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1. Southern Ocean carbon sink enhanced by sea-ice feedbacks at the Antarctic Cold Reversal

Author

Fogwill, C. J., Turney, C. S. M., Menviel, L., Baker, A., Weber, M. E., Ellis, B., Thomas, Z. A., Golledge, N. R., Etheridge, D., Rubino, M., Thornton, D. P., van Ommen, T. D., Moy, A. D., Curran, M. A. J., Davies, S., Bird, M. I., Munksgaard, N. C., Rootes, C. M., Millman, H., Vohra, J., Rivera, A., Mackintosh, A., Pike, J., Hall, I. R., Bagshaw, E. A., Rainsley, E., Bronk-Ramsey, C., Montenari, M., Cage, A. G., Harris, M. R. P., Jones, R., Power, A., Love, J., Young, J., Weyrich, L. S., and Cooper, A.

Published
2020
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2. Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

Author

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

Subjects
Climate Action, Physical Geography and Environmental Geoscience, Paleontology
Abstract

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful presite selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Published
2013

4. A 5-GHz Southern Hemisphere VLBI Survey of Compact Radio Sources - II

Author

Shen, Z. -Q., Wan, T. -S., Moran, J. M., Jauncey, D. L., Reynolds, J. E., Tzioumis, A. K., Gough, R. G., Ferris, R. H., Sinclair, M. W., Jiang, D. -R., Hong, X. -Y., Liang, S. -G., Edwards, P. G., Costa, M. E., Tingay, S. J., McCulloch, P. M., Lovell, J. E. J., King, E. A., Nicolson, G. D., Murphy, D. W., Meier, D. L., van Ommen, T. D., and White, G. L.

Subjects
Astrophysics
Abstract

We report the results of a 5-GHz southern-hemisphere snapshot VLBI observation of a sample of blazars. The observations were performed with the Southern Hemisphere VLBI Network plus the Shanghai station in 1993 May. Twenty-three flat-spectrum, radio-loud sources were imaged. These are the first VLBI images for 15 of the sources. Eight of the sources are EGRET (> 100 MeV) gamma-ray sources. The milliarcsecond morphology shows a core-jet structure for 12 sources, and a single compact core for the remaining 11. No compact doubles were seen. Compared with other radio images at different epochs and/or different frequencies, 3 core-jet blazars show evidence of bent jets, and there is some evidence for superluminal motion in the cases of 2 blazars. The detailed descriptions for individual blazars are given. This is the second part of a survey: the first part was reported by Shen et al. (AJ 114(1997)1999)., Comment: 35 pages (6 ps figures and 5 tables), to appear in AJ April 1998

Published
1998
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5. A 5 GHz Southern Hemisphere VLBI Survey of Compact Radio SOurces - I

Author

Shen, Z. -Q., Wan, T. -S., Moran, J. M., Jauncey, D. L., Reynolds, J. E., Tzioumis, A. K., Gough, R. G., Ferris, R. H., Sinclair, M. W., Jiang, D. -R., Hong, X. -Y., Liang, S. -G., Costa, M. E., Tingay, S. J., McCulloch, P. M., Lovell, J. E. J., King, E. A., Nicolson, G. D., Murphy, D. W., Meier, D. L., van Ommen, T. D., and Edwards, P. G.

Subjects
Astrophysics
Abstract

We report the results of a 5 GHz southern hemisphere VLBI survey of compact extragalactic radio sources. These observations were undertaken with the SHEVE array plus Shanghai station in November 1992. A sample of 22 sources was observed and images of 20 of them were obtained. Of the 20 sources imaged, 15 showed core-jet structure, one had a two-sided jet and 4 had only single compact cores. Eleven of the 16 core-jet (including one two-sided jet) sources show some evidence of bent jets. No compact doubles were found. A comparison with previous images and the temporal variability of the radio flux density showed evidence for superluminal motion in 4 of the sources. Five sources were high energy (>100 MeV) gamma-ray sources. Statistical analysis showed the dominance of highly polarized quasars among the detected gamma-ray sources, which emphasizes the importance of beaming effect in the gamma-ray emission., Comment: 39 pages including 7 ps figures and 5 tables, Latex, to appear in AJ

Published
1997
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6. Interstellar Broadening of Images in the Gravitational Lens PKS 1830-211

Author

Jones, D. L., Preston, R. A., Murphy, D. W., Jauncey, D. L., Reynolds, J. E., Tzioumis, A. K., King, E. A., McCulloch, P. M., Lovell, J. E. J., Costa, M. E., and van Ommen, T. D.

