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1

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

NSDL National Science Digital Library

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

2

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

3

Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland  

Microsoft Academic Search

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

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

2007-01-01

4

Recent rapid warming trend revealed from the isotopic record in Muztagata ice core, eastern Pamirs  

NASA Astrophysics Data System (ADS)

Many have made efforts to clarify the climatic significance of stable isotopic variations in ice cores around central Asia through the study of stable isotopes in present-day precipitation. A new shallow ice core from Muztagata, in the eastern Pamirs, allows for a detailed comparison of annual ?18O variation with local meteorological data as well as with global air temperature variations. On the basis of a comparison of seasonal fluctuations of ?18O in the local precipitation, the 41.6-m ice core drilled at 7010 m provides a record of about one-half century. The annual fluctuations of ?18O in this ice core are in good agreement (correlation coefficient of 0.67) with the annual air temperature changes at the nearby meteorological station Taxkorgen, indicating that the isotopic record from this ice core is a reliable temperature trend indicator. The most important discovery from the ?18O variation of this ice core is a rapid warming trend in the 1990s, which is consistent with a general global warming trend over this time period. This recent rapid warming at higher elevations in this area has led to the quick retreat of alpine glaciers.

Tian, Lide; Yao, Tandong; Li, Zhen; Macclune, Kenneth; Wu, Guangjian; Xu, Baiqing; Li, Yuefang; Lu, Anxian; Shen, Yongping

2006-07-01

5

Chernobyl nuclear accident revealed from the 7010 m Muztagata ice core record  

Microsoft Academic Search

The total activity variation with depth from a 41.6 m Muztagata ice core drilled at 7010 m, recorded not only the 1963 radioactive\\u000a layer due to the thermonuclear test, but also clearly the radioactive peak released by the Chernobyl accident in 1986. This\\u000a finding indicates that the Chernobyl nuclear accident was clearly recorded in alpine glaciers in the Pamirs of

LiDe Tian; TanDong Yao; GuangJian Wu; Zhen Li; BaiQing Xu; YueFang Li

2007-01-01

6

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

7

Ice Core Investigations  

ERIC Educational Resources Information Center

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

Krim, Jessica; Brody, Michael

2008-01-01

8

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

9

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.

10

Synchronizing ice cores from the Renland and Agassiz ice caps to the Greenland Ice Core Chronology  

Microsoft Academic Search

Four ice cores from the Agassiz ice cap in the Canadian high arctic and one ice core from the Renland ice cap in eastern Greenland have been synchronized to the Greenland Ice Core Chronology 2005 (GICC05) which is based on annual layer counts in the DYE-3, GRIP and NGRIP ice cores. Volcanic reference horizons, seen in electrical conductivity measurements (ECM)

B. M. Vinther; H. B. Clausen; D. A. Fisher; R. M. Koerner; S. J. Johnsen; K. K. Andersen; D. Dahl-Jensen; S. O. Rasmussen; J. P. Steffensen; A. M. Svensson

2008-01-01

11

Polar Ice Cores: Climatic and Environmental Records.  

National Technical Information Service (NTIS)

Ice cores from Greenland and Antarctica provide multiple proxy records of climatic and environmental parameters. They reveal the anthropogenic impact on aerosol concentrations in Greenland snow (i.e., S04 and N03) and on atmospheric greenhouse gases. For ...

C. Lorius

1992-01-01

12

Mg\\/Ca-based temperature record from Cariaco Basin reveals SST changes in phase with Greenland ice core records  

Microsoft Academic Search

The Cariaco Basin, an anoxic marine basin on the northern shelf of Venezuela, preserves a unique climate record of the eastern Caribbean. Records from this basin have been instrumental in establishing potential ties between tropical climate records and high latitude ice core and oceanic records for the Holocene, last glacial termination, and marine isotope stage 3. A definitive temperature record

D. W. Lea; D. K. Pak; L. C. Peterson; K. A. Hughen

2003-01-01

13

Mg\\/Ca-Based Temperature Record from Cariaco Basin Reveals SST Changes in Phase with Greenland Ice Core Records  

Microsoft Academic Search

The Cariaco Basin, an anoxic marine basin on the northern shelf of Venezuela, preserves a unique sedimentary record of the tropical North Atlantic ocean. Records from this basin have been instrumental in establishing potential ties between tropical climate records and high latitude ice core and oceanic records for the Holocene, last glacial termination, and marine isotope stage 3. A definitive

D. W. Lea; D. K. Pak; L. C. Peterson; K. A. Hughen

2001-01-01

14

Ice Core Dating Software for Interactive Dating of Ice Cores  

Microsoft Academic Search

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

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

2005-01-01

15

Ices in Starless and Starforming Cores  

NASA Astrophysics Data System (ADS)

Icy grain mantles are commonly observed through infrared spectroscopy toward dense clouds, cloud cores, protostellar envelopes and protoplanetary disks. Up to 80% of the available oxygen, carbon and nitrogen are found in such ices; the most common ice constituents - H2O, CO2 and CO - are second in abundance only to H2 in many star forming regions. In addition to being a molecular reservoir, ice chemistry is responsible for much of the chemical evolution from H2O to complex, prebiotic molecules. Combining the exisiting ISO, Spitzer, VLT and Keck ice data results in a large sample of ice sources (~80) that span all stages of star formation and a large range of protostellar luminosities (<0.1-105 L?). Here we summarize the different techniques that have been applied to mine this ice data set on information on typical ice compositions in different environments and what this implies about how ices form and evolve during star and planet formation. The focus is on how to maximize the use of empirical constraints from ice observations, followed by the application of information from experiments and models. This strategy is used to identify ice bands and to constrain which ices form early during cloud formation, which form later in the prestellar core and which require protostellar heat and/or UV radiation to form. The utility of statistical tests, survival analysis and ice maps is highlighted; the latter directly reveals that the prestellar ice formation takes place in two phases, associated with H2O and CO ice formation, respectively, and that most protostellar ice variation can be explained by differences in the prestellar CO ice formation stage. Finally, special attention is paid to the difficulty of observing complex ices directly and how gas observations, experiments and models help in constraining this ice chemistry stage.

Öberg, Karin I.; Boogert, A. C. Adwin; Pontoppidan, Klaus M.; van den Broek, Saskia; van Dishoeck, Ewine F.; Bottinelli, Sandrine; Blake, Geoffrey A.; Evans, Neal J.

2011-12-01

16

Synchronizing ice cores from the Renland and Agassiz ice caps to the Greenland Ice Core Chronology  

NASA Astrophysics Data System (ADS)

Four ice cores from the Agassiz ice cap in the Canadian high arctic and one ice core from the Renland ice cap in eastern Greenland have been synchronized to the Greenland Ice Core Chronology 2005 (GICC05) which is based on annual layer counts in the DYE-3, GRIP and NGRIP ice cores. Volcanic reference horizons, seen in electrical conductivity measurements (ECM) have been used to carry out the synchronization throughout the Holocene. The Agassiz ice cores have been matched to the NGRIP ice core ECM signal, while the Renland core has been matched to the GRIP ice core ECM signal, thus tying the cores to GICC05. Furthermore, it has been possible to synchronize the Renland ice core to NGRIP-GICC05 in the glacial period back to 60,000 years b2k (years before A.D. 2000), on the basis of a matching of transitions between stadials and interstadials. This work brings the total number of ice core records that have been rigorously tied to the GICC05 timescale up to nine. Renland annual layer thicknesses are increasing with depth during the period from 7 to 8.5 ka b2k, a highly unusual observation only matched by a similar thickness increase in the glacial section of the Renland core some 60 ka ago. Annual layer thicknesses in the Agassiz ice cores point to a well-developed Raymond bump in the Agassiz ice cap.

Vinther, B. M.; Clausen, H. B.; Fisher, D. A.; Koerner, R. M.; Johnsen, S. J.; Andersen, K. K.; Dahl-Jensen, D.; Rasmussen, S. O.; Steffensen, J. P.; Svensson, A. M.

2008-04-01

17

Little ice age clearly recorded in northern Greenland ice cores  

Microsoft Academic Search

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

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

1998-01-01

18

Climatic Seesaws Across The North Pacific As Revealed By High-Mountain Ice Cores Drilled At Kamchatka And Wrangell-St. Elias Mountains  

Microsoft Academic Search

We drilled ca. 210-m deep ice cores at Mt. Ushkovsky (Kamchatka: 1998), King Col of Mt. Logan (2002) and Mt. Wrangell (2004). Thanks to the high accumulation rates up to 2 m per year in these mountains, the ice cores are expected to unveil the climate and atmospheric changes in the northern North Pacific during the last several centuries. The

T. Shiraiwa; K. Goto-Azuma; S. Kanamori; S. Matoba; C. S. Benson; Y. D. Muravyev; A. N. Salamatin

2004-01-01

19

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

20

A review of sea ice proxy information from polar ice cores  

NASA Astrophysics Data System (ADS)

Sea ice plays an important role in Earth's climate system. The lack of direct indications of past sea ice coverage, however, means that there is limited knowledge of the sensitivity and rate at which sea ice dynamics are involved in amplifying climate changes. As such, there is a need to develop new proxy records for reconstructing past sea ice conditions. Here we review the advances that have been made in using chemical tracers preserved in ice cores to determine past changes in sea ice cover around Antarctica. Ice core records of sea salt concentration show promise for revealing patterns of sea ice extent particularly over glacial–interglacial time scales. In the coldest climates, however, the sea salt signal appears to lose sensitivity and further work is required to determine how this proxy can be developed into a quantitative sea ice indicator. Methane sulphonic acid (MSA) in near-coastal ice cores has been used to reconstruct quantified changes and interannual variability in sea ice extent over shorter time scales spanning the last ˜160 years, and has potential to be extended to produce records of Antarctic sea ice changes throughout the Holocene. However the MSA ice core proxy also requires careful site assessment and interpretation alongside other palaeoclimate indicators to ensure reconstructions are not biased by non-sea ice factors, and we summarise some recommended strategies for the further development of sea ice histories from ice core MSA. For both proxies the limited information about the production and transfer of chemical markers from the sea ice zone to the Antarctic ice sheets remains an issue that requires further multidisciplinary study. Despite some exploratory and statistical work, the application of either proxy as an indicator of sea ice change in the Arctic also remains largely unknown. As information about these new ice core proxies builds, so too does the potential to develop a more comprehensive understanding of past changes in sea ice and its role in both long and short-term climate changes.

Abram, Nerilie J.; Wolff, Eric W.; Curran, Mark A. J.

2013-11-01

21

ACEX Grain Size Analyses, Revealing Arctic Paleo-Ice Environments  

Microsoft Academic Search

Summer 2004 hosted an unprecedented event in Arctic research; the successful coring of Arctic sediments to obtain a paleo-climate record that extends through the Cenozoic Era. Low resolution grain size analyses of samples taken during the Arctic Coring Expedition (ACEX) reveal five ice rafted debris (IRD) relationships, which we hypothesize to correspond to five distinct Arctic paleo-ice environments. This study

C. E. Ashmankas; K. Moran; M. O'Regan; S. Sugisaki

2006-01-01

22

Irregular glacial interstadials recorded in a new Greenland ice core  

Microsoft Academic Search

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

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

1992-01-01

23

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.

24

International ice core community meets to discuss best practices for ice core curation  

NASA Astrophysics Data System (ADS)

Several countries now have national ice core laboratories, or substantial ice core facilities, where these proxy archives of the Earth's past climate and atmosphere are safeguarded, processed, and analyzed. Australia, China, Denmark, Japan, Argentina, and the United States have formal, dedicated ice core repositories with laboratories. India's is under construction, in Goa. France, Germany, Russia, and the U.K. have long had substantial ice core holdings and facilities for analysis of ice cores. Brazil, Chile, Italy, and Switzerland have expanding field acquisition and analytical programs that require favorable storage conditions for ice cores.Representatives of 12 countries gathered in Milan, Italy, in late August for a first meeting, InterICE, of “international ice core establishments,” to compare and discuss ideas about best practices for acquisition, storage, curation, and distribution of the ice cores that have been drilled from the polar and temperate glaciers of the world, representing up to a half-million years of the Earth's most recent past.

Hinkley, Todd

25

Ice-core records of atmospheric sulphur  

PubMed Central

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

Legrand, M.

1997-01-01

26

Ice-Core Records of Atmospheric Sulphur  

NASA Astrophysics Data System (ADS)

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

Legrand, Michel

1997-02-01

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

A New Paradigm for Ice Core Drilling  

Microsoft Academic Search

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

Mary Albert; Charles Bentley; Mark Twickler

2010-01-01

29

A New Greenland Deep Ice Core  

Microsoft Academic Search

The polar ice sheets are rich sources of information on past atmospheric conditions, including paleoclimates. A new deep ice core has been drilled in south Greenland. Comparison of the oxygen isotopic profile with that from Camp Century and with a deep-sea foraminifera record indicates that the new core reaches back to about 90,000 years before present in a continuous sequence.

W. Dansgaard; H. B. Clausen; N. Gundestrup; C. U. Hammer; S. F. Johnsen; P. M. Kristinsdottir; N. Reeh

1982-01-01

30

Late Cenozoic oscillations of Antarctic ice sheets revealed by provenance of basement clasts and grain detrital modes in ANDRILL core AND-1B  

NASA Astrophysics Data System (ADS)

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 an evolving provenance, documented by long-term shifts in compositional patterns that can be interpreted as reflecting variations in ice volume and ice sheet thermal regimes and changes in paleogeography related to the emergence of several volcanic centres during the deposition of the drill core over the past ca. 3.5 Ma. The most significant change in diamictite provenance (identified at 82.7 metre below the sea floor, mbsf), coincides with a change in sedimentary cycle architecture from sequences that are dominated by diamictites (Mid-Late Pleistocene, above 82.7 mbsf) to sequences characterised by cycles of diamictite (subglacial) and diatomite (open-marine) deposition (Pliocene, below 82.7 mbsf). In the Mid-Late Pleistocene glacial/interglacial cycles diamictites show high amounts of Skelton-Mulock sourced clasts, supplied from both basement and overlying Beacon and Ferrar supergroups, and they also include a variable contribution from reworking of glacial sediments that were deposited during earlier glacial activity. In the Pliocene to early Pleistocene diatomite-diamictite cycles basement clast compositions indicate the same provenance (Mulock-Skelton) but the main debris load was picked up from volcanic centres in the McMurdo Sound area. Similarly, associated glacial minima sediments (i.e., diatomite intervals) are dominated by volcanic clasts suggesting calving of glaciers from Ross Island or the Koettlitz Glacier region during interglacials. In agreement with previous glaciological reconstructions and numerical ice sheet models, the provenance of glacially transported material is firmly identified in the region between Ross Island and the Skelton-Mulock glacier area (South Victoria Land). The reconstructed ice directions and ice dynamic model are comparable to the configurations proposed for the grounded ice expansion within the McMurdo Sound during the Last Glacial Maximum, and they are also consistent with ice-flow patterns previously reconstructed for Pliocene and Pleistocene glacial settings in the region.

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

2012-10-01

31

Antifreeze thermal ice core drilling: an effective approach to the acquisition of ice cores  

Microsoft Academic Search

Antifreeze thermal electric drills have a long history of ice drilling in temperate, subpolar and polar glaciers. Shallow, intermediate and deep ice cores have been obtained in Arctic, Antarctic and on high elevation glaciers. Many merits and drawbacks of antifreeze thermal technology have been discovered over the past 25 years. A modified version of the antifreeze thermal electric ice coring

V Zagorodnov; L. G Thompson; J. J Kelley; B Koci; V Mikhalenko

1998-01-01

32

THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS  

SciTech Connect

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

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

2011-10-20

33

Interpreting ancient ice in a shallow ice core from the South Yamato (Antarctica) blue ice area using flow modeling and compositional matching to deep ice cores  

Microsoft Academic Search

We explore methods of dating a 101 m ice core from a bare ice ablation area in the Yamato Mountains, Dronning Maud Land, East Antarctica. There are two unknowns, the age of the ice at the surface and the age spanned by the core. The ice crystal growth rate was used to estimate the age span of the core at

John C. Moore; Fumihiko Nishio; Shuji Fujita; Hideki Narita; Elizabeth Pasteur; Aslak Grinsted; Anna Sinisalo; Norikazu Maeno

2006-01-01

34

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

35

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

36

Scientific plan for deep ice core drilling in central Greenland (GISP 2: Greenland Ice Sheet Project)  

Microsoft Academic Search

Ice sheets are natural archival systems that continously 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 drilled to bedrock only three times: at Camp Century, Greenland, in 1966 (1,384 meters), at Byrd Station, Antarctica,

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

1985-01-01

37

CO2 record in the Byrd ice core 50,000-5,000 years bp  

Microsoft Academic Search

The analysis of air in polar ice cores revealed 30% lower CO2 values during glacial periods than during interglacial periods. At present this is confirmed by results from six different ice cores, two from Greenland and four from Antarctica1-5. In all cores the CO2 change coincides with the change in the isotopic composition of the ice, expressed as either the

A. Neftel; H. Oeschger; T. Staffelbach; B. Stauffer

1988-01-01

38

New ice core record of atmospheric methane  

NASA Astrophysics Data System (ADS)

Atmospheric concentrations of methane, an important greenhouse gas, have varied in the past on time scales ranging from seasons to hundreds of thousands of years. Understanding past variations is important to interpreting current natural and anthropogenic changes. Mitchell et al. present a new high-precision, high-resolution atmospheric methane record covering 1000-1800 C.E. from an ice core from the West Antarctic Ice Sheet Divide project that has confirmed the existence of multidecadal-scale variability during this time period. The new record, which complements other existing ice core methane records, shows that multidecadal-scale methane variability is only weakly correlated or uncorrelated with reconstructed temperature and precipitation variations. The authors also found that time periods when war or plague resulted in population declines are coincident with global atmospheric methane decreases. (Journal of Geophysical Research-Biogeosciences, doi:10.1029/ 2010JG001441, 2011)

Tretkoff, Ernie

2011-06-01

39

Ice-core evidence of abrupt climate changes  

PubMed Central

Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica.

Alley, Richard B.

2000-01-01

40

Ice-core evidence of abrupt climate changes.  

PubMed

Ice-core records show that climate changes in the past have been large, rapid, and synchronous over broad areas extending into low latitudes, with less variability over historical times. These ice-core records come from high mountain glaciers and the polar regions, including small ice caps and the large ice sheets of Greenland and Antarctica. PMID:10677460

Alley, R B

2000-02-15

41

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

42

Beryllium 10 in the Greenland Ice Core Project ice core at Summit, Greenland  

Microsoft Academic Search

Concentrations of the cosmogenic isotope 10Be have been measured in more than 1350 samples from the Greenland Ice Core Project (GRIP) ice core drilled at Summit, Greenland. Although a dust-associated component of 10Be retained by 0.45 mum filters in some of the samples complicates the interpretations, the results confirm that the first-order origin of 10Be concentration variations is changes in

F. Yiou; G. M. Raisbeck; S. Baumgartner; J. Beer; C. Hammer; S. Johnsen; J. Jouzel; P. W. Kubik; J. Lestringuez; M. Stiévenard; M. Suter; P. Yiou

1997-01-01

43

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

Microsoft Academic Search

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

A. Schomacker; K. H. Kjaer

2007-01-01

44

A new deep ice core from Akademii Nauk ice cap, Severnaya Zemlya, Eurasian Arctic: first results  

Microsoft Academic Search

The paper presents first results from the upper 54 m of a 723.91 m ice core drilled on Akademii Nauk ice cap, Severnaya Zemlya, Eurasian Artctic, in 1999-2001, supplemented by data from shallow ice cores. The glacier's peculiarity is the infiltration and refreezing of melting water, which changes the original isotopic and chemical signals. Therefore, stratigraphical observations in these ice

Diedrich Fritzsche; Frank Wilhelms; Lev M. Savatyugin; Jean Francis Pinglot; Hanno Meyer; Hans-Wolfgang Hubberten; Heinz Miller

2002-01-01

45

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.

46

Tropical glaciers: Potential for ice core paleoclimatic reconstructions  

Microsoft Academic Search

The objective of this work is to evaluate the potential of tropical glaciers and ice caps for the reconstruction of past climatic conditions by the analysis of firm and ice cores. Samples were collected in pits and from cores retrieved on three snow fields in the South American Andes: Quelccaya Ice Cap and Huascarán in Peru and Chimborazo in Ecuador.

L. C. Thompson; E. Mosley-Thompson; P. M. Grootes; M. Pourchet; S. Hastenrath

1984-01-01

47

Heat generated by cutting ice in deep ice-core drilling  

Microsoft Academic Search

In order to understand and solve the 'warm-ice problem' in deep ice-core drilling, we applied the metal-cutting theory to ice and estimated the heat generated during ice coring taking into account the mechanical and thermal properties of the ice and cutters. We found that (1) most of the heat in cutting is generated by shear deformation at the shear plane

Nobuhiko Azuma; Ikuo Tanabe; Hideaki Motoyama

2007-01-01

48

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

NASA Astrophysics Data System (ADS)

Full understanding of Antarctic sea-ice variability suffers from scarcity of data in the pre-satellite era. Although sea-ice variability is but one of many factors affecting Antarctic ice cores, ice-core records from the adjacent continental ice sheet offer a possible solution to this challenging problem. We apply tools from the field of artificial neural networks (ANNs) to reconstruct centennial-scale records of West Antarctic sea-ice variability using ice-core datasets from 18 West Antarctic sites (e.g., Siple Dome, USITASE) and satellite-based records of sea ice. As a nonlinear, highly flexible tool, ANNs offer a potential solution for relating ice-core predictors to sea-ice targets, e.g., seasalt chemistry to sea ice edge. Results point to a well-trained ANN being a necessary but not always sufficient prerequisite for developing sea ice reconstructions outside the satellite era from extended ice-core datasets. As such, qualitative interpretations currently appear safest. Limited overlap (~20-25 years) of ice core and sea ice records strongly influences reconstruction uncertainty. Ice-core data outside the calibration period are not always similar enough to the training data to be trustworthy predictors. Trends in sea ice data also create problems (most notably in the Bellingshausen Sea Region). The most reliable reconstructions to date, for the Amundsen Sea (140-115 °W, 1890-1994) and based on complete seasalt Na records from 10 ice core sites, suggest both a change to reduced interannual variability in sea ice edge ca. 1950 and fewer negative anomalies. Overall, reconstructions are quite sensitive to predictor used: not all predictors appear to be useful.

Reusch, D. B.

2010-12-01

49

Preindustrial atmospheric carbonyl sulfide (OCS) from an Antarctic ice core  

Microsoft Academic Search

The concentration of carbonyl sulfide (OCS) has been determined in several preindustrial air samples extracted from a shallow ice core from Siple Dome, West Antarctica. The extraction of the air was carried out by shredding the core under vacuum, followed by analysis by gas chromatography with mass spectrometric detection. 11 ice core samples were analyzed, ranging in depth from 82.3

Murat Aydin; Warren J. De Bruyn; Eric S. Saltzman

2002-01-01

50

Cryobiological ice core analyses in Altai Mountains, Russia  

Microsoft Academic Search

Microorganism in two shallow ice cores from the Sofiskiy Glacier (25.1m in length, taken at 3,435 m a.s.l.. in Jul, 2001) and the Belukha Glacier (20.94m in length, taken at 4,110m a.s.l. in Jul, 2001), Altai range of Russia, were examined for potential use in ice core analyses of this area. These ice cores and pit samples collected at the

J. Uetake; S. Kohshima; F. Nakazawa; M. Kohno; T. Kameda; K. Suzuki; K. Fujita; N. Takeuchi; V. Aizen; S. Alkhipov; S. A. Nikitin

2004-01-01

51

Effect of climate and ice-flow transients on ice-divide position and ice-core records  

NASA Astrophysics Data System (ADS)

Transients in accumulation and in ice flow can drive ice-divide migration. However, it is likely that dynamical changes initiated near the ice-sheet margin control ice-divide position. Interior ice exhibits a rapid response to modern marginal changes, and larger marginal changes during glacial-interglacial transitions likely led to a larger response. We investigate how flux variations that drive ice-divide migrations on hundreds to tens of thousands of year timescales can affect the depth-age scale, the layer-thickness profile, and the ice-temperature profile at ice-core sites at or near a stable divide position. For this study we use a 2.5-D ice-flow model that sufficiently captures the broad-scale behavior of ice-sheet interiors including ice-divide migration. A simpler 1-D or 2-D model is often used to interpret ice-core records and we compare our flowband behavior to calculations with these models. We apply our ice-flow models to ice-sheet settings similar to 1) Central West Antarctica near the WAIS Divide ice-core site and to 2) Central Greenland near the GRIP and GISP2 ice-core sites. These interior sites may have experienced divide migrations of at least tens of kilometers and they have provided valuable ice-core records. While we do not know the actual migration histories at these sites we will explore the response to plausible changes in accumulation and ice flow on various timescales. We assess the degree to which upstream affects may need to be considered in order to characterize ice-sheet history at an ice-core site. In addition to using the ice-flow models with prescribed forcing to aid in the interpretation of ice-core records, the measured depth-age scale and ice-temperature profile may be used as additional data to constrain an inverse problem to infer histories of accumulation rate, ice thickness, and ice-divide position from radar-observed internal layers; it is important to understand the sensitivity of the measured values to the unknown values that we seek to infer. Assessing model realizations of ice-core records that have been generated with different ice-sheet histories is groundwork for this inverse problem.

Koutnik, M.; Waddington, E.; Fudge, T. J.; Neumann, T.; Rasmussen, S.; Dahl-Jensen, D.

2012-04-01

52

Antarctic ice core samples: culturable bacterial diversity.  

PubMed

Culturable bacterial abundance at 11 different depths of a 50.26 m ice core from the Tallaksenvarden Nunatak, Antarctica, varied from 0.02 to 5.8 × 10(3) CFU ml(-1) of the melt water. A total of 138 bacterial strains were recovered from the 11 different depths of the ice core. Based on 16S rRNA gene sequence analyses, the 138 isolates could be categorized into 25 phylotypes belonging to phyla Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria. All isolates had 16S rRNA sequences similar to previously determined sequences (97.2-100%). No correlation was observed in the distribution of the isolates at the various depths either at the phylum, genus or species level. The 25 phylotypes varied in growth temperature range, tolerance to NaCl, growth pH range and ability to produce eight different extracellular enzymes at either 4 or 18 °C. Iso-, anteiso-, unsaturated and saturated fatty acids together constituted a significant proportion of the total fatty acid composition. PMID:23041141

Shivaji, Sisinthy; Begum, Zareena; Shiva Nageswara Rao, Singireesu Soma; Vishnu Vardhan Reddy, Puram V; Manasa, Poorna; Sailaja, Buddi; Prathiba, Mambatta S; Thamban, Meloth; Krishnan, Kottekkatu P; Singh, Shiv M; Srinivas, Tanuku N R

2012-10-04

53

Seasonal precipitation timing and ice core records  

SciTech Connect

Commenting on our work with isotope tracers and the origin of moisture in general circulation model simulations suggest that changes in the seasonal distribution of precipitation may provide strong control on isotopic variability in Greenland ice cores. In principle, we agree with the thrust of their comment. In a broad sense, without consideration of specific processes, the seasonality effects discussed and the moisture source effects described in our report are two classes of the same general phenomenon: evaporation, distillation, and transport of isotopes over different temperature regimes. Although the analysis for Greenland precipitation over the last century suggests that seasonal effects are a significant component of interannual isotopic variability, general circulation model (GCMs) represent one of the few means of assessing the importance of this phenomenon for interpreting the isotopic record over glacial cycles. The GCM approach is important for understanding the relationship between {delta}{sup 18}O and temperature because (1) thermodynamic principles and analysis of modern isotopic data suggest that present-day spatial {delta}{sup 18}O-temperature correlations cannot be considered an exact surrogate for the temporal relationship between these variables (2) geographic isotopic variability-for example, the differences in isotopic values among ice cores-can best be examined with a three-dimensional mode. This short article goes on to explain the researchers` results and reasoning. 5 refs., 1 fig.

Charles, C.D. [Univ. of California at San Diego, La Jolla, CA (United States); Rind, D. [Goddard Inst. for Space Studies, New York, NY (United States); Jouzel, J. [Centre d`Etudes de Saclay, Gif-sur-Yvette (France)] [and others

1995-07-14

54

X-Ray Diffraction Topographic Studies of Antarctic Deep Core Ice  

Microsoft Academic Search

X-ray diffraction topographs of Antarctic deep core ice revealed mosaic strctures in comparatively large single crystals near the bottom of a 2000 m ice sheet. Strain fields around thin cleavage cracks produced on the relaxation process of the ice exhibited characteristic ``Butterfly-wing'' contrasts on the topograph scanned on (0001) with {11\\\\bar{2}0} reflection. Three types of characteristic contrasts are well interpreted

Hitoshi Shoji; Akira Higashi

1978-01-01

55

Continuous measurements of methane mixing ratios from ice cores  

NASA Astrophysics Data System (ADS)

This work presents a new, field-deployable technique for continuous, high-resolution measurements of methane mixing ratios from ice cores. The technique is based on a continuous flow analysis system, where ice core samples cut along the long axis of an ice core are melted continuously. The past atmospheric air contained in the ice is separated from the melt water stream via a system for continuous gas extraction. The extracted gas is dehumidified and then analyzed by a Wavelength Scanned-Cavity Ring Down Spectrometer for methane mixing ratios. We assess the performance of the new measurement technique in terms of precision (±0.8 ppbv, 1 ?), accuracy (±8 ppbv), temporal (ca. 100 s) and spatial resolution (ca. 6 cm). Using a firn air transport model, we compare the resolution of the measurement technique to the resolution of the atmospheric methane signal as preserved in ice cores in Greenland. We conclude that our measurement technique can resolve all climatically relevant variations as preserved in the ice down to an ice depth of at least 1980 m (66 000 yr before present) in the North Greenland Eemian Ice Drilling ice core. Furthermore, we describe the modifications which are necessary to make a commercially available spectrometer suitable for continuous methane mixing ratio measurements from ice cores.

Stowasser, C.; Buizert, C.; Gkinis, V.; Chappellaz, J.; Schüpbach, S.; Bigler, M.; Faïn, X.; Sperlich, P.; Baumgartner, M.; Schilt, A.; Blunier, T.

2012-01-01

56

Continuous measurements of methane mixing ratios from ice cores  

NASA Astrophysics Data System (ADS)

This work presents a new, field-deployable technique for continuous, high-resolution measurements of methane mixing ratios from ice cores. The technique is based on a continuous flow analysis system, where ice core samples cut along the long axis of an ice core are melted continuously. The past atmospheric air contained in the ice is separated from the melt water stream via a system for continuous gas extraction. The extracted gas is dehumidified and then analyzed by a Wavelength Scanned-Cavity Ring Down Spectrometer for methane mixing ratios. We assess the performance of the new measurement technique in terms of precision (±0.8 ppbv, 1?), accuracy (±8 ppbv), temporal (ca. 100 s), and spatial resolution (ca. 5 cm). Using a firn air transport model, we compare the resolution of the measurement technique to the resolution of the atmospheric methane signal as preserved in ice cores in Greenland. We conclude that our measurement technique can resolve all climatically relevant variations as preserved in the ice down to an ice depth of at least 1980 m (66 000 yr before present) in the North Greenland Eemian Ice Drilling ice core. Furthermore, we describe the modifications, which are necessary to make a commercially available spectrometer suitable for continuous methane mixing ratio measurements from ice cores.

Stowasser, C.; Buizert, C.; Gkinis, V.; Chappellaz, J.; Schüpbach, S.; Bigler, M.; Faïn, X.; Sperlich, P.; Baumgartner, M.; Schilt, A.; Blunier, T.

