These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

NSDL National Science Digital Library

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

Nation, Nsf S.; Institute, Jim W.

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

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

4

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

5

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

NASA Astrophysics Data System (ADS)

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for the Summit cores that are consistent with the GICC05modelext timescale by utilizing both existing and new unpublished gas data.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

Seierstad, Inger K.; Rasmussen, Sune O.

2014-05-01

6

Ice core drilling at Vostok  

NSF Publications Database

... Subject: Initial Environmental Evaluation (Deep Ice Core Drilling at Vostok Station, Antarctica ... for the National Science Foundation's Deep Ice Core Drilling project at Vostok Station, prepare an ...

7

Ice Core Exercise  

NSDL National Science Digital Library

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

Locke, William

8

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

9

Vostok Ice Core: Excel (Mac or PC)  

NSDL National Science Digital Library

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

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

10

Evidence of Historical Supernovae in Ice Cores  

NASA Astrophysics Data System (ADS)

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

Young, Donna

2011-05-01

11

Ice Core Paleoclimatology Research Group  

NSDL National Science Digital Library

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

Center, Byrd P.; University, Ohio S.

12

Vostok Ice Core Lab Activity  

NSDL National Science Digital Library

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

Sciences, Department O.; University, Columbia

13

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

14

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.

15

CO2 in the Ice Core Record  

NSDL National Science Digital Library

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

Productions, Geoff H.; Manual, Earth: T.

16

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

17

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

E-print Network

Using ice cores from the East Antarctic Ice Sheet, scientists have been able to study ice's ice sheets. Ice sheets are huge areas of permanent ice. There are only three ice sheets on Earth: the Greenland Ice Sheet, the West Antarctic Ice Sheet, and the East Antarctic Ice Sheet. The Greenland Ice Sheet

18

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.

19

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

20

Dielectric stratigraphy of ice: A new technique for determining total ionic concentrations in polar ice cores  

SciTech Connect

A 133 m deep Antarctic ice core from Dolleman Island, Antarctic Peninsula, has been profiled by dielectric measurements in the AF-LF (20 Hz - 100 kHz) frequency range. This has revealed large variations in dielectric relaxation and conductivity down the core. A comparison with the chemical stratigraphy along 45 m of the core demonstrates for the first time the decisive role played by acids and salts in determining the electrical behavior of natural ice. The total ionic concentration along the ice core can be deduced from the dielectric response. This technique may be applied rapidly in the field and, as it requires no contact between ice core and electrodes, the core is maintained in pristine condition for later chemical analysis.

Moore, J.C.; Mulvaney, R.; Paren, J.G. (British Antarctic Survey, Cambridge (England))

1989-10-01

21

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

PubMed

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

Ahn, Jinho; Brook, Edward J

2014-01-01

22

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

PubMed Central

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

Ahn, Jinho; Brook, Edward J.

2014-01-01

23

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

24

Color Reveals Translucent Seasonal Ice  

NASA Technical Reports Server (NTRS)

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

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

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

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

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

2007-01-01

25

ORIGINAL PAPER A bacterial ice-binding protein from the Vostok ice core  

E-print Network

Bacterial and yeast isolates recovered from a deep Antarctic ice core were screened for proteins with ice found in sea ice diatoms, a snow mold, and a sea ice bacterium. The protein has the ability to inhibit Introduction The Vostok Ice Core represents a cross-section of the East Antarctic Ice Sheet to a depth of over

Christner, Brent C.

26

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

27

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

PubMed

Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 - beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20(th) century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19(th) century and remains a significant source today. An estimated 660?t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21(st) century. PMID:25068819

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

2014-01-01

28

Measurements of ethane in Antarctic ice cores  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

29

Large variations in Holocene solar activity: Constraints from 10Be in the Greenland Ice Core Project ice core  

Microsoft Academic Search

Cosmogenic radionuclides extracted from ice cores hold a unique potential for reconstructing past solar activity changes beyond the direct instrumental period. Taking the geomagnetic modulation into account, the solar activity in terms of the heliospheric modulation function can quantitatively be reconstructed in high resolution throughout the Holocene. For this period our results reveal changes in heliospheric modulation of galactic cosmic

Maura Vonmoos; Jürg Beer; Raimund Muscheler

2006-01-01

30

NOAA Paleoclimatology Program - Vostok Ice Core Data  

NSDL National Science Digital Library

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

Center, National C.; Noaa

31

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

32

Tropical ice core records: evidence for asynchronous glaciation on Milankovitch  

Microsoft Academic Search

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

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

33

Biological proxies recorded in a Belukha ice core, Russian Altai  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

34

O record of NGRIP ice core  

NASA Astrophysics Data System (ADS)

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

Shao, Zhi-Gang; Wang, Hui-Hui

2014-10-01

35

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

36

Methane - The record in polar ice cores  

Microsoft Academic Search

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

H. Craig; C. C. Chou

1982-01-01

37

Early Holocene climate oscillations recorded in three Greenland ice cores  

Microsoft Academic Search

A new ice core chronology for the Greenland DYE-3, GRIP, and NGRIP ice cores has been constructed, making it possible to compare the ?18O and accumulation signals recorded in the three cores on an almost annual scale throughout the Holocene. We here introduce the new time scale and investigate ?18O and accumulation anomalies that are common to the three cores

S. O. Rasmussen; B. M. Vinther; H. B. Clausen; K. K. Andersen

2007-01-01

38

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

Microsoft Academic Search

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

Tandong Yao; Yafeng Shi; L. G. Thompson

1997-01-01

39

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

40

Ice Core Paleoclimate Research Group Ellen Mosley-Thompson  

E-print Network

Ice Core Paleoclimate Research Group Ellen Mosley-Thompson Henry Brecher Mary Davis Paolo Gabrielli Funding provided by: NSF: Paleoclimate and Polar Programs NASA: Earth Sciences (Glaciology) NOAA Speleothems Various archival systems provide paleoclimate records #12;Dasuopu Glacier Southern Tibet Ice cores

Howat, Ian M.

41

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

42

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

Microsoft Academic Search

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

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

1990-01-01

43

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

44

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

NASA Astrophysics Data System (ADS)

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

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

2010-11-01

45

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

NASA Astrophysics Data System (ADS)

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

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

2007-08-01

46

AVHRR imagery reveals Antarctic ice dynamics  

SciTech Connect

A portion of AVHRR data taken on December 5, 1987 at 06:15 GMT over a part of Antarctica is used here to show that many of the most significant dynamic features of ice sheets can be identified by a careful examination of AVHRR imagery. The relatively low resolution of this instrument makes it ideal for obtaining a broad view of the ice sheets, while its wide swath allows coverage of areas beyond the reach of high-resolution imagers either currently in orbit or planned. An interpretation is given of the present data, which cover the area of ice streams that drain the interior of the West Antarctic ice sheet into the Ross Ice Shelf. 21 refs.

Bindschadler, R.A.; Vornberger, P.L. (NASA, Goddard Space Flight Center, Greenbelt, MD (United States) STX Corp., Lanham, MD (United States))

1990-06-01

47

First investigations of an ice core from Eisriesenwelt cave (Austria)  

NASA Astrophysics Data System (ADS)

Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria). In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (?18O, ?D) and electrolytic conductivity profiles supplemented by specifically selected samples analysed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb derived tritium removing any ice accumulated, since at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses made radiocarbon dating inconclusive, though a crude estimate gave a maximum ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 4 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cyro-calcite layers, a extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (?D versus ?18O) of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow) freezing of dripping water.

May, B.; Spötl, C.; Wagenbach, D.; Dublyansky, Y.; Liebl, J.

2010-09-01

48

First investigations of an ice core from Eisriesenwelt cave (Austria)  

NASA Astrophysics Data System (ADS)

Investigations into the genesis and dynamical properties of cave ice are essential for assessing the climate significance of these underground glaciers. We drilled an ice core through a 7.1 m-thick ice body filling a large cavern of the dynamic ice cave Eisenriesenwelt (Austria). In addition to visual core inspections, quasi-continuous measurements at 2 cm resolution comprised particulate matter, stable water isotope (?18O, ?D) and electrolytic conductivity profiles supplemented by specifically selected samples analyzed for tritium and radiocarbon. We found that recent ablation led to an almost complete loss of bomb-derived tritium removing any ice accumulated since, at least, the early fifties leaving the actual ice surface even below the natural tritium level. The small particulate organic masses rendered radiocarbon dating inconclusive, though a crude estimate gave a basal ice age in the order of several thousand years. The visual stratigraphy and all investigated parameters showed a clear dichotomy between the upper 2 m and the bottom 3 m of the core, which points to a substantial change in the ice formation process. Main features of the core comprise the changing appearance and composition of distinct cryocalcite layers, extremely low total ion content and a surprisingly high variability of the isotope signature. Co-isotope evaluation (?D versus ?18O) of the core in comparison with data from precipitation and karst spring water clearly indicate that ice formation is governed by (slow) freezing of dripping water.

May, B.; Spötl, C.; Wagenbach, D.; Dublyansky, Y.; Liebl, J.

2011-02-01

49

A bacterial ice-binding protein from the Vostok ice core.  

PubMed

Bacterial and yeast isolates recovered from a deep Antarctic ice core were screened for proteins with ice-binding activity, an indicator of adaptation to icy environments. A bacterial strain recovered from glacial ice at a depth of 3,519 m, just above the accreted ice from Subglacial Lake Vostok, was found to produce a 54 kDa ice-binding protein (GenBank EU694412) that is similar to ice-binding proteins previously found in sea ice diatoms, a snow mold, and a sea ice bacterium. The protein has the ability to inhibit the recrystallization of ice, a phenotype that has clear advantages for survival in ice. PMID:18622572

Raymond, James A; Christner, Brent C; Schuster, Stephan C

2008-09-01

50

Investigating snow accumulation variability on the Antarctic Peninsula using Ground Penetrating Radar - A tool for interpreting ice core records  

Microsoft Academic Search

In this study Ground Penetrating Radar (GPR) has been used to investigate snow accumulation variability in the southwestern Antarctic Peninsula to aid the interpretation of a new ice core record. The GPR revealed homogeneity in the observed isochrones to a depth of 150 meters, encompassing the depth of the ice core (136 meters), over a 20 km radius from the

Elizabeth R. Thomas

51

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

52

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

53

North Atlantic Deep Water Formation: Information from Ice Cores  

NASA Technical Reports Server (NTRS)

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

Oeschger, H.

1984-01-01

54

Ice core drilling at McMurdo Dome  

NSF Publications Database

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

55

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

NASA Astrophysics Data System (ADS)

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

Schomacker, A.; Kjaer, K. H.

2007-12-01

56

Eemian interglacial reconstructed from a Greenland folded ice core.  

PubMed

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8?±?4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400?±?250 metres, reaching surface elevations 122,000 years ago of 130?±?300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future. PMID:23344358

2013-01-24

57

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

58

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

59

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

60

A first chronology for the NEEM ice core  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

61

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

62

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

63

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

64

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

65

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

66

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

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

68

Apollo Rock Reveals Moon Had Molten Core | Universe Additional Resources  

E-print Network

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

Weiss, Benjamin P.

69

Chemistry of microparticles trapped in last glacial period ice of EPICA-DML deep ice core  

NASA Astrophysics Data System (ADS)

The EDML ice core, drilled within the framework of the European project for Ice Coring in Antarctica, (EPICA), in the interior of Dronning Maud Land, DML, Antarctica (at 75°S, 0°E), is the first deep ice core in the Atlantic sector of the Southern Ocean region that provides higher-resolution atmosphere and climate records for the last glacial period, when compared with other ice cores retrieved from the East Antarctic plateau [1]. The chemical impurities embedded in the ice matrix of an ice sheet are basic proxies for climate reconstruction, and their concentration and composition usually determine the occurrence of distinct (cloudy or clear) strata in the ice sheet structure. The easiest observable impurities in polar ice are air bubbles. But a considerable amount of the impurities trapped inside ice layers are observed as microscopic deposits of solid (soluble or insoluble) particles, not bigger than a few micra in size, called microinclusions. Layers of ice with a high content of (micro)inclusions are in general called cloudy bands and are considered to have been formed from the precipitations deposited during colder periods. Roughly, we expect that the colder the climate during the time the snow accumulated, the cloudier the ice stratum that forms afterwards [2]. Mainly by means of in-situ micro-Raman spectroscopy, it has been shown that in Antarctic glacial ice the soluble microinclusions occur mostly as sulphate and nitrate salts [3], while in Arctic ice more commonly as carbonate salts [4]. These findings could be explained in terms of different aerosol compositions determined by the specific regional environments and climatic conditions [5]. Regarding the insoluble particles that might exist in natural ice, with higher frequency in ice layers formed during glacial type stages, the general findings classify them in the (alumino)silicate mineralogical class [6]. Microinclusions existent in solid samples taken from clear and cloudy ice layers, corresponding to the Marine Isotope Stage 2 of the EDML deep ice core, were subjected to in-situ Raman scattering measurements. The overall results [7] resemble the observations [8] that a high content of sulphate anions could characterize the chemical composition of the aerosols arriving at the EDML ice core drilling site. Many microparticles provided a Raman signal different from what would be expected if only simple compounds were forming them (and dissimilar with those in [3]). For example, it resulted that in the same microinclusion nonequivalent sulphate groups are present (20% of all), or that sulphate and silicate anions coexist (10% of all). On the one hand, this can be explained by a simple post-depositional aggregation of very small inclusions of simple sulphate salts into microclusters. On the other hand the results might be interpreted in terms of aerosol chemistry, when a mixture of sulphate salts could have been already formed prior to deposition. This work will offer answers for questions related with the existence of a post-depositional alteration of the initial impurities deposited in the LGP ice at the EDML ice core drilling site. [1] EPICA community members (2006). One-to-one coupling of glacial climate variability in Greenland and Antarctica, Nature, 444, 195-198. [2] Faria, S.H., Freitag, J., Kipfstuhl, S. (2010) Polar ice structure and the integrity of ice-core paleoclimate records, Quaternary Sci. Rev., 29, 1-2, 338-351. [3] Ohno H., M. Igarashi, T. Hondoh. 2005. Salt inclusions in polar ice core: Location and chemical form of water-soluble impurities, Earth Planet.Sci. Lett., 232, 171-178. [4] Sakurai T., Iizuka Y., Horikawa S., Johnsen S., Dahl-Jensen D., Steffensen J.P., Hondoh T. (2009). Direct observation of salts as micro-inclusions in the Greenland GRIP ice core. J. Glaciol., 55, 193, 777-783. [5] Iizuka Y., Horikawa S., Sakurai T., Johnson S, Dahl-Jensen D., Steffensen J.P., Hondoh T. (2008). A relationship between ion balance and the chemical compounds of salt inclusions found in the Greenland Ice Core Project and Dome Fuji ice cores. J. Geop

Nedelcu, Aneta F.; Faria, Sérgio H.; Kipfstuhl, Sepp; Kuhs, Werner F.

2010-05-01

70

High Resolution Continuous Flow Analysis System for Polar Ice Cores  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

71

VOLCANIC RECORDS AND DATING OF AN UPPER HALF OF THE H15 ICE CORE FROM MIZUHO PLATEAU, EAST ANTARCTICA  

Microsoft Academic Search

Two closely-spaced peaks of electrical conductivity were foundat depths between 45 and 50 m of the 120-m long ice core drilled at site H15 in Antarctica by the 32nd Japanese Antarctic Research Expedition in 1991. Chemical analysis of the core containing these peaks revealed that the ice layers were characterized by high acidity and high sulfate concentration suggesting volcanic signals.

Mika KOHNO; Takaaki FUKUOKA; Yoshiyuki FUJII; Minoru KUSAKABE

1996-01-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

73

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

74

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.

75

Mechanical properties of fresh ice core from Dye 3, Greenland  

NASA Astrophysics Data System (ADS)

Mechanical property studies were carried out on fresh ice-core samples as they were recovered at Dye 3, Greenland. Experiments were conducted in uniaxial compression tests under constant crosshead speed, simpler shear tests under constant load, and indentation hardness tests with Vickers pyramidal indenîer. Tests were made within a one-month period after each specimen was recovered to minimize the effect of volume relaxation. Experimental results from uniaxial compression and simple shear tests were analyzed in effective shear stress and effective strain rate space, taking into account the effect of high-pressure air bubbles included in each sample. The strain rate of Wisconsin ice is about one order of magnitude higher than that of randomly oriented laboratory ice at the same stress level, possibly enhanced by the effect of impurities in addition to that of fabrics. Indentation deformation was observed to be attributed to pileup, cracking, and creep of ice material around an indenter with c-axis orientation dependency.

Shoji, Hitoshi; Langway, Chester C., Jr.

76

South Pole paleowind from automated synthesis of ice core records  

Microsoft Academic Search

We develop a fully automated reconstruction of South Pole surface roughness as a measure of past wind intensity, using dynamic warping feature recognition and internal consistency checks to reduce subjectivity and analysis time. We synchronized millimeter-resolution optical profiles of deep South Pole glacial dust together with ice core data between the ages 26 and 90 thousand years B.P. The images

R. C. Bay; R. A. Rohde; P. B. Price; N. E. Bramall

2010-01-01

77

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

78

Ice Cube Observed PeV Neutrinos from AGN Cores  

E-print Network

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

Floyd W. Stecker

2013-05-31

79

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

80

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

81

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

82

Biological proxies recorded in a Belukha ice core, Russian Altai  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

83

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

NASA Astrophysics Data System (ADS)

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

Parrenin, F.

2014-10-01

84

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

85

Ice Core Evidence to support a Paleo Global Moonsoon  

NASA Astrophysics Data System (ADS)

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

Sowers, T. A.

2013-05-01

86

Atmospheric CO2 Over the Last 1000 Years: WAIS Divide Ice Core Record  

NASA Astrophysics Data System (ADS)

How atmospheric CO2 varied over the last thousands years is of great interest because we may see not only natural, but also anthropogenic variations (Ruddiman, Climatic Change, 2003). The Law Dome ice cores reveal decadal to centennial variations in CO2 over the last 2000 years (MacFarling Meure et al., Geophys. Res. Lett., 2006). However, these variations have not yet been well confirmed in other ice core records. Here we use a newly drilled WAIS Divide ice core, which is ideal for this purpose because WAIS Divide has relatively high snow accumulation rate and small gas age distribution that allow us to observe decadal CO2 variations with minimal damping. We have started an extensive study of CO2 in WAIS Divide core. So far we have obtained data for 960-1940 A.D. from the WDC05-A core drilled in 2005-2006. 344 ice samples from 103 depths were analyzed and the standard error of the mean is ~0.8 ppm on average. Ancient air in 8~12 g of bubbly ice is liberated by crushing with steel pins at -35 °C and trapped in stainless steel tubes at -262 °C. CO2 mixing ratio in the extracted air is precisely determined using a gas chromatographic method. Details of the high-precision methods are described in Ahn et al. (J. of Glaciology, in press). Our new results show preindustrial atmospheric CO2 variability of ~ 10 ppm. The most striking feature of the record is a rapid atmospheric CO2 decrease of 7~8 ppm within ~20 years at ~ 1600 A.D. Considering the larger smoothing of gas records in the WAIS Divide relative to Law Dome, our results confirm the atmospheric CO2 decrease of ~10 ppm in Law Dome records observed at this time. However, this event is not significant in the Dronning Maud Land ice core (Siegenthaler et al., Tellus, 2005), probably due to more extensive smoothing of gas records in the core. Similar rapid changes of CO2 at other times in the WAIS Divide record need to be confirmed with higher resolution studies. We also found that our WAIS Divide CO2 data are slightly higher than those of Law Dome by 3~5 ppm over most of the record. It is not clear whether the offset is due to real variability in ice cores or an analytical offset. We are participating in international laboratory intercalibration to determine the origin of the offset. Several WDC05-A and Law Dome ice samples are shared and will be analyzed for data comparison with CSIRO (Australian Common Wealth Scientific and Research Organization).

Ahn, J.; Brook, E. J.

2009-04-01

87

Preferred slip band orientations and bending observed in the Dome Concordia ice core  

E-print Network

Preferred slip band orientations and bending observed in the Dome Concordia ice core S´ergio H Oct. 2003 #12;Preferred slip band orientations and bending observed in the Dome Concordia ice core S, Columbusstra�e, D-27568 Bremerhaven, Germany ABSTRACT. Fabric analysis of the upper 1300 m of the Dome C ice core

88

Investigating the preservation of nitrate isotopic composition in a tropical ice core  

E-print Network

Investigating the preservation of nitrate isotopic composition in a tropical ice core from University, Columbus, Ohio, USA Abstract The nitrogen and oxygen isotopic composition of nitrate in ice cores of nitrate in ice cores, however, must first consider that nitrate in snow is vulnerable to postdepositional

Howat, Ian M.

89

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

90

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

NASA Astrophysics Data System (ADS)

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

Masson-Delmotte, V.; Landais, A.

