Paleohydrology of Andean saline lakes from sedimentological and isotopic records, Northwestern Argentina     

Blas Valero-Garcés  Antonio Delgado-Huertas  Norma Ratto  Ana Navas  Larry Edwards 《Journal of Paleolimnology》2000,24(3):343-359

The paleohydrological evolution of several high altitude, saline lakes located in the southernmost Altiplano (El Peinado and San Francisco basins, Catamarca province, NW Argentina) was reconstructed applying sedimentological, geochemical and isotopic techniques. Several playa lakes from the San Francisco basin (26° 56 S; 68° 08 W, 3800-3900 m a.s.l.) show evidence of a recent raise in the watertable that led to modern deposition of carbonate and diatomaceous muds. A 2 m - long core from El Peinado Lake (26° 29 59 S, 68°05 32 W, 3820 m a.s.l.) consists of calcitic crusts (unit 3), overlaid by an alternation of macrophyte-rich and travertine clast- rich, laminated muds (unit 2), and topped by travertine facies (unit 1). This sedimentary sequence illustrates a paleohydrological evolution from a subaerial exposure (unit 3) to a high lake stand (unit 2), and a subsequent smaller decrease in lake level (unit 1). The ¹³C_{organic matter}record also reflects the lake transgression between units 3 and 2. Although there is a general positive correlation between ¹⁸O_carbonate and salinity proxies (Na, Li and B content), the large data dispersion indicates that other factors besides evaporation effects control chemical and isotopic composition of lakewater. Consequently, the oxygen isotopic composition cannot be interpreted exclusively as an indicator of salinity or evaporation ratio. The degassing of CO₂ during groundwater discharge can explain the enriched ¹³C values for primary carbonates precipitated. The carbon budget in these high altitude, saline lakes seems to be controlled by physical rather than biological processes.The Altiplano saline lakes contain records of environmental and climatic change, although accurate ¹⁴C dating of these lacustrine sediments is hindered by the scarcity of terrestrial organic material, and the large reservoir effects. Sedimentologic evidence, a ²¹⁰Pb-based chronology, and a preliminary U/Th chronology indicate a very large reservoir effect in El Peinado, likely as a result of old groundwaters and large contributions of volcanic and geothermal ¹⁴C-free CO₂ to the lake system. Alternative chronologies are needed to place these paleorecords in a reliable chronological framework. A period of increased water balance in the San Francisco basin ended at about 1660 ± 82 yr B.P. (calendar yr U/Th age), and would correlates with the humid phase between 3000 and 1800 yr B.P detected in other sites of the southern Altiplano. Both, ²¹⁰Pb and preliminary U/Th dating favor a younger age for the paleohydrological changes in El Peinado. The arid period reflected by subaerial exposure and low lake levels in unit 3 would have ended with a large increase in effective moisture during the late 17th century. The increased lake level during deposition of unit 2 would represent the period between AD1650 - 1900, synchronous to the Little Ice Age. This chronological framework is coherent with other regional records that show an abrupt transition from more arid to more humid conditions in the early 17th century, and a change to modern conditions in the late 19th century. Although there are local differences, the Little Ice Age stands as a significant climatic event in the Andean Altiplano.  相似文献   

GPS sidereal filtering: coordinate- and carrier-phase-level strategies   总被引：6，自引：1，他引：6  

A. E. Ragheb  P. J. Clarke  S. J. Edwards 《Journal of Geodesy》2007,81(5):325-335

Multipath error is considered one of the major errors affecting GPS observations. One can benefit from the repetition of satellite geometry approximately every sidereal day, and apply filtering to help minimize this error. For GPS data at 1 s interval processed using a double-difference strategy, using the day-to-day coordinate or carrier-phase residual autocorrelation determined with a 10-h window leads to the steadiest estimates of the error-repeat lag, although a window as short as 2 h can produce an acceptable value with > 97% of the optimal lag’s correlation. We conclude that although the lag may vary with time, such variation is marginal and there is little advantage in using a satellite-specific or other time-varying lag in double-difference processing. We filter the GPS data either by stacking a number of days of processed coordinate residuals using the optimum “sidereal” lag (23 h 55 m 54 s), and removing these stacked residuals from the day in question (coordinate space), or by a similar method using double-difference carrier-phase residuals (observational space). Either method results in more consistent and homogeneous set of coordinates throughout the dataset compared with unfiltered processing. Coordinate stacking reduces geometry-related repeating errors (mainly multipath) better than carrier-phase residual stacking, although the latter takes less processing time to achieve final filtered coordinates. Thus, the optimal stacking method will depend on whether coordinate precision or computational time is the over-riding criterion.  相似文献   

