The use of principle component analyses in characterising trace and major elemental distribution in a 55 kyr peat deposit in tropical Australia: Implications to paleoclimate     

Joanne Muller  Malin Kylander  Antonio Martinez-Cortizas  Dominik Weiss  Kevin Blake  Raquel Garcia-Sanchez 《Geochimica et cosmochimica acta》2008,72(2):449-463

The Lynch’s Crater peat deposit in NE-Australia is a sensitive environmental archive located in the tropical Southern Hemisphere. This unique deposit illustrates that local and regional changes had a profound effect on the local Australian ecosystem over the past 55 kyr. To obtain a proxy of past climate changes, trace and major element geochemistry analyses were applied to a 13 m peat core from the crater. Principle component analysis (PCA) was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements. For example, Sc, Al, Cu, and Pb were found to be related to increased erosion of the basin soils, and from this, several periods of significant flux from atmospheric input and/or terrigenous run-off were identified. Geochemically mobile elements during rock weathering and pedogenesis, such as Mg, Ca, and Sr helped to identify the peat ombrotrophic-minerotrophic boundary at ∼1.5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit. Arsenic and V comparisons between the peat record (high concentrations in some peat sections) and in local basin rocks (very low concentrations), suggested the presence of a long range, atmospheric dust source early in the formation of the mire. The Lynch’s Crater peat record presents a continuous record of environmental change in tropical Australia and contributes new understanding to geochemical processes in peatlands.  相似文献   

Abundance, distribution and patch formation of zooplankton     

Gustav-Adolf Paffenhfer  Byron K. Sherman  Thomas N. Lee 《Progress in Oceanography》1987,19(3-4)

The goal of studies described here was to determine the responses of zooplankton taxa to phytoplankton patches which develop in and near intrusions of cold, nutrient-rich Gulf Stream water. To achieve this goal we determined the horizontal and vertical distributions of abundant mesozooplankton taxa on the south-eastern continental shelf of the USA between 29°30′ and 31°N. The study period was from June 23 to August 16, 1981. Highest concentrations of zooplankton usually occurred in and near patches of phytoplankton. Increased phytoplankton appeared to trigger the formation of patches of the calanoid copepod Temora turbinata and the cyclopoid copepods Oithona spp. and Oncaea spp. The patches of zooplankton had greater alongshore than cross-shelf dimensions. T. turbinata responded rapidly to increased concentrations of phytoplankton by reproducing and aggregating in and above intruded waters. Oithonidae which were often, but not always, abundant in phytoplankton patches eventually attained high concentrations over most of the middle and part of the inner shelf. Their concentration and that of Oncaeidae increased steadily. Oncaeidae were not abundant in recently upwelled waters, as was T. turbinata but reached high concentrations in older intrusions when the abundance of T. turbinata remained level or decreased slowly. Both cyclopoid taxa are thought to reproduce slowly (egg sacs) compared to T. turbinata. Another taxon, the doliolids, became abundant far more rapidly in intruded waters (by asexual reproduction) than did the other three taxa. Doliolids were the most opportunistic intrusion zooplankton form. They do not regularly occur in low abundance on the shelf, as do the three copepod taxa, but develop in pulses in regions where T. turbinata and Oncaea are not abundant. Of the four taxa studied the abundance of doliolids increased and decreased most rapidly, whereas Oithona and Oncaea increased slowly and did not decrease during the study period. T. turbinata and Oncaea were most abundant at 60% of all stations in the intruding water. Doliolids and Oithona on the other hand, were mostly in the thermocline and intrusion. Whereas phytoplankton patches, which developed in intrusions, were physically induced (PAFFENHÖFER and LEE, 1988), patches of zooplankton were biologically induced.  相似文献   

Coping with disaster: Rehabilitating coastal livelihoods and communities   总被引：4，自引：0，他引：4  

Robert S. Pomeroy  Blake D. Ratner  Stephen J. Hall  Jate Pimoljinda  V. Vivekanandan 《Marine Policy》2006,30(6):786-793