2012-05-01

57

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

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

Ice core evidence for extensive melting of the greenland ice sheet in the last interglacial.  

PubMed

Evidence from ice at the bottom of ice cores from the Canadian Arctic Islands and Camp Century and Dye-3 in Greenland suggests that the Greenland ice sheet melted extensively or completely during the last interglacial period more than 100 ka (thousand years ago), in contrast to earlier interpretations. The presence of dirt particles in the basal ice has previously been thought to indicate that the base of the ice sheets had melted and that the evidence for the time of original growth of these ice masses had been destroyed. However, the particles most likely blew onto the ice when the dimensions of the ice caps and ice sheets were much smaller. Ice texture, gas content, and other evidence also suggest that the basal ice at each drill site is superimposed ice, a type of ice typical of the early growth stages of an ice cap or ice sheet. If the present-day ice masses began their growth during the last interglacial, the ice sheet from the earlier (Illinoian) glacial period must have competely or largely melted during the early part of the same interglacial period. If such melting did occur, the 6-meter higher-than-present sea level during the Sangamon cannot be attributed to disintegration of the West Antarctic ice sheet, as has been suggested. PMID:17731883

Koerner, R M

1989-05-26

60

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

61

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

62

An Ice Core Melter System for Continuous Major and Trace Chemical Analyses of a New Mt. Logan Summit Ice Core  

NASA Astrophysics Data System (ADS)

The ice core melter system at the University of Maine Climate Change Institute has been recently modified and updated to allow high-resolution (<1-2 cm ice/sample), continuous and coregistered sampling of ice cores, most notably the 2001 Mt. Logan summit ice core (187 m to bedrock), for analyses of 34 trace elements (Sr, Cd, Sb, Cs, Ba, Pb, Bi, U, As, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, REE suite) by inductively coupled plasma mass spectrometry (ICP-MS), 8 major ions (Na+, Ca2+, Mg2+, K+, Cl-, SO42-, NO3-, MSA) by ion chromatography (IC), stable water isotopes (? 18O, ? D, d) and volcanic tephra. The UMaine continuous melter (UMCoM) system is housed in a dedicated clean room with HEPA filtered air. Standard clean room procedures are employed during melting. A Wagenbach-style continuous melter system has been modified to include a pure Nickel melthead that can be easily dismantled for thorough cleaning. The system allows melting of both ice and firn without wicking of the meltwater into unmelted core. Contrary to ice core melter systems in which the meltwater is directly channeled to online instruments for continuous flow analyses, the UMCoM system collects discrete samples for each chemical analysis under ultraclean conditions. Meltwater from the pristine innermost section of the ice core is split between one fraction collector that accumulates ICP-MS samples in acid pre-cleaned polypropylene vials under a class-100 HEPA clean bench, and a second fraction collector that accumulates IC samples. A third fraction collector accumulates isotope and tephra samples from the potentially contaminated outer portion of the core. This method is advantageous because an archive of each sample remains for subsequent analyses (including trace element isotope ratios), and ICP-MS analytes are scanned for longer intervals and in replicate. Method detection limits, calculated from de-ionized water blanks passed through the entire UMCoM system, are below 10% of average Mt. Logan values. A strong correlation (R2>0.9) between Ca and S concentrations measured on different fractions of the same sample by IC and ICP-MS validates sample coregistration. Preliminary analyses of data from the 2001 Mt. Logan summit ice core confirm subannual resolution sampling and annual scale variability of major and trace elements. Accumulation rate models and isotope data suggest that annual resolution will be possible to 1000-2000 y.b.p., with multi-annual to centennial resolution for the remainder of the Holocene and possibly including the last deglaciation. Dust proxy elements, including REEs, strongly co-vary in time-series and reveal concentration ratio fluctuations interpreted as source region changes. Volcanic eruptions are characterized by elevated concentrations of S, SO42-, Cu, Sb, Zn and other trace elements. Concentrations of potential anthropogenic contaminants are also discussed.

Osterberg, E. C.; Handley, M. J.; Sneed, S. D.; Mayewski, P. A.; Kreutz, K. J.; Fisher, D. A.

2004-12-01

63

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

64

First continuous phosphate record from Greenland ice cores  

NASA Astrophysics Data System (ADS)

A continuous and highly sensitive absorption method for detection of soluble phosphate in ice cores has been developed using a molybdate reagent and a 2 m liquid waveguide (LWCC). The method is optimized to meet the low concentrations of phosphate in Greenland ice, it has a detection limit of around 0.1 ppb and a depth resolution of approximately 2 cm. The new method has been applied to obtain phosphate concentrations from segments of two Northern Greenland ice cores: from a shallow firn core covering the most recent 120 yr and from the recently obtained deep NEEM ice core in which sections from the late glacial period have been analysed. Phosphate concentrations in 20th century ice are around 0.32 ppb with no indication of anthropogenic influence in the most recent ice. In the glacial part of the NEEM ice core concentrations in the cold stadial periods are significantly higher, in the range of 6-24 ppb, while interstadial ice concentrations are around 2 ppb. In the shallow firn core, a strong correlation between concentrations of phosphate and insoluble dust suggests a similar deposition pattern for phosphate and dust. In the glacial ice, phosphate and dust also correlate quite strongly, however it is most likely that this correlation originates from the phosphate binding to dust during transport, with only a fraction coming directly from dust. Additionally a constant ratio between phosphate and potassium concentrations shows evidence of a possible biogenic land source.

Kjær, H. A.; Svensson, A.; Vallelonga, P.; Kettner, E.; Schüpbach, S.; Bigler, M.; Steffensen, J. P.; Hansson, M. E.

2011-11-01

65

Ice core drilling, processing and initial data of the 3029m deep Dome Fuji Antarctic ice core  

Microsoft Academic Search

On January 2006, the Japanese Antarctic Research Expedition succeeded in drilling a 3029 m deep ice core at Dome Fuji in East Antarctica. Dome Fuji is the third place where a more than 3000 m deep ice core was collected in Antarctica, after Vostok (3623 m in depth, 1998) and Dome C (3270 m in depth, 2004). The drilling will

S. Fujita

2006-01-01

66

Timescale Calculations for Ice Core Drilling Sites on the Temperate Ice Caps in Iceland  

Microsoft Academic Search

Modelling of age vs. depth profiles and annual-layer thickness changes with depth in ice sheets forms part of the investigations carried out prior to the selection of ice core drilling sites. The well known Nye model, which assumes a constant vertical strain rate with depth in an ice sheet of thickness H is generally applicable in the upper half of

T. Thorsteinsson; B. Einarsson

2005-01-01

67

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

Microsoft Academic Search

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

M. R. Albert; C. R. Bentley; M. Twickler

2010-01-01

68

The Eemian ice from the new Greenland ice core at NEEM  

Microsoft Academic Search

Bedrock has been reached Tuesday July 27 2010 at the deep ice core drilling site, NEEM, on the Greenland Ice Sheet at the depth 2537.36 m. The NEEM scientists from the 14 nations participating in NEEM project are very excited and happy. The goals of 5 years work are reached and we have got what we came for. Ice from

D. Dahl-Jensen

2010-01-01

69

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

70

Raman spectroscopic and statistical studies on natural clathrates from the Greenland Ice Core Project ice core, and neutron diffraction studies on synthetic nitrogen clathrates  

Microsoft Academic Search

We present the results of Raman spectroscopic experiments on air clathrates in the GReenland Ice Core Project (GRIP) deep ice core, which differ markedly from previous measurements on the Dye 3 ice core. The N2\\/O2 ratio we observe is much closer to the atmospheric value. This has new implications for the interpretation of gas distributions in ice sheets. Raman spectroscopic

Frank Pauer; Josef Kipfstuhl; Werner F. Kuhs

1997-01-01

71

Cosmogenic analysis reveals a blue-ice moraine in Antarctica survived the last glacial cycle  

NASA Astrophysics Data System (ADS)

Cosmogenic isotope analysis shows that the ice-cored blue-ice moraine at Patriot Hills has survived for at least 80 kyr, i.e. since before the Last Glacial Maximum. The implication is that a biological refuge may also have survived for as long. Strong winds sweep over the Patriot Hills causing accelerated ablation of the glacier edge at the hill foot. In compensation ice flows towards the hills and compressive flow at the margin brings a folded debris band, dipping at angles of 70-800, to the ice surface. Subglacially-derived clasts emerge at the surface and ablation then concentrates them at the ice margin to form the ice-cored moraine. Cosmogenic isotope analysis reveals exposure ages of zero on stones emerging on the ice surface and a range from a few hundred to 29 kyr on the present ice-cored moraine. Relict moraines are draped across the hillside up to a height of ~ 340 m above the ice margin and mark the thinning of the ice over the last ~16 kyr. These moraines contain a mix of boulder ages ranging from a few thousand to ~ 80 kyr with a few ages as old as 424 kyr. The implication is that the moraine has existed at the ice edge for much of at least the last glacial cycle, but that it has migrated up (?) and down the mountain front as the ice elevation has responded to global sea-level change. If substantiated, this discovery would explain why it is so difficult to date moraines reflecting Holocene thinning in Antarctica. Further, the presence of pre-LGM erratics could be used to argue that the West Antarctic Ice Sheet survived the last interglacial intact.

Sugden, D. E.; Fogwill, C. J.; Bentley, M. J.; Hein, A. S.

2009-04-01

72

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

NASA Astrophysics Data System (ADS)

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

Reusch, D. B.

2009-12-01

73

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

74

Correlating Ice Cores from Quelccaya Ice Cap with Chronology from Little Ice Age Glacial Extents  

NASA Astrophysics Data System (ADS)

Proxy records indicate Southern Hemisphere climatic changes during the Little Ice Age (LIA; ~1300-1850 AD). In particular, records of change in and around the tropical latitudes require attention because these areas are sensitive to climatic change and record the dynamic interplay between hemispheres (Oerlemans, 2005). Despite this significance, relatively few records exist for the southern tropics. Here we present a reconstruction of glacial fluctuations of Quelccaya Ice Cap (QIC), Peruvian Andes, from pre-LIA up to the present day. In the Qori Kalis valley, extensive sets of moraines exist beginning with the 1963 AD ice margin (Thompson et al., 2006) and getting progressively older down valley. Several of these older moraines can be traced and are continuous with moraines in the Challpa Cocha valley. These moraines have been dated at <1050-1350-AD (Mercer and Palacios, 1977) and interpreted to have been deposited during the Little Ice Age. We present a new suite of surface exposure and radiocarbon dates collected in 2008 and 2009 that constrain the ages of these moraines. Preliminary 10Be ages of boulder surfaces atop the moraines range from ~350-1370 AD. Maximum and minimum-limiting radiocarbon ages bracketing the moraines are ~0-1800 AD. The chronology of past ice cap extents are correlated with ice core records from QIC which show an accumulation increase during ~1500-1700 AD and an accumulation decrease during ~1720-1860 AD (Thompson et al., 1985; 1986; 2006). In addition, other proxy records from Peru and the tropics are correlated with the records at QIC as a means to understand climate conditions during the LIA. This work forms the basis for future modeling of the glacial system during the LIA at QIC and for modeling of past temperature and precipitation regimes at high altitude in the tropics.

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.

2010-12-01

75

Statistical extraction of volcanic sulphate from nonpolar ice cores  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

76

Black carbon concentration in a Greenland Dye-3 ice core  

SciTech Connect

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

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

1992-10-01

77

The Eemian ice from the new Greenland ice core at NEEM  

NASA Astrophysics Data System (ADS)

Bedrock has been reached Tuesday July 27 2010 at the deep ice core drilling site, NEEM, on the Greenland Ice Sheet at the depth 2537.36 m. The NEEM scientists from the 14 nations participating in NEEM project are very excited and happy. The goals of 5 years work are reached and we have got what we came for. Ice from the warm interglacial Eemian period 130.000 to 115.000 years before present and even older ice found under the Eemian ice. The last 2 m of ice before the bedrock is full of material from the bedrock under the ice. We find stones from bedrock, conglomerates and mud and expect the ice to be rich in traces of DNA and pollen that can tell us how about the vegetation before the site was covered with ice and hopefully we will be able to determine how old these traces are. A flow model will be presented based on ice core data and internal radio echo sounding data discussing the origin of the ice from the Eemian climate period and the path of flow it has followed. A very important question to answer is how far back in time and at what depth we expect to have an undisturbed climate record and how what the record can tell us about the evolution of the Greenland ice sheet.

Dahl-Jensen, D.

2010-12-01

78

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

79

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

80

Raman spectroscopy on ice cores from Greenland and Antarctica  

NASA Astrophysics Data System (ADS)

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

Weikusat, C.; Kipfstuhl, S.

2012-04-01

81

Ice core evidence for a 20th century decline of sea ice in the Bellingshausen Sea, Antarctica  

Microsoft Academic Search

This study uses ice core methanesulphonic acid (MSA) records from the Antarctic Peninsula, where temperatures have been warming faster than anywhere else in the Southern Hemisphere, to reconstruct the 20th century history of sea ice change in the adjacent Bellingshausen Sea. Using satellite-derived sea ice and meteorological data, we show that ice core MSA records from this region are a

Nerilie J. Abram; Elizabeth R. Thomas; Joseph R. McConnell; Robert Mulvaney; Thomas J. Bracegirdle; Louise C. Sime; Alberto J. Aristarain

2010-01-01

82

Late Holocene fire activity recorded in a Greenland ice core  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

83

Mineralogy of atmospheric microparticles deposited along the Greenland Ice Core Project ice core  

NASA Astrophysics Data System (ADS)

The mineralogical composition of atmospheric dust particles changes along the Greenland Ice Core Project (GRIP) ice core in phase with other paleoatmospheric records, showing that climatic changes affect the location, the relative extent, and the surface characteristics of the dust source areas. Fifty GRIP ice samples from the Eemian to the last glacial maximum were analyzed using a scanning electron microscope coupled with X ray energy dispersive system microprobe. More than 20 mineral types or groups were identified and their relative abundance was evaluated. A different mineralogical composition was systematically observed in cold and warm time periods. Quartz, illite, chlorite, micas, and feldspars prevail in the mineral assemblage associated with cold stages or phases (marine isotope stage (MIS) 4, MIS 2, cold part of MIS 3 fast variations), while kaolinite and Fe (hydr)oxides dominate in warm episodes (MIS 5e5, warm parts of fast variations). The first dust mineral assemblage is related mainly to the mechanical weathering prevailing in arid and cold mid-high-latitude areas, while the second dust mineral assemblage is related mainly to deep chemical weathering in warm and humid low-latitude areas. K/C and O/Q ratios may be assumed as indicative of the relative importance of low-latitude versus arid and mid-high-latitude source areas. It is worthwhile to mention that the first warmer part of Eemian (5e5) differs in dust mineralogy from the second part (5e4-5e1) and that also the fast variations are accompanied by clear mineralogical changes of the dust microparticles. The changes of the atmospheric dust mineral background are possibly related to changes of the atmosphere dynamics (meridian pressure gradient, polar front shift, storm track changes, etc.) and or to changes in the relative extent of the deflation source areas.

Maggi, V.

1997-11-01

84

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

2012-08-28

85

A New Inverse Method to Construct a Common and Optimal Ice Chronology for EPICA Ice Cores  

NASA Astrophysics Data System (ADS)

Ice-cores dating is an essential issue to analyse data measured on ice samples in order to contribute to Earth climate history decephering. Several methods have been already implemented. Each method brings some valuable but incomplete information for building the depth-age relationship of an ice-core: some methods only apply on the top part of the core (e.g., annual layer counting) while others apply on the whole core (e.g. orbital tuning), some methods are accurate for absolute ages (e.g. absolute age markers) while others are accurate for events duration (e.g. ice flow modelling). Moreover, stratigraphic markers (e.g. volcanic horizons) bring additional information on the ice flow and allow to link the age scales of distinct cores. The aim of this study is to use an inverse method to gather this fragmented information. The new inverse method is based on the assumption of a non-deterministic ice flow model. It allows to construct a common and optimal age scale for several ice cores and to estimate its confidence interval.

Parrenin, F.; Lemieux-Dudon, B.; Blayo, E.; Raynaud, D.

2006-12-01

86

Physical properties of the P96 ice core from Penny Ice Cap, Baffin Island, Canada, and derived climatic records  

Microsoft Academic Search

Ice cores from nonpolar environments are being developed as valuable paleoclimatic resources. However, the recognition of a climatic signal and the development of timescales in those ice cores are both difficult due to heavy summer melting. A 177.91-m-long ice core (P96) was drilled in such a high-melt area from Penny Ice Cap, Baffin Island, Canada, in 1996. The core covers

Junichi Okuyama; Hideki Narita; Takeo Hondoh; Roy M. Koerner

2003-01-01

87

Volcanism and the Greenland ice-cores: the tephra record  

NASA Astrophysics Data System (ADS)

In recent years, increased awareness of the considerable potential offered by tephrochronology in palaeoclimatic studies has fuelled a renewed interest in the tephra record preserved within the Greenland ice-cores. This renewal has occurred in tandem with the development of continuous flow analysis techniques, which provide high-resolution volcanic aerosol records. These chemical records are of considerable value for identifying tephra horizons composed of glass shards and also provide the basis for a new high-precision ice-core timescale, thus allowing ages to be assigned to volcanic events. Tephra horizons of glass shards in the ice-cores play a critical role for (1) testing and building chronological frameworks for the ice-cores and other sequences, (2) synchronising disparate palaeoclimatic sequences and testing phase relationships, (3) atmospheric pathway reconstruction, and (4) verifying the source of volcanic aerosol peaks. Here we review the results of over 25 years of research into tephra horizons in the GRIP, GISP2 and NGRIP cores. We provide high-precision ages for horizons based on recently developed timescales and draw together geochemical characterisations of the products of 45 volcanic events deposited on the Greenland ice sheet and identified in the cores. There is a clear disparity between the number of volcanic aerosol peaks and the number of tephra horizons of glass shards identified thus far. However, this synthesis highlights the critical role of the Greenland ice-cores, firstly in the reconstruction of the history of Icelandic volcanic eruptions, and secondly the considerable value of some tephra horizons in facilitating the correlation of these key climatic archives to North Atlantic marine sequences. Other noteworthy issues include the potential of these cores to preserve tephra horizons from more distal volcanic sources such as North America, to resolve the debate surrounding the Thera eruption, and the observation that some tephra horizons are preserved within the ice without coeval volcanic aerosol signals.

Abbott, Peter M.; Davies, Siwan M.

2012-11-01

88

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

89

Preindustrial Atmospheric Carbonyl Sulfide (OCS) from an Antarctic Ice Core  

NASA Astrophysics Data System (ADS)

The concentration of carbonyl sulfide (OCS) has been determined in several preindustrial air samples extracted from a shallow ice core from Siple Dome, West Antarctica. The extraction of the air was carried out by shredding the core under vacuum, followed by analysis by gas chromatography with mass spectrometric detection. 11 ice core samples were analyzed, ranging in depth from 82.29 to 90.72 m. The ages assigned to OCS in the ice core samples range from 1619 to 1697 AD. The observed OCS mixing ratios range from 324.9 pptv to 445.4 pptv with a mean of 375.4+/-37.5 pptv. These levels are significantly lower than the present day atmospheric mixing ratio of 500 pptv and suggest that the anthropogenic sources comprise approximately 25% of the present day OCS budget.

Aydin, M.; De Bruyn, W. J.; Saltzman, E. S.

2002-05-01

90

Preindustrial atmospheric carbonyl sulfide (OCS) from an Antarctic ice core  

NASA Astrophysics Data System (ADS)

The concentration of carbonyl sulfide (OCS) has been determined in several preindustrial air samples extracted from a shallow ice core from Siple Dome, West Antarctica. The extraction of the air was carried out by shredding the core under vacuum, followed by analysis by gas chromatography with mass spectrometric detection. 11 ice core samples were analyzed, ranging in depth from 82.3 to 90.7 m. The ages assigned to OCS in the ice core samples range from 1616 to 1694 AD. The observed OCS mixing ratios range from 322.6 pptv to 442.3 pptv with a mean of 372.8 +/- 37.2 pptv. These levels are significantly lower than the present day atmospheric mixing ratio of 500 pptv and suggest that the anthropogenic sources comprise approximately 25% of the present day OCS budget.

Aydin, Murat; De Bruyn, Warren J.; Saltzman, Eric S.

2002-05-01

91

Annual layering in the NGRIP ice core during the Eemian  

NASA Astrophysics Data System (ADS)

The Greenland NGRIP ice core continuously covers the period from present day back to 123 ka before present, which includes several thousand years of ice from the previous interglacial period, MIS 5e or the Eemian. In the glacial part of the core annual layers can be identified from impurity records and visual stratigraphy, and stratigraphic layer counting has been performed back to 60 ka. In the deepest part of the core, however, the ice is close to the pressure melting point, the visual stratigraphy is dominated by crystal boundaries, and annual layering is not visible to the naked eye. In this study, we apply a newly developed setup for high-resolution ice core impurity analysis to produce continuous records of dust, sodium and ammonium concentrations as well as conductivity of melt water. We analyzed three 2.2 m sections of ice from the Eemian and the glacial inception. In all of the analyzed ice, annual layers can clearly be recognized, most prominently in the dust and conductivity profiles. Part of the samples is, however, contaminated in dust, most likely from drill liquid. It is interesting that the annual layering is preserved despite a very active crystal growth and grain boundary migration in the deep and warm NGRIP ice. Based on annual layer counting of the new records, we determine a mean annual layer thickness close to 11 mm for all three sections, which, to first order, confirms the modeled NGRIP time scale (ss09sea). The counting does, however, suggest a longer duration of the climatically warmest part of the NGRIP record (MIS5e) of up to 1 ka as compared to the model estimate. Our results suggest that stratigraphic layer counting is possible basically throughout the entire NGRIP ice core provided sufficiently highly-resolved profiles become available.

Svensson, A.; Bigler, M.; Kettner, E.; Dahl-Jensen, D.; Johnsen, S.; Kipfstuhl, S.; Nielsen, M.; Steffensen, J. P.

2011-02-01

92

Annual layering in the NGRIP ice core during the Eemian  

NASA Astrophysics Data System (ADS)

The Greenland NGRIP ice core continuously covers the period from present day back to 123 ka before present, which includes several thousand years of ice from the previous interglacial period, MIS 5e or the Eemian. In the glacial part of the core, annual layers can be identified from impurity records and visual stratigraphy, and stratigraphic layer counting has been performed back to 60 ka. In the deepest part of the core, however, the ice is close to the pressure melting point, the visual stratigraphy is dominated by crystal boundaries, and annual layering is not visible to the naked eye. In this study, we apply a newly developed setup for high-resolution ice core impurity analysis to produce continuous records of dust, sodium and ammonium concentrations as well as conductivity of melt water. We analyzed three 2.2 m sections of ice from the Eemian and the glacial inception. In all of the analyzed ice, annual layers can clearly be recognized, most prominently in the dust and conductivity profiles. Part of the samples is, however, contaminated in dust, most likely from drill liquid. It is interesting that the annual layering is preserved despite a very active crystal growth and grain boundary migration in the deep and warm NGRIP ice. Based on annual layer counting of the new records, we determine a mean annual layer thickness close to 11 mm for all three sections, which, to first order, confirms the modeled NGRIP time scale (ss09sea). The counting does, however, suggest a longer duration of the climatically warmest part of the NGRIP record (MIS5e) of up to 1 ka as compared to the model estimate. Our results suggest that stratigraphic layer counting is possible basically throughout the entire NGRIP ice core, provided sufficiently highly-resolved profiles become available.

Svensson, A.; Bigler, M.; Kettner, E.; Dahl-Jensen, D.; Johnsen, S.; Kipfstuhl, S.; Nielsen, M.; Steffensen, J. P.

2011-12-01

93

Electrical measurements on the Greenland Ice Sheet Project 2 Core  

NASA Astrophysics Data System (ADS)

The Greenland Ice Sheet Project 2 (GISP2) electrical conductivity measurement (ECM) record is an indication of the concentration of H + in the core. The ECM detected seasonal variations in the nitrate concentration of the core which were used to assist in dating the core by annual layer counting. Volcanic eruptions that produce acidic aerosols are recorded in the ECM record. Evidence of biomass burning is detected by the ECM because fire-related ammonium emissions neutralize the acids in the core. Rapid climate transitions associated with the Younger Dryas and Dansgaard/Oeschger interstadial events alter the concentration of alkaline dust and are detected by the ECM. The ECM has been used to develop stratigraphic ties between the GISP2 and the Greenland Ice Core Project cores. Users of the data should be aware of some instrument-related artifacts in the ECM record.

Taylor, Kendrick C.; Alley, Richard B.; Lamorey, Gregg W.; Mayewski, Paul

1997-11-01

94

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

Microsoft Academic Search

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

Lijia Wei

2008-01-01

95

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

96

Deep Rotary Core Drilling in Ice.  

National Technical Information Service (NTIS)

Rotary drilling equipment was modified and used to obtain cores from glaciers in Northwest Greenland, Byrd Station and Little America V, Antarctica. Using cold compressed air, specially designed bits and other modifications, cores were obtained to 1345 fe...

G. R. Lange

1973-01-01

97

Dating and climatic interpretation of two deep Greenland ice cores  

NASA Astrophysics Data System (ADS)

A continuous ?(18O) profile is measured along the new deep ice core from Dye 3, South Greenland. It allows absolute dating back to at least 7000 yrs BP. The Pleistocene to Holocene ? shift is discussed. The Wisconsin ice in the deepest 300 m has so many ? features in common with the Camp Century (CC) ice core that they must be of climatic significance. The deep parts of the two ? profiles are indirectly dated by tentative correlation with a deep sea foraminifera record. The CC record seems to be continuous to more than 125,000 yrs BP, and it suggests a dramatic termination of the Eem/Sangamon interglacial. The Dye 3 record, however, is hardly continuous to more than 90,000 yrs BP, although the deepest 22 m of silty ice is probably of Eem/Sangamon origin. The basic criteria for an ideal deep drilling site are listed.

Dansgaard, W.; Clausen, H. B.; Gundestrup, N.; Johnsen, S. J.; Rygner, C.

98

Raman spectroscopic study on the nitrogen/oxygen ratio in natural ice clathrates in the GRIP ice core  

NASA Astrophysics Data System (ADS)

We have carried out Raman spectroscopic experiments on air clathrates in the GReenland Ice Core Project (GRIP) deep ice core. We present new N2/O2 measurements that markedly differ from previous measurements of the Dye-3 ice core: the N2/O2 ratio we observe is much closer to atmospheric. This has new implications for the interpretation of gas distributions in ice sheets and the reconstruction of past atmospheric conditions.

Pauer, Frank; Kipfstuhl, Josef; Kuhs, Werner F.

1995-04-01

99

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. (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 general agreement of method 4 with methods 2 and 3 confirms that the bipolar seesaw antiphase happened during the last 140 kyr. Applying method 4 to the deeper section of the EDC core confirms that the ice flow is complex and can help to improve 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 suggest that it is due to an overestimation of the glacial lock-in depth (LID) by the firn densification model. In contrast, we find that method 1 very likely underestimates ?depth during Termination II, due either to an underestimated thinning function or to an underestimated LID. Finally, method 2 gives estimates within a few metres of methods 3 and 4 during the last deglacial warming, suggesting that the convective zone at Dome C cannot have been very large at this time, if it existed at all.

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

2012-08-01

100

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

NASA Astrophysics Data System (ADS)

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

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

1997-11-01

101

Evidence of Little Ice Age in an East Antarctica Ice Core  

NASA Astrophysics Data System (ADS)

An 80 meter ice core was retrieved from an East Antarctica location (76° S, 77° E) by the Chinese Antarctica Research Expedition in 1999. Chemical analysis of the ice core has yielded a record of ionic impurities in snow for the past 800 years (1200-1999 A.D.). The ice core is dated using a combination of annual layer counting and volcanic time stratigraphic horizons, resulting in an accurate chronology with high resolution. The ice core record demonstrates that, during the period of approximately 1300-1850 A.D., the concentrations of several chemical species, including nitrate and methanesulfonate, are sharply lower than the levels both prior to and after this period. This period coincides with the most recent neoglacial climatic episode, the "Little Ice Age (LIA)," that has been found in numerous Northern Hemisphere proxy and historic records. Additional evidence includes the sharply reduced net snow accumulation rates during this period. The significance of this new finding will be discussed in the context of LIA evidence in Antarctica ice cores, its probable regional and spatial variations, and chronological relationships to LIA signals in South America and in the Northern Hemisphere.

Cole-Dai, J.; Li, Y.; Zhou, L.

2003-12-01

102

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

103

The first Greenland ice core record of methanesulfonate and sulfate over a full glacial cycle  

SciTech Connect

The authors report on methanesulfonate and non-seasalt sulfate found in an artic ice core from Greenland. The ice core record stretches back in time roughly 130,000 years, through a full glacial cycle. This record reveals a decreasing concentration of MSA with the advance of the glacial period, and a drop in temperatures, while the non-seasalt sulfate increased in concentration. The MSA data is in contrast to similar measurements from the southern hemisphere. The ratio of MSA to non-seasalt sulfate is found to have a strong linear relationship to the temperature, higher ratios being associated with warmer climatic periods.

Hansson, M.E.; Saltzman, E.S. (Univ. of Miami, FL (United States))

1993-06-18

104

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

105

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

Microsoft Academic Search

Substantial data sets have been collected on the relaxation characteristics, density, grain size, c axis fabrics, and ultrasonic velocities of the Greenland Ice Sheet Project 2 (GISP2) core to its contact with bedrock at 3053.4 m. Changes in all these properties paralleled closely those found in cores from Byrd Station, Antarctica, and Dye 3, Greenland. Density increased progressively with depth

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

1997-01-01

106

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

Microsoft Academic Search

Substantial data sets have been collected on the relaxation characteristics, density, grain size, c axis fabrics, and ultrasonic velocities of the Greenland Ice Sheet Project 2 (GISP2) core to its contact with bedrock at 3053.4 m. Changes in all these properties paralleled closely those found in cores from Byrd Station, Antarctica, and Die 3, Greenland. Density increased progressively with depth

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

1997-01-01

107

Pre-cometary ice composition from hot core chemistry.  

PubMed

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

Tornow, Carmen; Kührt, Ekkehard; Motschmann, Uwe

2005-10-01

108

3D Imaging Radar for Deep Ice Core Site Selection  

NASA Astrophysics Data System (ADS)

The site selection for a deep ice core is critical because of the high cost of drilling, extracting, and analyzing the ice cores. CReSIS has developed several multichannel radar systems which provide information at a much higher level of detail than was possible from previous radar surveys for ice core sites. Among the inputs used in site selection, depth sounding radars provide information about the internal stratigraphy, bed topography, and basal conditions. The internal stratigraphy and bed topography are ideally smooth and flat-lying - an indication that there are no ice flow disturbances. The chronological order must be preserved in the stratigraphy and lack of flow disturbances helps ensure that. Also, internal layers that can be traced to an existing ice core to be dated allow paleo-accumulation rates to be estimated when coupled with an ice flow model. Determining the basal conditions, specifically whether or not the bed is wet or dry, helps determine if the bottom layers (i.e. the oldest ice) are melting. In 2005 and 2008, CReSIS conducted two ground based radar surveys covering the GRIP, GISP2, and NEEM ice core sites. Unlike traditional depth sounders, these radar systems are multichannel making 3D imaging possible. In 2006 an airborne version of the ground based system was fielded for the first time and 3D tomographic images have been produced with that system as well. This work will present results from these ground and airborne surveys and how the information provided from these data can be used to enable optimal site selections in the future. Fig 1 shows an example of how 3D imaging resolves the englacial features that indicate the flow disturbances discovered by the GRIP and GISP2 ice core analysis. In Fig 1a, the bed is the bright mass of targets from 0-4 km along-track at the bottom of the image. Note the distinct change in texture of the englacial scatterers, from specular layers to point targets, around 2750 m and below. Fig 1b shows the cross-track position of the dominant englacial scatterers. The scattering centers for the flat internal layers above 2750 m are located directly beneath the platform while the disturbed layers below 2750 m are spread out. Similar englacial targets are seen at the GISP2 site. a) Radar profile with GRIP core high-lighted by vertical line. b) Cross-track position of the englacial scatterers.