2013-12-01

91

Sources of excess CO2 in Greenland ice cores  

NASA Astrophysics Data System (ADS)

Analysis of air extracted from bubbles of Greenland ice show higher CO2 concentrations compared to coeval data from Antarctica with unexpected high variations of several ppm CO2 in adjacent samples. Both offset and variations are too large to be of atmospheric origin such as the inter-hemispheric gradient and can also not be explained by analytical uncertainties. Higher ice temperatures and impurity content favour post depositional processes such as reactions between the contained chemical species; this could explain enhanced variability and higher CO2 concentrations in Greenlandic compared to Antarctic ice. Various chemical reaction mechanisms leading to such CO2 in-situ production have been proposed (i.e. acidification of carbonates, oxidation of aldehydes and photodecarboxilation of humic like substances). We tested the above hypotheses combining analysis of CO2, ?13C-CO2 and chemical impurities in samples of various age and depth resolution including three Greenlandic sites (Eurocore, GRIP, NGRIP) which allowed quantification of inorganic and organic source contribution to the observed excess CO2 by using an isotopic mass balance model. The model output was investigated by comparison to the reaction-specific tracers of chemical impurities. In agreement with previous studies, our results suggest that the amount of excess CO2 in Greenland ice increases with time. We find the isotopic signature of the excess CO2 to have a more negative ?13C compared to the coeval atmospheric value. The isotopic mass balance model attributes the excess CO2 to a combination of organic and inorganic sources. The contribution from the organic source is dominant and increases with time, pointing to ongoing production in the ice for more than 1000 years. The contribution of the carbonate source is much smaller, independent of the age of the ice and tendentially enhanced in layers associated with high peaks of dust concentrations. The mechanisms and kinetics of the involved processes seem consistent between the different sites and ice sections of different ages. Based on our results we can furthermore not exclude that a small portion of the excess CO2 is already produced in the lock-in zone of the firn (i.e. during bubble close-off). If and to what extent this finding in Greenland ice cores is also present in Antarctic ice cores is part of the debate.

Jenk, T. M.; Rubino, M.; Etheridge, D. M.; Bigler, M.; Blunier, T.

2012-12-01

92

Could a new ice core offer an insight into the stability of the West Antarctic Ice Sheet during the last interglacial?  

NASA Astrophysics Data System (ADS)

Vaughan et al., in their 2011 paper 'Potential Seaways across West Antarctica' (Geochem. Geophys. Geosyst., 12, Q10004, doi:10.1029/2011GC003688), offer the intriguing prospect that substantial ice loss from the West Antarctic Ice Sheet during the previous interglacial period might have resulted in the opening of a seaway between the Weddell Sea and the Amundsen Sea. One of their potential seaways passes between the south western corner of the present Ronne Ice Shelf and the Pine Island Bay, through what is currently the course of the Rutford Ice Stream, between the Ellsworth Mountains and the Fletcher Promontory. To investigate whether this seaway could have existed (and to recover a paleoclimate and ice sheet history from the Weddell Sea), a team from the British Antarctic Survey and the Laboratoire de Glaciologie et Géophysique de l'Environnement drilled an ice core from a close to a topographic dome in the ice surface on the Fletcher Promontory in January 2012, reaching the bedrock at 654.3m depth from the surface. The site was selected to penetrate directly through the centre of a Raymond cupola observed in internal radar reflections from the ice sheet, with the intention that this would ensure we obtained the oldest ice available from the Fletcher Promontory. The basal ice sheet temperature measured was -18°C, implying the oldest ice would not have melted away from the base, while the configuration of the Raymond cupola in the radar horizons suggested stability in the ice dome topography during the majority of the Holocene. Our hypothesis is that chemical analysis of the ice core will reveal whether the site was ever relatively close to open sea water or ice shelf in the Rutford channel 20 km distant, rather than the current 700 km distance to sea ice/open water in either the Weddell Sea or the Amundsen Sea. While we do not yet have the chemistry data to test this hypothesis, in this poster we will discuss whether there is in reality any potential local meteoric ice remaining from the previous interglacial that could provide the evidence we need. We show likely age-depth models in an ice dome with a pronounced Raymond cupola and flat bedrock. The evidence from the stable water isotope temperature history from the site shows the Last Glacial Maximum/Holocene boundary substantially above the bedrock, implying the possibility of much older ice in the lowest ice layers.

Mulvaney, R.; Hindmarsh, R. C.

2013-12-01

93

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

94

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

95

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

96

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

SciTech Connect

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

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

1992-03-01

97

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

98

The Mount Logan (Yukon) Ice Cores: Preliminary Results  

NASA Astrophysics Data System (ADS)

Three ice cores were taken at different elevations on or near My Logan in the years 2001 and 2002. The summit core (PRCol) comes from the summit plateau ( 5340 masl, length 187 m to bedrock, mean temperature -29 C ) and was done by the Geological Survey of Canada. The NIPR group cored 210m on the flanks of the mountain at King Col (4200 masl mean temperature -16C) and the UNH group cored 20 km from the mountain at Eclipse "Dome" (3015 masl,length 345 m mean temperature -5C) . The three cores were done cooperatively by GSC, NIPR and UNH and cover nominally 30 ka, 1 ka and 2ka respectively . Located very close to the Gulf of Alaska these core records are thought to reflect the climate history of the Pacific Ocean and having three widely spaced elevations, the sites "see" different distances to different sources. The lowest site (Eclipse) has excellent seasonals but a very muted ? 18O history with no obvious little ice age, whereas the most recent 1ka of the PRCol summit sites contains two very large and sudden ? 18O and d (deuterium excess) shifts at 1850 AD and ~ 800 AD. The ? 18O shifts which happen from one year to the next are about 4 o/oo . The summit site (PRCol) ? 18O response is "backwards", ie the Little Ice Age ? 18O values are 4 o/oo more positive than recent ones. The PRCol ? 18O and d suggest that the source water can either be ëlocalí (Gulf of Alaska) or very distant (tropics) . The Eclipse site seems only to get the local water . A massive dust storm originating in central Asia (Gobi) in April 2001 dumped a visible layer all over the St Elias Mountains and this layer was sampled, to provide a calibration "Asian dust event". The satellite and isotoic signatures both agreed that Gobi was the source. The PRCol record covers the Holocene and well back into the ice age. The transition is defined by a sudden ECM shift on the flanks of a more gradual O18 shift. Acknowledgements. Logan consortium consists of : Geological Survey of Canada : Jocelyne Bourgeois, Mike Demuth, David Fisher, Roy Koerner,Chris Zdanowicz, James Zheng. University of Ottawa: Ian Clarke,Raphaelle Cardyn. National Institute of Polar Research (Japan): Kumiko Goto-Azuma University of New Hampshire: Cam Wake, Kaplan Yalcin. University of Maine: Karl Kreutz, Paul Mayewski, Erich Osterberg. Arctic Institute of North America: Gerald Holdsworth. University of Washington: Eric J. Steig, Summer B. Rupper. University of Copenhagen: Dorthe Dahl-Jensen. David Fisher is the presenter but many contributed to what is a joint preliminary offering.

Fisher, D. A.

2004-05-01

99

The contribution of ice core studies to the understanding of environmental processes  

NASA Astrophysics Data System (ADS)

Data obtained from the studies of polar ice cores supplement the records available from tree rings, peat bogs, lake and ocean sediments, and provide a relatively new data source to understand processes of the complex climatic and global cycles. The main sources of ice core data are stable and radioactive isotopes, soluble and particulate matter, and the composition of the gases occluded in the ice. Such information can be used to investigate the history and the variability of carbon dioxide and the climate system. Temperature and other climatic data obtained from ?18O measurements of polar ice cores can be correlated with similar information obtained from carbonate lake sediments. Comparison of the ?18O profiles of the Dye 3 ice core and central European lake sediments show distinct similarities such as the identification of the Older Dryas-Bolling/Allerød-Younger Dryas-Preboreal sequence. Measurements of the cosmic ray produced isotope 10Be on only 1 kg polar ice samples are possible by accelerator mass spectrometry. The resulting data reveals the 11-year solar modulation cycle and the Maunder Minimum of solar activity from 1645 to 1745 AD. The 10Be concentration values for the Maunder Minimum are a factor 1.6 higher than the average for the past 800 years. Using a carbon cycle model these 10Be variations can be compared to the 14C variations found in tree rings. The relatively good correlation suggests a common origin of the 10Be and 14C fluctuations and serves as a check of carbon cycle models. During the Wisconsin stage all of the Dye 3 ice core parameters measured to date (?18O, CO2/air, SO4-, NO3-, Cl-, dust) show values fluctuating between two different boundary conditions. This suggests that the climate system existing at that time oscillated between a cold and a warm state, probably strongly influenced by different ocean circulations and ice cover. During the Wisconsin stage a cold system dominated; the transition to the Holocene is considered as the final transition to a warm state. Thereafter the boundary conditions did not allow the systems to switch back to a cold state.

Oeschger, H.

100

Instruments and Methods Portable system for intermediate-depth ice-core drilling  

E-print Network

TD and operates in a fluid-free (dry) hole. Where the ice is warmer and rapid hole closure is possible, the slower- ate paper (Zagorodnov and others,1998). A BRIEF REVIEW OF DRY-HOLE EM ICE-CORE DRILL DEVELOPMENTInstruments and Methods Portable system for intermediate-depth ice-core drilling V. Zagorodnov, L

Howat, Ian M.

101

Modelisation of grain growth along the dome C EPICA ice core  

Microsoft Academic Search

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

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

2003-01-01

102

The Carrington event not observed in most ice core nitrate records E. W. Wolff,1  

E-print Network

The Carrington event not observed in most ice core nitrate records E. W. Wolff,1 M. Bigler,2 M. A of 14 well-resolved ice core records from Greenland and Antarctica has a nitrate spike dated to 1859 in nitrate in polar ice. Nitrate spikes cannot be used to derive the statistics of SEPs. Citation: Wolff, E

Cambridge, University of

103

Reconstruction of interannual Antarctic climate variability from ice cores  

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

104

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

105

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

106

Measurement of fracture toughness of an ice core from Antarctica  

NASA Astrophysics Data System (ADS)

The critical fracture toughness is a material parameter describing the resistance of a cracked body to further crack extension. It is an important parameter to simulate and predict the break-up behaviour of ice shelves from calving of single icebergs to the disintegration of entire ice shelves over a wide range of length scales. The fracture toughness values are calculated with equations that are derived from an elastic stress analysis. Additionally, an X-ray computer tomography (CT scanner) was used to identify the density as a function of depth. The critical fracture toughness of 91 Antarctic inland ice samples with densities between 840 to 870 kg m-3 has been determined by applying a four-point-bending technique on single edge v-notched beam samples. The examined ice core was drilled 70 m north of Kohnen Station, Dronnning Maud Land (75°00' S, 00°04' E, 2882 m). Supplementary data are available at doi:10.1594/PANGAEA.835321.

Christmann, J.; Müller, R.; Webber, K. G.; Isaia, D.; Schader, F. H.; Kipfstuhl, S.; Freitag, J.; Humbert, A.

2014-09-01

107

Volatility of unevenly sampled fractional Brownian motion: An application to ice core records  

NASA Astrophysics Data System (ADS)

The analysis of many natural time series and especially those related to ice core records often suffers from uneven sampling intervals. For fractional Brownian motion, we show that standard estimates of the volatility can be strongly biased due to uneven sampling. Taking these limitations into account, we study high-resolution records of temperature proxies obtained from Antarctic ice cores. We find that the volatility properties reveal a strong nonlinear component in the temperature time series for time scales of 5-200 kyr extending earlier results. These findings suggest in particular that temperature increments over these time scales appear in clusters of big and small increments—a big (positive or negative) change is most likely followed by a big (positive or negative) change and a small change is most likely followed by a small change.

Davidsen, Jörn; Griffin, James

2010-01-01

108

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

109

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

110

The Late Holocene Atmospheric Methane Budget Reconstructed from Ice Cores  

NASA Astrophysics Data System (ADS)

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

Mitchell, Logan E.

111

Polar ice structure and the integrity of ice-core paleoclimate records  

NASA Astrophysics Data System (ADS)

Polar ice is a unique archive of the climatic conditions in the past. However, ice sheets flow, and this flow may affect the integrity of paleoclimate records. A useful method to analyze the effect of ice flow upon climate records is the combination of microstructure mapping with ice-core line-scanning. Microstructure and stratigraphy have been mapped along the entire EPICA-DML ice core with this combined method. On the macroscale the stratigraphy seems perfectly preserved down to ca 1700 m depth (MIS4), below which minor undulations start to develop. Layers inclined up to 15° and millimeter-scale z-folds are observed below 2050 m depth. Notwithstanding, the EPICA-DML climate record appears not seriously disturbed down to ca 2400 m depth, which marks the climatic transition from the last interglacial (MIS5e) to the MIS6 glacial period. Below this depth the synchronization with the EPICA-Dome C record is lost, and stratigraphic disturbances appear up to the meter scale. On the microscopic scale, we observe dynamic recrystallization already in deep firn, leading to substantial microstructural changes prior to bubble close-off. The concentration of visible micro-inclusions in the Holocene part of the core seems to increase with depth, which could possibly indicate post-depositional formation of salts. In glacial period ice the concentration of visible micro-inclusions in certain layers is so high that these strata appear as light-scattering bands, often called "cloudy bands". Another interesting stratigraphic feature is what we call "bubble-free bands", viz. millimeter-thick strata deprived of bubbles and rich in clathrate hydrates, which are found within the bubble-hydrate transition zone (800-1200 m depth) and are probably caused by anomalously fast clathration. While there is hardly any interaction between visible micro-inclusions and grain boundaries down to 2500 m depth, in the deeper ice (warmer than -10 °C) many grain boundaries seem to harvest micro-inclusions. Here we discuss these observations and their relevance for the interpretation of climate records.

Faria, Sérgio H.; Freitag, Johannes; Kipfstuhl, Sepp

2010-01-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

113

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

NASA Astrophysics Data System (ADS)

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

Wei, Lijia

114

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

115

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

116

Ice Thickness and Basal Topography Near the Ross/Amundsen Ice Divide Revealed by Ground-based Radar and New Signal Processing  

NASA Astrophysics Data System (ADS)

The U.S. Science Plan for Deep Ice Coring in West Antarctica calls for a new ice core from a site near the Ross Sea/Amundsen Sea ice divide. The region is attractive because very thick ice in the region promises recovery of a long climate record with relatively high time resolution during the last glacial period. Ice thickness (together with accumulation rate history) is needed to estimate depth-age relationships for candidate core sites. However bed echoes from both airborne (Morse et al., Ann. Glac., v 35, 2002) and our ground-based radar profiles are often faint or not detected, especially in regions of very thick ice (up to 3500 m) that are preferred for potential core sites. Here we apply a combination of matched filtering and lateral averaging, which improves the signal-to-noise ratio of both englacial and bed echoes, to our 1.0 and 1.5MHz ground-based radar data collected in the vicinity of the western divide. Matched filtering requires a reflector model, which we derive from a strong, deep radar layer that is observed in nearly all transects. The signal model is consistent with bed echoes at sparse locations where the latter are reliable. Lateral averaging consists of coherent averaging at each point in the echogram, along lines of several slopes, followed by selection of the average of largest magnitude (constrained by an estimate of the maximum reflector slope). Lateral averaging is analogous to performing more stacking during acquisition to reveal fainter reflectors. Compared with data that have been processed by previous standard methods (eg. Gades et al., J. Glac. v 46, 2000), the new processing improves detection of the bed. Of particular interest is a profile along a flow line that crosses the ice divide at 42 km. The new processing clearly illuminates the bed at candidate site E at 15 km on the Ross Sea side of the divide; ice thickness there is 3460m. The bedrock divide is displaced 8 km west from the ice divide. No additional englacial layers were revealed by the processing in this case, and the deep radar stratigraphy is consistent with that found in a 1.5MHz transect that intersects the Byrd core. The basal topography near Site E is rough on the scale of 2-3km but the bed reflector itself is fairly coherent.

MacGregor, J. A.; Winebrenner, D. P.; Conway, H.; Sylvester, J.

2004-12-01

117

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

NASA Technical Reports Server (NTRS)

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

Alley, Richard B.

1991-01-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

119

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

E-print Network

record in the West Antarctic Ice Sheet (WAIS) Divide Ice Core N.W. Dunbar,1 W.C. McIntosh,1 A.V. Kurbatov of the eruption mentioned above suggest that some may be present in the WAIS Divide ice core. Deposits resulting in the WAIS Divide ice core. Mt. Moulton, Mt. Waesche, and Siple Dome A site on the shoulder of the ice

Dunbar, Nelia W.

120

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

PubMed

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

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

2001-01-01

121

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

122

Z .Cold Regions Science and Technology 28 1998 189202 Antifreeze thermal ice core drilling: an effective approach to the  

E-print Network

not combine with ice . Dry borehole coring to a depth of 350 m was possible 0165-232Xr98r$ - see front matter; Ice Drilling Tech- .nology, 1984, 1994 . Considering ice core quality as a major criterion a dry. Therefore, good quality ice core down to 400 m can be obtained efficiently with the combination of dry

Howat, Ian M.

123

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

124

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

Microsoft Academic Search

The abnormal spikes detected in some CO and CO2 polar ice core records indicate persistent chemical activity in glacial ice. Since CO and CO2 spikes are correlated, and their amplitudes scale with reported CO\\/CO2 yields for the photolysis of dissolved natural organic matter, a common photochemical source is implicated. Given that sufficient actinic radiation is constantly generated throughout ice by

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

2007-01-01

125

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

126

Solid and gaseous inclusions in the EDML deep ice core: origins and implications for the physical properties of polar ice  

NASA Astrophysics Data System (ADS)

The great value of polar deep ice cores stems mainly from two essential features of polar ice: its crystalline structure and its impurities. They determine the physical properties of the ice matrix and provide proxies for the investigation of past climates. Experience shows that these two essential features of polar ice manifest themselves in a multiscale diversity of dynamic structures, including dislocations, grain boundaries, solid particles, air bubbles, clathrate hydrates and cloudy bands, among others. The fact that these structures are dynamic implies that they evolve with time through intricate interactions between the crystalline structure, impurities, and the ice flow. Records of these interactions have been carefully investigated in samples of the EPICA deep ice core drilled in Dronning Maud Land, Antarctica (75°S, 0°E, 2882 m elevation, 2774.15 m core length). Here we show how the distributions of sizes and shapes of air bubbles correlate with impurities and the crystalline structure, how the interaction between moving grain boundaries and micro-inclusions changes with ice depth and temperature, as well as the possible causes for the abrupt change in ice rheology observed in the MIS6-MIS5e transition. We also discuss how these observations may affect the flow of the ice sheet and the interpretation of paleoclimate records. Micrograph of an EDML sample from 555m depth. One can identify air bubbles (dark, round objects), microinclusions (tiny defocused spots), and a grain boundary pinned by a bubble. The width of the image is 700 micrometers.

Faria, S. H.; Kipfstuhl, S.; Garbe, C. S.; Bendel, V.; Weikusat, C.; Weikusat, I.

2010-12-01

127

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

128

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

129

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

130

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

131

Ion chromatography as a measurement device in continuous flow analysis of ice cores  

NASA Astrophysics Data System (ADS)

Melter-based continuous chemical analysis of ice cores has been increasingly employed in ice core research for fast, high resolution measurements of the chemical impurities in snow and ice. In continuous flow analysis (CFA), a heated melter generates uncontaminated flowing streams of ice core meltwater which are channeled directly into measurement devices, such as spectrophotometers, mass spectrometers and flow injection analyzers. These devices essentially serve as on-line and quantitative detectors for the melter-generated flow streams. Ion chromatography (IC) has been the preferred analytical technique for the determination of major chemical impurities in ice cores. Using IC as the measurement or detection technique for continuous flow melter analysis would provide an analytical system for measurement of all major chemical impurities in ice cores. We have constructed such a system by interfacing an ice core melter with several ion chromatographs. This technique (CFA-IC) takes advantage of the fast sample preparation and sub-sampling speed provided by a melter and the all-ion capability with low detection limits of ion chromatography. Initial testing and ice core analysis demonstrate that the CFA-IC technique is capable of (1) measuring all major ions, (2) high analysis speed as a result of reduced sample preparation time, and (3) high temporal resolution while requiring less ice than the conventional discrete sampling method.

Budner, D. M.; Cole-Dai, J.; Ferris, D.

2005-12-01

132

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

133

Microbial activity and phylogeny in ice cores retrieved from Lake Paula, a newly detected freshwater lake in Antarctica  

NASA Astrophysics Data System (ADS)

A permanent ice covered water body, called Lake Paula, was detected in Patriot Hills in the West Antarctic and sampled for the first time ever for microbial life. The ice sheet measured approximately 2,5m thickness and the water body has a depth of about 10m. The lake is situated near a moraine which partly ablates from snow and provides meltwater from the slopes to the lake during austral summer. These running waters which are kept liquid by the heating up of the dark soil are penetrating the lower ice cover and thus softening up the lakeside part if the ice core. It is inoculated by nutrients, active microbes and diatoms of terrestrial origin. A distinct gradient concerning bacterial numbers, biomass and production which is 10 fold at the ice-water interface compared to the exposed part is observable. Temperature sensitivity of the embedded microbes reflect the gradient as well: Bacteria isolated from the upper part showed growth optima at 10°C, the lower part at 25°C, phylogenetic properties done by 16s rDNA reveal distinct communities depending on their vertical position, some clones are similar to those retrieved in Lake Vostok ice cores. These results offer the conclusion that even in this harsh environment like the Antarctic continent a dynamic system like microbial ice aggregates can be sustained as long as the supply of liquid water which is essential for an active bacterial metabolism is provided at least for a small time frame.