Subjects
Astrophysics
Abstract

The remarkably strong radio gravitational lens PKS 1830-211 consists of a one arcsecond diameter Einstein ring with two bright compact (milliarcsecond) components located on opposite sides of the ring. We have obtained 22 GHz VLBA data on this source to determine the intrinsic angular sizes of the compact components. Previous VLBI observations at lower frequencies indicate that the brightness temperatures of these components are significantly lower than 10E10 K, less than is typical for compact synchrotron radio sources and less than is implied by the short timescales of flux density variations. A possible explanation is that interstellar scattering is broadening the apparent angular size of the source and thereby reducing the observed brightness temperature. Our VLBA data support this hypothesis. At 22 GHz the measured brightness temperature is at least 10E11 K, and the deconvolved size of the core in the southwest compact component is proportional to the wavelength squared between 1.3 cm (22 GHz) and 18 cm (1.7 GHz). VLBI observations at still higher frequencies should be unaffected by interstellar scattering., Comment: Accepted by Ap.J. (Letters). Paper includes three postscript figures

Published
1996
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7. Discovery of a Sub-Parsec Radio Counterjet in the Nucleus of Centaurus A

Author

Jones, D. L., Tingay, S. J., Murphy, D. W., Meier, D. L., Jauncey, D. L., Reynolds, J. E., Tzioumis, A. K., Preston, R. A., McCulloch, P. M., Costa, M. E., Kemball, A. J., Nicolson, G. D., Quick, J. F. H., King, E. A., Lovell, J. E. J., Clay, R. W., Ferris, R. H., Gough, R. G., Sinclair, M. W., Ellingsen, S. P., Edwards, P. G., Jones, P. A., van Ommen, T. D., Harbison, P., and Migenes, V.

Subjects
Astrophysics
Abstract

A sub-parsec scale radio counterjet has been detected in the nucleus of the closest radio galaxy, Centaurus A (NGC 5128), with VLBI imaging at 2.3 and 8.4 GHz. This is one of the first detections of a VLBI counterjet and provides new constraints on the kinematics of the radio jets emerging from the nucleus of Cen A. A bright, compact core is seen at 8.4 GHz, along with a jet extending along P.A. 51 degrees. The core is completely absorbed at 2.3 GHz. Our images show a much wider gap between the base of the main jet and the counterjet at 2.3 GHz than at 8.4 GHz and also that the core has an extraordinarily inverted spectrum. These observations provide evidence that the innermost 0.4-0.8 pc of the source is seen through a disk or torus of ionized gas which is opaque at low frequencies due to free-free absorption., Comment: 3 pages, 2 postscript figures, scheduled for publication in August 1, 1996 issue of Ap.J. Letters

Published
1996
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9. The sub-parsec-scale structure and evolution of the jet in centaurus A

Author

Tingay, S. J., Jauncey, D. L., Preston, R. A., Reynolds, J. E., Tzioumis, A. K., Lovell, J. E. J., Costa, M. E., Murphy, D. W., Meier, D. L., McCulloch, P. M., Jones, D. L., Amy, S. W., Clay, R. W., Edwards, P. G., Ellingsen, S. P., Ferris, R. H., Gough, R. G., Harbison, P., Jones, P. A., King, E. A., Kemball, A. J., Migenes, V., Nicolson, G. D., Sinclair, M. W., van Ommen, T. D., Wark, R. M., White, G. L., and Kundt, Wolfgang, editor

Published
1996
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15. Revised records of atmospheric trace gases CO 2 , CH 4 , N 2 O, and δ13 C -CO 2 over the last 2000 years from Law Dome, Antarctica

Author

RUBINO, MAURO, Etheridge D. M., Thornton D. P., Howden R., Allison C. E., Francey R. J., Langenfelds R. L., Paul Steele L., Trudinger C. M., Spencer D. A., Curran M. A. J., Van Ommen T. D., Smith A. M., Rubino, Mauro, Etheridge, D. M., Thornton, D. P., Howden, R., Allison, C. E., Francey, R. J., Langenfelds, R. L., Paul Steele, L., Trudinger, C. M., Spencer, D. A., Curran, M. A. J., Van Ommen, T. D., and Smith, A. M.

Abstract

Ice core records of the major atmospheric greenhouse gases (CO2, CH4, N2O) and their isotopologues covering recent centuries provide evidence of biogeochemical variations during the Late Holocene and pre-industrial periods and over the transition to the industrial period. These records come from a number of ice core and firn air sites and have been measured in several laboratories around the world and show common features but also unresolved differences. Here we present revised records, including new measurements, performed at the CSIRO Ice Core Extraction LABoratory (ICELAB) on air samples from ice obtained at the high-accumulation site of Law Dome (East Antarctica). We are motivated by the increasing use of the records by the scientific community and by recent data-handling developments at CSIRO ICELAB. A number of cores and firn air samples have been collected at Law Dome to provide high-resolution records overlapping recent, direct atmospheric observations. The records have been updated through a dynamic link to the calibration scales used in the Global Atmospheric Sampling LABoratory (GASLAB) at CSIRO, which are periodically revised with information from the latest calibration experiments. The gas-age scales have been revised based on new ice-age scales and the information derived from a new version of the CSIRO firn diffusion model. Additionally, the records have been revised with new, rule-based selection criteria and updated corrections for biases associated with the extraction procedure and the effects of gravity and diffusion in the firn. All measurements carried out in ICELAB-GASLAB over the last 25 years are now managed through a database (the ICElab dataBASE or ICEBASE), which provides consistent data management, automatic corrections and selection of measurements, and a web-based user interface for data extraction. We present the new records, discuss their strengths and limitations, and summarise their main features. The records reveal changes in the carbon cycle and atmospheric chemistry over the last 2 millennia, including the major changes of the anthropogenic era and the smaller, mainly natural variations beforehand. They provide the historical data to calibrate and test the next inter-comparison of models used to predict future climate change (Coupled Model Inter-comparison Project - phase 6, CMIP6). The datasets described in this paper, including spline fits, are available at https://doi.org/10.25919/5bfe29ff807fb (Rubino et al., 2019).