Paden, J. D.; Blake, W.; Gogineni, P. S.; Leuschen, C.; Allen, C.; Dahl-Jensen, D.

2010-12-01

109

The role of the Greenland ice sheet in future sea level - based on palaeorecords from ice cores and present observations.  

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 previous warm Eemian period near the base. Is it thus clear that the Greenland Ice Sheet did exist for 120.000 years ago in the previous warm period where it was 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 120.000 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 1-2 m.

Dahl-Jensen, D.

2012-04-01

110

The Water Cycle: O-18 and Ice Cores  

NSDL National Science Digital Library

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

2011-08-01

111

3D Imaging Radar for Deep Ice Core Site Selection  

NASA Astrophysics Data System (ADS)

The site selection for a deep ice core is critical because of the high cost of drilling, extracting, and analyzing the ice cores. CReSIS has developed several multichannel radar systems which provide information at a much higher level of detail than was possible from previous radar surveys for ice-core sites. Among the inputs used in site selection, depth sounding radars provide information about the internal stratigraphy, bed topography, and basal conditions. The internal stratigraphy and bed topography are ideally smooth and flat-lying - an indication that there are no ice flow disturbances. The chronological order must be preserved in the stratigraphy and lack of flow disturbances helps ensure that. Also, internal layers that can be traced to an existing ice core to be dated allow paleo-accumulation rates to be estimated when coupled with an ice flow model. Determining the basal conditions, specifically whether or not the bed is wet or dry, helps determine if the bottom layers (i.e. the oldest ice) are melting. CReSIS has conducted several ground and airborne radar surveys around GRIP, GISP2, NGRIP, and NEEM ice core sites. Unlike traditional depth sounders, the radar systems are multichannel making 3D imaging possible. This work will present results from these ground and airborne surveys and how the information provided from these data can be used to enable optimal site selections in the future. Fig 1 shows an example of how 3D imaging resolves the englacial features that indicate the flow disturbances discovered by the GRIP and GISP2 ice core analysis. In Fig 1a, the bed is the bright mass of targets from 0-4 km along-track at the bottom of the image. Note the distinct change in texture of the englacial scatterers, from specular layers to point targets, around 2750 m and below. Fig 1b shows the cross-track position of the dominant englacial scatterers. The scattering centers for the flat internal layers above 2750 m are located directly beneath the platform while the disturbed layers below 2750 m are spread out. Similar englacial targets are seen at the GISP2 site.

Paden, J. D.; Li, J.; Gogineni, P. S.; Leuschen, C.; Dahl-Jensen, D.

2011-12-01

112

Annual layering in the NGRIP ice core during the Eemian  

NASA Astrophysics Data System (ADS)

The Greenland NGRIP ice core continuously covers the period from present day back to 123 ka before present, which includes several thousand years of ice from the previous interglacial period, MIS 5e or the Eemian. In the glacial part of the core annual layers can be identified from impurity records and visual stratigraphy, and stratigraphic layer counting has been performed back to 60 ka. In the deepest part of the core, however, the ice is close to the pressure melting point, the visual stratigraphy is dominated by ice crystal boundaries, and annual layering is not visible to the naked eye. In this study, we apply a newly developed setup for high-resolution ice core impurity analysis to produce continuous records of dust, sodium and ammonium concentrations as well as conductivity of melt water. We analyzed three 2.2 m sections of ice from the Eemian and the glacial inception. In all of the analyzed ice, annual layers can clearly be recognized, most prominently in the dust and conductivity profiles. Part of the samples is, however, contaminated in dust, most likely from drill liquid that entered the core through grain boundaries. It is interesting that the annual layering is preserved despite a very active crystal growth and grain boundary migration in the deep and warm NGRIP ice. Based on annual layer counting of the new records, we determine a mean annual layer thickness close to 10 mm for all three sections, which, to first order, confirms the modelled NGRIP time scale (ss09sea). The counting does, however, suggest a longer duration of the climatically warmest part of the NGRIP record (MIS5e) of up to 1 ka as compared to the model estimate. Our results suggest that stratigraphic layer counting is possible basically throughout the entire NGRIP ice core provided sufficiently highly-resolved profiles become available. A 120 ka independent Greenland time scale would provide an important tool for climate reconstruction of the late Quaternary and we hope to make such a chronology available in the coming years.

Svensson, Anders; Bigler, Matthias; Kettner, Ernesto; Nielsen, Maibritt; Johnsen, Sigfus; Dahl-Jensen, Dorthe; Steffensen, Jørgen Peder

2010-05-01

113

New aerosol measurements from the Greenland NEEM ice core  

NASA Astrophysics Data System (ADS)

A large number of aerosol constituents have been measured over the whole Greenland NEEM ice core in three extensive field seasons between 2009 and 2011. Here we present records of sodium, calcium, dust particle numbers, ammonium and nitrate in 1.1 m depth resolution gathered by Continuous Flow Analysis (CFA). Compared to GRIP data, the new records are extended in terms of measured species; in contrast to NGRIP, they now cover also large parts of the Holocene, except the brittle zone (corresponding to 4.5 - 7.5 ka BP in the NEEM ice core). At first glance surprisingly good correspondences between the three ice cores are found within their overlapping parts. This shows that they represent rather large-scale than regional signals for all considered aerosol constituents. Stadial and interstadial patterns are corresponding in great detail with largest amplitudes in mainly mineral dust derived species such as soluble calcium and insoluble particles. This variability is somewhat lower for the mainly marine derived sodium and virtually inexistent in nitrate. The latter remains constant over the whole last glacial-interglacial cycle. Ammonium representing biogenic sources shows lower glacial than interglacial levels opposite to sodium, calcium and dust. The largest ammonium differences between the three ice cores are found in the cold glacial periods around 20 ka and 65 ka BP. Apart from that, they correspond nicely. While concentration levels in some parts of the deepest ice might represent Eemian conditions, unexpected signal characteristics are observed at a closer look. This probably prevents a reliable examination of aerosol variability on shorter time scales in this part of the ice core.

Bigler, M.

2012-04-01

114

Climatic Changes on Tibetan Plateau Based on Ice Core Records  

NASA Astrophysics Data System (ADS)

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

Yao, T.

2008-12-01

115

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

116

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

117

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

118

In-Ice radio detection of air shower cores  

NASA Astrophysics Data System (ADS)

Radio receivers (RICE, AURA) have been deployed to detect impulsive emissions from neutrino interactions in ice at South Pole. An alternative source of pulses is the cores of cosmic ray induced air showers. AIRES and CORSIKA simulations suggest that >10% of the primary cosmic ray energy enters the ice within 20 cm of the primary axis impact point. The resulting 5-10 m cascade will make Askaryan type pulses that can be detected by in-ice receivers. Strategies are discussed for deploying a modest number of antennas which could operate in coincidence with IceCube to validate the in-situ detection of Askaryan pulses and produce a new discriminant for studying cosmic ray primary composition for energies above 1016 eV.

Seckel, David; Seunarine, Suruj; Clem, John; et al.

119

A TEM analysis of nanoparticulates in a Polar ice core  

SciTech Connect

This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar with some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates.

Esquivel, E.V.; Murr, L.E

2004-03-15

120

Timescale Calculations for Ice Core Drilling Sites on the Temperate Ice Caps in Iceland  

NASA Astrophysics Data System (ADS)

Modelling of age vs. depth profiles and annual-layer thickness changes with depth in ice sheets forms part of the investigations carried out prior to the selection of ice core drilling sites. The well known Nye model, which assumes a constant vertical strain rate with depth in an ice sheet of thickness H is generally applicable in the upper half of polar and temperate ice caps, but the assumption of a constant vertical strain rate is unrealistic near the bed in an ice sheet frozen to bedrock. Dansgaard-Johnsen (D-J) type models assume that the vertical strain rate is constant down to height h above bedrock and then decreases linearly with depth towards zero at the bed. The parameter h can be calibrated according to the way in which the horizontal velocity varies with depth. Here we introduce a new derivation of the D-J model that accounts for bottom melting due to the geothermal heat flux, which averages 200 mW/m2 in Iceland. The model is then applied to five different locations on the temperate ice caps in Iceland, with ice thicknesses varying between 220 m and 850 m and accumulation rates ranging between 2.0 and 3.6 m ice/year. Data from ice cores drilled at three of these sites are used to calibrate the model. For the summit location on the Hofsjokull ice cap (H = 300 m), we find that a D-J model with a relatively high h/H ratio reproduces the timescale from a 100 m ice core better than the Nye model. Results indicate that a continuous precipitation record covering the last 400-500 years could be retrieved at the Hofsjokull summit (1790 m a.s.l.), and the assumption of bottom melting has a large effect on the modelled timescale at this site, yielding 50% lower ages at 90% of the ice depth than model runs that neglect bottom melting. For deeper drillings in Iceland, the ice-filled caldera at Bardarbunga, NW-Vatnajokull (H = 850 m), where a 415 m core was drilled in 1972, is among the most promising sites. Selection of the h/H ratio in the D-J model for timescale calculation within the caldera rims is complicated by an unusual ice-flow pattern but results strongly indicate that a 700-800 m ice core could yield a record covering historical time in Iceland (870 AD - present). Model results predict that by 90% of ice depth, the annual layers have thinned to 17 cm at the Hofsjokull summit and 8 cm within the Bardarbunga caldera. Annual layers of this thickness are detectable with the methods used in pilot ice core drilling and processing efforts in Iceland in recent years.

Thorsteinsson, T.; Einarsson, B.

2005-12-01

121

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

122

Ice Core Quality in Electro-Mechanical Drilling.  

National Technical Information Service (NTIS)

Using an electro-mechanical drill working on the principle developed by J. Rand and H. Rufli, four holes have been drilled in different locations. In each of these drillings it has been observed that the core quality was excellent in the firn, but the ice...

F. Gillet D. Donnou C. Girard A. Manouvrier C. Rado

1984-01-01

123

The Berkner Island (Antarctica) ice-core drilling project  

Microsoft Academic Search

We describe a project to retrieve a 948 m deep ice core from Berkner Island, Antarctica. Using relatively lightweight logistics and a small team, the drilling operation over three austral summer seasons used electromechanical drilling technology, described in detail, from a covered shallow pit and a fluid-filled borehole. A basal temperature well below pressure-melting point meant that no drilling problems

Robert Mulvaney; Olivier Alemany; Philippe Possenti

2007-01-01

124

Eight glacial cycles from an Antarctic ice core  

Microsoft Academic Search

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

Laurent Augustin; Carlo Barbante; Piers R. F. Barnes; Jean Marc Barnola; Matthias Bigler; Emiliano Castellano; Olivier Cattani; Jerome Chappellaz; Dorthe Dahl-Jensen; Barbara Delmonte; Gabrielle Dreyfus; Gael Durand; Sonia Falourd; Hubertus Fischer; Jacqueline Flückiger; Margareta E. Hansson; Philippe Huybrechts; Gérard Jugie; Sigfus J. Johnsen; Jean Jouzel; Patrik Kaufmann; Josef Kipfstuhl; Fabrice Lambert; Vladimir Y. Lipenkov; Geneviève C. Littot; Antonio Longinelli; Reginald Lorrain; Valter Maggi; Valerie Masson-Delmotte; Heinz Miller; Robert Mulvaney; Johannes Oerlemans; Hans Oerter; Giuseppe Orombelli; Frederic Parrenin; David A. Peel; Jean-Robert Petit; Dominique Raynaud; Catherine Ritz; Urs Ruth; Jakob Schwander; Urs Siegenthaler; Roland Souchez; Bernhard Stauffer; Jorgen Peder Steffensen; Barbara Stenni; Thomas F. Stocker; Ignazio E. Tabacco; Roberto Udisti; Michiel van den Broeke; Jerome Weiss; Frank Wilhelms; Jan-Gunnar Winther; Eric W. Wolff; Mario Zucchelli

2004-01-01

125

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

126

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

127

Continuous analysis of phosphate in a Greenland shallow ice core  

NASA Astrophysics Data System (ADS)

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 may help to gain important knowledge about those processes. In the present study, we attach a phosphate detection line to an existing continuous flow analysis (CFA) setup for ice core analysis at the University of Copenhagen. The CFA system is optimized for high-resolution measurements of insoluble dust particles, electrolytic melt water conductivity, and the concentrations of ammonium and sodium. For the phosphate analysis we apply a continuous and highly sensitive absorption method that has been successfully applied to determine phosphate concentrations of sea water (Zhang and Chi, 2002). A line of melt water from the CFA melt head (1.01 ml per minute) is combined with a molybdate blue reagent and an ascorbic acid buffer. An uncompleted reaction takes place in five meters of heated mixing coils before the absorption measurement at a wavelength of 710 nanometer takes place in a 2 m long liquid waveguide cell (LWCC) with an inner volume of 0.5 ml. The method has a detection limit of around 0.1 ppb and we are currently investigating a possible interference from molybdate reacting with silicates that are present in low amounts in the ice. Preliminary analysis of early Holocene samples from the NGRIP ice core show phosphate concentration values of a few ppb. In this study, we will attempt to determine past levels of phosphate in a shallow Northern Greenland firn core with an annual layer thickness of about 20 cm ice equivalent. With a melt speed of 2.5 cm ice per minute our method should allow the resolution of any seasonal variability in phosphate concentrations.

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

2010-05-01

128

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

129

The Greenland Ice Core Chronology 2005 (GICC05)  

NASA Astrophysics Data System (ADS)

A new Greenland Ice Core Chronology (GICC05) covering the last 41 kyr has been constructed from annual layer counting of high-resolution records from three Greenland ice cores. At any depth, the dating is based on the ice core with the best available high-resolution data, and the ice cores are tied together using unambiguous reference horizons, such as volcanic ash layers or major acidity spikes. Dating of the Holocene period back to 10 kyr b2k (before AD 2000) is based on new and published stable isotope measurements of the Dye-3 (GISP1) ice core, and on Electrical Conductivity Measurements (ECM) and Continuous Flow Analysis (CFA) of three chemical species in the GRIP ice core. Beyond 10 kyr b2k the time scale is based on records from the NorthGRIP ice core: CFA of 5 chemical species, dust and electrolytical conductivity, ECM, and the light intensity curve of the Visual Stratigraphy (VS). During cold glacial periods, where annual layers are thin, the counting is mostly based on VS, ECM and electrolytical conductivity, which have the highest resolution. A conservative uncertainty estimate of the time scale is obtained from identification of 'uncertain' annual layers, which are counted as 0.5±0.5 years. On average the uncertainty is <1% during the Holocene and ~5% in the glacial. The maximum counting error at 41 kyr b2k is 1600 years. The new time scale places the Holocene/Pleistocene transition at 11.7±0.1 kyr b2k, the onset of Greenland Interstadial 3 (GIS3) at 27.8±0.8 kyr b2k, and the onset of GIS8 at 38.3±1.4 kyr b2k. In the glacial period, GICC05 is generally in good agreement with both the GISP2 counted time scale of Meese and Sowers and with the NorthGRIP modelled time scale 'ss09sea'. On shorter time scales, however, there are significant discrepancies. In particular, we determine a strong correspondence between annual layer thickness and climate across the Greenland Interstadials, which is generally not found for the GISP2 time scale.

Svensson, A.; Andersen, K. K.; Clausen, H. B.; Johnsen, S. J.; Rasmussen, S. O.; Steffensen, J. P.; Vinther, B.

2005-12-01

130

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

NASA Astrophysics Data System (ADS)

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

Malone, Terry; Hubbard, Bryn

2013-04-01

131

THE TROPICAL CONNECTION BETWEEN THE ATLANTIC SECTOR ICE CORES AND THE NORTH PACIFIC MT LOGAN ICE CORE  

Microsoft Academic Search

The stable isotope record from the Mt Logan, Yukon, Canada ice core spans the late Glacial to present and shows very large and sudden variations in O18 during the Holocene . It is hypothesized that they are driven by changes in the water sources ,which in turn, are determined by the state of ENSO. There seems to be no correlations

D. A. Fisher

2009-01-01

132

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

Microsoft Academic Search

One of the most important features of ice cores as climate and atmospheric paleoarchives is their potential for high temporal resolution. The measurement of chemical impurities in ice cores that fully exploits this high resolution has become standard with the advent of Continuous Flow Analysis (CFA) from continuously melted ice core segments, often performed in the field. Meanwhile, the measurement

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

2010-01-01

133

A new 122 mm electromechanical drill for deep ice-sheet coring (DISC): 4. Drill cable  

Microsoft Academic Search

The deep ice-sheet coring (DISC) drill developed by Ice Coring and Drilling Services (ICDS) under contract with the US National Science Foundation requires a drill cable capable of transmitting high amounts of electrical power as well as high rates of data. The DISC cable was designed and manufactured by the Rochester Corporation to core ice to depths of 4000 m.

Alexander J. Shturmakov; Paul J. Sendelbach

2007-01-01

134

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

135

A federative approach to date the Dome C ice core  

NASA Astrophysics Data System (ADS)

For the climatic interpretation of ice core records from Dome Concordia (central East Antarctica), a precise chronology is required. At low accumulation sites such as Dome C, the annual layer counting is not feasible and therefore we developped a glaciological method, combining an ice flow model and an accumulation model based on isotope measurements. However, due to badly known modelling parameters such as basal conditions at the base of the ice sheet (melting and sliding), flow parameters (vertical velocity profile) and accumulation parameters (accumulation-isotope relationship), the glaciological model has to be tuned to agree with independent chronological information (use of time markers, correlation with other dated paleorecords...). The chronology that we have constructed (DC-FGT0, Dome C Federative Glaciological Timescale 0) is a first tentative to optimally use the physical laws and the independent chronological information. To this end, we used an inverse procedure, numerically solved with the Metropolis-Hastings algorithm, to adjust the accumulation and ice flow parameters of the glaciological dating model with respect to the time markers. Our dating model seems to give a realistic chronology for Dome C, at least for the last 500,000 years. Concerning the accumulation model, we show that the classical isotope-accumulation relationship seems to overestimate the glacial accumulation rate. Moreover, we confirm that the thinning in the upper part of an ice sheet is more important at a dome than for the rest of the ice flow line.

Parrenin, F.; Jouzel, J.; Petit, J.-R.; Schwander, J.; Waelbroeck, C.; Wolff, E. W.

2003-04-01

136

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

NASA Astrophysics Data System (ADS)

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

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

2005-05-01

137

The delta18O record along the Greenland Ice Core Project deep ice core and the problem of possible Eemian climatic instability  

Microsoft Academic Search

Over 70,000 samples from the 3029-m-long Greenland Ice Core Project (GRIP) ice core drilled on the top of the Greenland Ice Sheet (Summit) have been analyzed for delta18O. A highly detailed and continuous delta18O profile has thus been obtained and is discussed in terms of past temperatures in Greenland. We also discuss a three-core stacked annual delta18O profile for the

Sigfús J. Johnsen; Henrik B. Clausen; Willi Dansgaard; Niels S. Gundestrup; Claus U. Hammer; Uffe Andersen; Katrine K. Andersen; Christine S. Hvidberg; Dorthe Dahl-Jensen; Jørgen P. Steffensen; Hitoshi Shoji; Árny E. Sveinbjörnsdóttir; Jim White; Jean Jouzel; David Fisher

1997-01-01

138

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

139

The duration of the Bølling-Allerød period (Greenland Interstadial 1) in the GRIP ice core  

NASA Astrophysics Data System (ADS)

A new dating of the Bølling-Allerød period (Greenland Interstadial event 1) in the GRIP ice core is presented. Newly measured profiles of ?D and ?18O, as well as existing profiles of Ca2+, NH4+, dust and NO3-, have been used for the dating. As seasonal variations can be observed in all six components, it was possible to simultaneously count annual layers in the profiles in order to obtain a multi-parameter dating. The new data presented in this study include a total of 36.85 m of stable-isotope profiles of 1 cm resolution from five sections of the Bølling-Allerød period in the GRIP ice core. The annual-layer counting suggests a duration of the complete Bølling-Allerød period, as revealed in the GRIP ice core, of 1627 ± 52 years. This estimate contrasts with an earlier finding from the same GRIP ice core, where the Bølling-Allerød was found to span 2168 years (Hammer, in press). This estimate was based on layer counting, using dust concentrations only.

Seierstad, Inger K.; Johnsen, Sigfús J.; Vinther, Bo M.; Olsen, Jesper

140

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

141

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

142

Low-latitude ice cores and freshwater availability  

NASA Astrophysics Data System (ADS)

Recent retreat of Tibetan Plateau glaciers affects at least half a billion people. Himalayan glaciers seasonally release meltwater into tributaries of the Indus, Ganges, and Brahmaputra Rivers and supply freshwater necessary to support agricultural and economic practices. Tibetan Plateau glaciers are retreating more rapidly than mountain glaciers elsewhere in the world, and this retreat is accelerating. The Naimona'nyi (30°27'N; 81°91'E, 6050 m a.s.l), Guliya (35°17'N; 81°29'E, 6710 m a.s.l.) and Dasuopu (28°23'N; 85°43'E, 7200 m a.s.l.) ice cores place this recent retreat into a longer time perspective through quantifying climate parameters such as past temperature, aridity, and atmospheric chemistry. Naimona'nyi has not accumulated mass since at least 1950, as evidenced by the virtual lack of radiogenic isotopes (36Cl, 3 H, and beta radioactivity) present in the ice core. These isotopes were produced by U.S. and Soviet atmospheric thermonuclear bomb tests conducted in the 1950s and 1960s and provide independent dating horizons for the ice cores. Lead-210 dates imply that the uppermost preserved glacial ice on Naimona'nyi formed during the 1940s. While this is the highest documented glacial thinning in the world other glaciers at elevations similar to that of Naimona'nyi, such as Kilimanjaro (3°4'S; 37°21'E, 5893 m a.s.l.), are also losing mass at their summits. The global scope of high-elevation glacial thinning suggests that ablation on the Earth's highest ice fields may be more prevalent as global mean temperatures continue to increase. Glacial thinning has not been taken into account in future projections of regional freshwater availability, and the net mass loss indicates that Himalayan glaciers currently store less freshwater than assumed in models. The acceleration of Tibetan Plateau glacial retreat has been hypothesized to be due in part to deposition of black carbon (BC) from biomass burning on to ice fields, thereby lowering the reflectivity of the glacier surface and melting the upper ice. The application of a novel technique of measuring and radiocarbon-dating ultra-small samples (< 100mug) of the BC and total organic carbon (TOC) fractions of Naimona'nyi demonstrates a decrease (˜12 to 14 ka versus ˜7 ka) in the composite age of BC in the upper 40 m and lowest 20 m of the 137 m ice core, suggesting the incorporation of radiocarbon-dead BC. Precambrian black shale in the Lesser Himalaya provide a natural source material which may be operationally defined as black carbon and which may incorporate radiocarbon-dead sediments into the bulk 14C measurements, yet as the mean 14C age is ˜10 ka, modern BC from biomass burning must also be incorporated into the ice core record. While the uppermost sample (5 m) contains 38% BC, 210 Pb dates show that this depth corresponds to an age before 1850 AD, or before the regional Industrial Revolution. As BC is a hydrophobic substance, the BC is unlikely to have migrated through the firn and glacial ice. Therefore, the high-elevation thinning on Naimona'nyi appears to be a response to increased temperatures rather than primarily driven by changes in surface albedo. This technique was applied to the annually-dated ice core from the accumulating summit of the Quleccaya ice cap, Peru (13'56'S; 70°50'W; 5670 m a.s.l.). A marked increase in modern BC and TOC was measured since 1880 AD. No increase in radiocarbon-dead (> 60,000 ka) BC or TOC was noted, suggesting that the source of the carbon was from biomass burning, with a possible contribution of Amazon slash and burn clearing, rather than the input of fossil fuel combustion. The age of the BC and TOC is thousands of years older than the age of the surrounding ice, and should not be used to date the ice core. Although Naimona'nyi provides challenges for constructing an ice core chronology due to its lack of independent horizons such as volcanic activity, methane gas measurements, 14C dates, 3H, 36Cl, or beta radioactivity, the oxygen isotopic record can be correlated with the neighboring Dasuopu and Guliya ice

Kehrwald, Natalie Marie

143

An automated approach for annual layer counting in ice cores  

NASA Astrophysics Data System (ADS)

A novel method for automated annual layer counting in seasonally-resolved paleoclimate records has been developed. It relies on algorithms from the statistical framework of Hidden Markov Models (HMMs), which originally was developed for use in machine speech-recognition. The strength of the layer detection algorithm lies in the way it is able to imitate the manual procedures for annual layer counting, while being based on statistical criteria for annual layer identification. The most likely positions of multiple layer boundaries in a section of ice core data are determined simultaneously, and a probabilistic uncertainty estimate of the resulting layer count is provided, ensuring an objective treatment of ambiguous layers in the data. Furthermore, multiple data series can be incorporated and used simultaneously. In this study, the automated layer counting algorithm has been applied to an ice core record from Greenland. The algorithm shows high skill in reproducing the results from manual layer counts.

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

2012-07-01

144

MIF in Volcanic Sulfate: Preliminary Results From Greenland Ice Cores  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

145

Improving ice core interpretation using in situ and reanalysis data  

Microsoft Academic Search

Back trajectory analysis, provided by the British Atmospheric Data Centre using meteorological parameters from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis ERA-40 (1980–2001) and operational analysis (2002–2006), is used to investigate transport pathways and source regions of climate proxies preserved in a new ice core (Gomez) from the southwestern Antarctic Peninsula. The ECMWF data are compared with automatic

E. R. Thomas; T. J. Bracegirdle

2009-01-01

146

Greenland and Antarctic ice core records of millennial scale variability  

Microsoft Academic Search

Greenland ice cores drilled at Summit and NorthGRIP provide high resolution records of north Atlantic millennial scale variability spanning the last glacial-interglacial cycle. We will review the Greenland temperature records of millennial scale variability and discuss the magnitude and pacing of the Dansgaard-Oeschger (D\\/O) events, using records of water stable isotopes and firn gas fractionation method estimates. Owing to the

V. Masson-Delmotte; T. Blunier; J. Chappellaz; D. Dahl-Jensen; H. Fischer; J. Jouzel; A. Landais; L. Loulergue; B. Stenni

2007-01-01

147

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

148

Sulfate and nitrate concentrations from a south Greenland ice core  

SciTech Connect

An ice core in south Greenland covering the period 1869 to 1984 was analyzed for oxygen isotopes and chloride, nitrate, and sulfate concentrations. The data show that the excess (nonsea-salt) sulfate concentration has tripled since approximately 1900 to 1910 and the nitrate concentration has doubled since approximately 1955. The increases may be attributable to the deposition of these chemical species from air masses carrying North American and Eurasian anthropogenic emissions. 22 references, 2 figures.

Mayewski, P.A.; Lyons, W.B.; Spencer, M.J.; Twickler, M.; Dansgaard, W.; Koci, B.; Davidson, C.I.; Honrath, R.E.

1986-05-23

149

Bipolar and chronological consequences of methane measurements in the Talos Dome ice core  

NASA Astrophysics Data System (ADS)

The international project IPICS of the International Polar Year 2007/09 aims in particular to use new coastal drillings in Antarctica to study the regional variability of Antarctic climate, and its relationship with climatic changes in other regions of the Earth. Here, we investigate a new drilling conducted by a consortium of five European nations led by Italy, on the coastal site of Talos Dome (Antarctica). It reached a depth of 1620 m during the field season 2007/2008. We measured the methane (CH4) mixing ratio in the Talos Dome ice core in the depth range from 73 (close-off) to 1620 m, at a depth resolution ranging from 0.5 to 4 m. Two laboratories (LGGE and Bern) were involved, using slightly different techniques. The well-known temporal evolution of this signal allows us to define tie points with respect to other ice cores from Greenland and Antarctica, using in particular the rapid CH4 changes associated with the last termination and the Dansgaard/Oeschger events. We also investigated the isotopic composition of molecular oxygen (making another dating tool in the gas phase of the ice core) in order to bring additional chronological constraints during periods where CH4 changes become more muted. It has been measured at the LSCE during MIS 2, 4, and the last glacial inception. Comparing these records with their counterpart in other ice cores, and using an ice flow model and an inverse method, we propose a preliminary age scale for the trapped gas and the surrounding ice at Talos Dome. It indicates that the Talos Dome stratigraphy is undisturbed down to 1560 m, corresponding to about 300 000 years BP. More importantly, the comparison of water isotopic profiles from the Talos Dome, EDC, and NGRIP ice cores, once put on a common time scale, reveals that during the last deglaciation, climatic changes at Talos Dome were essentially in phase with the Antarctic plateau, and that the bipolar seesaw with Greenland temperature is also valid for this coastal site, thus contradicting the neighbouring Taylor Dome ice core findings. We will also investigate if those conclusions can be extended to the last glacial period.

Buiron, D.; Chappellaz, J.; Schilt, A.; Parrenin, F.; Lemieux, B.; Capron, E.; Masson-Delmotte, V.; Landais, A.; Stenni, B.; Frezzotti, M.

2009-04-01

150

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

151

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

Microsoft Academic Search

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

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

2009-01-01

152

Two ice-cored ? 18 O records from Svalbard illustrating climate and sea-ice variability over the last 400 years  

Microsoft Academic Search

Ice cores from the relatively low-lying ice caps in Svalbard have not been widely exploited in climatic studies owing to uncertainties about the effect of meltwater percolation. However, results from two new Svalbard ice cores, at Lomonosovfonna and Austfonna, have shown that with careful site selection, high-resolution sampling and multiple chemical analyses it is possible to recover ice cores from

Elisabeth Isaksson; Jack Kohler; Veijo Pohjola; John Moore; Makoto Igarashi; Lars Karlöf; Tõnu Martma; Harro Meijer; Hideaki Motoyama; Rein Vaikmäe

2005-01-01

153

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

NASA Astrophysics Data System (ADS)

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

Yang, X.