Sattler, Birgit I.; Waldhuber, Sebastian; Fischer, Helgard; Semmler, Hans; Sipiera, Paul P.; Psenner, Roland

2004-11-01

134

Water isotopic ratios from a continuously melted ice core sample  

E-print Network

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 simultaneous water isotopic analysis of $\\delta^{18}$O and $\\delta$D on a continuous stream of liquid water as generated from a continuously melted ice rod. Injection of sub ${\\mu}$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. A calibration procedure allows for proper reporting of the data on the VSMOW--SLAP scale. Application of spectral methods yields the combined uncertainty of the system at below 0.1 permil and 0.5 permil for $\\delta^{18}$O and $\\delta$D, respectively. This performance is comparable to that achieved with mass spectrometry. Dispersion of the sampl...

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

2014-01-01

135

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

E-print Network

Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period R. These globally coincident volcanics were associated with abrupt cooling, often simultaneous with onsets or sudden (2006), Globally synchronous ice core volcanic tracers and abrupt cooling during the last glacial period

Price, P. Buford

136

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

Microsoft Academic Search

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

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

2003-01-01

137

Modeling Climate and Production-related Impacts on Ice-core Beryllium-10  

E-print Network

Modeling Climate and Production-related Impacts on Ice-core Beryllium-10 Christy Veeder Submitted Modeling Climate and Production-related Impacts on Ice-core Beryllium-10 Christy Veeder I use the Goddard Institute for Space Studies ModelE general circulation model to ex- amine the how beryllium-10, a cosmogenic

138

The Search for Supernovae Signatures in an Ice Core  

NASA Astrophysics Data System (ADS)

It has been proposed that ice cores may preserve detectable enhancements of some terrestrially rare, radioisotopes, ^10Be, ^26Al, ^36Cl, resulting from a near Earth, type II supernova [1]. A simple model is developed and calculations are presented to estimate the number of grains with ^26Al enhancements that could be deposited per cm^2 on the Earth by a type II supernova. We describe the search for supernova grains that may possess ^26Al enhancements amongst grains filtered from the 308.5m Guliya ice core recovered from the Qinghai-Tibetan plateau in China [2]. We have obtained Guliya grain samples from the epochs corresponding to previously discovered ^10Be and ^36Cl enhancements at 35ky and 60ky as well as ˜1-4ky samples surrounding the time periods 25ky, 55ky, 68ky. Additionally, we obtained a sample that spans the time period 2-10ky. The process of identifying potential supernova grains amongst their terrestrial cousins employs a procedure developed at the University of Chicago for detecting interstellar grains in meteoritic samples [3]. We report the identification of the potential supernova grains, CaAl_12O_19, Al_2O_3, and MgAl_2O4 in the samples. This work is supported in part by National Science Foundation grant PHY-9901241. [1] Ellis, J., Fields, B. D., Schramm, D. N. Astrophys. J., 470: 1227, 1996. [2] Thompson, L. G. et al. Science, 276: 1821, 1997. [3] Amari, S., Lewis, R.S., Anders, E. Geochim. Cosmochim. Acta, 58: 459, 1994.

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

2002-10-01

139

Snow precipitation at four ice core sites in East Antarctica: provenance, seasonality and blocking factors  

Microsoft Academic Search

Snow precipitation is the primary mass input to the Antarctic ice sheet and is one of the most direct climatic indicators,\\u000a with important implications for paleoclimatic reconstruction from ice cores. Provenance of precipitation and the dynamic conditions\\u000a that force these precipitation events at four deep ice core sites (Dome C, Law Dome, Talos Dome, and Taylor Dome) in East\\u000a Antarctica

Claudio Scarchilli; Massimo Frezzotti; Paolo Michele Ruti

140

Deuterium excess record in a southern Tibetan ice core and its potential climatic implications  

Microsoft Academic Search

A 55-m long ice core, drilled close to bedrock from Mt. Noijin Kangsang on the southern Tibetan Plateau in summer 2007, was\\u000a annually dated covering the period of 1864–2006 AD. The stable isotope ratios (?\\u000a 18O and ?D) of the ice core were measured and thereby the deuterium excess (d) was calculated by d = ?D ? 8*?\\u000a 18O for the individual ice samples.

Huabiao Zhao; Baiqing Xu; Tandong Yao; Guangjian Wu; Shubiao Lin; Jing Gao; Mo Wang

2011-01-01

141

Tropical Cyclones and Ice Cores: Developing a Long Term Perspective  

NASA Astrophysics Data System (ADS)

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

Urmann, D.

2006-12-01

142

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

143

Inferring paleo-accumulation records from ice-core data by an adjoint method: application to James Ross Island's ice core  

NASA Astrophysics Data System (ADS)

Ice cores contain a record of snow precipitation that includes information about past atmospheric circulation and mass imbalance in the polar regions. We present a novel adjoint method to reconstruct a climatic record by both optimally dating an ice-core and deriving from it a detailed accumulation history. The motivation of our work is the recent application of phase sensitive radar which measures the vertical velocity of an ice column. The velocity is dependent on the history of subsequent snow accumulation, compaction and compression; and in our inverse formulation of this problem, measured vertical velocity profiles can be utilized directly thereby reducing the uncertainty introduced by ice flow modelling. We first apply our method to synthetic data in order to study its capability and the effect of noise and gaps in the data on retrieved accumulation history. The method is then applied to the ice core retrieved from James Ross Island, Antarctica. We show that the method is robust and that the results depend on quality of the age-depth observations and the derived flow regime around the core site. The method facilitates the incorporation of increasing detail provided by ice-core analysis together with observed full-depth velocity in order to construct a complete climatic record of the polar regions.

Martín, C.; Mulvaney, R.; Gudmundsson, G. H.; Corr, H.

2014-09-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

145

Variations of air content in Dasuopu ice core from AD 1570e1927 and implications fore climate change  

E-print Network

(represented by volume) in ice was mainly dominated by the atmospheric pressure and temperature in the dry iceVariations of air content in Dasuopu ice core from AD 1570e1927 and implications fore climate June 2010 a b s t r a c t An ice core air content record that was recovered from the refrozen

Chappellaz, Jérôme

146

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

147

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

148

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

149

JOURNALOF GEOPHYSICALRESEARCH,VOL. 89, NO. D3, PAGES4638-4646, JUNE 20, 1984 TROPICAL GLACIERS: POTENTIAL FOR ICE CORE PALEOCLIMATIC RECONSTRUCTIONS  

E-print Network

- served and are most amenable to interpretation. Pit studies reveal a large variation in the seasonal.M. Grootes, M. Pourchet, and S. Hastenrath Abstract. The objective of this work is to evaluate the potential and ice cores. Samples were collected in pits and from cores retrieved on three snow fields in the South

Howat, Ian M.

150

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

151

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

152

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

153

The Design and Performance of IceCube DeepCore  

NASA Technical Reports Server (NTRS)

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

Stamatikos, M.

2012-01-01

154

Ultrasonic velocities and crystalline anisotropy in the ice core from Dye 3, Greenland  

NASA Astrophysics Data System (ADS)

Ultrasonic velocity measurements on polar ice core samples can be used to monitor the development of crystalline anisotropy through an ice sheet. In a single crystal of ice, P-waves travel about 170 ms-1 faster along the c-axis than along a-axes. A randomly-oriented, poly-crystalline aggregate of ice will appear accoustically isotropic. However, with depth in an ice sheet, as caxes become preferentially oriented in the vertical direction, the vertical velocity in the polycrystalline aggregate increases, as does the velocity difference, V. Ultrasonic velocities have been measured on 248 samples from 38 depth intervals on the 2037 m ice core from Dye 3, Greenland. These are the first measurements ever made on fresh, unrelaxed samples from a deep ice core. In the Dye 3 core, the velocity difference increases from near zero in the upper several hundred meters to about 80 ms-1 by a depth of 1700 m. There is an abrupt increase in V to values of over 120 ms-1 which occurs over a very short depth interval marking the Holocene-Wisconsin climatic transition. The ultrasonic velocity results obtained from the Dye 3 ice core will be compared to the measured fabric profile and to other physical properties measured throughout the core.

Herron, Susan L.; Langway, Chester C., Jr.; Brugger, Keith A.

155

High-resolution variations in size, number and arrangement of air bubbles in the EPICA DML (Antarctica) ice core  

E-print Network

(Antarctica) ice core Verena BENDEL,1� Kai J. UELTZHO¨ FFER,2 Johannes FREITAG,3 Sepp KIPFSTUHL,3 Werner F bubbles in the EPICA Dronning Maud Land (EDML) (Antarctica) ice core, down to the end of the bubble. Lipenkov (2000) observed that bubbles formed in cold periods in the Vostok (East Antarctica) ice core

Garbe, Christoph S.

156

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

157

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

158

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

159

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

161

Development of Melting Device for Measurement of Traceable Proxies in Ice Core  

NASA Astrophysics Data System (ADS)

It has been well known that various proxies in ice core can provide useful information about climate change and atmospheric environment in the past. However, ice core sample can be easily contaminated during drilling, shipping, cutting, and handling and especially, its breaks are the primary source of contamination of the inner core. Therefore, decontamination procedure of ice core sample to remove contaminants of outer layers in ice core is very important. Until now, as a decontamination method of ice core sample, conventional method has been broadly used. This indicates removal of pollutants by mechanical scraping with stainless steel knives or by a series of washing-baths with ultra-pure distilled water. It has advantages such as minimization of interferences between samples, flexible adaptation of extraction time, and stable instrumental analysis. As a disadvantage, there have been also reported as low efficiencies of ice core preparation owing to strict and complicated procedures, low resolution (10-20 cm/sample), and difficulties of application to on-line measurement system. As a result, the melting device was developed as an alternative of conventional decontamination method in the early 1990s. Contrary to conventional method, this represented high efficiencies of decontamination, high resolution (? 5 cm/sample), and the possibilities of application to on-line measurement system. However, the artifacts from melting head made of metals, the interferences between samples melted in series, recovery efficiencies of traceable element, and instability of instrumental analysis owing to short extraction time and scanning time have to be overcome. Even if various melting devices have been developed, prior to this study, little researches had been undertaken examining systematically them which would be expected to be important in on-line measurement system. In this study, melting head made of Ti and with 3-channels was constructed to decontaminate discrete ice core samples. The results of performance test of melting device conducted systematically and preliminary results applied to ice core drilled at Alpine and Antarctica will be presented.

Hong, S.; Hwang, H.; Lee, K.; Hur, S.; Hong, S.; Chung, J.; Yoon, A.; Yoon, H.

2009-12-01

162

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

163

Polychlorinated biphenyls in glaciers. 1. Deposition history from an Alpine ice core.  

PubMed

We present a highly time-resolved historical record of polychlorinated biphenyls (PCBs) from an Alpine ice core (Fiescherhorn glacier, Switzerland). Introduced in the 1940s, PCBs were widely used industrial chemicals. Because of their persistence they are still found in the environment, long after their production phase-out. The Fiescherhorn ice core record covers the entire time period of industrial use of PCBs, that is, 1940-2002. The total concentration of six PCBs varies from 0.5 to 5 ng L(-1) and reveals a temporal trend, with an 8-fold increase from the early 1940s to the peak value in the 1970s. The level in 2002 is comparable to the concentration in the 1940s, when PCBs were introduced into the market. The time trend of PCBs associated with the particulate fraction closely follows the trend found in the dissolved fraction, but the absolute values are a factor of 10 lower. In addition to changing emissions, fluctuations in the PCB record were explained by variabilty in convective transport and postdepositional processes such as surface melting. Concentrations of PCBs are in agreement with data from seasonal snow samples in the Alps, but are a factor of 100 higher than concentrations measured in the Arctic. Contrasting time trends and congener patterns between the Alpine and Arctic region indicate the importance of atmospheric transport and postdepositional effects. PMID:24968761

Pavlova, Pavlina Aneva; Schmid, Peter; Bogdal, Christian; Steinlin, Christine; Jenk, Theo M; Schwikowski, Margit

2014-07-15

164

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

NASA Astrophysics Data System (ADS)

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

Thomas, Elizabeth R.; Bracegirdle, Thomas J.

2014-06-01

165

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

166

A 600-year annual 10 Be record from the NGRIP ice core, Greenland  

E-print Network

A 600-year annual 10 Be record from the NGRIP ice core, Greenland A.-M. Berggren,1 J. Beer,2 G recent solar activity compared to the last 600 years. Citation: Berggren, A.-M., J. Beer, G. Possnert, A connections to past climate change [Beer et al., 1990]. The isotope concentra- tion in glacial ice is affected

Wehrli, Bernhard

167

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

168

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

Microsoft Academic Search

Acid layers of volcanic origin detected in polar snow and ice layers are commonly used to document past volcanic activity on a global scale or, conversely, to date 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

169

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

170

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

171

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

172

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

173

Holocene climate in West Antarctica from the Siple Dome ice core melt-layer record  

Microsoft Academic Search

Summer climate conditions in West Antarctica changed significantly during the Holocene, as recorded by frequency of occurrence of rare melt layers in the Siple Dome deep ice core. We present a record of millennial-scale melt-layer frequency through the Holocene from the Siple Dome ice-core which we interpret as a significant record of changing summer climate conditions for West Antarctica. Melting

S. B. Das; R. B. Alley; J. W. C. White

2003-01-01

174

A 2680 year volcanic record from the DT401 East Antarctic ice core  

Microsoft Academic Search

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

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

2010-01-01

175

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

176

Greenland ice Cores tell Tales on the Eemian Period and Beyond  

Microsoft Academic Search

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

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

2005-01-01

177

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

178

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

179

Holocene tephras highlight complexity of volcanic signals in Greenland ice cores  

NASA Astrophysics Data System (ADS)

Acidity peaks in Greenland ice cores have been used as critical reference horizons for synchronizing ice core records, aiding the construction of a single Greenland Ice Core Chronology (GICC05) for the Holocene. Guided by GICC05, we examined sub-sections of three Greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records, the dating of prehistoric tephras and the understanding of the eruptions. Here we report the identification of 14 horizons with tephra particles, including 11 that have not previously been reported from the North Atlantic region and that have the potential to be valuable isochrons. The positions of tephras whose major element data are consistent with ash from the Katmai AD 1912 and Öraefajökull AD 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years. We provide a more refined date for the so-called “AD860B” tephra, a widespread isochron found across NW Europe, and present new evidence relating to the 17th century BC Thera/Aniakchak debate that shows N. American eruptions likely contributed to the acid signals at this time. Our results emphasize the variable spatial and temporal distributions of volcanic products in Greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events.

Coulter, Sarah E.; Pilcher, Jonathan R.; Plunkett, Gill; Baillie, Mike; Hall, Valerie A.; Steffensen, J. P.; Vinther, Bo M.; Clausen, Henrik B.; Johnsen, Sigfus J.

2012-11-01

180

Ice Core Evidence for Amplification of the Recent Warming at High Elevations in the Tropics and the Likely Regional Impacts  

NASA Astrophysics Data System (ADS)

IPCC (2007) models predict an enhancement of warming at higher altitudes throughout the tropics where temperatures may warm twice as much as the globally-averaged increase of 3°C predicted for sea level by 2100 AD. Ice core data collected over the last thirty years from low-latitude, high-elevation glaciers, along with continuous monitoring of selected sites, document this amplification and suggest an imminent demise of many of these ice fields. A new, annually resolved climatic and environmental record from the Quelccaya ice cap (5670 m asl) in Peru extends back to 315 AD. A new record from the higher, colder and drier Coropuna ice field (6450 m asl), 350 km southwest of Quelccaya and only 70 km from the Pacific Ocean, provides a much longer, albeit lower resolution, ~16,000 year history. El Niño-Southern Oscillation variations are recorded at both sites and document millennial scale variability. A series of ice cores drilled across High Asia provides climatic and environmental histories that also document the amplification of air temperature at high elevations. Regional impacts of this warming may already be underway. Observations in 2006 on Naimona'nyi (6100 m asl, also known as Gurla Mandata), located near the headwaters of the Ganges and Indus Rivers, indicate that under current climate conditions this ice field is not gaining mass. Ice cores from the Dasuopu glacier (7200 m asl) in the central Himalaya provide a high-resolution record of fluctuations in the intensity of the South Asian Monsoon. Reductions in monsoon intensity are recorded by insoluble dust and chloride concentrations. The deeper, older sections of the Dasuopu record reveal numerous arid periods, but none were longer and more intense than the 1790 to 1796 A.D. drought. This event is also prominent in the soluble aerosol records from the Quelccaya and Coropuna cores on the eastern side of the Pacific Basin, suggesting decadal-scale teleconnections between these regions. The similarities and differences among these high-resolution paleoclimate records for the last 1500 years will be discussed. The ?18O data from the high accumulation ice core sites around the Pacific Basin are compared with Niño 4 sea surface temperatures (SSTs) since the 1890s and appear to capture decadal-scale variations. Thus, they may offer the potential to extend the central tropical Pacific SST record beyond the instrumental period.

Thompson, L. G.; Mosley-Thompson, E. S.; Davis, M. E.; Urmann, D.; Buffen, A.

2007-12-01

181

Atmospheric variability of methyl chloride during the last 300 years from an Antarctic ice core and firn air  

E-print Network

was extracted from the ice core samples using a dry extraction technique [Etheridge et al., 1988; SowersAtmospheric variability of methyl chloride during the last 300 years from an Antarctic ice core] Measurements of methyl chloride (CH3Cl) in Antarctic polar ice and firn air are used to describe

Saltzman, Eric

182

Kinetics of Heterogeneous Ice Nucleation on the Surfaces of Mineral Dust Cores Inserted into Aqueous Ammonium Sulfate Particles  

E-print Network

and dry conditions of the upper troposphere (e.g., 210- 230 K and 120-140% ice RH), ice nucleationKinetics of Heterogeneous Ice Nucleation on the Surfaces of Mineral Dust Cores Inserted, Massachusetts 02138 ReceiVed: July 11, 2002; In Final Form: December 13, 2002 Ice freezing of aqueous ammonium

183

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

PubMed

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

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

2012-08-01

184

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

185

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

Microsoft Academic Search

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

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

2008-01-01

186

A novel method for the detection of acidity in ice cores  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

187

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

188

The 1452 or 1453 A.D. Kuwae eruption signal derived from multiple ice core records  

E-print Network

, probably surpassing the total sulfate deposition of the Tambora eruption of 1815, which produced 59 kg SO4 core. Palmer et al. [2002] reported deposition of a large volcanic eruption during 1459­1461 in the LawThe 1452 or 1453 A.D. Kuwae eruption signal derived from multiple ice core records: Greatest

Robock, Alan

189

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

NASA Astrophysics Data System (ADS)

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

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

2006-01-01

190

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

191

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

192

Glacial ice cores: A model system for developing extraterrestrial decontamination protocols  

NASA Astrophysics Data System (ADS)

Evidence gathered from spacecraft orbiting Mars has shown that water ice exists at both poles and may form a large subsurface reservoir at lower latitudes. The recent exploration of the martian surface by unmanned landers and surface rovers, and the planned missions to eventually return samples to Earth have raised concerns regarding both forward and back contamination. Methods to search for life in these icy environments and adequate protocols to prevent contamination can be tested with earthly analogues. Studies of ice cores on Earth have established past climate changes and geological events, both globally and regionally, but only recently have these results been correlated with the biological materials (i.e., plant fragments, seeds, pollen grains, fungal spores, and microorganisms) that are entrapped and preserved within the ice. The inclusion of biology into ice coring research brings with it a whole new approach towards decontamination. Our investigations on ice from the Vostok core (Antarctica) have shown that the outer portion of the cores have up to 3 and 2 orders of magnitude higher bacterial density and dissolved organic carbon (DOC) than the inner portion of the cores, respectively, as a result of drilling and handling. The extreme gradients that exist between the outer and inner portion of these samples make contamination a very relevant aspect of geomicrobiological investigations with ice cores, particularly when the actual numbers of ambient bacterial cells are low. To address this issue and the inherent concern it raises for the integrity of future investigations with ice core materials from terrestrial and extraterrestrial environments, we employed a procedure to monitor the decontamination process in which ice core surfaces are painted with a solution containing a tracer microorganism, plasmid DNA, and fluorescent dye before sampling. Using this approach, a simple and direct method is proposed to verify the authenticity of geomicrobiological results obtained from ice core materials. Our protocol has important implications for the design of life detection experiments on Mars and the decontamination of samples that will eventually be returned to Earth.

Christner, Brent C.; Mikucki, Jill A.; Foreman, Christine M.; Denson, Jackie; Priscu, John C.

2005-04-01

193

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

194

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

PubMed

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

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

2012-02-01

195

Greenland ice cores tell tales on past climate changes (Louis Agassiz Medal Lecture)  

NASA Astrophysics Data System (ADS)

Greenland ice cores contain very highly resolved climate records reaching 128.000 years back in time. When dated and matched they tell tales on very abrupt climate changes especially during the glacial period demonstrating that internal energy exchange in the climate system can cause dramatic and fast changes with no external forcing. When the water stable isotope records from the six deep ice cores are compared they inform on both temperature changes and elevation changes of the Greenland ice sheet during glacial and interglacial periods. The temperature and elevation changes during the last 128.000 years are presented and the knowledge gained is used to discuss how this knowledge can be used to predict the future volume change of the Greenland ice sheet. This knowledge can improve estimates of future sea level rise predictions and is a demonstration of how knowledge from the past can be used to predict the future.

