Planktonic dimethylsulfide and cloud albedo: An estimate of the feedback response     

Jonathan A. Foley  Karl E. Taylor  Steven J. Ghan 《Climatic change》1991,18(1):1-15

Partial control of climate by the biosphere may be possible through a chain of processes that ultimately links marine plankton production of dimethylsulfide (DMS) with changes in cloud albedo (Charlson et al., 1987). Changes in cloud optical properties can have profound impacts on atmospheric radiation transfer and, hence, the surface environment. In this study, we have developed a simple model that incorporates empirically based parameterizations to account for the biological control of cloud droplet concentration in a first attempt to estimate the strength of the DMS-cloud albedo feedback mechanism. We find that the feedback reduces the global climatic response to imposed perturbations in solar insolation by less than 7%. Likewise, it modifies the strength of other feedbacks affecting surface insolation over oceans by roughly the same amount. This suggests that the DMS-cloud albedo mechanism will be unable to substantially reduce climate sensitivity, although these results should be confirmed with less idealized models when more is known about the net production of DMS by the marine biosphere and its relation to aerosol/cloud microphysics and climate.  相似文献   

Radioactivity on UK coasts     

Jonathan Side 《Marine pollution bulletin》1985,16(9):340-341

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MINI-MACtm—A new generation dual—Band surveyor     

Ladd  Jonathan W.  Welshe  Robert G.  Brown  Alison  Sturza  Mark 《Journal of Geodesy》1986,60(3):221-228

Summary Litton Divisions presently produce both high accuracy GPS surveyors and low—cost GPS navigation sets. Aero Service'sMACROMETER ^R Interferometric Surveyors, have become the standard against which GPS surveying equipment is measured. Litton Aero Products has developed a highly digitized, low costL ₁,C/A code GPS card set. The integration of these technologies had led to the development of a low-cost, high-precision, GPS survey system which can be configured with or without a codelessL ₂ capability. TheMINI-MAC surveying system is the first member of the new generation of GPS survey systems resulting from this joint development. The system design is described in this paper, and initial survey test results using a prototypeMINI-MAC surveying system are presented.  相似文献   

Editorial—geomorphic response to sea-level rise: Existing evidence and future impacts     

Jonathan R. French  Thomas Spencer  Denise J. Reed 《地球表面变化过程与地形》1995,20(1):1-6

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Importance of the Lu-Hf isotopic system in studies of planetary chronology and chemical evolution     

P.Jonathan Patchett 《Geochimica et cosmochimica acta》1983,47(1):81-91

The ¹⁷⁶Lu-¹⁷⁶Hf isotope method and its applications in earth sciences are discussed. Greater fractionation of Lu/Hf than Sm/Nd in planetary magmatic processes makes ${}^{176}\text{Hf}{}^{177}\text{Hf}$ a powerful geochemical tracer. In general, proportional variations of ${}^{176}\text{Hf}{}^{177}\text{Hf}$ exceed those of ${}^{143}\text{Nd}{}^{\mathrm{l44}}\text{Nd}$ by factors of 1.5–3 in terrestrial and lunar materials. Lu-Hf studies therefore have a major contribution to make in understanding of terrestrial and other planetary evolution through time, and this is the principal importance of Lu-Hf. New data on basalts from oceanic islands show unequivocally that whereas considerable divergences occur in ${}^{176}\text{Hf}{}^{177}\text{Hf}\text{-}{}^{87}\text{Sr}{}^{86}\text{Sr}$ and ${}^{143}\text{Nd}{}^{\mathrm{l44}}\text{Nd}\text{-}{}^{87}\text{Sr}{}^{86}\text{Sr}$ diagrams, ${}^{176}\text{Hf}{}^{177}\text{Hf}$ and ${}^{143}\text{Nd}{}^{144}\text{Nd}$ display a single, linear isotopic variation in the suboceanic mantle. These discordant ${}^{87}\text{Sr}{}^{86}\text{Sr}$ relationships may allow, with the acquisition of further Hf-Nd-Sr isotopic data, a distinction between processes such as mantle metasomatism, influence of seawater-altered material in the magma source, or recycling of sediments into the mantle. In order to evaluate the Hf-Nd isotopic correlation in terms of mantle fractionation history, there is a need for measurements of Hf distribution coefficients between silicate minerals and liquids, and specifically for a knowledge of Hf behavior in relation to rareearth elements. For studying ancient terrestrial Hf isotopic variations, the best quality Hf isotope data are obtained from granitoid rocks or zircons. New data show that very U-Pb discordant zircons may have upwardly-biased ${}^{176}\text{Hf}{}^{177}\text{Hf}$, but that at least concordant to slightly discordant zircons appear to be reliable carriers of initial ${}^{176}\text{Hf}{}^{177}\text{Hf}$. Until the controls on addition of radiogenic Hf to zircon are understood, combined zircon-whole rock studies are recommended. Lu-Hf has been demonstrated as a viable tool for dating of ancient terrestrial and extraterrestrial samples, but because it offers little advantage over existing methods, is unlikely to find wide application in pure chronological studies.  相似文献   

Trace element zoning in pyroxenes from ODP Hole 735B gabbros: diffusive exchange or synkinematic crystal fractionation?     

