Isotopic composition of nitrogen: implications for the past history of mars' atmosphere

Models are presented for the past history of nitrogen on Mars based on Viking measurements showing that the atmosphere is enriched in (15)N. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N(2) and by dissociative recombination of N(2)(+). The initial partial pressure of N(2) should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO(2) and HNO(3).     

Pliocene and pleistocene hominid-bearing sites from west of lake turkana, kenya

Pliocene and Pleistocene fossil localities near the western shoreline of Lake Turkana, ranging in age between 1 million and 3.5 million years in age, have produced important new hominid specimens including most of a Homo erectus skeleton and a relatively complete early robust australopithecine cranium. The lacustrine, fluviatile, and terrestrial strata are designated the Nachukui Formation, which is subdivided into eight members. The distribution of sedimentary facies within the Nachukui Formation suggests that, as today, the Labur and Murua Rith ranges formed the western margin of the basin and were drained by eastward-flowing rivers that fed into the forerunner of the present lake or a major river system. There is also stratigraphic evidence for tectonic movement during the deposition of these sediments. Twenty-three of the tuffs observed in the succession occur also in the Koobi Fora Formation east of the lake and in the Shungura Formation of the lower Omo Valley and permit precise correlation among these three localities. Fortyseven fossiliferous sites from West Turkana have yielded more than 1000 specimens of 93 mammalian species. The mammalian fossils represent nine sequential assemblages that augment information about faunal and environmental change from elsewhere in the basin.     

Isotopic composition of strontium in volcanic rocks from oahu

Analysis of several well-documented specimens from each of the three volcanic series on Oahu gives the following mean ratios of Sr(87) to Sr(86): the Waianae series, 0.7030 +/- 0.00010 (sigma); the Koolau series, 0.70385+/- 0.00009 (sigma); and the Honolulu series, 0.7029 ++/- 0.00006 ( sigma). The mean ratio of Sr(87) to Sr(86) of the Koolau series specimens is significantly higher than the means of the other two series. With one exception, significant differences in Sr(87)/ Sr(86) within a series were not found, even though some large compositional differences existed.     

The variability of holocene climate change: evidence from varved lake sediments

Varved sediments from a lake near the present forest-prairie border in northwestern Minnesota provide an annual record of climate change for the last 10,400 years. Climate-sensitive mineral, chemical, and biological components show that the mid-Holocene dry interval between 8500 and 4000 years ago is asymmetrical and actually consists of two distinct drier pulses separated by a moister interval that lasted about 600 years. Cyclic fluctuations with periods of several hundred years were abrupt and persistent throughout the Holocene and are most clearly recorded within the two drier pulses.     

The agulhas current during the late pleistocene: analysis of modern faunal analogs

Analysis of micropaleontologic evidence in a deep-sea core in the south-west Indian Ocean indicates that the Agulhas Current was not a dominant feature of this region during glacial intervals. Interpretation of the fossil record, based on the analysis of modern faunal analogs, indicates that during glacial intervals the Agulhas Current was not the strong, year-round current that it is today. Evidence shows that during summer months a weak tropical current was present. During winter months the current was replaced by cool, high-salinity waters. This interpretation suggests that seasonal changes in circulation may have been more pronounced in the southwest Indian Ocean during glacial intervals than today.     

Aldrin: removal from lake water by flocculent bacteria

Floc-forming bacteria isolated from Lake Erie adsorb and concentrate aldrin from colloidal dispersion so that the settling of the bacterial flocs removes aldrin from the water phase. Contemporary sediments forming in Lake Erie contain aldrin and could adsorb more. The sediments consist of a conglomerate floc of bacteria, diatoms, and inorganic and detrital particles. Flocculent bacteria also adsorb microparticulates, and this adsorption capacity represents a mechanism for sediment formation and for the removal of suspended particles including aldrin from the water column.     