2011-12-01

154

Ice core record of rising lead pollution in the North Pacific atmosphere  

Microsoft Academic Search

A high-resolution, 8000 year-long ice core record from the Mt. Logan summit plateau (5300 m asl) reveals the initiation of trans-Pacific lead (Pb) pollution by ca. 1730, and a >10-fold increase in Pb concentration (1981–1998 mean = 68.9 ng\\/l) above natural background (5.6 ng\\/l) attributed to rising anthropogenic Pb emissions from Asia. The largest rise in North Pacific Pb pollution

E. Osterberg; P. Mayewski; K. Kreutz; D. Fisher; M. Handley; S. Sneed; C. Zdanowicz; J. Zheng; M. Demuth; M. Waskiewicz; J. Bourgeois

2008-01-01

155

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

Microsoft Academic Search

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

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

2000-01-01

156

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

Microsoft Academic Search

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

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

2002-01-01

157

Ice core evidence for significant 100-year regional warming on the Antarctic Peninsula  

Microsoft Academic Search

We present a new 150-year, high-resolution, stable isotope record (?18O) from the Gomez ice core, drilled on the data sparse south western Antarctic Peninsula, revealing a ?2.7°C rise in surface temperatures since the 1950s. The record is highly correlated with satellite-derived temperature reconstructions and instrumental records from Faraday station on the north west coast, thus making it a robust proxy

E. R. Thomas; P. F. Dennis; T. J. Bracegirdle; C. Franzke

2009-01-01

158

Revised estimates of Greenland ice sheet thinning histories based on ice-core records  

NASA Astrophysics Data System (ADS)

Ice core records were recently used to infer elevation changes of the Greenland ice sheet throughout the Holocene. The inferred elevation changes show a significantly greater elevation reduction than those output from numerical models, bringing into question the accuracy of the model-based reconstructions and, to some extent, the estimated elevation histories. A key component of the ice core analysis involved removing the influence of vertical surface motion on the ?18O signal measured from the Agassiz and Renland ice caps. We re-visit the original analysis with the intent to determine if the use of more accurate land uplift curves can account for some of the above noted discrepancy. To improve on the original analysis, we apply a geophysical model of glacial isostatic adjustment calibrated to sea-level records from the Queen Elizabeth Islands and Greenland to calculate the influence of land height changes on the ?18O signal from the two ice cores. This procedure is complicated by the fact that ?18O contained in Agassiz ice is influenced by land height changes distant from the ice cap and so selecting a single location at which to compute the land height signal is not possible. Uncertainty in this selection is further complicated by the possible influence of Innuitian ice during the early Holocene (12-8 ka BP). Our results indicate that a more accurate treatment of the uplift correction leads to elevation histories that are, in general, shifted down relative to the original curves at GRIP, NGRIP, DYE-3 and Camp Century. In addition, compared to the original analysis, the 1-? uncertainty is considerably larger at GRIP and NGRIP. These changes reduce the data-model discrepancy reported by Vinther et al. (2009) at GRIP, NGRIP, DYE-3 and Camp Century. A more accurate treatment of isostasy and surface loading also acts to improve the data-model fits such that the residuals at all four sites for the period 8 ka BP to present are significantly reduced compared to the original analysis. Prior to 8 ka BP, the possible influence of Innuitian ice on the inferred elevation histories prevents a meaningful comparison.

Lecavalier, Benoit S.; Milne, Glenn A.; Vinther, Bo M.; Fisher, David A.; Dyke, Arthur S.; Simpson, Matthew J. R.

2013-03-01

159

East Antarctic ice core sulfur isotope measurements over a complete glacial-interglacial cycle  

Microsoft Academic Search

Both sulfur and oxygen isotopes of sulfate preserved in ice cores from Greenland and Antarctica have provided information on the relative sources of sulfate in the ice and their chemical transformation pathways in the atmosphere over various time periods. The mass-independent fractionation in the oxygen isotopes of sulfate from the Vostok ice core from east Antarctica suggests that gas-phase oxidation

B. Alexander; M. H. Thiemens; J. Farquhar; A. J. Kaufman; J. Savarino; R. J. Delmas

2003-01-01

160

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

NASA Astrophysics Data System (ADS)

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

Rybak, O.; Fürst, J.; Huybrechts, P.

2012-04-01

161

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We build an interface between an Infra Red Cavity Ring Down Spectrometer (IR-CRDS) and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of ?18O and ?D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ?l amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100 % efficiency in a home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on humidity levels. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1 ‰ and 0.5 ‰ for ?18O and ?D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of ?18O and ?D, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the framework of the NEEM deep ice core drilling project in Greenland, during the 2010 field season.

Gkinis, V.; Popp, T. J.; Blunier, T.; Bigler, M.; Schüpbach, S.; Johnsen, S. J.

2011-06-01

162

A novel radiocarbon dating technique applied to an ice core from the Alps indicating late Pleistocene ages  

NASA Astrophysics Data System (ADS)

Ice cores retrieved from high-altitude glaciers are important archives of past climatic and atmospheric conditions in midlatitude and tropical regions. Because of the specific flow behavior of ice, their age-depth relationship is nonlinear, preventing the application of common dating methods such as annual layer counting in the deepest and oldest part. Here we present a new approach and technique, allowing dating of any such ice core at arbitrary depth for the age range between ˜500 years B.P. and the late Pleistocene. This new, complementary dating tool has great potential for numerous ice core related paleoclimate studies since it allows improvement and extension of existing and future chronologies. Using small to ultrasmall sample size (100 ?g > carbon content > 5 ?g) accelerator mass spectrometry, we take advantage of the ice-included, water-insoluble organic carbon fraction of carbonaceous aerosols for radiocarbon (14C) dating. Analysis and dating of the bottom ice of the Colle Gnifetti glacier (Swiss-Italian Alps, 45°55'50?N, 7°52'33?E, 4455 m asl) has been successful in a first application, and the results revealed the core to cover most of the Holocene at the least with indication for late Pleistocene ice present at the very bottom.

Jenk, Theo M.; Szidat, SöNke; Bolius, David; Sigl, Michael; GäGgeler, Heinz W.; Wacker, Lukas; Ruff, Matthias; Barbante, Carlo; Boutron, Claude F.; Schwikowski, Margit

2009-07-01

163

Investigating the past and recent ?18O-accumulation relationship seen in Greenland ice cores  

NASA Astrophysics Data System (ADS)

Decadal means of ?18O and accumulation rates from 52 ice core locations in Greenland are presented. The accumulation rates are derived from annual layers determined in the ?18O curve. Investigation of the ?18O-accumulation relationship across the ice divide reveals a significant Foehn effect with anticorrelation of ?18O and accumulation rate on the lee side of the divide in Southern Greenland, while no effect is seen in Central Greenland. Furthermore, the sensitivity of accumulation rate to changes in temperature is found to be smaller in Northern Greenland than in the central and southern parts. Four records in the data set contain sufficient recent data that the period of observed temperature rise from the 1990s and onwards can be investigated. All four records are from locations close to the ice divide in Northern Greenland and while three of them show increased temperatures, no conclusive statement can be made about the accumulation rate from these data.

Buchardt, S. L.; Clausen, H. B.; Vinther, B. M.; Dahl-Jensen, D.

2012-12-01

164

THE TROPICAL CONNECTION BETWEEN THE ATLANTIC SECTOR ICE CORES AND THE NORTH PACIFIC MT LOGAN ICE CORE  

NASA Astrophysics Data System (ADS)

The stable isotope record from the Mt Logan, Yukon, Canada ice core spans the late Glacial to present and shows very large and sudden variations in O18 during the Holocene . It is hypothesized that they are driven by changes in the water sources ,which in turn, are determined by the state of ENSO. There seems to be no correlations between the Logan ice core isotope record and those from the North Atlantic (Greenland and Eastern Canadian Arctic). Using the stacked and co-dated Greenland and Eastern Canadian Arctic ice core records from the Holocene, it is possible to reproduce the Logan isotope record by subtracting the stacked Atlantic record from itself with an 1100 year lag. The correlations obtainable are -0.43 for 50 year average series. This correlation is significant at the 99.8 % level . The 1100 lag has also been found in previous studies comparing the Greenland to Antarctic ice cores (Stocker and Johnsen,2003). It is argued that such a lagged difference series is a proxy for the difference between the ocean water surface and deep temperatures in the tropical Pacific . ENSO’s amplitude is driven by this temperature difference, (Sun 2000). When the deep water is too warm, then the difference is too small to produce ENSO oscillations and strong tropical easterly winds persist (ie strong and constant La Nina). The ice core records from Mt Logan , Greenland and Eastern Arctic Canada all point to a similar history of ENSO oscillation strength. Prior to ~ 4200 BP the strong and constant La Nina tended to drive the tropical Pacific winds and moisture across to produce strong and reliable monsoons. Since 4200 BP the “modern” and variable pattern has been in place. There was a smaller scale shift about 1840 AD . For about a couple of centuries prior to 1840 AD , La Nina was in charge and after there were the oscillations that are thought of as normal. If the 1100 year lag between surface and bottom temperatures is true and if the bottom temperatures are echoes those from the N Atlantic 1100 years ago, there are implications for what we could expect from the tropical Pacific oscillations (ENSO) in the future. Sun D. 2000. Global climate change and El Nino: a theoretical framework. in "El Nino and The Southern Oscillation", editors H. F. Diaz and V. Markgraf. Cambridge UP. Stocker T.F. and S.J. Johnsen. 2003. A minimum thermodynamic model for the bipolar seesaw.. Paleoceanography vol 18, No 4 , pp11-19.

Fisher, D. A.

2009-12-01

165

Ice-age atmospheric concentration of nitrous oxide from an Antarctic ice core  

Microsoft Academic Search

Results from Antarctic ice cores are reported which show that the atmospheric N2O concentration was about 30 percent lower during the Last Glacial Maximum than during the Holocene epoch. The data also show that present-day N2O concentrations are unprecedented in the past 45 kyr and hence provide evidence that recent increases in atmospheric N2O are of anthropogenic origin.

Markus Leuenberger; Ulrich Siegenthaler

1992-01-01

166

The Incomplete Impact Record and Implications for Ice Core Studies  

NASA Astrophysics Data System (ADS)

The impact risk is extremely uncertain for objects of order 0.1-1 km diameter, with kinetic energies in the range 100 to 1 million Mt (megaton TNT ~ 4×1015 J) and recurrence times estimated in thousands to many tens of thousands of years. Millennial timescales are especially interesting, since the character of explosions (e.g. impacts, large volcanic eruptions) that only occur every 103 to 104 years lies just beyond the reckoning of modern cultural history. The impact rate predicted for the Earth based on observing nearby objects is much higher than the endemic rate estimated by counting known craters on Earth's surface. We have examined the latest account of confirmed craters from the Earth Impact Database (http://www.unb.ca/passc/ImpactDatabase/) over the last 100 Ma. The cratering record contains a large gap between 35 and 5 Ma, during which the apparent impact rate drops by an order of magnitude. The gap occurs during a period of substantial climate change, notably the initiation of large scale permanent glaciers, based on climate proxies from deep-sea sediment cores. A likely partial explanation is that climate change eroded or precluded crater formation in the recent geologic past. Taken together with constraints from inner solar system cratering and observations of near earth objects, the apparent gap in crater formation suggests that the terrestrial impact record is grossly incomplete over timescales much shorter than 100 Ma. If the true impact rate is more commensurate with the higher rates inferred from the local planetary environment, then some of the explosive fallout layers now observed in ice cores may actually be the result of recent impacts rather than volcanic eruptions. Like very large eruptions, impact ejecta are likely to be widely distributed, since impactors disrupt all levels of the atmosphere and generate ballistic debris and vapor plumes that can rise above the stratosphere. Polar ice core records of the last ~50-100 ka have become sufficiently extensive and synchronized to suggest an emerging pattern between explosive volcanic layers and abrupt climate change, although atmospheric focusing and preservation of deposits complicate analysis. By comparing ice core ash and acid signals of explosive volcanic fallout in Antarctica and Greenland, we have identified a number of common horizons which likely resulted from "eruptions" that dispersed material world-wide. These events appear to have preferentially occurred during onsets or intensifications of cooling phases, contributing to long-standing debates over possible feedbacks between climatic and geologic phenomena. The correlation may be evidence that abrupt climate change and associated changes in sea level and ice sheets can trigger volcanism. An intriguing and conspicuous alternative possibility is that catastrophic explosions force long term cooling. A relatively high rate for small impact events (objects hundreds of meters in size) could imply that impacts (instead of volcanism) are a causal factor in some of the climate variations observed during the last million years. Our method of optically probing outward from the boreholes created by ice coring missions is capable of detecting particulate layers which are invisible or largely missing in the cores, identifying candidate horizons for chemical analyses. Deliberate and discriminative analysis of the "ash" layers in ice cores could shed light on the recent impact rate. This research was supported by grant NSF ANT-0440609.

Bay, R. C.; Rohde, R. A.; Price, P. B.

2007-12-01

167

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

NASA Astrophysics Data System (ADS)

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

Thompson, L. G.

2001-12-01

168

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

Microsoft Academic Search

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

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

2011-01-01

169

A 60 000 year Greenland stratigraphic ice core chronology  

NASA Astrophysics Data System (ADS)

The Greenland Ice Core Chronology 2005 (GICC05) is a time scale based on annual layer counting of high-resolution records from Greenland ice cores. Whereas the Holocene part of the time scale is based on various records from the DYE-3, the GRIP, and the NorthGRIP ice cores, the glacial part is solely based on NorthGRIP records. Here we present an 18 ka extension of the time scale such that GICC05 continuously covers the past 60 ka. The new section of the time scale places the onset of Greenland Interstadial 12 (GI-12) at 46.9±1.0 ka b2k (before year AD 2000), the North Atlantic Ash Zone II layer in GI-15 at 55.4±1.2 ka b2k, and the onset of GI-17 at 59.4±1.3 ka b2k. The error estimates are derived from the accumulated number of uncertain annual layers. In the 40-60 ka interval, the new time scale has a discrepancy with the Meese-Sowers GISP2 time scale of up to 2.4 ka. Assuming that the Greenland climatic events are synchronous with those seen in the Chinese Hulu Cave speleothem record, GICC05 compares well to the time scale of that record with absolute age differences of less than 800 years throughout the 60 ka period. The new time scale is generally in close agreement with other independently dated records and reference horizons, such as the Laschamp geomagnetic excursion, the French Villars Cave and the Austrian Kleegruben Cave speleothem records, suggesting high accuracy of both event durations and absolute age estimates.

Svensson, A.; Andersen, K. K.; Bigler, M.; Clausen, H. B.; Dahl-Jensen, D.; Davies, S. M.; Johnsen, S. J.; Muscheler, R.; Parrenin, F.; Rasmussen, S. O.; Röthlisberger, R.; Seierstad, I.; Steffensen, J. P.; Vinther, B. M.

2008-03-01

170

A 60 000 year Greenland stratigraphic ice core chronology  

NASA Astrophysics Data System (ADS)

The Greenland Ice Core Chronology 2005 (GICC05) is a time scale based on annual layer counting of high-resolution records from Greenland ice cores. Whereas the Holocene part of the time scale is based on various records from the DYE-3, the GRIP, and the NorthGRIP ice cores, the glacial part is solely based on NorthGRIP records. Here we present an 18 kyr extension of the time scale such that GICC05 continuously covers the past 60 kyr. The new section of the time scale places the onset of Greenland Interstadial 12 (GI-12) at 46.9±1.0 kyr b2k (before year AD 2000), the North Atlantic Ash Zone 2 layer in GI-15 at 55.4±1.2 kyr b2k, and the onset of GI-17 at 59.4±1.3 kyr b2k. The error estimates are derived from the accumulated number of uncertain annual layers and can be regarded as 1? uncertainties. In the 40-60 kyr interval the new time scale has a discrepancy with the Meese-Sowers GISP2 time scale of up to 2.4 kyr, whereas GICC05 compares well to the dating of the Hulu Cave record with absolute age differences of less than 800 years throughout the 60 kyr period. The new time scale is generally in close agreement with other independently dated records and reference horizons, such as the Laschamp geomagnetic excursion and the Kleegruben speleothem record from the Austrian Alps, suggesting high accuracy of both event durations and absolute age estimates.

Andersen, K. K.; Bigler, M.; Clausen, H. B.; Dahl-Jensen, D.; Johnsen, S. J.; Rasmussen, S. O.; Seierstad, I.; Steffensen, J. P.; Svensson, A.; Vinther, B. M.; Davies, S. M.; Muscheler, R.; Parrenin, F.; Röthlisberger, R.

2007-11-01

171

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

172

New focuses of polar ice-core study: NEEM and Dome A  

Microsoft Academic Search

Ice core records from polar regions are of great value to study long-term climate and environmental change. Greenland ice-core\\u000a records are celebrated for their high resolution and have provided very important knowledge for understanding the late Quaternary\\u000a palaeoclimate, especially in reference to millennial-scale abrupt climatic flips during the last glaciation. Recently, a new\\u000a project to retrieve a deep ice-core from

JiaWen Ren; CunDe Xiao; ShuGui Hou; YuanSheng Li; Bo Sun

2009-01-01

173

Ice core evidence for a 20th century decline of sea ice in the Bellingshausen Sea, Antarctica  

NASA Astrophysics Data System (ADS)

This study uses ice core methanesulphonic acid (MSA) records from the Antarctic Peninsula, where temperatures have been warming faster than anywhere else in the Southern Hemisphere, to reconstruct the 20th century history of sea ice change in the adjacent Bellingshausen Sea. Using satellite-derived sea ice and meteorological data, we show that ice core MSA records from this region are a reliable proxy for regional sea ice change, with years of increased winter sea ice extent recorded by increased ice core MSA concentrations. Our reconstruction suggests that the satellite-observed sea ice decline in the Bellingshausen Sea during recent decades is part of a long-term regional trend that has occurred throughout the 20th century. The long-term perspective on sea ice in the Bellingshausen Sea is consistent with evidence of 20th century warming on the Antarctic Peninsula and may reflect a progressive deepening of the Amundsen Sea Low due to increasing greenhouse gas concentrations and, more recently, stratospheric ozone depletion. As a first-order estimate, our MSA-based reconstruction suggests that sea ice in the Bellingshausen Sea has retreated southward by ˜0.7° during the 20th century. Comparison with other 20th century sea ice observations, reconstructions, and model simulations provides a coherent picture of Antarctic sea ice decline during the 20th century, although with regional-scale differences evident in the timing and magnitude of this sea ice decline. This longer-term perspective contrasts with the small overall increase in Antarctic sea ice that is observed in post-1979 satellite data.

Abram, Nerilie J.; Thomas, Elizabeth R.; McConnell, Joseph R.; Mulvaney, Robert; Bracegirdle, Thomas J.; Sime, Louise C.; Aristarain, Alberto J.

2010-12-01

174

Using shallow ice coring experiments and melt modelling to determine mass balance of Devon Ice Cap, Canada  

Microsoft Academic Search

A combination of shallow ice-coring field experiments and degree-day melt modelling was employed to reconstruct the spatial pattern of mass balance across the Devon Ice Cap. This research is part of a wider program to quantify and to determine the causes of changes in the geometry and mass of the Devon Ice Cap over the last 40 years. In April-May

D. Mair; D. Burgess; M. Sharp

2003-01-01

175

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

A new technique for on-line high resolution isotopic analysis of liquid water, tailored for ice core studies is presented. We built an interface between a Wavelength Scanned Cavity Ring Down Spectrometer (WS-CRDS) purchased from Picarro Inc. and a Continuous Flow Analysis (CFA) system. The system offers the possibility to perform simultaneuous water isotopic analysis of ?18O and ?D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ?l amounts of liquid water is achieved by pumping sample through a fused silica capillary and instantaneously vaporizing it with 100% efficiency in a~home made oven at a temperature of 170 °C. A calibration procedure allows for proper reporting of the data on the VSMOW-SLAP scale. We apply the necessary corrections based on the assessed performance of the system regarding instrumental drifts and dependance on the water concentration in the optical cavity. The melt rates are monitored in order to assign a depth scale to the measured isotopic profiles. Application of spectral methods yields the combined uncertainty of the system at below 0.1‰ and 0.5‰ for ?18O and ?D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sample in the transfer lines limits the temporal resolution of the technique. In this work we investigate and assess these dispersion effects. By using an optimal filtering method we show how the measured profiles can be corrected for the smoothing effects resulting from the sample dispersion. Considering the significant advantages the technique offers, i.e. simultaneuous measurement of ?18O and ?D, potentially in combination with chemical components that are traditionally measured on CFA systems, notable reduction on analysis time and power consumption, we consider it as an alternative to traditional isotope ratio mass spectrometry with the possibility to be deployed for field ice core studies. We present data acquired in the field during the 2010 season as part of the NEEM deep ice core drilling project in North Greenland.

Gkinis, V.; Popp, T. J.; Blunier, T.; Bigler, M.; Schüpbach, S.; Kettner, E.; Johnsen, S. J.

2011-11-01

176

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

177

An automated approach for annual layer counting in ice cores  

NASA Astrophysics Data System (ADS)

A novel method for automated annual layer counting in seasonally-resolved paleoclimate records has been developed. It relies on algorithms from the statistical framework of hidden Markov models (HMMs), which originally was developed for use in machine speech recognition. The strength of the layer detection algorithm lies in the way it is able to imitate the manual procedures for annual layer counting, while being based on statistical criteria for annual layer identification. The most likely positions of multiple layer boundaries in a section of ice core data are determined simultaneously, and a probabilistic uncertainty estimate of the resulting layer count is provided, ensuring an objective treatment of ambiguous layers in the data. Furthermore, multiple data series can be incorporated and used simultaneously. In this study, the automated layer counting algorithm has been applied to two ice core records from Greenland: one displaying a distinct annual signal and one which is more challenging. The algorithm shows high skill in reproducing the results from manual layer counts, and the resulting timescale compares well to absolute-dated volcanic marker horizons where these exist.

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

2012-11-01

178

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

179

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

180

Tree ring and ice core time scales around the Santorini eruption  

NASA Astrophysics Data System (ADS)

When studying cosmogenic radionuclides in ice core and tree ring archives around the Santorini eruption a ~20 year discrepancy was found between the records (Muscheler 2009). In this study a new 10Be dataset from the NGRIP ice core is presented. It has a resolution of 7 years and spans the period 3752-3244 BP (1803-1295 BC). The NGRIP 10Be record and the previously published 10Be GRIP record were compared to the IntCal datasets to further investigate the discrepancy between the ice core and tree ring chronologies. By modelling the 14C production rate based on atmospheric 14C records a comparison could be made to the 10Be flux which is assumed to represent the 10Be production rate. This showed a time shift of ~23 years between the records. The sensitivity of the results to changes in important model parameters was evaluated. Uncertainties in the carbon cycle model cannot explain a substantial part of the timing differences. Potential influences of climate and atmospheric processes on the 10Be deposition were studied using ?18O from the respective cores and GISP2 ice core ion data. The comparison to ?18O revealed a small but significant correlation between 10Be flux and ?18O when the 14C-derived production signal was removed from the 10Be curves. The ion data, as proxies for atmospheric circulation changes, did not show any correlations to the 10Be record or the 10Be/14C difference. When including possible data uncertainties there is still a minimum discrepancy of ~10 years between the 10Be ice core and the 14C tree ring record. Due to lack of alternative explanations it is concluded that the ice core and/or the tree ring chronologies contains unaccounted errors in this range. This also reconciles the radiocarbon 1627-1600 BC (Friedrich et al., 2006) and ice core 1642±5 BC (Vinther et al., 2006) datings of the Santorini eruption. Friedrich, W.L., Kromer, B., Friedrich, M., Heinemeier, J., Pfeiffer, T., & Talamo, S., 2006: Santorini eruption radiocarbon dated to 1627-1600 BC. Science 312, 548-548. Muscheler, 2009: 14C and 10Be around 1650 cal BC. In Warburton, D.A., (ed.): Time's Up! Dating the Minoan Eruption of Santorini: acts of the Minoan Eruption Chronology Workshop, Sandbjerg November 2007: Monographs of the Danish Institute at Athens. Aarhus University Press, Aarhus. 298 pp. Vinther, B.M., Clausen, H.B., Johnsen, S.J., Rasmussen, S.O., Andersen, K.K., Buchardt, S.L., Dahl-Jensen, D., Seierstad, I.K., Siggaard-Andersen, M.L., Steffensen, J.P., Svensson, A., Olsen, J., & Heinemeier, J., 2006: A synchronized dating of three Greenland ice cores throughout the Holocene. Journal of Geophysical Research-Atmospheres 111, 11.

Löfroth, Elin; Muscheler, Raimund; Aldahan, Ala; Possnert, Göran; Berggren, Ann-Marie

2010-05-01

181

Thirty-seven year mass balance of Devon Ice Cap, Nunavut, Canada, determined by shallow ice coring and melt modeling  

Microsoft Academic Search

In April–May 2000, eight boreholes were drilled to ?15–20 m depth on the Devon Ice Cap. 137Cs ? activity profiles of each borehole showed a peak count rate at depth that is associated with fallout from atmospheric thermonuclear weapons testing in 1963. Snow, firn, and ice densities were measured at each core site and were used to estimate the average

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

182

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

183

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

184

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

185

New revelations on the nature of organic matter in ice cores  

Microsoft Academic Search

Analysis of organic species stored in ice cores provides a unique opportunity to obtain information about the environment of the past. Because of the trace nature of the organic components of interest, studying these species in molecular level detail within ice cores can be an analytical challenge. Using Fourier transform ion cyclotron resonance mass spectrometry with electrospray ionization, we have

Amanda M. Grannas; William C. Hockaday; Patrick G. Hatcher; Lonnie G. Thompson; Ellen Mosley-Thompson

2006-01-01

186

Reevaluation of past summer temperature reconstruction by melt features in Belukha ice cores, Russian Altai  

Microsoft Academic Search

Past summer temperature has been reconstructed by melt features in Belukha ice core in a previous study. We evaluated a climatic representativeness of isotope, net accumulation and melt feature by comparing two Belukha ice cores retrieved by different institutions and dated by different methods. We find a significant correlation between seasonal changes in stable isotope in precipitation and air temperature.

S. Okamoto; K. Fujita; H. Narita; J. Uetake; N. Takeuchi; T. Miyake; F. Nakazawa; V. Aizen; S. Nikitin; M. Nakawo

2009-01-01

187

Application Of Pollen Analysis For Seasonal Dating Of Alpine Glacier Ice Cores With Seasonal Missing Layers  

Microsoft Academic Search

Ice core studies from middle and low latitude glaciers have a problem that a reliable dating method has proved difficult due to wind erosion and vanishingly small amount of seasonal precipitation. They obscure the annual signal from the seasonal variations in chemical concentrations and oxygen isotope ratios that are typically used to date for ice cores. On the other hand,

F. Nakazawa; K. Fujita; N. Takeuchi; T. Fujiki; J. Uetake; V. Aizen; M. Nakawo

2004-01-01

188

Identification of major proton fluence events from nitrates in polar ice cores  

Microsoft Academic Search

Large transient concentrations of nitrates in polar ice cores have been identified as the signature of some major solar proton fluence events between 1940 and 1991. We review this solar proton proxy identification technique using nitrate concentration measurements in ice cores from the Arctic and Antarctic. Using this identification technique we go back in time in an attempt to identify

M. A Shea; D. F Smart; G. A. M Dreschhoff

1999-01-01

189

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

190

NAO signal recorded in the stable isotope record of Greenland ice cores  

Microsoft Academic Search

The winter delta18O signal is extracted from 7 Greenland ice cores covering the past ~700 years. To filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data. A comparison between the time series of the first principal component (PC1) with 67 years of winter (December to March)

B. M. Vinther; S. J. Johnsen; K. K. Andersen; A. W. Hansen; H. B. Clausen

2003-01-01

191

Applications of a Rapid Endospore Viability Assay for Monitoring UV Inactivation and Characterizing Arctic Ice Cores  

Microsoft Academic Search

We have developed a rapid endospore viability assay (EVA) in which endospore germination serves as an indicator for viability and applied it to (i) monitor UV inactivation of endospores as a function of dose and (ii) determine the proportion of viable endospores in arctic ice cores (Greenland Ice Sheet Project 2 (GISP2) cores; 94 m). EVA is based on the

Hannah S. Shafaat; Adrian Ponce

2006-01-01

192

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

193

Glaciological and climatic significance of Hercules Dome, Antarctica: An optimal site for deep ice core drilling  

Microsoft Academic Search

We present glaciological and climatological characteristics of Hercules Dome, Antarctica (86°S, 105°W), which demonstrate its potential as a deep ice core site. Annual layering in deltaD ratios from a 72 m ice core collected by the US-ITASE 2002 traverse indicate accumulation rates of 0.16-0.20 m\\/yr ice equivalent over the last 300 years. Age control from stratigraphy seen in the radio-echo

Robert W. Jacobel; Brian C. Welch; Eric J. Steig; David P. Schneider

2005-01-01

194

Glaciological and climatic significance of Hercules Dome, Antarctica: An optimal site for deep ice core drilling  

Microsoft Academic Search

We present glaciological and climatological characteristics of Hercules Dome, Antarctica (86°S, 105°W), which demonstrate its potential as a deep ice core site. Annual layering in ?D ratios from a 72 m ice core collected by the US-ITASE 2002 traverse indicate accumulation rates of 0.16–0.20 m\\/yr ice equivalent over the last 300 years. Age control from stratigraphy seen in the radio-echo

Robert W. Jacobel; Brian C. Welch; Eric J. Steig; David P. Schneider

2005-01-01

195

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

196

Glacial-interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-?15N measurements  

NASA Astrophysics Data System (ADS)

Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of ?15N of N2 in air trapped in ice core, assuming that ?15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-?15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our ?15N profiles reveal a heterogeneous response of the firn structure to glacial-interglacial climatic changes. While firn densification simulations correctly predict TALDICE ?15N variations, they systematically fail to capture the large millennial-scale ?15N variations measured at BI and the ?15N glacial levels measured at JRI and EDML - a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas-ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model-?15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the ?15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

Capron, E.; Landais, A.; Buiron, D.; Cauquoin, A.; Chappellaz, J.; Debret, M.; Jouzel, J.; Leuenberger, M.; Martinerie, P.; Masson-Delmotte, V.; Mulvaney, R.; Parrenin, F.; Prié, F.

2013-05-01

197

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

NASA Astrophysics Data System (ADS)

Abundant indirect evidence suggests that the West Antarctic Ice Sheet (WAIS) reduced in size during the Last Interglacial (LIG) compared to the Holocene. This study explores this possibility by comparing, for the first time, ice core stable isotope records for the LIG with output from a glacio-isostatic adjustment (GIA) model. The results show that ice core records from East Antarctica are remarkably insensitive to vertical movement of the solid land motion driven by a simulated hypothetical collapse of the WAIS. However, new and so far unexplored sites are identified which are sensitive to the isostatic signal associated with WAIS collapse and so ice core proxy data from these sites would be effective in testing this hypothesis further.

Bradley, S. L.; Siddall, M.; Milne, G. A.; Masson-Delmotte, V.; Wolff, E.

2012-05-01

198

Dark matter at DeepCore and IceCube  

SciTech Connect

With the augmentation of IceCube by DeepCore, the prospect for detecting dark matter annihilation in the Sun is much improved. To complement this experimental development, we provide a thorough template analysis of the particle physics issues that are necessary to precisely interpret the data. Our study is about nitty-gritty and is intended as a framework for detailed work on a variety of dark matter candidates. To accurately predict the source neutrino spectrum, we account for spin-correlations of the final state particles and the helicity-dependence of their decays, and absorption effects at production. We fully treat the propagation of neutrinos through the Sun, including neutrino oscillations, energy losses and tau regeneration. We simulate the survival probability of muons produced in the Earth by using the Muon Monte Carlo program, reproduce the published IceCube effective area, and update the parameters in the differential equation that approximates muon energy losses. To evaluate the zenith-angle dependent atmospheric background event rate, we track the Sun and determine the time it spends at each zenith-angle. Throughout, we employ neutralino dark matter as our example.

Barger, V. [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States); Gao, Y. [Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States); Marfatia, D. [Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045 (United States); Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)

2011-03-01

199

Holocene volcanic history as recorded in the sulfate stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core  

NASA Astrophysics Data System (ADS)

A detailed history of Holocene volcanism was reconstructed using the sulfate record of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core. This first complete Holocene volcanic record from an Antarctic core provides a reliable database to compare with long records from Antarctic and Greenland ice cores. A threshold method based on statistical treatment of the lognormal sulfate flux distribution was used to differentiate volcanic sulfate spikes from sulfate background concentrations. Ninety-six eruptions were identified in the EDC96 ice core during the Holocene, with a mean of 7.9 events per millennium. The frequency distribution (events per millennium) showed that the last 2000 years were a period of enhanced volcanic activity. EDC96 volcanic signatures for the last millennium are in good agreement with those recorded in other Antarctic ice cores. For older periods, comparison is in some cases less reliable, mainly because of dating uncertainties. Sulfate depositional fluxes of individual volcanic events vary greatly among the different cores. A volcanic flux normalization (volcanic flux/Tambora flux ratio) was used to evaluate the relative intensity of the same event recorded at different sites in the last millennium. Normalized flux variability for the same event showed the highest value in the 1100-1500 AD period. This pattern could mirror changes in regional transport linked to climatic variations such as slight warming stages in the Southern Hemisphere (Southern Hemisphere Medieval Warming-like period?).

