Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: IV. Lacustrine paleoecology     

Manuel?R.?Palacios-FestEmail author  Simone?R.?Alin  Andrew?S.?Cohen  Brandon?Tanner  Heather?Heuser 《Journal of Paleolimnology》2005,34(1):51-71

Fossil invertebrates from cores collected in Lake Tanganyika provide a record of probable nearshore ecological response to recent watershed deforestation and sediment erosion in several East African watersheds. We compared paleoecological profiles (primarily from ostracodes) from watersheds spanning a range of sizes and present-day deforestation disturbance levels to understand the timing and magnitude of faunal changes, and their relationship in time to terrestrially-derived disturbance indicators. Profiles from the Lubulungu and Nyasanga/Kahama Rivers (Tanzania) provide a record of faunal variability in watersheds that are currently undisturbed with respect to deforestation. These records indicate continuous faunal turnover through time. However, this pattern of turnover is accompanied by relatively high levels of diversity throughout the record, with no wholesale extinction events. Ostracode taphonomic data and other fossil abundance data from the Lubulungu area provide strong evidence in support of at least two episodes of lower lake levels, associated with episodes of Late Holocene aridity. Records from deltas of disturbed watersheds at the Kabesi River (Tanzania) and those of Northern Burundi all show a combination of profound and abrupt faunal turnover, in some cases accompanied by local extinction and establishment of a few dominant taxa. At the Mwamgongo River delta, fed from a very small, disturbed watershed, species turnover was subtler. In disturbed watershed cores showing abrupt faunal changes the transitions mostly occurred in the late 19th to early 20th centuries, predating the major mid-20th century increase in sediment mass accumulation rates, with the latter only correlated with changing fossil abundance and flux. However, the earlier faunal community changes are contemporaneous with both palynological and geochemical changes in the core profiles indicative of changing land-use patterns. This suggests that lacustrine ecosystem response to deforestation was a two-stage process, with an earlier phase of response to changing quality of sediments or dissolved matter being discharged from the watershed, and a subsequent phase responding to increased quantity of sediment.  相似文献   

Fine-scale stratigraphy in proximal and distal deposits of sediment dispersal systems in the East China Sea     

C.A Nittrouer  D.J DeMaster  B.A McKee 《Marine Geology》1984,61(1):13-24

The East China Sea contains the proximal deposit of the Changjiang (Yangtze) dispersal system and the distal deposit of the Huangho (Yellow) dispersal system. Despite similarity of sediment characteristics and oceanic setting, the two deposits show a significant difference in fine-scale stratigraphy. The proximal Changjiang deposit is characterized by physically stratified mud and the distal Huangho deposit is characterized by homogeneous mud. The difference in fine-scale stratigraphy is explained by the ratio of mixing rate to accumulation rate, which is much larger for the distal Huangho deposit (～ 17) than for the proximal Changjiang deposit (? 1); a larger ratio allows biological mixing to destroy physical stratification. With increasing distance away from the mouth of a major river, generally mixing rate increases and accumulation rate decreases along the sediment dispersal system. Therefore, the ratio of mixing rate to accumulation rate should increase and sedimentary structure should change from physically stratified to homogeneous. At the leading edge (extreme distal portion) of a prograding mud deposit, the relatively rapid mixing and slow accumulation can cause a transitional boundary between the mud and the ambient sediment (which is transgressive sand in the East China Sea). For a prograding mud deposit of a major dispersal system, sedimentary sequences should reveal the following upward changes: a transitional boundary with underlying sediment, homogeneous sediment representing distal deposits, successively more stratified sediment representing proximal deposits.  相似文献   

Constructing a coherent joint prior while respecting biological realism: application to marine mammal stock assessments   总被引：1，自引：0，他引：1  

Brandon  John R.; Breiwick  Jeffrey M.; Punt  Andre E.; Wade  Paul R. 《ICES Journal of Marine Science》2007,64(6):1085-1100

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Impact of Partially Cemented and Non-persistent Natural Fractures on Hydraulic Fracture Propagation     

Wei Fu  Brandon C. Ames  Andrew P. Bunger  Alexei A. Savitski 《Rock Mechanics and Rock Engineering》2016,49(11):4519-4526

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Reducing zero-point systematics in dark energy supernova experiments     

L. Faccioli  A.G. Kim  R. Miquel  G. Bernstein  A. Bonissent  M. Brown  W. Carithers  J. Christiansen  N. Connolly  S. Deustua  D. Gerdes  L. Gladney  G. Kushner  E.V. Linder  S. McKee  N. Mostek  H. Shukla  A. Stebbins  C. Stoughton  D. Tucker 《Astroparticle Physics》2011,34(12):847-857