Yongjun Gao  Jochen Hoefs  Eric Hellebrand  Anette von der Handt  Jonathan E. Snow 《Contributions to Mineralogy and Petrology》2007,153(4):429-442

Major and trace element profiles of clinopyroxene grains in oceanic gabbros from ODP Hole 735B have been investigated by a combined in situ analytical study with ion probe, and electron microprobe. In contrast to the homogeneous major element compositions, trace elements (REE, Y, Cr, Sr, and Zr) show continuous core to rim zoning profiles. The observed trace element systematics in clinopyroxene cannot be explained by a simple diffusive exchange between melts and gabbros along grain boundaries. A simultaneous modification of the melt composition is required to generate the zoning, although Rayleigh fractional crystallization modelling could mimic the general shape of the profiles. Simultaneous metasomatism between the cumulate crystal and the porous melt during crystal accumulation is the most likely process to explain the zoning. Deformation during solidification of the crystal mush could have caused squeezing out of the incompatible element enriched residual melts (interstitial liquid). Migration of the melt along grain boundaries might carry these melt out of the system. This process named as synkinematic differentiation or differentiation by deformation (Natland and Dick in J Volcanol Geotherm Res 110(3–4):191–233, 2001) may act as an important magma evolution mechanism in the oceanic crust, at least at slow-spreading ridges.  相似文献   

The effects of organic removal treatment on the integrity of δ<Superscript>18</Superscript>O measurements from biogenic silica     

Jonathan J. Tyler  Melanie J. Leng  Hilary J. Sloane 《Journal of Paleolimnology》2007,37(4):491-497

Prior to oxygen isotope analysis of biogenic silica by fluorination techniques, sediments must be cleaned of all organic compounds. Despite the expanding volume of research utilising oxygen isotope ratios in biogenic silica in palaeoclimatology, very little is known about the effects of different standard preparation methods for the removal of organic matter on the isotope values. Here we compare a number of methods for the removal of organic matter in order to assess their effectiveness and influence on subsequent isotope measurements. Not all the methods described here effectively removed organic matter, the best treatments were H₂O₂ and ignition in air at 550°C. Ignition in air at 950°C, and heating in vacuum at 250 and 450°C results in marked alteration of isotope values, whereas use of hydrogen peroxide (H₂O₂), nitric acid (HNO₃) and plasma ashing have little or no effect, within the bounds of analytical error. Ignition in air at 550°C was the most effective technique, and induced no alteration of δ¹⁸O_silica, but practical constraints may limit the application of this method routinely. Our findings indicate that considerable caution is required when preparing sediment for isotope analysis of biogenic silica.  相似文献   

Controls on sediment export from the Waipaoa River basin, New Zealand     

Jonathan D. Phillips  Basil Gomez† 《Basin Research》2007,19(2):241-252

A stability model of drainage basin mass balance is used to interpret historic and prehistoric patterns of sediment production, storage and output from the Waipaoa River basin, New Zealand and assess the sensitivity of basin sediment yield to land use change in the historic period. Climate and vegetation cover changed during the late Holocene, but the drainage basin mass balance system was stable before the basin was deforested by European colonists in the late 19th and early 20th centuries. In this meso‐scale dispersal system sediment sources and sinks are closely linked, and before that time there was also little variability in the rate of terrigenous mass accumulation on the adjacent continental shelf. However, despite strong first‐order geologic controls on erosion and extensive alluvial storage, sediment delivery to the continental shelf is sensitive and highly responsive to historic hillslope destabilization driven by land use change. Alluvial buffering can mask the effects of variations in sediment production within a basin on sediment yield at the outlet, but this is most likely to occur in basins where alluvial storage is large relative to yield and where the residence time of alluvial sediment is long relative to the time scale of environmental change. At present, neither situation applies to the Waipaoa River basin. Thus, the strength of the contemporary depositional signal may not only be due to the intensity of the erosion processes involved, but also to the fact that land use change in the historic period destabilized the drainage basin mass balance system.  相似文献   

Flow and deposition of pyroclastic granular flows: A type example from the 1975 Ngauruhoe eruption,New Zealand     

Gert Lube  Shane J. Cronin  Thomas Platz  Armin Freundt  Jonathan N. Procter  Cargill Henderson  Michael F. Sheridan 《Journal of Volcanology and Geothermal Research》2007

Small-volume pyroclastic density currents (PDCs) are generated frequently during explosive eruptions with little warning. Assessing their hazard requires a physical understanding of their transport and sedimentation processes which is best achieved by the testing of experimental and numerical models of geophysical mass flows against natural flows and/or deposits. To this end we report on one of the most detailed sedimentological studies ever carried out on a series of pristine small-volume PDC deposits from the 1975 eruption of Ngauruhoe volcano, whose emplacement were also witnessed during eruption. Using high-resolution GPS surveys, a series of lateral excavations across the deposits, and bulk sedimentological analysis we constrained the geomorphology, internal structure and texture of the deposits with respect to laterally varying modes of deposition.  相似文献   

Global-Scale Relationships between Climate and the Dengue Fever Vector, Aedes Aegypti     

Marianne J. Hopp  Jonathan A. Foley 《Climatic change》2001,48(2-3):441-463

Considerable interest exists inthe potential role climate may play in human healthissues, especially regarding the effect of climatechange on vector-borne disease. The Aedesaegypti mosquito, the principal vector for dengue,considered the most important vector-borne viraldisease in the world, is particularly susceptible toclimate variability and climatic change. Here wepresent a modeling analysis focusing on global-scaleassociations between climate and the development,potential distribution, and population dynamics ofAe. aegypti. We evaluate the model by comparingand contrasting model data with observed mosquitodensities. There is good agreement between theobserved and modeled global distribution of themosquito; however, the model results suggest thepotential for increased latitudinal distributionsduring warmer months. Seasonal fluctuations inmosquito abundance also compare well to observed data. Discrepancies possibly reflect the relatively lowresolution of the climate data and model output andthe inability of the model to account for localmicroclimate effects, especially in coastal areas.Future modeling efforts will involve study ofinterannual variability in mosquito dynamics.  相似文献