Koffman B.G.,University of Maine, United States |
Koffman B.G.,Lamont Doherty Earth Observatory |
Kreutz K.J.,University of Maine, United States |
Breton D.J.,University of Maine, United States |
And 7 more authors.
Climate of the Past | Year: 2014
We present the first high-resolution (sub-annual) dust particle data set from West Antarctica, developed from the West Antarctic Ice Sheet (WAIS) Divide deep ice core (79.468° S, 112.086 W), and use it to reconstruct changes in atmospheric circulation over the past 2400 years. We find a background dust flux of ∼4 mg mĝ̂'2 yearĝ̂'1 and a mode particle size of 5-8 Î1/4m diameter. Through comparing the WAIS Divide record with other Antarctic ice core particle records, we observe that coastal and lower-elevation sites have higher dust fluxes and coarser particle size distributions (PSDs) than sites on the East Antarctic plateau, suggesting input from local dust sources at these lower-elevation sites. In order to explore the use of the WAIS Divide dust PSD as a proxy for past atmospheric circulation, we make quantitative comparisons between both mid-latitude zonal wind speed and West Antarctic meridional wind speed and the dust size record, finding significant positive interannual relationships. We find that the dust PSD is related to mid-latitude zonal wind speed via cyclonic activity in the Amundsen Sea region. Using our PSD record, and through comparison with spatially distributed climate reconstructions from the Southern Hemisphere (SH) middle and high latitudes, we infer that the SH westerlies occupied a more southerly position from circa 1050 to 1400 CE (Common Era), coinciding with the Medieval Climate Anomaly (MCA). Subsequently, at ca. 1430 CE, the wind belt shifted equatorward, where it remained until the mid-to-late twentieth century. We find covariability between reconstructions of El Niño-Southern Oscillation (ENSO) and the mid-latitude westerly winds in the eastern Pacific, suggesting that centennial-scale circulation changes in this region are strongly influenced by the tropical Pacific. Further, we observe increased coarse particle deposition over the past 50 years, consistent with observations that the SH westerlies have been shifting southward and intensifying in recent decades. © Author(s) 2014. CC Attribution 3.0 License. Source
Robins J.G.,U.S. Department of Agriculture |
Jensen K.B.,U.S. Department of Agriculture |
Jones T.A.,U.S. Department of Agriculture |
Waldron B.L.,U.S. Department of Agriculture |
And 6 more authors.
Rangeland Ecology and Management | Year: 2013
The choice of plant materials is an important component of revegetation following disturbance. To determine the utility and effectiveness of various perennial grass species for revegetation on varied landscapes, a meta analysis was used to evaluate the stand establishment and persistence of 18 perennial cool-season grass species in 34 field studies in the Intermountain and Great Plains regions of the United States under monoculture conditions. Combined across the 34 studies, stand establishment values ranged from 79% to 43% and stand persistence values ranged from 70% to 0%. Intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D. R. Dewey), tall wheatgrass (Thinopyrum ponticum [Podp.] Z.-W. Liu & R.-C. Wang), crested wheatgrass (Agropyron spp.), Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy), and meadow brome (Bromus riparius Rehmann) possessed the highest stand establishment (≥ 69%). There were no significant differences among the 12 species with the largest stand persistence values. Basin wildrye (Leymus cinereus (Scribn. & Merr.) Á. Löve), Altai wildrye (Leymus angustus [Trin.] Pilg.), slender wheatgrass (Elymus trachycaulus [Link] Gould ex Shinners), squirreltail (Elymus spp.), and Indian ricegrass (Achnatherum hymenoides [Roem. & Schult.] Barkworth) possessed lower stand persistence (≤ 32%) than the majority of the other species, and Indian ricegrass (0%) possessed the lowest stand persistence of any of the species. Correlations between environmental conditions and stand establishment and persistence showed mean annual study precipitation to have the most consistent, although moderate effect (r = ∼0.40) for establishment and persistence. This relationship was shown by the relatively poor stand establishment and persistence of most species at sites receiving less than 310 mm of annual precipitation. These results will be a tool for land managers to make decisions concerning the importance of stand establishment, stand persistence, and annual precipitation for revegetation projects on disturbed sites. © 2013 The Society for Range Management. Source
Tilak A.S.,University of Birmingham |
Ojewole S.,Invensys |
Williford C.W.,University of Mississippi |
Fox G.A.,Oklahoma State University |
And 2 more authors.
Journal of Environmental Quality | Year: 2013
Manganese oxide (MnOx(s)) occurs naturally in soil and has a highaffinity for trace metals adsorption. In this work, we quantifiedthe factors (pH; flow rate; use of oxidants such as bleach, H2O2,and O3; initial Mn(II) concentrations; and two types of geologicmedia) affecting MnOx(s) coatings onto Ottawa and aquifer sandusing batch and column experiments. The batch experimentsconsisted of manual and automated titration, and the columnexperiments mimicked natural MnOx(s) adsorption and oxidationcycles as a strategy for in situ adsorption. A Pb solution of 50 mgL-1 was passed through MnOx(s)-coated sand at a flow rate of 4 mLmin-1 to determine its adsorption capacity. Batch experimentalresults showed that MnOx(s) coatings increased from pH 6 to 8,with maximum MnOx(s) coating occurring at pH 8. RegardingMnOx(s) coatings, bleach and O3 were highly effective comparedwith H2O2. The Ottawa sand had approximately twice the MnOx(s)coating of aquifer sand. The sequential increase in initial Mn(II)concentrations on both sands resulted in incremental buildup of MnOx(s). The automated procedure enhanced MnOx(s) coatings by 3.5 times compared with manual batch experiments. Column resultsshowed that MnOx(s) coatings were highly dependent on initial Mn(II) and oxidant concentrations, pH, flow rate, number of cycles(h), and the type of geologic media used. Manganese oxide coatingexceeded 1700 mg kg-1 for Ottawa sand and 130 mg kg-1 for aquifersand. The Pb adsorption exceeded 2200 mg kg-1 for the Ottawa sandand 300 mg kg-1 for the aquifer sand. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. Source
Stearns L.A.,University of Kansas |
Hamilton G.S.,University of Maine, United States |
Van Der Veen C.J.,University of Kansas |
Finnegan D.C.,USACE Cold Regions Research and Engineering Laboratory |
And 3 more authors.
Journal of Geophysical Research F: Earth Surface | Year: 2015
Hubbard Glacier, located in southeast Alaska, is the world's largest nonpolar tidewater glacier. It has been steadily advancing since it was first mapped in 1895; occasionally, the advance creates an ice or sediment dam that blocks a tributary fjord (Russell Fiord). The sustained advance raises the probability of long-term closure in the near future, which will strongly impact the ecosystem of Russell Fiord and the nearby community of Yakutat. Here, we examine a 43 year record of flow speeds and terminus position to understand the large-scale dynamics of Hubbard Glacier. Our long-term record shows that the rate of terminus advance has increased slightly since 1895, with the exception of a slowed advance between approximately 1972 and 1984. The short-lived closure events in 1986 and 2002 were not initiated by perturbations in ice velocity or environmental forcings but were likely due to fluctuations in sedimentation patterns at the terminus. This study points to the significance of a coupled system where short-term velocity fluctuations and morainal shoal development control tidewater glacier terminus position. ©2015. The Authors. Source