Abundance, distribution and patch formation of zooplankton

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.     

1957-1996台风对中国降水的影响

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。     

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

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.     

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

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.     

Precise orbit determination for the GRACE mission using only GPS data

The GRACE (gravity recovery and climate experiment) satellites, launched in March 2002, are each equipped with a BlackJack GPS onboard receiver for precise orbit determination and gravity field recovery. Since launch, there have been significant improvements in the background force models used for satellite orbit determination, most notably the model for the geopotential. This has resulted in significant improvements to orbit accuracy for very low altitude satellites. The purpose of this paper is to investigate how well the orbits of the GRACE satellites (about 470 km in altitude) can currently be determined using only GPS data and based on the current models and methods. The orbit accuracy is assessed using a number of tests, which include analysis of orbit fits, orbit overlaps, orbit connecting points, satellite Laser ranging residuals and K-band ranging (KBR) residuals. We show that 1-cm radial orbit accuracy for the GRACE satellites has probably been achieved. These precise GRACE orbits can be used for such purposes as improving gravity recovery from the GRACE KBR data and for atmospheric profiling, and they demonstrate the quality of the background force models being used.     

A three-level framework for multi-risk assessment

The effective management of the risks posed by natural and man-made hazards requires all relevant threats and their interactions to be considered. This paper proposes a three-level framework for multi-risk assessment that accounts for possible hazard and risk interactions. The first level is a flow chart that guides the user in deciding whether a multi-hazard and risk approach is required. The second level is a semi-quantitative approach to explore if a more detailed, quantitative assessment is needed. The third level is a detailed quantitative multi-risk analysis based on Bayesian networks. Examples that demonstrate the application of the method are presented.     

Reducing errors in the GRACE gravity solutions using regularization

The nature of the gravity field inverse problem amplifies the noise in the GRACE data, which creeps into the mid and high degree and order harmonic coefficients of the Earth’s monthly gravity fields provided by GRACE. Due to the use of imperfect background models and data noise, these errors are manifested as north-south striping in the monthly global maps of equivalent water heights. In order to reduce these errors, this study investigates the use of the L-curve method with Tikhonov regularization. L-curve is a popular aid for determining a suitable value of the regularization parameter when solving linear discrete ill-posed problems using Tikhonov regularization. However, the computational effort required to determine the L-curve is prohibitively high for a large-scale problem like GRACE. This study implements a parameter-choice method, using Lanczos bidiagonalization which is a computationally inexpensive approximation to L-curve. Lanczos bidiagonalization is implemented with orthogonal transformation in a parallel computing environment and projects a large estimation problem on a problem of the size of about 2 orders of magnitude smaller for computing the regularization parameter. Errors in the GRACE solution time series have certain characteristics that vary depending on the ground track coverage of the solutions. These errors increase with increasing degree and order. In addition, certain resonant and near-resonant harmonic coefficients have higher errors as compared with the other coefficients. Using the knowledge of these characteristics, this study designs a regularization matrix that provides a constraint on the geopotential coefficients as a function of its degree and order. This regularization matrix is then used to compute the appropriate regularization parameter for each monthly solution. A 7-year time-series of the candidate regularized solutions (Mar 2003–Feb 2010) show markedly reduced error stripes compared with the unconstrained GRACE release 4 solutions (RL04) from the Center for Space Research (CSR). Post-fit residual analysis shows that the regularized solutions fit the data to within the noise level of GRACE. A time series of filtered hydrological model is used to confirm that signal attenuation for basins in the Total Runoff Integrating Pathways (TRIP) database over 320 km radii is less than 1 cm equivalent water height RMS, which is within the noise level of GRACE.