This paper examines lessons from past approaches to natural disasters, as well as early lessons from the post-2004 Asian tsunami rehabilitation, to draw out general principles for rehabilitating livelihoods in poor coastal communities. We contend that avoiding the mistakes of the past requires: (1) a framework for understanding the diversity of coastal people's livelihood strategies and the sources of their vulnerability, (2) a process for designing interventions that build on this understanding in order to strengthen and revitalize coastal communities, including a means of assessing and selecting the most promising livelihood options, and (3) a focus on the longer-term challenge of building future resilience and sustainability in the communities by addressing the root causes of vulnerability.  相似文献   

Ratios of stable carbon isotopes in some High Arctic plants and lake sediments   总被引：1，自引：0，他引：1  

Weston Blake Jr. 《Journal of Paleolimnology》1991,6(2):157-166

¹³C/¹²C ratios for a number of High Arctic vascular plants (51 determinations), mosses (11), and freshwater algae (11) show considerable variation, particularly among the freshwater algae (range from-6.9 to -36.3). In some cases the stable carbon ratios on modern and fossil materials provide guidance as to whether marine waters formerly occupied a given pond or lake basin. In other cases the ¹³C values for algae collected along the present-day shore of a pond or lake bear no relation to the values obtained on constituents preserved within the bottom sediments, suggesting that major changes have occurred in the last few thousand years.Geological Survey of Canada Contribution No. 17291. Contribution No. 41 from the Cape Herschel Project.  相似文献   

1957-1996台风对中国降水的影响   总被引：15，自引：0，他引：15  

Ren Fumin  Byron Gleason  David Easterling 《大气科学进展》2002,19(5):943-952

台风活动中国气候的重要特点之一，它能带来大量降水并造成严重的财产损失。在一些地区，台风降水甚至可以在总降水量中占很大比例。本文目的是研究那些对中国产生影响的台风并重点关注台风对中国降水的影响。文中涉及四个方面的工作。首先，研究了影响中国台风的频率，结果表明台风影响的主要季节为5－11月，尤其以7－9月频繁；在过去40年中影响台风的频率没有明显的变化趋势。第二，对台站台风降水的气候特征分析结果显示，海南和东南沿海地区受台风的影响最大，而且长江以南大部地区每年都受到台风的影响；另外，影响区域大部分地区的台风降水在过去40年中表现出下降的趋势，但是只有东北地区南部这种趋势是显著的。第三，对台风个例的分析表明，个例降水总量和影响面积之间存在着显著的线性关系。最后，对台风造成的中国范围降水总量进行了分析，初步结果显示台风降水总量在1957－1996年间显著减少。  相似文献   

Response of the cladoceran community to trophic state change in Lake Apopka, Florida     

Byron C. Shumate  Claire L. Schelske  Thomas L. Crisman  William F. Kenney 《Journal of Paleolimnology》2002,27(1):71-77

A paleolimnological evaluation of cladoceran microfossils was initiated to study limnological changes in Lake Apopka, a large (125 km²), shallow (mean depth = 1.6 m), warm, polymictic lake in central Florida. The lake switched from macrophyte to algal dominance in the late 1940s, creating a Sediment Discontinuity Layer (SDL) that can be visually used to separate sediments derived from macrophytes and phytoplankton. Cladoceran microfossils were enumerated as a means of corroborating extant eutrophication data from the sediment record. Inferences about the timing and trajectory of eutrophication were made using the cladoceran-based paleo-reconstruction. The cladoceran community of Lake Apopka began to change abruptly in both total abundance and relative percent abundance just before the lake shifted from macrophyte to algal dominance. Alona affinis, a mud-vegetation associated cladoceran, disappeared before the SDL was formed. Planktonic and benthic species also began to increase below the SDL, indicating an increase in production of both planktonic and benthic species. Chydorus cf. sphaericus, an indicator of nutrient loading, increased relative to all other cladocerans beginning in the layer below the SDL and continuing upcore. Changes in the transitional sediment layer formed before the lake switched to phytoplankton dominance, including an increase in total phosphorus concentration, suggest a more gradual eutrophication process than previously reported. Data from this study supported conclusions from other paleolimnological studies that suggested anthropogenic phosphorus loading was the key factor in the hypereutrophication of Lake Apopka.  相似文献   

Ion microprobe measurements of O/O ratios of phosphate minerals in the Martian meteorites ALH84001 and Los Angeles     

