, we found that fast ice streaming motion is a consequence of a thicker WAIS pushing flow lines to the west and introducing clasts from the Byrd Glacier source area to the drill site. The detailed analysis of diamictites in AND-1B demonstrates that Pliocene glacial intervals were warmer than in the Pleistocene when polar ice sheets grew from local inland ice to regional ice streams.

Cowan, Ellen A.; Christoffersen, Poul; Powell, Ross D.; Talarico, Franco M.

2014-08-01

357

Estimating the differential diffusion length of the stable water isotope signals obtained from ice core records.  

NASA Astrophysics Data System (ADS)

Stable water isotope signals retrieved from polar ice core records are smoothed by diffusion in the firn stage. The total amount of diffusion a layer has experienced can be quantified in terms of the diffusion length, which is the average displacement of a molecule due to diffusion. This length is a function of the firn temperature and the accumulation rate which makes it a valuable proxy for past local temperatures (Johnsen et al, 2000, Simonsen et al, 2011). In principle this proxy can be derived from either of the individual isotope signals (Oxygen-18 or Deuterium), but it is much better constrained when the difference in diffusion length between the two isotopes is used. The individual diffusion lengths and the differential diffusion lengths are commonly calculated using the power spectral densities (PSD) of the isotope data. The Maximum Entropy Method (MEM) is often used for the calculation of the PSD, but other methods such as the fast fourier transform or ones based on the autocorrelation series of the isotope data can also be used. However, in all these methods a parameter has to be chosen, for example the auto regression order in the MEM. Additionally, it is necessary to define a cut off frequency in order to use only the red part of the power spectrum. These choices can significantly influence diffusion length obtained with these methods. We present a new method which circumvents these issues, based on the correlation between the Oxygen-18 and Deuterium records. The measured Deuterium record is numerically diffused, after which the correlation between this record and the measured Oxygen-18 record is calculated. The correlation reaches a maximum when the diffusion lengths of the two records are equal. This allows us to recon