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1

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

NSDL National Science Digital Library

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

2

Climate connections between the hemisphere revealed by deep sea sediment core\\/ice core correlations  

Microsoft Academic Search

Correlation of Southern Ocean deep sea sediment core records with ice core records of polar climate delineates with unprecedented detail the relationship between high latitude climate and the ocean's thermohaline circulation over the last 80,000 years. Our observations suggest that, while North Atlantic Deep Water variability manifests itself clearly in Southern Ocean nutrient proxy records over periods as short as

Christopher D. Charles; Jean Lynch-Stieglitz; Ulysses S. Ninnemann; Richard G. Fairbanks

1996-01-01

3

Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland  

PubMed Central

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

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

2009-01-01

4

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.

5

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

6

The GRIP Ice Coring Effort  

NSDL National Science Digital Library

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

7

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

8

Making an Ice Core.  

ERIC Educational Resources Information Center

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

Kopaska-Merkel, David C.

1995-01-01

9

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

10

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

11

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

12

Global Ice Core Research  

NSDL National Science Digital Library

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

13

High latitude biospheric activity during the Last Glacial Cycle revealed by ammonium variations in Greenland Ice Cores  

NASA Astrophysics Data System (ADS)

The short (325 m) Renland ice core from East Greenland was the first ice core to provide a continuous record of ammonium (NH4+) through the whole glacial period. The deep ice cores GRIP and GISP2 from Summit have confirmed that it is representative of the NH4+ deposition on Greenland. We argue that high levels of NH4+ in the ice during periods of warming (at the end of the last glaciation, during Dansgaard/Oeschger events, in MIS 5a and 5c, and during the Eem interglacial) provide evidence for rapid response by high latitude ecosystems and soils since the atmospheric turn-over time of ammonia (including its existence as NH4+) is short. Sources which emit ammonia usually also emit methane. High Greenland NH4+ levels coincide with high global methane concentrations. Northern high latitude biogenic sources are here suggested to contribute significantly to global methane concentrations during periods of warming during the last glacial period.

Hansson, Margareta; Holmén, Kim

14

The Glacial-Interglacial Deuterium Excess Signal in the Illimani ice Core (Bolivia) Reveals Long Term and Abrupt Climate Changes  

Microsoft Academic Search

The Illimani ice core, located on the Bolivian Cordillera Real (16S, 67W, 6350m) and covering approximately the last 18,000 years, has provided a wealth of paleoclimate information relative to the Andean and Amazonian regions. Specifically, isotopic composition of the ice has documented well known past climate changes (the Last Glacial Maximum, the Younger Dryas period, the Holocene Optimum and the

F. Vimeux; E. Ramirez; F. Sylvestre; G. Hoffmann

2006-01-01

15

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

16

The Glacial-Interglacial Deuterium Excess Signal in the Illimani ice Core (Bolivia) Reveals Long Term and Abrupt Climate Changes  

NASA Astrophysics Data System (ADS)

The Illimani ice core, located on the Bolivian Cordillera Real (16S, 67W, 6350m) and covering approximately the last 18,000 years, has provided a wealth of paleoclimate information relative to the Andean and Amazonian regions. Specifically, isotopic composition of the ice has documented well known past climate changes (the Last Glacial Maximum, the Younger Dryas period, the Holocene Optimum and the last thousand years) that might be interpreted in terms of changes in precipitation over Amazonia. Here, we present new isotopic measurements from this ice core: deuterium excess at a 1cm- depth resolution (i.e around 30-year resolution) from the bottom of the core to around 5,000 years BP present. Deuterium excess (d= delta D-8*deltaO18) is a measure of the degree to which phase change occurs away from the thermodynamic equilibrium along air masses trajectory and therefore changes with the meteorological conditions (relative humidity, surface temperature and wind) during non-total evaporation (from the ocean surface, stagnant waters as lakes, rivers or flooded soil, droplets, or canopy-intercepted water) and with the supersaturation during condensation to ice. It thus might be sensitive to climate changes 1- impacting humidity and saturation conditions of the atmosphere and 2- changing the relative moisture sources contribution of Andean precipitation (recycling versus advective moisture). Based on a calibration combining isotopic composition of modern precipitation and modeling works, we discuss the significant glacial-interglacial deuterium excess change of about 3 permil as well as the very abrupt changes (between 4 and 12 per mil) occuring during well known lacustrine Tauca phase.

Vimeux, F.; Ramirez, E.; Sylvestre, F.; Hoffmann, G.

2006-12-01

17

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.

18

Little ice age clearly recorded in northern Greenland ice cores  

Microsoft Academic Search

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

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

1998-01-01

19

Tropical Ice Cores Measure Climate  

NSDL National Science Digital Library

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

Sciencenow, Nova; Domain, Teachers'

20

SCIENCE BRIEFING Ice cores and climate change  

E-print Network

seen during Earth's emergence from the last ice age around 12,000 years ago). CO2 concentration-known from other records, and the coldest periods in Antarctica are the times when we had ice ages.Ice sheetsSCIENCE BRIEFING Ice cores and climate change Slices of ice core, drilled from the depths

Little, John B.

21

Ice Core Paleoclimatology Research Group  

NSDL National Science Digital Library

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

Byrd Polar Research Center

22

Ice Core Dating Software for Interactive Dating of Ice Cores  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

23

Ice cores and global change  

Microsoft Academic Search

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

Paul A. Mayewski

1988-01-01

24

Vostok Ice Core Lab Activity  

NSDL National Science Digital Library

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

Department of Earth and Environmental Sciences

25

Ice Core Tomography with Laser Ultrasonics  

Microsoft Academic Search

Establishing annual layering to date ice cores is a difficult, but crucial component of paleoclimate studies. We present ultrasonic tomography as an additional tool to expose variations in (thermo) elastic properties of ice, related to annual layering. These variations can be the result of seasonal variations in precipitation, ice chemistry and temperature. While the ice core is kept in a

T. D. Mikesell; K. van Wijk

2006-01-01

26

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.

27

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.

28

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

29

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.

30

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

NASA Astrophysics Data System (ADS)

Petrological investigations of the sand fraction and of granule- to cobble-sized clasts in the Plio-Pleistocene sedimentary cycles of the AND-1B drill core at the NW edge of the Ross Ice Shelf (McMurdo Sound) highlight significant down-core modal and compositional variations. These variations provide: (i) direct information about potential source regions during both glacial maxima and minima; and (ii) evidence of an evolving provenance, documented by long-term shifts in compositional patterns that can be interpreted as reflecting variations in ice volume and ice sheet thermal regimes and changes in paleogeography related to the emergence of several volcanic centres during the deposition of the drill core over the past ca. 3.5 Ma. The most significant change in diamictite provenance (identified at 82.7 metre below the sea floor, mbsf), coincides with a change in sedimentary cycle architecture from sequences that are dominated by diamictites (Mid-Late Pleistocene, above 82.7 mbsf) to sequences characterised by cycles of diamictite (subglacial) and diatomite (open-marine) deposition (Pliocene, below 82.7 mbsf). In the Mid-Late Pleistocene glacial/interglacial cycles diamictites show high amounts of Skelton-Mulock sourced clasts, supplied from both basement and overlying Beacon and Ferrar supergroups, and they also include a variable contribution from reworking of glacial sediments that were deposited during earlier glacial activity. In the Pliocene to early Pleistocene diatomite-diamictite cycles basement clast compositions indicate the same provenance (Mulock-Skelton) but the main debris load was picked up from volcanic centres in the McMurdo Sound area. Similarly, associated glacial minima sediments (i.e., diatomite intervals) are dominated by volcanic clasts suggesting calving of glaciers from Ross Island or the Koettlitz Glacier region during interglacials. In agreement with previous glaciological reconstructions and numerical ice sheet models, the provenance of glacially transported material is firmly identified in the region between Ross Island and the Skelton-Mulock glacier area (South Victoria Land). The reconstructed ice directions and ice dynamic model are comparable to the configurations proposed for the grounded ice expansion within the McMurdo Sound during the Last Glacial Maximum, and they are also consistent with ice-flow patterns previously reconstructed for Pliocene and Pleistocene glacial settings in the region.

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

2012-10-01

31

Ice Core Tomography with Laser Ultrasonics  

NASA Astrophysics Data System (ADS)

Establishing annual layering to date ice cores is a difficult, but crucial component of paleoclimate studies. We present ultrasonic tomography as an additional tool to expose variations in (thermo) elastic properties of ice, related to annual layering. These variations can be the result of seasonal variations in precipitation, ice chemistry and temperature. While the ice core is kept in a cold chamber with optical windows, scanning lasers excite and detect ultrasonic waves transmitted through the ice core. Our method is non-contacting, non- destructive and allows for millimeter-scale resolution. We test our proof-of-concept data acquisition system on a sample ice core from the South Pole, Antarctica. We observe distinct variations in the vertical component of the elastic wave front: a simple cross correlation is performed with the tomography data to determine layer boundaries. These results are then compared to a back-lighted photograph.

Mikesell, T. D.; van Wijk, K.

2006-12-01

32

Ice Core Tomography with Laser Ultrasonics  

Microsoft Academic Search

but crucial component of paleoclimate studies. We present ultrasonic tomography toward an additional tool to determine variations in (thermo-)elastic properties of ice, related to annual layering. These variations can be the result of seasonal changes in precipitation, ice chemistry and temperature. Our non-contacting and non- destructive method is tested on lab-manufactured ice and a sample ice core from the South

T. D. Mikesell; A. V. Kurbatov; P. A. Mayewski

33

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

34

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

35

laser ultrasonic characterization of ice cores  

NASA Astrophysics Data System (ADS)

We present preliminary measurements on ice cores of elastic wave forms at ultrasonic frequencies. The aim of the project is to map out internal properties of the ice to improve our understanding of the processes responsible for the ice structure. Annual layering is one of the targets, but the alignment of ice crystals is another.We use a system based on laser sources and receivers for a number of reasons. First, the lasers allow us to probe the ice in a non-destructive and non-contacting matter through optical windows into our cold room. Second, the lasers/core system is controlled via computerized stages, which allow us to have unprecedented data density, repeatable data acquisition, and high fidelity in each waveform. We calibrated layering properties with man-made ice structures, and we will present ongoing tests on Antarctic cores from various depths and locations.

van Wijk, K.; Otheim, L. T.; Marshall, H.; Kurbatov, A.; Spaulding, N. E.

2013-12-01

36

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

37

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

E-print Network

in the bubbles is about the same age as the ice, so scientists use bubbles to learn about the ancient atmosphereUsing 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

38

Ice coring on Vestfonna Ice Cap Contact person: John Moore (jmoore@ulapland.fi).  

E-print Network

Ice coring on Vestfonna Ice Cap Contact person: John Moore (jmoore@ulapland.fi). Participants, Polish Academy of Science glowacki@igf.edu.pl Science: Ice cores from the glaciers outside the main ice during the summer season, which could alter the original ice core record. Many of the scientists

Moore, John

39

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

40

NOAA Paleoclimatology Program - Vostok Ice Core Data  

NSDL National Science Digital Library

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

National Climatic Data Center

41

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

42

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

Microsoft Academic Search

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

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

1997-01-01

43

white paper, 9 March 2009 An ice core to reconstruct Greenland ice sheet mass balance  

E-print Network

through the Pleistocene ice age and even reaching the end of the Eemian warmthwhite paper, 9 March 2009 1 An ice core to reconstruct Greenland ice sheet mass balance Recent satellite and GPS observations spanning

Box, Jason E.

44

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

45

Post-coring entrapment of modern air in some shallow ice cores collected near the firn-ice transition: evidence from CFC-12 measurements in Antarctic firn air and ice cores  

NASA Astrophysics Data System (ADS)

In this study, we report measurements of CFC-12 (CCl2F2) in firn air and in air extracted from shallow ice cores from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, some of the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for the presence of modern air entrapped in the shallow ice core samples that likely contained open pores at the time of collection. We propose that this is due to closure of the open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our results reveal that open porosity can exist below the maximum depth at which firn air samples can be collected, particularly at sites with lower accumulation rates. CFC-12 measurements demonstrate that post-drilling closure of open pores can lead to a change in the composition of bubble air in shallow ice cores through purely physical processes. The results have implications for investigations involving trace gas composition of bubbles in shallow ice cores collected near the firn-ice transition.

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

2010-06-01

46

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

48

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

49

Post-coring entrapment of modern air in polar ice cores collected near the firn-ice transition: evidence from CFC-12 measurements in Antarctic firn air and shallow ice cores  

NASA Astrophysics Data System (ADS)

In this study, we report the first measurements of CFC-12 (CCl2F2) in air extracted from shallow ice cores along with firn air CFC-12 measurements from three Antarctic sites. The firn air data are consistent with the known atmospheric history of CFC-12. In contrast, the ice core samples collected near the firn-ice transition exhibit anomalously high CFC-12 levels. Together, the ice core and firn air data provide evidence for presence of modern air entrapped in shallow ice core samples. We propose that this is due to closure of open pores after drilling, entrapping modern air and resulting in elevated CFC-12 mixing ratios. Our measurements reveal the presence of open porosity below the depth at which firn air samples can be collected and demonstrate how the composition of bubble air in shallow ice cores can be altered during the post-drilling period through purely physical processes. These results have implications for investigations involving trace gas composition of bubbles in shallow ice cores.

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

2010-01-01

50

Magnetic measurements of Greenland and Himalayan ice-core samples  

Microsoft Academic Search

This paper summarizes Isothermal Remanence (IRM300mT) measurements from Holocene ice-core samples from two contrasting glaciological regimes: (i) the Greenland ice sheet and (ii) a Himalayan glacier. Cores had been previously characterized in terms of chronologies, geochemistry and, for the Himalayan core, microparticle concentrations. Six samples from the Greenland 20-D ice core from the time period AD 1876-1983 did not yield

J. T. S. Sahota; P. A. Mayewski; F. Oldfield; M. S. Twickler

1996-01-01

51

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

52

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

53

Evidence from lake sediments, marine sediments, and ice cores  

E-print Network

Evidence from lake sediments, marine sediments, and ice cores #12;Outline · Archives · Proxies #12;Geographical distribution ­ Lakes: all land areas ­ Marine: all oceans ­ Ice: ice caps sediments: age Wohlfarth et al. Geology 2008 #12;Lake sediments - proxies Wohlfarth et al. Geology 2008 #12

Sengun, Mehmet Haluk

54

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

55

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

56

Deep ice cores: the need for going back in time  

Microsoft Academic Search

After the success of EPICA, the European Project for Ice coring in Antarctica which, at Dome C (East Antarctica) has provided access to climate and environmental records covering the last 800 ka (thousands of years), the ice core community is now engaged in the challenge to obtain older records. Obtaining a 1.5 million year (Ma) record of climate and greenhouse gases is

Jean Jouzel; Valérie Masson-Delmotte

2010-01-01

57

First continuous phosphate record from Greenland ice cores  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

58

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

Microsoft Academic Search

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

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

2009-01-01

59

Tributaries of West Antarctic Ice Streams Revealed by RADARSAT Interferometry.  

PubMed

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

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

1999-10-01

60

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

61

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

62

Greenland ice core evidence of the 79 AD Vesuvius eruption  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

63

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

Microsoft Academic Search

A detailed history of Holocene volcanism was reconstructed using the sulfate record of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core. This first complete Holocene volcanic record from an Antarctic core provides a reliable database to compare with long records from Antarctic and Greenland ice cores. A threshold method based on statistical treatment of the

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

2005-01-01

64

Greenland Ice Core Records and Rapid Climate Change  

Microsoft Academic Search

Long ice cores from Greenland yield records of annually resolved climate change for the past ten to twenty thousand years, and decadal resolution for one hundred thousand years or more. These cores are ideally suited to determine the rapidity with which major climate changes occur. The termination of the Younger Dryas, which marks the end of the last glacial period,

J. A. Dowdeswell; J. W. C. White

1995-01-01

65

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

NASA Astrophysics Data System (ADS)

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

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

2002-05-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2002-05-01

67

The isotopic composition of methane in polar ice cores  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

68

The isotopic composition of methane in polar ice cores.  

PubMed

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that (i) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (ii) that the carbon-13 to carbon-12 ratio of atmospheric CH(4) in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent (13)CH(4) enrichment, although other factors may also contribute. PMID:17788420

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

1988-12-23

69

Greenland ice core evidence of the 79 AD Vesuvius eruption  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

70

Evolution of the texture along the EPICA Dome C ice core Gael Durand  

E-print Network

records in ice cores back to 800 kyr [2]. Besides this increase in the age of ice core records, alsoEvolution of the texture along the EPICA Dome C ice core Ga¨el Durand , Anders Svensson , Asbjørn Dahl-Jensen Niels Bohr institute, Ice and Climate Group, University of Copenhagen, Denmark. Contact

Gagliardini, Olivier

71

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

73

A first chronology for the NEEM ice core  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

74

Shifted Ice Cap Unexpectedly Reveals Life  

NSDL National Science Digital Library

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

Christopher Joyce

75

A comparison of the volcanic records over the past 4000 years from the Greenland Ice Core Project and Dye 3 Greenland ice cores  

Microsoft Academic Search

Since 1980 the electrical conductivity method (ECM) has been used to infer volcanic acid signals in Greenland ice cores. The method reveals the great majority of major volcanic eruptions, including several known from historic records. Subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition, i.e., the concentration of the volcanic acids H2SO4, HCl, and HF plus,

Henrik B. Clausen; Claus U. Hammer; Christine S. Hvidberg; Dorthe Dahl-Jensen; Jørgen P. Steffensen; Josef Kipfstuhl; Michel Legrand

1997-01-01

76

Glaciochemistry of polar ice cores: A review  

Microsoft Academic Search

Human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world. The study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability

Michel Legrand; Paul Mayewski

1997-01-01

77

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

78

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

79

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

NASA Astrophysics Data System (ADS)

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

Malone, Terry; Hubbard, Bryn

2013-04-01

80

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

81

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

82

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

83

A TEM analysis of nanoparticulates in a Polar ice core  

SciTech Connect

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

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

2004-03-15

84

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.

85

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.

86

Eight glacial cycles from an Antarctic ice core  

Microsoft Academic Search

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

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

2004-01-01

87

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.

Stecker, Floyd W

2013-01-01

88

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

E-print Network

the simple fact that there appears to be an ice core recordcounted ice ages and firn air dating, and the fact that theice core data and the multiproxy climate record, which have unre- lated chronologies. [ 23 ] The fact

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

2008-01-01

89

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

90

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

91

Gas ageice age differences and the chronology of the Vostok ice core, M. L. Bender,1  

E-print Network

Gas age­ice age differences and the chronology of the Vostok ice core, 0­100 ka M. L. Bender,1 G the ice in which it is embedded. The age difference is not well constrained for slowly accumulating ice chronologies that use different assumptions to calculate gas age­ice age differences. We then evaluate

Chappellaz, Jérôme

92

Last deglaciation and last glacial climatic record from the new coastal TALDICE ice core (East Antarctica)  

NASA Astrophysics Data System (ADS)

The TALDICE project retrieved a new ice core from a peripheral dome of East Antarctica. Talos Dome (72° 49’ S, 159° 11’ E; 2315 m; 80 kg m-2 yr-1; -41°C) is located in the Northern Victoria Land, close from the Ross Sea. Back-trajectory analyses suggest that the site is mostly fed by air masses arriving both from the Pacific (and Ross Sea) and Indian Ocean sectors. In December 2007 the drilling team reached the depth of 1619.2 m. A preliminary dating based on an ice flow model and an inverse method suggests an age of about 300,000 years BP at 1560 m of depth. We measured the methane (CH4) mixing ratio in the Talos Dome ice core at a depth resolution ranging from 0.5 to 4 m. Two laboratories (LGGE and Bern) were involved, using slightly different techniques. The CH4 mixing ratio measured in the TALDICE ice core allows us to define tie points with respect to other ice cores from Greenland and Antarctica, using in particular the rapid CH4 changes associated with the last termination and the D/O events. Additional chronological constraints are offered by the isotopic composition of molecular oxygen, the dust profile, and volcanic peaks. The comparison of water isotopic profiles from Talos Dome, EDC, EDML (Antarctica) and North-GRIP (Greenland) ice cores, once put on a common time scale, reveals that during the last deglaciation, climatic changes at Talos Dome were essentially in phase with the Antarctic plateau, and that the bipolar seesaw is also valid for this coastal site. A similar comparison extended to the last glacial period (work in progress) enables us to evaluate the timing, shape and duration of the Talos Dome warm events with respect to AIM events on the Antarctic plateau, and to the Dansgaard/Oeschger events in Greenland.

Buiron, D.; Stenni, B.; Frezzotti, M.; Chappellaz, J.; Lemieux-Dudon, B.

2009-12-01

93

A new 122 mm electromechanical drill for deep ice-sheet coring (DISC): 1. Design concepts  

Microsoft Academic Search

The Deep Ice Sheet Coring (DISC) drill, developed by Ice Coring and Drilling Services (ICDS) under contract with the US National Science Foundation, is an electromechanical drill designed to take 122 mm diameter ice cores to depths of 4000 m. The conceptual design of the DISC drill was developed in 2002\\/03 based on science requirements written by K. Taylor and

Alexander J. Shturmakov; Donald A. Lebar; William P. Mason; Charles R. Bentley

2007-01-01

94

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

E-print Network

Ice core paleovolcanic records from the St. Elias Mountains, Yukon, Canada Kaplan Yalcin,1 Icefield (St. Elias Mountains, Yukon, Canada). The acquisition of two new ice cores from Eclipse Icefield-third of the eruptions recorded in St. Elias ice cores are from Alaskan and Kamchatkan volcanoes. Although

Kurapov, Alexander

95

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

96

Quantifying signal dispersion in a hybrid ice core melting system.  