Isotopic composition of neodymium in waters from the drake passage

The isotopic composition of neodymium has been determined in seawaters from the Drake Passage. The Antarctic Circumpolar Current, which controls interocean mixing, flows through this passage. The parameter epsilon(Nd)(0) which is a function of the ratio of neodymium-143 to neodymium-144, is found to be uniform with depth at two stations with a value which is intermediate between the values for the Atlantic and the Pacific and indicates that the Antarctic Circumpolar current consists of about 70 percent Atlantic water. Cold bottom water from a site in the south central Pacific has the neodymium isotopic signature of the waters in the Drake Passage. By using a box model to describe the exchange of water between the Southern Ocean and the ocean basins to the north together with the isotopic results, an upper limit of approximately 33 million cubic meters per second is calculated for the rate of exchange between the Pacific and the Southern Ocean. Concentrations of samarium and neodymium were also determined and found to increase approximately linearly with depth. These results suggest that neodymium may be a valuable tracer in oceanography and may be useful in paleo-oceanographic studies.     

Tough times at la brea: tooth breakage in large carnivores of the late pleistocene

One million to two million years ago, most of today's large, predatory mammals coexisted with larger extinct species, such as saber-toothed cats and giant running bears. Comparisons of tooth fracture frequencies from modern and Pleistocene carnivores imply that predator-prey dynamics and interspecific interactions must have been substantially different 36,000 to 10,000 years ago. Tooth fracture frequencies of four Rancho La Brea species-dire wolf, coyote, saber-toothed cat, and American lion-were about three times that of extant carnivores. Consequently, these findings suggest that these species utilized carcasses more fully and likely competed more intensely for food than presentday large carnivores.     

Eutrophication and recovery in experimental lakes: implications for lake management

Combinations of phosphorus, nitrogen, and carbon were added to several small lakes in northwestern Ontario, Canada, at rates similar to those in many culturally eutrophied lakes. Phosphate and nitrate caused rapid eutrophication. A similar result was obtained with phosphate, ammonia, and sucrose, but recovery was almost immediate when phosphate additions only were discontinued. When two basins of one lake were fertilized with equal amounts of nitrate and sucrose, and phosphorus was also added to one of the basins, the phosphateenriched basin quickly became highly eutrophic, while the basin receiving only nitrogen and carbon remained at prefertilization conditions. These results, and the high affinity of sediments for phosphorus indicate that rapid abatement of eutrophication may be expected to follow phosphorus control measures.     

Uranium-series dating of sediments from searles lake: differences between continental and marine climate records

One of the major unresolved questions in Pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial delta(18)O marine record. Searles Lake in California, now a dry salt pan, is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 x 10(6) years. Uraniumseries dates on the salt beds range from 35 x 10(3) to 231x 10(3) years. This range of dates allows identification of lake-sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3/4 boundary back to the 8/9 boundary. The 5/6 boundary coincided with a deepening of the lake, but the analogous 1/2 boundary coincided with desiccation. The 3/4, 4/5, 6/7, 7/8, and 8/9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate. These hydrologic results demonstrate that the continental paleoclimate record at this mid-latitude site does not mimic the marine record.     

Circum-pacific late cenozoic structural rejuvenation: implications for sea floor spreading

The hypothesis of sea floor spreading and lithosphere plates seems to unify the origins of both oceanic ridges and volcanic arc-trench systems; therefore knowledge of well-known land areas should shed light upon sea floor tectonics. Impressive evidence of a major mid-Cenozoic discontinuity in the tectonic history of circum-Pacific land areas suggests a roughly synchronous change in sea floor development, more evidence for which may be anticipated in the future.     

Global water resources: vulnerability from climate change and population growth

The future adequacy of freshwater resources is difficult to assess, owing to a complex and rapidly changing geography of water supply and use. Numerical experiments combining climate model outputs, water budgets, and socioeconomic information along digitized river networks demonstrate that (i) a large proportion of the world's population is currently experiencing water stress and (ii) rising water demands greatly outweigh greenhouse warming in defining the state of global water systems to 2025. Consideration of direct human impacts on global water supply remains a poorly articulated but potentially important facet of the larger global change question.     

