Transformation of Irradiance Measurements into Spectral Actinic Flux for Photolysis Rates Determination     

HÉLÈNE COTTE  CLAUDE DEVAUX  PATRICK CARLIER 《Journal of Atmospheric Chemistry》1997,26(1):1-28

The actinic flux is the only radiometric quantity suitable for photolysisfrequency determination. It is derived from solar spectral irradiancemeasurements performed by a portable spectroradiometer in the 300–850nm wavelength range. The spectral irradiance is first divided into a directpart and a diffuse part, according to the atmospheric conditions, and thenconverted into the corresponding actinic flux quantity. As an intermediary,the ratio of diffuse actinic flux to diffuseirradiance is calculated by the spherical harmonics radiative code withrespect to wavelength, solar zenith angle, surface albedo, and aerosolproperties.The results of extensive sensitivity studies of asa function of the main atmospheric parameters are discussed and lead to theconclusion that aerosol optical depth is the major critical value for aprecise determination. The global algorithm totransform spectral irradiance into actinic flux is finally applied forphotodissociation rate calculations by convolution of the obtained actinicflux spectra with the absorption cross-sections and quantum yields of themolecule studied. Photolysis rates of different atmospheric photooxidants havebeen measured with this spectroradiometric method during the summers of 1993and 1994 in Brittany and in Portugal. The ozone and nitrogen dioxidephotodissociation rates obtained present a good agreement with thej(O₃) and j(NO₂) actinometerresults, for the same experimental conditions in Brittany.  相似文献   

USE OF PRECIPITATION RECORDS IN THE CORRELATION OF STREAMFLOW RECORDS     

Robert O. R. MARTIN 《水文科学杂志》2013,58(4):24-31

Abstract

An empirical study using three pairs of stream basins in Eastern United States showed that the regression of monthly streamflow from one basin on that from a nearby basin generally was improved by use of a regression model which included, as an additional variable, the difference in precipitation on the two basins.  相似文献   

Late Pleistocene–early Holocene polychaete borings in NE Spitsbergen and their palaeoecological and climatic implications: an example from the Basissletta area     

NILS‐MARTIN HANKEN  ALFRED UCHMAN  STEN LENNART JAKOBSEN 《Boreas: An International Journal of Quaternary Research》2012,41(1):42-55

Hanken, N.‐M., Uchman, A. & Jakobsen, S. L. 2012 (January): Late Pleistocene–early Holocene polychaete borings in NE Spitsbergen and their palaeoecological and climatic implications: an example from the Basissletta area. Boreas, Vol. 41, pp. 42–55. 10.1111/j.1502‐3885.2011.00223.x. ISSN 0300‐9483 Limestone and dolomite bedrock surfaces, together with blocks derived from these underlying bedrocks, at Basissletta, NE Spitsbergen, contain Late Pleistocene–early Holocene, shallow‐marine, spionid polychaete borings Caulostrepsis taeniola Clarke, Caulostrepsis contorta Bromley & D'Alessandro, and Maeandropolydora isp. The borings occur about 9–78 m above present sea level, and this is the northernmost known occurrence of these trace fossils. ¹⁴C dating of wood, whalebone and bivalves in the vicinity and in neighbouring areas indicates that the borings have a radiocarbon age spanning from about 7 to 11 ka. Recent borings of these ichnotaxa have not been found in the sea around Spitsbergen. The presence of the fossil borings indicates that invasion of boring polychaetes to the northern part of the Barents Sea region was limited to a Late Pleistocene–early Holocene temperature optimum. The presence of Caulostrepsis and Maeandropolydora on subaerially exposed shallow‐water Pleistocene–Holocene bedrock surfaces in arctic areas can be a valuable tool with which to evaluate both postglacial emergence and climatic oscillations because they indicate a summer surface water temperature of at least 8 °C.  相似文献   

Three-dimensional transport and concentration of SF₆     

A. SCOTT DENNING  MARK. HOLZER  KEVIN R. GURNEY  MARTIN HEIMANN  RACHEL M. LAW  PETER J. RAYNER  INEZ Y. FUNG  SONG-MIAO FAN  SHOICHI TAGUCHI  PIERRE FRIEDLINGSTEIN  YVES BALKANSKI  JOHN TAYLOR  MANFRED MAISS  INGEBORG LEVIN 《Tellus. Series B, Chemical and physical meteorology》1999,51(2):266-297