PubMed

We describe a microcontroller-based ice core melting and data logging system allowing simultaneous depth coregistration of a continuous flow analysis (CFA) system (for microparticle and conductivity measurement) and a discrete sample analysis system (for geochemistry and microparticles), both supplied from the same melted ice core section. This hybrid melting system employs an ice parcel tracking algorithm which calculates real-time sample transport through all portions of the meltwater handling system, enabling accurate (1 mm) depth coregistration of all measurements. Signal dispersion is analyzed using residence time theory, experimental results of tracer injection tests and antiparallel melting of replicate cores to rigorously quantify the signal dispersion in our system. Our dispersion-limited resolution is 1.0 cm in ice and ~2 cm in firn. We experimentally observe the peak lead phenomenon, where signal dispersion causes the measured CFA peak associated with a given event to be depth assigned ~1 cm shallower than the true event depth. Dispersion effects on resolution and signal depth assignment are discussed in detail. Our results have implications for comparisons of chemistry and physical properties data recorded using multiple instruments and for deconvolution methods of enhancing CFA depth resolution. PMID:23050603

Breton, Daniel J; Koffman, Bess G; Kurbatov, Andrei V; Kreutz, Karl J; Hamilton, Gordon S

2012-11-01

97

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

98

Critical Fracture Toughness Measurements of an Antarctic Ice Core  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

99

High-resolution mineral dust and sea ice proxy records from the Talos Dome ice core  

NASA Astrophysics Data System (ADS)

In this study we report on new non-sea salt calcium (nssCa2+, mineral dust proxy) and sea salt sodium (ssNa+, sea ice proxy) records along the East Antarctic Talos Dome deep ice core in centennial resolution reaching back 150 thousand years (ka) before present. During glacial conditions nssCa2+ fluxes in Talos Dome are strongly related to temperature as has been observed before in other deep Antarctic ice core records, and has been associated with synchronous changes in the main source region (southern South America) during climate variations in the last glacial. However, during warmer climate conditions Talos Dome mineral dust input is clearly elevated compared to other records mainly due to the contribution of additional local dust sources in the Ross Sea area. Based on a simple transport model, we compare nssCa2+ fluxes of different East Antarctic ice cores. From this multi-site comparison we conclude that changes in transport efficiency or atmospheric lifetime of dust particles do have a minor effect compared to source strength changes on the large-scale concentration changes observed in Antarctic ice cores during climate variations of the past 150 ka. Our transport model applied on ice core data is further validated by climate model data. The availability of multiple East Antarctic nssCa2+ records also allows for a revision of a former estimate on the atmospheric CO2 sensitivity to reduced dust induced iron fertilisation in the Southern Ocean during the transition from the Last Glacial Maximum to the Holocene (T1). While a former estimate based on the EPICA Dome C (EDC) record only suggested 20 ppm, we find that reduced dust induced iron fertilisation in the Southern Ocean may be responsible for up to 40 ppm of the total atmospheric CO2 increase during T1. During the last interglacial, ssNa+ levels of EDC and EPICA Dronning Maud Land (EDML) are only half of the Holocene levels, in line with higher temperatures during that period, indicating much reduced sea ice extent in the Atlantic as well as the Indian Ocean sector of the Southern Ocean. In contrast, Holocene ssNa+ flux in Talos Dome is about the same as during the last interglacial, indicating that there was similar ice cover present in the Ross Sea area during MIS 5.5 as during the Holocene.

Schüpbach, S.; Federer, U.; Kaufmann, P. R.; Albani, S.; Barbante, C.; Stocker, T. F.; Fischer, H.

2013-12-01

100

Low-latitude ice cores and freshwater availability  

NASA Astrophysics Data System (ADS)

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

Kehrwald, Natalie Marie

2009-12-01

101

Interaction between Antarctic sea ice and synoptic activity in the circumpolar trough: implications for ice-core interpretation  

E-print Network

by insulating the ocean from the atmosphere, thus considerably reducing the turbulent heat and moisture fluxes-microwave measurements. Total Antarctic sea-ice extent does not show large interannual variations. However, large of ice cores. Two case studies of extraordinary sea-ice concentration anomalies in relation

Schlosser, Elisabeth

102

The Greenland Summit Ice Cores CD-ROM  

NSDL National Science Digital Library

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

Program., National G.

1997-01-01

103

Measuring ?23 with IceCube DeepCore  

NASA Astrophysics Data System (ADS)

The IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station includes the DeepCore infill array which could extend visible energies as low as the 10 GeV region. This allows for investigation of atmospheric neutrino mixing parameters by observing the zenith direction and energy of neutrino-induced charged leptons. With O(10^4) neutrino events observed within the first year, the status of this ongoing high-statistics measurement will be discussed.

Gladstone, Laura

2013-04-01

104

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

105

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

Microsoft Academic Search

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

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

2005-01-01

106

A thermal drill for ice coring on high-elevation glaciers, NCCR Climate VIVALDI (Variability in Ice, Vegetation, and Lake Deposits - Integrated)  

Microsoft Academic Search

Project description: Non-polar ice cores have now been obtained from all continents except Australia, almost exclusively by small teams from one or two institutions, and with a modest amount of funding compared to polar ice coring projects. However, many areas remain from which no ice cores have been retrieved yet. This is especially true for temperate glaciers, where the ice

Margit Schwikowski; Anja Eichler; Susan Kaspari; Leonhard Tobler; Michael Sigl; Anita Ciric; Dieter Stampfli; Felix Stampfli

107

Greenland ice core 'signal' characteristics - An expanded view of climate change  

NASA Astrophysics Data System (ADS)

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

Mayewski, P. A.; Meeker, L. D.; Morrison, M. C.; Twickler, M. S.; Whitlow, S. I.; Ferland, K. K.; Meese, D. A.; Legrand, M. R.; Steffensen, J. P.

1993-07-01

108

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

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

109

Ice cores from Svalbarduseful archives of past climate and pollution history  

E-print Network

elevation. The anthropogenic influence on Svalbard environment is illustrated by increased levels of nonIce cores from Svalbard­­useful archives of past climate and pollution history Elisabeth Isaksson a Ice cores from the relatively low-lying ice caps in Svalbard have not been widely exploited

Moore, John

110

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

111

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

Microsoft Academic Search

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

Markus Leuenberger; Ulrich Siegenthaler

1992-01-01

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

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

E-print Network

traverse indicate accumulation rates of 0.16­0.20 m/yr ice equivalent over the last 300 years. Age controlGlaciological and climatic significance of Hercules Dome, Antarctica: An optimal site for deep ice as a deep ice core site. Annual layering in dD ratios from a 72 m ice core collected by the US-ITASE 2002

Jacobel, Robert W.

114

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

115

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

Microsoft Academic Search

Methane and nitrous oxide are two important greenhouse gases. In order to predict their future concentrations, their present budgets and past variations need to be understood. Recent data have revealed surprising variations in the stable isotope signatures of CH4 over the past millennium which underlines the need of deltaD measurements of methane from air trapped in ice core. M We

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

2009-01-01

116

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

117

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

118

Ultra-sensitive Flow Injection Analysis (FIA) determination of calcium in ice cores at ppt level.  

PubMed

A Flow Injection Analysis (FIA) spectrofluorimetric method for calcium determination in ice cores was optimised in order to achieve better analytical performances which would make it suitable for reliable calcium measurements at ppt level. The method here optimised is based on the formation of a fluorescent compound between Ca and Quin-2 in buffered environment. A careful evaluation of operative parameters (reagent concentration, buffer composition and concentration, pH), influence of interfering species possibly present in real samples and potential favourable effect of surfactant addition was carried out. The obtained detection limit is around 15 ppt, which is one order of magnitude lower than the most sensitive Flow Analysis method for Ca determination currently available in literature and reproducibility is better than 4% for Ca concentrations of 0.2 ppb. The method was validated through measurements performed in parallel with Ion Chromatography on 200 samples from an alpine ice core (Lys Glacier) revealing an excellent fit between the two chemical series. Calcium stratigraphy in Lys ice core was discussed in terms of seasonal pattern and occurrence of Saharan dust events. PMID:17586118

Traversi, R; Becagli, S; Castellano, E; Maggi, V; Morganti, A; Severi, M; Udisti, R

2007-07-01

119

Rapid climate changes recorded in Greenland ice cores  

SciTech Connect

Exceptionally large, rapid climate changes have repeatedly affected the North Atlantic basin and beyond over the last 100,000 years, as recorded in Greenlandic ice cores. The changes involve regional or global conditions (large changes in methane, in storm tracks, and in atmospheric loading of windblown sea salt and continental dust) as well as local conditions (several degrees C in temperature, twofold change in snow accumulation). Changes occurred over decades to as little as a single year. {open_quotes}Flickering{close_quotes} behavior occurred at some transitions, with rapid fluctuations between two states over years to decades before longer-term stabilization in one of the states. Such changes almost certainly are linked to large-scale reorganizations of the atmosphere-ocean system. One significant event occurred as recently as 8,000 years ago, after the low-latitude ice sheets had largely melted, casting doubt on the hypothesis that the low-latitude ice sheets are necessary to destabilize North Atlantic climate.

Alley, R.B.

1995-12-31

120

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

121

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

122

Water isotopic ratios from a continuously melted ice core sample  

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

123

Tree ring and ice core time scales around the Santorini eruption  

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

124

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

125

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

126

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

Microsoft Academic Search

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

Douglas Mair; David Burgess; Martin Sharp

2005-01-01

127

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

PubMed Central

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. Previously, a bacterium (isolate 3519-10) recovered from a depth of 3,519?m below the surface in the Vostok ice core was shown to secrete an ice-binding protein (IBP) that inhibits the recrystallization of ice. To explore the 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 cultures grown between 4 and 25°C and analyzed by reverse transcription-PCR indicated constitutive expression of the IBP gene. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of 3519-10’s extracellular proteins revealed a polypeptide of the predicted size of the 54-kDa IBP at all temperatures tested. In the presence of 100??g?mL?1 of extracellular protein from 3519-10, the survival of Escherichia coli was increased by greater than 100-fold after 5 freeze-thaw cycles. Microscopic analysis of ice formed in the presence of the IBP indicated that per square millimeter 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 filtered 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. A myriad of molecular adaptations are likely to play a role in bacterial persistence under frozen conditions, but the ability of 3519-10’s IBP to control ice crystal structure, and thus the liquid vein network within the ice, may provide one explanation for its successful survival deep within the Antarctic ice sheet for thousands of years. PMID:22207866

Achberger, Amanda Marie; Brox, Timothy Ian; Skidmore, Mark Leslie; Christner, Brent Craig

2011-01-01

128

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

129

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

130

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

131

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

NSDL National Science Digital Library

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

Kathy Benison

132

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

E-print Network

complements our related work in an unpublished paper where the sea ice cover response to the Coriolis forcingRecent mechanical weakening of the Arctic sea ice cover as revealed from larger inertial ice motion in the frequency domain, and particularly in the inertial range. This study further

Paris-Sud XI, Université de

133

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

Microsoft Academic Search

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

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

1996-01-01

134

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

Microsoft Academic Search

Depth profiles along the Vostok ice core of methanesulfonate and non-seasalt sulfate are presented which provide the first historical record of biogenic sulfur emissions from the Southern Hemisphere oceans over a complete glacial-interglacial cycle. Those measurements confirm and extend some previous observations made on a very limited data set from the Dome C ice core in Antarctica, which indicated increased

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

1991-01-01

135

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

Microsoft Academic Search

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

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

2003-01-01

136

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

137

An 1800-year Ice Core History of Climate and Environment in the Andes of Southern Peru  

E-print Network

we present 1800-year temperature and precipitation proxy records extracted from an ice core drilled261 Chapter 23 An 1800-year Ice Core History of Climate and Environment in the Andes of Southern Peru and its Relationship with Highland/Lowland Cultural Oscillations Lonnie G. Thompson and Mary E

Howat, Ian M.

138

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

139

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

140

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

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

141

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

USGS Publications Warehouse

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

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

1996-01-01

142

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

143

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

144

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

145

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

146

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

NASA Astrophysics Data System (ADS)

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

Dahl-Jensen, D.

2012-12-01

147

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

PubMed

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

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

2011-05-15

148

Ice Core Records of Atmospheric CO2 Around the Last Three Glacial Terminations  

NSDL National Science Digital Library

This resource gives data from an article published in Science, Vol. 283 by researchers at Scripps Institute of Oceanography. Their study investigated the global carbon cycle and relation between greenhouse gases and climate in the past using air trapped in bubbles in polar ice cores. Users can access Vostok ice core data (HTML format) used in the study, showing carbon dioxide concentrations, G4 and G5 scores, and age from approximately 1105-2856 meters core depth.

149

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

150

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

NASA Astrophysics Data System (ADS)

In the framework of the International Partnerships in Ice Core Sciences, one of the most important targets is to retrieve an Antarctic ice core that extends over the last 1.5 million years (i.e. an ice core that enters the climate era when glacial-interglacial cycles followed the obliquity cycles of the earth). In such an ice core the annual layers of the oldest ice would be thinned by a factor of about 100 and the climatic information of a 10 000 yr interval would be contained in less than 1 m of ice. The gas record in such an Antarctic ice core can potentially reveal the role of greenhouse gas forcing on these 40 000 yr cycles. However, besides the extreme thinning of the annual layers, also the long residence time of the trapped air in the ice and the relatively high ice temperatures near the bedrock favour diffusive exchanges. To investigate the changes in the O2 / N2 ratio, as well as the trapped CO2 concentrations, we modelled the diffusive exchange of the trapped gases O2, N2 and CO2 along the vertical axis. However, the boundary conditions of a potential drilling site are not yet well constrained and the uncertainties in the permeation coefficients of the air constituents in the ice are large. In our simulations, we have set the drill site ice thickness at 2700 m and the bedrock ice temperature at 5-10 K below the ice pressure melting point. Using these conditions and including all further uncertainties associated with the drill site and the permeation coefficients, the results suggest that in the oldest ice the precessional variations in the O2 / N2 ratio will be damped by 50-100%, whereas CO2 concentration changes associated with glacial-interglacial variations will likely be conserved (simulated damping 5%). If the precessional O2 / N2 signal will have disappeared completely in this future ice core, orbital tuning of the ice-core age scale will be limited.

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

2014-02-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

152

Climate Scientists Dig Deep Into Greenland's Ice  

NSDL National Science Digital Library

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

153

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

154

Properties of grain boundary networks in the NEEM ice core  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

155

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

156

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

SciTech Connect

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

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

1993-07-20

157

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

158

Quanti¢cation of viable endospores from a Greenland ice core  

Microsoft Academic Search

Endospores (i.e., bacterial spores) embedded in polar ices present an opportunity to investigate the most durable form of life in an ideal medium for maintaining long-term viability. However, little is known about the endospore distribution and viability in polar ices. We have determined germinable endospore concentrations of bacterial spores capable of germination in a Greenland ice core (GISP2 94m, ID#

Pun To Yung; Hannah S. Shafaat; Stephanie A. Connon; Adrian Ponce

159

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

Microsoft Academic Search

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

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

2006-01-01

160

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

E-print Network

connections to past climate change [Beer et al., 1990]. The isotope concentra- tion in glacial ice is affected dynamo and its potential relationship to climate changes on decadal and centennial time scales. A recentA 600-year annual 10 Be record from the NGRIP ice core, Greenland A.-M. Berggren,1 J. Beer,2 G

Wehrli, Bernhard

161

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

162

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

Microsoft Academic Search

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. The authors have analyzed the major ions contained in the Greenland Ice Sheet Project 2 (GISP 2) ice core from the present to â¼674 A.D. to yield an environmental reconstruction for this period that includes a description

P. A. Mayewski; L. D. Meeker; M. C. Morrison; M. S. Twickler; S. I. Whitlow; K. K. Ferland; D. A. Meese; M. R. Legrand; J. P. Steffensen

1993-01-01

163

Greenland ice core 'signal' characteristics - An expanded view of climate change  

Microsoft Academic Search

The last millenium of Earth history is of particular interest because it documents the environmental complexities of both natural variability and anthropogenic activity. We have analyzed the major ions contained in the Greenland Ice Sheet Project 2 ice core from the present to about 674 A.D. to yield an environmental reconstruction for this period that includes a description of nitrogen

P. A. Mayewski; L. D. Meeker; M. C. Morrison; M. S. Twickler; S. I. Whitlow; K. K. Ferland; D. A. Meese; M. R. Legrand; J. P. Steffensen

1993-01-01

164

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

165

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

Microsoft Academic Search

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

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

2002-01-01

166

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

167

Decadal-Interdecadal Climate Variability over Antarctica and4 Linkages to the Tropics: Analysis of Ice Core, Instrumental, and5  

E-print Network

#12;1 Abstract23 The Antarctic continent contains the majority of the global ice volume and plays-interdecadal time scales. Antarctic surface temperature31 anomalies inferred from the ice cores are consistent: Analysis of Ice Core, Instrumental, and5 Tropical Proxy Data6 7 Yuko M. Okumura1,2 , David Schneider2

Hurrell, James

168

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

170

Carbonyl sulfide hydrolysis in Antarctic ice cores and an atmospheric history for the last 8000 years  

NASA Astrophysics Data System (ADS)

sulfide (COS) was measured in Antarctic ice core samples from the Byrd, Siple Dome, Taylor Dome, and West Antarctic Ice Sheet Divide sites covering the last 8000 years of the Holocene. COS levels decrease downcore in most of these ice cores. The magnitude of the downcore trends varies among the different ice cores and is related to the thermal histories of the ice sheet at each site. We hypothesize that this is due to the temperature-dependent hydrolysis of COS that occurs in situ. We use a one-dimensional ice flow and heat flux model to infer temperature histories for the ice core samples from different sites and empirically determine the kinetic parameters for COS hydrolysis. We estimate e-folding lifetimes for COS hydrolysis ranging from 102 years to 106 years over a temperature range of 0°C to -50°C. The reaction kinetics are used to estimate and correct for the in situ COS loss, allowing us to reconstruct paleoatmospheric COS trends during the mid-to-late Holocene. The results suggest a slow, long-term increase in atmospheric COS that may have started as early as 5000 years ago. Given that the largest term in the COS budget is uptake by terrestrial plants, this could indicate a decline in terrestrial productivity during the late Holocene.

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

2014-07-01

171

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

172

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

174

Recent variations in the mass-independent fractionation of the oxygen isotopes of sulfate: Measurements from Greenland ice cores  

NASA Astrophysics Data System (ADS)

The mass-independent fractionation in the oxygen isotopes (? 17O=? 17O-0.5*? 18O) of sulfate serves as a tracer of the mechanism of oxidation in the atmosphere. Aqueous-phase oxidation of sulfur (IV) species by isotopically enriched ozone and hydrogen peroxide results in mass-independently fractionated (? 17O!=q0) sulfate. In contrast, sulfate formed in the gas-phase through oxidation by the hydroxyl radical is mass-dependently fractionated (? 17O=0). Measurement of ? 17O and ? 18O thus provides insight into relative amounts of gas and aqueous-phase sulfate formation processes, a parameter that has implications in the indirect effect of sulfate on climate. Due to the slow oxygen exchange rate of sulfate, its oxygen isotopic composition is preserved in ice-core sulfate over the thousands of years it is trapped in the ice, providing information about sulfur oxidation processes on a variety of timescales. The ? 17O value of sulfate preserved in Antarctic ice cores has shown a distinct variation with climate. Here, we present isotopic measurements of sulfate preserved in two, more recent, ice cores from Greenland. The Milicent core represents the transition from the Medieval Warm Period to the Maunder Minimum. The Site A core is roughly centered at the Industrial Revolution, revealing potential anthropogenic-induced changes to the oxidation pathways of atmospheric sulfur species. In addition to providing information on variations in sulfate formation processes on these timescales, these measurements may provide insight into variations in the oxidant concentrations themselves.

Alexander, B.; Savarino, J.; Thiemens, M. H.

2002-05-01

175

Reconstruction of millennial changes in dust emission, transport and regional sea ice coverage using the deep EPICA ice cores from the Atlantic and Indian Ocean sector of Antarctica  

Microsoft Academic Search

Continuous sea salt and mineral dust aerosol records have been studied on the two EPICA (European Project for Ice Coring in Antarctica) deep ice cores. The joint use of these records from opposite sides of the East Antarctic plateau allows for an estimate of changes in dust transport and emission intensity as well as for the identification of regional differences

Hubertus Fischer; Felix Fundel; Urs Ruth; Birthe Twarloh; Anna Wegner; Roberto Udisti; Silvia Becagli; Emiliano Castellano; Andrea Morganti; Mirko Severi; Eric Wolff; Genevieve Littot; Regine Röthlisberger; Rob Mulvaney; Manuel A. Hutterli; Patrik Kaufmann; Urs Federer; Fabrice Lambert; Matthias Bigler; Margareta Hansson; Ulf Jonsell; Martine de Angelis; Claude Boutron; Marie-Louise Siggaard-Andersen; Jorgen Peder Steffensen; Carlo Barbante; Vania Gaspari; Paolo Gabrielli; Dietmar Wagenbach

2007-01-01

176

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.  

PubMed

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

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

2014-12-30

177

Sulphate record from a northeast Greenland ice core over the last 1200 years based on continuous flow analysis  

E-print Network

Sulphate record from a northeast Greenland ice core over the last 1200 years based on continuous ABSTRACT. A 150 m deep ice core from the low-accumulation area of northeast Greenland was analyzed-core studies from Greenland have been evaluated in detail mainly over the last 200years (with only few records

Fischer, Hubertus

178

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

SciTech Connect

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

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

2013-03-01

179

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

180

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

181

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

182

Microbial Analyses of Ancient Ice Core Sections from Greenland and Antarctica  

PubMed Central

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

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

2013-01-01

183

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

184

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

185

Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics  

PubMed Central

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

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

2014-01-01

186

Methyl chloride in a deep ice core from Siple Dome, Antarctica  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) is a naturally occurring ozone-depleting substance and a significant component of the atmospheric chlorine burden. In this study CH3Cl was analyzed in air bubbles from the West Antarctic Siple Dome deep ice core with gas ages ranging from about 65 kyr BP to the Late Holocene. CH3Cl levels were below the modern Antarctic atmospheric level of 530 ppt in glacial ice (456 +/- 46 ppt, 33-65 kyr BP) and above it during the early Holocene (650-700 ppt, 10-11 kyr BP). For most of the Holocene, CH3Cl levels were 500-550 ppt, with good agreement between CH3Cl levels in this core and in the Dome Fuji ice core (Saito et al., 2007). Several late Holocene ice core samples (<2 kyr BP), show evidence of enrichment in CH3Cl relative to South Pole ice core samples of overlapping gas age. The Siple Dome record suggests that CH3Cl levels in the glacial Southern Hemisphere atmosphere were about 16% lower than those during the mid-late Holocene.

Saltzman, Eric S.; Aydin, Murat; Williams, Margaret B.; Verhulst, Kristal R.; Gun, Baris

2009-02-01

187

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

NASA Astrophysics Data System (ADS)

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

Rybak, Oleg; Huybrechts, Philippe

2013-04-01

188

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

189

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

NASA Astrophysics Data System (ADS)

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

Stenni, B.

2009-04-01

190

Low time resolution analysis of polar ice cores cannot detect impulsive nitrate events  

E-print Network

Ice cores are archives of climate change and possibly large solar proton events (SPEs). Wolff et al. (2012) used a single event, a nitrate peak in the GISP2-H core, which McCracken et al. (2001a) time associated with the poorly quantified 1859 Carrington event, to discredit SPE-produced, impulsive nitrate deposition in polar ice. This is not the ideal test case. We critique the Wolff et al. analysis and demonstrate that the data they used cannot detect impulsive nitrate events because of resolution limitations. We suggest re-examination of the top of the Greenland ice sheet at key intervals over the last two millennia with attention to fine resolution and replicate sampling of multiple species. This will allow further insight into polar depositional processes on a sub-seasonal scale, including atmospheric sources, transport mechanisms to the ice sheet, post-depositional interactions, and a potential SPE association.