Published
2019

16. A Counterjet in the Nucleus of Centaurus A

Author

Jones, D. L., Tingay, S. J., Preston, R. A., Jauncey, D. L., Reynolds, J. E., Lovell, J. E. J., McCulloch, P. M., Tzioumis, A. K., Costa, M. E., Murphy, D. W., Meier, D. L., Clay, R. W., Edwards, P. G., Ellingsen, S. P., Ferris, R. H., Gough, R. G., Harbison, P., Jones, P. A., King, E. A., Kemball, A. J., Migenes, V., Nicolson, G. D., Sinclair, M. W., van Ommen, T. D., Wark, R. M., White, G. L., Ekers, R., editor, Fanti, C., editor, and Padrielli, L., editor

Published
1996
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17. Monitoring the Jet in Centaurus a at 0.1 Parsec Resolution

Author

Preston, R. A., Tingay, S. J., Jauncey, D. L., Reynolds, J. E., Lovell, J. E. J., McCulloch, P. M., Tzioumis, A. K., Costa, M. E., Murphy, D. W., Meier, D. L., Jones, D. L., Clay, R. W., Edwards, P. G., Ellingsen, S. P., Ferris, R. H., Gough, R. G., Harbison, P., Jones, P. A., King, E. A., Kemball, A. J., Migenes, V., Nicolson, G. D., Sinclair, M. W., van Ommen, T. D., Wark, R. M., White, G. L., Ekers, R., editor, Fanti, C., editor, and Padrielli, L., editor

Published
1996
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19. Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica

Author

Turney, C, Fogwill, C, Golledge, N, McKay, N, Van Sebille, E, Jones, R, Etheridge, D, Rubino, M, Thornton, D, Davies, S, Bronk Ramsey, C, Thomas, Z, Bird, M, Munksgaard, N, Kohno, M, Woodward, J, Winter, K, Weyrich, L, Rootes, C, Millman, H, Albert, P, Rivera, A, van Ommen, T, Curran, M, Moy, A, Rahmstorf, S, Kawamura, K, Hillenbrand, C-D, Weber, M, Manning, C, Young, J, Cooper, A, Turney, C, Fogwill, C, Golledge, N, McKay, N, Van Sebille, E, Jones, R, Etheridge, D, Rubino, M, Thornton, D, Davies, S, Bronk Ramsey, C, Thomas, Z, Bird, M, Munksgaard, N, Kohno, M, Woodward, J, Winter, K, Weyrich, L, Rootes, C, Millman, H, Albert, P, Rivera, A, van Ommen, T, Curran, M, Moy, A, Rahmstorf, S, Kawamura, K, Hillenbrand, C-D, Weber, M, Manning, C, Young, J, and Cooper, A

Abstract

The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) (129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (∼2 m), ocean thermal expansion, and melting mountain glaciers (∼1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic me- ridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and envi- ronmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is under- lain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet mod- eling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.

Published
2020

20. Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica.

Author

Turney, CSM, Fogwill, CJ, Golledge, NR, McKay, NP, van Sebille, E, Jones, RT, Etheridge, D, Rubino, M, Thornton, DP, Davies, SM, Ramsey, CB, Thomas, ZA, Bird, MI, Munksgaard, NC, Kohno, M, Woodward, J, Winter, K, Weyrich, LS, Rootes, CM, Millman, H, Albert, PG, Rivera, A, van Ommen, T, Curran, M, Moy, A, Rahmstorf, S, Kawamura, K, Hillenbrand, C-D, Weber, ME, Manning, CJ, Young, J, Cooper, A, Turney, CSM, Fogwill, CJ, Golledge, NR, McKay, NP, van Sebille, E, Jones, RT, Etheridge, D, Rubino, M, Thornton, DP, Davies, SM, Ramsey, CB, Thomas, ZA, Bird, MI, Munksgaard, NC, Kohno, M, Woodward, J, Winter, K, Weyrich, LS, Rootes, CM, Millman, H, Albert, PG, Rivera, A, van Ommen, T, Curran, M, Moy, A, Rahmstorf, S, Kawamura, K, Hillenbrand, C-D, Weber, ME, Manning, CJ, Young, J, and Cooper, A

Abstract

The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) (129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (∼2 m), ocean thermal expansion, and melting mountain glaciers (∼1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic meridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and environmental change from the Weddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is underlain by major methane hydrate reserves. Constrained by a widespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet modeling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice-climate feedbacks that further amplify warming.