  相似文献   

PREFACE: THE MOUNTAIN CRYOSPHERE – A HOLISTIC VIEW ON PROCESSES AND THEIR INTERACTIONS     

STEPHAN GRUBER  MARKUS EGLI  ISABELLE GÄRTNER‐ROER  MARTIN HOELZLE 《Geografiska Annaler: Series A, Physical Geography》2012,94(2):177-182

Gruber, S., Egli, M., Gärtner‐Roer, I. and Hoelzle, M., 2012. Preface: The mountain cryosphere – a holistic view on processes and their interactions. Geografiska Annaler: Series A, Physical Geography, ??, ??–??. doi :10.1111/j.1468‐0459.2012.00468.x  相似文献   

The intrinsic effect of shape on the retrogradation motif and timing of drowning of carbonate patch reef systems (Lower Frasnian,Bugle Gap,Canning Basin,Western Australia)     

ERWIN W. ADAMS  CLAUDE‐ALAIN HASLER 《Sedimentology》2010,57(4):956-984

The evolution and architecture of a set of retreating Lower Frasnian patch reef outcrops in the Canning Basin of Western Australia were evaluated, and their depositional and stratigraphic contacts spatially recorded using digital surveying tools. The geological data, together with high‐resolution digital elevation models, were assembled in three‐dimensional visualization and modelling software and subsequently used for building two‐dimensional surface models and three‐dimensional volumetric models. Numerical data on geometry and shape were extracted from these models and used to quantitatively assess the retrogradation motif of patch reef development. The development of the patch reefs comprises three stages. During stages 1 and 2, the patch reefs exhibited an overall retrogradational escarpment‐type configuration displayed by, on average, 60° steep reef‐margin walls that lacked the support of coeval slope deposits. The subdivision between stages 1 and 2 is based on minor backstepping reducing less than 10% of the platform‐top area. The onset of stage 3 is recognized by stromatolite development fringing reef‐margin walls. During stage 3 an aggrading accretionary reef‐margin developed, comprising allochthonous and autochthonous slope deposits. Both types of slope deposit onlap the previous stages and are distributed unevenly with allochthonous slope deposits being noticeably absent around the smaller and more elongate patch reefs. The variation in distribution of slope sediment type can be explained by the amount, linked to platform size, of platform‐top shedding. Small patch reefs were unable to fill the available accommodation adjacent to escarpments with allochthonous slope sediments and were thus encroached by autochthonous slope sediments. The variation, which cannot be explained by the size difference in the platform‐top factory, has been related to the difference in perimeter length. For patch reefs with similar platform‐top production areas, a more elongate patch reef inherits a longer perimeter and a proportionally smaller volume of allochthonous slope sediment per margin length will be transported to the flanks. Thus, the more elongate patch reef intrinsically contained more sites within which autochthonous slope sediments developed. Digital outcrop modelling and numerical evaluation of the evolution of the patch reefs revealed the major differences in retrogradation motif. The quantified variations in progressive decline of platform‐top area with height were confirmed by hypothetical decline curves for ellipse‐shaped carbonate systems for which aspect ratio (ratio between length and width) varied. This mathematical model demonstrates that the progressive decline of the production area is highly sensitive to shape and can be used to numerically assess and predict the relative timing of drowning, i.e. when the platform‐top production area becomes nil, of retrogradational isolated carbonate platforms that are controlled by high accommodation. Wider implications can be surmised for highstand systems tracts and prograding carbonate systems. For example, for equally sized platforms with hypothetically similar carbonate factories and identical external forces, the potential to prograde by platform‐top shedding is higher with a smaller aspect ratio because the shorter perimeter implies less accommodation space needing to be filled up to commence slope progradation. Clearly, there are intrinsic effects of shape on the development of carbonate platform systems.  相似文献   

The subglacial record of northern Hudson Bay: insights into the Hudson Strait Ice Stream catchment     

MARTIN ROSS  PATRICK LAJEUNESSE  KEVIN G. A. KOSAR 《Boreas: An International Journal of Quaternary Research》2011,40(1):73-91