Smart, D F; Melott, A L; Laird, C M

2015-01-01

191

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

192

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

193

Measurements and numerical simulation of fabric evolution along the Talos Dome ice core, Antarctica  

NASA Astrophysics Data System (ADS)

We present measurements of fabrics and microstructures made along the Talos Dome ice core, a core drilled in East Antarctica in the framework of the TALDICE project. Fabric and average grain size data are analyzed regarding changes in climatic conditions. In particular, the fabric strength increases sharply going downward from Holocene to Wisconsin ice. Following (Durand et al., 2007), this change is associated with a positive feedback between variations in ice viscosity, due to variations in dust content, and the impact of a shear stress component, increasing with depth. A ViscoPlastic Self-Consistent modeling approach is used to simulate the fabric evolution for a "perfect dome" configuration. The discrepancies between the measured and the simulated fabrics highlight the depth ranges where shear strongly affects the fabric strengthening. Finally, the grain size and fabric analyses show the occurrence of dynamic recrystallization mechanisms (continuous and discontinuous) along the core.

Montagnat, M.; Buiron, D.; Arnaud, L.; Broquet, A.; Schlitz, P.; Jacob, R.; Kipfstuhl, S.

2012-12-01

194

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

195

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

196

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

NASA Astrophysics Data System (ADS)

The climate of the past can be successfully investigated through the study of polar ice sheets. Paleotemperature reconstructions from Antarctic ice cores are based on water isotope profiles, thanks to the existing relationship between ?18O (or ?D) and the temperature at the site. Here we present the climate record of the past 2000 years resulting from the stable isotope analysis of the ice core drilled at Talos Dome in East Antarctica from 2003 to 2007 in the framework of the European TALDICE (TALos Dome Ice CorE) project. Talos Dome (72°49'S, 159°11'E; 2315 m; -41°C) is an ice dome on the edge of the East Antarctic plateau. The snow accumulation rate of the site (80 kg m-2 yr-1) allows extracting high-resolution data for the past millennia. The main moisture sources of snow precipitation at this near-coastal site are located in the Indian Ocean and the Ross Sea. Isotopic analyses of TALDICE detailed (10 cm) samples have been performed in the framework of the ESF-HOLOCLIP project, whose main objective is to integrate the ice core, the marine core and the modeling data to investigate the climate variability of the high latitude southern hemisphere over the Holocene. The isotopic record obtained from the TALDICE ice core is here compared with a shallow firn core (89 m long) previously drilled at Talos Dome, at a 5 km distance, and covering the past 800 years. The two isotopic records are stacked to reduce the stratigraphic noise and compared with other available isotopic records from Antarctica to highlight common trends and regional variability in the climatic signal over the past two millennia. We compare the data with a simulation performed with a three-dimensional earth system model of intermediate complexity (LOVECLIM) with and without data assimilation. Considering the ?18O profile from the TALDICE ice core and comparing it with the ones from the other available records we can observe common negative isotopic anomalies in the period from about 1450 to 1850 AD preceded by several positive and negative anomalies on centennial scale.

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

2013-04-01

197

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

USGS Publications Warehouse

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

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

2000-01-01

198

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

E-print Network

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

Howat, Ian M.

199

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

200

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

201

North Pacific Atmospheric Circulation and Tropical Teleconnections Over the Past 1500 Years From a Mt. Logan Ice Core  

NASA Astrophysics Data System (ADS)

A calibrated 1500 year-long glaciochemical proxy record for the strength of the wintertime (November-March) Aleutian Low (ALOW) from the Mt. Logan summit (PR Col; 5300 m a.s.l.) ice core [Na+] time series reveals a strong ALOW from ca. 650-900 A.D., ca. 1300-1550 A.D., and ca. 1700-1998 A.D., and a weaker ALOW from ca. 900-1300 A.D. and ca. 1550-1700 A.D. The proxy record was calibrated to instrumental sea-level pressure data using standard regression techniques, and verified using statistical, spectral, and spatial correlation analyses. The Mt. Logan ALOW proxy record shows strong similarities with sea surface temperature, precipitation, and glacier extent proxy records from the Pacific basin sensitive to the El Niño-Southern Oscillation, indicating a robust coupling between high-latitude and tropical Pacific climate during the late Holocene. The Medieval Warm Period was characterized by more persistent La Niña-like conditions (weak ALOW), while the Little Ice Age (LIA) was characterized by at least two intervals of more persistent El Niño-like conditions (strong ALOW; 1300-1550 A.D., 1700-1998 A.D.). The LIA intensification of the ALOW is similar to the LIA intensification of the Icelandic Low in the North Atlantic (based on the GISP2, Greenland ice core [Na+] calibrated proxy record) and the Amundsen Sea Low in the high-latitude South Pacific (based on the Siple Dome, West Antarctica ice core [Na+] calibrated proxy record).

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

2007-12-01

202

A 12,000 year record of explosive volcanism in the Siple Dome Ice Core, West Antarctica  

E-print Network

the Siple Dome A (SDMA) ice core, West Antarctica. The largest volcanic sulfate spike (280 mg/L) occurs are synchronous with many sulfate peaks detected in the SDMA volcanic ice chemistry record. The microprobe ``fingerprinting'' of glass shards in the SDMA core points to the following Antarctic volcanic centers as sources

Dunbar, Nelia W.

203

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

NASA Astrophysics Data System (ADS)

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

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

2003-12-01

204

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

205

The chemical composition of cold events within the Eemian section of the Greenland Ice Core Project ice core from Summit, Greenland  

NASA Astrophysics Data System (ADS)

Selected segments from the Eemian period of the Greenland Ice Core Project (GRIP) core from Summit, Greenland, have been analyzed by ion chromatography and Coulter Multisizer. The results will be discussed with special emphasis on the sudden cooling events, event 1 and event 2, in the record as observed in the ?18O profile [GRIP members, 1993; Dansgaard et al., 1993]. Whether the sudden cooling events of the Eemian represent a real climatic signal or they are a consequence of disturbed ice core st ratigraphy is still a matter of debate [Chappellaz et al., this issue]. However, several features of the chemical profiles across these cooling events are difficult to explain if they were a result of disturbed stratigraphy. We will focus our discussion on the unique profiles of nitrate, methane sulfonic acid (MSA), and ammonium across event 1 and argue that even if we allow for movement of ions by diffusion or displacement of ions by physical or chemical interactions, events 1 and 2 are not likely to consist of ice from other climatic periods which have been inserted in the Eemian strata by folding processes. Furthermore, our records do not show any layers in the vicinity of the Eemian strata which can be a possible source of the ice in event 1. We believe that the events represent a climate signal, and we will discuss other possible explanations of the profiles. Our conclusion that the cold events in the Eemian represent a real climatic signal runs counter to other evidence from gas measurements. However, whatever their cause, the unusual chemical signals require further discussion and explanation.

Steffensen, JøRgen Peder; Clausen, Henrik B.; Hammer, Claus U.; Legrand, Michel; de Angelis, Martine

1997-11-01

206

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

207

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

NASA Astrophysics Data System (ADS)

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

Breton, Daniel; Hamilton, Gordon

2009-10-01

208

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

209

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

210

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

211

PeV Neutrinos Observed by IceCube from Cores of Active Galactic Nuclei  

NASA Technical Reports Server (NTRS)

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

Stecker, Floyd W.

2013-01-01

212

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

Microsoft Academic Search

Methane and nitrous oxide are important greenhouse gases which show a strong increase in atmospheric mixing ratios since pre-industrial time as well as large variations during past climate changes. The understanding of their biogeochemical cycles can be improved using stable isotope analysis. However, high-precision isotope measurements on air trapped in ice cores are challenging because of the high susceptibility to

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

2011-01-01

213

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

PubMed

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

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

2014-01-01

214

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

E-print Network

record of volcanism correlates with Glacial abrupt climate change at a 95% to >99.8% ($3s) significance periods recorded in Greenland over the last glacial phase. Connec- tions drawn between glaciation changes histories from ice coring of Greenland and Antarctica over the period 2 to 45 ka, using SO4 anomalies

Price, P. Buford

215

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

216

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

E-print Network

stratospheric aerosol loading from ice core data: radioactive deposition from nuclear bomb tests, Pinatubo 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

Robock, Alan

217

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

Microsoft Academic Search

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

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

1995-01-01

218

CO2 & global temperature: Analysis of ice core and marine sediment data in  

E-print Network

CO2 & global temperature: Analysis of ice core and marine sediment data in combination proxy EOF Analysis: temperature pattern & time series #12;Global warming Indian Ocean warming (10%) 3°C;#12;Deglaciation: Data and Models CO2 leads global temperature Marine reservoir ages Deglacial Warming leads

Sengun, Mehmet Haluk

219

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

220

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

223

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

SciTech Connect

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

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

2000-02-27

224

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

USGS Publications Warehouse

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

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

2000-01-01

225

Centennial mineral dust variability in high-resolution ice core data from Dome C, Antarctica  

NASA Astrophysics Data System (ADS)

Ice core data from Antarctica provide detailed insights into the characteristics of past climate, atmospheric circulation, as well as changes in the aerosol load of the atmosphere. We present high-resolution records of soluble calcium (Ca2+), non-sea-salt soluble calcium (nssCa2+), and particulate mineral dust aerosol from the East Antarctic Plateau at a depth resolution of 1 cm, spanning the past 800 000 years. Despite the fact that all three parameters are largely dust-derived, the ratio of nssCa2+ to particulate dust is dependent on the particulate dust concentration itself. We used principal component analysis to extract the joint climatic signal and produce a common high-resolution record of dust flux. This new record is used to identify Antarctic warming events during the past eight glacial periods. The phasing of dust flux and CO2 changes during glacial-interglacial transitions reveals that iron fertilization of the Southern Ocean during the past nine glacial terminations was not the dominant factor in the deglacial rise of CO2 concentrations. Rapid changes in dust flux during glacial terminations and Antarctic warming events point to a rapid response of the southern westerly wind belt in the region of southern South American dust sources on changing climate conditions. The clear lead of these dust changes on temperature rise suggests that an atmospheric reorganization occurred in the Southern Hemisphere before the Southern Ocean warmed significantly.

Lambert, F.; Bigler, M.; Steffensen, J. P.; Hutterli, M.; Fischer, H.

2012-03-01

226

Towards understanding North Pacific climate variabilty with instrumental and ice core records  

NASA Astrophysics Data System (ADS)

Reconstructing climate variability prior to the instrumental era is critical to advance our understanding of the Earth's climate system. Although many paleoclimate records from the North Atlantic basin have been studied, relatively few paleoclimate records have been recovered in the North Pacific leaving a gap in our knowledge concerning North Pacific climate variability. The Eclipse and Mount Logan Prospector-Russell ice cores are favorably located in the St. Elias Mountains, Yukon, Canada to document North Pacific climate variability over the late Holocene. Detailed analysis reveals a consistent relationship of surface air temperature (SAT) anomalies associated with extreme Arctic Oscillation (AO) and Pacific-North America (PNA) index values, and a consistent relationship of North Pacific sea level pressure (SLP) anomalies associated with extreme Mt. Logan annual [Na+] and Eclipse cold season accumulation values. Spatial SAT anomaly patterns are most consistent for AO and PNA index values ?1.5 and ?-1.5 during the period 1872-2010. The highest and lowest ˜10% of Eclipse warm and cold season stable isotopes are associated with distinct atmospheric circulation patterns. The most-fractionated isotope values occur with a weaker Aleutian Low, and the least-fractionated isotope values occur with an amplification of the Aleutian Low and northwestern North American ridge. The assumption of stationarity between ice core records and sea-level pressure was tested for the Eclipse cold season accumulation and Mt. Logan annual sodium concentration records for 1872-2001. A stationary relationship was found for ?95% of years when Mt. Logan sodium concentrations were ?1.32 microg/L, with positive SLP anomalies in the eastern North Pacific. This high frequency supports the use of low sodium values at Mt. Logan for a reconstruction of SLP prior to 1872. Negative SLP anomalies in the North Pacific occurred for extreme high sodium concentration years and positive SLP anomalies occurred in the North Pacific for 70-90% of the highest accumulation seasons at Eclipse. These results contribute to our knowledge of North Pacific climate variability and can be applied to improve future North Pacific climate reconstructions.

Kelsey, Eric P.

227

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

SciTech Connect

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

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

1993-02-05

228

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.

229

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

230

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

231

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

232

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

233

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

234

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

PubMed Central

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

Schneider, David P.; Steig, Eric J.

2008-01-01

235

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

236

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

237

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

Microsoft Academic Search

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

Jean-Robert Petit; Martine Briat; Alain Royer

1981-01-01

238

A modified extraction technique for liberating occluded gases from ice cores  

NASA Astrophysics Data System (ADS)

We have developed a new dry extraction technique to extract air from large pieces of glacial ice. The primary reason for developing this technique was to be able to perform a single extraction and measure a single sample of air from an ice core sample for as many atmospheric constituents as possible. The procedure is modeled after the dry extraction -"cheese grater" design of Etheridge et al. [1988]. Extracted air samples are analyzed for the elemental and isotopic composition of O2 and N2 as well as the CH4 concentration. Extensive experimental work to determine the integrity of the extraction procedure yielded blank values and external precision which are comparable with exiting extraction procedures. Overall external precision for ?O2/N2, ?18O of O2, and ?15of N2 analyses is ±2.1‰, ±0.074‰, and ±0.045‰, respectively. Variable ?O2/N2 results from ice which is either completely bubbly or clathrated are in good agreement with previous measurements. Variable ?O2/N2 results from Greenland Ice Sheet Project (GISP) II ice samples spanning the clathrate formation region (1000-1500 m) are markedly different from previous results obtained with a "wet" extraction procedure. We attribute the differences to variable ?O2/N2 ratios in bubbles and clathrates in the clathrate formation region combined with a 21% difference in our extraction efficiency for bubbly versus clathrated ice. The overall uncertainty and blank value for CH4 measurements are ±19 ppb and 16 ppb, respectively. CH4 concentrations for ice between 115 and 140 meters below the surface (mbs) from the GISPII ice core appear to be 4.3% higher than the average value measured by five other laboratories. We attribute our elevated values to uncertainties in the actual concentration of our working standard and small differences in the CH4 concentration of the liberated air relative to the total air trapped in ice. Our corrected CH4 data spanning the last 25 kyr are indistinguishable from the Brook et al. (1996) CH4 record from the same period.

Sowers, Todd; Jubenville, Jennifer

2000-12-01

239

Lack of Southern Ocean paleoproductivity changes in biogenic aerosol records in the EPICA ice cores  

NASA Astrophysics Data System (ADS)

The Southern Ocean (SO) has been recognized as a key player in explaining glacial/interglacial carbon dioxide changes. In general two principal hypotheses have been put forward to explain a glacial drawdown of carbon dioxide in the SO: a) changes in SO overturning circulation and b) an enhanced biological export production in the SO due to iron fertilization. The latter is suggested by the 20 times higher glacial dust flux found in Antarctic ice cores. However, observational evidence for an enhanced biological productivity in the glacial SO is controversial and modeling studies show only a limited capacity of additional carbon uptake by iron fertilization. Here we present the first high-precision records of biogenic ammonium from the two EPICA ice cores reflecting biomass production in the SO. These records show essential no glacial/interglacial change in ammonium deposition fluxes indicating no change in atmospheric ammonium concentrations and, thus, also little change in the biological productivity in SO surface waters in the glacial. The result from the ammonium record is corroborated by the lack of glacial/interglacial changes in biogenic sulfate, essentially reflecting DMS producing plankton species in the seasonal sea ice zone. Both ammonium and sulfate fluxes show secondary changes on the order of 20-30%, which are within the uncertainty of the accumulation rate estimate used to calculate deposition fluxes. Nevertheless we investigate in how far these minor changes may be related to dust deposition, sea ice coverage as well as aerosol transport.

Kaufmann, P.; Fundel, F.; Fischer, H.; Wolff, E.; Hansson, M.; Udisti, R.; Steffensen, J. P.; de Angelis, M.; Wagenbach, D.

2009-04-01

240

Cosmic ray event of A.D. 774-775 shown in quasi-annual 10Be data from the Antarctic Dome Fuji ice core  

NASA Astrophysics Data System (ADS)

content in tree rings and 10Be concentration records in polar ice core provide information about past cosmic ray intensities. The A.D. 774-775 cosmic ray event has been identified by 14C measurement in several tree rings from all over the world. Although the quasi-decadal 10Be Dome Fuji data in the Antarctic ice core also shows a sharp peak around A.D. 775, annual 10Be variations in the Dome Fuji core or in other cores have not been revealed. We have measured quasi-annual 10Be concentrations from approximately A.D. 763-794 in the Dome Fuji ice core, and detected a clear increase (~80% above the baseline) in 10Be concentration around A.D. 775. However, an accurate height of this increase is not straightforwardly estimated due to the background variation in 10Be concentration. The 10Be increase can be due to the same cosmic ray event as shown in the 14C content in A.D. 774-775.

Miyake, Fusa; Suzuki, Asami; Masuda, Kimiaki; Horiuchi, Kazuho; Motoyama, Hideaki; Matsuzaki, Hiroyuki; Motizuki, Yuko; Takahashi, Kazuya; Nakai, Yoichi

2015-01-01

241

Depletion of chlorine into HCl ice in a protostellar core  

E-print Network

The freezeout of gas-phase species onto cold dust grains can drastically alter the chemistry and the heating-cooling balance of protostellar material. In contrast to well-known species such as carbon monoxide (CO), the freezeout of various carriers of elements with abundances $chlorine in the protostellar core, OMC-2 FIR 4. We observed transitions of HCl and H2Cl+ towards OMC-2 FIR 4 using the Herschel Space Observatory and Caltech Submillimeter Observatory facilities. Our analysis makes use of state of the art chlorine gas-grain chemical models and newly calculated HCl-H$_{2}$ hyperfine collisional excitation rate coefficients. A narrow emission component in the HCl lines traces the extended envelope, and a broad one traces a more compact central region. The gas-phase HCl abundance in FIR 4 is 9e-11, a factor of only 0.001 that of volatile elemental chlorine. The H2Cl+ lines are detected in absorption and trace a tenuous fo...

Kama, M; Lopez-Sepulcre, A; Wakelam, V; Dominik, C; Ceccarelli, C; Lanza, M; Lique, F; Ochsendorf, B B; Lis, D C; Caballero, R N; Tielens, A G G M

2014-01-01

242

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

243

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

E-print Network

. J. Curran,3,4 J. E. Dibb,5 M. M. Frey,1,6 M. Legrand,7 and J. R. McConnell8 Received 6 March 2012. W., M. Bigler, M. A. J. Curran, J. E. Dibb, M. M. Frey, M. Legrand, and J. R. McConnell (2012 of objections to this interpretation of ice core nitrate have been raised [e.g., Legrand and Delmas, 1986; Wolff

Cambridge, University of

244

Antarctic Ice Sheet: Stable Isotope Analyses of Byrd Station Cores and Interhemispheric Climatic Implications  

Microsoft Academic Search

Oxygen- and hydrogen-isotope analyses from the core hole through the Antarctic Ice Sheet at Byrd Station define temperature variations over more than 75,000 years. Synchronism between major climatic changes in Antarctica and the Northern Hemisphere is strongly indicated. The Wisconsin cold interval extended from 75,000 to 11,000 years ago. Three intra-Wisconsin warmer phases were all colder than pre- or post-Wisconsin

Samuel Epstein; R. P. Sharp; A. J. Gow

1970-01-01

245

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

246

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

247

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, Jürg; Brunner, Irene; Christl, Marcus; Fischer, Hubertus; Heikkilä, Ulla; Kubik, Peter W.; Mann, Mathias; McCracken, Ken G.; Miller, Heinrich; Miyahara, Hiroko; Oerter, Hans

2012-01-01

248

The ratio of MSA to non-sea-salt sulphate in Antarctic Peninsula ice cores  

NASA Astrophysics Data System (ADS)

Methane sulphonic acid (MSA) in an ice core from Dolleman Island shows significantly high concentrations (typically 1-2 microns, but up to 5 micronsM) compared to values recorded in ice cores and in snowfall from elsewhere in Antarctica. MSA data from two other higher altitude Antarctic Peninsula ice cores, Dyer Plateau and Gomez Nunatak, show that the high concentrations measured at Dolleman Island are not representative of the Peninsula region as a whole. Exceptionally high concentrations observed at Dolleman Island may be related to its proximity to the biologically productive Weddell Sea, an important source of dimethyl sulphide (DMS), the precursor of MSA. In a near-surface section, MSA variations are in phase with non sea-salt sulphate, with a maximum concentration in the summer layer. A change in the season of deposition of MSA from winter to summer in the recent past is not considered likely. An alternative explanation is that there has been a relocation of the MSA from summer to winter layers during burial.

Mulvaney, Robert; Pasteur, Elizabeth C.; Peel, David A.; Saltzman, Eric S.; Whung, Pai-Yei

1992-09-01

249

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

250

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

251

Changes in black carbon deposition to Antarctica from two ice core records, A.D. 1850-2000  

E-print Network

density and snow accumulation rate at the ice #12;core drilling site. For annual accumulation derived from Measurement Technologies, Boulder, Colorado) coupled to an ultrasonic nebulizer/desolvation (CETAC UT5000

Meskhidze, Nicholas

252

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

253

Climatic changes on orbital and sub-orbital time scale recorded by the Guliya ice core in Tibetan Plateau  

Microsoft Academic Search

Based on ice core records in the Tibetan Plateau and Greenland, the features and possible causes of climatic changes on orbital\\u000a and sub-orbital time scale were discussed. Orbital time scale climatic change recorded in ice core from the Tibetan Plateau\\u000a is typically ahead of that from polar regions, which indicates that climatic change in the Tibetan Plateau might be earlier

Tandong Yao; Baiqing Xu; Jianchen Pu

2001-01-01

254

Clocking the Speed of Climate Change: The End of the Younger Dryas as Recorded by Four Greenland Ice Cores  

Microsoft Academic Search

The warming at the end of the Younger Dryas (about 11,500 years bp) was the first large, rapid climate change to be studied in detail in ice cores, and remains the most recent, large, rapid climate change that we can study with near-annual resolution. Early studies examined this climate change using the DYE3 ice core in southern Greenland, and later

J. W. White; T. Popp; S. J. Johnsen; V. Masson; J. Jouzel

2001-01-01

255

The spring nitrate peak in snow and ice cores at Summit, Greenland  

NASA Astrophysics Data System (ADS)

The concentration profiles of nitrate from a snow pit and ice core collected at Summit, Greenland show double (spring and summer) peaks in some years. The summer peak is annually produced and well-understood as the result of active photochemical reactions under summer sunshine; while the spring peak appears irregularly and the origin is questioned. To investigate the origin of the spring nitrate peak, we measured ?15N and ?17O (?17O = ?17O - 0.52×?18O) of nitrate collected from a snow pit which has been dated at the sub-annual scale. The seasonality of ?15N-NO3- (Figure 1) reveals a positive ?15N signature from the spring peak (similar to that of summer, higher than that of winter). This indicates a non fossil fuel combustion source of NOx, which contains negative ?15N signature. The anomaly of ?17O-NO3- of the spring peak is between those of summer and winter nitrate, suggesting a combination of summer mode (OH oxidation, low ?17O-NO3-) and winter mode (O3 oxidation, high ?17O-NO3-) of nitrate production. The enhanced summer mode oxidation producing extra nitrate during the spring, when the spring peak appears, is hypothesized to be caused by increased UV light reaching the lower atmosphere due to the depletion of springtime column ozone in the Arctic stratosphere. Further work is under way to investigate the periodicity of the spring nitrate peaks and time profiles of surface UV and column ozone at Summit to test the above hypothesis. Figure 1. Concentrations (ug L-1), ?15N (‰) and ?17O (‰) of nitrate from a Summit snow pit. Summer peak and spring peak are as indicated.