Published
2020

21. Domain Adaptation by Using Causal Inference to Predict Invariant Conditional Distributions

Author

Magliacane, S., van Ommen, T., Claassen, T., Bongers, S., Versteeg, P., Mooij, J.M., Bengio, S., Wallach, H., Larochelle, H., Grauman, K., Cesa-Bianchi, N., Garnett, R., and Amsterdam Machine Learning lab (IVI, FNWI)

Abstract

An important goal common to domain adaptation and causal inference is to make accurate predictions when the distributions for the source (or training) domain(s) and target (or test) domain(s) differ. In many cases, these different distributions can be modeled as different contexts of a single underlying system, in which each distribution corresponds to a different perturbation of the system, or in causal terms, an intervention. We focus on a class of such causal domain adaptation problems, where data for one or more source domains are given, and the task is to predict the distribution of a certain target variable from measurements of other variables in one or more target domains. We propose an approach for solving these problems that exploits causal inference and does not rely on prior knowledge of the causal graph, the type of interventions or the intervention targets. We demonstrate our approach by evaluating a possible implementation on simulated and real world data.

Published
2019

22. VLBI Observations of Gamma-Ray-Quiet AGN: Comparing Radio Core Brightness Temperatures

Author

Tingay, S. J, Murphy, D. W, Lovell, J. E. J, Costa, M. E, McCulloch, P, Edwards, P. G, Jauncey, D. L, Reynolds, J. E, Tzioumis, A. K, King, E. A, Jones, D. L, Preston, R. A, Meier, D. L, van Ommen, T. D, Nicolson, G. D, and Quick, J. F. H

Subjects
Astrophysics
Abstract

We present VLBI and Australia Telescope Compact Array images, and derive source frame radio-core brightness temperatures for three prominent, flat-spectrum extragalactic radio sources, notable because they have not been detected as gamma-ray sources with the EGRET instrument.

Published
1998

23. The Sub-Parsec-Scale Structure and Evolution of Centaurus A

Author

Tingay, S. J, Jauncey, D. L, Reynolds, J. E, Tzioumis, A. K, King, E. A, Preston, R. A, Jones, D. L, Murphy, D. W, Meier, D. L, van Ommen, T. D, McCulloch, P. M, Ellingsen, S. P, Costa, M. E, Edwards, P. G, Lovell, J. E. J, Nicolson, G. D, Quick, J. F. H, and Kemball, A. J

Subjects
Astronomy
Abstract

We present high-resolution VLBI radio images of the closest classical radio galaxy, Centaurus A, including the highest resolution image yet for this source.

Published
1998

25. Discovery of a Sub-Parsec Radio counterjet in the Nucleus of Centarus A

Author

Jones, Dayton L, Tingay, Steven J, Murphy, David W, Meier, David L, Jauncey, David L, Reynolds, John E, Tzoumis, Anastosios K, Preston, Robert A, McCulloch, Peter M, Costa, Marco E, Kemball, Athol J, Nicholson, George D, Quick, Jonathan F. H, King, Edward A, Lovell, James E. J, Clay, R. W, Ferris, Richard H, Gough, R. G, Sinclair, M. W, Ellingsen, S. P, Edwards, P. G, Jones, P. A, van Ommen, T. D, Harbison, Paul, and Mignes, Victor

Abstract

A sub-parsec scale radio counterjet has been detected in the nucleus of the closest radio galaxy, Centarus A (NGC 5128), with VLBI imaging at 2.3 and 8.4 GHz.

Published
1996

28. Interstellar Broadening of Images in the Gravitational Lens PKS 1830-211

Author

van Ommen, T. D, Costa, M. E, Lovell, J. E. J, McCulloch, P. M, King, E. A, Tzioumis, A. K, Reynolds, J. E, Jauncey, D. L, Murphy, D. W, Preston, R. A, and Jones, D. L

Abstract

The remarkably strong radio gravitational lens PKS 1830-211 consists of a one arcsecond diameter Einstein ring with two bright compact (milliarcsecond) components located on opposite sides of the ring. We have obtained 22GHz VLBA data on this source to determine the intrinsic angular sizes of the compact components.

Published
1996

29. Time delay in the Einstein ring PKS 1830-211

Author

Van Ommen, T. D, Jones, D. L, Preston, R. A, and Jauncey, D. L

Subjects
Astrophysics
Abstract

We present radio observations of the gravitational lens PKS 1830-211 at 8.4 and 15 GHz acquired using the Very Large Array. The observations were made over a 13 month period. Significant flux density changes over this period provide strong constraints on the time delay between the two lensed images and suffest a value of 44 +/- 9 days. This offers new direct evidence that this source is indeed a gravitational lens. The lens distance is dependent upon the model chosen, but reasonable limits on the mass of the lensing galaxy suggest that it is unlikely to be at a redshift less than a few tenths, and may well be significantly more distant.