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

2005-03-01

200

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

USGS Publications Warehouse

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

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

1996-01-01

201

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

202

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

203

Atmospheric Moisture Variability Inferred from a Central Tibetan Plateau Ice Core  

NASA Astrophysics Data System (ADS)

A 33 m ice core was retrieved from the Tanggula Mts, central Tibetan Plateau at 5743 m a.s.l. in August 2005. The ice core location exists directly within the boundary region of westerly-dominated and monsoon-dominated moisture sources. Annual layer-counted dating reveals the ice core represents the time period 1850-2004. Stable isotope (? 18O, ? D) values were measured in 630 samples for the entire core length at 3-5 cm resolution. Although ? 18O values increase during the time period, the degree of increase is inconsistent with documented increasing temperatures especially since the 1980s. ? 18O values are not significantly correlated with local station temperatures indicating other factors, such as monsoon water vapor sources, impact the preserved stable isotopes at this study location. Deuterium excess, a second order parameter used to provide information related to moisture sources, revealed two distinct periods; one from 1850-1934 with higher d-excess values (maximum value of 26.3% , mean of 19.8&permil), and one from 1942-2004 with lower d-excess values (minimum value of 6.6% , mean of 16.5&permil). A transition period of sharply decreasing d-excess values from 1935-1941 is present between the two periods, coinciding with a time of documented severe drought. The upper core section representing the time period 1942-2004 exhibits a significant negative correlation between ? 18O and N. India rainfall amount, while the lower core section (1850-1934) with higher d-excess values does not reveal a negative correlation. Results suggest a shift in the moisture sources at this study location around the mid-1930s; from more westerly or local moisture evaporated under drier conditions to more humid evaporated moisture sources. In addition, significant impact from monsoon moisture may be responsible for a dampening effect on the ? 18O temperature signal, which increases less dramatically compared to local and regional temperature increase.

Joswiak, D. R.; Yao, T.

2011-12-01

204

Combining ice core records and ice sheet models to explore the evolution of the East Antarctic Ice sheet during the Last Interglacial period  

NASA Astrophysics Data System (ADS)

This study evaluates the influence of plausible changes in East Antarctic Ice sheet (EAIS) thickness and the subsequent glacio-isostatic response as a contributor to the Antarctic warming indicated by ice core records during the Last Interglacial period (LIG). These higher temperatures have been estimated primarily using the difference in the ?D peak (on average ~ 15‰) in these LIG records relative to records for the Present Interglacial (PIG). Using a preliminary exploratory modelling study, it is shown that introducing a relatively moderate reduction in the amount of thickening of the EAIS over the LIG period introduces a significant increase (up to 8‰) in the predicted elevation-driven only ?D signal at the central Antarctic Ice sheet (AIS) ice core sites compared to the PIG. A sensitivity test in response to a large prescribed retreat of marine-based ice in the Wilkes and Aurora subglacial basins (equivalent to ~ 7 m of global mean sea-level rise) results in a distinct elevation signal that is resolvable within the ice core stable isotope records at three sites (Taylor Dome, TALDICE and EPICA Dome C). These findings have two main implications. First, EAIS elevation's only effects could account for a significant fraction of the LIG warming interpreted from ice core records. This result highlights the need for an improved estimate to be made of the uncertainty and size of this elevation-driven ?D signal which contributes to this LIG warming and that these effects need to be deconvolved prior to attempting to extract a climatic-only signal from the stable isotope data. Second, a fingerprint of significant retreat of ice in the Wilkes and Aurora basins should be detectable from ice core ?D records proximal to these basins and therefore used to constrain their contribution to elevated LIG sea levels, after accounting for ice sheet-climate interactions not considered in our approach.

Bradley, S. L.; Siddall, M.; Milne, G. A.; Masson-Delmotte, V.; Wolff, E.

2013-01-01

205

Caldicellulosiruptor Core and Pangenomes Reveal Determinants for  

SciTech Connect

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

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

2012-01-01

206

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

207

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

208

CO2 diffusion in polar ice: observations from naturally formed CO2 spikes in the Siple Dome (Antarctica) ice core  

NASA Astrophysics Data System (ADS)

One common assumption in interpreting ice-core CO2 records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO2 diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO2 associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO2 diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), electrical conductivity and Ca2+ ion concentrations to show that substantial CO2 diffusion may occur in ice on timescales of thousands of years. We estimate the permeation coefficient for CO2 in ice is ˜4 × 10-21 mol m-1 s-1: Pa-1 at -23°C in the top 287 m (corresponding to 2.74 kyr). Smoothing of the CO2 record by diffusion at this depth/age is one or two orders of magnitude smaller than the smoothing in the firn. However, simulations for depths of ˜930-950 m (˜60-70 kyr) indicate that smoothing of the CO2 record by diffusion in deep ice is comparable to smoothing in the firn. Other types of diffusion (e.g. via liquid in ice grain boundaries or veins) may also be important but their influence has not been quantified.

Ahn, Jinho; Headly, Melissa; Wahlen, Martin; Brook, Edward J.; Mayewski, Paul A.; Taylor, Kendrick C.

209

Predicted age-depth scales for Siple Dome and Inland WAIS Ice Cores in west Antarctica  

NASA Astrophysics Data System (ADS)

Geophysical data are used with ice flow models and generalized accumulation histories to estimate age and annual layer thickness versus depth for two anticipated ice core sites in West Antarctica: Siple Dome (81.65°S, 148.81°W) and an inland site on the West Antarctic Ice Sheet (WAIS). This modeling experiment predicts that 104 year-old ice is at ?50% depth and 105 year-old ice is at ?90% depth at both sites. Both of these cores could contain climate information through the last glacial cycle with annual resolution through the Holocene. The predicted similarity in resolution and record length between the two cores suggests that they could be compared in detail to obtain both spatial and temporal information about the paleoclimate and history of the West Antarctic ice sheet.

Nereson, N. A.; Waddington, E. D.; Raymond, C. F.; Jacobson, H. P.

210

115 year ice-core data from Akademii Nauk ice cap, Severnaya Zemlya: high-resolution record of Eurasian Arctic climate change  

Microsoft Academic Search

From 1999 to 2001 a 724 m deep ice core was drilled on Akademii Nauk ice cap, Severnaya Zemlya, to gain high-resolution proxy data from the central Russian Arctic. Despite strong summertime meltwater percolation, this ice core provides valuable information on the regional climate and environmental history. We present data of stable water isotopes, melt-layer content and major ions from

Thomas Opel; Diedrich Fritzsche; Hanno Meyer; Rainer Schütt; Karin Weiler; Urs Ruth; Frank Wilhelms; Hubertus Fischer

2009-01-01

211

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

Microsoft Academic Search

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

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

1993-01-01

212

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

213

Variation of Biological Activity on a Himalayan Glacier Recovered from a Shallow Ice Core  

NASA Astrophysics Data System (ADS)

There is a diverse biological community on the snow and ice surface of glaciers. Recent change of glaciers reported in many parts in the world may affect the biological community on the glaciers. Temporal variation of biological activity on a Himalayan glacier was recovered from a 15 m deep ice core drilled in 1998. The dating showed that the core covers 37 years (1962-98) including the two hiatuses of annual layer. Microscopy revealed that the core contained filamentous cyanobacteria growing on the glacial surface. They discontinuously appeared in mid 1960s, mid 1970s, and 1990s. In particular, the biomass in 1990s is significantly larger than before, indicating their significant bloom in the period. The annual variation of biomass was compared with the variations of dust flux, mass balance, stable isotope, and chemical composition. The comparison suggests that the bloom of the cyanobacteria may be attributed to the combination of climate warming and eutrophication on the glacial surface in 1990s.

Takeuchi, N.; Fujita, K.; Nakazawa, F.; Matoba, S.; Nakawo, M.; Rana, B.

2004-12-01

214

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

215

Thirty-seven year mass balance of Devon Ice Cap, Nunavut, Canada, determined by shallow ice coring and melt modeling  

Microsoft Academic Search

In April-May 2000, eight boreholes were drilled to ~15-20 m depth on the Devon Ice Cap. 137Cs gamma activity profiles of each borehole showed a peak count rate at depth that is associated with fallout from atmospheric thermonuclear weapons testing in 1963. Snow, firn, and ice densities were measured at each core site and were used to estimate the average

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

216

Beryllium 10 concentrations in the Greenland Ice Sheet Project 2 ice core from 3-40 ka  

Microsoft Academic Search

A nearly continuous record of 10Be (half-life of 1.5×106 years) concentrations is reported in the Greenland Ice Sheet Project 2 (GISP2) ice core for the time period between 3288 and 40,055 years B.P. The resolution is between 20 and 50 years in the Holocene. During the Pleistocene, sampling was coarser, with the resolution ranging between 50 and 200 years. Both

R. C. Finkel; K. Nishiizumi

1997-01-01

217

Asian provenance of glacial dust (stage 2) in the Greenland Ice Sheet Project 2 Ice Core, Summit, Greenland  

Microsoft Academic Search

Samples of dust from the Greenland Ice Sheet Project 2 (GISP2) ice core, Summit, Greenland, dated within marine isotope stage 2 (between 23,340 and 26,180 calendar years B.P.), around the time of the coldest, local, last glacial temperatures, have been analyzed to determine their provenance. To accomplish this, we have compared them with approximately coeval aeolian sediments (mostly loesses) sampled

P. E. Biscaye; F. E. Grousset; M. Revel; S. Van der Gaast; G. A. Zielinski; A. Vaars; G. Kukla

1997-01-01

218

Greenland ice core ?18O records - from Camp Century to NEEM  

NASA Astrophysics Data System (ADS)

During the past five decades deep ice cores have been drilled at six locations on the Greenland Ice Sheet, all cores yielding records of ?18O from the past. Hence ?18O records from southern, central and north-western Greenland locations can now be interpreted. Furthermore several ?18O records from ice cores drilled on small ice caps in the vicinity of the Greenland Ice Sheet are available. An inter-comparison of the Holocene sections of the ice cores has suggested that both climate change and ice sheet elevation change played major parts in determining the millennial scale evolution of the ?18O signals seen in the records [Vinther et al. 2009]. While all glacial ?18O records show very prominent abrupt climate change in the form of Dansgaard-Oeschger cycles it is interesting to note that long term trends in glacial ?18O differ between the records. A significant part of these differences are likely to be a consequence of different elevation histories in the different areas of the Greenland Ice Sheet during the glacial period. Reference: Vinther, B.M, Buchardt, S.L., Clausen, H.B., Dahl-Jensen, D., Johnsen, S.J., Fisher, D.A., Koerner, R.M., Raynaud, D., Lipenkov, V., Andersen, K.K, Blunier, T., Rasmussen, S.O., Steffensen, J.P., Svensson, A.M., Holocene thinning of the Greenland ice sheet, Nature, 461, 385-388, 2009.

Vinther, B. M.

2012-04-01

219

The Search for Supernova Signatures in an Ice Core  

NASA Astrophysics Data System (ADS)

It has been suggested that ice cores may preserve detectable enhancements of some terrestrially rare radioisotopes, 10Be, 26Al, 36Cl, resulting from a near-Earth core-collapse supernova(SN) [J. Ellis, B.D. Fields and D.N. Schramm, Astrophys. J. 470 (1996) 1227]. Both 10Be and 36Cl are also produced by atmospheric cosmic ray spallation and hence are influenced by processes that modulate the Earth's cosmic ray flux. Previous studies [G.M. Raisbeck, F. Yiou, D. Bourles, C. Lorius, J. Jouzel and N. I. Barkov, Nature 326 (1987) 273], [L.G. Thompson, T. Yao, M.E. Davis, K.A. Henderson, E. Mosley-Thompson, P.-N. Lin, J. Beer, H.-A. Synal, J. Cole-Dai and J.F. Bolzan, Science 276 (1997) 1821] have suggested that enhancements occurred in the 10Be and 36Cl fluxes at ˜35 ky and at ˜60 ky for 10Be. Thus we have searched for potential SN condensates with 26Al amongst grains filtered from the 308.6m Guliya ice core recovered from the Qinghai-Tibetan plateau in China [L.G. Thompson, T. Yao, M.E. Davis, K.A. Henderson, E. Mosley-Thompson, P.-N. Lin, J. Beer, H.-A. Synal, J. Cole-Dai and J.F. Bolzan, Science 276 (1997) 1821].We searched for potential core-collapse SN condensate grains corundum (Al2O3), hibonite (CaAl12O19) and spinel (MgAl2O4) (see [D.S. Ebel and L. Grossman, Geochim. Cosmochim. Acta 65 (2001) 469]) in Guliya grain samples from the following time periods: ˜2-10 ky, ˜25-27 ky, ˜34-36 ky, ˜53-57 ky, ˜59-62 ky and ˜68-72 ky. These minerals are rare among terrestrial rocks and fine-grained atmospheric dust of terrestrial origin. Furthermore, they are insoluble in the acids employed in the sample preparation process and therefore separable from other minerals, such as silicates, that have high terrestrial abundances. Candidate SN condensate grains were identified among their terrestrial diluents employing a procedure developed at the University of Chicago for detecting presolar grains in meteoritic samples [S. Amari, R.S. Lewis and E. Anders, Geochim. Cosmochim. Acta 58 (1994) 459]. A set of 37 grains from the ˜34-36 ky, ˜53-57 ky and ˜59-62 ky samples were analyzed with the NanoSIMS at Washington University to measure their oxygen isotopic ratios. The preliminary results indicate that the analyzed grains, representing < 15% of those identified, do not possess the extreme O isotopic ratios expected to characterize a SN source [S. Amari and E. Zinner, Nucl. Phys. A 621 (1997) 99c], [T. Rauscher, A. Heger, R.D. Hoffman and S.E. Woosley, Astrophys. J. 576 (2002) 323].

Cole, A. L.; Boyd, R. N.; Davis, M. E.; Thompson, L. G.; Davis, A. M.; Lewis, R. S.; Zinner, E.

2005-07-01

220

A 25,000-year tropical climate history from bolivian ice cores  

PubMed

Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial Stage (LGS). Oxygen isotopic ratios of the ice decreased 5.4 per mil between the early Holocene and the Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes as the probable drivers. Regional accumulation increased during the LGS, during deglaciation, and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover. PMID:9836630

Thompson; Davis; Mosley-Thompson; Sowers; Henderson; Zagorodnov; Lin; Mikhalenko; Campen; Bolzan; Cole-Dai; Francou

1998-12-01

221

A new 122 mm electromechanical drill for deep ice-sheet coring (DISC): 5. Experience during Greenland field testing  

Microsoft Academic Search

The Deep Ice Sheet Coring (DISC) drill developed by Ice Coring and Drilling Services under contract with the US National Science Foundation is an electromechanical ice-drill system designed to take 122 mm ice cores to depths of 4000 m. The new drill system was field-tested near Summit camp in central Greenland during the spring\\/summer of 2006. Testing was conducted to

Jay A. Johnson; William P. Mason; Alexander J. Shturmakov; Scott T. Haman; Paul J. Sendelbach; Nicolai B. Mortensen; Laurent J. Augustin; Kristina R. Dahnert

2007-01-01

222

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.

223

Duration of Greenland Stadial 22 and ice-gas ?age from counting of annual layers in Greenland NGRIP ice core  

NASA Astrophysics Data System (ADS)

The NorthGRIP ice core chronology GICC05modelext is composed of the annual-layer counted GICC05 chronology to 60 kyr before 2000 AD (b2k), and an ice flow model dating the deepest part of the ice core to 123 kyr b2k. Determination of annual strata in ice beyond 60 kyr b2k has been challenged by the thinning of annual layers to <1 cm and the appearance of microfolds in some early glacial strata. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses, constraining the duration of the Greenland Stadial (GS-22) between Greenland Interstadials (GIs) 21 and 22 which occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21) depending on the chronology used. Multiple analytes (insoluble dust particles, electrolytic conductivity, ammonium and sodium) were determined in annual layers of ice often thinner than 1 cm. From annual layer counting, we find that GS-22 lasted 2894 ± 198 yr and was followed by a GI-21 pre-cursor event lasting 350 ± 19 yr. Our layer-based counting agrees with the duration of GS-22 determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr). These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the NorthGRIP ice depth-gas depth (5.67 ± 0.18 m) and ice age-gas age (550 ± 52 yr) differences at the warming onset of GI-21, observing that ?15N increases before CH4 concentration by no more than a few decades.

Vallelonga, P.; Bertagna, G.; Blunier, T.; Kjær, H. A.; Popp, T. J.; Rasmussen, S. O.; Steffensen, J. P.; Stowasser, C.; Svensson, A. S.; Warming, E.; Winstrup, M.; Bigler, M.; Kipfstuhl, S.

2012-07-01

224

Greenland ice core {open_quotes}signal{close_quotes} characteristics: An expanded view of climate change  

SciTech Connect

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. The authors have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to {approximately}674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen and sulfur cycling, volcanic emissions, sea salt and terrestrial influences. They have adapted and extended mathematical procedures for extracting sporadic (e.g., volcanic) events, secular trends, and periodicities found in the data sets. Finally, by not assuming that periodic components (signals) were {open_quotes}stationary{close_quotes} and by utilizing evolutionary spectral analysis, they were able to reveal periodic processes in the climate system which change in frequency, {open_quotes}turn on,{close_quotes} and {open_quotes}turn off{close_quotes} with other climate transitions such as that between the little ice age and the medieval warm period. 42 refs., 4 figs., 2 tabs.

Mayewski, P.A.; Meeker, L.D.; Morrison, M.C.; Twickler, M.S.; Whitlow, S.I.; Ferland, K.K. [Univ. of New Hampshire, Durham, NH (United States); Meese, D.A. [Cold Regions Research and Engineering Laboratory, Hanover, NH (United States); Legrand, M.R. [Laboratoire de Glaciologie et Geophysique de Environnement, St.-Martin-D`Heres (France); Steffensen, J.P. [Univ. of Copenhagen (Denmark)

1993-07-20

225

2,000-year record of atmospheric methyl bromide from a South Pole ice core  

NASA Astrophysics Data System (ADS)

This study reports measurements of methyl bromide (CH3Br) in air bubbles from a South Pole ice core, with gas ages covering the past two millennia. The air was extracted by mechanical shredding of the core under vacuum and the evolved gases were analyzed by gas chromatography with high resolution mass spectrometry and isotope dilution. These samples had estimated mean gas ages ranging from 160 BCE to 1860 CE. The mean CH3Br mixing ratio in the ice core samples was 5.39 ±.06 ppt (1s.e., n = 113). The CH3Br measurements from this core agree with those from a Siple Dome ice core for mean gas ages between 1671 and 1860 CE, where there is overlap between the cores. The data show no linear trend over the 2000 year period prior to industrialization. Together, Antarctic ice core and firn air measurements clearly demonstrate that the increase in atmospheric CH3Br during the twentieth century exceeds natural variability during the past 2000 years. There is evidence of centennial-scale variability in CH3Br on the order of ±10-20% that may indicate a natural climate sensitivity of the atmospheric levels of this ozone depleting substance. The analysis of CH3Br in additional Antarctic ice cores will be needed to confirm that the centennial-scale variability observed in this core represents a southern hemisphere atmospheric history.

Saltzman, Eric S.; Aydin, Murat; Tatum, Cheryl; Williams, Margaret B.

2008-03-01

226

First Results From The Epica Deep Ice Core (EDML) In Dronning Maud Land  

NASA Astrophysics Data System (ADS)

Presently there are two deep ice core drillings ongoing in the frame of the European Project for Ice Coring in Antarctica (EPICA). The first ice core has been drilled at Dome Concordia (DC, 75^o06.10'S, 123^o23.71'E, 3233 m). The second ice core (labelled EDML, 75^o0.10'S, 0^o4.1'E, 2882 m) has been drilled in Dronning Maud Land (DML) in an area with an higher accumulation rate (65 kg m-2 a-1) to attain an higher resolution climate record for the last 150,000 years. Precipitation over Dronning Maud Land is supposed to be more affected by the Atlantic sector. Thus the EDML ice core should provide a better link between Southern and Northern hemisphere climate over the last glacial cycle as being recorded in the Greenlandic ice cores. The present preliminary dating of the first 450 m of the EDML ice core (drilling depth at the end of the 2001/02 season) was done by dielectric profiling (DEP) and inter comparison with the DEP profiles and volcanic events recorded in the DC and Vostok ice cores. It suggests a covered time span of about 7,000 years back in time. The dating will be improved as soon as the evaluated CFA profiles are available. One can expect that annual layer counting is possible down to the present depth. The 2002/03 season in Dronning Maud Land starts beginning of December 2002 and we hope to drill much deeper down into the last glacial period. DEP will be recorded in the field and the drilled new core will be dated preliminarily. After the planned return mid February 2003 we will present brand new first results from this deep drilling based on the information contained in the DEP record.

Wilhelms, F.; Epica-Dml Team

2003-04-01

227

Phylogenetic and Physiological Diversity of Microorganisms Isolated from a Deep Greenland Glacier Ice Core  

Microsoft Academic Search

We studied a sample from the GISP 2 (Greenland Ice Sheet Project) ice core to determine the diversity and survival of microorganisms trapped in the ice at least 120,000 years ago. Previously, we examined the phylogenetic relationships among 16S ribosomal DNA (rDNA) sequences in a clone library obtained by PCR amplification from genomic DNA extracted from anaerobic enrichments. Here we

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

2004-01-01

228

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

229

Origin and characterisation of microparticles in an ice core from the Central Dronning Maud Land, East Antarctica.  

PubMed

The scanning electron microscopy-energy dispersive spectroscopic (SEM-EDS) study of selected samples from an ice core collected from Central Dronning Maud Land (CDML), East Antarctica, revealed several microparticles. They are mainly siliceous and carbonaceous particles and have distinct variations in their shape and composition. The morphology and major element chemistry of the particles suggest their origin from either volcanic eruptions or continental dust. The EDS analysis revealed that the volcanic particles are enriched in silica (average SiO2 62%), compared to the continental dust particle (average SiO2 56%). We found that the tephra relating to Agung (1963) and Karkatau (1883) volcanic eruptions, as recorded, in the ice core harbored microbial cells (both coocoid and rods). The occurrence of organic and inorganic particles which bear relation to volcanic eruption and continental dust implies significant environmental changes in the recent past. PMID:18301999

Laluraj, C M; Krishnan, K P; Thamban, M; Mohan, R; Naik, S S; D'Souza, W; Ravindra, R; Chaturvedi, A

2008-02-27

230

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

NASA Astrophysics Data System (ADS)

The accumulation, isotopic and chemical signals of an ice core from James Ross Island, Antarctica, are investigated for the interval from 1967 to 2008. Over this interval, comparison with station, satellite and reanalysis data allows for a detailed assessment of the environmental information preserved in the ice. Accumulation at James Ross Island is enhanced during years when the circumpolar westerlies are weak, allowing more precipitation events to reach the northeastern Antarctic Peninsula. The stable water isotope composition of the ice core has an interannual temperature dependence consistent with the spatial isotope-temperature gradient across Antarctica, and preserves information about both summer and winter temperature variability in the region. Sea salts in the ice core are derived from open water sources in the marginal sea ice zone to the north of James Ross Island and transported to the site by strengthened northerly and westerly winds in the winter. A strong covariance with temperature means that the sea salt record may be able to be utilized, in conjunction with the isotope signal, as an indicator of winter temperature. Marine biogenic compounds in the ice core are derived from summer productivity within the sea ice zone to the south of James Ross Island. This source region may have become significant only in recent decades, when the collapse of nearby ice shelves established new sites of open water with high summer productivity. These findings provide a foundation for interpreting the environmental signals in the James Ross Island ice core, which extends though the whole Holocene and represents the oldest ice core that has been recovered from the Antarctic Peninsula region.

Abram, Nerilie J.; Mulvaney, Robert; Arrowsmith, Carol

2011-10-01

231

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

Microsoft Academic Search

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

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

2004-01-01

232

Duration of Greenland Stadial 22 and ice-gas ?age from counting of annual layers in Greenland NGRIP ice core  

NASA Astrophysics Data System (ADS)

High-resolution measurements of chemical impurities and methane concentrations in Greenland ice core samples from the early glacial period allow the extension of annual-layer counted chronologies and the improvement of gas age-ice age difference (?age) essential to the synchronization of ice core records. We report high-resolution measurements of a 50 m section of the NorthGRIP ice core and corresponding annual layer thicknesses in order to constrain the duration of the Greenland Stadial 22 (GS-22) between Greenland Interstadials (GIs) 21 and 22, for which inconsistent durations and ages have been reported from Greenland and Antarctic ice core records as well as European speleothems. Depending on the chronology used, GS-22 occurred between approximately 89 (end of GI-22) and 83 kyr b2k (onset of GI-21). From annual layer counting, we find that GS-22 lasted between 2696 and 3092 years and was followed by a GI-21 pre-cursor event lasting between 331 and 369 yr. Our layer-based counting agrees with the duration of stadial 22 as determined from the NALPS speleothem record (3250 ± 526 yr) but not with that of the GICC05modelext chronology (2620 yr) or an alternative chronology based on gas-marker synchronization to EPICA Dronning Maud Land ice core. These results show that GICC05modelext overestimates accumulation and/or underestimates thinning in this early part of the last glacial period. We also revise the possible ranges of NorthGRIP ?depth (5.49 to 5.85 m) and ?age (498 to 601 yr) at the warming onset of GI-21 as well as the ?age range at the onset of the GI-21 precursor warming (523 to 654 yr), observing that temperature (represented by the ?15N proxy) increases before CH4 concentration by no more than a few decades.

Vallelonga, P.; Bertagna, G.; Blunier, T.; Kjær, H. A.; Popp, T. J.; Rasmussen, S. O.; Steffensen, J. P.; Stowasser, C.; Svensson, A. S.; Warming, E.; Winstrup, M.; Bigler, M.; Kipfstuhl, S.

2012-11-01

233

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

Microsoft Academic Search

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

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

2003-01-01

234

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

Microsoft Academic Search

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

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

2003-01-01

235

Application of LA-ICP-MS in polar ice core studies  

Microsoft Academic Search

The direct determination of element signatures in polar ice core samples from Greenland by laser ablation with subsequent inductively coupled plasma mass spectrometry analysis has been investigated. A cryogenic sample chamber enables the element determination in ice directly from the solid (frozen) state. A procedure was developed to analyse up to 38 elements (traces: Mg, Al, Fe, Zn, Cd, Pb

H. Reinhardt; M. Kriews; H. Miller; C. Lüdke; E. Hoffmann; J. Skole

2003-01-01

236

Evolution of the texture along the EPICA Dome C ice core  

Microsoft Academic Search

New measurements of ice texture made along the EPICA Dome C ice core, together with a review of previous studies of fabric and microstructure, are pre- sented. Mean grain size increases steadily with age, and so depth. However, sharp decreases are observed for all the climatic terminations. These sharp decreases are be- lieved to be mainly driven by the change

Anders Svensson; Asbjørn Persson; Olivier Gagliardini; Fabien Gillet-Chaulet; Dorthe Dahl-Jensen

237

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

Microsoft Academic Search

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

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

2004-01-01

238

Orbital Forcing and Endogenous Nonlinearity in the Pleistocene: The Greenland Ice Core  

Microsoft Academic Search

The succession of ice ages and interglacials during the Pleistocene is understood to have been caused primarily by shifts in the earth's orbit. At the same time, there is evidence of high variability in climate at suborbital frequencies. This paper conducts a statistical analysis of Pleistocene climate using the Greenland Ice Core Research Project (GRIP) data. Factoring temperature into the

Gordon R. Richards

1998-01-01

239

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

Microsoft Academic Search

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

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

2003-01-01

240

Visual-stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application  

NASA Astrophysics Data System (ADS)

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.

1997-11-01

241

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

Microsoft Academic Search

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

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

1981-01-01

242

Origin and characterisation of microparticles in an ice core from the Central Dronning Maud Land, East Antarctica  

Microsoft Academic Search

The scanning electron microscopy–energy dispersive spectroscopic (SEM–EDS) study of selected samples from an ice core collected\\u000a from Central Dronning Maud Land (CDML), East Antarctica, revealed several microparticles. They are mainly siliceous and carbonaceous\\u000a particles and have distinct variations in their shape and composition. The morphology and major element chemistry of the particles\\u000a suggest their origin from either volcanic eruptions or

C. M. Laluraj; K. P. Krishnan; M. Thamban; R. Mohan; S. S. Naik; W. D’Souza; R. Ravindra; A. Chaturvedi

2009-01-01

243

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

244

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

245

Climatic and environmental records from Altai glaciers, Siberia, recovered from ice-cores and snow samples  

Microsoft Academic Search

A depth\\/accumulation scale for the Altai glaciers, Siberia, established based on delta18O and deltaD firn-ice cores analysis. In sequences of annual layers in the firn-ice cores recovered in 2001 and 2002, the mean annual snow accumulation was found to be 800 mm at 4115 m of the Belukha Snow-Firn Plateau. The transfer function was developed using the seasonality of accumulation

V. B. Aizen; E. M. Aizen; K. J. Kreutz; K. Fujita; D. Cecil; S. A. Nikitin

2002-01-01

246

A Comparison of Methyl Chloride Measurements in Ice Cores from Five Antarctic Sites  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) is the most abundant naturally occurring halocarbon in the atmosphere, with a global mean mixing ratio of 550 parts per trillion (Clerbaux et al., 2006). Previous studies suggest that a paleoatmospheric record may be preserved in Antarctic firn and shallow ice (Williams et al., 2007). In this study, methyl chloride (CH3Cl) was analyzed in Holocene samples from the Taylor Dome and Vostok deep ice cores from East Antarctica. Ice core samples from Taylor Dome with gas ages from 1.2-9.4 kyr BP gave CH3Cl levels of 443 ± 34 ppt (n=36). Vostok ice core samples with gas ages from 0.8-3.2 kyr BP yielded 454 ± 19 ppt (n=7). The CH3Cl levels in these two cores are similar to previously measured late Holocene CH3Cl levels from South Pole (Williams et al., 2007). These CH3Cl levels are roughly 15% below the modern atmospheric level over Antarctica of about 515 ppt. The CH3Cl levels found in these cores are significantly lower than ice core samples of similar age from Siple Dome, West Antarctica and Dome Fuji, East Antarctica (Saito et al., 2007; Saltzman et al., 2009). Those cores exhibited mean levels of approximately 500 ppt over the same time period. This discrepancy underscores the fact that the origin or preservation of CH3Cl signals in polar ice may vary from site to site, perhaps as a function of mean annual temperature and impurity levels in ice. Further measurements on multiple ice cores will be needed in order to establish a long-term atmospheric history for this trace gas.

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

2009-12-01

247

What can be learnt from the comparison between ice core temperature records and climate model simulations?  