Geng, L.; Cole-Dai, J.; Alexander, B.

2010-12-01

256

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

257

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

258

Rare earth elements in an ice core from Mt. Everest: Seasonal variations and potential sources  

NASA Astrophysics Data System (ADS)

Rare earth element (REE) concentrations in ice samples from the upper 8.4 m of a Mt. Everest ice core retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the northeast ridge of Mt. Everest in September 2002 are presented. REEs display large seasonal variations, with high concentrations in the non-monsoon season and low concentrations in the summer monsoon season. This seasonality is useful for ice core dating. When normalized to a shale standard, the Mt. Everest REEs exhibit a consistent shale-like pattern with a slight enrichment of middle REEs during both seasons. However, individual monsoon REE patterns display differences, possibly resulting from diversified sources. Non-monsoon REE patterns are stable and are associated with the westerlies. Investigation of potential sources for the Everest REEs suggests an absence of anthropogenic contributions and minimal input from local provenances. REEs in Mt. Everest samples are most likely representative of a stable well-mixed REE background of the upper troposphere consisting of a mixture of aerosols transported by the atmospheric circulation from the west windward arid regions such as the Thar Desert, West Asia, the Sahara Desert and other uncertain provenances.

Zhang, Qianggong; Kang, Shichang; Kaspari, Susan; Li, Chaoliu; Qin, Dahe; Mayewski, Paul A.; Hou, Shugui

2009-10-01

259

Continuous high-temporal resolution black carbon ice core records from Antarctica  

NASA Astrophysics Data System (ADS)

The Antarctic ice cap is a unique vantage point from which to observe the global background of black carbon aerosol (BC). Far removed from sources, BC in the Antarctic atmosphere is largely due to biomass burning at low- to mid-latitudes modulated by upper tropospheric (and perhaps stratospheric) transport, climate variability and human activity. BC aerosols have been investigated at several locations in Antarctica including the coastal stations Halley, Syowa and Neumayer, Amundsen-Scott at the South Pole and the South Shetland islands north of the Antarctic Peninsula. Beyond these time series little is known regarding the history of BC over Antarctica. Pioneering research by Petr Chylek demonstrated that it was possible to develop BC records from Antarctic ice cores, albeit with great difficulty and at low temporal resolution. We have recently developed an extremely sensitive analytical method capable of determining BC in Antarctic ice cores at sub annual resolution. This method has allowed us to build upon the research of Chylek and reconstruct BC deposition to Antarctica over the past 200 years at ~ monthly time scales. These "new- generation" records will be presented and the extent of which they reflect large scale BC aerosol variability discussed.

Edwards, R.; McConnell, J. R.; Aristarain, A. J.; Curran, M. A.; Pedro, J.; Cataldo, M.; Evangelista, H.

2008-12-01

260

Late Glacial Stage and Holocene Tropical Ice Core Records from Huascaran, Peru  

NASA Astrophysics Data System (ADS)

Two ice cores from the col of Huascaran in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Wurm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8^circ to 12^circC cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio ?18O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5^circ to 6^circC cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.

Thompson, L. G.; Mosley-Thompson, E.; Davis, M. E.; Lin, P.-N.; Henderson, K. A.; Cole-Dai, J.; Bolzan, J. F.; Liu, K.-B.

1995-07-01

261

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

262

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

263

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

264

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

NASA Astrophysics Data System (ADS)

Herein we produce a record of Crete volcanism based solely on an objective definition of individual volcanic events in the ice core record. There are 92 acidity peaks in the 1420-year record. Since at least 26 percent of the post-1600 eruptions are of local (Icelandic) origin, we estimate a mean recurrence interval of 20.8 years for hemispheric-scale eruptions rich in sulphate. On decadal time scales, volcanism has varied by a factor of three-four over the last 1400 years. However, the climate-volcanism correlation is considerably less impressive (r = -0.23) than previously concluded (r = -0.52). The good correspondence between volcanism and climate previously reported are due to background acidity levels that show a significant Little Ice Age increase. The background increase may reflect changes in ocean productivity.

Crowley, Thomas J.; Criste, Tamara A.; Smith, Neil R.

1993-02-01

265

Ices and the Extinction Curve in the Quiescent Medium of Isolated Dense Cores  

NASA Astrophysics Data System (ADS)

For a sample of 31 stars behind isolated dense cores, ground-based and Spitzer spectra and photometry in the 1-25 um wavelength range are combined. We use this unique dataset to (1) investigate the composition of the ices before Young Stellar Objects (YSOs) are formed and (2) determine the 'high resolution' extinction curve. We find that the strengths of the 6.0 and 6.85 um ice absorption bands are in line with those of YSOs. Thus, their carriers, which, besides H2O and CH3OH, may include NH4+, HCOOH, H2CO, and NH3, are readily formed in the dense core phase. The 3.53 um 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 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. Furthermore, the extinction curve is derived empirically from the 1-25 um spectra. Its high resolution allows for the separation of continuum and feature extinction. The extinction between 13 and 25 um is 50% relative to that at 2.2 um. This probably indicates the presence of a population of large grains (RV>=5.5). However, the peak optical depth of the 9.7 um band of silicates relative to the continuum extinction at 2.2 um is significantly shallower than in the diffuse ISM. This extends the results of Chiar et al. to a larger sample and higher extinctions.

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

2012-01-01

266

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

NASA Astrophysics Data System (ADS)

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

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

267

Variations of ion concentrations in the deep ice core and surface snow at NEEM, Greenland  

NASA Astrophysics Data System (ADS)

Discrete samples were collected from the CFA (Continuous Flow Analysis) melt fractions during the field campaign carried out at NEEM, Greenland in 2009-2011, and were distributed to different laboratories. Ionic species were analyzed at National Institute of Polar Research (Japan) and Alfred Wegener Institute for Polar and Marine Research (Germany). Here we present and compare the ion concentration data obtained by both institutes. Most of the ions show good agreement between the two institutes. As is indicated with the CFA data (Bigler and the NEEM Aerosol Consortium members, EGU 2012), ion chromatograph data also display that calcium and sodium, mainly originated from terrestrial dust and sea-salt, respectively, show large variations associated with Dansgaard-Oeschger (DO) events. Chloride, fluoride, sulfate, sodium, potassium and magnesium also show such variations, as has been already reported for other Greenland ice cores. New ion data obtained from the NEEM deep core also show large variability of oxalate and phosphate concentrations during DO events. Acetate, which is thought to be mainly derived from biomass burning, as is oxalate, appears to show variability associated with DO events, but to a lesser extent. On the other hand, nitrate, ammonium and methanesulfonate do not show such variations. Together with ion data from the deep ice core, we present those from the pits dug during the NEEM field campaign to discuss seasonal variations of ionic species. The seasonal and millennial scale variations of ions are thought to be caused by changes in atmospheric circulation and source strength.

Goto-Azuma, K.; Wegner, A.; Hansson, M.; Hirabayashi, M.; Kuramoto, T.; Miyake, T.; Motoyama, H.; NEEM Aerosol Consortium members

2012-04-01

268

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

269

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

270

Continuous flow analysis method for determination of dissolved reactive phosphorus in ice cores.  

PubMed

Phosphorus (P) is an essential macronutrient for all living organisms. Phosphorus is often present in nature as the soluble phosphate ion PO4(3-) and has biological, terrestrial, and marine emission sources. Thus PO4(3-) detected in ice cores has the potential to be an important tracer for biological activity in the past. In this study a continuous and highly sensitive absorption method for detection of dissolved reactive phosphorus (DRP) in ice cores has been developed using a molybdate reagent and a 2-m liquid waveguide capillary cell (LWCC). DRP is the soluble form of the nutrient phosphorus, which reacts with molybdate. The method was optimized to meet the low concentrations of DRP in Greenland ice, with a depth resolution of approximately 2 cm and an analytical uncertainty of 1.1 nM (0.1 ppb) PO4(3-). The method has been applied to segments of a shallow firn core from Northeast Greenland, indicating a mean concentration level of 2.74 nM (0.26 ppb) PO4(3-) for the period 1930-2005 with a standard deviation of 1.37 nM (0.13 ppb) PO4(3-) and values reaching as high as 10.52 nM (1 ppb) PO4(3-). Similar levels were detected for the period 1771-1823. Based on impurity abundances, dust and biogenic particles were found to be the most likely sources of DRP deposited in Northeast Greenland. PMID:24128116

Kjær, Helle Astrid; Vallelonga, Paul; Svensson, Anders; Kristensen, Magnus Elleskov L; Tibuleac, Catalin; Bigler, Matthias

2013-11-01

271

Marine bacteria in deep Arctic and Antarctic ice cores: a proxy for evolution in oceans over 300 million generations  

NASA Astrophysics Data System (ADS)

Using fluorescence spectrometry to map autofluorescence of chlorophyll (Chl) and tryptophan (Trp) versus depth in polar ice cores in the US National Ice Core Laboratory, we found that the Chl and Trp concentrations often showed an annual modulation of up to 25%, with peaks at depths corresponding to local summers. Using epifluorescence microscopy (EFM) and flow cytometry (FCM) triggered on 670 nm fluorescence (red) to study microbes from unstained melts of the polar ice, we inferred that picocyanobacteria may have been responsible for the red fluorescence in the cores. Micron-size bacteria in all ice melts from 2 Arctic and 6 Antarctic sites showed FCM patterns of scattering and of red vs. orange fluorescence (interpreted as due to Chl vs. phycoerythrin (PE)) that bore similarities to patterns of cultures of unstained picocyanobacteria Prochlorococcus and Synechococcus. Concentrations in ice from all sites were low but measurable at ~1 to ~103 cells cm-3. Calibrations showed that FCM patterns of mineral grains and volcanic ash could be distinguished from microbes with high efficiency by triggering on scattering instead of by red fluorescence. Average Chl and PE autofluorescence intensities showed no decrease per cell with time during up to 150 000 yr of storage in glacial ice. Taking into account the annual modulation of ~25% and seasonal changes of ocean temperatures and winds, we suggest that picocyanobacteria are wind-transported year-round from warmer ocean waters onto polar ice. Ice cores offer the opportunity to study evolution of marine microbes over ~300 million generations by analyzing their genomes vs. depth in glacial ice over the last 700 000 yr as frozen proxies for changes in their genomes in oceans.

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

2012-06-01

272

Marine bacteria in deep Arctic and Antarctic ice cores: a proxy for evolution in oceans over 300 million generations  

NASA Astrophysics Data System (ADS)

Using fluorescence spectrometry to map autofluorescence of chlorophyll (Chl) and tryptophan (Trp) versus depth in polar ice cores in the US National Ice Core Laboratory, we found that the Chl and Trp concentrations often showed an annual modulation of up to 25%, with peaks at depths corresponding to local summers. Using epifluorescence microscopy (EFM) and flow cytometry (FCM) triggered on red fluorescence at 670 nm to study microbes from unstained melts of the polar ice, we inferred that picocyanobacteria may have been responsible for the red fluorescence in the cores. Micron-size bacteria in all ice melts from Arctic and Antarctic sites showed FCM patterns of scattering and of red vs. orange fluorescence (interpreted as due to Chl vs. phycoerythrin (PE)) that bore similarities to patterns of cultures of unstained picocyanobacteria Prochlorococcus and Synechococcus. Concentrations in ice from all sites were low, but measurable at ~ 1 to ~ 103 cells cm-3. Calibrations showed that FCM patterns of mineral grains and volcanic ash could be distinguished from microbes with high efficiency by triggering on scattering instead of by red fluorescence. Average Chl and PE autofluorescence intensities showed no decrease per cell with time during up to 150 000 yr of storage in glacial ice. Taking into account the annual modulation of ~ 25% and seasonal changes of ocean temperatures and winds, we suggest that picocyanobacteria are wind-transported year-round from warmer ocean waters onto polar ice. Ice cores offer the opportunity to study evolution of marine microbes over ~ 300 million generations by analysing their genomes vs. depth in glacial ice over the last 700 000 yr as frozen proxies for changes in their genomes in oceans.

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

2012-10-01

273

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

274

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

275

Modelling of Kealey ice rise, Antarctica, reveals stable ice-flow conditions in East Ellsworth Land over millennia  

NASA Astrophysics Data System (ADS)

Ice divides are dynamical features, and their evolution or stability reflects the conditions of the surrounding ice masses. The East of Ellsworth Land, West Antarctic Ice Sheet, is ringed by divides showing linear features parallel to the ridge in satellite imagery and a conspicuous layering in the ground-penetrating radar data known as Raymond bumps. These features have been shown to be the result of stability over a time-scale comparable to the characteristic time of the divide, ice thickness divided by accumulation, that varies between centuries and millennia in this area. In this study, we focus in Kealey ice rise, an ice divide situated between two distributaries of Rutford ice stream, Carlson and Talutis Inlets.Through numerical modelling, by using an anisotropic full-Stokes thermomechanical flow solver, we analyze the stability of Kealey ice rise and the time-scales involved. We show that our modelling approach can reproduce the radar data only if we use a non-linear anisotropic rheology, and that the asymmetry observed in radar data is forced mainly by the topography of the bedrock. We conclude that the features observed in the surface and stratigraphy of Kealey ice rise are a consequence of, at least, 5 kyr of flow regime stability. However, we can not exclude the possibility of a recent flow reorganization in the last century that could only be reflected in the shallower areas of the ice rise. We stress that the signs of stability observed in Kealey Ice Rise are widespread in the Ellsworth Land area, suggesting recent stability on the millennium time-scale.

Martin, Carlos; Hilmar Gudmundsson, G.

2013-04-01

276

Single particle mineralogy of aeolian dust in the East Rongbuk ice core from Mt. Qomolangma (Everest)  

NASA Astrophysics Data System (ADS)

A recent work demonstrated the practical applicability of the combined use of two techniques, attenuated total reflectance FT-IR (ATR-FT-IR) imaging and a quantitative energy-dispersive electron probe X-ray microanalysis, low-Z particle EPMA, for the characterization of individual aerosol particles. These single particle analytical techniques provide complementary information on the physicochemical characteristics of the same individual particles, such as low-Z particle EPMA on morphology and elemental concentrations and the ATR-FT-IR imaging on molecular species, crystal structures, functional groups, and physical states. In this work, this analytical methodology was applied to characterize an insoluble mineral particle sample in the East Rongbuk ice core from Mt. Qomolangma (Everest). On the basis of morphological, X-ray spectral, and ATR-FT-IR spectral data, 140 individual particles were classified into different mineral types, such as SiO2, montmorillonite, montmorillonite + K-feldspar, K-feldspar, Na-feldspar, carbonaceous, FeOx, muscovite, illite, vermiculite, and AlSiO3. In Figure 1, typical X-ray spectrum and ATR-FT-IR spectrum of a particle selected from the ice core sample are shown. This work demonstrates that more detailed physiochemical properties of individual airborne particles can be obtained using this approach than when either the low-Z particle EPMA or ATR-FT-IR imaging technique is used alone.

Hwang, H.; Jung, H.; Eom, H.; Malek, M. A.; Hur, S.; Ro, C.

2011-12-01

277

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

278

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

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

279

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

280

Detection prospects for GeV neutrinos from collisionally heated gamma-ray bursts with IceCube/DeepCore.  

PubMed

Jet reheating via nuclear collisions has recently been proposed as the main mechanism for gamma-ray burst (GRB) emission. In addition to producing the observed gamma rays, collisional heating must generate 10-100 GeV neutrinos, implying a close relation between the neutrino and gamma-ray luminosities. We exploit this theoretical relation to make predictions for possible GRB detections by IceCube + DeepCore. To estimate the expected neutrino signal, we use the largest sample of bursts observed by the Burst and Transient Source Experiment in 1991-2000. GRB neutrinos could have been detected if IceCube + DeepCore operated at that time. Detection of 10-100 GeV neutrinos would have significant implications, shedding light on the composition of GRB jets and their Lorentz factors. This could be an important target in designing future upgrades of the IceCube + DeepCore observatory. PMID:25165903

Bartos, I; Beloborodov, A M; Hurley, K; Márka, S

2013-06-14

281

Ice  

NSDL National Science Digital Library

When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.

Harris, Kathryn L.

282

A 16,000-yr tephra framework for the Antarctic ice sheet: a contribution from the new Talos Dome core  

NASA Astrophysics Data System (ADS)

A detailed tephra record for the last 16,000 years of the TALDICE ice core drilled at Talos Dome (East Antarctica, Pacific/Ross Sea sector) is documented. Traces of 26 different explosive volcanic eruptions, dated by ice core chronology and framed within the climate (?18O) record for the core, have been identified. Glass major element composition and grain size data indicate that all prominent tephra layers derive from Antarctic volcanic activity and likely originated in proximal volcanoes of the Melbourne Volcanic Province (Northern Victoria Land). Two other Antarctic horizons may have originated from the more distant volcanoes of Mount Berlin (Marie Byrd Land, West Antarctica) and Mount Erebus (Ross Island, Southern Victoria Land). Moreover, based on glass-shard geochemistry and a 20-year analysis of atmospheric back trajectories suggesting ash transport from South America to the drilling site by the circumpolar westerly circulation, a few faint microtephra horizons are attributed to Andean volcanic activity. Two of these tephras are interpreted to be related to known Holocene explosive eruptions from the volcanoes of Mount Hudson and Mount Burney. Finally, by comparing compositional features in conjunction with age data, three TALDICE tephras have been successfully correlated with volcanic layers in other ice records of the Antarctic ice sheet. Altogether, our results expand the Antarctic tephrostratigraphic framework and add value to the prospects for continental-scale correlations between ice cores and Southern Hemisphere sediment archives.

Narcisi, Biancamaria; Petit, Jean Robert; Delmonte, Barbara; Scarchilli, Claudio; Stenni, Barbara

2012-08-01

283

Atmosphere aerosol/dust composition over central Asia and western Siberia derived from snow/ice core records and calibrated with NASA remote sensing data  

NASA Astrophysics Data System (ADS)

The vast arid and semi-arid regions of central Asia, Mongolia, and Northern China are the world's second largest source of atmospheric mineral dust. In recent years, severe dust storms in Asia have intensified in frequency, duration, and areal coverage. However, limited spatial and temporal extent of aerosol measurements precludes definitive statements to be made regarding relationship between the Asian aerosol generation and climate. It has been well known that glaciers are the natural archives of environmental records related to past climate and aerosol generation. In our research, we utilized central Asian and western Siberia shallow ice-core records recovered from Altai, Tien Shan and Pamir mountain glaciers. Despite the fact that ice-core data may extend climate/aerosol records back in time, their sparse coverage is inadequate to document aerosol spatial distribution. The NASA products from Aura, Terra and Aqua satellite missions address this gap identifying aerosol sources, transport pathways, and area of deposition. The main objective of our research is to evaluate an affect of climate variability on dynamics of Asian aerosol loading to atmosphere and changes in aerosol transport pathways. Dust particle, major and rare earth element analysis from dust aerosols deposited and accumulated in Altai, Tien Shan and Pamir glaciers suggests that loess from Tajikistan, Afghanistan and north-western China are main sources of aerosol loading into the upper troposphere over the central Asia and western Siberia. At the same time, the soluble ionic component of the ice-cores, related to aerosol generated from evaporate deposits, demonstrated both anthropogenic and natural impacts on atmospheric chemistry over these regions. Large perturbations of Ca2+ derived from CaCO3- rich dust transported from Goby Desert to Altai and Tien Shan. Origin and pathway of the ice-core aerosol depositions for the last 10-years were identified through calibrating ice-core records with dust storm land surface records and remote sensing aerosol data at the monthly/seasonal/annual to event/daily scale. For instance, in southwestern Asia, severe drought developed from 1998 to 2002 has intensified the frequency, duration, and spatial coverage of large dust storms originated in Iran, Afghanistan, Tajikistan, Taklimakan and Goby Deserts. The Pamir and Tien Shan ice-core records revealed, that concentration of major and REE elements during summer is about two times greater in period of 1998-2002 than at the following years. Our qualitative analysis based on ice-core records, the MODIS and SeaWiFS images and determined the origin of dust, transport pathways and aerosol spatial distribution over central Asia and western Siberia in summer 2000, 2001 and 2002. The transport pathways were reconstructed on the basis of visibility observations and NCAR MM5-predicted winds with further validation against of satellite data and isotope- geochemical ice-core data analysis.

Aizen, V. B.; Aizen, E. M.; Joswiak, D. R.; Surazakov, A. B.; Takeuchi, N.

2007-12-01

284

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

PubMed

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

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

2013-09-20

285

New high-resolution aerosol proxy data from the Greenland NEEM ice core covering the last 128,000 years  

NASA Astrophysics Data System (ADS)

High-resolution multicomponent continuous flow analysis (CFA) measurements have been performed over the entire depth of the NEEM ice core in three field seasons 2009-2011. Only in the brittle ice section, covering an age of approx. 4,000-8,000 years, continuous measurements could not be performed due to the bad ice quality which hampered such analyses. On all the other ice, continuous records of tracers for sea salt aerosol (sodium), mineral dust aerosol (calcium), inorganic and biogenic nitrogen compounds (nitrate and ammonium), hydrogen peroxide, and electrolytic conductivity were recorded. Data evaluation and quality control of the raw data of the 2.5 km long ice core have recently been finalised, resulting in the final multi-proxy CFA dataset of the NEEM ice core presented here. It covers the last 128,000 years including the entire (stratigraphically folded) Eemian warm period in Greenland. Our chemical CFA measurements are performed in a nominal resolution of 0.5 mm, allowing for the resolution of seasonal cycles over the top 1500 m of the ice core. Thus, seasonality of aerosol tracers can be studied as far back as the early Holocene, and to a certain extent even further back in time. The lower part of the ice core, however, including the last glacial period as well as the Eemian ice section, is subject to such strong thinning of the ice that no unambiguous seasonal cycles can be resolved any more. Nevertheless, long-term glacial-interglacial and stadial-interstadial changes on the one side and the peculiarities of the first Greenland Eemian aerosol record in comparison to the Holocene on the other can be investigated in highest resolution. Here, the new NEEM aerosol proxy records are presented and compared to NGRIP and GRIP CFA records focussed on the early Holocene and last glacial period. Thanks to the particularly high resolution we can furthermore closely investigate the timing and phasing of fast climate transitions such as Termination I and Dansgaard-Oeschger events during the last glacial period.