James P. Greenwood  Ruth E. Blake 《Geochimica et cosmochimica acta》2003,67(12):2289-2298

Oxygen isotope ratios of merrillite and chlorapatite in the Martian meteorites ALH84001 and Los Angeles have been measured by ion microprobe in multicollector mode. δ¹⁸O values of phosphate minerals measured in situ range from ∼3 to 6‰, and are similar to Martian meteorite whole-rock values, as well as the δ¹⁸O of igneous phosphate on Earth. These results suggest that the primary, abiotic, igneous phosphate reservoir on Mars is similar in oxygen isotopic composition to the basaltic phosphate reservoir on Earth. This is an important first step in the characterization of Martian phosphate reservoirs for the use of δ¹⁸O of phosphate minerals as a biomarker for life on Mars. Cumulative textural, major-element, and isotopic evidence presented here suggest a primary, igneous origin for the phosphates in Los Angeles and ALH84001; textural and chemical evidence suggests that phosphates in ALH84001 were subsequently shock-melted in a later event.  相似文献   

Using Hydrogeochemical Methods To Evaluate Complex Quaternary Subsurface Stratigraphy Block Island,Rhode Island,USA     

Anne I. Veeger  Byron D. Stone 《Hydrogeology Journal》1996,4(4):69-82

One of the major problems in hydrogeologic investigations of glaciated regions is the determination of complex stratigraphic relationships in the subsurface where insufficient information is available from drilling and geophysical records. In this paper, chemical characteristics of groundwater were used to identify stratigraphic changes in glacial deposits that were previously inferred on Block Island, Rhode Island, USA, an emergent remnant of the late Wisconsinan terminal moraine, located approximately 16 km south of the Rhode Island mainland. Two chemically distinct water types are recognized on the island: 1) high-iron, characterized by dissolved silica levels in excess of 20 mg/L, bicarbonate greater than 30 mg/L and dissolved iron ranging from 1-20 mg/L; and 2) low-iron, characterized by dissolved silica levels below 16 mg/L, bicarbonate less than 30 mg/L, and less than 0.3 mg/L dissolved iron. The spatial distribution of iron-bearing minerals and organic matter and the resulting redox conditions are believed to control the occurrence of high-iron groundwater. The high-iron waters occur almost exclusively in the eastern half of the island and appear to coincidence with the presence of allochthonous blocks of Cretaceous-age coastal-plain sediments that were incorporated into Pleistocene-age deposits derived from the Narragansett Bay-Buzzard's Bay lobe of the Late Wisconsinan Laurentide ice sheet. The low-iron waters occur in the western half of the island, where the occurrence of these Cretaceous-age blocks is rare and the sediments are attributed to a sublobe of the Hudson-Champlain lobe of the Late Wisconsinan ice-sheet. RÉSUMÉ: L'un des principaux problèmes dans les études hydrogeologiques des régions qui ont été englacées est la définition des relations stratigraphiques complexes sous la surface, lá où les informations fournies par les forages et par la géophysique sont insuffisantes. Dans l'exemple traité, les caractéristiques chimiques de l'eau souterraine sont utilisées pour identifier les variations stratigraphiques dans les dépôts glaciaires qui avaient auparavant été supposées, sur l'île de Block (Rhode Island), restes émergeant d'une moraine terminale du Wisconsinien récent, situé à environ 16 km au sud de Rhode Island. Deux types d'eau chimiquement distincts ont été reconnus dans l'île: 1) à fortes teneurs en fer, caractérisées par des concentrations en silice supérieures à 20 mg/L, en bicarbonates supérieures à 30 mg/L et en fer comprises entre 1 et 20 mg/L; et 2) à faibles teneurs en fer, marquées par des concentrations en silice inférieures à 16 mg/L, en bicarbonate inférieures à 30 mg/L et en fer dissous inférieures à 0.3 mg/L. La distribution spatiale des minéraux riches en fer et de la matière organique et les conditions redox résultantes contrôlent probablement la présence de fer dans les eaux souterraines à fortes concentrations. Les eaux à fortes teneurs en fer sont connues presque exclusivement dans la moitié orientale de l'île et semblent coïncider avec la présence de blocs allochtones provenant des sédiments côtiers crétacés, introduits dans les formations pléistocènes liées au lobe glaciaire des baies de Narragansett et du Busard de la calotte glaciaire laurentide du Wisconsinien récent. Les eaux à faibles teneurs en fer apparaissent dans la moitié occidentale de l'île, là où ces blocs de Crétacé sont rares et où les sédiments sont attrbués à une digitation du lobe de l'Hudson-Champlain de la calotte glaciaire du Wisconsinien récent. RESUMEN: Uno de los mayores problemas en la investigación hidrogeológica en regiones glaciares es la determinación de las complejas relaciones estratigráficas en el subsuelo, donde la información procedente de registros de perforaciones y de geofísica no es suficiente. En este artículo, se han usado las características químicas del agua subterránea para identificar unos cambios estratigráficos que se habían predicho previamente en unos depósitos glaciares en Block Island, Rhode Island (Estados Unidos), un remanente emergente de la morrena terminal del Winsconsiniense tardío, situada unos 16 km al sur de la Rhode Island continental. En la isla se encuentran dos tipos de agua distintos: 1) de alto contenido en hierro, caracterizada por niveles de sílice disuelto superando los 20 mg/L, bicarbonatos por encima de 30 mg/L y hierro disuelto oscilando entre 1-20 mg/L; y 2) de bajo contenido en hierro, caracterizada por niveles de sílice disuelto inferiores a 16 mg/L, bicarbonatos por debajo de 30 mg/L y menos de 0.3 mg/L de hierro disuelto. La distribución espacial de los minerales ricos en hierro y de la materia orgánica, así como las condiciones redox resultantes se supone que condicionan la presencia de aguas de alto contenido en hierro. Estas aguas aparecen casi exclusivamente en la mitad oriental de la isla y parecen coincidir con la presencia de bloques alóctonos de sedimentos costeros, de edad cretácica, que se incorporaron a los depósitos de edad pleistocena procedentes del lóbulo de la Bahía de Narragansett-Bahía de Buzzard, correspondiente a la capa glaciar del Winsconsiniense-Lauréntido tardío. Las aguas de bajo contenido en hierro aparecen en la mitad occidental de la isla, donde la presencia de estos sedimentos de edad cretácica es rara y los sedimentos se suponen procedentes de un sublóbulo del lóbulo de Hudson-Camplain, correspondiente a la capa glaciar del Winsconsiniense tardío.  相似文献   