Published
1995
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30. Subparsec-scale structure and evolution of Centaurus A (NGC5128)

Author

Jauncey, D.L., Tingay, S.J., Preston, R.A., Reynolds, J.E., Lovell, J.E.J., McCulloch, P.M., Tzioumis, A.K., Costa, M.E., Murphy, D.W., Meier, D.L., Jones, D.L., Amy, S.W., Biggs, J.D., Blair, D.G., Clay, R.W., Edwards, P.G., Ellingsen, S.P., Ferris, R.H., Gough, R.G., Harbison, P., Jones, P.A., King, E.A., Kemball, A.J., Migenes, V., Nicolson, G.D., Sinclair, M.W., Van Ommen, T., Wark, R.M., and White, G.L.

Subjects
Galactic nuclei -- Research, Very long baseline interferometry -- Usage, Cosmological distances -- Observations, Galaxies -- Evolution, Science and technology
Abstract

We present a series of 8.4-GHz very-long-baseline radio interferometry images of the nucleus of Centaurus A (NGC5128) made with a Southern Hemisphere array, representing a 3.33-year monitoring effort. The nuclear radio jet is [approximate]50 milliarcseconds in extent, or at the 3.5-megaparsec distance of NGC5128, [approximate] 1 parsec in length. Sub-luminal motion is seen and structural changes are observed on time scales shorter than 4 months. High-resolution observations at 4.8 and 8.4 GHz made in November 1992 reveal a complex morphology and allow us to unambiguously identify the self-absorbed core located at the southwestern end of the jet.

Published
1995

31. Algebraic Equivalence of Linear Structural Equation Models

Author

van Ommen, T., Mooij, J.M., Elidan, G., Kersting, K., and Amsterdam Machine Learning lab (IVI, FNWI)

Abstract

Despite their popularity, many questions about the algebraic constraints imposed by linear structural equation models remain open problems. For causal discovery, two of these problems are especially important: the enumeration of the constraints imposed by a model, and deciding whether two graphs define the same statistical model. We show how the half-trek criterion can be used to make progress in both of these problems. We apply our theoretical results to a small-scale model selection problem, and find that taking the additional algebraic constraints into account may lead to significant improvements in model selection accuracy.

Published
2017

32. Computing Minimax Decisions with Incomplete Observations

Author

van Ommen, T. and Amsterdam Machine Learning lab (IVI, FNWI)

Abstract

Decision makers must often base their decisions on incomplete (coarse) data. Recent research has shown that in a wide variety of coarse data problems, minimax optimal strategies can be recognized using a simple probabilistic condition. This paper develops a computational method to find such strategies in special cases, and shows what difficulties may arise in more general cases.

Published
2017

33. Where to find 1.5 million yr old ice for the IPICS 'Oldest-Ice' ice core

Author

Fischer, H., Severinghaus, J., Brook, E., Wolff, E., Albert, M., Alemany, O., Arthern, R., Bentley, C., Blankenship, D., Chappellaz, J., Creyts, T., Dahl-Jensen, D., Dinn, M., Frezzotti, M., Fujita, S., Gallee, H., Hindmarsh, R., Hudspeth, D., Jugie, G., Kawamura, K., Lipenkov, V., Miller, H., Mulvaney, R., Parrenin, Frédéric, Pattyn, F., Ritz, C., Schwander, J., Steinhage, D., Van Ommen, T., Wilhelms, F., Fischer, H., Severinghaus, J., Brook, E., Wolff, E., Albert, M., Alemany, O., Arthern, R., Bentley, C., Blankenship, D., Chappellaz, J., Creyts, T., Dahl-Jensen, D., Dinn, M., Frezzotti, M., Fujita, S., Gallee, H., Hindmarsh, R., Hudspeth, D., Jugie, G., Kawamura, K., Lipenkov, V., Miller, H., Mulvaney, R., Parrenin, F., Pattyn, F., Ritz, C., Schwander, J., Steinhage, D., Van Ommen, T., Wilhelms, F., Max Planck Institute for Solar System Research (MPS), Max-Planck-Gesellschaft, Scripps Institution of Oceanography (SIO), University of California [San Diego] (UC San Diego), University of California-University of California, British Antarctic Survey (BAS), Natural Environment Research Council (NERC), Département de Physique Théorique, University of Geneva [Switzerland], CLIPS, Laboratoire de glaciologie et géophysique de l'environnement (LGGE), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS), Centre for Ice and Climate [Copenhagen], Niels Bohr Institute [Copenhagen] (NBI), Faculty of Science [Copenhagen], University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU)-Faculty of Science [Copenhagen], University of Copenhagen = Københavns Universitet (KU)-University of Copenhagen = Københavns Universitet (KU), Italian National agency for new technologies, Energy and sustainable economic development [Frascati] (ENEA), National Institute of Polar Research [Tokyo] (NiPR), Physical Science Division, Natural Environment Research Council (NERC)-Natural Environment Research Council (NERC), Arctic and Antarctic Research Institute (AARI), Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet), Institut des Géosciences de l’Environnement (IGE), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Université Libre de Bruxelles [Bruxelles] (ULB), Physics Institute, University of Berne, Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Recherche pour le Développement (IRD)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Université libre de Bruxelles (ULB), Max-Planck-Institut für Sonnensystemforschung = Max Planck Institute for Solar System Research (MPS), Scripps Institution of Oceanography (SIO - UC San Diego), University of California (UC)-University of California (UC), Université de Genève = University of Geneva (UNIGE), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH)-Faculty of Science [Copenhagen], University of Copenhagen = Københavns Universitet (UCPH)-University of Copenhagen = Københavns Universitet (UCPH), Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), and Universität Bern [Bern] (UNIBE)