Dahl-Jensen, Dorthe

2014-05-01

196

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

197

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

198

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

199

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

200

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

201

A method for analysis of vanillic acid in polar ice cores  

NASA Astrophysics Data System (ADS)

Biomass burning generates a wide range of organic compounds that are transported via aerosols to the polar ice sheets. Vanillic acid is a product of conifer lignin combustion, which has previously been observed in laboratory and ambient biomass burning aerosols. In this study a method was developed for analysis of vanillic acid in melted polar ice core samples. Vanillic acid was chromatographically separated using reversed phase LC and detected using electrospray triple quadrupole mass spectrometry (ESI-MS/MS). Using a 100 ?L injection loop and analysis time of 4 min, we obtained a detection limit (S : N = 2) of 58 ppt (parts per trillion by mass) and an analytical precision of ±10 %. Measurements of vanillic acid in Arctic ice core samples from the Siberian Akademii Nauk core are shown as an example application of the method.

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

2014-07-01

202

First discovery of meteoritic events in deep Antarctic (EPICA-Dome C) ice cores  

NASA Astrophysics Data System (ADS)

Two distinct dust layers in the EPICA-Dome C ice core (75°06'S, 123°21'E, East Antarctic Plateau) have been shown to relate to individual meteoritic events. Particles forming these layers, investigated by electron microprobe, show peculiar textural, mineralogical and geochemical features and closely resemble extraterrestrial debris in deep-sea sediments and polar caps. Preliminary estimates of cosmic debris input at the studied layers, obtained from Coulter Counter measurements, are 4-5 orders of magnitude greater than the yearly micrometeorite flux in East Antarctic snow and ice. The cosmic events are accurately dated through glaciological models at 434 +/- 6 and 481 +/- 6 ka, respectively and are located in the core climatic stratigraphy near the ``Mid-Brunhes Event''. This is the first report of well-dated cosmic horizons in deep Antarctic ice cores. It significantly improves the extraterrestrial record of Antarctica and opens new correlation perspectives between long climatic records of the South polar region.

Narcisi, Biancamaria; Petit, Jean Robert; Engrand, Cécile

2007-08-01

203

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

205

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

206

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

207

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

PubMed

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

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

2013-09-01

208

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

209

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

210

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

211

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

212

Spatial and temporal variability of snow accumulation using ground-penetrating radar and ice cores on a Svalbard glacier  

E-print Network

Spatial and temporal variability of snow accumulation using ground-penetrating radar and ice cores,Villava« gen16, S-752 36 Uppsala, Sweden ABSTRACT. A 50 MHz ground-penetrating radar was usedto detect, Svalbard (Fig. 1), using ground-pene- trating radar (GPR) data and data from three ice cores along

Moore, John

213

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

214

Holocene climatic changes in Greenland: Different deuterium excess signals at Greenland Ice Core Project (GRIP) and NorthGRIP  

Microsoft Academic Search

Water stable isotope measurements (?D and ?18O) have been conducted on the Holocene part of two deep Greenland ice cores (Greenland Ice Core Project (GRIP) and NorthGRIP), located ?320 km apart. These combined measurements provide the first two continuous Greenland Holocene deuterium excess profiles (d = ?D ? 8?18O), a parameter strongly influenced by changes in moisture sources. We discuss

V. Masson-Delmotte; A. Landais; M. Stievenard; O. Cattani; S. Falourd; J. Jouzel; S. J. Johnsen; D. Dahl-Jensen; A. Sveinsbjornsdottir; J. W. C. White; T. Popp; H. Fischer

2005-01-01

215

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

Microsoft Academic Search

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

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

2000-01-01

216

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

217

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

Microsoft Academic Search

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

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

1986-01-01

218

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

219

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

PubMed

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

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

2013-05-24

220

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

SciTech Connect

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

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

1994-12-31

221

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

PubMed

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

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

2014-01-01

222

Inferring paleo-accumulation records from ice-core data by an adjoint method  

NASA Astrophysics Data System (ADS)

Ice cores contain a record of Earth's climate, and are used to understand how recently observed changes in climate fit within a long history of natural climatic variability. For a complete climatic record, a dated history of snow-accumulation needs to be derived as this gives information about past atmospheric circulation and a history of mass imbalance for the polar regions. We present here a novel adjoint method to construct a complete climatic record by both optimally dating an ice-core and deriving from it a detailed accumulation history. Our modelling approach uses all the available data extracted from the ice-core of the distribution with depth of age and thickness of an annual layer and present temperature. We discuss the applicability of our method to different ice-core characteristics and time-scales, and compare our method results with more commonly employed Bayesian techniques. We conclude that our methodology is more efficient and deals better with noise in the observed variables.

Martin, Carlos; Hilmar Gudmundsson, G.; Mulvaney, Robert; Corr, Hugh

2014-05-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

224

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

Microsoft Academic Search

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

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

2010-01-01

225

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

Microsoft Academic Search

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

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

2000-01-01

226

Ice core paleovolcanic records from the St. Elias Mountains, Yukon, Canada  

E-print Network

large eruptions such as Tambora (A.D. 1815), Cosiguina (A.D. 1835), Krakatau (A.D. 1883), Katmai (A a record of regionally significant volcanic eruptions in the North Pacific using an ice core from Eclipse). Correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one

Kurapov, Alexander

227

Isotopic studies of ice core nitrate and atmospheric nitrogen oxides in polar regions  

Microsoft Academic Search

Atmospheric nitrogen oxides regulate concentrations of natural and anthropogenic trace gases through interactions with tropospheric oxidants. Understanding past and present changes in atmospheric NOx (NO + NO2) is possible through measurements of nitrate (NO3- or nitric acid, HNO3) in polar ice cores. This dissertation is comprised of four studies which contribute towards understanding the controls on nitrate isotopes preserved in

Julia C. Jarvis

2008-01-01

228

Low latitude ice cores record Pacific sea surface temperatures R. S. Bradley,1  

E-print Network

; published 22 February 2003. [1] Oxygen isotope variations in ice cores from Bolivia and Peru are highly locations. INDEX TERMS: 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 1833 Hydrology: Hydroclimatology; 1827 Hydrology: Glaciology (1863); 1620 Global Change: Climate dynamics (3309); 1655 Global

Bradley, Raymond S.

229

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

PubMed Central

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

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

2014-01-01

230

Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century  

NASA Astrophysics Data System (ADS)

Over the past 50 years, warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves. A key driver of ice loss is summer melting; however, it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic. Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice. During the past millennium, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6°C lower than that of 1981-2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%. The warming has occurred in progressive phases since about AD 1460, but intensification of melt is nonlinear, and has largely occurred since the mid-twentieth century. Summer melting is now at a level that is unprecedented over the past 1,000 years. We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature.

Abram, Nerilie J.; Mulvaney, Robert; Wolff, Eric W.; Triest, Jack; Kipfstuhl, Sepp; Trusel, Luke D.; Vimeux, Françoise; Fleet, Louise; Arrowsmith, Carol

2013-05-01

231

Supplemental Text Analysis of the ice core samples  

E-print Network

and pollen. Dating the Kilimanjaro Cores As noted in the main text dating the Kilimanjaro required chronostratigraphic layer by a massive, temporary deposition of low density snow. It is nearly certain that this snow (1961 to 1964) (1s). #12;Application of the Nye model Establishing time scales for the five Kilimanjaro

Massachusetts at Amherst, University of

232

Oxygen-18 concentrations in recent precipitation and ice cores on the Tibetan Plateau  

USGS Publications Warehouse

A detailed study of the climatic significance of ??18O in precipitation was completed on a 1500 km southwest-northeast transect of the Tibetan Plateau in central Asia. Precipitation samples were collected at four meteorological stations for up to 9 years. This study shows that the gradual impact of monsoon precipitation affects the spatial variation of ??18O-T relationship along the transect. Strong monsoon activity in the southern Tibetan Plateau results in high precipitation rates and more depleted heavy isotopes. This depletion mechanism is described as a precipitation "amount effect" and results in a poor ??18O-T relationship at both seasonal and annual scales. In the middle of the Tibetan Plateau, the effects of the monsoon are diminished but continue to cause a reduced correlation of ??18O and temperature at the annual scale. At the monthly scale, however, a significant ??18O-T relationship does exist. To the north of the Tibetan Plateau beyond the extent of the effects of monsoon precipitation, ??18O in precipitation shows a strong temperature dependence. ??18O records from two shallow ice cores and historic air temperature data were compared to verify the modern ??18O-T relationship. ??18O in Dunde ice core was positively correlated with air temperature from a nearby meteorological station in the north of the plateau. The ??18O variation in an ice core from the southern Plateau, however, was inversely correlated with precipitation amount at a nearby meteorological station and also the accumulation record in the ice core. The long-term variation of ??18O in the ice core record in the monsoon regions of the southern Tibetan Plateau suggest past monsoon seasons were probably more expansive. It is still unclear, however, how changes in large-scale atmosphere circulation might influence summer monsoon precipitation on the Tibetan Plateau.

Tian, L.; Yao, T.; Schuster, P.F.; White, J.W.C.; Ichiyanagi, K.; Pendall, E.; Pu, J.; Yu, W.

2003-01-01

233

The Carrington event not observed in most ice core nitrate records  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

234

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

NASA Astrophysics Data System (ADS)

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

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

2003-05-01

235

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

NASA Astrophysics Data System (ADS)

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

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

2003-10-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

237

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.

238

An ice-core based history of Siberian forest fires since AD 1250 Anja Eichler a,b,*, Willy Tinner b,c  

E-print Network

and 1680, following an extremely dry period AD 1540e1600. Ice-core pollen data suggest distinct forestAn ice-core based history of Siberian forest fires since AD 1250 Anja Eichler a,b,*, Willy Tinner b: Palaeoecology Ice core Altai Fire history Charcoal Pollen a b s t r a c t Forest fires play a key role

Bern, Universität

239

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

240

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

241

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

NASA Astrophysics Data System (ADS)

three decades of stable isotope ratios and surface mass balance (SMB) data from eight shallow firn cores retrieved at Fimbul Ice Shelf, East Antarctica, in the Austral summers 2009-2011 have been investigated. An additional longer core drilled in 2000/2001 extends the series back to the early eighteenth century. Isotope ratios and SMB from the stacked record of all cores were also related to instrumental temperature data from Neumayer Station on Ekström Ice Shelf. Since the second half of the twentieth century, the SMB shows a statistically significant negative trend, whereas the ?18O of the cores shows a significant positive trend. No trend is found in air temperature at the nearest suitable weather station, Neumayer (available since 1981). This does not correspond to the statistically significant positive trend in Southern Annular Mode (SAM) index, which is usually associated with a cooling of East Antarctica. SAM index and SMB are negatively correlated, which might be explained by a decrease in meridional exchange of energy and moisture leading to lower precipitation amounts. Future monitoring of climate change on the sensitive Antarctic ice shelves is necessary to assess its consequences for sea level change.

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

2014-06-01

242

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

243

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

244

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

245

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

PubMed Central

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

2006-01-01

246

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

247

Climate patterns revealed by pollen and oxygen isotope records of a Tyrrhenian sea core  

Microsoft Academic Search

THE analysis of pollen from marine cores has produced continental palaeoclimate records which have been directly correlated with the oxygen isotope record of global ice volume and regional climate1-3. Here we tie the palaeoclimate of southern Europe to this global climate signal by reporting continuous pollen and delta18O records of a well-dated core in the Tyrrhenian Sea for the time

Martine Rossignol-Strick; Nadine Planchais

1989-01-01

248

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

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

249

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

250

A 270-year Ice Core Record of Atmospheric Mercury Deposition to Western North America  

NASA Astrophysics Data System (ADS)

The Upper Fremont Glacier (UFG), a mid-latitude glacier in the Wind River Range, Wyoming, U.S.A., contains a record of atmospheric mercury deposition. Although some polar ice-core studies have provided a limited record of past mercury deposition, polar cores are, at best, proxy indicators of historic mercury deposition in the mid-latitudes. Two ice cores removed from the UFG in 1991 and 1998 (totaling 160 meters in length) provided a chronology and paleoenvironmental framework. This aids in the interpretation of the mercury deposition record. For the first time reported from a mid-latitude ice core, using low-level procedures, 97 ice core samples were analyzed to reconstruct a 270-year atmospheric mercury deposition record based in the western United States. Trends in mercury concentration from the UFG record major releases to the atmosphere of both natural and anthropogenic mercury from regional and global sources. We find that mercury concentrations are significantly, but for relatively short time intervals, elevated during periods corresponding to volcanic eruptions with global impact. This indicates that these natural events "punctuate" the record. Anthropogenic activities such as industrialization (global scale), gold mining and war-time manufacturing (regional scale), indicate that chronic levels of elevated mercury emissions have a greater influence on the historical atmospheric deposition record from the UFG. In terms of total mercury deposition recorded by the UFG during approximately the past 270 years: anthropogenic inputs contributed 52 percent; volcanic events contributed 6 percent; and pre-industrialization or background accounted for 42 percent of the total input. More significantly, during the last 100 years, anthropogenic sources contributed 70 percent of the total mercury input. A declining trend in mercury concentrations is obvious during the past 20 years. Declining mercury concentrations in the upper section of the ice core are corroborated by recent declining trends observed in sediment cores. This is also verified by similar concentrations in UFG snow samples collected in 1999. This decline may be in response to the United States Clean Air Act of 1970.

Schuster, P. F.; Krabbenhoft, D. P.; Naftz, D. L.; Cecil, L. D.; Olson, M. L.; DeWild, J. F.; Susong, D. D.; Green, J. R.

2001-05-01

251

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

252

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

253

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

254

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

255

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

256

Evidence from an Ice Core of a Large Impact Circa 1443 A.D  

Microsoft Academic Search

Published data on melt water from the Siple Dome ice core show distinct anomalies at 1443.16 A.D. The Ca value is 111 ppb, over 9 times the next highest Ca value between 850-1760 A.D. The K value is 20 ppb, about 1.4 times the next highest K value. The Ca anomaly may be due to partial dissolution of CaCO3 microfossils

D. Abbott; P. Biscaye; J. Cole-Dai; D. Breger

2005-01-01

257

Tropical Glacier and Ice Core Evidence of Climate Change on Annual to Millennial Time Scales  

Microsoft Academic Search

This paper examines the potential of the stable isotopic ratios, 18O\\/16O (d 18Oice)and 2H\\/1H (d Dice), preserved in mid to low latitude glaciers as a toolfor paleoclimate reconstruction. Ice cores are particularly valuable as they contain additional data, such as dust concentrations, aerosol chemistry, and accumulation rates, that can be combined with the isotopic information to assist with inferences about

Lonnie G. Thompson; Ellen Mosley-Thompson; M. E. Davis; P.-N. Lin; K. Henderson; T. A. Mashiotta

2003-01-01

258

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

Microsoft Academic Search

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

Christy V. Field; Gavin A. Schmidt

2009-01-01

259

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

Microsoft Academic Search

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

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

2002-01-01

260

Laurentide ice sheet meltwater recorded in gulf of Mexico deep-sea cores.  

PubMed

Oxygen isotopic measurements in three Late Quaternary deep-sea cores from the Gulf of Mexico record a major anomaly between about 15,000 and 12,000 years ago superimposed on a more characteristic oceanic oxygen isotopic curve. This resulted from major influx of isotopically light glacial meltwater via the Mississippi River from the disintegrating Late Wisconsin Laurentide Ice Sheet 2000 kilometers to the north. PMID:17813734

Kennett, J P; Shackleton, N J

1975-04-11

261

Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa  

Microsoft Academic Search

Six ice cores from Kilimanjaro provide an ~11.7-thousand-year record of Holocene climate and environmental variability for eastern equatorial Africa, including three periods of abrupt climate change: ~8.3, ~5.2, and ~4 thousand years ago (ka). The latter is coincident with the ``First Dark Age,'' the period of the greatest historically recorded drought in tropical Africa. Variable deposition of F- and Na+

Lonnie G. Thompson; Ellen Mosley-Thompson; Mary E. Davis; Keith A. Henderson; Henry H. Brecher; Victor S. Zagorodnov; Tracy A. Mashiotta; Ping-Nan Lin; Vladimir N. Mikhalenko; Douglas R. Hardy; Jürg Beer

2002-01-01

262

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

263

New ice core evidence for a volcanic cause of the A.D. 536 dust veil  

Microsoft Academic Search

New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533-534 +\\/- 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and

L. B. Larsen; B. M. Vinther; K. R. Briffa; T. M. Melvin; H. B. Clausen; P. D. Jones; M.-L. Siggaard-Andersen; C. U. Hammer; M. Eronen; H. Grudd; B. E. Gunnarson; R. M. Hantemirov; M. M. Naurzbaev; K. Nicolussi

2008-01-01

264

New ice core evidence for a volcanic cause of the A.D. 536 dust veil  

Microsoft Academic Search

New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533–534 ± 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and

L. B. Larsen; B. M. Vinther; K. R. Briffa; T. M. Melvin; H. B. Clausen; P. D. Jones; M.-L. Siggaard-Andersen; C. U. Hammer; M. Eronen; H. Grudd; B. E. Gunnarson; R. M. Hantemirov; M. M. Naurzbaev; K. Nicolussi

2008-01-01

265

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

Microsoft Academic Search

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

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

1996-01-01

266

A new dating method for Dome Fuji ice core using data assimilation  

NASA Astrophysics Data System (ADS)

Understanding of past climate changes is regarded as a key for predicting the future climate. In particular, ice cores have been providing excellent records of the past climatic and environmental changes. The second Dome Fuji deep ice core (DF2 core) was drilled to 3,035 m below surface, and the comparison of its isotopic record with that of EDC core suggests that the DF2 core reaches ~700 kyr ago. In order to accurately date the core, one needs good estimation of accumulation rate and thinning function especially in the deep part (within ~500 m from the bed corresponding to ~340-700 kyr ago). The thinning function, which results from the horizontal stretching and vertical compression of an ice layer, is a function of several factors such as depth, temperature, basal sliding and geothermal heat flux. Using Data Assimilation, we try to make a new dating method but based on the glaciological dynamics of Parrenin et al. (2004, 2007). Trough Kalman filter and smoothing method, we could gain a new tracking method for the age of ice. In this time, we treat the age of ice as an object for the data assimilation and we don't assimilate both of accumulation rates and thinning function individually. It is still in the experimental stage but we will introduce the method and indicate the results. The new method has an advantage in the speed for calculation of parameterizations over the other models. We will indicate the results of calculation times and the optimized parameters in comparison with the other models. From reductions of calculation times, we would be able to calculate sampling of larger members for parameterization using another data assimilation method like a particle filter which needs a huge cost of calculations. In the use of Kalman Filter, it is difficult to treat both of the accumulation rate and the thinning function as variable in the state space model because there is the exponential equation for the accumulation rate. We will design a new state space model be applied with the other data assimilation method in the next step.

Suzuki, Kazue; Kawamura, Kenji; Nakano, Shin'ya; Nagao, Hiromichi; Abe-Ouchi, Ayako; Saito, Fuyuki; Higuchi, Tomoyuki; Parrenin, Frédéric

2013-04-01

267

Rapid changes in ice core gas records - Part 2: Understanding the rapid rise in atmospheric CO2 at the onset of the Bølling\\/Allerød  

Microsoft Academic Search

During the last glacial\\/interglacial transition the Earth's climate underwent rapid changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling\\/Allerød (B\\/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B\\/A is accompanied by a rapid sea level rise of about 20 m during meltwater

P. Köhler; G. Knorr; D. Buiron; A. Lourantou; J. Chappellaz

2010-01-01

268

Abrupt rise in atmospheric CO2 at the onset of the Bølling\\/Allerød: in-situ ice core data versus true atmospheric signals  

Microsoft Academic Search

During the last glacial\\/interglacial transition the Earth's climate underwent abrupt changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling\\/Allerød (B\\/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B\\/A was accompanied by a rapid sea level rise of about 20 m during meltwater

P. Köhler; G. Knorr; D. Buiron; A. Lourantou; J. Chappellaz

2011-01-01

269

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

270

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

PubMed Central

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

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

2012-01-01

271

Evidence for an early Holocene climate optimum in the Antarctic deep ice-core record  

SciTech Connect

In the interpretation of the Antarctic deep ice-core data, little attention has been given to the Holocene part of the records. As far as translation of the stable isotope content in terms of temperature is concerned, this can be understood because expected temperature changes may be obscured by isotopic noise of various origins and because no {sup 14}C dating has yet been available for this type of sequence. In this article, we focus on the Dome C and Vostok cores and on a new 850-m long ice core drilled out at Komsomolskaia by the Soviet Antarctic Expeditions. These three sites are located in East Antarctica, on the Antarctic plateau, in a region essentially undisturbed by ice-flow conditions, so that their detailed intercomparison may allow us to identify the climatically significant isotopic signal. Our results compare well with the proximal records of Southern Hemisphere high latitudes and support the existence of a warmer {open_quotes}climatic optimum{close_quotes} between 10 and 6 ka y BP. Maximum temperatures are reached just at the end of the last deglaciation, which confirms previous observations at high latitudes, in contrast with later dates for the Atlantic and hypsithermal optima in Europe and North America. 60 refs., 6 figs.