From “old school” to “farm-to-school”: Neoliberalization from the ground up

Farm-to-school (FTS) programs have garnered the attentions and energies of people in a diverse array of social locations in the food system and are serving as a sort of touchstone for many in the alternative agrifood movement. Yet, unlike other alternative agrifood initiatives, FTS programs intersect directly with the long-established institution of the welfare state, including its vestiges of New Deal farm programs and public entitlement. This paper explores how FTS is navigating the liminal terrain of public and private initiative, particularly the ways in which it interfaces with neoliberalism as both a material and discursive project. It examines the political emergence of school food programs and finds that FTS is strikingly similar to traditional school programs in objectives, but differs in approach. Yet, in their efforts to fill in the gaps created by political and economic neoliberalization, FTS advocates are in essence producing neoliberal forms and practices afresh. These include those associated with contingent labor relationships, private funding sources, and the devolution of responsibility to the local, all of which have serious consequences for social equity. The paper also discusses how FTS programs are employing the rhetoric of neoliberal governmentality, including personal responsibility and individual success, consumerism, and choice. While these may be tactical choices used to secure funding in a competitive environment, they may also contribute to the normalization of neoliberalism, further circumscribing the possibilities of what can be imagined and created to solve social problems.     

Mississippian fossils from southern appalachian metamorphic rocks and their implications for late paleozoic tectonic evolution

Fossils of Periastron reticulatum Unger emended. Beck recovered from the Erin Slate of the Talladega slate belt of Alabama establish that these rocks have a Mississippian (Kinderhookian-Tournaisian) age. The Talladega slate belt, the southwestern extension of the western Blue Ridge belt, was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the Acadian orogeny. This fossil find indicates that metamorphism and deformation of the Talladega belt occurred after the Early Carboniferous (Alleghanian), requiring a reevaluation of tectonic interpretations of the southernmost Appalachians.     

Venus: implications from microwave spectroscopy of the atmospheric content of water vapor

From comparison of theoretical and observed microwave brightness temperatures of Venus at 1.35 centimeters, the center of a water-vapor line, we obtain an upper limit of 0.8 percent for the water-vapor mixing ratio in the lower atmosphere. This limit is consistent with the amount of water vapor detected by Venera 4, the existence of aqueous ice clouds, and a greenhouse effect caused by water vapor and carbon dioxide. The computed spectra suggest that a sensitive procedure for detection of water vapor is examination of the wavelength region between I and 1.4 centimeters.     

Late glacial climate record of midwestern United States from the hydrogen isotope ratio of lake organic matter

A hydrogen isotope time series obtained from an analysis of organic matter extracted from a lake core in Kalamazoo, southwestern Michigan, reveals four distinct isotope stages within the last 12,000 years that can be interpreted in terms of oscillations between cold and warm, dry climates. The most dramatic are a cold phase between 12,000 and 9000 years before present (B.P.), a warm, dry period between 8500 and 2000 years B.P., a cold period between 2000 and 1000 years B.P., and a warming trend since 1000 years B.P. The warming trend of the last 1000 years is comparable in magnitude to the mid-Holocene warm phase.     

Isotopic paleoceanography of the Caribbean and East pacific: role of panama uplift in late neogene time

Comparisons of carbon isotopic data on benthic foraminifera from Deep Sea Drilling Project sites 502 (western Caribbean) and 503 (eastern Pacific) indicate that the difference between the Atlantic and the Pacific in the per mil enrichment in carbon-13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago, when the difference reached the modern level (1 per mil). Comparisons of planktonic foraminiferal oxygen isotopic data for the Caribbean and the Pacific suggest that the salinity of Caribbean surface waters began increasing 4 million years ago, possibly in response to shoaling of the Panama isthmus. These results suggest that modern circulation patterns in the Caribbean and eastern Pacific developed by 3 million years ago in concert with changing tectonic, climatic, and biogeographic patterns.     

Calcium-41 concentration in terrestrial materials: prospects for dating of pleistocene samples

Calcium-41 has been suggested as a new tool for radiometric dating in the range of 10(5) to 10(6) years. The concentration of cosmogenic calcium-41 in natural samples of terrestrial origin has now been determined by high-sensitivity accelerator mass spectrometry after pre-enrichment in calcium-41 with an isotope separator. Ratios of calcium-41 to total calcium between 2 x 10(-14) and 3 x 10(-15) were measured for samples of contemporary bovine bone and from limestone deposits. Some prospects for the use of calcium-41 for dating Middle and Late Pleistocene bone and for other geophysical applications are discussed.