Schüpbach, Simon; Bigler, Matthias; Gfeller, Gideon; Fischer, Hubertus

2014-05-01

286

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

NASA Astrophysics Data System (ADS)

The analysis of gases and chemical impurities trapped in ice provides knowledge of earth's past climate. Deep ice cores from Greenland act as climate archives with high temporal resolution for more than the last 100,000 years covering Holocene, last glacial period and part of the previous interglacial called Eemian. Traditionally methane concentrations from ice cores are measured by gas chromatography. This technique is time consuming, labor intensive and generally not field deployable. Here we present results from the first laboratory and field tests of a new method for measuring methane concentrations from deep ice cores with high temporal resolution using a commercially available but slightly modified near-infrared cavity ring-down spectrometer (NIR-CRDS; http://www.picarro.com/). The NIR-CRDS is connected to a Continuous Flow Analysis (CFA) system, where air bubbles are continuously extracted from the melted ice water stream with the help of a hydrophobic membrane. The extracted gases are forwarded into the NIR-CRDS where the methane concentration is measured every 4 to 5 seconds. As the sample is diluted with helium during the extraction process an oxygen sensor is built into the NIR-CRDS. The continuous extraction of air and the high measurement frequency yield an extremely high temporal resolution, thus better exploiting the temporal resolution available from ice cores. At a typical CFA melt rate of 35 mm/min we obtain concentration measurements approximately every 3 mm of ice. The system is robust, compact and therefore suited for field measurements in combination with a continuous melting device. It was tested on the Greenland ice sheet during the 2009 field season of the North Greenland Eemian Ice Drilling (NEEM) project coupled to the University of Bern CFA system and under laboratory conditions with NGRIP ice coupled to the Copenhagen CFA system. The precision of the measurements of the first field season is encouraging but does not match the precision of gas chromatography measurements. The system is being improved and we expect to out compete or at least match gas chromatography for precision. Measurements of ice from the Eemian period are scheduled for the 2010 field season of the NEEM project.

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

2010-05-01

287

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

288

Subsurface imaging reveals a confined aquifer beneath an ice-sealed Antarctic lake  

NASA Astrophysics Data System (ADS)

water oases are rare under extreme cold desert conditions found in the Antarctic McMurdo Dry Valleys. Here we report geophysical results that indicate that Lake Vida, one of the largest lakes in the region, is nearly frozen and underlain by widespread cryoconcentrated brine. A ground penetrating radar survey profiled 20 m into lake ice and facilitated bathymetric mapping of the upper lake basin. An airborne transient electromagnetic survey revealed a low-resistivity zone 30-100 m beneath the lake surface. Based on previous knowledge of brine chemistry and local geology, we interpret this zone to be a confined aquifer situated in sediments with a porosity of 23-42%. Discovery of this aquifer suggests that subsurface liquid water may be more pervasive in regions of continuous permafrost than previously thought and may represent an extensive habitat for microbial populations.

Dugan, H. A.; Doran, P. T.; Tulaczyk, S.; Mikucki, J. A.; Arcone, S. A.; Auken, E.; Schamper, C.; Virginia, R. A.

2015-01-01

289

Can we retrieve a clear paleoclimatic signal from the deeper part of the EPICA Dome C ice core?  

NASA Astrophysics Data System (ADS)

An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (?D-?18Oice, ?18Oatm, total air content, CO2, CH4, N2O, dust, high resolution chemistry, ice texture) of the bottom 60 m of the EPICA Dome C ice core from central Antarctica. These bottom layers have been subdivided in two sections: the lower 12 m showing visible solid inclusions (basal ice) and the 48 m above which we refer to as "deep ice". Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies. It is demonstrated that neither large scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end-term from a previous/initial ice sheet configuration) can explain the observed bottom ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate "from within", and not from incorporation processes of allochtone material at the ice-bedrock interface. We also discuss how the proposed mechanism is compatible with the other variables described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the time scale has been considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice.

Tison, J.-L.; de Angelis, M.; Littot, G.; Wolff, E.; Fischer, H.; Hansson, M.; Bigler, M.; Udisti, R.; Wegner, A.; Jouzel, J.; Stenni, B.; Johnsen, S.; Masson-Delmotte, V.; Landais, A.; Lipenkov, V.; Loulergue, L.; Barnola, J.-M.; Petit, J.-R.; Delmonte, B.; Dreyfus, G.; Dahl-Jensen, D.; Durand, G.; Bereiter, B.; Schilt, A.; Spahni, R.; Pol, K.; Lorrain, R.; Souchez, R.; Samyn, D.

2015-01-01

290

Synoptic controls on precipitation pathways and snow delivery to high-accumulation ice core sites in the Ross Sea region, Antarctica  

NASA Astrophysics Data System (ADS)

Dominant storm tracks to two ice core sites on the western margin of the Ross Sea, Antarctica (Skinner Saddle (SKS) and Evans Piedmont Glacier), are investigated to establish key synoptic controls on snow accumulation. This is critical in terms of understanding the seasonality, source regions, and transport pathways of precipitation delivered to these sites. In situ snow depth and meteorological observations are used to identify major accumulation events in 2007-2008, which differ considerably between sites in terms of their magnitude and seasonal distribution. While snowfall at Evans Piedmont Glacier occurs almost exclusively during summer and spring, Skinner Saddle receives precipitation year round with a lull during the months of April and May. Cluster analysis of daily back trajectories reveals that the highest-accumulation days at both sites result from fast-moving air masses, associated with synoptic-scale low-pressure systems. There is evidence that short-duration pulses of snowfall at SKS also originate from mesocyclone development over the Ross Ice Shelf and local moisture sources. Changes in the frequency and seasonal distribution of these mechanisms of precipitation delivery will have a marked impact on annual accumulation over time and will therefore need careful consideration during the interpretation of stable isotope and geochemical records from these ice cores.

Sinclair, K. E.; Bertler, N. A. N.; Trompetter, W. J.

2010-11-01

291

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

292

Evidence for Pacific Climate Regime Shifts as Preserved in a Southeast Alaska Ice Core  

NASA Astrophysics Data System (ADS)

Climate modes emanating from the Pacific sector have far-reaching effects across the globe. The El Niño/Southern Oscillation (ENSO) reflects anomalies in the sea surface temperature and pressure fields over the tropical Pacific, but climate implications from these anomalies extend to monsoon regions of Asia to North America and even Europe. The Pacific Decadal Oscillation (PDO) explains sea surface temperature anomalies in the North Pacific sector and influences the long-term behavior of the ENSO cycle as well as the storm track over North America expressed as the Pacific/North American Pattern (PNA). The impacts of both climate change and drastically reduced Arctic sea ice cover on these teleconnection patterns are poorly understood, and with little knowledge about their past behavior, predicting the changes in these climate modes is extremely difficult. An ice core from the col between Mt. Bona and Mt. Churchill in southeast Alaska provides an opportunity to examine the PDO prior to both the start of instrumental records and the more recent effects of anthropogenic climate change. The Bona-Churchill records of isotopic, dust, and chemical composition are compared to nearby meteorological station and 20th century reanalysis data to evaluate their strength as climate recorders. Climate indices such as the PDO and PNA, along with indices created to describe the strength and position of the Aleutian Low and Siberian High, are incorporated into the analysis to determine if proxy relationships are altered under different climate regimes. Satellite records of sea ice extent within the Sea of Okhotsk and the Bering Sea, when compared to the Bona-Churchill data, show a distinct change in behavior in the mid-1990s possibly in response to the temporary negative shift in the PDO. This behavioral shift is explored and placed into a broader climate context to determine whether similar events have occurred in the past or if this shift is unique to a rapidly warming Arctic.

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

2012-12-01

293

Implication of azelaic acid in a Greenland Ice Core for oceanic and atmospheric changes in high latitudes  

NASA Astrophysics Data System (ADS)

A Greenland ice core (450 years) has been studied for low molecular weight dicarboxylic acids (C2-C10) using a capillary gas chromatography and mass spectrometer. Their molecular distribution generally showed a predominance of succinic acid (C4) followed by oxalic (C2), malonic (C3), glutaric (C5), adipic (C6), and azelaic (C9) acids. Azelaic acid, that is a specific photochemical reaction product of biogenic unsaturated fatty acids, gave a characteristic historical trend in the ice core; i.e., the concentrations are relatively low during late 16th to 19th century (Little Ice Age) but become very high in late 19th to 20th century (warmer periods) with a large peak in 1940s AD. Lower concentrations of azelaic acid may have been caused by a depressed emission of unsaturated fatty acids from seawater microlayers due to enhanced sea ice coverage during Little Ice Age. Inversely, increased concentrations of azelaic acid in late 19th to 20th century are likely interpreted by an enhanced sea-to-air emission of the precursor unsaturated fatty acids due to a retreat of sea ice and/or by the enhanced production due to a potentially increased oxidizing capability of the atmosphere.

Kawamura, K.; Yokoyama, K.; Fujii, Y.; Watanabe, O.

294

Validity of the Temperature Reconstruction from Water Isotopes in Ice Cores  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

295

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

296

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, Joël; Sofen, Eric D.; Schauer, Andrew J.

2014-01-01

297

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

PubMed

Nitrogen stable isotope ratio (?(15)N) 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 ?(15)N and major ions (e.g., NO3(-), SO4(2-)) over the last ?200 y show that the decrease in ?(15)N is not always associated with increasing NO3(-) concentrations, and the decreasing trend actually leveled off ?1970. Correlation of ?(15)N with H(+), NO3(-), and HNO3 concentrations, combined with nitrogen isotope fractionation models, suggests that the ?(15)N 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 NO3(-) and SO4(2-) also leveled off ?1970, reflecting the effect of air pollution mitigation strategies in North America on anthropogenic NO(x) 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 ?(15)N ?1970, which, together with the leveling off of NO3(-) concentrations, suggests a regional mitigation of anthropogenic impact on the nitrogen cycle. Our results highlight the importance of atmospheric processes in controlling ?(15)N of nitrate and should be considered when using ?(15)N 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, Joël; Sofen, Eric D; Schauer, Andrew J

2014-04-22

298

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

299

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

USGS Publications Warehouse

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

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

2003-01-01

300

Vostok ice core - A continuous isotope temperature record over the last climatic cycle (160,000 years)  

Microsoft Academic Search

A continuous deuterium record along the Vostok ice core has been obtained and is interpreted in terms of local surface temperature changes over the past 160 kyr. The record is dominated by the large glacial-interglacial signal occurring at about 100 kyr with a total temperature amplitude of about 11 C. It is confirmed that the warmest part of the Last

J. Jouzel; C. Genthon; C. Lorius; J. R. Petit; N. I. Barkov; V. M. Kotlyakov; V. M. Petrov

1987-01-01

301

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

E-print Network

Holocene climatic changes in Greenland: Different deuterium excess signals at Greenland Ice Core temperature record. Citation: Masson-Delmotte, V., et al. (2005), Holocene climatic changes in Greenland, D14102, doi:10.1029/2004JD005575. 1. Introduction [2] In the context of the ongoing climate change

Fischer, Hubertus

302

Atmospheric CO2 Concentration from 60 to 20 Kyr BP from the Taylor Dome Ice Core, Antarctica  

NSDL National Science Digital Library

In the first of half of 2000, several data files were added to the North American Pollen Database. These include data from the recent publication: "Atmospheric CO2 Concentration from 60 to 20 Kyr BP from the Taylor Dome Ice Core, Antarctica" by Indermuhle et al.

Indermühle, A.

2000-01-01

303

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

Microsoft Academic Search

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

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

2002-01-01

304

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

305

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

306

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

307

A 2000 year atmospheric history of methyl chloride from a South Pole ice core: Evidence for climate-controlled variability  

E-print Network

levels. Citation: Williams, M. B., M. Aydin, C. Tatum, and E. S. Saltzman (2007), A 2000 year atmospheric from Siple Dome, Antarctica covering the past 300 years suggest that the twentieth century increaseA 2000 year atmospheric history of methyl chloride from a South Pole ice core: Evidence for climate

Saltzman, Eric

308

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

309

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

310

Study of a 200?m core from the lomonosov ice plateau on spitsbergen and the paleoclimatic implications  

Microsoft Academic Search

A 200?m ice core obtained in 1976 on the Lomonosov Plateau in Spitsbergen is compared with isotope profiles obtained at the Camp Century and Crete stations on Greenland and on Devon Island as well as temperature curves for Iceland and England. All of them clearly show a cool 19th century and a warm 16th century. The Spitsbergen data, both for

F. G. Gordiyenko; V. M. Kotlyakov; R. Vairmäe

1981-01-01

311

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

312

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

313

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

314

A Centrifuge-Based Technique for Dry Extraction of Air for Ice Core Studies of Carbon Dioxide.  

NASA Astrophysics Data System (ADS)

High resolution CO2 data from the Law Dome ice core document an abrupt ~10 ppm drop in CO2 at about 1600 AD (MacFarling Meure et al., Geophys. Res Lett., v. 33, L14810), which has been attributed to changes in human activities. CO2 measurements in ice cores are difficult, however, making verification of this feature an important task. We are undertaking a high-resolution study of CO2 between 1400 and 1800 AD in the WAIS Divide (Antarctica) ice core with a new dry extraction technique. The need for a dry extraction technique as opposed to a melt-refreeze technique in studies of CO2 from ice cores arises because of the well-documented artifacts in CO2 imposed by the presence of liquid water. Three dry-extraction methods have been employed by previous workers to measure CO2: needle-crushing method, ball-bearings method, and cheese-grater method (B. Stauffer, in: Encyclopedia of Quaternary Science, p. 1181, Elsevier 2007). Each has limitations, and we propose a simpler dry extraction technique, based on a large-capacity refrigerated centrifuge (the "centrifuge technique"), which eliminates the need to employ cryogenic temperatures to collect extracted gas and is more compatible with high sample throughput. The technique is now being tested on ~25-gram WAIS Divide samples in conjunction with CO2 measurements with a gas chromatograph. The technique employs a Beckman J- 6B centrifuge, in which evacuated stainless steel flask is placed: the flask has a weight inside positioned directly over a tall-standing piece of ice whose cross-section is small compared to that of the flask. Upon acceleration to 3000 rpm the weight moves down and presses the ice sample into a thin tablet covering flask's bottom, yielding the air extraction efficiency of ~80%. Preliminary tests suggest that precision and accuracy can be achieved at the level of ~1 ppm once the system is fine-tuned.

Grachev, A. M.; Brook, E. J.

2008-12-01

315

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

316

Time-Series Trends of Trace Elements in AN Ice Core from Antarctica.  

NASA Astrophysics Data System (ADS)

Trace element measurements were made by instrumental neutron activation analysis on stratigraphically dated ice core samples from Byrd Station, Antarctica, to determine the concentration levels of natural and anthropogenic substances. Sampling was continuous between 1926 A.D. and 1989 A.D. and selective between 1711 A.D. and 1926 A.D. Twenty-one elements with concentrations above the detection limits were determined. The time period between 1969 A.D. and 1989 A.D. showed an enhanced impact on the Antarctic ice sheets from natural sources in the form of marine and crustal aerosols. A disturbed ocean-atmosphere interface due to El Nino Southern Oscillation (ENSO) events seems to be a candidate especially for the enhanced marine aerosol deposition in Antarctica. Time-series trend of the concentration of deposited aluminum, which is mainly a crustal aerosol related element, shows a strong negative correlation with the time-series trend of annual average total column ozone concentrations homogenized between the 60^circS and 90^circS latitudes from the Total Ozone Mapping Spectrometer (TOMS) ozone data set. Although the time period is not long enough to draw a strong conclusion (1979-1989), tbe special role of crustal origin clay minerals on cloud nucleation dynamics might be a factor in the heterogeneous stratospheric ozone depletion chemistry through polar stratospheric cloud dynamics, assuming some troposphere-stratosphere mixing of these aerosols. The correlation of antimony and arsenic enrichments with known or suspected volcanic events was established. These marker elements was shown to be useful especially for the identification of specific historical volcanic events with low sulfur emissions. Although a cleat anthropogenic impact was not observed, concentrations of arsenic, chromium. and zinc, which might come from both natural and anthropogenic sources, indicated an increase after 1960's. Principal component factor analysis indicated a possible transition-metal (especially manganese and iron) catalyzed bromine chemistry cycle, which has been suggested as the cause of tropospheric surface-level ozone depletion observed in Greenland. Calculated snow-to-air scavenging ratios indicated more efficient scavenging for crustal aerosols followed by marine and volatile elements. A new method was developed for direct air content determination in small deep ice core samples through the measurement of enclosed argon gas by instrumental neutron activation analysis. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617 -253-5668; Fax 617-253-1690.).

Keskin, Siddik Sinan

317

Evidence for Past Melting at the Base of the GISP2 Ice Core from Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for silty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The expected age of these samples is >150 kyr based on counting ice layers. We separated the samples into several fractions by filtration and analyzed the <50 nm (truly dissolved + particulate) and >200 nm (particulate) filtered fractions. In the <50 nm fractions, low Th/U mass ratios of 0.51-0.65 indicate that a large portion (86-89%) of U is truly dissolved and not associated with particles. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent 230Th loss and/or 234U addition to the samples. This Th/U fractionation is not consistent with an age >150 kyr. Since liquid water is characterized by 230Th/234U activity ratios <<1, these results suggest that recent melting/freezing event(s) have occurred at the base of the GISP2 core. The particulate (>200 nm) fraction is characterized by Th/U ratios of ~4.4-4.9, 234U/238U activity ratios of 1.049-1.056, and 230Th/234U activity ratios of 1.12-1.23. The U-Th disequilibrium in the particles is consistent with recent (<350 kyr) fractionation of U-Th in these ice samples. We have modeled these results using a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. The main assumption is that all of the 232Th in the <50 nm fraction is due to particles, due to the low aqueous solubility of 232Th. By mass balance, 230Th/234U activity ratios for the truly dissolved fraction are 0.031-0.062, and dates for when the samples were last frozen are 3.5-6.9 kyr. These results are consistent with the notion of ice melting at the base of large continental ice sheets, with recent evidence of large sub-glacial lakes in Antarctica and active melting at the base of the nearby N-GRIP Greenland ice core. There also appears to be a significant difference in age for the deepest ice sample (3.5 kyr; 3052 m) and the other samples (5.2-6.9 kyr; 3040-3048 m), suggesting that the deepest part of the ice core adjacent to bedrock at 3053.3 m depth may have existed as liquid water for at least several hundred - few thousand years.

Goldstein, S. J.; Lee, V. E.; Nishiizumi, K.; Murrell, M. T.; Amato, R. S.; Nunn, A. J.

2011-12-01

318

Seasonally resolved ice core records from West Antarctica indicate a sea ice source of sea-salt aerosol and a biomass burning source of ammonium  

NASA Astrophysics Data System (ADS)

sources and transport pathways of aerosol species in Antarctica remain uncertain, partly due to limited seasonally resolved data from the harsh environment. Here, we examine the seasonal cycles of major ions in three high-accumulation West Antarctic ice cores for new information regarding the origin of aerosol species. A new method for continuous acidity measurement in ice cores is exploited to provide a comprehensive, charge-balance approach to assessing the major non-sea-salt (nss) species. The average nss-anion composition is 41% sulfate (SO42-), 36% nitrate (NO3-), 15% excess-chloride (ExCl-), and 8% methanesulfonic acid (MSA). Approximately 2% of the acid-anion content is neutralized by ammonium (NH4+), and the remainder is balanced by the acidity (Acy ? H+ - HCO3-). The annual cycle of NO3- shows a primary peak in summer and a secondary peak in late winter/spring that are consistent with previous air and snow studies in Antarctica. The origin of these peaks remains uncertain, however, and is an area of active research. A high correlation between NH4+ and black carbon (BC) suggests that a major source of NH4+ is midlatitude biomass burning rather than marine biomass decay, as previously assumed. The annual peak in excess chloride (ExCl-) coincides with the late-winter maximum in sea ice extent. Wintertime ExCl- is correlated with offshore sea ice concentrations and inversely correlated with temperature from nearby Byrd station. These observations suggest that the winter peak in ExCl- is an expression of fractionated sea-salt aerosol and that sea ice is therefore a major source of sea-salt aerosol in the region.

Pasteris, Daniel R.; McConnell, Joseph R.; Das, Sarah B.; Criscitiello, Alison S.; Evans, Matthew J.; Maselli, Olivia J.; Sigl, Michael; Layman, Lawrence

2014-07-01

319

Ocean interactions with the base of Amery Ice Shelf, Antarctica  

NASA Astrophysics Data System (ADS)

Using a two-dimensional ocean thermohaline circulation model, we varied the cavity shape beneath Amery Ice Shelf in an attempt to reproduce the 150-m-thick marine ice layer observed at the "G1" ice core site. Most simulations caused melting rates which decrease the ice thickness by as much as 400 m between grounding line and G1, but produce only minor accumulation at the ice core site and closer to the ice front. Changes in the seafloor and ice topographies revealed a high sensitivity of the basal mass balance to water column thickness near the grounding line, to submarine sills, and to discontinuities in ice thickness. Model results showed temperature/salinity gradients similar to observations from beneath other ice shelves where ice is melting into seawater. Modeled outflow characteristics at the ice front are in general agreement with oceanographic data from Prydz Bay. A freshwater flux across the grounding line, derived from melting beneath the grounded ice sheet, would have to be anomalously large to produce the basal marine ice layer and account for the Ice Shelf Water outflow. We concur with Morgan's inference that the G1 core may have been taken in a basal crevasse filled with marine ice. This ice is formed from water cooled by ocean/ice shelf interactions along the interior ice shelf base.

Hellmer, Hartmut H.; Jacobs, Stanley S.