Ciais, P.; Lipenkov, V.; Nicolaiev, V. [Institute of Geography, Moscow (Russian Federation)

1992-01-01

272

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

PubMed

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

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

2012-04-17

273

Diagnose oscillation properties observed in an Antarctic ice core oxygen isotope record  

NASA Astrophysics Data System (ADS)

We investigate water isotope ratio profile obtained in a shallow ice core drilled at Dome Fuji, East Antarctica. Two sets of time series will be discussed; the first set was analyzed at NIPR (National Institute of Polar Research) with temporal resolution of about 5 years for the past 1900 years, and the second was obtained at RIKEN very recently with temporal resolution of less than a year for the past 400 years. Paying our attention on uncertainty in the depth-age relation, time series analyses to the measured oxygen isotope variations will be presented. A preliminary result for the former time series shows a ~200-year periodicity, which is by chance the same with one of solar activity cycles reported from tree ring studies. We note that snow and ice core samples obtained at Dome Fuji are known to contain much information on the stratosphere than those recovered from other sites in both the hemisphere. Considering this, we will further discuss possible mechanism to cause oscillation in oxygen isotope record in a Dome Fuji ice core.

Motizuki, Y.

2013-12-01

274

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

PubMed

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

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

2010-02-01

275

corded in ice cores is not steady; instead it comes in a series of pulses-just what you  

E-print Network

depths of between 500 and 700 meters-just where the ice-age drop in sea level might have decomposedcorded in ice cores is not steady; instead it comes in a series of pulses-just what you would signal-and the cloud of methane rising from the sea sur- face might choke the engines of planes. While

Doebley, John

276

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

PubMed

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

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

2014-08-01

277

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

Microsoft Academic Search

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

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

1993-01-01

278

Large perturbations of ammonium and organic acids content in the Summit-Greenland ice core - Fingerprint from forest fires?  

Microsoft Academic Search

Polar ice cores provide a unique record of precipitation whose chemistry reflects the atmospheric composition at the time of deposition. The analysis of such ice samples therefore allows an estimate to be made of the concentration of atmospheric impurities in the past. During the first season of the deep drill operation (GRIP) at Summit, Central Greenland continuous ammonium (NH4+) measurements

M. Legrand; M. de Angelis; T. Staffelbach; A. Neftel; B. Stauffer

1992-01-01

279

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

280

Ice core evidence for secular variability and 200-year dipolar oscillations in atmospheric circulation over East Antarctica during the Holocene  

Microsoft Academic Search

Two Holocene ice core records from East Antarctica (Vostok and EPICA-Dome C) were analysed for dust concentration and size\\u000a distribution at a temporal resolution of 1 sample per ~50 years. A series of volcanic markers randomly distributed over the\\u000a common part of the ice cores (from 9.8 to 3.5 kyear BP) ensures accurate relative dating (±33 years). Dust-size records from\\u000a the two sites

Barbara Delmonte; Jean Robert Petit; Gerhard Krinner; Valter Maggi; Jean Jouzel; Roberto Udisti

2005-01-01

281

Holocene climatic changes in Greenland: Different deuterium excess signals at Greenland Ice Core Project (GRIP) and NorthGRIP  

Microsoft Academic Search

Water stable isotope measurements (deltaD and delta18O) have been conducted on the Holocene part of two deep Greenland ice cores (Greenland Ice Core Project (GRIP) and NorthGRIP), located ~320 km apart. These combined measurements provide the first two continuous Greenland Holocene deuterium excess profiles (d = deltaD - 8delta18O), a parameter strongly influenced by changes in moisture sources. We discuss

V. Masson-Delmotte; A. Landais; M. Stievenard; O. Cattani; S. Falourd; J. Jouzel; S. J. Johnsen; D. Dahl-Jensen; A. Sveinsbjornsdottir; J. W. C. White; T. Popp; H. Fischer

2005-01-01

282

A battery powered, instrumented deep ice core drill for liquid filled holes  

NASA Astrophysics Data System (ADS)

The ice core drill used at Dye 3 for coring to bedrock at 2038-m depth is described. The main design criteria was low cost and weight, and easy maintenance in the field. The drill is divided into two main parts. The upper section consists of the antitorque section that prevents rotation of the upper part, the motors and the electronics. During drilling, the ice chips produced by the cutters are sucked into the lower, rotating part of the drill and transported with the drill to the surface, where the drill is clamped to a 6 m tower and tilted to horizontal position for easy core removal and drill cleaning. The cutters work like a plane, with an aggressive cutting angle that reduces the cutting power and provides stable penetration essentially independent of the load on the cutters. The drill is powered by a rechargeable battery pack, charged through the 6.4-mm cable. A microcomputer built into the drill controls 7 functions (battery charge and temperature, motor rotation speed and direction, etc.) at the same time that it measures 32 parameters. All this information is transmitted to a data terminal at the surface. The length of the drill is 11.5 m and its weight is 180 kg. The tower and the winch, including an electro-hydraulic pumpstation and 2500 m of cable, weigh 900 kg total. Core length is about 2.2 m per run, and the weekly core retrieval is 120 m of 10 cm diameter core at the 2000 m depth. The core recovery is better than 99.9%. Close to bedrock the hole deviates 6 degrees from the vertical, and the temperature is -13°C (-20°C at surface).

Gundestrup, N. S.; Johnsen, S. J.

283

Redefining deuterium excess in ice cores: Antarctic-wide evidence for ITCZ and polar jet variability during abrupt climate change  

NASA Astrophysics Data System (ADS)

We examine a new, high-resolution ice core record of water isotopes (?18O and deuterium excess) and atmospheric methane from West Antarctica, focusing on the millennial events of the most recent glacial period. High temporal resolution and a small gas-age/ice-age difference enable unprecedented precision in the analysis of phasing between these records. Our analysis reveals large amplitude millennial variability in the deuterium excess, a proxy for moisture source conditions and atmospheric circulation, which is out of phase with local site temperatures. On the other hand, this variability is in phase with atmospheric methane, which likely records changes in tropical hydrology and co-varies with Greenland temperatures during abrupt millennial Dansgaard-Oeschger (DO) events. Using a logarithmic definition of the deuterium excess, we show that these changes were probably near symmetric around Antarctica; the historical (linear) definition of the parameter appears to misrepresent millennial to multi-millennial variability at high East Antarctic ice core sites. Modeling experiments show that asymmetric warming of the hemispheres, a defining characteristic of these millennial events, should shift the position of the Inter Tropical Convergence Zone (ITCZ) and in turn the Southern sub-polar jet. Postulated ITCZ shifts can, in principle, help to explain the rapid rise in methane that accompanies abrupt Northern Hemisphere warming events by varying tropical rainfall patterns. Our observations are the first to show that these tropical changes may have directly influenced moisture sources and atmospheric circulation in the high southern latitudes, as recorded by the deuterium excess. We support these paleoclimate observations with isotope tracing atmospheric modeling experiments.

Markle, B. R.; Steig, E. J.; Schoenemann, S. W.; Sowers, T. A.; Buizert, C.; Ding, Q.; Fudge, T. J.; White, J. W.

2013-12-01

284

Snow precipitation at four ice core sites in East Antarctica: provenance, seasonality and blocking factors  

NASA Astrophysics Data System (ADS)

Snow precipitation is the primary mass input to the Antarctic ice sheet and is one of the most direct climatic indicators, with important implications for paleoclimatic reconstruction from ice cores. Provenance of precipitation and the dynamic conditions that force these precipitation events at four deep ice core sites (Dome C, Law Dome, Talos Dome, and Taylor Dome) in East Antarctica were analysed with air mass back trajectories calculated using the Lagrangian model and the mean composite data for precipitation, geopotential height and wind speed field data from the European Centre for Medium Range Weather Forecast from 1980 to 2001. On an annual basis, back trajectories showed that the Atlantic-Indian and Ross-Pacific Oceans were the main provenances of precipitation in Wilkes Land (80%) and Victoria Land (40%), respectively, whereas the greatest influence of the ice sheet was on the interior near the Vostok site (80%) and in the Southwest Ross Sea (50%), an effect that decreased towards the coast and along the Antarctic slope. Victoria Land received snowfall atypically with respect to other Antarctica areas in terms of pathway (eastern instead of western), seasonality (summer instead of winter) and velocity (old air age). Geopotential height patterns at 500 hPa at low (>10 days) and high (2-6 days) frequencies during snowfall cycles at two core sites showed large positive anomalies at low frequencies developing in the Tasman Sea-Eastern Indian Ocean at higher latitudes (60-70°S) than normal. This could be considered part of an atmospheric blocking event, with transient eddies acting to decelerate westerlies in a split region area and accelerate the flow on the flanks of the low-frequency positive anomalies.

Scarchilli, Claudio; Frezzotti, Massimo; Ruti, Paolo Michele

2011-11-01

285

Annually resolved southern hemisphere volcanic history from two Antarctic ice cores  

NASA Astrophysics Data System (ADS)

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

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

1997-07-01

286

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

287

A method to measure Kr/N2 ratios in air bubbles trapped in ice cores and its application in reconstructing past mean ocean temperature  

E-print Network

A method to measure Kr/N2 ratios in air bubbles trapped in ice cores and its application method for precise measurement of Kr/N2 ratios in air bubbles trapped in ice cores and the first measured Kr/N2 in air bubbles in Greenland (GISP2) ice from the late Holocene and LGM, using the present

Severinghaus, Jeffrey P.

288

Simulating ice core 10Be on the glacial-interglacial timescale  

NASA Astrophysics Data System (ADS)

10Be ice core measurements are an important tool for paleoclimate research, e.g. allowing for the reconstruction of past solar activity or variation in the natural 14C production rate. However, especially on multi-millennial timescales, the share of production and climate induced variations of respective 10Be ice core records is still up to debate. Here we present the first quantitative climatological model of the 10Be ice concentration up to the glacial-interglacial timescale. The model approach is composed of (i) a coarse resolution global atmospheric transport model and (ii) a local 10Be air-firn-transfer model. Extensive global-scale observational data of short-lived radionuclides as well as new polar 10Be snow pit measurements are used for model calibration and validation. Being specifically configured for polar 10Be, this tool thus allows for a straight-forward investigation of production and non-production related modulation of this nuclide. We find that the polar 10Be ice concentration does not record a globally mixed cosmogenic production signal. In fact, the geomagnetic modulation of Greenland 10Be is up to 50% lower than in case of the global atmospheric 10Be inventory. Using geomagnetic modulation and revised Greenland snow accumulation rate changes as model input we simulate the observed Greenland Summit (GRIP and GISP2) 10Be ice core records over the last 75 kyr (on the GICC05modelext timescale). We show that our basic model is capable to reproduce the largest portion of the observed 10Be changes. However, model-measurements differences exhibit multi-millennial oscillations with amplitudes up to 87% of the mean observed Holocene 10Be concentration. Focusing on the (12-37) kyr b2k (before the year 2000 AD) period, mean model-measurements differences of 30% cannot be imputed to production changes. However, unconsidered climate-induced changes could likely explain the model shortcomings. In fact, the 10Be ice concentration is very sensitive to snow accumulation changes. Here the reconstructed Greenland Summit (GRIP) snow accumulation rate record would require revision of +28% to solely account for the (12-37) kyr b2k measurements-model differences.

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

2014-02-01

289

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

NASA Astrophysics Data System (ADS)

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

Fischer, Hubertus

2014-05-01

290

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

USGS Publications Warehouse

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

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

2006-01-01

291

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

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

292

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

USGS Publications Warehouse

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

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

1998-01-01

293

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

294

Melting and metallization of silica in the cores of gas giants, ice giants and super Earths  

E-print Network

The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants and of Earth like exoplanets now discovered with masses up to several times the mass of the Earth remains mostly unknown. Here, we report on theoretical predictions of the properties of silica, SiO$_2$, up to 4 TPa and about 20,000K using first principle molecular dynamics simulations based on density functional theory. For conditions found in the Super-Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that MgSiO$_3$ silicate has not only dissociated into MgO and SiO$_2$, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid SiO$_2$ and solid (Mg,Fe)O.

Mazevet, S; Taniuchi, T; Benuzzi-Mounaix, A; Guyot, F

2014-01-01

295

Indian Monsoon and North Atlantic Oscillation Signals Reflected by Cl and Na-+ in a Shallow Ice Core from the Dasuopu Glacier, Xixiabangma, Himalaya  

E-print Network

Indian Monsoon and North Atlantic Oscillation Signals Reflected by Cl and Na- + in a Shallow Ice Atlantic Oscillation. #12; the existence of a teleconnection between the Cl and Na- + concentrations in this shallow ice core and the North

Howat, Ian M.

296

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

NASA Astrophysics Data System (ADS)

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

Edwards, Jon; Brook, Edward; Fegyveresi, John; Lee, James; Mitchell, Logan; Sowers, Todd; Alley, Richard; McConnell, Joe; Severinghaus, Jeff; Baggenstos, Daniel

2014-05-01

297

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

298

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

NASA Technical Reports Server (NTRS)

The prediction of future greenhouse-gas-warming depends critically on the sensitivity of earth's climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial-interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.

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

1990-01-01

299

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

NASA Astrophysics Data System (ADS)

The prediction of future greenhouse-gas-warming depends critically on the sensitivity of earth's climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial-interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.

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

1990-09-01

300

C2-C4 alkanes measured in a South Pole ice core: Are atmospheric histories of light hydrocarbons preserved in Antarctic ice?  

NASA Astrophysics Data System (ADS)

Non-methane hydrocarbons play a significant role in global atmospheric photochemical system, but we have little knowledge about their atmospheric variability on long time scales. In this study, we analyze ethane (C2H6), propane (C3H8) and n-butane (C4H10) in a South Pole ice core, to examine the potential for using polar ice cores to reconstruct atmospheric histories of these gases. Air was dry- extracted from 124 ice core samples from the SPRESSO core, a 295 m core drilled in 2002 near South Pole as part of the ITASE campaign. The mean gas ages estimated for these samples range from 150 B.C.E. to 1720 C.E. The average mixing ratios for ethane, propane, and n-butane are 798±417 ppt, 234±89 ppt and 117±48 ppt, respectively. Point to point variability generally lies within the estimate of analytical uncertainty. These measurements demonstrate that 1) recoverable amounts of light hydrocarbons exist in polar ice, and 2) there is no evidence of down-core trends to suggest systematic loss or production with time. However, the hydrocarbon levels in this ice core are considerably higher than those in modern air over Antarctica (by factors of 2, 7, and 10 respectively for ethane, propane, and n-butane). The ice core data are not normally distributed, but appear to have a lower limit with superimposed variability. These "baseline levels" are roughly 300 ppt (C2H6), 80 ppt (C3H8), and 40 ppt (C4H10) and are consistent with modern ambient air and firn air levels measured at South Pole. A working hypothesis to explain these results is that alkane levels in ice reflect a combination of two components: 1) entrapped air possibly recording the atmospheric histories of these gases, and 2) some source of alkane contamination that is generated at or near bubble close-off, but does not continue at depth. It is unlikely that the elevated alkane levels reflect contamination during storage, extraction, or analysis.

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

2007-12-01

301

The nature of abrupt climate change during the last glacial period from detailed isotopic records from the NGRIP ice core  

NASA Astrophysics Data System (ADS)

Isotopic and chemical impurity records from Greenland ice cores with sub-annual resolution across three fast climate transitions of the last deglacial termination reveal complex patterns of environmental change for the onset of Greenland Interstadial 1 (GI-1 or Bølling), the onset of Greenland Stadial 1 (GS-1 or Younger Dryas), and the onset of the Holocene. In the NGRIP ice core each of these transitions is initiated by a 1-3 year mode shift in deuterium excess, which is a proxy for the Greenland precipitation moisture source. These mode shifts in deuterium excess are decoupled in time from the isotopic (deuterium and oxygen-18) transitions from which they are derived. In general the abrupt isotopic transitions follow the corresponding deuterium excess shifts and span decades rather than years. Similar data from GISP2 confirms the clear deuterium excess mode shifts for transitions from cold states to warm states; however the abrupt deuterium excess transition at the onset of GS-1 is not expressed in a similar way at GISP2. Ironically, it appears that this cooling at the beginning of the Younger Dryas, for which we have theories of the triggering event, is less clearly recorded than warming events, the triggering of which is still poorly understood. Along with other available paleo-data, these results indicate that the sum of an abrupt climate change is composed of multiple responses from different parts of the climate system. These responses can be separated by as little as a single year to a few decades and the collection of these responses result in a variety of abrupt transitions giving each a unique anatomy. Here we expand this type of analysis with new isotope, deuterium excess, and accumulation rate time series from NGRIP across the abrupt transitions associated with several interstadial events of the Last Glacial period (Dansgaard-Oeschger events). Indeed the temporal phasing of deuterium excess and the isotopic content of the ice can vary from one event to the next and emerging patterns may depend on the conditions associated with specific events such as Heinrich Events and ice volume boundary conditions. Together with modeling and chemical impurity data, these patterns will provide clues to the timing and origin of ocean and atmospheric changes that comprise an abrupt climate change. The emerging picture indicates that abrupt climate changes have both a temporal and geographic anatomy that can change from one event to the next in how they are recorded across Greenland.

Popp, T. J.; Svensson, A.; Steffensen, J. P.; Johnsen, S. J.; White, J. W. C.

2009-04-01

302

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

NASA Astrophysics Data System (ADS)

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

Kozachek, Anna

2014-05-01

303

Thallium as a tracer for preindustrial volcanic eruptions in an ice core record from Illimani, Bolivia.  

PubMed

Trace element records from glacier and ice sheet archives provide insights into biogeochemical cycles, atmospheric circulation changes, and anthropogenic pollution history. We present the first continuous high-resolution thallium (Tl) record, derived from an accurately dated ice core from tropical South America, and discuss Tl as a tracer for volcanic eruptions. We identify four prominent Tl peaks and propose that they represent signals from the massive explosive eruptions of the "unknown 1258" A.D. volcano, of Kuwae ( approximately 1450 A.D.), Tambora (1815 A.D.), and Krakatoa (1883 A.D.). The highly resolved record was obtained with an improved setup for the continuous analysis of trace elements in ice with inductively coupled plasma sector field mass spectrometry (ICP-SFMS). The new setup allowed for a stronger initial acidification of the meltwater and shorter tubing length, thereby reducing the risk of memory effects and losses of analytes to the capillary walls. With a comparison of the continuous method to the established conventional decontamination and analysis procedure for discrete samples, we demonstrate the accuracy of the continuous method for Tl analyses. PMID:20050662

Kellerhals, Thomas; Tobler, Leonhard; Brütsch, Sabina; Sigl, Michael; Wacker, Lukas; Gäggeler, Heinz W; Schwikowski, Margit

2010-02-01

304

Ice and Dust in the Quiescent Medium of Isolated Dense Cores  

NASA Astrophysics Data System (ADS)

The relation between ices in the envelopes and disks surrounding young stellar objects (YSOs) and those in the quiescent interstellar medium (ISM) is investigated. For a sample of 31 stars behind isolated dense cores, ground-based and Spitzer spectra and photometry in the 1-25 ?m wavelength range are combined. The baseline for the broad and overlapping ice features is modeled, using calculated spectra of giants, H2O ice and silicates. The adopted extinction curve is derived empirically. Its high resolution allows for the separation of continuum and feature extinction. The extinction between 13 and 25 ?m is ~50% relative to that at 2.2 ?m. The strengths of the 6.0 and 6.85 ?m absorption bands are in line with those of YSOs. Thus, their carriers, which, besides H2O and CH3OH, may include NH+ 4, HCOOH, H2CO, and NH3, are readily formed in the dense core phase, before stars form. The 3.53 ?m C-H stretching mode of solid CH3OH was discovered. The CH3OH/H2O abundance ratios of 5%-12% are larger than upper limits in the Taurus molecular cloud. The initial ice composition, before star formation occurs, therefore depends on the environment. Signs of thermal and energetic processing that were found toward some YSOs are absent in the ices toward background stars. Finally, the peak optical depth of the 9.7 ?m band of silicates relative to the continuum extinction at 2.2 ?m is significantly shallower than in the diffuse ISM. This extends the results of Chiar et al. to a larger sample and higher extinctions. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Boogert, A. C. A.; Huard, T. L.; Cook, A. M.; Chiar, J. E.; Knez, C.; Decin, L.; Blake, G. A.; Tielens, A. G. G. M.; van Dishoeck, E. F.

2011-03-01

305

Natural and Anthropogenic Impacts on the Stable Isotopes of Nitrogen and Oxygen of Ice-Core Nitrate  

NASA Astrophysics Data System (ADS)

The stable isotopes of nitrogen and oxygen of the Ross Ice Drainage System (RIDS) ice-core nitrate were measured in approximately 2-3 year time resolution using a Delta V Isotope Ratio Mass Spectrometer (IRMS). The nitrogen isotope variation (?15N) and the mass-independent fractionation of oxygen (?17O = ?17O - 0.52*?18O) yield a detailed picture of the changes in the global nitrogen cycling and the shift in the oxidation capacity of the atmosphere in response to natural and anthropogenic induced climate change. This is one of the few studies on stable isotopes of ice-core nitrate for time periods prior to the 1800's and will increase our understanding of the oxidation feedbacks of the atmosphere in response to volcanic events, the Little Ice Age, the Maunder Minimum, and anthropogenic emissions in the Southern Hemisphere.