Ross, M., Lajeunesse, P. & Kosar, K. G. A. 2010: The subglacial record of northern Hudson Bay: insights into the Hudson Strait Ice Stream catchment. Boreas, 10.1111/j.1502‐3885.2010.00176.x. ISSN 0300‐9483. In this paper, we present new insights into the glacial dynamics and potential configuration of the Hudson Strait Ice Stream catchment in the northern Hudson Bay–western Hudson Strait region. Our reconstruction is based on new field observations and till compositional data from Southampton Island, remote sensing imagery and multibeam bathymetric data from the Hudson Bay sea floor, as well as on a re‐examination of previously published data from this vast region. Our findings suggest that, during the late Quaternary, the HSIS catchment consisted of a number of ice‐stream tributaries feeding a curvilinear trunk that potentially extended into western Hudson Bay. In contrast to previous interpretations, the occurrence of fluted bedrock hills, over‐deepened basins, Dubawnt erratics and carbonaceous till on the islands at the head of Hudson Strait is taken to imply that cold‐based conditions did not prevail on these islands. The upland area of Southampton Island and the surrounding channels played an important role in controlling the location of the main tributaries, with the higher central terrain forming a large inter‐ice‐stream zone lacking carbonate detritus. Coats Island contains abundant evidence of vigorous ice flow, such as mega‐scale glacial lineations (MSGLs). MSGLs also occur on the sea floor southwest of Coats Island but the sea‐floor imprint is highly discontinuous. Observations on the western Hudson Bay mainland show evidence of southeastward fast ice flow that is spatially consistent with the Dubawnt dispersal train. Despite the geomorphological discontinuities, this may indicate that the HSIS onset zone extended far inside the Laurentide Ice Sheet and across contrasting geological domains.  相似文献   

Re‐evaluation of the Last Glacial Maximum typesite at Dimlington,UK     

MARK D. BATEMAN  PAUL C. BUCKLAND  MARTIN A. WHYTE  ROBERT A. ASHURST  CLAIRE BOULTER  EVA PANAGIOTAKOPULU 《Boreas: An International Journal of Quaternary Research》2011,40(4):573-584

Bateman, M. D., Buckland, P. C., Whyte, M. A., Ashurst, R. A., Boulter, C. & Panagiotakopulu, E. 2011: Re‐evaluation of the Last Glacial Maximum typesite at Dimlington, UK. Boreas, 10.1111/j.1502‐3885.2011.00204.x. ISSN 0300‐9483. Recent erosion has allowed re‐examination of the stratigraphy and sampling for both optically stimulated luminescence dating and palaeoecological analysis of the key sections in the Last Glacial Maximum deposits at Dimlington in East Yorkshire, England. Both stratigraphy and fossil insect evidence support a subaerial origin for laminated and cross‐bedded sediments between two diamictons previously interpreted as synchronous. The fossil biota indicates conditions similar to those of a pond on sandur in the high Arctic, with little or no vegetation cover. The existence of distinct oscillations of the ice front is indicated. The first, within the period 21.7–16.2 ka, appears coincident with climate warming, as deduced from Greenland ice‐core evidence, and is interpreted as an ice stream associated with changing flow patterns within the British–Irish Ice Sheet (BIIS). The second, dating between 16.2 and 15.5 ka, appears to coincide with a climatic cooling, although current models show that the BIIS had by this period already retreated back to ice centres. This new evidence supports the view that the eastern sector of the BIIS did not reach its maximal extent synchronously with other parts of the BIIS.  相似文献   

Rapid Temporal Changes in Ocean Island Basalt Composition: Evidence from an 800 m Deep Drill Hole in Eiao Shield (Marquesas)   总被引：1，自引：1，他引：1  

CAROFF  MARTIAL; MAURY  RENE C.; VIDAL  PHILIPPE; GUILLE  GERARD; DUPUY  CLAUDE; COTTEN  JOSEPH; GUILLOU  HERVE; GILLOT  PIERRE-YVES 《Journal of Petrology》1995,36(5):1333-1365