1992-12-01

320

A 12,000 year record of explosive volcanism in the Siple Dome Ice Core, West Antarctica  

NASA Astrophysics Data System (ADS)

Air mass trajectories in the Southern Hemisphere provide a mechanism for transport to and deposition of volcanic products on the Antarctic ice sheet from local volcanoes and from tropical and subtropical volcanic centers. This study extends the detailed record of Antarctic, South American, and equatorial volcanism over the last 12,000 years using continuous glaciochemical series developed from the Siple Dome A (SDMA) ice core, West Antarctica. The largest volcanic sulfate spike (280 ?g/L) occurs at 5881 B.C.E. Other large signals with unknown sources are observed around 325 B.C.E. (270 ?g/L) and 2818 B.C.E. (191 ?g/L). Ages of several large equatorial or Southern Hemisphere volcanic eruptions are synchronous with many sulfate peaks detected in the SDMA volcanic ice chemistry record. The microprobe "fingerprinting" of glass shards in the SDMA core points to the following Antarctic volcanic centers as sources of tephra found in the SDMA core: Balenny Island, Pleiades, Mount Berlin, Mount Takahe, and Mount Melbourne as well as Mount Hudson and possibly Mount Burney volcanoes of South America. Identified volcanic sources provide an insight into the poorly resolved transport history of volcanic products from source volcanoes to the West Antarctic ice sheet.

Kurbatov, A. V.; Zielinski, G. A.; Dunbar, N. W.; Mayewski, P. A.; Meyerson, E. A.; Sneed, S. B.; Taylor, K. C.

2006-06-01

321

Tracing volcanic events in the NGRIP ice-core and synchronising North Atlantic marine records during the last glacial period  

NASA Astrophysics Data System (ADS)

Five basaltic tephra horizons have been identified in the NGRIP ice-core during the last glacial period. Geochemical analyses indicate that these tephras are of Icelandic origin with one horizon identified as the Faroe Marine Ash Zone III (FMAZ III) — an important marker horizon in several marine records within the Faroe Islands margin. The FMAZ III is a few millimetres thick and is constrained to 38,122 ± 723 yr b2k (before year AD 2000) according to the Greenland Ice Core Chronology (GICC05). This event falls directly at the thermal peak of Greenland Interstadial 8 (GI-8) and a marine-ice correlation, based on the position of this tephra, suggests a close coupling of the marine and atmospheric systems at this time. The remaining tephras originate from the Eastern Volcanic Zone with the Katla volcanic system pinpointed as the dominant source. These are thought to represent previously unknown volcanic events which add considerably to our knowledge of Icelandic volcanism during this period. Independent ages are assigned to these events and together with major element characterisation, form the backbone of the tephrochronology framework presented here. Despite the identification of these tephras, this study also demonstrates that the sulphate record may not always act as a suitable proxy for the identification of tephra horizons in ice-core records.

Davies, S. M.; Wastegård, S.; Abbott, P. M.; Barbante, C.; Bigler, M.; Johnsen, S. J.; Rasmussen, T. L.; Steffensen, J. P.; Svensson, A.

2010-05-01

322

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

323

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

324

Solar and climate influences on ice core 10Be records from Antarctica and Greenland during the neutron monitor era  

NASA Astrophysics Data System (ADS)

Cosmogenic 10Be in polar ice cores is a primary proxy for past solar activity. However, interpretation of the 10Be record is hindered by limited understanding of the physical processes governing its atmospheric transport and deposition to the ice sheets. This issue is addressed by evaluating two accurately dated, annually resolved ice core 10Be records against modern solar activity observations and instrumental and reanalysis climate data. The cores are sampled from the DSS site on Law Dome, East Antarctica (spanning 1936-2009) and the Das2 site, southeast Greenland (1936-2002), permitting inter-hemispheric comparisons. Concentrations at both DSS and Das2 are significantly correlated to the 11-yr solar cycle modulation of cosmic ray intensity, rxy=0.54 with 95% CI [0.31; 0.70], and rxy=0.45 with 95% CI [0.22; 0.62], respectively. For both sites, if fluxes are used instead of concentrations then correlations with solar activity decrease. The strength and spectral coherence of the solar activity signal in 10Be is enhanced when ice core records are combined from both Antarctica and Greenland. The amplitudes of the 11-yr solar cycles in the 10Be data appear inconsistent with the view that the ice sheets receive only 10Be produced at polar latitudes. Significant climate signals detected in the 10Be series include the zonal wave three pattern of atmospheric circulation at DSS, rxy=-0.36 with 95% CI [-0.57; -0.10], and the North Atlantic Oscillation at Das2, rxy=-0.42 with 95% CI [-0.64; -0.15]. The sensitivity of 10Be concentrations to modes of atmospheric circulation advises caution in the use of 10Be records from single sites in solar forcing reconstructions.

Pedro, J. B.; McConnell, J. R.; van Ommen, T. D.; Fink, D.; Curran, M. A. J.; Smith, A. M.; Simon, K. J.; Moy, A. D.; Das, S. B.

2012-11-01

325

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

326

Measurements of Bacterial Concentrations on a Millimeter Scale in Ice Cores With a Scanning Laser Fluorescence Spectrometer  

NASA Astrophysics Data System (ADS)

We report non-destructive detection of variability on a mm depth scale in the organic content of ice cores at NICL, as determined by the fluorescence spectrum measured by a Targeted Ultraviolet Chemical Sensor (TUCS). Many of the spectra we obtained are consistent with the amino acid tryptophan, a strongly fluorescing constituent in microbes. Identification with native fluorescence of microbes is supported by previous measurements of varying microbial concentration in samples from selected regions of the GISP2 core (Tung et al., 2005; 2006) that are consistent with our observations at the same depths. Sub-mm depth resolution was achieved and structure at this scale was observed. At each depth the fluorescence emission spectrum was measured at 5 wavelengths using 20-nm narrow band filters plus a long pass channel. The spectrum of microbes was calibrated by making lab measurements of fluorescence of various species and is distinguishable from mineral dust and metals due to differences in spectral shape. In bulk ice samples from 3 depths in the GISP2 core, where a table of methane concentrations (Ed Brook, unpublished) had shown several excesses above the atmospheric contribution, Tung et al. (2005) found 10-fold excesses of microbial concentrations at 2954 m and 3036 m and a 3-fold excess at 3018 m. In the present work we found strong, rapidly varying organic signals at all three depths. At 3018 m the peak value was much stronger than that obtained by Brook and occurred in the core section below the one he studied. Since he measured methane at several-meter depth intervals, and since we found the microbial excesses to be concentrated in 0.3 m intervals, we conclude that of order 30 microbe-rich regions may be present in GISP2. The 3 microbe-rich depths found by Tung et al. (2005) were less than 90 m above the basal ice at 3041-3053 m. The large fluctuations in apparent tryptophan concentrations that we found at 2954, 3018, and 3036 m are consistent with microbe-rich wetland material from the base of GISP2 being repeatedly entrained into the ice. In the basal ice, which contains very high concentrations of both silt and microbes (Tung et al., 2006), the tryptophan signal seems to have been obscured by mineral grains. In many sections of ice cores we found very high spikes of tryptophan-like fluorescence in sub-mm depth regions. Our interpretation, which we will follow up in future work, is that the TUCS laser-excitation beam occasionally intersected veins at triple junctions in the ice, where organic material had been concentrated via rejection from the growing ice grains. Micron-size microbes in veins are known to metabolize at a very low rate via redox reactions on impurities (Price, 2000). An additional virtue of the TUCS technique is its ability to serve as a very sensitive probe of drill fluid contamination. We identified residual drill fluid on interior surfaces of a number of Vostok core sections, with the amount of contamination varying by orders of magnitude from sample to sample. In support of the WAIS Divide drilling project we also measured the rate of evaporation of drill fluid at -24 C after it was deliberately coated onto ice samples for our inspection at NICL. Though a valuable probe of drill fluid contamination, even low levels of drill fluid can prevent the TUCS from registering an accurate reading of native fluorescence. The success of this initial survey of ice cores indicates that UV fluorimetry can be a powerful new non-destructive tool with numerous applications to microbiology and climatology. This research was supported in part by NSF grant ANT-0440609.

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

2006-12-01

327

Aerosol data over the last 3000 years in seasonal resolution from the Greenland NEEM ice core  

NASA Astrophysics Data System (ADS)

During the field season in summer 2009, the first 600 m (corresponding to 3 kyr b2k (3000 years before A.D. 2000) on the GICC05 timescale) of the Greenland NEEM ice core have been analysed for a variety of aerosol constituents using Continuous Flow Analysis (CFA). Here, the records of electric conductivity, sodium (Na+), calcium (Ca2+), particle numbers of insoluble dust, ammonium (NH4+), nitrate (NO3-) and hydrogen peroxide (H2O2) are presented with an average effective resolution of 1-2 cm, depending on the component. Since the annual layer thickness ? amounts to 15cm at minimum sub-annual signals are resolved in all components over the Holocene period. We achieved to extend the aerosol record over the early Holocene period except for a large gap over the brittle zone from 5-9 kyr b2k. Seasonal variations and extreme events are preserved in great detail and all components. H2O2 is a reliable proxy for the strength of photochemical processes in the lower atmosphere and thus shows its minima and maxima at the summer and winter solstice, respectively. Dust-derived species (insoluble dust, Ca2+) show peak concentrations in early spring and minima in mid-summer. The marine-derived Na+peaks in mid-winter and is lowest during early summer. The mean annual variability in concentrations is about 20 ppbw for both Ca2+andNa+. Moreover, it is of the same order of magnitude in NH4+, butconsiderably larger in NO3- (100 ppbw), both representing continental biogenic sources peaking in spring and showing minima in autumn. The interpretation itsclimatic signal is restricted by NO3- undergoing post-depositional redistribution processes. Not only is the analysis of impurities in sub-annual resolution crucial for the accurate dating of the ice core, but also for establishing a detailed chronology of the occurrence of extreme events such as volcanic eruptions and wildfires. Furthermore, possible changes in the seasonal variability of aerosol concentrations can be investigated. First results are presented here.

Leuenberger, Daiana; Gfeller, Gideon; Schüpbach, Simon; Bigler, Matthias; Fischer, Hubertus

2013-04-01

328

Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals.  

PubMed

Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60 degrees S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April-May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean-sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a "blind spot" in our sampling coverage, enabling the establishment of a truly global ocean-observing system. PMID:18695241

Charrassin, J-B; Hindell, M; Rintoul, S R; Roquet, F; Sokolov, S; Biuw, M; Costa, D; Boehme, L; Lovell, P; Coleman, R; Timmermann, R; Meijers, A; Meredith, M; Park, Y-H; Bailleul, F; Goebel, M; Tremblay, Y; Bost, C-A; McMahon, C R; Field, I C; Fedak, M A; Guinet, C

2008-08-19

329

Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals  

PubMed Central

Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60°S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April–May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean–sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a “blind spot” in our sampling coverage, enabling the establishment of a truly global ocean-observing system. PMID:18695241

Charrassin, J.-B.; Hindell, M.; Rintoul, S. R.; Roquet, F.; Sokolov, S.; Biuw, M.; Costa, D.; Boehme, L.; Lovell, P.; Coleman, R.; Timmermann, R.; Meijers, A.; Meredith, M.; Park, Y.-H.; Bailleul, F.; Goebel, M.; Tremblay, Y.; Bost, C.-A.; McMahon, C. R.; Field, I. C.; Fedak, M. A.; Guinet, C.

2008-01-01

330

Properties of starless and prestellar cores in Taurus revealed by Herschel: SPIRE/PACS imaging  

NASA Astrophysics Data System (ADS)

The density and temperature structures of dense cores in the L1495 cloud of the Taurus star-forming region are investigated using Herschel Spectral and Photometric Imaging Receiver and Photodetector Array Camera and Spectrometer images in the 70, 160, 250, 350 and 500 ?m continuum bands. A sample consisting of 20 cores, selected using spectral and spatial criteria, is analysed using a new maximum likelihood technique, COREFIT, which takes full account of the instrumental point spread functions. We obtain central dust temperatures, T0, in the range 6-12 K and find that, in the majority of cases, the radial density falloff at large radial distances is consistent with the asymptotic r-2 variation expected for Bonnor-Ebert spheres. Two of our cores exhibit a significantly steeper falloff, however, and since both appear to be gravitationally unstable, such behaviour may have implications for collapse models. We find a strong negative correlation between T0 and peak column density, as expected if the dust is heated predominantly by the interstellar radiation field. At the temperatures we estimate for the core centres, carbon-bearing molecules freeze out as ice mantles on dust grains, and this behaviour is supported here by the lack of correspondence between our estimated core locations and the previously published positions of H13CO+ peaks. On this basis, our observations suggest a sublimation-zone radius typically ˜104 au. Comparison with previously published N2H+ data at 8400 au resolution, however, shows no evidence for N2H+ depletion at that resolution.

Marsh, K. A.; Griffin, M. J.; Palmeirim, P.; André, Ph.; Kirk, J.; Stamatellos, D.; Ward-Thompson, D.; Roy, A.; Bontemps, S.; Francesco, J. Di; Elia, D.; Hill, T.; Könyves, V.; Motte, F.; Nguyen-Luong, Q.; Peretto, N.; Pezzuto, S.; Rivera-Ingraham, A.; Schneider, N.; Spinoglio, L.; White, G.

2014-04-01

331

Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth.  

PubMed

Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules. PMID:23300286

Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L; Braslavsky, Ido

2013-01-22

332

A high altitude paleoclimate record from an ice core retrieved at the northern margin of the Mediterranean basin  

NASA Astrophysics Data System (ADS)

Atmospheric temperatures in the Alps are increasing at twice the global rate and this change may be amplified at the highest elevations. There is a scarcity of paleo-climate information from high altitudes to place this current rapid climate change in a paleo-perspective. The 'Ortles Project' is an international scientific effort gathering institutes from six nations with the primary goal of obtaining a high altitude paleo-climate record in the Mediterranean area. In 2011 four ice cores were extracted from Alto dell'Ortles (3859 m, South Tyrol, Italy) the highest glacier in the eastern Alps. This site is located ~30 km away from where the famous ~5.2 kyr old Tyrolean Ice Man was discovered emerging from an ablating ice field (Hauslabjoch, 3210 m) in 1991. The good state of conservation of this mummy suggested that the current warming trend is unprecedented in South Tyrol during the late Holocene and that unique prehistoric ice was still present in this region. During the ice core drilling operations we found that the glacier Alto dell'Ortles shows a very unusual thermic behavior as it is transitioning from a cold to a temperate state. In fact, below a 30 meter thick temperate firn portion, we observed cold ice layers sitting on a frozen bedrock (-2.8 C). These represent remnants of the colder climate before ~1980 AD, when an instrumental record indicates a ~2 C lower temperature in this area during the period 1864-1980 AD. By analyzing one of the Ortles cores for stable isotopes, dust and major ions, we found an annually preserved climatic signal embedded in the deep cold ice of this glacier. Alto dell'Ortles is therefore the first low-accumulation (850 mm w.e. per year) alpine drilling site where both winter and summer layers can be identified. Preliminary annual layer counting and two absolute time markers suggest that the time period covered by the Ortles ice cores spans from several centuries to a few millennia. In particular, a Larix (larch) leaf discovered at 74 m depth suggests a 14C bottom ice age of 2664 ×166 years (early European Iron Age) supporting the idea that exceptional prehistoric ice is still present at the highest elevations of South Tyrol. Here we present the records of the first Ortles core analyzed in terms of ?18O (proxy of mid-tropospheric temperature), major ions and dust. We found that ?18O measured in the shallowest layers of this glacier exceeds the average deeper values indicating that the Ortles cores capture the recent increase in atmospheric temperatures at high elevation and that this is anomalous over a time scale that extends from hundreds to thousands of years.

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

2013-12-01

333

A 50,000-year climatic record from the new coastal TALDICE ice core: consequences on millennial-scale variability features through the Antarctic continent  

NASA Astrophysics Data System (ADS)

The TALDICE project retrieved a new ice core from a peripheral dome of East Antarctica. Talos Dome (72° 49' S, 159° 11' E; 2315 m; mean accumulation rate 80 kg m-2 yr-1; mean annual temp. -41°C) is located in the Northern Victoria Land, close to the Ross Sea. Back-trajectory analyses suggest that the site is mostly fed by air masses arriving both from the Pacific (and Ross Sea) and Indian Ocean sectors. The drilling team reached the depth of 1619.2 m in December 2007, covering more than 300,000 years of climatic records according to a preliminary age scale. Up to 50,000 years before present, the ice core dating is based on the use of a glaciological model and an inverse method, constrained by numerous and reliable age markers. They are defined from the synchronization of CH4 records of Talos Dome and Greenland ice cores, using in particular the rapid CH4 changes associated with the last termination and the D/O events. Measurements of the CH4 mixing ratio have been performed by LGGE and Bern laboratories using slightly different techniques, with a depth resolution ranging between 0.5 to 4 m. The comparison of water isotopic profiles from Talos Dome, EDC, EDML (Antarctica) and North-GRIP (Greenland) ice cores, once put on a common time scale deduced from CH4 and the optimisation from the inverse method, reveals that during the last deglaciation and the last glacial period, climatic changes at Talos Dome were essentially in phase with the Antarctic plateau, extending the bipolar seesaw sequence to this coastal site. This comparison also highlights different climatic behaviors between sites situated in the Indo/Pacific sector and in the Atlantic sector of the Southern Ocean, the latter showing more abrupt swings toward relatively warm conditions of the Antarctic Isotope Maxima. We will discuss this feature with respect to the bipolar seesaw model of Stocker (2003) and with respect to other climatic proxies.

Buiron, Daphné; Stenni, Barbara; Frezzoti, Massimo; Chappellaz, Jerome; Lemieux, Benedicte; Masson-Delmotte, Valérie; Schilt, Adrian

2010-05-01

334

Methyl chloride variability in the Taylor Dome ice core during the Holocene  

NASA Astrophysics Data System (ADS)

Methyl chloride (CH3Cl) is a naturally occurring, ozone-depleting trace gas and one of the most abundant chlorinated compounds in the atmosphere. CH3Cl was measured in air from the Taylor Dome ice core in East Antarctica to reconstruct an atmospheric record for the Holocene (11-0 kyr B.P.) and part of the last glacial period (50-30 kyr B.P.). CH3Cl variability throughout the Holocene is strikingly similar to that of atmospheric methane (CH4), with higher levels in the early and late Holocene, and a well-defined minimum during mid-Holocene. The sources and sinks of atmospheric CH3Cl and CH4 are located primarily in the tropics, and variations in their atmospheric levels likely reflect changes in tropical conditions. CH3Cl also appears to correlate with atmospheric CH4 during the last glacial period (50-30 kyr B.P.), although the temporal resolution of sampling is limited. The Taylor Dome data provide information about the range of natural variability of atmospheric CH3Cl and place a new constraint on the causes of past CH4variability.

Verhulst, Kristal R.; Aydin, Murat; Saltzman, Eric S.

2013-11-01

335

Major Ion concentrations in the new NEEM ice core in Greenland  

NASA Astrophysics Data System (ADS)

The drilling of the new deep ice core in NEEM (77.45°N 51.06°W) was terminated in 2010. Using a continuous flow analysis system (CFA), discrete samples were filled and analyzed for major ion concentrations (Na, K, Mg, Ca, Cl, SO_4 and NO_3) using Ion Chromatography (IC). The samples were measured at Alfred Wegener Institute for Polar and Marine Research (Germany) and National Institute of Polar Research (Japan). Here we present preliminary results of the major Ion concentrations. We found highest variations in concentrations of Calcium and Magnesium which are mainly originating from terrestrial sources with concentrations between 5-10 ppb and 4 ppb during the Holocene compared to 800 ppb and 80 ppb during the LGM. This is in line with measurements of particulate dust concentrations. Sulphate concentrations closely follow DO events and vary between 25 ppb during the Holocene and ~400 ppb during the LGM. Sodium concentrations vary between ~ 8 ppb during the Holocene and up to 100 ppb during the LGM. We discuss influences of changes in the source areas and atmospheric transport intensity on the different time scales.

Wegner, A.; Azuma, K. G.; Hirabayashi, M.; Schmidt, K.; Hansson, M.; Twarloh, B.

2012-12-01

336

Preliminary Black Carbon Record (1805 - 1943 AD) from the High Altitude Dasuopu Ice Core (7200 m) in the Central Himalaya  

NASA Astrophysics Data System (ADS)

Black carbon (BC) produced by the incomplete combustion of fossil and biofuels both amplifies mid-tropospheric atmospheric warming and decreases glacier surface albedo, and thus may influence regional climatic trends and water resource availability. The rapidly developing economies in Asia have been identified as significant sources of BC to the atmosphere on a continental scale in recent decades, but records available from this region to reconstruct BC concentrations spatially and temporally are limited. The analysis of BC preserved in glacier ice can provide a record of atmospheric BC content over time. We analyzed the Dasuopu Glacier ice core (Central Himalaya) for BC concentration at ~5 cm resolution using a Single Particle Soot Photometer (Droplet Measurement Technologies), and use the resultant record to describe trends in atmospheric BC from 1805 - 1943 AD. The Dasuopu ice core is unique because it was obtained at an exceptionally high elevation (7200 m a.s.l.) which may insolate it from local BC sources and reflect BC trends in a more mixed upper troposphere. Preliminary analysis of discrete sections shows that the Dasuopu ice core captures the seasonal BC deposition signal exceptionally well, with higher BC concentrations during winter-spring and lower concentrations during the summer monsoon season. Peak winter-spring concentrations pre-1890 are 10 ng g-1, increasing to as high as 30 ng g-1 during the 1890s - 1943. Additionally, background BC concentrations prior to 1890 are less than 0.5 ng g-1, and are consistently higher than 0.5 ng g-1 during the 1890s - 1943. The early 20th century BC increases are coincident with post-colonial industrialization of the Indian subcontinent. Preliminary results from the Dasuopu ice core highlight the utility of the BC record to detect perturbations in the carbon cycle at a regional scale, and the importance of an exceptionally high altitude location for detecting and preserving an atmospheric BC record. Future analyses will measure BC concentrations through the entire Dasuopu ice core and provide a continuous record of BC deposition in the region spanning 1442 - 1997.

Barker, J. D.; Kaspari, S.; Wegner, A.; Thompson, L. G.; Gabrielli, P.

2013-12-01

337

Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas.  