Walters, W.; Michalski, G. M.

2013-12-01

306

The 1452 A.D. Kuwae Eruption Signal Derived from Multiple Ice Core Records: Greatest Eruption over the Past 700 Years  

NASA Astrophysics Data System (ADS)

We combined 20 ice core records, 10 from the Northern Hemisphere and 10 from the Southern Hemisphere to determine the timing and magnitude of the Great Kuwae Eruption in the mid-15th century. The volcanic deposition signals were extracted by applying a high pass loess filter to each time series and examining peaks that exceed twice the 30-yr running median absolute deviation. By accounting for the dating uncertainties associated with each record, these ice core records together reveal a large volcanogenic acid deposition event during 1453-1457 A.D. The results suggest only one major stratospheric injection from the Kuwae eruption and confirm previous findings that the Kuwae eruption took place in 1452, which may serve as a reference to evaluate and improve the dating of ice core records. The average total sulfate deposition from the Kuwae eruption was 103 kg SO4/km2 in Antarctica and 44 kg SO4/km2 in Greenland. By applying the same technique to the other major eruptions of the past 700 yr, our result suggests that the Kuwae eruption was the largest stratospheric sulfate event of that period, probably surpassing the total sulfate deposition of the Tambora eruption of 1815, which produced 65 kg SO4/km2 in Antarctica and 49 SO4/km2 in Greenland.

Gao, C.; Robock, A.; Self, S.; Witter, J.; Steffenson, J.; Clausen, H.; Siggaard-Andersen, M.; Johnsen, S.; Mayewski, P. A.; Ammann, C.

2005-12-01

307

Human and climate impacts on Holocene fire activity recorded in polar and mountain ice cores  

NASA Astrophysics Data System (ADS)

Fire is one of the major influences of biogeochemical change on local to hemispheric scales through emitting greenhouse gases, altering atmospheric chemistry, and changing primary productivity. Levoglucosan (1,6-anhydro-?-D-glucopyranose) is a specific molecular that can only be produced by cellulose burning at temperatures > 300°C, comprises a major component of smoke plumes, and can be transported across > 1000 km distances. Levoglucosan is deposited on and archived in glaciers over glacial interglacial cycles resulting in pyrochemical evidence for exploring interactions between fire, climate and human activity. Ice core records provide records of past biomass burning from regions of the world with limited paleofire data including polar and low-latitude, high-altitude regions. Here, we present Holocene fire activity records from the NEEM, Greenland (77° 27'N; 51° 3'W; 2454 masl), EPICA Dome C, Antarctica (75° 06'S; 123° 21'E; 3233 masl), Kilimanjaro, Tanzania (3° 05'S, 21.2° E, 5893 masl) and the Muztagh, China (87.17° E; 36.35° N; 5780 masl ice cores. The NEEM ice core reflects boreal fire activity from both North American and Eurasian sources. Temperature is the dominant control of NEEM levoglucosan flux over decadal to millennial time scales, while droughts influence fire activity over sub-decadal timescales. Our results demonstrate the prominence of Siberian fire sources during intense multiannual droughts. Unlike the NEEM core, which incorporates the largest land masses in the world as potential fire sources, EPICA Dome C is located far from any possible fire source. However, EPICA Dome C levoglucosan concentrations are consistently above detection limits and demonstrate a substantial 1000-fold increase in fire activity beginning approximately 800 years ago. This significant and sustained increase coincides with Maori arrival and dispersal in New Zealand augmented by later European arrival in Australia. The EPICA Dome C levoglucosan profile is similar to regional charcoal compilations from New Zealand and southeastern Australia. Evidence from Kilimanjaro demonstrates a major increase in fire activity centered around 800-1000 years ago, corresponding to both increased temperatures and aridity as recorded in regional lake cores. This peak in fire activity is an order of magnitude higher than at any other time in the record including the most recent period. Environmental and anthropological studies suggest that upslope human migrations have occurred in response to the warmer, drier conditions. Kilimanjaro is surrounded by flammable savanna vegetation, yet the Muztagh core is located in an especially arid section of the Tibetan Plateau and consistently contains levoglucosan concentrations that are 100 to 1000 times greater than the mean Kilimanjaro flux. These high concentrations and the lack of available fuel suggest that regional rather than local biomass burning may be the source of the fire products. Biomass burning aerosols are a major component of the South Asian Brown Cloud and may influence the composition and concentration of pyrogenic aerosols across the Tibetan Plateau. The relative impact of human activity versus climate change on Holocene biomass burning varies regionally. Combining ice and sediment core data with model output can help place these regional differences into a global context with implications for a warming climate.

Kehrwald, Natalie; Zennaro, Piero; Kirchgeorg, Torben; Li, Quanlian; Wang, Ninglian; Power, Mitchell; Zangrando, Roberta; Gabrielli, Paolo; Thompson, Lonnie; Gambaro, Andrea; Barbante, Carlo

2014-05-01

308

Mineral dust and elemental black carbon records from an Alpine ice core (Colle Gnifetti glacier) over the last millennium  

Microsoft Academic Search

Black carbon (BC) and mineral dust aerosols were analyzed in an ice core from the Colle Gnifetti glacier (Monte Rosa, Swiss-Italian Alps, 45°55?N, 7°52?E, 4455 m above sea level) using chemical and optical methods. The resulting time series obtained from this summer ice record indicate that BC transport was primarily constrained by regional anthropogenic activities, i.e., biomass and fossil fuel

Florian Thevenon; Flavio S. Anselmetti; Stefano M. Bernasconi; Margit Schwikowski

2009-01-01

309

Reconstriction of atmospheric carbon dioxide and isotopic carbon-13 dioxide from air occluded in ice cores from Greenland and Antarctica  

Microsoft Academic Search

Carbon dioxide (COâ) dioxide (COâ) mixing ratio and isotopic carbon-13 dioxide δ¹³COâ was measured in the air extracted form ice cores from Greenland (GISP 2, Greenland Ice Sheet Project 2) and from Antarctica (Vostok). The goals are to determine the phasing between temperature and atmospheric COâ changes during periods of different climatic conditions and to gain insight into the mechanisms

Wahlen

1994-01-01

310

Detection and Isolation of Ultrasmall Microorganisms from a 120,000YearOld Greenland Glacier Ice Core  

Microsoft Academic Search

The abundant microbial population in a 3,043-m-deep Greenland glacier ice core was dominated by ultra- small cells (<0.1 m3) that may represent intrinsically small organisms or starved, minute forms of normal- sized microbes. In order to examine their diversity and obtain isolates, we enriched for ultrasmall psychro- philes by filtering melted ice through filters with different pore sizes, inoculating anaerobic

Vanya I. Miteva; Jean E. Brenchley

2005-01-01

311

Basal Crevasses Reveal a Dynamic Ice-Ocean Interface in an Embayment of the Whillans Ice Stream Grounding Line, West Antarctica  

NASA Astrophysics Data System (ADS)

The transition from limited- or no-slip conditions at the base of grounded ice to free-slip conditions beneath floating ice occurs across the few-kilometers-wide grounding zone of ice sheets. This transition is either an elastic flexural transition from bedrock- to hydrostatically-supported ice (often tidally influenced), or a transition from thicker to thinner ice over a flat bed, or some combination of these processes. In either case, the stress-change in the basal layers of ice can result in brittle deformation that may produce crevassing. Thus the position and morphology of basal crevasses reveal important information about the stress state across the grounding zone. We conducted ground-based radar surveys at two locations of the Whillans Ice Stream grounding zone, one over a subglacial peninsula where the transition to floatation is abrupt, and the second over a subglacial embayment where several dynamic subglacial lakes drain to the ocean, likely resulting in episodic high sediment and water flux across the grounding line. Our surveys indicate a complex pattern of basal crevasses. Some are associated with steeper surface slopes, but others appear to be related to ice flexure across an incised basal channel carrying water and sediment to the ocean. Here we image pairs of crevasses from either side of the channel that produce curious signatures in the radar profiles showing a high degree of symmetry at both shorter and longer arrival times than the nadir bed echo. In other locations, due to the high reflectivity of seawater and the relatively shallow ice thickness, we image many off-nadir crevasses where the radar energy is first reflected from the ice-water interface and then from the crevasse, producing an echo signature with a reversed phase due to the second reflection. In several cases these crevasse echoes appear to mimic the geometry of a sub-ice "wedge" dipping into the sediment, while in reality the radar never penetrates below the basal interface. Our results indicate that basal crevasses offer a rich, but unexploited, dataset for diagnosing stress state and ice/ocean interaction processes across grounding zones and that special care is needed when interpreting subglacial returns in radar data.

Jacobel, Robert; Christianson, Knut; Wood, Adam; DallaSanta, Kevin; Gobel, Rebecca

2014-05-01

312

Chlorine-36 and cesium-137 in ice-core samples from mid-latitude glacial sites in the Northern Hemisphere  

USGS Publications Warehouse

Chlorine-36 (36Cl) concentrations, 36Cl/Cl ratios, and 36Cl fluxes in ice-core samples collected from the Upper Fremont Glacier (UFG) in the Wind River Mountain Range, Wyoming, United States and the Nangpai Gosum Glacier (NGG) in the Himalayan Mountains, Nepal, were determined and compared with published results from the Dye-3 ice-core drilling site on the Greenland Ice Sheet. Cesium-137 (137Cs) concentrations in the NGG also were determined. The background fluxes for 36Cl for each glacial site were similar: (1.6??0.3)??10-2 atoms/cm2 s for the UFG samples, (0.7??0.1)??10-2 atoms/cm2 s for the NGG samples, and (0.4??0.1)??10-2 atoms/cm2 s for the Dye-3 samples. The 36Cl fluxes in ice that was deposited as snow during peak atmospheric nuclear weapon test (1957-1958) were (33??1)??10-2 atoms/cm2 s for the UFG site, (291??3)??10-2 atoms/cm2 s for the NGG site, and (124??5)??10-2 atoms/ cm2 s for the Dye-3 site. A weapon test period 137Cs concentration of 0.79??0.05 Bq/kg in the NGG ice core also was detected in the same section of ice that contained the largest 36Cl concentration. ?? 2000 Elsevier Science B.V. All rights reserved.

Green, J.R.; Cecil, L.D.; Synal, H.-A.; Kreutz, K.J.; Wake, C.P.; Naftz, D.L.; Frape, S.K.

2000-01-01

313

ESCRT-I Core and ESCRT-II GLUE Domain Structures Reveal Role for GLUE  

E-print Network

ESCRT-I Core and ESCRT-II GLUE Domain Structures Reveal Role for GLUE in Linking to ESCRT-I) with the yeast-specific zinc- finger insertion within the GLUE domain of Vps36 (ESCRT-II). The crystal structure of the GLUE domain missing this insertion reveals it is a split PH domain, with a noncanonical lipid binding

Williams, Roger L.

314

Greenland ice sheet contribution to sea level rise during the last interglacial period: a modelling study driven and constrained by ice core data  

NASA Astrophysics Data System (ADS)

As pointed out by the forth assessment report of the Intergovernmental Panel on Climate Change, IPCC-AR4 (Meehl et al., 2007), the contribution of the two major ice sheets, Antarctica and Greenland, to global sea level rise, is a subject of key importance for the scientific community. By the end of the next century, a 3-5 °C warming is expected in Greenland. Similar temperatures in this region were reached during the last interglacial (LIG) period, 130-115 ka BP, due to a change in orbital configuration rather than to an anthropogenic forcing. Ice core evidence suggests that the Greenland ice sheet (GIS) survived this warm period, but great uncertainties remain about the total Greenland ice reduction during the LIG. Here we perform long-term simulations of the GIS using an improved ice sheet model. Both the methodologies chosen to reconstruct palaeoclimate and to calibrate the model are strongly based on proxy data. We suggest a relatively low contribution to LIG sea level rise from Greenland melting, ranging from 0.7 to 1.5 m of sea level equivalent, contrasting with previous studies. Our results suggest an important contribution of the Antarctic ice sheet to the LIG highstand.

Quiquet, A.; Ritz, C.; Punge, H. J.; Salas y Mélia, D.

2013-02-01

315

Dating of a Dome Fuji (Antarctica) shallow ice core by volcanic signal synchronization with B32 and EDML1 chronologies  

NASA Astrophysics Data System (ADS)

We found extremely good synchronization of volcanic eruption signals between a shallow ice core drilled at Dome Fuji in 2001 (DF01 core) and the B32 shallow ice core from Dronning Maud Land, East Antarctica. We then applied volcanic signature matching to transfer the B32 chronology constructed by annual layer counting to a portion of the DF01 core for which annual layer counting was difficult because of the low precipitation rate. Matching was done by careful comparison of non-sea-salt sulfate (nssSO42-) data, which have a temporal resolution of about 1 yr, between the DF01 and B32 cores. The newly obtained chronology is called DFS1 (Dome Fuji Shallow ice core 1). In total, 31 volcanic eruptions were synchronized from AD 1900 back to AD 187, the earliest volcanic eruption date in the B32 core. The mean accumulation rate between synchronized volcanic horizons of the Dome Fuji core relative to rates at the B32 core drilling site did not differ significantly between these dates, increasing our confidence in this matching approach. We also used the B32-correlated EDML1/EDC3 chronology obtained from the top part of the EPICA Dronning Maud Land (DML) deep ice core to date a portion of the DF01 core. This new chronology, called DFS2 (Dome Fuji Shallow ice core 2), uses the correlations between B32 and EDML1/EDC3 ages to date the DF01 core from AD 1900 back to AD 199; moreover, four volcanic eruption dates from the EDML1/EDC3 chronology were used to date the interval from AD 199 back to AD 1. Because the EDML1/EDC3 ages were determined by adopting the B32 chronology back to AD 1170, DFS1 and DFS2 dates are identical between AD 1170 and 1900. These two methods enabled us to obtain a detailed chronology of the DF01 core, in particular the part before the last millennium, which has been difficult before this. We also present the absolute mean accumulation rates at Dome Fuji between AD 1 and 1900, based on the DFS1 and DFS2 chronologies.

Motizuki, Y.; Nakai, Y.; Takahashi, K.; Igarashi, M.; Motoyama, H.; Suzuki, K.

2014-01-01

316

Central Asian Water Cycle Variability over the past Century from Ice-core Isotope Records (Altai, Tien Shan)  

NASA Astrophysics Data System (ADS)

The Altai and Tien Shan ice cores records are expanding our understanding of the inter-Hemispheric water cycle and climate dynamics: the moisture advection from Atlantic and Pacific Oceans, and from Aral-Caspian closed drainage basin to the Arctic Ocean defining the interaction over time between the westerly jet stream, and the Asian monsoon, Siberian and Tibetan Highs and deciphering local verses regional change over the temperate and high latitudes. The multi-parameter high-resolution (i.e., sub-seasonal) glacio-climatic and environmental records from the upper fifty meter of the 175 m surface to bottom ice core recovered in 2003 from the Belukha snow-firn plateau at 4115 m (Altai Mts.) and the upper 20 m of the 160 m deep ice-core recovered in 2000 from the head of Inylchek Glacier at 5200 m (Tien Shan Mts.) were developed and evaluated. The long-term meteorological, synoptic, dust storm and forest fire records and physical stratigraphy data were the basis for calibration, validation and interpretation. The mean annual snow accumulation on the Inylchek glacier for the period from 1992 to 1998 was found to be 116 g cm-2/yr. Validation of the Altai ice core records through the marker horizon of volcanic eruptions showed monthly accordance in the dating century accumulation ice core records with the mean accumulation rate of 650 g cm-2/yr. The ? 18O, ? D and d excess records showed well-preserved seasonal variation, which is significantly controlled by air temperature, by share of cold/or warm season precipitation amount and origin, transport and recycling of moisture. The ? 18O-? D relationship in the upper 50 m of the Altai ice core records has the same slope to the co-variance as that of the global meteoric water line (i.e., 8), while the Tien Shan ice-core records has lower slope (i.e., 7). The snow accumulation of central Asian glaciers was formed from oceanic precipitation and the moisture originated over Aral-Caspian sources. The Northern Atlantic contributed 15% of moisture, while Black and Eastern Mediterranean Seas 32% to the 20 m Inylchek accumulation. The rest precipitation on the Tien Shan glacier has inter-continental origin. The d-excess show means maximum in winter and minimum in summer in both ice-cores records. About 70% of the Altai snow firn core d-excess records vary within 6% and 15% with maximum of more than 40% within the range from 8% to 13% with the shift to higher values in the upper part of ice core pointing on increased share of moisture recycled over intercontinental Asia. More than half of accumulation on the Altai records had Atlantic Ocean origin. Precipitation from the Arctic and Pacific Oceans had the smallest deuterium excess and their share in total accumulation is increasing. Ice core analysis of the composition of ? 18O reflected different synoptic situations, which will be reconstructed along with air temperature for about the century of ice core records.

Aizen, V.; Aizen, E.; Mayewski, P.; Kreutz, K.; Joswiak, D.; Takeuchi, N.; Fujita, K.

2004-12-01

317

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

318

Characterizing atmospheric circulation signals in Greenland ice cores: insights from a weather regime approach  

NASA Astrophysics Data System (ADS)

Greenland ice cores offer seasonal to annual records of ?18O, a proxy for precipitation-weighted temperature, over the last few centuries to millennia. Here, we investigate the regional footprints of the North Atlantic weather regimes on Greenland isotope and climate variability, using a compilation of 22 different shallow ice-cores and the atmospheric pressure conditions from the twentieth century reanalysis (20CR). As a first step we have verified that the leading modes of winter and annual ?18O are well correlated with oceanic (Atlantic multidecadal oscillation) and atmospheric [North Atlantic oscillation (NAO)] indices respectively, and also marginally with external forcings, thus confirming earlier studies. The link between weather regimes and Greenland precipitation, precipitation-weighted temperature and ?18O is further explored by using an isotope simulation from the LMDZ-iso model, where the 3-dimensional wind fields are nudged to those of 20CR. In winter, the NAO+ and NAO- regimes in LMDZ-iso produce the largest isotopic changes over the entire Greenland region, with maximum anomalies in the South. Likewise, the Scandinavian blocking and the Atlantic ridge also show remarkable imprints on isotopic composition over the region. To assess the robustness and model dependency of our findings, a second isotope simulation from the isotopic model is also explored. The percentage of Greenland ?18O variance explained by the ensemble of weather regimes is increased by a factor near two in both LMDZ-iso and IsoGSM when compared to the contribution of the NAO index only. Similarly, weather regimes provide a net gain in the ?18O variance explained of similar magnitude for the whole set of ice core records. Greenland ?18O also appears to be locally affected by the low-frequency variations in the centres of action of the weather regimes, with clearer imprints in the LMDZ-iso simulation. This study opens the possibility for reconstructing past changes in the frequencies of occurrence of the weather regimes, which would rely on the sensitive regions identified here, and the use of additional proxies over the North Atlantic region.

Ortega, Pablo; Swingedouw, Didier; Masson-Delmotte, Valérie; Risi, Camille; Vinther, Bo; Yiou, Pascal; Vautard, Robert; Yoshimura, Kei

2014-11-01

319

New ice core evidence for a volcanic cause of the A.D. 536 dust veil  

NASA Astrophysics Data System (ADS)

New and well-dated evidence of sulphate deposits in Greenland and Antarctic ice cores indicate a substantial and extensive atmospheric acidic dust veil at A.D. 533-534 +/- 2 years. This was likely produced by a large explosive, near equatorial volcanic eruption, causing widespread dimming and contributing to the abrupt cooling across much of the Northern Hemisphere known from historical records and tree-ring data to have occurred in A.D. 536. Tree-ring data suggest that this was the most severe and protracted short-term cold episode across the Northern Hemisphere in the last two millennia, even surpassing the severity of the cold period following the Tambora eruption in 1815.

Larsen, L. B.; Vinther, B. M.; Briffa, K. R.; Melvin, T. M.; Clausen, H. B.; Jones, P. D.; Siggaard-Andersen, M.-L.; Hammer, C. U.; Eronen, M.; Grudd, H.; Gunnarson, B. E.; Hantemirov, R. M.; Naurzbaev, M. M.; Nicolussi, K.

2008-02-01

320

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

321

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

322

Intra-annual variations in atmospheric dust and tritium in the North Pacific region detected from an ice core from Mount Wrangell, Alaska  

Microsoft Academic Search

The North Pacific is subject to various seasonal climate phenomena and material circulations. Therefore intra-annual ice core data are necessary for an assessment of the climate variations. To assess past variations, a 50-m ice core was drilled at the summit of Mount Wrangell Volcano, Alaska. The dust number, tritium concentrations, and stable hydrogen isotope were analyzed. The period covered was

Teppei J. Yasunari; Takayuki Shiraiwa; Syosaku Kanamori; Yoshiyuki Fujii; Makoto Igarashi; Koji Yamazaki; Carl S. Benson; Takeo Hondoh

2007-01-01

323

Large variability of trace element mass fractions determined by ICP-SFMS in ice core samples from worldwide high altitude glaciers  

E-print Network

Large variability of trace element mass fractions determined by ICP-SFMS in ice core samples from and mass fractions of trace elements in melted acidified ice core samples measured by Inductively Coupled. Twenty trace elements (Ag, Al, As, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Pb, Rb, Sb, Sn, Ti, Tl, U, V and Zn

Howat, Ian M.