Subjects
Paléontologie et paléoécologie, Antarctic Plateau, sub-01, lcsh:Environmental protection, glaciation, heat flux, Stratigraphie, ice flow, Physical Geography and Environmental Geoscience, Quaternary, Environnement et pollution, lcsh:Environmental pollution, Dome Concordia, paleoclimate, lcsh:TD169-171.8, [SDU.STU.GL]Sciences of the Universe [physics]/Earth Sciences/Glaciology, lcsh:Environmental sciences, ComputingMilieux_MISCELLANEOUS, lcsh:GE1-350, Paleontology, Calluna vulgaris, East Antarctica, cryosphere, Climate Action, greenhouse gas, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, geothermal energy, lcsh:TD172-193.5, Antarctica, bedrock, ice core, ice thickness
Abstract

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful presite selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e. more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
2013
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34. Late Pleistocene and early Holocene change in the Weddell Sea: A new climate record from the Patriot Hills, Ellsworth Mountains, West Antarctica

Author

Turney C., Fogwill C., Van Ommen T. D., Moy A. D., Etheridge D., Rubino M., Curran M. A. J., Rivera A., Turney, C., Fogwill, C., Van Ommen, T. D., Moy, A. D., Etheridge, D., Rubino, M., Curran, M. A. J., and Rivera, A.

Subjects
Blue Ice Area, Katabatic wind, Sea ice, Southern Annular Mode, West Antarctic Ice Sheet, Meridional Overturning Circulation
Abstract

The transition from the late Pleistocene to the Holocene (30 000-5000 years ago) was a period of considerable climate variability, which has been associated with changes in deep water formation and the intensity of the Meridional Overturning Circulation. Although numerous records exist across the North Atlantic region, few Antarctic ice core records have been obtained from the south. Here we exploit the potential of upwelling ancient ice - so-called blue ice areas (BIAs) - from the Patriot Hills in the Ellsworth Mountains to derive the first deuterium isotope record (δD) from continental Antarctica south of the Weddell Sea. Gas analysis and glaciological considerations provide a first relative chronology. Inferred temperature trends from the Patriot Hills BIA and snow pit suggest changing climate influences during the transition between the last glacial period and Holocene. Under modern conditions, the interplay between the Antarctic high-pressure system and the Southern Annular Mode appears to play a significant role in controlling katabatic wind flow over the site while the BIA record suggests that greater sea ice extent during the last glacial period was a major control. Our results demonstrate the considerable potential of the Patriot Hills site for reconstructing past climate change in the south Atlantic region. © 2013 John Wiley & Sons, Ltd.

Published
2013

35. A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

Author

RAISED Consortium, Bentley, J, Cofaigh, O, Anderson, B, Conway, H., Davies, B, Graham, C, Hillenbrand, D, Hodgson, A, Jamieson, R, Larter, D, Mackintosh, A, Smith, A, Verleyen, E., Ackert, P, Bart, J, Berg, S, Brunstein, D, Canals, M, Colhoun, A, Crosta, X, Dickens, A, Domack, E, Dowdeswell, A, Dunbar, R, Ehrmann, W, Evans, J, Favier, V, Fink, D, Fogwill, J, Glasser, F, Gohl, K, Golledge, R, Goodwin, I, Gore, B, Greenwood, L, Hall, L, Hall, K, Hedding, W, Hein, S, Hocking, P, Jakobsson, M, Johnson, S, Jomelli, V, Jones, S, Klages, P, Kristoffersen, Y, Kuhn, G, Leventer, A, Licht, K, Lilly, K, Lindow, J, Livingstone, J, Masse, G, McGlone, S, McKay, M, Melles, M, Miura, H, Mulvaney, R., Nel, W, Nitsche, O, O'Brien, E, Post, L, Roberts, J, Saunders, M, Selkirk, M, Simms, R, Spiegel, C, Stolldorf, D, Sugden, E, van der Putten, N., van Ommen, T, Verfaillie, D, Vyverman, W., Wagner, B, White, A, Witus, E, and Zwartz, D

Abstract

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.