Review of challenges of and practices for sustainable management of mountain flood hazards     

Desirée Tullos  Elizabeth Byron  Gerald Galloway  Jayantha Obeysekera  Om Prakash  Yung-Hsin Sun 《Natural Hazards》2016,83(3):1763-1797

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Wind-Driven Dissolved Organic Matter Dynamics in a Chesapeake Bay Tidal Marsh-Estuary System     

J. Blake Clark  Wen Long  Maria Tzortziou  Patrick J. Neale  Raleigh R. Hood 《Estuaries and Coasts》2018,41(3):708-723

Controls on organic matter cycling across the tidal wetland-estuary interface have proved elusive, but high-resolution observations coupled with process-based modeling can be a powerful methodology to address shortcomings in either methodology alone. In this study, detailed observations and three-dimensional hydrodynamic modeling are used to examine biogeochemical exchanges in the marsh-estuary system of the Rhode River, MD, USA. Analysis of observations near the marsh in 2015 reveals a strong relationship between marsh creek salinity and dissolved organic matter fluorescence (fDOM), with wind velocity indirectly driving large amplitude variation of both salinity and fDOM at certain times of the year. Three-dimensional model results from the Finite Volume Community Ocean Model implemented for the wetland system with a new marsh grass drag module are consistent with observations, simulating sub-tidal variability of marsh creek salinity. The model results exhibit an interaction between wind-driven variation in surface elevation and flow velocity at the marsh creek, with northerly winds driving increased freshwater signal and discharge out of the modeled wetland during precipitation events. Wind setup of a water surface elevation gradient axially along the estuary drives the modeled local sub-tidal flow and thus salinity variability. On sub-tidal time scales (>36 h, <1 week), wind is important in mediating dissolved organic matter releases from the Kirkpatrick Marsh into the Rhode River.  相似文献