Microsoft Academic Search

Past temperature reconstructions are available from Greenland and Antarctica using different temperature reconstruction methods applied on ice cores and boreholes. Here we focus on two time periods : (i) the temperature increase from the Last Glacial Maximum to present-day, (ii) the temperature difference between the last interglacial period and present-day. For these two periods, ice-core data are compared to the

V. Masson-Delmotte

2007-01-01

248

Temperature and methane records over the last 2 ka in Dasuopu ice core  

Microsoft Academic Search

High resolution ?18O and methane records over the last 2ka have been reconstructed from Dasuopu ice core recovered from the Himalayas. Analysis\\u000a shows that the ?18O record correlates well with the Northern Hemispheric temperature, Dunde ice core record, and with temperature record in\\u000a eastern China. The warming trend detected in ?18O record from the last century is similar to that

Tandong Yao; L. G. Thompson; Keqin Duan; Baiqing Xu; Ninglian Wang; Jianchen Pu; Lide Tian; Weizhen Sun; Shichang Kang; Xiang Qin

2002-01-01

249

Reconstruction of the undiffused seasonal oxygen isotope signal in central Greenland ice cores  

Microsoft Academic Search

The climatologically important seasonal signal in ice core oxygen isotope records as altered by diffusion with time. Here we use the diffusion model of Whillans and Grootes [1985] to calculate the effects of isotopic diffusion in nine shallow ice cores recovered over a 150×150km grid centered on Summit, Greenland. Two different computational methods give similar results for the back-diffused delta18O

John F. Bolzan; Veijo Allan Pohjola

2000-01-01

250

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

251

A new Greenland ice core chronology for the last glacial termination  

Microsoft Academic Search

We present a new common stratigraphic timescale for the North Greenland Ice Core Project (NGRIP) and GRIP ice cores. The timescale covers the period 7.9-14.8 kyr before present and includes the Bølling, Allerød, Younger Dryas, and early Holocene periods. We use a combination of new and previously published data, the most prominent being new high-resolution Continuous Flow Analysis (CFA) impurity

S. O. Rasmussen; K. K. Andersen; A. M. Svensson; J. P. Steffensen; B. M. Vinther; H. B. Clausen; M.-L. Siggaard-Andersen; S. J. Johnsen; L. B. Larsen; D. Dahl-Jensen; M. Bigler; R. Röthlisberger; H. Fischer; K. Goto-Azuma; M. E. Hansson; U. Ruth

2006-01-01

252

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

NASA Astrophysics Data System (ADS)

Recent developments in ice melter systems and continuous flow analysis (CFA) techniques now allow higher-resolution ice core analysis. Here, we present a new method to aid interpretation of high-resolution ice core stable water isotope records. Using a set of simple isotopic recording and postdepositional assumptions, the European Centre for Medium-Range Weather Forecasts' 40 year reanalysis time series of temperature and precipitation are converted to "virtual core" depth series across the Antarctic Peninsula, helping us to understand what information can be gleaned from the CFA high-resolution observations. Virtual core temperatures are transferred onto time using three different depth-age transfer assumptions: (1) a perfect depth-age model, (2) a depth-age model constructed from single or dual annual photochemical tie points, and (3) a cross-dated depth-age model. Comparing the sampled temperatures on the various depth-age models with the original time series allows quantification of the effect of ice core sample resolution and dating. We show that accurate annual layer count depth-age models should allow some subseasonal temperature anomalies to be recovered using a sample resolution of around 40 mm, or 10-20 samples per year. Seasonal temperature anomalies may be recovered using sample lengths closer to 60 mm, or about 7-14 samples per year. These results tend to confirm the value of current CFA ice core sampling strategies and indicate that it should be possible to recover about a third of subannual (but not synoptic) temperature anomaly information from annually "layer-counted" peninsula ice cores.

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

2011-10-01

253

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

SciTech Connect

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

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

1996-02-01

254

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

SciTech Connect

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

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

2012-01-20

255

International Partnerships in Ice Coring Sciences (IPICS) and the IPICS-IPY Initiative  

NASA Astrophysics Data System (ADS)

Ice-core studies have revolutionized our view of the Earth system, documenting the recent rise of greenhouse gas concentrations beyond historical norms, the existence of abrupt climate changes, and the tight coupling in the past of climate and greenhouse gas concentrations. International Partnerships in Ice Core Sciences (IPICS) is a group of scientists, engineers and logistics experts from the leading laboratories and national operators carrying out ice core science, charged with planning the next decade or more of international ice coring efforts. IPICS has identified four new priority programs: 1. A 1.2+ million year ice core from east Antarctica. This record of climate and greenhouse gases would address the nature and origin of the mid-Pleistocene transition from 41 ka to 100 ka climate cycles, and the role of the atmosphere in that transition. 2. The North Greenland Eemian ice core (NEEM). This core is planned for Northwest Greenland, at a site with a high priority of recovering a full record of the last interglacial period, which is lacking in all other ice cores from Greenland. 3. A network of ice cores from both hemispheres documenting the sequence of events from the last glacial maximum to the present. The few existing cores that span this time period are not sufficient to document spatial variations in the transition. The new network will include existing and new records and provide fingerprints of climate change mechanisms. 4. A network of ice core climate records for the last millennia, also from both hemispheres, and from high and low latitudes. The polar regions are poorly represented in global climate reconstructions for this period. A new network of ice core records covering this time period will provide a more quantitative context with which to view current environmental change in these regions. The IPICS-IPY Initiative has identified key elements of the above programs that can start in IPY, including survey work for the 1.2+ million year record, initiation of NEEM drilling, completion of planned projects in Antarctica that penetrate the last glacial maximum (WAIS Divide, Talos Dome), extension of ITASE to 1000 year records, and SOFIA (Search for Oldest Firn Interstitial Air).

Brook, E. J.; Wolff, E.

2005-12-01

256

Continuous field deployable methane concentration measurements from ice cores with near-infrared cavity ring-down spectroscopy  

Microsoft Academic Search

The analysis of gases and chemical impurities trapped in ice provides knowledge of earth's past climate. Deep ice cores from Greenland act as climate archives with high temporal resolution for more than the last 100,000 years covering Holocene, last glacial period and part of the previous interglacial called Eemian. Traditionally methane concentrations from ice cores are measured by gas chromatography.

Christopher Stowasser; Thomas Blunier; Vasileios Gkinis; Trevor Popp; Ernesto Kettner

2010-01-01

257

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

258

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

259

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

NASA Astrophysics Data System (ADS)

Studies of ice cores yield important information about the history of ice sheets and past climates. Interpretation of paleoclimate records from ice cores depends on understanding the ice sheet flow to determine depth-age relationships and whether the ice has been affected by folding. The alignment of crystals in ice, called fabric, is an important factor in understanding ice sheet flow since preferentially aligned crystals cause the ice to flow more easily in certain directions, and less easily in others. Fabric is commonly determined using thin sections cut at intervals from an ice core. Another method of determining fabric is sonic logging, where a probe is lowered into a borehole to measure the velocity of compressional waves through the ice. Sonic logging is a valuable tool for understanding ice fabric because it provides a continuous profile of the ice fabric and averages the alignment of ice crystals over a much larger volume than do thin sections. The objective of this project is to measure sonic velocity profiles at a variety of ice core borehole sites and use these profiles to: 1) improve the understanding of the relationship between thin section and sonic velocity data; 2) determine if sonic velocity data can be used to identify the depth at which paleoclimate record continuity is lost and if so, formulate criteria to identify this depth; and 3) provide verification and input data for anisotropic flow law models. Fabric estimates from sonic velocity profiles recently measured at the GISP2 and GRIP boreholes in Greenland and from the borehole at Siple Dome, Antarctica are compared to fabrics estimated from thin section data. The GISP2 site located 28 km west of Summit experiences flank flow while the GRIP and Siple Dome sites are both dome divides. For the GISP2 borehole, the sonic velocity profile is also compared to sonic velocity measurements made on sections of the GISP2 ice core. The sonic velocity profiles are also used to determine if the depth at which the paleoclimate record continuity is lost can be identified from sonic logging.

Lamorey, G. W.

2002-12-01

260

Antarctic climate signature in the Greenland ice core record  

PubMed Central

A numerical algorithm is applied to the Greenland Ice Sheet Project 2 (GISP2) dust record from Greenland to remove the abrupt changes in dust flux associated with the Dansgaard–Oeschger (D–O) oscillations of the last glacial period. The procedure is based on the assumption that the rapid changes in dust are associated with large-scale changes in atmospheric transport and implies that D–O oscillations (in terms of their atmospheric imprint) are more symmetric in form than can be inferred from Greenland temperature records. After removal of the abrupt shifts the residual, dejumped dust record is found to match Antarctic climate variability with a temporal lag of several hundred years. It is argued that such variability may reflect changes in the source region of Greenland dust (thought to be the deserts of eastern Asia). Other records from this region and more globally also reveal Antarctic-style variability and suggest that this signal is globally pervasive. This provides the potential basis for suggesting a more important role for gradual changes in triggering more abrupt transitions in the climate system.

Barker, Stephen; Knorr, Gregor

2007-01-01

261

A synchronized dating of three Greenland ice cores throughout the Holocene  

NASA Astrophysics Data System (ADS)

As part of the effort to create the new Greenland Ice Core Chronology 2005 (GICC05) a synchronized stratigraphical timescale for the Holocene parts of the DYE-3, Greenland Ice Core Project (GRIP), and North Greenland Ice Core Project (NGRIP) ice cores is made by using volcanic reference horizons in electrical conductivity measurements to match the cores. The main annual layer counting is carried out on the most suited records only, exploiting that the three ice cores have been drilled at locations with different climatic conditions and differences in ice flow. However, supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the validity of the match. After the verification, the main dating is transferred to all records using the volcanic reference horizons as tie points. An assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores. The data used for the main annual layer counting of the past 7900 years are the DYE-3, GRIP, and NGRIP stable isotope records. As the high accumulation rate at the DYE-3 drill site makes the seasonal cycle in the DYE-3 stable isotopes very resistant to firn diffusion, an effort has been made to extend the DYE-3 Holocene record. The new synchronized dating relies heavily on this record of ˜75,000 stable isotope samples. The dating of the early Holocene consists of an already established part of GICC05 for GRIP and NGRIP which has now been transferred to the DYE-3 core. GICC05 dates the Younger Dryas termination, as defined from deuterium excess, to 11,703 years before A. D. 2000 (b2k), 130 years earlier than the previous GRIP dating.

Vinther, B. M.; Clausen, H. B.; Johnsen, S. J.; Rasmussen, S. O.; Andersen, K. K.; Buchardt, S. L.; Dahl-Jensen, D.; Seierstad, I. K.; Siggaard-Andersen, M.-L.; Steffensen, J. P.; Svensson, A.; Olsen, J.; Heinemeier, J.

2006-07-01

262

Reassessing Lake Vostok's behaviour from existing and new ice core data  

NASA Astrophysics Data System (ADS)

Interpretation of new ice core data and reappraisal of existing data, both from the basal part of the Vostok ice core, give strong support to a kind of thermohaline circulation in Lake Vostok. Although the salinity of the lake is considered as weak (less than 1‰), the prominent influence of salinity at high pressure and low temperature on water density makes such a circulation possible. As a consequence, subglacial melting along the northern shores of the lake is balanced, further south, by frazil ice production in the upper water column, its accretion and consolidation at the ice-water interface followed by accreted ice export out of the system together with the southeasterly glacier flow. The dynamics of the system is documented by a stable water isotope budget estimate, by inferences concerning accreted ice formation and by an investigation of ice properties at the transition between meteoric ice and accreted ice. This complex behaviour is the controlling factor on water, biota and sediment fluxes in the lake environment.

Souchez, R.; Petit, J.-R.; Jouzel, J.; de Angelis, M.; Tison, J.-L.

2004-01-01

263

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

NASA Astrophysics Data System (ADS)

The Toba eruption that occurred some 74 ka ago in Sumatra, Indonesia, is among the largest volcanic events on Earth over the last 2 million years. Tephra from this eruption has been spread over vast areas in Asia where it constitutes a major reference horizon close to the Marine Isotope Stage 3/4 (MIS 3/4) boundary. Up to now, no tephra has been associated with Toba neither in Greenland nor in Antarctic ice cores, but based on Toba tephra identified in marine records from the Arabian Sea it is very likely that Greenland ice core acidity spikes related to Toba occur towards the end of Greenland Interstadial 20 (GI-20). Furthermore, the linking of Greenland and Antarctic ice cores by gas records suggests that the Antarctica counterpart should be 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 based on matching of a pattern of bi-polar volcanic spikes and annual layer counting in both cores around 74 ka BP. The synchronization pattern covers some 2000 years in GI-20 and AIM 19/20 and includes 5 major and several minor acidity peaks that are recognized in both ice cores. The most prominent acidity spikes in this time interval that occur towards the end of GI-20, are those thought to originate from Toba, but the proposed linking is independent of the source of the volcanic spikes. Although the linking of Greenland and Antarctic ice cores around Toba is already quite well constrained by matching of gas records, the relative phasing between ice cores from the two hemispheres still has some uncertainty related to the offset in the age of ice and air bubbles in the ice cores (delta-gas age). The identification of a direct Toba synchronization may help to determine the exact phasing of inter-hemispheric climate during this period and to constrain delta-gas ages. It also provides a way to place paleo-environmental records other than ice cores into a precise climatic context.

Svensson, A.; Bigler, M.; Fischer, H.; Johnsen, S. J.; Kipfstuhl, S.; Parrenin, F.; Rasmussen, S. O.; Steffensen, J. P.; Vinther, B. M.; Wegner, A.

2012-04-01

264

Greenland ice Cores tell Tales on the Eemian Period and Beyond  

NASA Astrophysics Data System (ADS)

The deep NGRIP ice core from North Greenland (75N, 42W) is 3090m deep and reaches 125.000 years back in time. The climate record has an extremely high resolution with annual layers of the order of 1 cm right down to the base because basal melt reduces the thinning of the basal layers. The lowest 60 m of the ice core contains ice from the last interglacial period, the Eemian period (OIS-5e) and it is seen from the stable isotopes that the period was 5 deg C warmer in Greenland than our present interglacial period and very stable. The transition to glacial conditions occurred gradually over several thousand years. The NGRIP ice core contains the first undisturbed record of the Eemian period from the North Atlantic region. The NGRIP results contribute with a fix point in the predictions for sea level rise from a globale warming: a 5 deg warming over Greenland corresponds to the global sealevel rise of 5 m as that observed during the Eemian period. To evaluate the area and volume of the Greenland Ice Sheet during the Eemian period, it is worth noting that we find Eemian ice in the Dye3 ice core in South Greenland, in the central Greenland Ice cores GRIP and GISP2, in NGRIP and in the little 350m thich ice cap, Renland, on the east coast of Greenland. It can directly be concluded that the there was an significant ice sheet covering Greenland during the warm Eemian period and that the reduction of the Greenland ice sheet at most contributed with a sea level rise of 1-2 m of the observed 5 m. At the melting base of the NGRIP ice core two macroscopic plant remains were recovered. One is a wood fragment of willow (Salix) and the other is a fragment of a bud scale, probably also from willow. Also a few tiny fragments of spruce or larch (Picea/Larix) were found found. The fragments cannot be identified at the species level, but willow, spruce and larch remains are common in the Kap Kobenhavn Formation, dated to around 2.4 Ma BP. The Greenland Ice Sheet did not exist when the Kap Kobenhavn Formation was deposited, as shown by the occurrence of numerous warmth demanding plants and animals.

Dahl-Jensen, D.; Bennike, O.; Willerslev, E.

2005-12-01

265

A 70 ka Record of Methyl Chloride From a Siple Dome, West Antarctica Ice Core  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) is most abundant naturally occurring halocarbon in the atmosphere, with a modern mean mixing ratio of 550 parts per trillion (ppt). Prior studies in Antarctic ice and firn suggest that reconstruction of a paleoatmospheric record may be possible (Williams et al., 2007), but there is also some evidence for in situ production in glacial polar ice with high dust content (Saito et al., 2007). In this study, CH3Cl was extracted and analyzed in 42 samples from the Siple Dome, West Antarctic ice core covering the past 70 ka. Over the whole record, CH3Cl mixing ratios ranged from 407 to 819 ppt. Glacial core samples from 30-70 ka had a mean of 455?46 ppt, significantly lower than the Holocene mean of 532?61 ppt in this core. There are no data from the period between ~25-33 ka. Four data points around the last glacial maximum between 21-25 ka are higher, with a mean level of 625?141 ppt. It is unclear whether these higher CH3Cl mixing ratios reflect higher atmospheric levels or in situ production within the ice. The observation of lower CH3Cl levels in glacial ice compared to interglacial ice is in apparent contradiction with earlier measurements from the Dome Fuji, East Antarctica ice core, which showed increased CH3Cl levels in glacial ice compared to interglacial ice (Saito et al., 2007). That core showed a strong correlation between CH3Cl and Ca+2 levels, implicating in situ production related to glacial dust. At Siple Dome, Ca+2 levels are generally lower, and there is no correlation with CH3Cl in the data set as a whole. However, the increased levels of CH3Cl at the last glacial maximum may indicate in situ production in samples with the highest dust loads.

Verhulst, K.; Aydin, M.; Williams, M. B.; Saltzman, E. S.

2007-12-01

266

The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change and Our Future  

NASA Astrophysics Data System (ADS)

Enhanced greenhouse warming attributable to our profligate consumption of fossil fuels has established itself as perhaps the most contentious environmental issue currently being debated in the international political arena. To a large extent, the debate over whether societies should undertake actions to mitigate potentially adverse effects of climate change focuses on uncertainties in climate predictions and societal impacts. In an effort to reduce some of the uncertainty the climate community has expended considerable efforts to obtain detailed records of past climates, recognizing that the past may hold the key to our future.The Two-Mile Time Machine by Richard Alley tells the captivating story of how one such record reconstructed from the GISP2 core, drilled through the more than 3-km thick Greenland Ice Sheet, has revealed startling clues about past climates and shattering many of our ideas on how climate operates.

van der Veen, C. J.

267

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

268

Annually resolved southern hemisphere volcanic history from two Antarctic ice cores  

Microsoft Academic Search

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

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

1997-01-01

269

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

270

Observations reveal external driver for Arctic sea-ice retreat  

NASA Astrophysics Data System (ADS)

The very low summer extent of Arctic sea ice that has been observed in recent years is often casually interpreted as an early-warning sign of anthropogenic global warming. For examining the validity of this claim, previously IPCC model simulations have been used. Here, we focus on the available observational record to examine if this record allows us to identify either internal variability, self-acceleration, or a specific external forcing as the main driver for the observed sea-ice retreat. We find that the available observations are sufficient to virtually exclude internal variability and self-acceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration. Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today.

Notz, Dirk; Marotzke, Jochem

2012-04-01

271

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

Microsoft Academic Search

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

Gregory A. Zielinski

1995-01-01

272

Ice-core pollen record of climatic changes in the central Andes during the last 400 yr  

Microsoft Academic Search

This paper presents a high-resolution ice-core pollen record from the Sajama Ice Cap, Bolivia, that spans the last 400 yr. The pollen record corroborates the oxygen isotopic and ice accumulation records from the Quelccaya Ice Cap and supports the scenario that the Little Ice Age (LIA) consisted of two distinct phases—a wet period from AD 1500 to 1700, and a

Kam-biu Liu; Carl A. Reese; Lonnie G. Thompson

2005-01-01

273

Atmospheric soluble dust records from a Tibetan ice core: Possible climate proxies and teleconnection with the Pacific Decadal Oscillation  

NASA Astrophysics Data System (ADS)

In autumn 2005, a joint expedition between the University of Maine and the Institute of Tibetan Plateau Research recovered three ice cores from Guoqu Glacier (33°34'37.8?N, 91°10'35.3?E, 5720 m above sea level) on the northern side of Mt. Geladaindong, central Tibetan Plateau. Isotopes (?18O), major soluble ions (Na+, K+, Mg2+, Ca2+, Cl-, NO3-, SO42-), and radionuclide (?-activity) measurements from one of the cores revealed a 70-year record (1935-2005). Statistical analysis of major ion time series suggests that atmospheric soluble dust species dominate the chemical signature and that background dust levels conceal marine ion species deposition. The soluble dust time series have interspecies relations and common structure (empirical orthogonal function (EOF) 1), suggesting a similar soluble dust source or transport route. Annual and seasonal correlations between the EOF 1 time series and National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis climate variables (1948-2004) suggest that the Mt. Geladaindong ice core record provides a proxy for local and regional surface pressure. An approximately threefold decrease of soluble dust concentrations in the middle to late 1970s, accompanied by regional increases in pressure and temperature and decreases in wind velocity, coincides with the major 1976-1977 shift of the Pacific Decadal Oscillation (PDO) from a negative to a positive state. This is the first ice core evidence of a potential teleconnection between central Asian atmospheric soluble dust loading and the PDO. Analysis of temporally longer ice cores from Mt. Geladaindong may enhance understanding of the relationship between the PDO and central Asian atmospheric circulation and subsequent atmospheric soluble dust loading.

Grigholm, B.; Mayewski, P. A.; Kang, S.; Zhang, Y.; Kaspari, S.; Sneed, S. B.; Zhang, Q.

2009-10-01

274

Glacial records of global climate: A 1500-year tropical ice core record of climate  

SciTech Connect

A general discussion is given of climate variability over the last 1500 years as interpreted from two ice cores from the Quelccaya ice cap, Peru. The possible role of climatic variability in prehistory over this period is discussed with emphases on (1) relationships between climate and the rise and decline of coastal and highland cultures; (2) the possible causes of two major dust events recorded in the quelccaya ice cores around AD 920 and AD 600; (3) implications of climatic variation for the occupation and abandonment of the Gran Pajaten area. The remarkable similarity between changes in highland and coastal cultures and changes in accumulation as determined from the Quelccaya ice cores implies a strong connection between human activities and climate in this region of the globe. Two ice cores drilled to bedrock from the 6047 masl col of Huascaran in the Cordillera Blanca, Peru in 1993 offer the potential of an annual to decadal climatic and environmental record which should allow the study of human-climate and human-environmental relationships over 10,000+ years. The 1991 and 1993 evidence from the Quelccaya ice cap indicates that recent and rapid warming is currently underway in the tropical Andes. Thus, many of the unique glacier archives are in imminent danger of being lost forever.

Thompson, L.G.; Davis, M.E.; Mosley-Thompson, E. (Ohio State Univ., Columbus, OH (United States))

1994-03-01

275

Investigation of Molecular Marker Lipids in Alpine Ice Cores Via Stir Bar Sorptive Extraction  

NASA Astrophysics Data System (ADS)

Recently developed analytical techniques were employed to identify and quantify organic molecular markers trapped in high-altitude ice. While various compounds represent potentially useful proxies for biomass burning, vegetation type, atmospheric circulation, and anthropogenic activity, prior attempts to measure organic compounds in ice cores have typically required large volumes of sample material that are incompatible with generation of high-resolution paleoclimate records. We employed stir bar sorptive extraction (SBSE) and thermal desorption (TD), coupled with gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS), to examine the organic content of small quantities (? 30 ml) of ice. To test the utility of the approach, post-industrial ice core samples from the Huascarán and Sajama sites (Andes), the Dasuopu and Puruogangri sites (Tibetan Plateau), and Mt. Kilimanjaro (east Africa) were tested. n-Alkanes, n-alkanoic acids, n-alkyl amides and nitriles, polycyclic aromatic hydrocarbons (PAHs), and various diterpenoids were identified in this suite of cores. These marker compounds suggest inputs from biomass burning, fresh vascular plant material, and anthropogenic activities such as fossil fuel combustion. Differences in distributions of the alkyl amide and nitrile homologues between the different sites suggest a predominantly local or regional supply of organic matter. Pre-industrial samples from the Sajama and Puruogangri ice cores were also analyzed in order to assess the character of biomarker assemblages in the absence of anthropogenic contributions and investigate changes in inputs over time. PAHs and diterpenoids, which may result from biomass burning and were observed in the modern Sajama samples, occurred in two Holocene Sajama samples, but not in a last glacial sample. Enhanced inputs of terrestrial vegetation combustion biomarkers were consistent with periods of enhanced aridity in both cores. This study demonstrates the utility of SBSE, TD, and GC/TOF-MS for isolating organic compounds from small amounts of alpine ice and paves the way for development of high-resolution molecular stratigraphic records from tropical ice cores.

Makou, M. C.; Eglinton, T. I.; Thompson, L. G.; Hughen, K. A.

2005-12-01

276

Ammonium concentration in ice cores: A new proxy for regional temperature reconstruction?  

NASA Astrophysics Data System (ADS)

We present a reconstruction of tropical South American temperature anomalies over the last ˜1600 years. The reconstruction is based on a highly resolved and carefully dated ammonium record from an ice core that was drilled in 1999 on Nevado Illimani in the eastern Bolivian Andes. Concerning the relevant processes governing the observed correlation between ammonium concentrations and temperature anomalies, we discuss anthropogenic emissions, biomass burning, and precipitation changes but clearly favor a temperature-dependent source strength of the vegetation in the Amazon Basin. That given, the reconstruction reveals that Medieval Warm Period- and Little Ice Age-type episodes are distinguishable in tropical South America, a region for which until now only very limited temperature proxy data have been available. For the time period from about 1050 to 1300 AD, our reconstruction shows relatively warm conditions that are followed by cooler conditions from the 15th to the 18th century, when temperatures dropped by up to 0.6°C below the 1961-1990 average. The last decades of the past millennium are characterized again by warm temperatures that seem to be unprecedented in the context of the last ˜1600 years.

Kellerhals, T.; Brütsch, S.; Sigl, M.; Knüsel, S.; GäGgeler, H. W.; Schwikowski, M.

2010-08-01

277

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

NASA Astrophysics Data System (ADS)

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

Rybak, Oleg; Huybrechts, Philippe

2013-04-01

278

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

279

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

280

Comparison between wet and dry extractions for isotope analysis of Methane and Nitrous Oxide from ice cores  

NASA Astrophysics Data System (ADS)

Methane and nitrous oxide are two important greenhouse gases. In order to predict their future concentrations, their present budgets and past variations need to be understood. Recent data have revealed surprising variations in the stable isotope signatures of CH4 over the past millennium which underlines the need of ?D measurements of methane from air trapped in ice core. M We present a new dry extraction method for ice core air coupled to an isotope ratio mass spectrometry (IRMS) technique developed for CH4 and N2O isotope analysis on atmospheric air samples. Ice samples are grated in a stainless steel pot provided with a perforated cylinder (cheese grater) by shaking at -30°C. Subsequently, the air released from the air bubbles in the ice is adsorbed on Hayesep D in a glass bottle at liquid nitrogen temperature. Before the Hayesep D trap, N2O is cryogenically separated in a U-shape glass. Subsequently, the N2O is flushed in a helium carrier gas to the IRMS system to measure ?15N and ?18O. Simultaneoulsy, the extracted air from the Hayesep D trap is flushed in a He carrier gas to another IRMS system where methane is extracted on a second Hayesep D trap, cryo-focused, and sent to the IRMS for ?13C or ?D measurements . Our extraction method allows high precision measurements of ?D (?=2 per mil) and ?13C (?=0.2 per mil) of methane and is still under testing for the N2O isotopes. In parallel, a standard wet extraction method was set up for comparison with the dry extraction aiming to determine if any contamination appears during the grating process. Results of an intercalibration between our extraction system and other systems measuring as well methane isotopes from air trapped in ice core will also be presented.

Sapart, C. J.; Bock, M.; Roeckmann, T.; Fischer, H.; Vigano, I.; van de Veen, C.; Brass, M.

2009-04-01

281

A 300 000 year isotopic record from the TALDICE ice core (East Antarctica)  

NASA Astrophysics Data System (ADS)

The TALos Dome Ice CorE (TALDICE) project retrieved an ice core from a peripheral dome of East Antarctica. This international project aimed at drilling an ice core reaching back in time the past two climatic cycles (about 250,000 years). Talos Dome (72Ë? 49' S, 159Ë? 11' E; 2315 m; 80 kg m-2 yr-1; -41Ë? C) is located at about 290 km from the Southern Ocean, 250 km from the Ross Sea, 275 km from the Zucchelli Station (Terra Nova Bay). Backtrajectory analyses suggest that Talos Dome is mainly influenced by air masses arriving both from the Pacific (Ross Sea) and Indian Ocean sectors. In December 2007 the drilling team reached the depth of 1619.2 m. A preliminary dating based on an ice flow model and an inverse method suggests for the upper 1560 m an age of about 300 000 years BP. This near coastal site allows a higher climate resolution study for the Holocene compared to the ones obtained from the more inland drilling sites. The paleotemperature reconstructions from Antarctic ice cores relies mainly on ^D and ^18O records. The main factors controlling the observed distribution of their surface values in Antarctic snow are mainly related to the condensation temperature and the origin of moisture. Measuring both isotopes in the ice allow the determination of the deuterium excess (d=^D-8*^18O) which is mainly controlled by the climatic conditions in the moisture source regions. The ice cores have been cut in the cold laboratory of the Alfred Wegener Institut at Bremerhaven. ^18O and ^D measurements have been performed on a continuous basis of 100 cm ("bag samples") and 10 cm (detailed samples) in Italy and France. The full ^18O record obtained from the bag samples is presented here along with a preliminary deuterium excess data set. The long term climate variability is in good agreement with the EPICA Dome C ice core with the exception of trends during interglacial periods (present and past interglacial). While most of the Holocene record shows a good agreement with EPICA EDML and EDC ice cores, the lack of early Holocene optimum at Talos Dome may be linked with changes in local ice sheet elevation. This new isotopic record shows similar millennial scale climate variability (AIM events) during the last glacial period and the deglaciation.

Stenni, B.

2009-04-01

282

In situ photolysis of deep ice core contaminants by Çerenkov radiation of cosmic origin  

NASA Astrophysics Data System (ADS)

Ice core contaminants should provide permanent paleoclimatic records if, as it is generally assumed, they remained frozen in place and isolated from sunlight by the reflective overlaying snow layers. The excess CO levels recently detected in 1100-1600 AD Greenland ice core air bubbles relative to their Antarctic counterparts [Haan and Raynaud, 1998] amount, however, to an average production of about 5 +/- 2 CO molecules cm-3 ice s-1 in that period. Here we show that such rates are quantitatively consistent with the in situ photodecarbonylation of the chromophoric organic matter present in Greenland, but not in the cleaner Antarctic, ice under the Çerenkov radiation fluxes generated by penetrating muons of cosmic origin. The normal CO levels of modern (1600-1800 AD) Greenland records, and their variability earlier in the last millennium correlate significantly with the occurrence of boreal fires and the associated release of organic aerosol [Savarino and Legrand, 1998].

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

2003-02-01

283

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

2012-01-10

284

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

285

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

286

IceCube/DeepCore and IceCube/PINGU: Prospects for Few-GeV Scale ? Physics in the Ice  

NASA Astrophysics Data System (ADS)

IceCube and its low energy extension, DeepCore, have been fully deployed at the South Pole and taking data since early 2010. With a neutrino energy threshold of about 10 GeV, DeepCore endows IceCube with access to a rich variety of atmospheric neutrino oscillation physics and enhanced sensitivity for indirect searches for WIMP dark matter. A new in-fill array, dubbed PINGU, is under consideration as a way to further lower the neutrino energy threshold to a regime with the potential to measure the type of the neutrino hierarchy. We describe early results from DeepCore and simulation studies of the sensitivity of PINGU to the hierarchy.

IceCube/PINGU Collaboration; Clark, K.; Cowen, D. F.