The Dominique drill hole has penetrated the volcanic shieldof Eiao island (Marquesas) down to a depth of 800 m below thesurface and 691•5 m below sea-level with a percentage ofrecovery close to 100%. All the lavas encountered were emplacedunder subaerial conditions. From the bottom to the top are distinguished:quartz and olivine tholeiites (800–686 m), hawaiites,mugearites and trachyte (686–415 m), picritic basalts,olivine tholeiites and alkali basalts (415–0 m). The coredvolcanic pile was emplaced between 5•560•07 Ma and5•220•06 Ma. Important chemical changes occurred during this rather shorttime span (0•34 0•13 Ma). In particular, the lowerbasalts differ from the upper ones in their lower concentrationsof incompatible trace elements and their Sr, Nd and Pb isotopicsignature being closer to the HIMU end-member, whereas the upperbasalts are EM II enriched. The chemical differences betweenthe two basalt groups are consistent with a time-related decreasein the degree of partial melting of isotopically heterogeneoussources. It seems unlikely that these isotopic differences reflectchanges in plume dynamics occurring in such a short time span,and we tentatively suggest that they result from a decreasingdegree of partial melting of a heterogeneous EM II–HIMUmantle plume. Some of the intermediate magmas (the uppermost hawaiites andmugearites) are likely to be derived from parent magmas similarto the associated upper basalts through simple fractionationprocesses. Hawaiites, mugearites and a trachyte from the middlepart of the volcanic sequence have Sr–Nd isotopic signaturessimilar to those of the lower basalts but they differ from themin their lower ²⁰⁶Pb/²⁰⁴Pb ratios, resulting in an increasedDMM signature. Some of the hawaiites-mugearites also displayspecific enrichments in P₂O₅, Sr and REE which are unlikelyto result from simple fractionation processes. The isotopicand incompatible element compositions of the intermediate rocksare consistent with the assimilation of MORB-derived wall rocksduring fractional crystallization. The likely contaminant correspondsto Pacific oceanic crust, locally containing apatite-rich veinsand hydrothermal sulphides. We conclude that a possible explanationfor the DMM signature in ocean island basalts is a chemicalcontribution from the underlying oceanic crust and that studiesof intermediate rocks may be important to document the originof the isotopic features of plume-derived magmas. KEY WORDS: alkali basalt; assimilation; mantle heterogeneity; Marquesas; tholeiile ^*Corresponding author  相似文献   

Progressive Low-Grade Metamorphism of a Black Shale Formation, Central Swiss Alps, with Special Reference to Pyrophyllite and Margarite Bearing Assemblages   总被引：1，自引：0，他引：1  

FREY  MARTIN 《Journal of Petrology》1978,19(1):95-135

The unmetamorphosed equivalents of the regionally metamorphosedclays and marls that make up the Alpine Liassic black shaleformation consist of illite, irregular mixed-layer illite/montmorillonite,chlorite, kaolinite, quartz, calcite, and dolomite, with accessoryfeldspars and organic material. At higher grade, in the anchizonalslates, pyrophyllite is present and is thought to have formedat the expense of kaolinite; paragonite and a mixed-layer paragonite/muscovitepresumably formed from the mixed-layer illite/montmorillonite.Anchimetamorphic illite is poorer in Fe and Mg than at the diageneticstage, having lost these elements during the formation of chlorite.Detrital feldspar has disappeared. In epimetamorphic phyllites, chloritoid and margarite appearby the reactions pyrophyllite + chlorite = chloritoid + quartz+ H₂O and pyrophyllite + calcite ± paragonite = margarite+ quartz + H₂O + CO₂, respectively. At the epi-mesozone transition,paragonite and chloritoid seem to become incompatible in thepresence of carbonates and yield the following breakdown products:plagioclase, margarite, clinozoisite (and minor zoisite), andbiotite. The maximum distribution of margarite is at the epizone-mesozoneboundary; at higher metamorphic grade margarite is consumedby a continuous reaction producing plagioclase. Most of the observed assemblages in the anchi-and epizone canbe treated in the two subsystems MgO (or FeO)-Na₂O–CaO–Al₂O₃–(KAl₃O₅–SiO₂–H₂O–CO₂).Chemographic analyses show that the variance of assemblagesdecreases with increasing metamorphic grade. Physical conditions are estimated from calibrated mineral reactionsand other petrographic data. The composition of the fluid phasewas low in X_CO2 throughout the metamorphic profile, whereasX_CH4 was very high, particularly in the anchizone where a_H2Owas probably as low as 0.2. P-T conditions along the metamorphicprofile are 1–2 kb/200–300 °C in the anchizone(Glarus Alps), and 5 kb/500–550 °C at the epi-mesozonetransition (Lukmanier area). Calculated geothermal gradientsdecrease from 50 °C/km in the anchimetamorphic Glarus Alpsto 30 °C/km at the epi-mesozone transition of the Lukmanierarea.  相似文献