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61.
Eric N. Powell Julie D. Gauthier Elizabeth A. Wilson Alanna Nelson Roger R. Fay James M. Brooks 《Marine Ecology》1992,13(3):243-270
62.
Tessa M. Hill Gregg R. Brooks David S. Duncan Franco S. Medioli 《Marine Geology》2003,200(1-4):263-272
The sedimentology, stratigraphic position, and benthic foraminiferal biostratigraphy of early- to mid-Holocene deposits from the west-central Florida shelf suggest that barrier islands developed along this coast as early as 8.3 ka, in an environment that was more arid than today. Predominant foraminifera of three paralic sedimentary facies deposited between 5.3 and 8.3 ka include miliolids, Elphidium spp., and Ammonia spp., all of which are common in back-barrier environments. Foraminiferal assemblages also suggest that early back-barrier sediments were deposited in a hypersaline environment, similar to that of the arid Laguna Madre of the western Gulf of Mexico. Modern back-barrier foraminifera in the Tampa Bay region are indicative of the humid subtropical climate of today. Thus, the climate of west-central Florida at approximately 8 ka was more arid than today, which is consistent with recent studies showing that climate in the Gulf of Mexico was dryer and cooler during this time period. 相似文献
63.
C. R. Fisher J. M. Brooks J. S. Vodenichar J. M. Zande J. J. Childress R. A. Burke Jr. 《Marine Ecology》1993,14(4):277-289
Abstract. In April 1990 a new species of mytilid containing bacterial endosymbionts was discovered at a deep-water seep site within Alaminos Canyon in the Gulf of Mexico. Activities of ribulose bisphosphate carboxylase/oxygenase and ATP sulfurylase, as well as the presence of substantial levels of elemental sulfur in the gill tissues indicate the presence of chemoautotrophic sulfur-oxidizing symbionts in the gills. Methanol dehydrogenase activity and the tissue stable carbon isotope ratios indicate the presence of methanotrophic bacteria in the gills of the same animals. Two distinct size classes and morphological types of gram negative bacteria are visible in transmission electron micrographs of the gill tissue, one of which contains the complex internal membranes typical of methanotrophs. Both general types of symbionts have been demonstrated singly in related species of deep-sea mytilids. In this species, however, both types are found in single individuals, often within the same cell vacuole. 相似文献
64.
Summary Numerical simulations of thunderstorms using initial conditions from an Oklahoma storm event on 26 April 1984 have been carried out using the Klemp-Wilhelmson cloud model. Two thermodynamic and two horizontal wind profiles are mixed to create four initial storm environments. The two initial thermodynamic profiles are designated as moderately and highly unstable. Both hodographs have considerable vertical wind shear, with the extremely unstable profile having substantially stronger storm-relative curvature shear in the lowest few kilometers, as measured by the helicity of the environment. Storms are initialized with two different temperature-perturbation warm bubbles. A variety of storms, qualitatively covering the range observed on this day, are simulated. With a strongly sheared, moderate instability environment, the two different temperature-perturbation simulations differ qualitatively, unlike the other pairs of simulations.Of particular interest is the simulation carried out with the weaker temperature-perturbation. It displays many of the characteristics of observed low-precipitation (LP) supercell storms. Without artificially suppressing rainfall, this storm produces very little precipitation over the first 6000 s of its lifetime. During this time, there is no strong downdraft at the lowest model level and vorticity at that level is much less than the values aloft. We hypothesize that LP storms can be generated by smaller initial impulses than classic supercells in environments typically associated with a supercell storm, as speculated by Bluestein and Parks (1983), since they are more susceptible to turbulent entrainment in highly sheared environments.With 15 Figures 相似文献
65.