2012-12-01

287

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

288

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

289

Simultaneous stable isotope analysis of methane and nitrous oxide on ice core samples  

NASA Astrophysics Data System (ADS)

Methane and nitrous oxide are important greenhouse gases which show a strong increase in atmospheric mixing ratios since pre-industrial time as well as large variations during past climate changes. The understanding of their biogeochemical cycles can be improved using stable isotope analysis. However, high-precision isotope measurements on air trapped in ice cores are challenging because of the high susceptibility to contamination and fractionation. Here, we present a dry extraction system for combined CH4 and N2O stable isotope analysis from ice core air, using an ice grating device. The system allows simultaneous analysis of ?D(CH4) or ?13C(CH4), together with ?15N(N2O), ?18O(N2O) and ?15N(NO+ fragment) on a single ice core sample, using two isotope mass spectrometry systems. The optimum quantity of ice for analysis is about 600 g with typical "Holocene" mixing ratios for CH4 and N2O. In this case, the reproducibility (1? ) is 2.1‰ for ?D(CH4), 0.18‰ for ?13C(CH4), 0.51‰ for ?15N(N2O), 0.69‰ for ?18O(N2O) and 1.12‰ for ?15N(NO+ fragment). For smaller amounts of ice the standard deviation increases, particularly for N2O isotopologues. For both gases, small-scale intercalibrations using air and/or ice samples have been carried out in collaboration with other institutes that are currently involved in isotope measurements of ice core air. Significant differences are shown between the calibration scales, but those offsets are consistent and can therefore be corrected for.

Sapart, C. J.; van der Veen, C.; Vigano, I.; Brass, , M.; van de Wal, R. S. W.; Bock, M.; Fischer, H.; Sowers, T.; Buizert, C.; Sperlich, P.; Blunier, T.; Behrens, M.; Schmitt, J.; Seth, B.; Röckmann, T.

2011-12-01

290

Simultaneous stable isotope analysis of methane and nitrous oxide on ice core samples  

NASA Astrophysics Data System (ADS)

Methane and nitrous oxide are important greenhouse gases which show a strong increase in atmospheric mixing ratios since pre-industrial time as well as large variations during past climate changes. The understanding of their biogeochemical cycles can be improved using stable isotope analysis. However, high-precision isotope measurements on air trapped in ice cores are challenging because of the high susceptibility to contamination and fractionation. Here, we present a dry extraction system for combined CH4 and N2O stable isotope analysis from ice core air, using an ice grating device. The system allows simultaneous analysis of ?D(CH4) or ?13C(CH4), together with ?15N(N2O), ?18O(N2O) and ?15N(NO+fragment) on a single ice core sample, using two isotope mass spectrometry systems. The optimum quantity of ice for analysis is about 600g with typical "Holocene" mixing ratios for CH4 and N2O. In this case, the reproducibility (1?) is 2.1 ‰ for ?D(CH4), 0.18 ‰ for ?13C(CH4), 0.51 ‰ for ?15N(N2O), 0.69 ‰ for ?18O(N2O) and 1.12 ‰ for ?15N(NO+fragment). For smaller amounts of ice the standard deviation increases, particularly for N2O isotopologues. For both gases, small-scale intercalibrations using air and/or ice samples have been carried out with other institutes that are currently involved in isotope measurements of ice core air. Significant differences are shown between the calibration scales, but those offsets are consistent and can be corrected for.

Sapart, C. J.; van der Veen, C.; Vigano, I.; Brass, M.; van de Wal, R. S. W.; Bock, M.; Fischer, H.; Sowers, T.; Buizert, C.; Sperlich, P.; Blunier, T.; Behrens, M.; Schmitt, J.; Seth, B.; Röckmann, T.

2011-07-01

291

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

292

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

293

Sub-millennial climate variability during past interglacial periods: insights from new high resolution deuterium measurements conducted on the EPICA Dome C ice core (Invited)  

Microsoft Academic Search

The study of past climates and particularly interglacials (or warm periods) is of prime importance today to place in a broader perspective the climate of the Holocene (the present interglacial) and its future evolution. Thanks to the analysis of 55cm samples from the EPICA Dome C ice core (EDC), a continuous but low resolution stable isotope signal has previously revealed

K. Pol; V. Masson-Delmotte; M. Bigler; E. Capron; O. Cattani; M. Debret; G. B. Dreyfus; G. Durand; S. Falourd; S. J. Johnsen; J. Jouzel; A. Landais; B. Minster; F. Parrenin; C. Ritz; H. Steen-Larsen; B. Stenni

2010-01-01

294

Physical properties of Reykjanes Ridge sediments and their linkage to high-resolution Greenland Ice Sheet Project 2 ice core data  

Microsoft Academic Search

Five gravity cores taken from the Reykjanes Ridge have been used to establish a link between sediment physical properties and atmospheric records documented by delta18O variations in Greenland ice cores over the last 45,000 calendar years. Marine Gamma Ray Attenuation Porosity Evaluator density and magnetic susceptibility variations could be linked with the ice core Dansgaard-Oeschger and Bond cycles. This is

M. Moros; R. Endler; K. S. Lackschewitz; H.-J. Wallrabe-Adams; J. Mienert; W. Lemke

1997-01-01

295

Physical properties of Reykjanes Ridge sediments and their linkage to high-resolution Greenland Ice Sheet Project 2 ice core data  

Microsoft Academic Search

Five gravity cores taken from the Reykjanes Ridge have been used to establish a link between sediment physical properties and atmospheric records documented by ?18O variations in Greenland ice cores over the last 45,000 calendar years. Marine Gamma Ray Attenuation Porosity Evaluator density and magnetic susceptibility variations could be linked with the ice core Dansgaard-Oeschger and Bond cycles. This is

M. Moros; R. Endler; K. S. Lackschewitz; H.-J. Wallrabe-Adams; J. Mienert; W. Lemke

1997-01-01

296

A high-resolution air chemistry record from an Alpine ice core: Fiescherhorn glacier, Swiss Alps  

NASA Astrophysics Data System (ADS)

Glaciochemical studies at midlatitudes promise to contribute significantly to the understanding of the atmospheric cycling of species with short atmospheric lifetimes. Here we present results of chemical analyses of environmentally relevant species performed on an ice core from Fiescherhorn glacier, Swiss Alps (3890 m above sea level). This glacier site is unique since it is located near the high-alpine research station Jungfraujoch. There long-term meteorological and air quality measurements exist, which were used to calibrate the paleodata. The 77-m-long ice core was dated by annual layer counting using the seasonally varying signals of tritium and ?18O. It covers the time period 1946-1988 and shows a high net accumulation of water of 1.4 m yr-1 allowing for the reconstruction of high-resolution environmental records. Chemical composition was dominated by secondary aerosol constituents as well as mineral dust components, characterizing the Fiescherhorn site as a relatively unpolluted continental site. Concentrations of species like ammonium, nitrate, and sulfate showed an increasing trend from 1946 until about 1975, reflecting anthropogenic emission trends in western Europe. For mineral dust tracers, no trends were obvious, whereas chloride and sodium showed slightly higher levels from 1965 until 1988, indicating a change in the strength of sea-salt transport. Good agreement between the sulfate paleorecord with direct atmospheric measurements was found (correlation coefficient r2 = 0.41). Thus a "calibration" of the paleorecord over a significant period of time could be conducted, revealing an average scavenging ratio of 180 for sulfate.

Schwikowski, M.; Brütsch, S.; GäGgeler, H. W.; Schotterer, U.

1999-06-01

297

The Last 1 Million Years at Tenaghi Philippon: Terrestrial, Marine and Ice Core Comparisons  

NASA Astrophysics Data System (ADS)

Palaeoenvironmental archives spanning multiple glacial-interglacial cycles provide a unique perspective into the evolution of Quaternary climate variability. However, while marine and ice core records may furnish the best estimates of global climate variability, we still remain in relative ignorance as to how these changes translate to events on land, because of a shortage of suitable terrestrial sequences and inadequate chronological control. Continuous, pollen-bearing lake sediment sequences are found only in exceptional circumstances and a handful of these occur in S. Europe. Here we examine the longest of these records, from Tenaghi Philippon (TP), northeast Greece, spanning the last 1 million years. A new astronomical calibration procedure, based on a correspondence between changes in certain vegetation elements and March and June perihelion configurations, is applied to the entire section, leading to a revised timescale especially for the lower part of the sequence. The TP sequence shows a close correspondence between marine and terrestrial stages over the last million years, although individual boundaries may not be precisely isochronous. However, inspection of the record reveals a significant departure in terms of the amplitude of glacial-interglacial variability, with the onset of more extreme interglacials occurring after MIS 16, rather than MIS 12 as seen in marine and ice core records. More specifically, TP interglacials before MIS 16 are characterized by lower arboreal pollen increases, as a result of sustained presence of grasses. Part of this grass signal is derived from local semi-aquatic vegetation, suggesting increased marsh area and lower water levels. This may be a function of local factors (e.g. tectonic changes) altering the hydrological regime of the Philippi plain. Alternatively, the occurrence of a shift in interglacial amplitudes right at the MIS 16/15 transition, may suggest a climatic control. Comparisons with other records are needed in order to establish the local or regional character of such changes.

Tzedakis, P. C.; Hooghiemstra, H.; Wijmstra, T. A.

2004-12-01

298

Identification of major proton fluence events from nitrates in polar ice cores.  

PubMed

Large transient concentrations of nitrates in polar ice cores have been identified as the signature of some major solar proton fluence events between 1940 and 1991. We review this solar proton proxy identification technique using nitrate concentration measurements in ice cores from the Arctic and Antarctic. Using this identification technique we go back in time in an attempt to identify major solar proton events during the past several centuries. There is a very large nitrate increase corresponding to the Carrington flare of 1859 evident in the Arctic ice core. Other significant nitrate increases may indicate that major solar proton events occurred toward the end of the last century. The problems associated with this new technique of using nitrates as proxies to identify solar proton events are discussed. PMID:11543137

Shea, M A; Smart, D F; Dreschhoff, G A

1999-06-01

299

Ice core evidence for a second volcanic eruption around 1809 in the Northern Hemisphere  

NASA Astrophysics Data System (ADS)

A volcanic signal observed in ice cores from both polar regions six years prior to Tambora is attributed to an unknown tropical eruption in 1809. Recovery of dacitic tephra from the 1809 horizon in a Yukon ice core (Eclipse) that is chemically distinct from andesitic 1809 tephra found in Antarctic ice cores indicates a second eruption in the Northern Hemisphere at this time. Together with the similar magnitude and timing of the 1809 volcanic signal in the Arctic and Antarctic, this could suggest a large tropical eruption produced the sulfate and Antarctic tephra and a minor Northern Hemisphere eruption produced the Eclipse tephra. Nonetheless, the possibility that there were coincidental eruptions of similar magnitude in both hemispheres, rather than a single tropical eruption, should not be discounted. Correctly attributing the source of the 1809 volcanic signal has important implications for modeling the magnitude and latitudinal distribution of volcanic radiative forcing.

Yalcin, Kaplan; Wake, Cameron P.; Kreutz, Karl J.; Germani, Mark S.; Whitlow, Sallie I.

2006-07-01

300

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

301

HST Reveals the Core Properties of Ultraluminous IR Galaxies  

NASA Astrophysics Data System (ADS)

We report on an analysis of HST imaging observations of the bright multiple cores (starburst knots or merger remnant nuclei?) at the centers of ultraluminous IR galaxies (ULIRGs). ULIRGs are strongly starbursting, heavily dust-enshrouded, and engaged in strong tidal/merger events. Our analyses of WFPC2 I-band and NICMOS H-band images are revealing the nature, physical properties, likely origin, and probable future evolutionary state of these cores. We will present results on core sizes, luminosities, colors, light profiles, separations, and frequency of occurence. Support for this work was provided by NASA through grants # GO-6346.01-95A and GO-7896.01-96A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

Bushouse, H. A.; Borne, K. D.; Colina, L.; Lucas, R. A.

1998-12-01

302

The Ice Core Data Gateway: The one stop gateway to ice core data held at the Antarctic Glaciological Data Center (AGDC), the World Data Center for Paleoclimatology, and the Arctic System Science's Data Coordination Center (ADCC).  

NASA Astrophysics Data System (ADS)

The Ice Core Data Gateway archives and distributes physical and geochemical data from ice cores collected in both the northern and southern hemispheres. Typical data sets include age-depth relationships, oxygen and hydrogen isotope concentrations, major element chemistry, accumulation rates and pollen. The data are in general presented as ASCII files with a short text metadata description. The archive is designed to provide access to ice core data sets over the long term, thereby making them available for comparison with future data: a critical component of change detection studies. By facilitating broad data access, the center promotes interdisciplinary scientific research. Investigators are encouraged to contribute data sets derived from ice cores to the Ice Core Data Gateway. Data center staff will work with you to compile data set documentation prior to making the data available to users. Contributing scientists are given prominent recognition in the documentation, and while the data center answers technical questions about format, citations for usage, etc., it can refer scientific questions to contributors if requested. Contributing your data to the Ice Core Data Gateway and associated data centers directly supports to NSF Office of Polar Programs Guidelines and Award Conditions for Scientific Data (http://www.nsf.gov/pubsys/ods/getpub.cfm?opp991). This effort is being coordinated with the West Antarctic Ice Sheet (WAIS) Initiative and U.S. component of the International Trans Antarctic Science Expedition (ITASE), and includes data from the Arctic System Science Program's Greenland Ice Sheet Project 2 (GISP2) ice core.

Bauer, R.; Scambos, T.; Eakin, M.; Anderson, D.; McNeave, C.

2002-12-01

303

Antarctic climate variability from ice core records over the last two millennia  

NASA Astrophysics Data System (ADS)

The climate of the past can be successfully investigated through the study of polar ice sheets. Paleotemperature reconstructions from Antarctic ice cores are based on water isotope profiles, thanks to the existing relationship between ?18O (or ?D) and the temperature at the site. Here we present the climate record of the past 2000 years resulting from the stable isotope analysis of the ice core drilled at Talos Dome in East Antarctica from 2003 to 2007 in the framework of the European 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. The snow accumulation rate of the site (80 kg m-2 yr-1) allows extracting high-resolution data for the past millennia. The main moisture sources of snow precipitation at this near-coastal site are located in the Indian Ocean and the Ross Sea. Isotopic analyses of TALDICE detailed (10 cm) samples have been performed in the framework of the ESF-HOLOCLIP project, whose main objective is to integrate the ice core, the marine core and the modeling data to investigate the climate variability of the high latitude southern hemisphere over the Holocene. The isotopic record obtained from the TALDICE ice core is here compared with a shallow firn core (89 m long) previously drilled at Talos Dome, at a 5 km distance, and covering the past 800 years. The two isotopic records are stacked to reduce the stratigraphic noise and compared with other available isotopic records from Antarctica to highlight common trends and regional variability in the climatic signal over the past two millennia. We compare the data with a simulation performed with a three-dimensional earth system model of intermediate complexity (LOVECLIM) with and without data assimilation. Considering the ?18O profile from the TALDICE ice core and comparing it with the ones from the other available records we can observe common negative isotopic anomalies in the period from about 1450 to 1850 AD preceded by several positive and negative anomalies on centennial scale.

Braida, Martina; Stenni, Barbara; Masson-Delmotte, Valerie; Dreossi, Giuliano; Oerter, Hans; Selmo, Enricomaria; Severi, Mirko; Goosse, Hugues; Mezgec, Karin

2013-04-01

304

A new Greenland ice core chronology for the last glacial termination  

NASA Astrophysics Data System (ADS)

We present a new common stratigraphic timescale for the North Greenland Ice Core Project (NGRIP) and GRIP ice cores. The timescale covers the period 7.9-14.8 kyr before present and includes the Bølling, Allerød, Younger Dryas, and early Holocene periods. We use a combination of new and previously published data, the most prominent being new high-resolution Continuous Flow Analysis (CFA) impurity records from the NGRIP ice core. Several investigators have identified and counted annual layers using a multiparameter approach, and the maximum counting error is estimated to be up to 2% in the Holocene part and about 3% for the older parts. These counting error estimates reflect the number of annual layers that were hard to interpret, but not a possible bias in the set of rules used for annual layer identification. As the GRIP and NGRIP ice cores are not optimal for annual layer counting in the middle and late Holocene, the timescale is tied to a prominent volcanic event inside the 8.2 kyr cold event, recently dated in the DYE-3 ice core to 8236 years before A. D. 2000 (b2k) with a maximum counting error of 47 years. The new timescale dates the Younger Dryas-Preboreal transition to 11,703 b2k, which is 100-150 years older than according to the present GRIP and NGRIP timescales. The age of the transition matches the GISP2 timescale within a few years, but viewed over the entire 7.9-14.8 kyr section, there are significant differences between the new timescale and the GISP2 timescale. The transition from the glacial into the Bølling interstadial is dated to 14,692 b2k. The presented timescale is a part of a new Greenland ice core chronology common to the DYE-3, GRIP, and NGRIP ice cores, named the Greenland Ice Core Chronology 2005 (GICC05). The annual layer thicknesses are observed to be log-normally distributed with good approximation, and compared to the early Holocene, the mean accumulation rates in the Younger Dryas and Bølling periods are found to be 47 ± 2% and 88 ± 2%, respectively.

Rasmussen, S. O.; Andersen, K. K.; Svensson, A. M.; Steffensen, J. P.; Vinther, B. M.; Clausen, H. B.; Siggaard-Andersen, M.-L.; Johnsen, S. J.; Larsen, L. B.; Dahl-Jensen, D.; Bigler, M.; RöThlisberger, R.; Fischer, H.; Goto-Azuma, K.; Hansson, M. E.; Ruth, U.

2006-03-01

305

Anatomy of a Dansgaard-Oeschger warming transition: High-resolution analysis of the North Greenland Ice Core Project ice core  

NASA Astrophysics Data System (ADS)

Large and abrupt temperature oscillations during the last glacial period, known as Dansgaard-Oeschger (DO) events, are clearly observed in the Greenland ice core record. Here we present a new high-resolution chemical (2 mm) and stable isotope (20 mm) record from the North Greenland Ice Core Project (NGRIP) ice core at the onset of one of the most prominent DO events of the last glacial, DO-8, observed ˜38,000 years ago. The unique, subannual-resolution NGRIP record provides a true sequence of change during a DO warming with detailed annual layer counting of very high depth resolution geochemical measurements used to determine the exact duration of the transition. The continental ions, indicative of long-range atmospheric loading and dustiness from East Asia, are the first to change, followed by the snow accumulation, the moisture source conditions, and finally the atmospheric temperature in Greenland. The sequence of events shows that atmospheric and oceanic source and circulation changes preceded the DO warming by several years.

Thomas, Elizabeth R.; Wolff, Eric W.; Mulvaney, Robert; Johnsen, Sigfus J.; Steffensen, Jorgen P.; Arrowsmith, Carol

2009-04-01

306

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

307

A Model for Late Quaternary Methane Ice Core Signals: Wetlands Versus a Shallow Marine Source  

NASA Astrophysics Data System (ADS)

Late quaternary glacial and stadial climate was likely more arid compared to today and together with lower sea level, wetlands were unlikely to have been well developed. Whether wetlands could develop rapidly enough at the termination of cold periods to be the source of ice core methane signals has been already questioned (Kennett et al. 2003, AGU monograph). Here, a three-reservoir model with first order kinetics for methane records in the Vostok (Antarctica) and GISP2 (Greenland) ice cores reproduces the quasi periodic sawtooth pattern and the minimum and maximum concentrations (approx. 350 to 700 ppb) in the ice cores. The model also returns an atmospheric methane relaxation time of about 10 years for both cores, the same as current estimates. The short atmospheric relaxation time together with the sawtooth patterns in the ice cores require a strong source to maintain atmospheric methane concentrations. According to the model, the characteristics of the source reservoir are long relaxation times (33.3 and 100 ka) and high initial methane concentrations (2500 and 7000 ppm) for GISP2 and Vostok, respectively. The causes of the differences between the Greenland and Antarctic sources is currently unclear. Modern day wetlands have an insufficient methane flux and insufficient storage capacity to represent these source characteristics, suggesting wetland sources at late Quaternary glacial and stadial terminations were also inadequate. The model source characteristics, however, are consistent with gas hydrate sources in shallow marine sediments which have the required long relaxation times and high source strength (O'Hara, 2008, GRL).

O'Hara, K. D.

2008-05-01

308

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

309

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

310

Ice core gas thermometry at Dansgaard-Oeschger 8, Greenland  

Microsoft Academic Search

The Greenland temperature record from O18 of the ice shows millennial-duration Dansgaard-Oeschger or Interstadial events. One such event, Interstadial 8, began with a warming at 38.4 ky BP (before present; GISP2 timescale). The magnitude of these warmings has been uncertain because factors other than temperature affect O18, such as seasonality of precipitation. Borehole thermometry provides low-frequency calibration of O18, but

J. Severinghaus; A. Grachev; M. Spencer; R. Alley; E. Brook

2003-01-01

311

The 8.2 ka event from Greenland ice cores  

Microsoft Academic Search

We present a collection of high-resolution chemistry and stable isotope records from the plateau of the Greenland ice cap during the cold event 8200yr ago. Using a composite of four records, the cold event is observed as a 160.5yr period during which decadal-mean isotopic values were below average, within which there is a central event of 69yr during which values

Elizabeth R. Thomas; Eric W. Wolff; Robert Mulvaney; Jorgen P. Steffensen; Sigfus J. Johnsen; Carol Arrowsmith; James W. C. White; Bruce Vaughn; Trevor Popp

2007-01-01

312

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

313

Volcanic Forcing of Climate over the Past 1500 Years: An Improved Ice-Core-Based Index for Climate Models  

Microsoft Academic Search

Evaluating natural causes of climate change is vital in order 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 40 ice core records from both Greenland and Antarctica. Our extensive collection of ice core data (more than double

C. Gao; A. Robock; C. Ammann

2006-01-01

314

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

315

Modelisation of grain growth along the dome C EPICA ice core  

NASA Astrophysics Data System (ADS)

Along polar ice cores, climatic transitions are marked by strong variations of the average grain size. Consequently, grain size has been proposed in the past as being a true paleothermometer. Here, we study ice microstructure (grains size, grain shape) along the Dome Concordia ice core and its evolution with depth, temperature, impurities content. We show that normal grain growth is strongly affected by the pinning effect of dust particles and bubbles on grain boundaries. This pinning effect is strong enough to stop grain growth because particles are located along grain boundaries, as demonstrated by a X-ray tomography of the ice. A Lagrangian model of grain size evolution is developed that take into account normal grain growth, as well as the pinning by dust particles and bubbles. As the ice elementary volume goes down, its temperature and its thinning are reset at each time step, following the outpout of an ice sheet model.. The striking agreement between measured and modeled grain sizes demonstrates that the average grain size is not a direct paleothermomether. Instead, grain size is governed non linearly by the dust content which itself show brutal variations with climatic changes.

Durand, G.; Weiss, J.; Parrenin, F.; Ritz, C.

2003-04-01

316

Stable Isotopes of N and Ar as Tracers to Retrieve Past Air Temperature from Air Trapped in Ice Cores  

Microsoft Academic Search

\\u000a Ice cores are paleoclimatic archives that permit the reconstruction of past local precipitation temperature (from the measurements\\u000a of water isotopes) and past atmospheric gas concentration (from the analysis of the air trapped in the ice) over the past\\u000a 800,000 years. However, water isotopes are not a quantitative tracer for past temperature in Greenland ice cores. Moreover,\\u000a because of the entrapment

A. Landais

317

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

318

Constraints on the major sources of dissolved organic carbon in Alpine ice cores from radiocarbon analysis over the bomb-peak period  

NASA Astrophysics Data System (ADS)

Radiocarbon (14C) has proven to be a powerful tool in distinguishing modern and fossil fuel sources contributing to organic aerosols. By applying this concept to ice core records of the dissolved organic carbon (DOC) fraction, we developed a setup dedicated to the extraction of DOC from Alpine ice core samples for 14C microanalysis. With respect to the difficulties and limitations of this analytical method, it is shown that a total process blank mass of (6 ± 3) ?gC with a 14C signature of (0.71 ± 0.17) can be obtained, corresponding to a minimum sample size between 200 g for industrial and 800 g for pre-industrial ice. Radiocarbon analyses of eight DOC ice core samples from the high accumulation glacier Col du Dôme (European Alps) were mainly performed over the bomb-peak period. These data, being associated with snow deposition over the summer half-years, show an overall mean fossil contribution of (25 ± 9) %. Adaptation of the DO14C values to the atmospheric 14CO2 record revealed that the biogenic input to ice core DOC is associated with a fast recycling biospheric component, likely linked to a turnover time of less than 3 years.

May, B.; Wagenbach, D.; Hoffmann, H.; Legrand, M.; Preunkert, S.; Steier, P.

2013-04-01

319

CO2 Ice in Cold Dense Dark Cloud Cores: Abundance versus Visual Extinction  

NASA Astrophysics Data System (ADS)

Ice mantle composition in cold dense cores may trace their chemical and physical evolution. Here we present the results of Spitzer IRS observations of the ice absorption features within cold dense dark cloud cores as a function of the visual extinction across the cores. We used 2MASS stars with high extinction as targets located behind the cores.We observed several target stars, with Av = 5 to 50 mag, across each core. Our results for IC 5146 E & W suggest a clear correlation between the CO2 absorption with increasing Av.We find that CO2 absorption begins to show up only in regions with Av greater than about 18 mag. Our results suggest a threshold (Av) for the dust column density required for the CO2 mantle formation and evolution. This threshold appears to be significantly higher than that for CO (5 - 11 mag), and H2O (3.3 mag) ices. Our CO2 results are consistent with the depletion and catalysis of CO deep in the cores. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Velusamy, T.; Langer, W. D.; Willacy, K.

320

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

321

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

NASA Astrophysics Data System (ADS)

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

Breton, Daniel; Hamilton, Gordon

2009-10-01

322

Characterization of Particles Recovered From a 4 Km Ice Core Above Lake Vostok, Antarctica  

NASA Astrophysics Data System (ADS)

Nine samples of glacial ice from distinct glacial maxima and interglacial periods have been recovered from depths ranging from 179 to 3351 meters above Lake Vostok, Antarctica, representing a record of { ~}420,000 years, and three samples of ice from depths of 3540-3590 meters interpreted as having accreted from Lake Vostok, have been analyzed to determine the mineralogic and biologic constituents of these ice cores. Known quantities of ice were melted and particulate matter was collected on 0.2 micron filters for imaging and analysis using cryo-SEMBSE and EDS techniques. The mineralogy of the glacial ice generally follows continental crustal abundances, with modal quartz (19-65%)> alkali feldspar (16-42%)>plagioclase (5-25%). Combined micas (bio-musc-chlor) range from 1-43%, with the higher values recorded in interglacial intervals. Volcanic glass constitutes up to 34% of some samples. Most of the analyzed grains are sub-angular to sub-rounded and occur in the size range of 1-5 microns; 5-10 micron particles of angular volcanic glass and ternary feldspars occur in both glacial and interglacial intervals. In addition, one grain with a Fe-Ni composition is interpreted as a micrometeorite, and fibrous grains of a Mg-Fe silicate are interpreted as enstatite "whiskers". Organic matter occurs irregularly throughout the ice column and includes fragments of diatom frustules, mats of organic debris, and rare rods and coccoids that are most likely microbial. In contrast, sediments in the accreted ice typically have grain sizes <1 micron, with modal biotite (73%)> quartz (13%)> Kspar (9%)>plagioclase (2%). Rod-shaped bacterial cells are readily observed on the filter substrate and attached to mats of organic debris (Priscu et al., 1999). There is a clear distinction in particle composition and morphology and the type of organic material found in the glacial ice compared with accreted ice. Sediments in the glacial ice contain minerals representative of typical continental crust, with little evidence of sorting by grain size or composition. Airborne modifications of the modal mineralogy of the glacial ice may occur through episodic infusions of volcanic ash or crystallites, enrichment of micas through aeolian sorting, and rare capture of meteoric particles. Enrichment of biotite in the accreted ice is interpreted as the result of differential settling in the lake waters prior to accretion. The relatively large abundances of bacteria in the accreted ice implies that Lake Vostok may support microbial life, whereas rare microbes and fragments of diatom frustules in the glacial ice may have been transported and deposited by aeolian processes.

Priscu, J.; Mogk, D.; Foreman, C.; Mikucki, J.; Denson, J.; Wolf, C.; Adams, E.; Welch, K.; Voytek, M.

2001-12-01

323

Surface melting of ice Ih single crystals revealed by glancing angle x-ray scattering  

Microsoft Academic Search

We present glancing angle x-ray scattering experiments at [00.1], [10.0], and [11.0] surfaces of ice Ih single crystals. The temperature dependence of the evanescent Bragg scattering upon heating reveals a quasiliquid surface layer well below the melting point of each investigated ice surface. At [10.0] and [11.0] surfaces, thermal faceting is observed, which is briefly discussed. The ``oxygen-forbidden'' (00.4) Bragg

A. Lied; H. Dosch; J. H. Bilgram

1994-01-01

324

Measurements of preindustrial methyl chloride from an Antarctic ice core: Natural variability and its implications  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) mixing ratios were measured in preindustrial air extracted from a shallow ice core from Siple Dome, West Antarctica. Ice core samples were shredded under vacuum and the extracted air was analyzed by gas chromatography with mass spectrometric detection. The samples range in depth from 57 m to 83 m and the gas ages assigned to them span the calendar years 1690 to 1915 AD. The mean CH3Cl mixing ratio in 22 samples is 499+/-28 pptv. The data exhibit two full cycles of a 100-year oscillation with an amplitude of approximately 60 pptv, suggesting that there is periodic natural variability in atmospheric CH3Cl. The origin of this variability is unknown. Assuming that this oscillation in atmospheric CH3Cl persisted during the last century, the ice core results suggest that the present day natural levels would be 470-480 pptv. Compared with the modern mean value of 530 pptv over Antarctica, these results suggest that the current anthropogenic impact on the atmospheric burden is roughly 10%. Such an extrapolation of the ice core data also implies that there may be a 10% increase in the atmospheric CH3Cl levels over the next 50 years due to this natural variability.

Aydin, M.; de Bruyn, W. J.; Saltzman, E. S.

2002-12-01

325

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

326

Snow and ice-core stable isotopes time series and precipitation in Altai Mountains (Siberia)  

Microsoft Academic Search

The Altai's glaciers provide information on internal and external hydrological cycles over the Eurasia, storing long-term records of fresh water transport from Atlantic and Pacific Oceans and the Central Asia closed drainage basin. The 22 m firn-ice cores and 3 m snow pits from the Belukha firn Plateau (4109 - 4115 m) were used to recover climatic records through physical

E. M. Aizen; V. B. Aizen; K. Fujita; S. A. Nikitin; K. Kreutz

2003-01-01

327

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

Microsoft Academic Search

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

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

2009-01-01

328

Sulfur cycle at Last Glacial Maximum: Model results versus Antarctic ice core data  

Microsoft Academic Search

For the first time, an atmospheric general circulation and sulfur chemistry model is used to simulate sulfur deposition in Antarctica at the Last Glacial Maximum (LGM). Dimethylsulfide (DMS), emitted by phytoplankton, is the dominant source of atmospheric sulfur in Antarctica. Once in the atmosphere, it is oxidized into sulfur aerosols which are measured in ice cores. Such measurements allow for

H. Castebrunet; C. Genthon; P. Martinerie

2006-01-01

329

Ice-core palaeoclimate records in tropical South America since the Last Glacial Maximum  

Microsoft Academic Search

Ice-core records spanning the last 25 000 yr from the tropical Andes of South America are reviewed. These records from Quelccaya, Huascaran and Sajama present a high temporal resolution picture of both the Late Glacial Stage (LGS) and the Holocene climatic and environmental conditions in the South American Andes. Late Glacial Stage conditions at high elevations appear to have been

Lonnie G. Thompson; Ellen Mosley-Thompson; Keith A. Henderson

2000-01-01

330

Ash layers from Iceland in the Greenland GRIP ice core correlated with oceanic and land sediments  

Microsoft Academic Search

Four previously known ash layers (Ash Zones I and II, Saksunarvatn and the Settlement layer) all originating in Iceland, have been identified in the Central Greenland ice core GRIP. This correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash. This establishes and confirms detailed correlations between the

Karl Grönvold; Níels Óskarsson; Sigfús J. Johnsen; Henrik B. Clausen; Claus U. Hammer; Gerard Bond; Edouard Bard

1995-01-01

331

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica  

NASA Astrophysics Data System (ADS)

A new deep ice core drilling program, TALDICE, has been successfully handled by a European team at Talos Dome, in the Ross Sea sector of East Antarctica, down to 1620 m depth. Using stratigraphic markers and a new inverse method, we produce the first official chronology of the ice core, called TALDICE-1. We show that it notably improves an a priori chronology resulting from a one-dimensional ice flow model. It is in agreement with a posteriori controls of the resulting accumulation rate and thinning function along the core. An absolute uncertainty of only 300 yr is obtained over the course of the last deglaciation. This uncertainty remains lower than 600 yr over Marine Isotope Stage 3, back to 50 kyr BP. The phasing of the TALDICE ice core climate record with respect to the central East Antarctic plateau and Greenland records can thus be determined with a precision allowing for a discussion of the mechanisms at work at sub-millennial time scales.

