Export 4 results:
Sort by: [ Author  (Asc)] Title Type Year
A B C D E [F] G H I J K L M N O P Q R S T U V W X Y Z   [Show ALL]
Fain, X, Ferrari CP, Dommergue A, Albert MR, Battle M, Severinghaus J, Arnaud L, Barnola JM, Cairns W, Barbante C, Boutron C.  2009.  Polar firn air reveals large-scale impact of anthropogenic mercury emissions during the 1970s. Proceedings of the National Academy of Sciences of the United States of America. 106:16114-16119.   10.1073/pnas.0905117106   AbstractWebsite

Mercury (Hg) is an extremely toxic pollutant, and its biogeochemical cycle has been perturbed by anthropogenic emissions during recent centuries. In the atmosphere, gaseous elemental mercury (GEM; Hg degrees) is the predominant form of mercury (up to 95%). Here we report the evolution of atmospheric levels of GEM in mid- to high-northern latitudes inferred from the interstitial air of firn (perennial snowpack) at Summit, Greenland. GEM concentrations increased rapidly after World War II from approximate to 1.5 ng m(-3) reaching a maximum of approximate to 3 ng m(-3) around 1970 and decreased until stabilizing at approximate to 1.7 ng m(-3) around 1995. This reconstruction reproduces real-time measurements available from the Arctic since 1995 and exhibits the same general trend observed in Europe since 1990. Anthropogenic emissions caused a two-fold rise in boreal atmospheric GEM concentrations before the 1970s, which likely contributed to higher deposition of mercury in both industrialized and remotes areas. Once deposited, this toxin becomes available for methylation and, subsequently, the contamination of ecosystems. Implementation of air pollution regulations, however, enabled a large-scale decline in atmospheric mercury levels during the 1980s. The results shown here suggest that potential increases in emissions in the coming decades could have a similar large-scale impact on atmospheric Hg levels.

Fischer, H, Severinghaus J, Brook E, Wolff E, Albert M, Alemany O, Arthern R, Bentley C, Blankenship D, Chappellaz J, Creyts T, Dahl-Jensen D, Dinn M, Frezzotti M, Fujita S, Gallee H, Hindmarsh R, Hudspeth D, Jugie G, Kawamura K, Lipenkov V, Miller H, Mulvaney R, Parrenin F, Pattyn F, Ritz C, Schwander J, Steinhage D, van Ommen T, Wilhelms F.  2013.  Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core. Climate of the Past. 9:2489-2505.   10.5194/cp-9-2489-2013   AbstractWebsite

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 2500m would be required to find 1.5 Myr old ice (i.e., more than 700m 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.

Fricker, HA, Powell R, Priscu J, Tulaczyk S, Anandakrishnan S, Christner B, Fisher AT, Holland D, Horgan H, Jacobel R, Mikucki J, Mitchell A, Scherer R, Severinghaus J.  2011.  Siple Coast subglacial aquatic environments; the Whillans ice stream subglacial access research drilling project. Geophysical Monograph. 192:199-219.   10.1029/2010gm000932   AbstractWebsite

The Whillians Ice Stream Subglacial Access Research Drilling (WISSARD) project is a 6-year (2009-2015) integrative study of ice sheet stability and subglacial geobiology in West Antarctica, funded by the Antarctic Integrated System Science Program of National Science Foundation's Office of Polar Programs, Antarctic Division. The overarching scientific objective of WISSARD is to assess the role of water beneath a West Antarctic Ice Stream in interlinked glaciological, geological, microbiological, geochemical, hydrological, and oceanographic systems. The WISSARD's important science questions relate to (1) the role that subglacial and ice shelf cavity waters and wet sediments play in ice stream dynamics and mass balance, with an eye on the possible future of the West Antarctic Ice Sheet and (2) the microbial metabolic and phylogenetic diversity in these subglacial environments. The study area is the downstream part of the Whillans Ice Stream on the Siple Coast, specifically Subglacial Lake Whillans and the part of the grounding zone across which it drains. In this chapter, we provide background on the motivation for the WISSARD project, detail the key scientific goals, and describe the new measurement tools and strategies under development that will provide the framework for conducting an unprecedented range of scientific observations.

Fudge, TJ, Steig EJ, Markle BR, Schoenemann SW, Ding QH, Taylor KC, McConnell JR, Brook EJ, Sowers T, White JWC, Alley RB, Cheng H, Clow GD, Cole-Dai J, Conway H, Cuffey KM, Edwards JS, Edwards RL, Edwards R, Fegyveresi JM, Ferris D, Fitzpatrick JJ, Johnson J, Hargreaves G, Lee JE, Maselli OJ, Mason W, McGwire KC, Mitchell LE, Mortensen N, Neff P, Orsi AJ, Popp TJ, Schauer AJ, Severinghaus JP, Sigl M, Spencer MK, Vaughn BH, Voigt DE, Waddington ED, Wang XF, Wong GJ, Members WDP.  2013.  Onset of deglacial warming in West Antarctica driven by local orbital forcing. Nature. 500:440-+.   10.1038/nature12376   AbstractWebsite

The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate(1,2). Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago(3,4). An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently(2,5). Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere(6) associated with an abrupt decrease in Atlantic meridional overturning circulation(7). However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.