324

Nitrogen isotopes in ice core nitrate linked to anthropogenic atmospheric acidity change  

PubMed Central

Nitrogen stable isotope ratio (?15N) in Greenland snow nitrate and in North American remote lake sediments has decreased gradually beginning as early as ?1850 Christian Era. This decrease was attributed to increasing atmospheric deposition of anthropogenic nitrate, reflecting an anthropogenic impact on the global nitrogen cycle, and the impact was thought to be amplified ?1970. However, our subannually resolved ice core records of ?15N and major ions (e.g., , ) over the last ?200 y show that the decrease in ?15N is not always associated with increasing concentrations, and the decreasing trend actually leveled off ?1970. Correlation of ?15N with H+, , and HNO3 concentrations, combined with nitrogen isotope fractionation models, suggests that the ?15N decrease from ?1850–1970 was mainly caused by an anthropogenic-driven increase in atmospheric acidity through alteration of the gas?particle partitioning of atmospheric nitrate. The concentrations of and also leveled off ?1970, reflecting the effect of air pollution mitigation strategies in North America on anthropogenic NOx and SO2 emissions. The consequent atmospheric acidity change, as reflected in the ice core record of H+ concentrations, is likely responsible for the leveling off of ?15N ?1970, which, together with the leveling off of concentrations, suggests a regional mitigation of anthropogenic impact on the nitrogen cycle. Our results highlight the importance of atmospheric processes in controlling ?15N of nitrate and should be considered when using ?15N as a source indicator to study atmospheric flux of nitrate to land surface/ecosystems. PMID:24711383

Geng, Lei; Alexander, Becky; Cole-Dai, Jihong; Steig, Eric J.; Savarino, Joel; Sofen, Eric D.; Schauer, Andrew J.

2014-01-01

325

Dating the Vostok ice core record by importing the Devils Hole chronology  

USGS Publications Warehouse

The development of an accurate chronology for the Vostok record continues to be an open research question because these invaluable ice cores cannot be dated directly. Depth-to-age relationships have been developed using many different approaches, but published age estimates are inconsistent, even for major paleoclimatic events. We have developed a chronology for the Vostok deuterium paleotemperature record using a simple and objective algorithm to transfer ages of major paleoclimatic events from the radiometrically dated 500,000-year ??18O-paleotemperature record from Devils Hole, Nevada. The method is based only on a strong inference that major shifts in paleotemperature recorded at both locations occurred synchronously, consistent with an atmospheric teleconnection. The derived depth-to-age relationship conforms with the physics of ice compaction, and internally produces ages for climatic events 5.4 and 11.24 which are consistent with the externally assigned ages that the Vostok team needed to assume in order to derive their most recent chronology, GT4. Indeed, the resulting V-DH chronology is highly correlated with GT4 because of the unexpected correspondence even in the timing of second-order climatic events that were not constrained by the algorithm. Furthermore, the algorithm developed herein is not specific to this problem; rather, the procedure can be used whenever two paleoclimate records are proxies for the same physical phenomenon, and paleoclimatic conditions forcing the two records can be considered to have occurred contemporaneously. The ability of the algorithm to date the East Antarctic Dome Fuji core is also demonstrated.

Landwehr, J.M.; Winograd, I.J.

2001-01-01

326

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

Microsoft Academic Search

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

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

2006-01-01

327

Millennial-scale variability during the last glacial: The ice core record E.W. Wolff a,*, J. Chappellaz b  

E-print Network

Millennial-scale variability during the last glacial: The ice core record E.W. Wolff a,*, J Interstadials (GI) and cold Greenland Stadials (GS) at millennial- scale during the last glacial period. Here we is the millennial variability that is particularly noticeable in the last glacial (Marine Isotope Stages (MIS) 4, 3

Chappellaz, Jérôme

328

Evidence from polar ice cores for the increase in atmospheric CO2 in the past two centuries  

Microsoft Academic Search

Measurements of the CO2 gas concentration enclosed in an ice core from Siple Station, Antarctica, are reported which allow the development of atmospheric CO2 to be traced from a period overlapping the Mauna Loa record back over the past two centuries. The results indicate that atmospheric CO2 concentration around 1750 was 280 + or - 5 ppmv and has increased

A. Neftel; E. Moor; H. Oeschger; B. Stauffer

1985-01-01

329

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

Microsoft Academic Search

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

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

2011-01-01

330

Hubertus Fischer Birgit Mieding A 1,000-year ice core record of interannual to multidecadal variations in  

E-print Network

-known North Atlantic Oscillation (NAO) (Hurrell et al. 2001; Wallace and Gutzler 1981). Empirical orthogonal to multidecadal time scales. For instance, a multidecadal variation in SST and SLP in the North Atlantic regionHubertus Fischer Ã? Birgit Mieding A 1,000-year ice core record of interannual to multidecadal

Fischer, Hubertus

331

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

E-print Network

Ionic species especially give valuable information as they have many different sources. Water soluble input from the middle of the 20th century.2­4 Ion chromatography exhibits high sensitivity and is well from a relatively long ice core comparison have been published earlier. In this paper we compare

Moore, John

332

Lithology and chronology of ice-sheet fluctuations (magnetic susceptibility of cores from the western Ross Sea)  

NASA Technical Reports Server (NTRS)

The goals of the marine geology part of WAIS include reconstructing the chronology and areal extent of ice-sheet fluctuations and understanding the climatic and oceanographic influences on ice-sheet history. As an initial step toward attaining these goals, down-core volume magnetic susceptibility (MS) logs of piston cores from three N-S transects in the western Ross Sea are compared. The core transects are within separate petrographic provinces based on analyses of till composition. The provinces are thought to reflect the previous locations of ice streams on the shelf during the last glaciation. Magnetic susceptibility is a function of magnetic mineral composition, sediment texture, and sediment density. It is applied in the western Ross Sea for two purposes: (1) to determine whether MS data differentiates the three transects (i.e., flow lines), and thus can be used to make paleodrainage reconstructions of the late Wisconsinan ice sheet; and (2) to determine whether the MS data can aid in distinguishing basal till diamictons from diamictons of glacial-marine origin and thus, aid paleoenvironmental interpretations. A comparison of the combined data of cores in each transect is presented.

Jennings, Anne E.

1993-01-01

333

The Younger Dryas Termination and North Atlantic Deep Water Formation: Insights from climate model simulations and Greenland Ice Cores  

Microsoft Academic Search

Results from the GISP2 and GRIP ice cores show that the termination of the Younger Dryas (YD) climate event in Greenland was a large and extremely fast climate change. A reinitiation of North Atlantic Deep Water formation following a shutdown, and its associated winter release of heat to the atmosphere, has been suggested as the most likely cause of this

Peter J. Fawcett; Anna Maria Ágústsdóttir; Richard B. Alley; Christopher A. Shuman

1997-01-01

334

The Younger Dryas termination and North Atlantic Deep Water formation: Insights from climate model simulations and Greenland ice cores  

Microsoft Academic Search

Results from the GISP2 and GRIP ice cores show that the termination of the Younger Dryas (YD) climate event in Greenland was a large and extremely fast climate change. A reinitiation of North Atlantic Deep Water formation following a shutdown, and its associated winter release of heat to the atmosphere, has been suggested as the most likely cause of this

Peter J. Fawcett; Anna Maria Ágústsdóttir; Richard B. Alley; Christopher A. Shuman

1997-01-01

335

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

E-print Network

at Nevado Sajama, Bolivia C.A. REESE,1 K.B. LIU,2 L.G. THOMPSON3 1 Department of Geography and Geology the results of pollen analysis performed on an ice core recovered from Nevado Sajama, Bolivia, dated to 25 ka

Howat, Ian M.

336

Modified HNO3 seasonality in volcanic layers of a polar ice core - Snowpack effect or photochemical perturbation?  

Microsoft Academic Search

Changes in atmospheric HNO3 chemistry following the Laki (1783), Tambora (1815), and Katmai (1912) volcanic eruptions are presently investigated in view of a central Greenland ice core's chemical composition. Attention is given to the concentration of several cations and anions, using ion chromatography. Following the eruptions, the ratio of winter to summer depositions of NO3(-) was significantly higher than during

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

1993-01-01

337

Analytical Comparisons of Tree Ring Data, Greenland Ice Core Temperatures and Temperature Fluctuations of the Sargasso Sea  

Microsoft Academic Search

Embedded in various events on Earth are data that allow us to map the temperature of the Earth over many years. In this work we have chosen the temperature fluctuations in the Sargasso Sea, the changing patterns in tree ring growth and temperature fluctuations in Greenland ice core samples for comparison with a goal to understanding the patterns in global

James Roberts; Jai Dahiya

2010-01-01

338

Analysis of vanillic acid in polar ice cores as a biomass burning proxy - preliminary results from the Akademii Nauk Ice Cap in Siberia  

NASA Astrophysics Data System (ADS)

Biomass burning influences global climate change and the composition of the atmosphere. The drivers, effects, and climate feedbacks related to fire are poorly understood. Many different proxies have been used to reconstruct past fire frequency from lake sediments and polar ice cores. Reconstruction of historical trends in biomass burning is challenging because of regional variability and the qualitative nature of various proxies. Vanillic acid (4-hydroxy-3-methoxybenzoic acid) is a product of the combustion of conifer lignin that is known to occur in biomass burning aerosols. Biomass burning is likely the only significant source of vanillic acid in polar ice. In this study we describe an analytical method for quantifying vanillic acid in polar ice using HPLC with electrospray ionization and tandem mass spectrometric detection. The method has a detection limit of 100 pM and a precision of × 10% at the 100 pM level for analysis of 100 ?l of ice melt water. The method was used to analyze more than 1000 discrete samples from the Akademii Nauk ice cap on Severnaya Zemlya in the high Russia Arctic (79°30'N, 97°45'E) (Fritzsche et al., 2002; Fritzsche et al., 2005; Weiler et al., 2005). The samples range in age over the past 2,000 years. The results show a mean vanillic acid concentration of 440 × 710 pM (1?), with elevated levels during the periods from 300-600 and 1450-1550 C.E.

Grieman, M. M.; Jimenez, R.; McConnell, J. R.; Fritzsche, D.; Saltzman, E. S.

2013-12-01

339

?13Catm and [CO2] measurements in Antarctic ice cores, 160 kyrBP - present  

NASA Astrophysics Data System (ADS)

Measurements from Antarctic ice cores allow us to reconstruct atmospheric concentrations of climatically important gases including CO2 over the past 800 kyr. Such measurements show that [CO2] has varied in parallel with Antarctic temperatures on glacial-interglacial timescales. Knowledge of the variations of the stable carbon isotope of CO2, ?13Catm, can help us better understand the processes involved in these fluctuations. Here, we present a first complete ?13Catmrecord extending from 160 kyrBP to the present accompanied by ?15N2 measurements during Marine Isotope Stage 3 (MIS 3, 57 - 29 kyrBP). The present record, measured primarily on ice from the EPICA Dome C and Talos Dome ice cores, has an average resolution of 500 yr, focused mainly on the Last Glacial Maximum and termination (180 yr; Schmitt et al., 2012), MIS 3 (660 yr), and Termination II through MIS 5.4 (590 yr; Schneider et al., 2013). Throughout the record, ?13Catm varies between approximately -6.8 and -6.4‰Following a period of relatively constant ?13Catm at the end of MIS 6 (around -6.8), the boundaries of MIS 5 correspond roughly with the beginning and end of a gradual enrichment in this isotope. In comparison, the more recent record depicts three more abrupt excursions to lighter values around 63 - 59, 46, and 17 kyrBP, in each case followed by a slower return (0.4o over the course of 5 - 15 kyr) to more enriched isotopic values. These coincide with Heinrich events 6, 5, and 1, respectively. No direct correlation is observed between the concentration and carbon isotope of CO2 over the last 160 kyr. The data indicate rather that numerous processes, such as uptake and release of atmospheric CO2 by the ocean and land biosphere, perhaps influenced by regions of growing permafrost during MIS 3 and 4, acting on a variety of timescales must be considered in explaining the evolution of ?13Catm on glacial-interglacial timescales. References: Schmitt, J. et al. Science 336, 711-714 (2012) Schneider, R. et al. Clim. Past, 9, 2507-2523 (2013)

Eggleston, Sarah; Schmitt, Jochen; Schneider, Robert; Joos, Fortunat; Fischer, Hubertus

2014-05-01

340

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

341

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

342

Geophysical characteristics of an active subglacial lake revealed by radar and seismic experiments, Whillans Ice Stream, Antarctica  

NASA Astrophysics Data System (ADS)

Satellite remote sensing techniques have recently identified several hundred active subglacial lakes under the ice in Antarctica. Water and sediment at the basal interface of glaciers and ice sheets provide the environment that supports microbial life as well as exerting primary control on ice dynamics. Thus a clear understanding of this system is of key importance to scientists from a range of disciplines. We have recently undertaken ground-based geophysical experiments to characterize one of these lakes in the lower trunk of Whillans Ice Stream in West Antarctica. Subglacial Lake Whillans is being studied as part of a multidisciplinary project called the Whillans Ice Stream Subglacial Access Research Drilling project (WISSARD) that will investigate the physical, geochemical and biological conditions at the base of the ice stream as water and sediment are transported from inland to the grounding line. We present data from ice-penetrating radar, active-source seismic and GPS experiments undertaken during the 2010-2011 field season that characterize basal conditions 800 meters beneath Whillans Ice Stream. The hydropotential map derived from high-density surface topography and ice thickness measurements reveals a lake basin of approximately 60 square kilometers with water thickness on the order of 5-6 m deep at the time of the survey defined by seismic reflections. Both infill and outflow appear to come primarily from a narrow opening in the upflow direction, though the entire south portion of the basin shows high reflectivity, indicating a wet bed. In contrast, a prominent bedrock ridge defines a distinct north margin of the lake while elevated topography forms a boundary in the downflow direction. Together with information from satellite remote sensing of the surface, we describe the evolution of the basal hydraulic system from the start of the ICESat era to the present as we prepare for lake access drilling in 2012-13.

Jacobel, R. W.; Christianson, K.; Horgan, H.; Anandakrishnan, S.; Gobel, R.; Keisling, B.; Snyder, L.

2011-12-01

343

Generated using version 3.2 of the official AMS LATEX template Reemergence Mechanisms for North Pacific Sea Ice Revealed1  

E-print Network

Pacific Sea Ice Revealed1 Through Nonlinear Laplacian Spectral Analysis2 Mitchell Bushuk, Dimitrios-mail: bushuk@cims.nyu.edu 1 #12;ABSTRACT4 This paper studies spatiotemporal modes of variability of sea ice physical units. The coupled NLSA modes are10 utilized to investigate North Pacific sea ice reemergence

Majda, Andrew J.

344

Generated using version 3.2 of the official AMS LATEX template Reemergence Mechanisms for North Pacific Sea Ice Revealed1  

E-print Network

Pacific Sea Ice Revealed1 through Nonlinear Laplacian Spectral Analysis2 Mitchell Bushuk, Dimitrios-mail: bushuk@cims.nyu.edu 1 #12;ABSTRACT4 This paper studies spatiotemporal modes of variability of sea ice physical units. The coupled NLSA modes are utilized to investigate10 North Pacific sea ice reemergence

Majda, Andrew J.

345

Multisite high resolution measurements of carbon monoxide along Greenland ice cores: evidence for in-situ production and potential for atmospheric reconstruction  

NASA Astrophysics Data System (ADS)

Carbon monoxide (CO) is the principal sink for hydroxyl radicals (OH) in the troposphere. Consequently, changes in atmospheric CO levels can considerably perturb the oxidizing capacity of the atmosphere, affecting mixing ratios of a host of chemical species oxidized by OH, including methane. In addition, CO variations (and changes in its stable isotopic composition) are expected to be good tracers of changes in biomass burning emissions. Investigating past mixing ratios of carbon monoxide is thus a promising approach towards reducing uncertainty related to the past oxidative capacity of the atmosphere and biogeochemical cycling of methane. Recent developments in optical spectrometry (Optical Feedback Cavity Enhanced Absorption Spectrometry, OFCEAS), combined with continuous flow analysis (CFA) systems, allow efficient, precise measurements of CO concentrations in ice cores. Coupling our OFCEAS spectrometer with the CFA melter operated at DRI (Reno, USA) provided the first continuous CO measurements along the NEEM (Greenland) core covering the last 1800 yr at an unprecedented resolution. Although the most recent section of this record (i.e., since 1700 AD) agreed with existing discrete CO measurements from the Eurocore ice core and the deep NEEM firn, it was difficult to interpret in terms of atmospheric CO variation due to high frequency, high amplitudes spikes related to in-situ production (Faïn et al., Climate of the Past Discussion). During a recent 8-week analytical campaign, three different ice archives from Greenland were melted on the DRI CFA and analyzed continuously for CO with the OFCEAS spectrometer: (i) the D4 core (spanning the last 170 yr), (ii) the NEEM core (extending the existing record from 200 AD to 800 BC), and (iii) the Tunu core (spanning the last 1800 yr). Although in-situ production of CO is observed at all sites, these new records reveal different CO patterns and trends. This multisite approach allows us to better characterize the processes involved in CO in-situ production by evaluating the influence of site-specific factors such as surface accumulation rate (10, 22 and 41 cm ice yr-1 for Tunu, NEEM, and D4 respectively), surface temperature, or aerosols loading (with e.g., median black carbon concentration ranging from 0.9 to 2.3 ng g-1 among the investigated sites). However, a quantitative understanding of the past evolution of atmospheric CO above Greenland remains challenging due to the existence of these artifacts.

Faïn, Xavier; Chappellaz, Jérôme; Rhodes, Rachael; Stowasser, Christopher; Blunier, Thomas; McConnell, Joseph; Brook, Edward; Desbois, Thibault; Romanini, Daniele

2014-05-01

346

Is methane-driven deglaciation consistent with the ice core record?  

NASA Astrophysics Data System (ADS)

The rapid climate changes at the terminations marking the end of the last glaciation are poorly understood. This study uses the Cambridge two-dimensional atmospheric model to investigate the impact of a large marine sediment slump or permafrost rupture releasing 4000 Tg of CH4 into the high latitudes of the northern hemisphere, with particular emphasis on the evolution of atmospheric CH4 concentrations, which may have led to an associated direct radiative effect of the order of 1 W m-2, persisting for a few decades, because of enhanced levels of atmospheric CH4. The model-generated CH4 concentrations were converted into synthetic ice core signals for 66°N and 85°S, representing Arctic and Antarctic cores, respectively. A range of possible averaging times was considered. The results show that irrespective of the site or enclosure time chosen, with the current sampling interval of ˜300 years, it is not possible to discount completely the existence of a spike as a result of the instantaneous release of 4000 Tg of CH4. Detection or refutation of a CH4 spike would, however, be probable if the sampling interval were reduced to around 50-100 years.

Thorpe, R. B.; Law, K. S.; Bekki, S.; Pyle, J. A.; Nisbet, E. G.

1996-12-01

347

Spatial and temporal isotopic patterns across the West Antarctic Ice Sheet Divide from new snowpits and firn cores  

NASA Astrophysics Data System (ADS)

Studies have shown significant warming through the 1990's in the West Antarctic Ice Sheet (WAIS) divide but the ice core isotopic records used in those studies end in 2000-2001. Fourteen sub-annually resolved snowpits and firn cores were collected during traverses in 2010 and 2011 across the WAIS divide. One of the new cores overlaps in time with a core drilled in 2000 at the same location. These two cores correlate significantly with each other, giving confidence in the utility of the new data. These new isotopic records are combined with existing isotopic data in the region to quantify the spatial and temporal patterns in the isotopes, and extend the previous records through 2011. Significance of these isotopic patterns across WAIS is determined and is used to re-evaluate the warming of the West Antarctic interior over recent decades. The proposed mechanisms for the warming due to regional changes in atmospheric circulation, sea surface temperature, and sea ice will be re-evaluated using these updated isotopic records and new GCM simulations with isotopic tracers.

Williams, J.; Rupper, S.; Burgener, L. K.; Ding, Q.; Steig, E. J.; Christensen, W. F.; Koenig, L.; Miege, C.; Koutnik, M. R.; Brucker, L.; Forster, R. R.; Carpenter, M.; Meadows, M.; Riley, L.; Smith, R.; Keeler, D.; Wagner, J.; Jensen, M.; Cook, P.