Buiron, D.; Chappellaz, J.; Stenni, B.; Frezzotti, M.; Baumgartner, M.; Capron, E.; Landais, A.; Lemieux-Dudon, B.; Masson-Delmotte, V.; Montagnat, M.; Parrenin, F.; Schilt, A.

2011-01-01

332

The Last 1 Million Years at Tenaghi Philippon: Terrestrial, Marine and Ice Core Comparisons  

Microsoft Academic Search

Palaeoenvironmental archives spanning multiple glacial-interglacial cycles provide a unique perspective into the evolution of Quaternary climate variability. However, while marine and ice core records may furnish the best estimates of global climate variability, we still remain in relative ignorance as to how these changes translate to events on land, because of a shortage of suitable terrestrial sequences and inadequate chronological

P. C. Tzedakis; H. Hooghiemstra; T. A. Wijmstra

2004-01-01

333

Ice cores as an index of global volcanism from 1850 to the present  

Microsoft Academic Search

To evaluate an important cause of past climate change, climate researcher need reliable estimates of volcanic aerosol loading in the atmosphere. Previous indices, the dust veil index, volcanic explosivity index, and those by Mitchell (1970), Sato et al. (1993) and Khmelevtsov et al. (unpublished manuscript, 1993), all have drawbacks. Ice core acidity and sulfate records, because they contain physical evidence

Alan Robock; Melissa P. Free

1995-01-01

334

Ice core from Akademii Nauk ice cap, Severnaya Zemlya (Russian Arctic), dated with a Nye model modified for a growing glacier  

Microsoft Academic Search

From 1999 to 2001 a 724 m deep ice core has been drilled from surface to bedrock close to summit of the Akademii Nauk ice cap, Severnaya Zemlya (Russian Arctic), within a joint German-Russian project. The analysis of stable water isotopes and major ion concentration in high resolution were used for reconstruction of past climate and environmental changes. The upper

Diedrich Fritzsche; Thomas Opel; Hanno Meyer

2010-01-01

335

Ages and composition of gas trapped in Allan Hills and Byrd core ice  

NASA Astrophysics Data System (ADS)

Gas is extracted from large (6-31 kg) Antarctic ice samples to obtain sufficient CO 2 for 14C measurements with small low-level proportional counters. The 14C ages of Byrd core ice are in accord with glaciological estimates ranging from (2.2 -1.1+1.4)×10 3 yr at 271 m depth to more than 8 × 10 3 yr at 1071 m depth. The CO 2 abundances in gas extracted from Byrd core ice range from 0.0216 to 0.051%, with below present-day atmosphere CO 2 abundances for ice from 1068 and 1469 m depths. The CO 2 abundance in gas from Allan Hills surface ice samples ranges between four and six times the atmospheric value and the CO 2 had a specific activity three times that of contemporary carbon. A possible explanation for the anomalously high specific activity is surface melting with the incorporation into CO 2 of 14C produced by cosmic ray spallation of oxygen in ice. The CO 2 abundance in gas extracted from subsurface Allan Hills ice ranged from 0.030 to 0.065%, and the specific activities are below contemporary carbon, indicating ages greater than ˜5×10 3 yr. The 18O/ 16O ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the 18O/ 16O ratio in the ice. The O 2, N 2, and Ar abundances and isotopic compositions are similar to those in contemporary air, except for positive 15N/ 14N ratios in a few samples.

Fireman, E. L.; Norris, T. L.

1982-10-01

336

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

337

Towards interpreting nitrate-?15N records in ice cores in terms of nitrogen oxide sources  

NASA Astrophysics Data System (ADS)

The isotopic composition of nitrate preserved in ice cores offers unique potential for reconstructing past contributions of nitrogen oxides (NOx = NO and NO2) to the atmosphere. Sources of NOx imprint a nitrogen stable isotopic (?15N) signature, which can be conserved during subsequent oxidation to form nitrate. Major sources of NOx include fossil fuels combustion, biomass burning, microbial processes in soils, and lightning, and thus a quantitative tracer of emissions would help detail connections between the atmosphere, the biosphere, and climate. Unfortunately, the ?15N signatures of most NOx sources are not yet well enough constrained to allow for quantitative partitioning, though new methodology for directly collecting NOx for isotopic analysis is promising (Fibiger and Hastings, A43D-0265, AGU 2010). Still, a growing network of ice core ?15N records may offer insight into source signatures, as different sources are important to different regions of the world. For example, a 300-year ice core record of nitrate-?15N from Summit, Greenland shows a clear and significant 12% (vs. N2) decrease since the Preindustrial that reflects emissions from fossil fuel combustion and/or soils related to changing agricultural practices in North America and Europe. Over the same time period, Antarctic ice cores show no such trend in ?15N. This would be consistent with previous work suggesting that biomass burning and/or stratospheric intrusion of NOx produced from N2O oxidation are dominant sources for nitrate formation at high southern latitudes. In comparison to the polar records, nitrate in tropical ice cores should represent more significant inputs from lightning, microbial processes in soils, and biomass burning. This may be reflected in new results from a high-elevation site in the Peruvian Andes that shows strong seasonal ?15N cycles of up to 15% (vs. N2). We compare and contrast these records in an effort to evaluate the contribution of NOx sources to nitrate over time.

Hastings, M. G.; Buffen, A. M.

2011-12-01

338

North Pacific Climate Variability in Ice Core Accumulation Records From Eclipse Icefield, Yukon, Canada  

NASA Astrophysics Data System (ADS)

Three annually dated ice cores from Eclipse Icefield, Yukon, Canada provide records of net accumulation spanning the last 100 to 500 years. The ice cores were dated by annual layer counting verified by reference horizons provided by radioactive fallout and volcanic eruptions. Annual layers become progressively thinner with depth in the Eclipse ice cores, requiring reconstruction of original annual layer thicknesses by correcting for ice creep. An empirical approach was used that is based on the observed layer thicknesses from annual layer counting of the Eclipse ice cores. Accumulation records are highly reproducible with 73% of the signal shared between the three cores. The accumulation time-series shows considerable decadal scale variability that can be related to climate regimes that characterize the North Pacific. For example, periods of high accumulation are noted from 1470-1500, 1540-1560, and 1925-1975. Periods of low accumulation are observed between 1500-1540, 1680-1780, and 1875-1925. The strongest multi-year drop in accumulation is seen between 1979 and 1984, although there are isolated years with lower accumulation. This drop in accumulation is possibly related to the 1977 regime shift in the Pacific Decadal Oscillation. However, PDO regime shifts are not always reflected in the accumulation time series, implying a non-linear response or modulation by other modes of climate variability such as ENSO. Its is noteworthy that the Eclipse accumulation time series is out of phase with the accumulation time series from nearby Mount Logan on all time scales for reasons to be investigated.

Yalcin, K.; Wake, C. P.; Kreutz, K. J.

2005-12-01

339

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

340

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

341

Stable isotope variability in an ice core from the Tanggula Mountains, Central Tibetan Plateau  

NASA Astrophysics Data System (ADS)

A 33 m ice core was retrieved from the Tanggula Mts, central Tibetan Plateau at 5743 m a.s.l. in August 2005. Annual average ?18O values were determined for the upper 17 m depth (14.6 m w.eq.), representing the time series since the mid-1930s. Data are compared to previous results of an ice core from Mt. Geladaindong, 100 km to the northwest, for the period 1935-2003. During the time 1935-1960, ?18O values differed by 2-3‰ between the two ice cores, with generally lower ratios preserved in the Tanggula 2005 core. Differences in interannual variability and overall average ratios between the two study locations highlight the spatially variable climate controls on ice core isotope ratios within the boundary of monsoon- and westerly-impacted regions of the central Tibetan Plateau. Despite the statistically significant increase in isotope ratios, isotopic temperature dependence was not evident, based on comparison with long-term data from meteorological stations to the north and southwest of the study location. Lack of correlation between average ?18O values and temperature is likely due to monsoon influence, which results in relatively greater isotopic depletion of moisture during the warm season. Evidence of monsoon impacts on precipitation in the central Tibetan Plateau has been previously documented, and statistically significant negative correlation (r=-0.37, p<0.01) between the annual average ice core ?18O values and N. India monsoon rainfall was observed for the period 1935-2004. Although the ?18O data agree well with the monsoon rainfall amount, no significant correlation was observed between the core accumulation and the monsoon rainfall amount. Previous model and observational results suggest monsoon impact on ?18O in precipitation may extend beyond the immediate extent of heavy monsoon rainfall, reaching the central Tibetan Plateau. These results provide evidence that the ?18O variability at this study location may be sensitive to southern monsoon intensity. Recent ?D results may further quantify the ice core isotope variability in the context of moisture source regions, transport, and recycling.

Joswiak, D.; Yao, T.; Wu, G.; Xu, B.; Zheng, W.

2010-12-01

342

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

SciTech Connect

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

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

2000-02-27

343

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

PubMed Central

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

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

2009-01-01

344

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

345

Climatic and atmospheric circulation pattern variability from ice-core isotope\\/geochemistry records (Altai, Tien Shan and Tibet)  

Microsoft Academic Search

Several firn\\/ice cores were recovered from the Siberian Altai (Belukha plateau), central Tien Shan (Inilchek glacier) and the Tibetan Plateau (Zuoqiupu glacier, Bomi) from 1998 to 2003. The comparison analyses of stable-isotope\\/geochemistry records obtained from these firn\\/ice cores identified the physical links controlling the climate-related signals at the seasonal-scale variability. The core data related to physical stratigraphy, meteorology and synoptic

Vladimir B. Aizen; Elena M. Aizen; Daniel R. Joswiak; Koji Fujita; Nozomu Takeuchi; Stanislav A. Nikitin

2006-01-01

346

Black carbon concentration in Byrd Station ice core - From 13,000 to 700 years before present  

NASA Astrophysics Data System (ADS)

The concentration of black carbon in 22 ice core samples from Byrd Station (West Antarctica) covering the time period from about 13,000 to 700 years before present has been determined. For the first time, black carbon concentrations were obtained in an ice core which included a part of the last climatic transition. An average black carbon concentration of 0.1 micrograms/kg during the Wisconsin-Holocene climatic transition. After the transition the black carbon concentration in the ice core oscillated between 0.1 and 0.95 micrograms/kg, with an average concentration of 0.5 micrograms/kg. The increase in black carbon concentration occurred several hundred years after changes in delta-O-18, CO2 and CH4 characterizing the end of the last (Wisconsin) ice age. Expansion of the land biomass during the early Holocene was responsible for the observed increase of black carbon concentration in the Byrd Station ice core.

Chylek, P.; Johnson, B.; Wu, H.

1992-08-01

347

Microstructural variations in the Siple Dome, Antarctica ice core: Evidence of climate change?  

NASA Astrophysics Data System (ADS)

The Wisconsin section of the Siple Dome (Antarctica) ice core contains zones where mean crystal size and fabric change suddenly. One of these, at 675 m (15 ka) is coincident with evidence of abrupt climate change. Another, at 726 m (22 ka), may reflect a climate event, however, is more likely due to physical processes. In contrast to the larger crystal size and girdle orientation that develops between 360 m and 686 m, ice from 700 m to 800 m is remarkably fine-grained and has a strong vertical c-axis fabric. The latter is associated with strong horizontal shear, and may be related to the nearby Kamb and Bindschadler Ice Streams. However, there are a number of other factors potentially at work, including migration crystallization that begins around 600 m and a high number of volcanic ash layers between 700 m and 800 m. Further, after several years the core below 800 m remains brittle, indicating residual stress. Using electron backscatter diffraction and energy dispersive spectroscopy in an FEI XL-30 field emission gun environmental scanning electron microscope, we examine ice core samples from these periods to examine grain orientation and misorientation as a function of location and impurities in the grain boundaries in an effort to determine if changes in microstructure are manifestations of physical changes or if they reflect the changes in climate known to have taken place at least once during this period. This research was supported by the U.S. National Science Foundation Grant OPP-0738975.

Obbard, R. W.; Sieg, K. E.; Meese, D.; Baker, I.

2010-12-01

348

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

SciTech Connect

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

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

1993-02-05

349

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

350

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

351

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

NASA Astrophysics Data System (ADS)

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

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

352

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

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

353

Interpreting ice core records of inter-annual temperature change across the Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

The Antarctica Peninsula has a rapidly changing climate, however there is a paucity of long term meterological observations of temperature across the region. Decadal to centennial ice cores records can potentially help to fill this gap. Interpretation of the ice cores requires an understanding of the relationship between temperature change and the accumulation record recovered from each Peninsula core site. To facilitate this interpretation, we present an analysis of 22 years (1980-2002) of ECMWF ERA40 surface temperature, precipitation, and accumulation data. Inter-annual variability in temperature is quite is similar across the Peninsula. However, changes in the covariance between accumulation and temperature over the Peninsula region at the seasonal and synoptic time periods strongly affect the potential ice core recording of temperature change: with a clear trend in the fraction of inter-annual temperature change recorded along the Peninsula. It is likely that only about 25% of the actual inter-annual temperature change will be visible in the accumulation record at the northern end of the Peninsula near James Ross Island, 70% at Dyer in the central regions, and 120% at the southern end in the Gomez region. This study is likely to facilitate understand of decadal to centennial temperature change obtained from stable water isotopes in this sensitive polar region.

Sime, L.; Marshall, G.

2009-04-01

354

Variability of atmospheric dust loading over the central Tibetan Plateau based on ice core glaciochemistry  

NASA Astrophysics Data System (ADS)

A Mt. Geladaindong (GL) ice core was recovered from the central Tibetan Plateau (TP) spanning the period 1940-2005 AD. High-resolution major ion (Na + , K + , Ca 2+ , Mg 2+ , Cl - , SO 4 2- , NO 3 - ) time-series are used to investigate variations in atmospheric dust loading through time. The crustal source ions vary seasonally with peaks in dust concentrations occurring during the winter and spring which are consistent with atmospheric dust observations at local meteorological stations. However, both similarities and dissimilarities are displayed between the decadal variation of atmospheric dust in the GL core and dust observation records from meteorological stations, which can be attributed to local environmental effects at the stations. This paper compares the 1980s and 1970s as case periods for low and high atmospheric dust loading, respectively, two periods reflecting shifts in spring atmospheric circulation (a weakening of zonal and meridional winds) from the 1970s (a period of enhanced dust aerosol transportation to central TP) to the 1980s (a period of diminished dust aerosol transportation to central TP), especially a significant decrease of meridional wind speeds in the 1980s. GL ice core dust proxies (Ca 2+ and K + ) are correlated with Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) data in spring over the TP and in the northwestern China (especially for K + ). Thus variability of crustal ions in central TP ice core provides a proxy for reconstructing a history of atmospheric dust loading not only on the TP, but also in northwestern China.

Kang, Shichang; Zhang, Yulan; Zhang, Yongjun; Grigholm, Bjorn; Kaspari, Susan; Qin, Dahe; Ren, Jiawen; Mayewski, Paul

2010-08-01

355

Deconvolution-based resolution enhancement of chemical ice core records obtained by continuous flow analysis  

NASA Astrophysics Data System (ADS)

Continuous flow analysis (CFA) has become a popular measuring technique for obtaining high-resolution chemical ice core records due to an attractive combination of measuring speed and resolution. However, when analyzing the deeper sections of ice cores or cores from low-accumulation areas, there is still need for further improvement of the resolution. Here a method for resolution enhancement of CFA data is presented. It is demonstrated that it is possible to improve the resolution of CFA data by restoring some of the detail that was lost in the measuring process, thus improving the usefulness of the data for high-resolution studies such as annual layer counting. The presented method uses deconvolution techniques and is robust to the presence of noise in the measurements. If integrated into the data processing, it requires no additional data collection. The method is applied to selected ice core data sequences from Greenland and Antarctica, and the results demonstrate that the data quality can be significantly improved.

Rasmussen, S. O.; Andersen, K. K.; Johnsen, S. J.; Bigler, M.; McCormack, T.

2005-09-01

356

Applications of a rapid endospore viability assay for monitoring UV inactivation and characterizing arctic ice cores.  

PubMed

We have developed a rapid endospore viability assay (EVA) in which endospore germination serves as an indicator for viability and applied it to (i) monitor UV inactivation of endospores as a function of dose and (ii) determine the proportion of viable endospores in arctic ice cores (Greenland Ice Sheet Project 2 [GISP2] cores; 94 m). EVA is based on the detection of dipicolinic acid (DPA), which is released from endospores during germination. DPA concentrations were determined using the terbium ion (Tb3+)-DPA luminescence assay, and germination was induced by L-alanine addition. The concentrations of germinable endospores were determined by comparison to a standard curve. Parallel EVA and phase-contrast microscopy experiments to determine the percentage of germinable spores yielded comparable results (54.3% +/- 3.8% and 48.9% +/- 4.5%, respectively), while only 27.8% +/- 7.6% of spores produced CFU. EVA was applied to monitor the inactivation of spore suspensions as a function of UV dose, yielding reproducible correlations between EVA and CFU inactivation data. The 90% inactivation doses were 2,773 J/m2, 3,947 J/m2, and 1,322 J/m2 for EVA, phase-contrast microscopy, and CFU reduction, respectively. Finally, EVA was applied to quantify germinable and total endospore concentrations in two GISP2 ice cores. The first ice core contained 295 +/- 19 germinable spores/ml and 369 +/- 36 total spores/ml (i.e., the percentage of germinable endospores was 79.9% +/- 9.3%), and the second core contained 131 +/- 4 germinable spores/ml and 162 +/- 17 total spores/ml (i.e., the percentage of germinable endospores was 80.9% +/- 8.8%), whereas only 2 CFU/ml were detected by culturing. PMID:17021233

Shafaat, Hannah S; Ponce, Adrian

2006-10-01

357

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

358

The Southern Hemisphere at glacial terminations: insights from the Dome C ice core  

NASA Astrophysics Data System (ADS)

The many different proxy records from the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core allow for the first time a comparison of nine glacial terminations in great detail. Despite the fact that all terminations cover the transition from a glacial maximum into an interglacial, there are large differences between single terminations. For some terminations, Antarctic temperature increased only moderately, while for others, the amplitude of change at the termination was much larger. For the different terminations, the rate of change in temperature is more similar than the magnitude or duration of change. These temperature changes were accompanied by vast changes in dust and sea salt deposition all over Antarctica. Here we investigate the phasing between a South American dust proxy (non-sea-salt calcium flux, nssCa2+), a sea ice proxy (sea salt sodium flux, ssNa+) and a proxy for Antarctic temperature (deuterium, ?D). In particular, we look into whether a similar sequence of events applies to all terminations, despite their different characteristics. All proxies are derived from the EPICA Dome C ice core, resulting in a relative dating uncertainty between the proxies of less than 20 years. At the start of the terminations, the temperature (?D) increase and dust (nssCa2+ flux) decrease start synchronously. The sea ice proxy (ssNa+ flux), however, only changes once the temperature has reached a particular threshold, approximately 5°C below present day temperatures (corresponding to a ?D value of -420‰). This reflects to a large extent the limited sensitivity of the sea ice proxy during very cold periods with large sea ice extent. At terminations where this threshold is not reached (TVI, TVIII), ssNa+ flux shows no changes. Above this threshold, the sea ice proxy is closely coupled to the Antarctic temperature, and interglacial levels are reached at the same time for both ssNa+ and ?D. On the other hand, once another threshold at approximately 2°C below present day temperature is passed (corresponding to a ?D value of -402‰), nssCa2+ flux has reached interglacial levels and does not change any more, despite further warming. This threshold behaviour most likely results from a combination of changes to the threshold friction velocity for dust entrainment and to the distribution of surface wind speeds in the dust source region.

Röthlisberger, R.; Mudelsee, M.; Bigler, M.; de Angelis, M.; Fischer, H.; Hansson, M.; Lambert, F.; Masson-Delmotte, V.; Sime, L.; Udisti, R.; Wolff, E. W.

2008-12-01

359

2000 Year Atmospheric History of Methyl Bromide and Methyl Chloride from an Antarctic Ice Core  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) and methyl bromide (CH3Br) mixing ratios have been measured in air extracted from 50 Antarctic ice core samples from South Pole (SPRESSO-2002), extending the atmospheric history for these trace gases to roughly 2000 years before present. Ice core samples (~ 500g) were shredded at -40°C to -50°C to extract ~ 40 cm3 of air that was analyzed by a gas chromatography/mass spectrometry system. CH3Br mixing ratios vary between 4.5 ppt to 6.5 ppt with a mean of 5.6±0.8 ppt. These results are in good agreement with the 350-year record of CH3Br previously measured in ice cores from Siple Dome, Antarctica. The ice core data provide evidence that, for over 2000 years, CH3Br levels were 2-4 ppt lower that the modern ambient levels of 7-8 ppt (Southern Hemisphere) that peaked in late 1990s and have been declining since regulation of its use as part of Montreal protocol. The mean mixing ratio of CH3Cl is 463.0±16.0 ppt with values ranging from 418.0 ppt to 543.0 ppt. These levels are also consistent with the range of values measured in the Siple Dome core. Modern ambient mixing ratios in the Southern Hemisphere are on the order of 500-550ppt, indicating that anthropogenic contributions to the modern CH3Cl budget are relatively small. Measured CH3Cl levels vary by as much as 50ppt over 50 year periods. Periodicity in CH3Cl observed in Siple Dome is not obvious in this record, but cannot be precluded due to the lower time resolution of the SPRESSO core. These measurements constitute the longest atmospheric record for both gases and demonstrate the fidelity of the ice core gas record for these trace gases over millennial time scales. There is potential for constructing records extending beyond the Holocene, and over glacial/interglacial transitions for these trace gases. It is unclear how either of these gases responds to changing climate. Shifts in plant emissions, soil uptake, ocean production, and atmospheric oxidation capacity due to past climate changes may all manifest in CH3Cl and CH3Br records. Establishing a paleoatmospheric record for these and other trace gases should improve the understanding of these feedbacks.

Williams, M. B.; Aydin, M.; Saltzman, E. S.

2005-12-01

360

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

361

A 100 yr Ice Core Record of Anthropogenic Activity, Volcanic Eruptions, and Biomass Burning From the Siberian Altai  

NASA Astrophysics Data System (ADS)

The 50m upper part from 170m of total deep ice core was retrieved from the Belukha snow-ice plateau (49°48°N, 86°32°E, 4110m.a.s.l.) in the summer of 2003 representing the time series since the beginning of the 20th Century. Data on high-resolution physical stratigraphy and density, as well as geochemical data including major ions, stable (?18O) and radiogenic (?3H) isotopes were developed for ice-core dating, climatic and environmental analysis. A clear tritium isotope ratio peak associated with the global maximum nuclear testing of the early 1960's, and a soluble major ion peak coincident with the eruption of Mt. Katmai in 1912 reveals a linear depth-age scale for the upper 50m and indicates an average accumulation rate of 376m.w.e. Major soluble ions sulfate and nitrate showed the greatest increase subsequent to the 1950's, and provides evidence for direct effects associated with increased atmospheric aerosol loading from industrialized activity in central Asia. Extremely low sulfate and nitrate concentrations (<3.0?Eq/L average) before the 1950's approximate atmospheric background levels. Sulfate concentrations decrease rapidly during the time period associated with the early 1990's, providing an example of the effects of short-run deindustrialization subsequent to the dissolution of the Soviet Union. Ammonium concentrations reveal an association with documented periods of extended boreal forest fires during the 1960's and 1970's. Elevated calcium concentrations during the 1950's and 1960's correspond to the reported period of maximum dust activity in China since 1950.

Joswiak, D. R.; Aizen, E.; Aizen, V.; Takeuchi, N.; Sneed, S.

2007-12-01

362

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

363

Assessment of the Relationship between Andean Ice Core Precipitation Indicators and Amazon River Discharge  

NASA Astrophysics Data System (ADS)

Prior to the last 100 years, there is a significant lack of hydrologic knowledge for the Amazon Basin. A 100- year record of discharge from the city of Manaus, located at the confluence of the Solimoes and Negro rivers, is the most complete record for the basin. Inundated wetlands play a key role in carbon out-gassing to the atmosphere whereas discharge from the Amazon River contributes about 20% of the total freshwater flux delivered to the world's oceans. As discharge (Q) and inundation are directly related to precipitation, we are developing a method to extend our understanding of Q and inundation into the 19^{th} century. Using proxy data preserved in Andean glaciers and ice caps and recovered from ice cores, annually resolved histories of ?^{18)O and mass accumulation are available. The latter is a proxy for local precipitation amount whereas ?18O is influenced by continental scale processes (i.e., evaporation, convection) as well as by temperature and hence, by varying climate regimes. We have correlated the accumulation and ?18O records from Core 1 drilled on the Quelccaya ice-cap in the southern Andes of Peru with the Manaus discharge data. As ice core annual layers correspond to the thermal year (in Peru, July to June of the following year) and the discharge records are kept daily (January to December), we averaged 365 days of Q data seeking the optimal correlation for each start and end date. The best statistical relationship between ?18O and Q (r = -0.41, p = < 0.001) is attained when Q is averaged from March 16 to March 15 of the following year. We also correlated 23 years of ENSO events, which are linked to both Amazon River discharge and ice core ?18O (r = -0.60, p = < 0.001). These linear relationships are used to create Amazon discharge for the 20^{th} century and to extrapolate Q into the 19^{th} century. Previously developed relationships between Q and mainstem inundated area are then used to estimate inundated area along the main Amazon channel for the past 200 years. The ice core-derived estimate of inundated area for the past 100 years compares well with the previous and more straightforward estimates based on discharge and remote sensing data.

Johnson, N.; Alsdorf, D.; Thompson, L.; Mosley-Thompson, E.; Melack, J.

2006-12-01

364

Anomalous sulfur isotope compositions of volcanic sulfate over the last millennium in Antarctic ice cores  

NASA Astrophysics Data System (ADS)

The reconstruction of past volcanism from glaciological archives is based on the measurement of sulfate concentrations in ice. This method does not allow a proper evaluation of the climatic impact of an eruption owing to the uncertainty in classifying an event between stratospheric or tropospheric. This work develops a new method, using anomalous sulfur isotope composition of volcanic sulfate in order to identify stratospheric eruptions over the last millennium. The advantages and limits of this new method are established with the examination of the 10 largest volcanic signals in ice cores from Dome C and South Pole, Antarctica. Of the 10, seven are identified as stratospheric eruptions. Among them, three have been known to be stratospheric (Tambora, Kuwae, the 1259 Unknown Event) and they exhibit anomalous sulfur isotope compositions. Three unknown events (circa 1277, 1230, 1170 A.D.) and the Serua eruption have been identified as stratospheric eruptions, which suggests for the first time that they could have had significant climatic impact. However, the Kuwae and the 1259 Unknown Event stratospheric eruptions exhibit different anomalous sulfur isotope compositions between South Pole and Dome C samples. Differences in sulfate deposition and preservation patterns between the two sites can help explain these discrepancies. This study shows that the presence of an anomalous sulfur isotope composition of volcanic sulfate in ice core indicates a stratospheric eruption, but the absence of such composition does not necessarily lead to the conclusion of a tropospheric process because of differences in the sulfate deposition on the ice sheet.

Baroni, MéLanie; Savarino, JoëL.; Cole-Dai, Jihong; Rai, Vinai K.; Thiemens, Mark H.

2008-10-01

365

Atmospheric methane, record from a Greenland ice core over the last 1000 year  

SciTech Connect

This paper describes results of two recent analyses of ice core samples drilled in Greenland for enclosed methane. Ice cores provide a record of some atmospheric gases which dates back far into the past. Improved drilling techniques, in conjunction with better analysis has allowed more accurate dating and more accurate measurements of methane concentrations, which allows the resolution of variations in the record over the past 1000 years. The hope is that by correlating such variations with different climatic events or factors, one can gain information on how the earth responds to changes in the methane concentrations in the atmosphere. Recent anthropogenic increases have been recorded, but the response of sinks is not well understood.

Blunier, T.; Schwander, J.; Stauffer, B. (Univ. of Bern (Switzerland)); Chappellaz, J.A.; Barnola, J.M.; Raynaud, D. (CNRS Laboratorie de Glaciologie, Grenoble (France))

1993-10-22

366

An ice-core record of atmospheric response to anthropogenic sulphate and nitrate  

NASA Astrophysics Data System (ADS)

RECORDS of sulphate and nitrate concentrations in ice cores show that these concentrations have increased recently because of the long-range transport of pollution from middle latitudes1-5. But these records have been neither complete enough nor long enough to allow an assessment of their sensitivity to variations in the emissions of sulphate and nitrate precursors. We have now analysed sections from an ice core in South Greenland which have allowed us to extend its sulphate and nitrate record back from 1869 to 1767. This longer record has enabled us to determine the pre-industrial natural interannual variability of non-sea-salt sulphate and nitrate. We find that the background concentration in the remote atmosphere over South Greenland is sensitive to changes in the anthropogenic emissions of sulphate and nitrate, and responds to these variations on a timescale of the order of decades.

Mayewski, P. A.; Lyons, W. B.; Spencer, M. J.; Twickler, M. S.; Buck, C. F.; Whitlow, S.

1990-08-01

367

Seasonal climate information preserved in West Antarctic ice core water isotopes: relationships to temperature, large-scale circulation, and sea ice  

NASA Astrophysics Data System (ADS)

As part of the United States' contribution to the International Trans-Antarctic Scientific Expedition (ITASE), a network of precisely dated and highly resolved ice cores was retrieved from West Antarctica. The ITASE dataset provides a unique record of spatial and temporal variations of stable water isotopes (?18O and ?D) across West Antarctica. We demonstrate that, after accounting for water vapor diffusion, seasonal information can be successfully extracted from the ITASE cores. We use meteorological reanalysis, weather station, and sea ice data to assess the role of temperature, sea ice, and the state of the large-scale atmospheric circulation in controlling seasonal average water isotope variations in West Antarctica. The strongest relationships for all variables are found in the cores on and west of the West Antarctic Ice Sheet Divide and during austral fall. During this season positive isotope anomalies in the westernmost ITASE cores are strongly related to a positive pressure anomaly over West Antarctica, low sea ice concentrations in the Ross and Amundsen Seas, and above normal temperatures. Analyses suggest that this seasonally distinct climate signal is due to the pronounced meridional oriented circulation and its linkage to enhanced sea ice variations in the adjacent Southern Ocean during fall, both of which also influence local to regional temperatures.

Küttel, Marcel; Steig, Eric J.; Ding, Qinghua; Monaghan, Andrew J.; Battisti, David S.

2012-10-01

368

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01