PubMed

One explanation of the abrupt cooling episode known as the Younger Dryas (YD) is a cosmic impact or airburst at the YD boundary (YDB) that triggered cooling and resulted in other calamities, including the disappearance of the Clovis culture and the extinction of many large mammal species. We tested the YDB impact hypothesis by analyzing ice samples from the Greenland Ice Sheet Project 2 (GISP2) ice core across the Bølling-Allerød/YD boundary for major and trace elements. We found a large Pt anomaly at the YDB, not accompanied by a prominent Ir anomaly, with the Pt/Ir ratios at the Pt peak exceeding those in known terrestrial and extraterrestrial materials. Whereas the highly fractionated Pt/Ir ratio rules out mantle or chondritic sources of the Pt anomaly, it does not allow positive identification of the source. Circumstantial evidence such as very high, superchondritic Pt/Al ratios associated with the Pt anomaly and its timing, different from other major events recorded on the GISP2 ice core such as well-understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction, hints for an extraterrestrial source of Pt. Such a source could have been a highly differentiated object like an Ir-poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis. PMID:23878232

Petaev, Michail I; Huang, Shichun; Jacobsen, Stein B; Zindler, Alan

2013-08-01

338

Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas  

PubMed Central

One explanation of the abrupt cooling episode known as the Younger Dryas (YD) is a cosmic impact or airburst at the YD boundary (YDB) that triggered cooling and resulted in other calamities, including the disappearance of the Clovis culture and the extinction of many large mammal species. We tested the YDB impact hypothesis by analyzing ice samples from the Greenland Ice Sheet Project 2 (GISP2) ice core across the Bølling-Allerød/YD boundary for major and trace elements. We found a large Pt anomaly at the YDB, not accompanied by a prominent Ir anomaly, with the Pt/Ir ratios at the Pt peak exceeding those in known terrestrial and extraterrestrial materials. Whereas the highly fractionated Pt/Ir ratio rules out mantle or chondritic sources of the Pt anomaly, it does not allow positive identification of the source. Circumstantial evidence such as very high, superchondritic Pt/Al ratios associated with the Pt anomaly and its timing, different from other major events recorded on the GISP2 ice core such as well-understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction, hints for an extraterrestrial source of Pt. Such a source could have been a highly differentiated object like an Ir-poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis. PMID:23878232

Petaev, Michail I.; Huang, Shichun; Jacobsen, Stein B.; Zindler, Alan

2013-01-01

339

Accurate age scale of the Dome Fuji ice core, Antarctica from O2/N2 ratio of trapped air  

NASA Astrophysics Data System (ADS)

Chronology of the first Dome Fuji deep ice core (core length: 2,500 m, ice thickness: 3,035 m) for the age range from 80 kyr to 340 kyr ago was established by orbital tuning of measured O2/N2 ratios in trapped air to local summer insolation, with precision better than about 2,000 years (Kawamura et al., 2007). The O2/N2 ratios found in polar ice cores are slightly lower than the atmospheric ratio because of size-dependent molecular fractionation during bubble close-off. The magnitude of this gas fractionation is believed to be governed by the magnitude of snow metamorphism when the layer was originally at the surface, which in turn is controlled by local summer insolation (Fujita et al., 2009). A strong advantage of the O2/N2 chronology is that there is no need to assume a lag between climatic records in the ice core and orbital forcings, becacuse O2/N2 ratios record local insolation through physical processes. Accuracy of the chronology was validated by comparing the O2/N2 chronology with U-Th radiometric chronology of speleothem records (Cheng et al., 2009) for the ends of Terminations II, III and IV, as well as several large climatic events, for which both ice-core CH4 and speleothem ?18O (a proxy for precipitation) show abrupt shifts as seen in the last glacial period. All ages from O2/N2 and U-Th chronology agreed with each other within ~2,000 yr. The O2/N2 chronology permits comparisons between Antarctic climate, greenhouse gases, astronomically calculated orbital parameters, and radiometrically-dated sea level and monsoon records. Here, we completed the measurements of O2/N2 ratios of the second Dome Fuji ice core, which reached bedrock, for the range from 2,400 to 3,028 m (320 - 700 kyr ago) at approximately 2,000-year time resolution. We made significant improvements in ice core storage practices and mass spectrometry. In particular, the ice core samples were stored at about -50 ° C until the air extraction, except during short periods of transportation, in order to prevent size-dependent fractionation due to gas loss during storage. The precision of the new O2/N2 data set is improved by a factor of 3 over the previous data. Clear imprint of local insolation is recognizable in the O2/N2 data towards the deepest depths, even around 400 kyr ago when summer insolation wiggles are small due to small orbital eccentricity. A new chronology using this O2/N2 data set will be established by applying the inverse method for EDC3 age scale (Parrenin et al., 2007) for the entire 700 kyr, and climatic implications will also be discussed especially on Terminations and interglacial periods.

Kawamura, K.; Aoki, S.; Nakazawa, T.; Suzuki, K.; Parrenin, F.

2012-04-01

340

NGRIP CH4 concentration from 120 to 10 kyr before present and its relation to a ?15N temperature reconstruction from the same ice core  

NASA Astrophysics Data System (ADS)

During the last glacial cycle, Greenland temperature showed many rapid temperature variations, the so called Dansgaard-Oeschger (DO) events. The past atmospheric methane concentration closely followed these temperature variations, which implies that the warmings recorded in Greenland were probably hemispheric in extent. Here we substantially extend and complete the North Greenland Ice Core Project (NGRIP) methane record from Termination 1 back to the end of the last interglacial period with a mean time resolution of 54 yr. We relate the amplitudes of the methane increases associated with DO events to the amplitudes of the NGRIP temperature increases derived from stable nitrogen isotope (?15N) measurements, which have been performed along the same ice core. We find the sensitivity to oscillate between 5 parts per billion by volume (ppbv) per °C and 18 ppbv °C-1 with the approximate frequency of the precessional cycle. A remarkably high sensitivity of 25.5 ppbv °C-1 is reached during Termination 1. Analysis of the timing of the fast methane and temperature increases reveals significant lags of the methane increases relative to NGRIP temperature for the DO events 5, 9, 10, 11, 13, 15, 19, and 20. We further show that the relative interpolar concentration difference of methane is 4.6 ± 0.7% between the DO events 18 and 19 and 4.4 ± 0.8% between the DO events 19 to 20, which is in the same order as in the stadials before and after DO event 2 around the Last Glacial Maximum.

Baumgartner, M.; Kindler, P.; Eicher, O.; Floch, G.; Schilt, A.; Schwander, J.; Spahni, R.; Capron, E.; Chappellaz, J.; Leuenberger, M.; Fischer, H.; Stocker, T. F.

2013-08-01

341

Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers  

NASA Astrophysics Data System (ADS)

Predictions of the Greenland Ice Sheet's response to climate change are limited in part by uncertainty in the coupling between meltwater lubrication of the ice-sheet bed and ice flow. This uncertainty arises largely from a lack of direct measurements of water flow characteristics at the bed of the ice sheet. Previous work has been restricted to indirect observations based on seasonal and spatial variations in surface ice velocities and on meltwater flux. Here, we employ rhodamine and sulphur hexafluoride tracers, injected into the drainage system over three melt seasons, to observe subglacial drainage properties and evolution beneath the Greenland Ice Sheet, up to 57km from the margin. Tracer results indicate evolution from a slow, inefficient drainage system to a fast, efficient channelized drainage system over the course of the melt season. Further inland, evolution to efficient drainage occurs later and more slowly. An efficient routing of water was established up to 41km or more from the margin, where the ice is approximately 1km thick. Overall, our findings support previous interpretations of drainage system characteristics, thereby validating the use of surface observations as a means of investigating basal processes.

Chandler, D. M.; Wadham, J. L.; Lis, G. P.; Cowton, T.; Sole, A.; Bartholomew, I.; Telling, J.; Nienow, P.; Bagshaw, E. B.; Mair, D.; Vinen, S.; Hubbard, A.

2013-03-01

342

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

NASA Astrophysics Data System (ADS)

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.

Buffett, Bruce

2014-03-01

343

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

344

Testing the integrity of stable isotope records of two Spitsbergen ice cores by using high-resolution tritium data.  

NASA Astrophysics Data System (ADS)

The ratios of 1H16O2H and 1H18O1H in precipitation water vary with temperature and can therefore be used as a proxy for past climate. Ever since the 1960-s, retrieving these isotope signals has been the main motivation for the drilling of deep ice cores. Most of the ice core records originate from selected sites in Greenland and Antarctica. Other Arctic locations are much less used. However, since the late 1990-s ice cores have been drilled on the Lomonosovfonna and Holtedahlfonna ice caps in Spitsbergen. The advantages of drilling at these sites lies in the high accumulation rate present in Spitsbergen, as well as the very location of the Spitsbergen archipelago. However, due to relatively high temperatures in this region, the isotope record is affected by melt and subsequent percolation, thereby potentially losing its value for climatic studies. In an attempt to test the integrity of the Spitsbergen cores, we measured the concentration of the radioactive isotope of hydrogen (tritium) at high spatial (and thus temporal) resolution. Due to above-ground nuclear bomb tests in the 1950-s and 1960-s, the tritium signal in the atmosphere has been highly variable in that period, with distinct peaks. Moreover, due to the high load of tritium in the stratosphere at that time, spring and early summer mixing between stratosphere and troposphere induced a clear seasonal pattern in precipitation records for two decades. The tritium concentration in precipitation has been measured (monthly average) since the 1950-s. After precipitation the tritium record is altered due to decay, diffusion and melt. Incorporating information of these three processes into a numerical model, we produce a quantitative estimate how much the isotope record is influenced by melt and percolation. This gives us a tool to determine whether the stable isotope record is a valid proxy for past temperatures.

van der Wel, L. G.; Meijer, H. A. J.; Isaksson, E.; Helsen, M. M.; van de Wal, R. S. W.; Martma, T.; Pohjola, V. A.; Moore, J. C.

2009-04-01

345

A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores  

NASA Astrophysics Data System (ADS)

Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were characterised by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval; the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grímsvötn, Grímsvötn-Kverkfjöll and either Reykjanes or Veidivötn-Bárdarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICC05 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.

Abbott, Peter M.; Davies, Siwan M.; Steffensen, Jørgen Peder; Pearce, Nicholas J. G.; Bigler, Matthias; Johnsen, Sigfus J.; Seierstad, Inger K.; Svensson, Anders; Wastegård, Stefan

2012-03-01

346

Revealing potential past collapses of the West Antarctic Ice Sheet - Upcoming drilling in the Amundsen Sea Embayment  

NASA Astrophysics Data System (ADS)

The West Antarctic Ice-Sheet (WAIS) is likely to have been subject to very dynamic changes during its history as most of its base is grounded below modern sea-level, making it particularly sensitive to climate changes. Its collapse would result in global sea-level rise of 3-5 m. The reconstruction and quantification of possible partial or full collapses of the WAIS in the past can provide important constraints for ice-sheet models, used for projecting its future behaviour and resulting sea-level rise. Large uncertainties exist regarding the chronology, extent, rates as well as spatial and temporal variability of past advances and retreats of the WAIS across the continental shelves. By using the seafloor drilling device MeBo during an RV Polarstern cruise scheduled for early 2015, a series of sediment cores will be drilled on the Amundsen Sea Embayment (ASE) shelf, where seismic data show glacially-derived sequences covered by only a thin veneer of postglacial deposits in some areas. From analyses of seismic data, we infer that interglacial sediments can be sampled which may have been deposited under seasonally open water conditions and thus contain datable microfossil-bearing material. A shallow basin near the Pine Island Glacier front will be one of the prime targets for the drilling. The near-horizontal seismic reflection horizons may represent a sequence of continuously deposited, mainly terrigenous material, including ice-rafted debris, meltwater deposits and hemipelagic sediments deposited rapidly during the Holocene or a series of unconformities caused by erosion resulting from grounding line oscillations through many glacial cycles. Subglacial bedforms imaged in multibeam bathymetric data indicate fast glacial flow over some shelf areas of the ASE, where seismic profiles show acoustic basement near the seafloor. It is unknown, whether fast ice-flow in these areas was facilitated by water-lubricated sliding over bedrock or presence of a thin layer of deformable till (perhaps less than a metre in thickness). The nature of this layer holds important clues for understanding the processes that operated beneath the margin of the ice-sheet, beneath ice-flows and on ridges between ice-streams during the Last Glacial Maximum. Grounding zone wedges (GZWs) are widely thought to be important in stabilising grounding line positions during ice-sheet retreat, but hypotheses about the processes and duration of their formation and their composition, are mainly based on conceptual models. Drill sites on and near GZWs are aimed to establish the nature of their sediments, their formation processes, their rates of growth and the palaeo-environmental conditions in their surroundings.

Kuhn, Gerhard; Gohl, Karsten; Uenzelmann-Neben, Gabriele; Bickert, Torsten; Schulz, Michael; Larter, Robert D.; Hillenbrand, Claus-Dieter

2014-05-01

347

The agricultural history of human-nitrogen interactions as recorded in ice core ?15N-NO3-  

NASA Astrophysics Data System (ADS)

The advent and industrialization of the Haber Bosch process in the early twentieth century ushered in a new era of reactive nitrogen distributions on Earth. Since the appearance of the first commercial scale Haber Bosch fertilizer plants, fertilizer application rates have greatly increased in the U.S. While the contributions of fertilizer runoff to eutrophication and anoxic dead zones in coastal regions have been well-documented, the potential influences of increased fertilizer applications on air quality and precipitation chemistry are poorly constrained. Here we combine a 255-year record of precipitation nitrate isotopes preserved in a Greenland ice core, historical reconstructions of fertilizer application rates, and field characterization of the isotopic composition of nitrogen oxides produced biogenically in soils, to provide new constraints on the contributions of biogenic emissions to North American NOx inventories. Our results indicate that increases in twentieth century commercial fertilizer use led to large increases in soil NO, a byproduct released during nitrification and denitrification reactions. These large shifts in soil NO production are evidenced by sharp declines in ice core ?15N-NO3- values. Further, these results suggest that biogenic NOx emissions are underestimated by two to four fold in the U.S. NOx emission inventories used to construct global reactive nitrogen budgets. These results demonstrate that nitrate isotopes in ice cores, coupled with newly constrained ?15N-NOx values for NOx emission sources, provide a novel means for estimating contemporary and historic contributions from individual NOx emission sources to deposition.

Felix, J. David; Elliott, Emily M.

2013-04-01

348

Unexpected increase in elemental carbon concentrations and deposition in a Svalbard ice core since 1970 and its implications for Arctic warming  

NASA Astrophysics Data System (ADS)

Changes in albedo and related feedbacks in the Arctic have been suggested to be one of the driving mechanisms for the observed amplified Arctic warming. 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. Its climate effects are intensified in the Arctic where its deposition on snow and ice decreases surface albedo. BC has been suggested to have caused 20% of the Arctic melting hitherto. Despite the significant role of BC in Arctic warming, there is little information on its concentrations and climate effects in the area in the past. Here we present results on elemental carbon (EC, proxy for BC) concentrations and deposition on a Svalbard glacier (Holtedahlfonna) from 1700 to 2004. The inner part of a 125 m deep ice core was melted, filtered through a quartz fiber filter and analyzed for EC using a thermal optical method. The EC values increased after 1850 and peaked around 1910, similar to previous ice core records from Greenland. Strikingly, EC values increase abruptly since 1970. Such a rise is not seen in Greenland ice cores, and it seems to contradict atmospheric measurements indicating decreasing atmospheric BC concentrations since 1989 in the Arctic. However, the trend gains additional credence from a melt index derived from the same ice core indicating increased summer melt since 1970. The rise in EC values since 1970 is possibly explained by increased washout ratio of BC especially due to increased temperatures. In addition, post-depositional processes, such as increased melt, may enrich EC in most recent ice layers. These processes enable rising EC values in the ice core while atmospheric concentrations have decreased. Possible explanations for the differences in the recorded ice core BC trends from Greenland and Svalbard in the recent decades are partly different sources and the vertical distribution of emissions in the atmosphere. Specifically, the Svalbard ice core may record flaring emissions from northern Russia that do not reach the Greenland ice core sites. The results indicate that BC deposition may not necessarily be straightforwardly connected to atmospheric BC concentrations and that BC trends recorded from different ice cores may be dissimilar due to several factors independent of atmospheric concentrations. Regardless of the cause for the increasing EC values, the present results have significant implications for the past radiative transfer at the coring site. It remains to be determined how broad the signal and its albedo implications are. The results may give rise for further investigations on the significance of BC deposition to the Arctic sea ice retreat.

Ruppel, Meri; Isaksson, Elisabeth; Ström, Johan; Beaudon, Emilie; Svensson, Jonas; Pedersen, Christina A.; Korhola, Atte

2014-05-01

349

Acidity decline in Antarctic ice cores during the Little Ice Age linked to changes in atmospheric nitrate and sea salt concentrations  

NASA Astrophysics Data System (ADS)

is an important chemical variable that impacts atmospheric and snowpack chemistry. Here we describe composite time series and the spatial pattern of acidity concentration (Acy = H+ - HCO3-) during the last 2000 years across the Dronning Maud Land region of the East Antarctic Plateau using measurements in seven ice cores. Coregistered measurements of the major ion species show that sulfuric acid (H2SO4), nitric acid (HNO3), and hydrochloric acid (HCl) determine greater than 98% of the acidity value. The latter, also described as excess chloride (ExCl-), is shown mostly to be derived from postdepositional diffusion of chloride with little net gain or loss from the snowpack. A strong inverse linear relationship between nitrate concentration and inverse accumulation rate provides evidence of spatially homogenous fresh snow concentrations and reemission rates of nitrate from the snowpack across the study area. A decline in acidity during the Little Ice Age (LIA, 1500-1900 Common Era) is observed and is linked to declines in HNO3 and ExCl- during that time. The nitrate decline is found to correlate well with published methane isotope data from Antarctica (?13CH4), indicating that it is caused by a decline in biomass burning. The decrease in ExCl- concentration during the LIA is well correlated to published sea surface temperature reconstructions in the Atlantic Ocean, which suggests increased sea salt aerosol production associated with greater sea ice extent.

Pasteris, Daniel; McConnell, Joseph R.; Edwards, Ross; Isaksson, Elizabeth; Albert, Mary R.

2014-05-01

350

Spores of many common airborne fungi reveal no ice nucleation activity in oil immersion freezing experiments  

NASA Astrophysics Data System (ADS)

Fungal spores are ubiquitous biological aerosols, which are considered to act as ice nuclei. In this study the ice nucleation (IN) activity of spores harvested from 29 fungal strains belonging to 21 different species was tested in the immersion freezing mode by microscopic observation of water-in-oil emulsions. Spores of 8 of these strains were also investigated in a microdroplet freezing array instrument. The focus was laid on species of economical, ecological or sanitary significance. Besides common molds (Ascomycota), some representatives of the widespread group of mushrooms (Basidiomycota) were also investigated. Fusarium avenaceum was the only sample showing IN activity at relatively high temperatures (about 264 K), while the other investigated fungal spores showed no freezing above 248 K. Many of the samples indeed froze at homogeneous ice nucleation temperatures (about 237 K). In combination with other studies, this suggests that only a limited number of species may act as atmospheric ice nuclei. This would be analogous to what is already known for the bacterial ice nuclei. Apart from that, we selected a set of fungal strains from different sites and exposed them to occasional freezing stress during their cultivation. This was in order to test if the exposure to a cold environment encourages the expression of ice nuclei during growth as a way of adaptation. Although the total protein expression was altered by this treatment, it had no significant impact on the IN activity.

Pummer, B. G.; Atanasova, L.; Bauer, H.; Bernardi, J.; Druzhinina, I. S.; Fröhlich-Nowoisky, J.; Grothe, H.

2013-12-01

351

Major Subglacial Meltwater Channels Reveal Former Dynamic Ice Sheet in West Antarctica  

NASA Astrophysics Data System (ADS)

The Eocene-Oligocene boundary (ca. 34 Ma) marks the onset of widespread, continental-scale glaciation in Antarctica, due to declining atmospheric carbon dioxide levels and the opening of the Drake Passage. The marine-based West Antarctic Ice Sheet (WAIS) is considered highly susceptible to change, experiencing numerous oscillations since its formation. In order to assess how past changes to the WAIS are relevant for understanding its future behaviour, it is important to comprehend the glaciological processes involved in those changes. Central to this is an appreciation of climate and ice flow regimes, in particular the extent to which former ice sheets have experienced surface melting (as in Greenland today). Geomorphic analysis of subglacial topography has played a key role in reconstructing the nature of former ice masses in Antarctica, as landscape form can be linked to glacial process. While radio-echo sounding (RES) is the primary tool used to map boundary conditions beneath ice sheets, recent developments have demonstrated that satellite imagery of the ice surface can provide insights into subglacial topography, where RES is unavailable. Using this combination of datasets, we have identified a series of major, elongate subglacial features, which we interpret as preserved subglacial channels, developed through the action of water. They are incised into a subglacial plateau in the region between the Möller and Foundation ice streams (MIS and FIS, respectively), in West Antarctica. The channels are observed across an area of ~17,700 km2 and extend 200 km inland from the grounding line. They are located below sea level and track over present-day reverse slopes, indicating a subglacial (rather than pre-glacial) fluvial origin. In order to form, these channels require significant, probably periodic (seasonal), meltwater inputs to the base of the ice sheet. We suggest the channels are the result of meltwater inputs to the subglacial environment from the ice surface, in a setting analogous to present-day Greenland. This allows us to bracket the most recent date at which this may have occurred. The Pliocene (2.6-5.3 Ma) represents the most recent period in the geologic past when atmospheric temperatures for West Antarctica were high enough to generate surface melt comparable to that observed on the Greenland Ice Sheet today. These features provide evidence for temperate basal thermal conditions and thus, a former ice flow regime that differs markedly from the present-day polar ice sheet conditions of West Antarctica. We envisage bed channel formation occurred under temperate ice sheet conditions, when the subglacial plateau was overridden by a temperate ice mass. If this interpretation is correct, it means that ice was still present (at least periodically) in this location, during the warm conditions of the Pliocene. The discovery of these channels also highlights what little was known about this large region of West Antarctica, prior to the Institute-Möller geophysical survey.

Rose, Kathryn; Ross, Neil; Bingham, Robert; Corr, Hugh; Ferraccioli, Fausto; Jordan, Tom; LeBrocq, Anne; Rippin, David; Siegert, Martin

2014-05-01

352

EPICA Dome C ice core fire record demonstrates a major biomass burning increase over the past 500 years  

NASA Astrophysics Data System (ADS)

Natural factors and human activity influence fire variability including changes in temperature and precipitation, increasing greenhouse gas concentrations, altering ignitions, vegetation cover and fuel availability. Ice cores archive chemical signatures of both past climate and fire activity, and understanding this interaction is increasingly important in a warming climate. The specific molecular marker levoglucosan (1,6-anhydro-ß-D-glucopyranose) can only be produced by burning woody tissue at temperatures greater than 300°C. Levoglucosan is present in the fine fraction of smoke plumes, is transported distances of thousands of kilometers, is deposited on glacier surfaces, and is detectable in both polar and mountain ice cores providing an unambiguous fire history. Here, we present a high-resolution 10,000-year levoglucosan record in the EPICA Dome C (75°06'S, 123°21'E, 3233 masl) ice core and implications for determining natural and human-caused fire variability. A recent provocative hypothesis by Ruddiman suggests that humans may have had a significant impact on the Earth's climate thousands of years ago through carbon and methane emissions originating from biomass burning associated with early agriculture. This hypothesis is centered on the observation that atmospheric carbon dioxide and methane levels recorded in ice cores increased irrespective of insolation changes beginning 7,000 to 5,000 years before present. The EDC levoglucosan record does not demonstrate augmented fire activity at 5000 and/or 7000 years ago in the Southern Hemisphere. We are currently determining Holocene levoglucosan concentrations in the NEEM, Greenland (77°27' N; 51°3'W, 2454 masl) ice core to provide a Northern Hemisphere comparison at 5000 and/or 7000 years ago. The highest EDC Holocene fire activity occurs during the past 500 years. Mean levoglucosan concentrations between 500 to 10,000 BP are approximately 50 ppt, but rise to 300 ppt at present. This substantial increase is not present in NEEM. Unlike methane and its isotopic signatures, levoglucosan is not a globally mixed marker, and these hemispheric differences are consistent with the atmospheric lifetime, sources, and transport of levoglucosan. This considerable increase in fire activity over the past 500 years is also present in Southern Hemisphere compilations of charcoal records. The EDC levoglucosan profile is most similar to regional charcoal compilations from New Zealand and southeastern Australia. Transport models demonstrate the possibility of New Zealand and Australia as major levoglucosan sources to EDC. This contemporary biomass burning increase is likely due to human activity as opposed to the Holocene background levels between 500 to 10,000 BP.