2012-12-01

348

Cosmogenic 36Cl and 10Be in the WAIS Divide ice core from 6-21 kyr BP  

NASA Astrophysics Data System (ADS)

Cosmogenic nuclides such as 10Be and 36Cl, produced in the atmosphere by spallation reactions of primary and secondary cosmic ray particles with atoms in the atmosphere, are deposited to the surface with precipitation and stored in glacial ice sheet archives. The final concentration of these nuclides in the ice is dependent upon a number of factors including variations in solar activity, strength of the geomagnetic field, atmospheric transport patterns and snow accumulation rates. Although 10Be is the most commonly measured cosmogenic isotope in ice cores, the measurement of a single isotope may not be sufficient to disentangle these factors. Here we present measurements of 10Be and 36Cl from the West Antarctic Ice Sheet (WAIS) Divide ice core from approximately 6-21 kyr BP. Owing to the differing production rates of 10Be and 36Cl as a function of cosmic ray energy, changes in their ratio may provide information about changes in solar activity in the past. We will also compare this ratio to the accumulation rate at WAIS Divide in order to investigate differences in deposition between the two isotopes. This work was supported by NSF grants ANT-0839042 and 0839137.

Woodruff, T. E.; Welten, K. C.; Caffee, M. W.; Nishiizumi, K.

2013-12-01

349

Iceshelf instability and the collapsing NW margin of the Laurentide Ice Sheet: core evidence from Viscount Melville Sound, Arctic Canada  

NASA Astrophysics Data System (ADS)

Recent work in the western Canadian Arctic Archipelago has seen a dramatic re-evaluation of the timing and extent of Late Wisconsinan glaciation by a primarily cold-based Laurentide Ice sheet. This has included the occupation by ice of formerly-considered ice free terrain and the extension of grounded ice from the main channels of the Northwest Passage, westwards onto the Beaufort Sea continental shelf. Nonetheless, while the pattern of ice extent and initial retreat is now well constrained, significant questions remain regarding the main phase of ice retreat southeastwards onto mainland Canada and the stability of the retreating margin in response to ameliorating climate and sea-level change. Earlier terrestrially-based research along the Victoria, and Melville Island coasts of Viscount Melville Sound have demonstrated the retreat of grounded glacial ice from this >105 000 km2 basin by '13.5 cal ka BP followed by the re-establishment of a floating iceshelf impinging on the coasts of Viscount Melville Sound ~10.9 cal ka BP. Molluscan chronologies suggest the establishment of the iceshelf was extremely rapid, persisting for some 800 years, and subsequently undergoing an equally rapid collapse. This new and ongoing study investigates a series of Geological Survey of Canada / ArcticNet piston cores from the central part of Viscount Melville Sound, considered to have been beneath the short-lived ice shelf, thus permitting a detailed examination of the potential mechanisms and dynamics of iceshelf formation and collapse. Analyses of ice-rafted debris (IRD), coupled with micropalaeontological and chronostratigraphic investigation; data suggest a rapid ice advance into Viscount Melville Sound consistent with terrestrial interpretations. The presence of "rain-out tills" and IRD indicative of a Victoria Island / M'Clintock Channel origin is considered a result of deposition from a debris-rich tongue of floating glacial ice associated with streaming ice exiting M'Clintock Channel, permitting the on-shore rafting of ice and emplacement of coastal till sequences and iceshelf moraines. The rapid transition from sub-iceshelf sediments to ice proximal to distal sediments is also consistent with terrestrial evidence for the rapid retreat of the Viscount Melville Sound Iceshelf. AMS 14C-dated benthic foraminifera from above the iceshelf-marine transition provide a minimum age on iceshelf collapse of ~9.0 cal ka BP. Age-depth model projections bellow the lowermost core date assuming enhance ice-proximal sedimentation rates permit an approximate iceshelf collapse date similar to that indicated by terrestrial sequences. This ongoing study contributes towards an improved understanding of the glaciological constraints placed on the streaming of ice from M'Clintock Channel into the Sound and the resulting draw-down and destabilization of the NW sector of the Laurentide Ice Sheet. Furthermore, emerging foraminiferal, diatom, and biogeochemical data provide valuable insights into the deglacial and postglacial history of the western sector of the Northwest Passage.

Furze, Mark; Pienkowski, Anna; England, John; da Silveira Ramos Esteves, Mariana; Bennett, Robbie; Krywko, Jack; Glembiski, Danna; McLean, Brian; Blasco, Steve

2013-04-01

350

Recently exposed vegetation reveals Holocene changes in the extent of the Quelccaya Ice Cap, Peru  

Microsoft Academic Search

Radiocarbon dating of well-preserved, in-place vegetation exposed by the retreating Quelccaya Ice Cap of southeastern Peru constrains the last time the ice cap's extent was smaller than at present. Seventeen plant samples from two sites along the central western margin collectively date to 4700 and 5100 cal yr BP and strongly indicate that current ice cap retreat is unprecedented over the

Aron M. Buffen; Lonnie G. Thompson; Ellen Mosley-Thompson

2009-01-01

351

High Resolution CO2 Reconstructions from the WAIS Divide Ice Core  

NASA Astrophysics Data System (ADS)

A clear connection exists between atmospheric greenhouse gases, climate, and ice sheet volume during glacial-interglacial cycles. Establishing the role of carbon dioxide (CO2), both as a feedback and forcing, during the most recent glacial and deglacial periods provides an excellent opportunity for understanding how this connection operates. To do this, a precise, high-resolution, well-dated record of atmospheric CO2 is a prerequisite. We will present a carbon dioxide record from 40-35 and 28-9 ka from the last glacial and deglacial periods from a new ice core from West Antarctica with an average sampling resolution of 25-50 yrs. Our record shows that CO2 variations during the glacial period have a clear relationship with abrupt climate changes in the Northern Hemisphere that continues into the deglacial period. In addition, instead of being gradual (several millennia), nearly half of the ~85ppm rise in CO2 during the deglaciation occurred in three abrupt 10-15ppm steps that took place in less than 100-200 yrs and were followed by concentration plateaus. Each transition was synchronous with abrupt changes in methane (CH4), suggesting a rapid reorganization of the carbon cycle. These rapid changes in atmospheric CO2 and CH4 concentrations are also recorded during the Heinrich Stadials of MIS 3, demonstrating an important mechanism that operates on centennial time scales during the glacial and deglaciation, which may point to important thresholds in the global carbon cycle. We will present our most recent results and newest interpretation.

Marcott, S. A.; Bauska, T. K.; Sowers, T. A.; Edwards, J. S.; Buizert, C.; Kalk, M.; Brook, E.

2013-12-01

352

Surface elevation change artifact at the NEEM ice core drilling site, North Greenland.  

NASA Astrophysics Data System (ADS)

The NEEM deep drilling site (77.45°N 51.06°W) is located at the main ice divide in North Greenland. For the ice core drilling project, a number of buildings was erected and left on the snow surface during the five-year project period. The structures created snowdrifts that formed accordingly to the predominant wind direction on the lee side on the buildings and the overwintering cargo. To get access to the buildings, the snowdrifts and the accumulated snow were removed and the surface in the camp was leveled with heavy machinery each summer. In the camp a GPS reference pole was placed as a part of the NEEM strain net, 12 poles placed in three diamonds at distances of 2,5 km, 7,5 km and 25 km they were all measured with high precision GPS every year. Around the reference pole, a 1 km x 1 km grid with a spacing of 100 m was measured with differential GPS each year. In this work, we present results from the GPS surface topography measurements in and around the campsite. The mapping of the topography in and around the campsite shows how the snowdrifts evolve and are the reason for the lift of the camp site area. The accumulated snowdrifts are compared to the dominant wind directions from year to year. The annual snow accumulation at the NEEM site is 0.60 m. The reference pole in the camp indicates an additional snow accumulation of 0.50 m per year caused by collected drifting snow. The surface topography mapping shows that this artificially elevated surface extends up to several kilometers out in the terrain. This could have possible implications on other glaciological and geophysical measurements in the area i.e. pit and snow accumulation studies.

Berg Larsen, Lars; Schøtt Hvidberg, Christine; Dahl-Jensen, Dorthe; Lilja Buchardt, Susanne

2014-05-01

353

Glacial-interglacial changes in moisture sources for Greenland: Influences on the ice core record of climate  

SciTech Connect

Large, abrupt shifts in the [sup 18]O/[sup 16]O ratio found in Greenland ice must reflect real features of the climate system variability. These isotopic shifts can be viewed as a result of air temperature fluctuations, but determination of the cause of the changes - the most crucial issue for future climate concerns - requires a detailed understanding of the controls on isotopes in precipitation. Results from general circulation model experiments suggest that the sources of Greenland precipitation varied with different climate states, allowing dynamic atmospheric mechanisms for influencing the ice core isotope shifts.

Charles, C.D. (Univ. of California, San Diego, CA (United States)); Rind, D. (Goddard Institute for Space Studies, New York, NY (United States)); Jouzel, J. (Laboratoire de Modelisation du Climat et de l'Environnement (France)); Koster, R.D. (National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, MD (United States)); Fairbanks, R.G. (Columbia Univ., New York, NY (United States))

1994-01-28

354

Modified HNO3 seasonality in volcanic layers of a polar ice core - Snow-pack effect or photochemical perturbation?  

NASA Astrophysics Data System (ADS)

Changes in atmospheric HNO3 chemistry following the Laki (1783), Tambora (1815), and Katmai (1912) volcanic eruptions are presently investigated in view of a central Greenland ice core's chemical composition. Attention is given to the concentration of several cations and anions, using ion chromatography. Following the eruptions, the ratio of winter to summer depositions of NO3(-) was significantly higher than during nonvolcanic periods. While this may be due to ice pack effects, it is proposed that large concentrations of the stratospheric H2SO4 particles ejected by the volcanoes favored HNO3 removal during Arctic winter.

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

1993-04-01

355

Modified HNO3 seasonality in volcanic layers of a polar ice core - Snow-pack effect or photochemical perturbation?  

NASA Technical Reports Server (NTRS)

Changes in atmospheric HNO3 chemistry following the Laki (1783), Tambora (1815), and Katmai (1912) volcanic eruptions are presently investigated in view of a central Greenland ice core's chemical composition. Attention is given to the concentration of several cations and anions, using ion chromatography. Following the eruptions, the ratio of winter to summer depositions of NO3(-) was significantly higher than during nonvolcanic periods. While this may be due to ice pack effects, it is proposed that large concentrations of the stratospheric H2SO4 particles ejected by the volcanoes favored HNO3 removal during Arctic winter.

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

1993-01-01

356

Evidence from an Ice Core of a Large Impact Circa 1443 A.D.  

NASA Astrophysics Data System (ADS)

Published data on melt water from the Siple Dome ice core show distinct anomalies at 1443.16 A.D. The Ca value is 111 ppb, over 9 times the next highest Ca value between 850-1760 A.D. The K value is 20 ppb, about 1.4 times the next highest K value. The Ca anomaly may be due to partial dissolution of CaCO3 microfossils from the 24 km Mahuika bolide impact crater on the southern New Zealand shelf. Deep-sea samples of the Mahuika ejecta layer contain >98% carbonate microfossils. The Mahuika impact may have produced tsunami runups of 130 meters in Jervis Bay, Australia. The Australian megatsunami deposits date to 1450±50 A.D. We analyzed the melt water from 8 ice-core samples from the West Antarctic Siple Dome ice core that date from 1440-1448 A.D. The 1443 A.D. level contained a peak in K of 53 ppb as compared to a background of ~6-7 ppb. Ca was high at 26 ppb but this is not as pronounced as reported earlier. We extracted solid material from the melt water. Except for the 1443 A.D. horizon and one fractured grain at the 1442 A.D. level, most samples were barren except for typical dust. At the 1443 A.D. level, we found 5 carbonate microfossils (coccoliths?) from 5 to 20 microns across. Two were round and solid. One microfossil appeared either caught during mitosis or broken during deformation and elongation. Another carbonate microfossil was unbroken, but appeared deformed into a square. We found a Cu grain with a small amount of oxygen. It is most likely a grain of native copper with an oxidized surface. Deformed microfossils and native minerals are both characteristic of bolide impacts. We also found many microcrystalline magnetite cubes, with an average crystal size of 0.3 microns or less. The high magnetic susceptibility of impact ejacta layers is caused by microcrystalline magnetite. We found a grain of conchoidally fractured feldspar ~15 microns long. A semi-quantitive EDAX analysis found 21% Si, 55% O, 9% Al, 5% Na, 3% K, 2% Fe, and 1% Ca (atomic %), well within the range of K-feldspar compositions. Because Fe does not fit into the feldspar structure, its occurrence implies either that the Fe-bearing feldspar is a glass, or that the Fe is in microcracks within the grain. As ice is not Fe-rich, the former is more likely. Because conchoidal fracture is characteristic of glass, this suggests that the feldspar is a glass (maskelynite) derived from an impact onto continental crust. We also found Al Fe oxide, Ti Al oxide, and amphibole. A semi-quantitative EDAX analysis of the latter found 53% O, 20% Si, 5% Na, 4% Al, Mg, and Fe, 3% Ca, and 0.5% K (atomic %) with trace Ti, S and Cl, close to the composition of the alkali amphibole richterite, which forms in contact metamorphosed limestones (skarns). The Al Fe oxide is most likely hercynite, a spinel that forms in contact metamorphic aureoles in silica-poor environments. All mineral grains had distinct edges. We also found radiating, fibrous crystals of a Ca Na silicate. An EDAX analysis of the mineral found 59% O, 13% Ca, 8% Si, 3% Na, and 1% Mg (atomic %). The Ca Na silicate is most likely pectolite (NaCa2Si3O8), which has radiating, fibrous crystals and forms in skarns. The presence of minerals characteristic of contact metamorphism is important as we have found abundant skarn facies minerals in the Mahuika ejecta layer within deep sea sediment. Thus, our data taken together are most consistent with an impact ejecta layer within the Siple Dome ice core that comes from the Mahuika impact event about 4044 kilometers away; providing a well-constrained date for the event around 1443 A.D.

Abbott, D.; Biscaye, P.; Cole-Dai, J.; Breger, D.

2005-12-01

357

Palaeoglaciology of the Alexander Island ice cap, western Antarctic Peninsula, reconstructed from marine geophysical and core data  

NASA Astrophysics Data System (ADS)

The glacial history of the continental shelf northwest of Alexander Island is not well known, due mainly to a lack of targeted marine data on Antarctica's palaeo-ice sheets in their inter-ice-stream areas. Recently it has been argued that the region was ice-free at the Last Glacial Maximum (LGM) and thus a potential site for glacial refugia. In this paper, multibeam swath bathymetry, sub-bottom profiles and sediment cores are used to map the Alexander Island sector of the Antarctic Peninsula margin, in order to reconstruct the shelf's palaeoglaciology. Sea-floor bedforms provide evidence that an independent ice cap persisted on Alexander Island through the LGM and deglaciation. We show that this ice cap drained via two major, previously-undescribed tidewater outlets (Rothschild and Charcot Glaciers) sourced from an ice dome centred over the west of the island and near-shore areas. The glaciers grounded along deep, fjord-like cross-shelf troughs to within at least ˜10-20 km of the shelf edge, and probably reached the shelf break. Only one small outer-shelf zone appears to have remained free of ice throughout an otherwise extensive LGM. During retreat, grounding-line geomorphology indicates periodic stabilisation of Charcot Glacier on the mid-shelf after 13,500 cal yrs BP, while Rothschild Glacier retreated across its mid-shelf by 14,450 cal yrs BP. The timing of these events is in phase with retreat in nearby Marguerite Trough, and we take this as evidence of a common history and forcing with the Antarctic Peninsula Ice Sheet. The fine details of ice flow documented by our new reconstruction highlight the importance of capturing complex ice flow patterns in models (e.g. in inter-stream areas), for understanding how region-specific parts of Antarctica may change in the future. Moreover, the reconstruction shows that glacial refugia, if present, cannot have been extensive on the Alexander Island shelf at the LGM as indicated by previous biological studies; instead, we argue that any ice-free refugia were probably restricted to isolated outer-shelf pockets, that opened, closed, or were maintained through diachronous ice-sheet advance and retreat.

Graham, Alastair G. C.; Smith, James A.

2012-03-01

358

Asian Ice Core Array (AICA): Late Holocene Atmospheric Dust Reconstruction over Asia  

NASA Astrophysics Data System (ADS)

Atmospheric dust aerosols play a significant role in the earth’s climate system; scattering and/or absorbing incoming shortwave radiation; influencing atmospheric chemical reactions; and as a source of cloud condensation nuclei and nutrients for biological systems. Central Asia contains vast regions of arid and semi-arid lands and is one of the Northern Hemisphere’s major dust emission sources. Past instrumental and observational records of atmospheric dust conditions in Asia rarely pre-date the mid-20th century. Fortunately, central Asia is a prime location for the retrieval of ice cores as it contains several of the Earth’s highest mountain ranges (e.g. Himalayas, Tien Shan, Altai, Pamirs) and the Tibetan Plateau (TP). The Asian Ice Core Array (AICA) is an international effort (USA, Japan, and China) focusing on reconstructing climate and environmental conditions from six different glaciers in central Asia utilizing continuous, co-registered, and multi-parameter measurements of major ions (Na+, K+, Ca2+, Mg2+, Cl-, NO3-, SO42+), trace elements (Na, Mg, Al, Fe, Ca, Sr, Cd, Cs, Pb, Ba, La, Ce, Pr, Dy, Ho, Er, Bi, U, Ti, V, Cr, Mn, Cu, and REE), and stable isotopes (?18O and ?D), along with selected sections for radionuclide analysis. AICA sites are well distributed throughout central Asia, essentially covering the northern, southern, western peripheral mountain ranges as well as the central TP. Reconstructed glaciochemical records yield temporal and spatial information on the past variability of atmospheric dust (e.g. Ca2+, Al, Fe, REE) concentrations and compositions on multiple time-scales (ranging from sub-annual to centennial) reflecting changes in emission sources and/or atmospheric circulation. Additionally, AICA sites are very valuable because they provide context for assessing modern atmospheric conditions (e.g. natural vs. anthropogenic sources) and for predicting future atmospheric dust trends, which may have impacts on Earth’s radiative balance as well as consequences on regional socio-economics. Preliminary analysis suggests that atmospheric dust concentrations have generally declined at AICA sites in recent decades. Longer AICA records from the Himalayas (Everest) and central TP (Geladaindong) show generally opposite dust concentration trends over that last ~350 years and may be suggestive of regionally varying emission strength and/or atmospheric transport (e.g. westerly vs. monsoonal dominated circulation).

Grigholm, B. O.; Mayewski, P. A.; Aizen, V. B.; Kang, S.; Aizen, E.; Kreutz, K. J.; Kaspari, S.; Fujita, K.; Takeuchi, N.; Wake, C. P.; Kurbatov, A.

2010-12-01

359

The 1452 or 1453 A.D. Kuwae eruption signal derived from multiple ice core records: Greatest volcanic sulfate event of the past 700 years  

NASA Astrophysics Data System (ADS)

We combined 33 ice core records, 13 from the Northern Hemisphere and 20 from the Southern Hemisphere, to determine the timing and magnitude of the great Kuwae eruption in the mid-15th century. 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. By accounting for the dating uncertainties associated with each record, these ice core records together reveal a large volcanogenic acid deposition event during 1453-1457 A.D. The results suggest only one major stratospheric injection from the Kuwae eruption and confirm previous findings that the Kuwae eruption took place in late 1452 or early 1453, which may serve as a reference to evaluate and improve the dating of ice core records. The average total sulfate deposition from the Kuwae eruption was 93 kg SO4/km2 in Antarctica and 25 kg SO4/km2 in Greenland. The deposition in Greenland was probably underestimated since it was the average value of only two northern Greenland sites with very low accumulation rates. After taking the spatial variation into consideration, the average Kuwae deposition in Greenland was estimated to be 45 kg SO4/km2. By applying the same technique to the other major eruptions of the past 700 years our result suggests that the Kuwae eruption was the largest stratospheric sulfate event of that period, probably surpassing the total sulfate deposition of the Tambora eruption of 1815, which produced 59 kg SO4/km2 in Antarctica and 50 kg SO4/km2 in Greenland.

Gao, Chaochao; Robock, Alan; Self, Stephen; Witter, Jeffrey B.; Steffenson, J. P.; Clausen, Henrik Brink; Siggaard-Andersen, Marie-Louise; Johnsen, Sigfus; Mayewski, Paul A.; Ammann, Caspar

2006-06-01

360

Geomagnetic fluctuations reveal stable stratification at the top of the Earth's core.  

PubMed

Modern observations of the geomagnetic field reveal fluctuations with a dominant period of about 60?years. These fluctuations are probably a result of waves in the liquid core, although the precise nature of the waves is uncertain. Common suggestions include a type of magnetic wave, known as a torsional oscillation, but recent studies favour periods that are too short to account for a 60-year fluctuation. Another possibility involves MAC waves, which arise from the interplay between magnetic, Archimedes and Coriolis forces. Waves with a suitable period can emerge when the top of the core is stably stratified. Here I show that MAC waves provide a good description of time-dependent zonal flow at the top of the core, as inferred from geomagnetic secular variation. The same wave motion can also account for unexplained fluctuations in the dipole field. Both of these independent predictions require a 140-kilometre-thick stratified layer with a buoyancy frequency comparable to the Earth's rotation rate. Such a stratified layer could have a thermal origin, implying a core heat flow of about 13?terawatts. Alternatively, the layer could result from chemical stratification. In either case, the existence of a stratified layer at the top of the core obscures the nature of flow deeper in the core, where the magnetic field is continually regenerated. PMID:24670768

Buffett, Bruce

2014-03-27