Erratum to: “A robust surface matching technique for coastal geohazard assessment and management” [ISPRS J. Photogramm. Remote Sens. 63 (2008) 529–542]     

Pauline Miller  Jon Mills  Stuart Edwards  Paul Bryan  Stuart Marsh  Harvey Mitchell  Peter Hobbs 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(2):243-245

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Late Quaternary paleoclimate of western Alaska inferred from fossil chironomids and its relation to vegetation histories     

Joshua Kurek  Les C. Cwynar  Thomas A. Ager  Mark B. Abbott  Mary E. Edwards 《Quaternary Science Reviews》2009,28(9-10):799-811

Fossil Chironomidae assemblages (with a few Chaoboridae and Ceratopogonidae) from Zagoskin and Burial Lakes in western Alaska provide quantitative reconstructions of mean July air temperatures for periods of the late-middle Wisconsin (～39,000–34,000 cal yr B.P.) to the present. Inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination. Paleotemperature trends reveal substantial differences in the timing of climatic warming following the late Wisconsin at each site, although chronological uncertainty exists. Zagoskin Lake shows early warming beginning at about 21,000 cal yr B.P., whereas warming at Burial Lake begins ～4000 years later. Summer climates during the last glacial maximum (LGM) were on average ～3.5 °C below the modern temperatures at each site. Major shifts in vegetation occurred from ～19,000 to 10,000 cal yr B.P. at Zagoskin Lake and from ～17,000 to 10,000 cal yr B.P. at Burial Lake. Vegetation shifts followed climatic warming, when temperatures neared modern values. Both sites provide evidence of an early postglacial thermal maximum at ～12,300 cal yr B.P. These chironomid records, combined with other insect-based climatic reconstructions from Beringia, indicate that during the LGM: (1) greater continentality likely influenced regions adjacent to the Bering Land Bridge and (2) summer climates were, at times, not dominated by severe cold.  相似文献   

Seasonal cycles and long-term trends of plankton in shelf and oceanic habitats of the Norwegian Sea in relation to environmental variables     

Jrg Aßmus  Webjrn Melle  Dag Tjstheim  Martin Edwards 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(21-22):1895

The plankton abundance data of the Continuous Plankton Recorder (CPR) route from Bergen or Rotterdam to Weather Station Mike (6444^′N, 2E) from 1949 to 1981 were analysed for long-term trends and seasonal production cycles, and were related to environmental data. The data were explored using the canonical correlation analysis and nonparametric techniques like the Nadaraya–Watson regression. While large copepods such as Calanus spp. and Metridia lucens did not show any temporal trends, a sharp decrease in the abundances of smaller copepods and phytoplankton was observed after 1960. The temporal trends were not related to the NAO, but did show a correlation with the wind direction. Seasonal abundance curves showed that production of both phytoplankton and zooplankton taxa started earlier in coastal water compared to Atlantic water. From the 1950s to the 1970s most taxa showed a delay in the start of the seasonal production cycles, indicating a reduction in the length of the productive cycle. This may to some extent explain the reduced abundance of smaller copepods, phytoplankton and other species during the 1960s and 1970s.  相似文献   

Reproduction in the sea pen Funiculina quadrangularis (Anthozoa: Pennatulacea) from the west coast of Scotland     

Daniel C.B. Edwards  Colin G. Moore 《Estuarine, Coastal and Shelf Science》2009

The sea pen Funiculina quadrangularis (Pallas, 1766) is a species of conservation concern in Scottish coastal waters, due to its restricted geographical distribution and high sensitivity to demersal fishing activities. Reproduction in F. quadrangularis was investigated in a population located in southern Loch Linnhe, west Scotland. This was accomplished through the analysis of trends in oocyte size-frequency distribution and relative fecundity over a 12-month period. Funiculina quadrangularis is dioecious and the study population exhibited a sex ratio of 1:1. Oogenesis in female F. quadrangularis is characterised by the maintenance of a large pool of asynchronously developing oocytes throughout the year, of which a small proportion (<10%) mature with increasing sychronicity and are spawned in midwinter. The reasons for this distinct pattern of oogenesis and winter spawning remain unclear, although the potential influence of environmental cues and the role of endogenous factors in relation to this sea pen's deep-sea habit are discussed. Whilst the duration of oogenesis is prolonged (>12 months), it is proposed that spawning is a brief and synchronous annual event. Relative fecundity is high and is independent of colony size, varying between approximately 500–2000 oocytes per 1 cm rachial midsection. This measure of fecundity exhibited pronounced seasonality and was significantly lower during the post-spawning winter months. Total fecundity in F. quadrangularis is considered to be high; although a small proportion of the total number of oocytes is spawned annually, this is compensated for by large colony size. Funiculina quadrangularis produces large oocytes (>800 μm), indicative of the production of lecithotrophic larvae.  相似文献   