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Embedding scale: new thinking of scale in machine learning and geographic representation     

Yuan  May  McKee  Arlo 《Journal of Geographical Systems》2022,24(3):501-524

Journal of Geographical Systems - Concepts of scale are at the heart of diverse scientific endeavors that seek to understand processes and how observations and analyses influence our understanding....  相似文献   

Holocene valley-floor deposition and incision in a small drainage basin in western Colorado, USA     

Lawrence S. Jones  Margaret Rosenburg  Kathleen McKee  Jenna Hunter 《Quaternary Research》2010,74(2):199-206

The valley floor of a 33.9 km² watershed in western Colorado experienced gradual sedimentation from before ∼ 6765 to ∼ 500 cal yr BP followed by deep incision, renewed aggradation, and secondary incision. In contrast, at least four terraces and widespread cut-and-fill architecture in the valley floor downstream indicate multiple episodes of incision and deposition occurred during the same time interval. The upper valley fill history is atypical compared to other drainages in the Colorado Plateau.One possible reason for these differences is that a bedrock canyon between the upper and lower valley prevented headward erosion from reaching the upper valley fill. Another possibility is that widespread, sand-rich, clay-poor lithologies in the upper drainage limited surface runoff and generally favored alluviation, whereas more clay-rich lithologies in the lower drainage resulted in increased surface runoff and more frequent incision. Twenty-two dates from valley fill charcoal indicate an approximate forest fire recurrence interval of several hundred years, similar to that from other studies in juniper-piñon woodlands. Results show that closely spaced vertical sampling of alluvium in headwater valleys where linkages between hillslope processes and fluvial activity are relatively direct can provide insight about the role of fires in alluvial chronologies of semi-arid watersheds.  相似文献   

Alkyl amides in two organic-rich anoxic sediments: A possible new abiotic route for N sequestration     

Georgina A. McKee 《Geochimica et cosmochimica acta》2010,74(22):6436-6450

Fixed nitrogen (N) plays an integral role in global cycling; while most is recycled to refuel primary productivity, a small fraction escapes to be preserved and stabilised in sediments. Despite decades of research, the functionality and reactivity of this sequestered organic N has been poorly understood. This study was undertaken to shed light on this problem by characterising the bulk sediment organic matter using nuclear magnetic resonance (NMR), followed by molecular level analysis using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We studied two organic-rich anaerobic sediments, one from a freshwater system and another from a marine paralic basin. Mangrove Lake, Bermuda (marine) and Mud Lake, Florida (freshwater) have been shown in past studies to contain high levels of N-containing organic matter. Our resulting multidimensional NMR data suggests the existence of a new type of amide functionality in both these lake sediments, and we investigated this further using FT-ICR-MS and gas chromatography mass spectrometry (GC-MS). FT-ICR-MS confirmed the existence of homologous series of CHNO containing compounds, whose structures are verified using GC-MS as alkyl amides. Model reactions involving naturally occurring esters and ammonia suggest the source of alkyl amides to be amidation of esters with sedimentary ammonia derived from anaerobic degradation of organic matter. This expands upon previous hypotheses for preservation of amide containing compounds that call upon biological/abiological protection of proteins and peptides or the formation of refractory nitrogenous adducts.  相似文献   

Imprints of mass accretion on properties of galaxy clusters     

Andreas Faltenbacher  Brandon Allgood  Stefan Gottlöber  Gustavo Yepes  Yehuda Hoffman 《Monthly notices of the Royal Astronomical Society》2005,362(3):1099-1108

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Bandlimited implicit Runge–Kutta integration for Astrodynamics     

Ben K. Bradley  Brandon A. Jones  Gregory Beylkin  Kristian Sandberg  Penina Axelrad 《Celestial Mechanics and Dynamical Astronomy》2014,119(2):143-168

We describe a new method for numerical integration, dubbed bandlimited collocation implicit Runge–Kutta (BLC-IRK), and compare its efficiency in propagating orbits to existing techniques commonly used in Astrodynamics. The BLC-IRK scheme uses generalized Gaussian quadratures for bandlimited functions. This new method allows us to use significantly fewer force function evaluations than explicit Runge–Kutta schemes. In particular, we use a low-fidelity force model for most of the iterations, thus minimizing the number of high-fidelity force model evaluations. We also investigate the dense output capability of the new scheme, quantifying its accuracy for Earth orbits. We demonstrate that this numerical integration technique is faster than explicit methods of Dormand and Prince 5(4) and 8(7), Runge–Kutta–Fehlberg 7(8), and approaches the efficiency of the 8th-order Gauss–Jackson multistep method. We anticipate a significant acceleration of the scheme in a multiprocessor environment.  相似文献