Published
2014

36. Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination

Author

Fogwill, C. J., primary, Turney, C. S. M., additional, Golledge, N. R., additional, Etheridge, D. M., additional, Rubino, M., additional, Thornton, D. P., additional, Baker, A., additional, Woodward, J., additional, Winter, K., additional, van Ommen, T. D., additional, Moy, A. D., additional, Curran, M. A. J., additional, Davies, S. M., additional, Weber, M. E., additional, Bird, M. I., additional, Munksgaard, N. C., additional, Menviel, L., additional, Rootes, C. M., additional, Ellis, B., additional, Millman, H., additional, Vohra, J., additional, Rivera, A., additional, and Cooper, A., additional

Published
2017
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37. Robust probability updating

Author

Van Ommen, T. (Thijs), Koolen-Wijkstra, W.M. (Wouter), Feenstra, T.E. (Thijs), Grünwald, P.D. (Peter), Van Ommen, T. (Thijs), Koolen-Wijkstra, W.M. (Wouter), Feenstra, T.E. (Thijs), and Grünwald, P.D. (Peter)

Published
2016
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38. Individual particle morphology, coatings, and impurities of black carbon aerosols in Antarctic ice and tropical rainfall

Author

Ellis, A., Edwards, R., Saunders, M., Chakrabarty, R., Subramanian, R., Timms, N., Van Riessen, Arie, Smith, A., Lambrinidis, D., Nunes, L., Vallelonga, P., Goodwin, I., Moy, A., Curran, M., van Ommen, T., Ellis, A., Edwards, R., Saunders, M., Chakrabarty, R., Subramanian, R., Timms, N., Van Riessen, Arie, Smith, A., Lambrinidis, D., Nunes, L., Vallelonga, P., Goodwin, I., Moy, A., Curran, M., and van Ommen, T.

Abstract

© 2016 American Geophysical Union. All Rights Reserved. Black carbon (BC) aerosols are a large source of climate warming, impact atmospheric chemistry, and are implicated in large-scale changes in atmospheric circulation. Inventories of BC emissions suggest significant changes in the global BC aerosol distribution due to human activity. However, little is known regarding BC's atmospheric distribution or aged particle characteristics before the twentieth century. Here we investigate the prevalence and structural properties of BC particles in Antarctic ice cores from 1759, 1838, and 1930 Common Era (C.E.) using transmission electron microscopy and energy-dispersive X-ray spectroscopy. The study revealed an unexpected diversity in particle morphology, insoluble coatings, and association with metals. In addition to conventionally occurring BC aggregates, we observed single BC monomers, complex aggregates with internally, and externally mixed metal and mineral impurities, tar balls, and organonitrogen coatings. The results of the study show BC particles in the remote Antarctic atmosphere exhibit complexity that is unaccounted for in atmospheric models of BC.

Published
2016

39. Where to find 1.5 million yr old ice for the IPICS 'Oldest-Ice' ice core

Author

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

Subjects
530 Physics
Abstract

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Published
2013
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40. Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy

Author

Ellis, A., Edwards, R., Saunders, M., Chakrabarty, R. K., Subramanian, R., van Riessen, A., Smith, A. M., Lambrinidis, Dionisia, Nunes, L. J., Vallelonga, P., Goodwin, I. D., Moy, A. D., Curran, M. A. J., van Ommen, T. D., Ellis, A., Edwards, R., Saunders, M., Chakrabarty, R. K., Subramanian, R., van Riessen, A., Smith, A. M., Lambrinidis, Dionisia, Nunes, L. J., Vallelonga, P., Goodwin, I. D., Moy, A. D., Curran, M. A. J., and van Ommen, T. D.

Abstract

Antarctic ice cores have been used to study the history of black carbon (BC), but little is known with regards to the physical and chemical characteristics of these particles in the remote atmosphere. Characterization remains limited by ultra-trace concentrations in ice core samples and the lack of adequate methods to isolate the particles unaltered from the melt water. To investigate the physical and chemical characteristics of these particles, we have developed a tangential flow filtration (TFF) method combined with transmission electron microscopy (TEM). Tests using ultrapure water and polystyrene latex particle standards resulted in excellent blanks and significant particle recovery. This approach has been applied to melt water from Antarctic ice cores as well as tropical rain from Darwin, Australia with successful results: TEM analysis revealed a variety of BC particle morphologies, insoluble coatings, and the attachment of BC to mineral dust particles. The TFF-based concentration of these particles has proven to give excellent results for TEM studies of BC particles in Antarctic ice cores and can be used for future studies of insoluble aerosols in rainwater and ice core samples.