61～50kaBP亚洲季风百年尺度气候振荡的黔西南石笋记录     

王军彬  孔兴功  程海  汪永进  R L Edwards 《海洋地质与第四纪地质》2008,28(5)

12个U/Th年龄测试结果显示,黔西南普安县雾露洞长度分别为667mm和830mm的两支石笋覆盖了61～50kaBP时段。据两支石笋999个δ18O数据建立了平均分辨率达15年的亚洲夏季风强度变化序列。雾露洞δ18O记录揭示了4个振幅达1.7‰的千年尺度季风增强事件,对应于格陵兰冰心DO17—DO14事件。在总体特征上,该记录峰谷振荡特征及振幅与贵州董歌洞、南京葫芦洞记录一致,进一步证实亚洲季风区大气降水同位素组成变化在大范围空间内具有一致性。在百年尺度上,亚洲季风区石笋δ18O清晰记录了MIS3早期6个DO亚旋回事件,而且在更短时间尺度上具有类似高纬气温振荡特征。这种低纬季风系统与北高纬气候变化的耦合关系表明,大气环流快速重组和传输可能是连接高低纬DO旋回及亚旋回气候变化的主要纽带。  相似文献   

Dispersion measure variations and their effect on precision pulsar timing     

X. P. You  G. Hobbs  W. A. Coles  R. N. Manchester  R. Edwards  M. Bailes  J. Sarkissian  J. P. W. Verbiest  W. van Straten  A. Hotan  S. Ord  F. Jenet  N. D. R. Bhat  A. Teoh 《Monthly notices of the Royal Astronomical Society》2007,378(2):493-506

We present an analysis of the variations seen in the dispersion measures (DMs) of 20-ms pulsars observed as part of the Parkes Pulsar Timing Array project. We carry out a statistically rigorous structure function analysis for each pulsar and show that the variations seen for most pulsars are consistent with those expected for an interstellar medium characterized by a Kolmogorov turbulence spectrum. The structure functions for PSRs J1045−4509 and J1909−3744 provide the first clear evidence for a large inner scale, possibly due to ion–neutral damping. We also show the effect of the solar wind on the DMs and show that the simple models presently implemented into pulsar timing packages cannot reliably correct for this effect. For the first time we clearly show how DM variations affect pulsar timing residuals and how they can be corrected in order to obtain the highest possible timing precision. Even with our presently limited data span, the residuals (and all parameters derived from the timing) for six of our pulsars have been significantly improved by correcting for the DM variations.  相似文献   

A Comparison of Global Magnetic Field Skeletons and Active-Region Upflows     

S. J. Edwards  C. E. Parnell  L. K. Harra  J. L. Culhane  D. H. Brooks 《Solar physics》2016,291(1):117-142

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Introduction,preliminary handling,and diseases of grass carp in New Zealand     

D. J. Edwards  P. M. Hine 《新西兰海洋与淡水研究杂志》2013,47(3):441-454

Fry of grass carp, Ctenopharyngodon idella (Val.), were air‐freighted from Hong Kong to New Zealand in October 1971. The fish were at first kept in tanks with a recirculating water supply, where they soon showed symptoms of parasitic infestation and suffered heavy mortality.

Attempts were made to remove parasites with chemotherapeutic treatment. Tripartiella sp., Dactylogyrus ctenopharyngodonis, and Gyrodactylus clenopharyngodontis were eliminated by prolonged bathing of the infected fish with quinine. Chemical treatment failed to eliminate Ichthyophthirius mullifiliis from the body surface and the gills, but the rate of spontaneous recovery of the fish from this disease was accelerated by keeping them in clean, running water. Experiments to remove the cestode Bothriocephalus gowkongensis from the intestine of the fish with tetravalent tin compounds and to control the intermediate host (Cyclops) in the water resulted in the eradiction of the cestode.

When parasitic infestations had been brought under control the fish were transferred to outdoor ponds, where they began to feed on aquatic and terrestrial vegetation and rapidly increased in size.  相似文献