Kehrwald, Natalie; Power, Mitchell; Zennaro, Piero; McWethy, David; Whitlock, Cathy; Zangrando, Roberta; Gambaro, Andrea; Barbante, Carlo

2013-04-01

353

Evidence for Recent Melting at the Base of the GISP2 Ice Core From Uranium-Thorium Disequilibrium Measurements  

NASA Astrophysics Data System (ADS)

We measured 238U-234U-230Th disequilibria by mass spectrometric methods for a set of dusty ice samples from the base of the GISP2 Greenland ice core, at a depth of 3040-3052 m. The goal of this work was to further test the Fireman (1986) recoil-based model for producing uranium-series disequilibria in dusty ice on samples thought to be > 150 ka in age based on layer counting. However, the base of the GISP2 core is greatly disturbed in chemistry and dustiness relative to upper portions of the core. Samples consisted of 11 cm sections of ice core with sample weights of 340-430 g. We separated the samples into several fractions by filtration and analyzed the < 0.05 um fraction. This fraction had exceedingly high U and Th concentrations (2.5- 5 ppb U; 1.4-2.7 ppb Th). These U and Th concentrations are a factor of 1000 higher than measured for ice at Allan Hills, Antarctica. Low Th/U ratios of 0.51-0.65 indicate that a large portion of the uranium present in the samples is dissolved and not associated with particles, which are expected to have Th/U ratios around 3. However, 234U/238U activity ratios range from 0.972-0.992 (+/- 0.001), indicating a depletion of 234U relative to secular equilibrium of 1-3%. In addition, 230Th/234U activity ratios are quite low (0.18-0.24), suggesting either recent Th loss and/or U addition to the samples. This recent Th/U fractionation is not consistent with an age > 150 ka. Since liquid water would be characterized by 230Th/234U activity ratios ?1, the low 230Th/234U activity ratios likely indicate that recent melting/freezing event(s) have occurred at the base of the GISP2 core. We can model these results with a two component mass balance calculation, with dissolved and particulate pools for each radionuclide. Although several assumptions are required to calculate ages, preliminary results of these calculations suggest that the melting events may be as young as <10 ka.

Goldstein, S. J.; Murrell, M. T.; Nunn, A. J.; Nishiizumi, K.

2007-12-01

354

Paleo-Climate and Glaciological Reconstruction in Central Asia through the Collection and Analysis of Ice Cores and Instrumental Data from the Tien Shan  

SciTech Connect

While the majority of ice core investigations have been undertaken in the polar regions, a few ice cores recovered from carefully selected high altitude/mid-to-low latitude glaciers have also provided valuable records of climate variability in these regions. A regional array of high resolution, multi-parameter ice core records developed from temperate and tropical regions of the globe can be used to document regional climate and environmental change in the latitudes which are home to the vase majority of the Earth's human population. In addition, these records can be directly compared with ice core records available from the polar regions and can therefore expand our understanding of inter-hemispheric dynamics of past climate changes. The main objectives of our paleoclimate research in the Tien Shan mountains of middle Asia combine the development of detailed paleoenvironmental records via the physical and chemical analysis of ice cores with the analysis of modern meteorological and hydrological data. The first step in this research was the collection of ice cores from the accumulation zone of the Inylchek Glacier and the collection of meteorological data from a variety of stations throughout the Tien Shan. The research effort described in this report was part of a collaborative effort with the United State Geological Survey's (USGS) Global Environmental Research Program which began studying radionuclide deposition in mid-latitude glaciers in 1995.

Vladimir Aizen; Donald Bren; Karl Kreutz; Cameron Wake

2001-05-30

355

Assessing the differences between the IntCal and Greenland ice-core time scales for the last 14,000 years via the common cosmogenic radionuclide variations  

NASA Astrophysics Data System (ADS)

Variations in galactic cosmic rays reaching the Earth's atmosphere produce globally synchronous variations in the production rates of cosmogenic radionuclides. In consequence, they leave their imprint in tree-ring 14C and ice-core 10Be records. By identifying this signal and correcting for the known geochemical influences on the radionuclides, it is possible to compare and synchronize the tree-ring chronology and the Greenland ice-core time scale. Here, we compare the IntCal13 and the GICC05 time scales for the last 14,000 years via identification and synchronization of the common short-term variations in the ice-core 10Be and tree-ring 14C records most likely induced by variations in the solar modulation of galactic cosmic rays. We conclude that systematic time-scale differences have to be accounted for if ice-core and 14C-dated records are compared on decadal time scales. These are mostly within the uncertainties of the time scales and the method proposed here. However, for large parts of the mid to late Holocene (i.e. after 7000 yrs BP) the best agreement between ice-core 10Be and tree-ring 14C records is obtained for time shifts outside the stated errors of the respective time scales. A transfer function is proposed that can be applied to synchronize the GICC05 ice-core time scale to the radiocarbon time scale.

Muscheler, Raimund; Adolphi, Florian; Knudsen, Mads F.

2014-12-01

356

Searches for Dark Matter with IceCube and DeepCore : New constraints on theories predicting dark matter particles  

NASA Astrophysics Data System (ADS)

The cubic-kilometer sized IceCube neutrino observatory, constructed in the glacial ice at the South Pole, searches indirectly for dark matter via neutrinos from dark matter self-annihilations. It has a high discovery potential through striking signatures. This thesis presents searches for dark matter annihilations in the center of the Sun using experimental data collected with IceCube. The main physics analysis described here was performed for dark matter in the form of weakly interacting massive particles (WIMPs) with the 79-string configuration of the IceCube neutrino telescope. For the first time, the DeepCore sub-array was included in the analysis, lowering the energy threshold and extending the search to the austral summer. Data from 317 days live-time are consistent with the expected background from atmospheric muons and neutrinos. Upper limits were set on the dark matter annihilation rate, with conversions to limits on the WIMP-proton scattering cross section, which initiates the WIMP capture process in the Sun.These are the most stringent spin-dependent WIMP-proton cross-sections limits to date above 35 GeV for most WIMP models. In addition, a formalism for quickly and directly comparing event-level IceCube data with arbitrary annihilation spectra in detailed model scans, considering not only total event counts but also event directions and energy estimators, is presented. Two analyses were made that show an application of this formalism to both model exclusion and parameter estimation in models of supersymmetry. An analysis was also conducted that extended for the first time indirect dark matter searches with neutrinos using IceCube data, to an alternative dark matter candidate, Kaluza-Klein particles, arising from theories with extra space-time dimensions. The methods developed for the solar dark matter search were applied to look for neutrino emission during a flare of the Crab Nebula in 2010.

Danninger, Matthias

357

Molecular Probe Dynamics Reveals Suppression of Ice-Like Regions in Strongly Confined Supercooled Water  

PubMed Central

The structure of the hydrogen bond network is a key element for understanding water's thermodynamic and kinetic anomalies. While ambient water is strongly believed to be a uniform, continuous hydrogen-bonded liquid, there is growing consensus that supercooled water is better described in terms of distinct domains with either a low-density ice-like structure or a high-density disordered one. We evidenced two distinct rotational mobilities of probe molecules in interstitial supercooled water of polycrystalline ice [Banerjee D, et al. (2009) ESR evidence for 2 coexisting liquid phases in deeply supercooled bulk water. Proc Natl Acad Sci USA 106: 11448–11453]. Here we show that, by increasing the confinement of interstitial water, the mobility of probe molecules, surprisingly, increases. We argue that loose confinement allows the presence of ice-like regions in supercooled water, whereas a tighter confinement yields the suppression of this ordered fraction and leads to higher fluidity. Compelling evidence of the presence of ice-like regions is provided by the probe orientational entropy barrier which is set, through hydrogen bonding, by the configuration of the surrounding water molecules and yields a direct measure of the configurational entropy of the same. We find that, under loose confinement of supercooled water, the entropy barrier surmounted by the slower probe fraction exceeds that of equilibrium water by the melting entropy of ice, whereas no increase of the barrier is observed under stronger confinement. The lower limit of metastability of supercooled water is discussed. PMID:23049747

Banerjee, Debamalya; Bhat, Shrivalli N.; Bhat, Subray V.; Leporini, Dino

2012-01-01

358

TRACEing Last Glacial Period (25-80 ka b2k) Tephra Horizons between North Atlantic marine-cores and the Greenland ice-cores  

NASA Astrophysics Data System (ADS)

Tephrochronological investigations are currently being undertaken on a network of marine cores from a range of locations and depositional settings within the North Atlantic. This work forms a component of the ERC-funded project Tephra constraints on Rapid Climate Events (TRACE). The main aim of this project is to utilise isochronous tephra horizons as direct tie-lines to correlate North Atlantic marine sequences and the Greenland ice-cores to determine the relative timing of oceanic and atmospheric changes associated with the rapid climate events that dominated the last glacial period. Early comparisons of six North Atlantic marine records (MD99-2251, MD04-2820CQ, MD04-2829CQ, MD04-2822, MD01-2461 and JM11-19PC) and the Greenland ice-cores highlight six tephra horizons common to the ice record and one or more marine sequences. These horizons are within GS-3 (26,740 ± 390 a b2k and 29,130 ± 456 a b2k), GS-9 (38,300 ± 703 a b2k), GS-10 (40,220 ± 792 a b2k) and GS-12 (43,680 ± 877 a b2k) and the widespread North Atlantic Ash Zone II (55,380 ± 1184 a b2k). New high-resolution proxy information from MD04-2820CQ allows us to explore the relative timing of climatic changes between the Goban Spur, North Atlantic and Greenland over GI-12 to GI-8 using two tephra correlations that link the records. Tephra horizons have been identified in the marine records through the successful use of cryptotephra extraction techniques more commonly applied to the study of terrestrial sequences. All horizons have an Icelandic source with horizons of both rhyolitic and basaltic composition isolated. The acquisition of high-resolution profiles of shard concentration and comprehensive geochemical characterisations for horizons is vital to this work. This allows us to disentangle the processes that transported material to core sites, which can include primary airfall, sea-ice rafting and iceberg rafting, and the potential impact of secondary reworking processes such as bottom current reworking and bioturbation on the stratigraphic integrity of horizons. We are also applying the innovative techniques of micromorphology and X-ray tomography to the study of these processes.

Abbott, Peter; Davies, Siwan; Griggs, Adam; Bourne, Anna; Cook, Eliza; Austin, William; Chapman, Mark; Hall, Ian; Purcell, Catriona; Rasmussen, Tine; Scourse, James

2014-05-01

359

Net accumulation rates derived from ice core stable isotope records of Pío XI glacier, Southern Patagonia Icefield  

NASA Astrophysics Data System (ADS)

Pío XI, the largest glacier of the Southern Patagonia Icefield, reached its neoglacial maximum extent in 1994 and is one of the few glaciers in that area which is not retreating. In view of the recent warming it is important to understand glacier responses to climate changes. Due to its remoteness and the harsh conditions in Patagonia, no systematic mass balance studies have been performed. In this study we derived net accumulation rates for the period 2000 to 2006 from a 50 m (33.2 4 m weq) ice core collected in the accumulation area of Pío XI (2600 m a.s.l., 49°16´40´´ S, 73°21´14´´ W). Borehole temperatures indicate near temperate ice, but the average melt percent is only 16% ± 14%. Records of stable isotopes are well preserved and were used for identification of annual layers. Net accumulation rates range from 3.4 to 7.1 water equivalent (m weq) with an average of 5.8 m weq, comparable to precipitation amounts at the Chilean coast, but not as high as expected for the Icefield. Ice core stable isotope data correlate well with upper air temperatures and may be used as temperature proxy.

Schwikowski, M.; Schläppi, M.; Santibañez, P.; Rivera, A.; Casassa, G.

2012-12-01

360

GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 15, doi:10.1002/2013GL057149, 2013 The effect of an asymmetric core on convection in Enceladus' ice  

E-print Network

a hemispheric dichotomy in tectonics and heat flux. With a spherical core, convection produces global of an asymmetric core on convection in Enceladus' ice shell: Implications for south polar tectonics and heat flux: Implications for south polar tectonics and heat flux, Geophys. Res. Lett., 40, doi:10.1002/2013GL057149. 1

361

A multi-century ice-core perspective on 20th-century climate change with new contributions from high-Arctic and  

E-print Network

A multi-century ice-core perspective on 20th-century climate change with new contributions from high-Arctic and Greenland (PARCA) cores Ellen MOSLEY-THOMPSON,1,2 Lonnie G. THOMPSON,1,3 Ping-Nan LIN1 suggest modest to strong 20th-century warming. The recent warming over Greenland has been modest

Howat, Ian M.

362

A new bipolar ice core record of volcanism from WAIS Divide and NEEM and implications for climate forcing of the last 2000 years  

NASA Astrophysics Data System (ADS)

Volcanism is a natural climate forcing causing short-term variations in temperatures. Histories of volcanic eruptions are needed to quantify their role in climate variability and assess human impacts. We present two new seasonally resolved, annually dated non-sea-salt sulfur records from polar ice cores—WAIS Divide (WDC06A) from West Antarctica spanning 408 B.C.E. to 2003 C.E. and NEEM (NEEM-2011-S1) from Greenland spanning 78 to 1997 C.E.—both analyzed using high-resolution continuous flow analysis coupled to two mass spectrometers. The high dating accuracy allowed placing the large bi-hemispheric deposition event ascribed to the eruption of Kuwae in Vanuatu (previously thought to be 1452/1453 C.E. and used as a tie-point in ice core dating) into the year 1458/1459 C.E. This new age is consistent with an independent ice core timescale from Law Dome and explains an apparent delayed response in tree rings to this volcanic event. A second volcanic event is detected in 1453 C.E. in both ice cores. We show for the first time ice core signals in Greenland and Antarctica from the strong eruption of Taupo in New Zealand in 232 C.E. In total, 133 volcanic events were extracted from WDC06A and 138 from NEEM-2011-S1, with 50 ice core signals—predominantly from tropical source volcanoes—identified simultaneously in both records. We assess the effect of large bipolar events on temperature-sensitive tree ring proxies. These two new volcanic records, synchronized with available ice core records to account for spatial variability in sulfate deposition, provide a basis for improving existing time series of volcanic forcing.

Sigl, Michael; McConnell, Joseph R.; Layman, Lawrence; Maselli, Olivia; McGwire, Ken; Pasteris, Daniel; Dahl-Jensen, Dorthe; Steffensen, JøRgen Peder; Vinther, Bo; Edwards, Ross; Mulvaney, Robert; Kipfstuhl, Sepp

2013-02-01

363

Bedform signature of a West Antarctic palaeo-ice stream reveals a multi-temporal record of flow and substrate control  

NASA Astrophysics Data System (ADS)

The presence of a complex bedform arrangement on the sea floor of the continental shelf in the western Amundsen Sea Embayment, West Antarctica, indicates a multi-temporal record of flow related to the activity of one or more ice streams in the past. Mapping and division of the bedforms into distinct landform assemblages reveals their time-transgressive history, which implies that bedforms can neither be considered part of a single downflow continuum nor a direct proxy for palaeo-ice velocity, as suggested previously. A main control on the bedform imprint is the geology of the shelf, which is divided broadly between rough bedrock on the inner shelf, and smooth, dipping sedimentary strata on the middle to outer shelf. Inner shelf bedform variability is well preserved, revealing information about local, complex basal ice conditions, meltwater flow, and ice dynamics over time. These details, which are not apparent at the scale of regional morphological studies, indicate that past ice streams flowed across the entire shelf at times, and often had onset zones that lay within the interior of the Antarctic Ice Sheet today. In contrast, highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice stream flow, and may be a truer representation of fast palaeo-ice flow in these locations. A revised model for ice streams on the shelf captures complicated multi-temporal bedform patterns associated with an Antarctic palaeo-ice stream for the first time, and confirms a strong substrate control on a major ice stream system that drained the West Antarctic Ice Sheet during the Late Quaternary.

Graham, Alastair G. C.; Larter, Robert D.; Gohl, Karsten; Hillenbrand, Claus-Dieter; Smith, James A.; Kuhn, Gerhard

2009-12-01

364

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

E-print Network

orientational distribution of slip bands and discuss some of their possible causes. Natural and artificial to the basal planes of the lattice; 2) in glaciers and ice sheets, the (visco-)plastic defor- mation (creep

365

Sources of uncertainty in ice core data A contribution to the Workshop on  

E-print Network

(Fischer et al., 2004; Kreutz et al., 2000); and snow accumulation (Monaghan et al., 2007; Hanna et al and temperature on the Antarctic (Monaghan et al., 2007; Schneider et al., 2006) and Greenland ice sheets (Mc

366

Temporal changes in methane stable isotopes in polar ice cores: big picture and implications for ecosystem changes  

NASA Astrophysics Data System (ADS)

Methane (CH4) is the third most important greenhouse gas after water vapour and carbon dioxide (CO2). Since the industrial revolution the mixing ratio of CH4 in the atmosphere rose to ~1800 ppb, a value never reached within the last 800 000 years. Nowadays, CH4 contributes ~20% to the total radiative forcing from all of the long-lived greenhouse gases. This CH4 increase can only be assessed in relation to natural methane changes in the past. Firn air and air enclosures in polar ice cores represent the only direct paleoatmospheric archive. The latter show that atmospheric CH4 concentrations changed in concert with northern hemisphere temperature during both glacial/interglacial transitions as well as rapid climate changes (Dansgaard-Oeschger events), however, the sources of the methane concentration changes are still a matter of debate. Stable isotopes of methane (?13CH4 and ?D(CH4)) may help to distinguish differences in the magnitude of source type emissions (e.g. Bock et al. 2010). However, recently we could show that it is difficult to interpret the atmospheric loading of methane by relative source mix changes alone (Möller et al. 2013). In fact it appears, that the carbon isotopic signature (?13CH4) of e.g. tropical wetlands undergoes drastic shifts connected to climate, CO2, sea level or potentially other unknown processes. Here we present the big picture derived from the EDML (European Project for Ice Coring in Antarctica, Dronning Maud Land) and Vostok ice cores (Möller et al. 2013) and additional new dual isotope data from 4 ice cores from both poles that cover three interglacials: the Holocene, MIS 5 and MIS 11. The contribution sheds light on our current understanding of methane biogeochemistry and discusses open questions. References: Bock, M., J. Schmitt, L. Möller, R. Spahni, T. Blunier, H. Fischer (2010). 'Hydrogen Isotopes Preclude Marine Hydrate CH4 Emissions at the Onset of Dansgaard-Oeschger Events', Science, 328, 1686-1689 Möller, L., T. Sowers, M. Bock, R. Spahni, M. Behrens, J. Schmitt, H. Miller and H. Fischer (2013). "Independent variations of CH4 emissions and isotopic composition over the past 160,000 years" Nature Geoscience, 10.1038/ngeo1922. Bock, M., J. Schmitt, J. Beck, R. Schneider, H. Fischer (2013). "Improving accuracy and precision of ice core ?D(CH4) analyses using methane pre- and hydrogen post-pyrolysis trapping and subsequent chromatographic separation', Atmos. Meas. Tech. Discuss., 6, 11279-11307, doi:10.5194/amtd-6-11279-2013, 2013. Schmitt J., B. Seth, M. Bock and H. Fischer (2014). "Online technique for isotope and mixing ratios of CH4, N2O, Xe and mixing ratios of organic trace gases on a single ice core sample', submitted to Atmos. Meas. Tech. Discuss.

Bock, Michael; Schmitt, Jochen; Seth, Barbara; Beck, Jonas; Fischer, Hubertus

2014-05-01

367

Interglacial Greenland aerosol deposition: comparison of continuous high resolution chemical ice core records from the Eemian and Holocene  

NASA Astrophysics Data System (ADS)

Earth's climate system has been oscillating over the last million years between cold glacials and warm interglacials, leaving the imprints of their climate states in form of isotopes variations and chemical impurities in polar ice caps. In the course of the North Greenland Eemian Ice Drilling (NEEM) project, the NEEM ice core has been entirely analysed in very high depth resolution with a Continuous Flow Analysis (CFA) system for the concentrations of chemical aerosol tracers in the ice. Only in the brittle ice zone (600-1100 m depth equivalent to the time interval 3000-8000 years before present) most of the ice had to be discarded due to multifractured core material. Based on the unique reconstructed age scale to unfold the stratigraphically disturbed part from about 2200 m depth downwards (NEEM community members, Nature, 2013), we are able to present the first Greenland chemistry record over the entire last interglacial, the so called Eemian period (about 128'000 to 115'000 years ago). As the Eemian is believed to have been 4 to 8 degrees C warmer than the modern climate, it can be used as an analogue for our present warming climate and, thus, contributes to a better understanding of processes causing natural variations. By means of the chemistry records we are able to assess the natural variability of Greenland Eemian climate and gain insight in its biogeochemical state. Here, short-term variability as well as long term trends of soluble chemical impurities in the Eemian are investigated and compared with those in the Holocene. Changes of organic processes in soils and biomass burning for example are assessed through soluble ammonium and nitrate concentrations. In comparison to the Holocene, ammonium concentrations were about 25% higher during the Eemian. Nitrate, on the other hand, shows about 25% lower concentrations. Sodium concentrations, reflecting changes in sea salt aerosol, are about 35% lower during the Eemian than during the Holocene. Calcium, generally regarded as a long range transport proxy, shows similar concentration during both periods.

Gfeller, Gideon; Bigler, Matthias; Schüpbach, Simon; Mini, Olivia; Leuenberger, Daiana; Fischer, Hubertus

2014-05-01

368

Systematic network lesioning reveals the core white matter scaffold of the human brain  

PubMed Central

Brain connectivity loss due to traumatic brain injury, stroke or multiple sclerosis can have serious consequences on life quality and a measurable impact u