Published
2015

41. Historically unprecedented global glacier decline in the early 21st century

Author

Ahlström, A. P., Anderson, B., Arenillas, M., Bajracharya, S., Baroni, C., Bidlake, W. R., Braun, L. N., Caceres, B., Casassa, G., Ceballos, J. L., Cobos, G., Davila, L. R., Delgado Granados, H., Demberel, O., Demuth, M. N., Espizua, L., Fischer, A., Fujita, K., Gadek, B., Ghazanfar, A., Hagen, J. O., Hoelzle, M., Holmlund, Per, Karimi, N., Li, Z., Martinez De Pison, E., Pelto, M., Pitte, P., Popovnin, V. V., Portocarrero, C. A., Prinz, R., Ramirez, J., Rudell, A., Sangewar, C., Severskiy, I, Sigurdsson, O., Soruco, A., Tielidze, L., Usubaliev, R., Van Ommen, T., Vincent, C., Yakovlev, A., Ahlström, A. P., Anderson, B., Arenillas, M., Bajracharya, S., Baroni, C., Bidlake, W. R., Braun, L. N., Caceres, B., Casassa, G., Ceballos, J. L., Cobos, G., Davila, L. R., Delgado Granados, H., Demberel, O., Demuth, M. N., Espizua, L., Fischer, A., Fujita, K., Gadek, B., Ghazanfar, A., Hagen, J. O., Hoelzle, M., Holmlund, Per, Karimi, N., Li, Z., Martinez De Pison, E., Pelto, M., Pitte, P., Popovnin, V. V., Portocarrero, C. A., Prinz, R., Ramirez, J., Rudell, A., Sangewar, C., Severskiy, I, Sigurdsson, O., Soruco, A., Tielidze, L., Usubaliev, R., Van Ommen, T., Vincent, C., and Yakovlev, A.

Abstract

Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (similar to 42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (similar to 5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.

Published
2015
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45. Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy

Author

Ellis, A., primary, Edwards, R., additional, Saunders, M., additional, Chakrabarty, R. K., additional, Subramanian, R., additional, van Riessen, A., additional, Smith, A. M., additional, Lambrinidis, D., additional, Nunes, L. J., additional, Vallelonga, P., additional, Goodwin, I. D., additional, Moy, A. D., additional, Curran, M. A. J., additional, and van Ommen, T. D., additional

Published
2015
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48. Ocean access to a cavity beneath Totten Glacier in East Antarctica

Author

Greenbaum, J. S., primary, Blankenship, D. D., additional, Young, D. A., additional, Richter, T. G., additional, Roberts, J. L., additional, Aitken, A. R. A., additional, Legresy, B., additional, Schroeder, D. M., additional, Warner, R. C., additional, van Ommen, T. D., additional, and Siegert, M. J., additional

Published
2015
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50. A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

Author

Bentley, MJ, Ocofaigh, C, Anderson, JB, Conway, H, Davies, B, Graham, AGC, Hillenbrand, CD, Hodgson, DA, Jamieson, SSR, Larter, RD, Mackintosh, A, Smith, JA, Verleyen, E, Ackert, RP, Bart, PJ, Berg, S, Brunstein, D, Canals, M, Colhoun, EA, Crosta, X, Dickens, WA, Domack, E, Dowdeswell, JA, Dunbar, R, Ehrmann, W, Evans, J, Favier, V, Fink, D, Fogwill, CJ, Glasser, NF, Gohl, K, Golledge, NR, Goodwin, I, Gore, DB, Greenwood, SL, Hall, BL, Hall, K, Hedding, DW, Hein, AS, Hocking, EP, Jakobsson, M, Johnson, JS, Jomelli, V, Jones, RS, Klages, JP, Kristoffersen, Y, Kuhn, G, Leventer, A, Licht, K, Lilly, K, Lindow, J, Livingstone, SJ, Massé, G, McGlone, MS, McKay, RM, Melles, M, Miura, H, Mulvaney, R, Nel, W, Nitsche, FO, O'Brien, PE, Post, AL, Roberts, SJ, Saunders, KM, Selkirk, PM, Simms, AR, Spiegel, C, Stolldorf, TD, Sugden, DE, van der Putten, N, van Ommen, T, Verfaillie, D, Vyverman, W, Wagner, B, White, DA, Witus, AE, Zwartz, D, Bentley, MJ, Ocofaigh, C, Anderson, JB, Conway, H, Davies, B, Graham, AGC, Hillenbrand, CD, Hodgson, DA, Jamieson, SSR, Larter, RD, Mackintosh, A, Smith, JA, Verleyen, E, Ackert, RP, Bart, PJ, Berg, S, Brunstein, D, Canals, M, Colhoun, EA, Crosta, X, Dickens, WA, Domack, E, Dowdeswell, JA, Dunbar, R, Ehrmann, W, Evans, J, Favier, V, Fink, D, Fogwill, CJ, Glasser, NF, Gohl, K, Golledge, NR, Goodwin, I, Gore, DB, Greenwood, SL, Hall, BL, Hall, K, Hedding, DW, Hein, AS, Hocking, EP, Jakobsson, M, Johnson, JS, Jomelli, V, Jones, RS, Klages, JP, Kristoffersen, Y, Kuhn, G, Leventer, A, Licht, K, Lilly, K, Lindow, J, Livingstone, SJ, Massé, G, McGlone, MS, McKay, RM, Melles, M, Miura, H, Mulvaney, R, Nel, W, Nitsche, FO, O'Brien, PE, Post, AL, Roberts, SJ, Saunders, KM, Selkirk, PM, Simms, AR, Spiegel, C, Stolldorf, TD, Sugden, DE, van der Putten, N, van Ommen, T, Verfaillie, D, Vyverman, W, Wagner, B, White, DA, Witus, AE, and Zwartz, D

Abstract

A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20ka, 15ka, 10ka and 5ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorit. © 2014 The Authors.

Published
2014

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