Danielle Schreve Andy Howard Andrew Currant Stephen Brooks Simon Buteux Russell Coope Barnaby Crocker Michael Field Malcolm Greenwood James Greig Phillip Toms 《第四纪科学杂志》2013,28(2):118-130
This paper reports the discovery of a rare partial skeleton of a woolly rhinoceros (Coelodonta antiquitatis Blumenbach, 1799) and associated fauna from a low Pleistocene terrace of the River Tame at Whitemoor Haye, Staffordshire, UK. A study of the sedimentary deposits around the rhino skeleton and associated organic‐rich clasts containing pollen, plant and arthropod remains suggests that the animal was rapidly buried on a braided river floodplain surrounded by a predominantly treeless, herb‐rich grassland. Highlights of the study include the oldest British chironomid record published to date and novel analysis of the palaeoflow regime using caddisfly remains. For the first time, comparative calculations of coleopteran and chironomid palaeotemperatures have been made on the same samples, suggesting a mean July temperature of 8–11 °C and a mean December temperature of between ?22 and ?16 °C. Radiocarbon age estimates on skeletal material, supported by optically stimulated luminescence ages from surrounding sediments, indicate that the rhino lived around 41–43 k cal a BP. The combined geochronological, stratigraphic and palaeoenvironmental evidence places the assemblage firmly within the Middle Devensian (Marine Oxygen Isotope Stage 3). This would agree with other regional evidence for the timing of aggradation for the lowest terrace of the Trent and its tributary systems. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
66.
Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits
preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies
identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are
interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000
and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between
about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent
sedimentation within a ‘large’ lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression,
Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved
within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late
Mattawa-Stanley phase between 9,500–9,300 and 9,000–8,400 cal BP (~8,500–8,300 and ~8,000–7,600 BP), when the water surface
of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP),
the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the
base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the
cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough
low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower
French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold
had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake
occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits
marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional
sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved
pre-9,500 cal BP (~8,500 BP) post-glacial deposits. 相似文献
67.
The CIRS infrared spectrometer onboard the Cassini spacecraft has scanned Saturn's A ring azimuthally from several viewing angles since its orbit insertion in 2004. A quadrupolar asymmetry has been detected in this ring at spacecraft elevations ranging between 16° to 37°. Its fractional amplitude decreases from 22% to 8% from 20° to 37° elevations. The patterns observed in two almost complete azimuthal scans at elevations 20° and 36° strongly favor the self-gravity wakes as the origin of the asymmetry. The elliptical, infinite cylinder model of Hedman et al. [Hedman, M.M., Nicholson, P.D., Salo, H., Wallis, B.D., Buratti, B.J., Baines, K.H., Brown, R.H., Clark, R.N., 2007. Astron. J. 133, 2624-2629] can reproduce the CIRS observations well. Such wakes are found to have an average height-to-spacing ratio H/λ=0.1607±0.0002, a width-over-spacing W/λ=0.3833±0.0008. Gaps between wakes, which are filled with particles, have an optical depth τG=0.1231±0.0005. The wakes mean pitch angle ΦW is 70.70°±0.07°, relative to the radial direction. The comparison of ground-based visible data with CIRS observations constrains the A ring to be a monolayer. For a surface mass density of 40 g cm−2 [Tiscarino, M.S., Burns, J.A., Nicholson, P.D., Hedman, M.M., Porco, C.C., 2007. Icarus 189, 14-34], the expected spacing of wakes is λ≈60 m. Their height and width would then be H≈10 m and W≈24 m, values that match the maximum size of particles in this ring as determined from ground-based stellar occultations [French, R.G., Nicholson, P.D., 2000. Icarus 145, 502-523]. 相似文献
68.
Robert J. Kieber Jeremy Smith Katherine M. Mullaugh Melissa W. Southwell G. Brooks Avery Jr. Joan D. Willey 《Journal of Atmospheric Chemistry》2009,64(2-3):149-158
The influence of sunlight and dissolved organic carbon (DOC) on the photochemically mediated cycling of hydrogen peroxide (H2O2) was investigated in rainwater samples collected in Wilmington, North Carolina USA. Upon exposure to simulated sunlight 14 of 19 authentic rainwater samples exhibited significant decreases in H2O2. The concentration of hydrogen peroxide did not change significantly in organic-free synthetic rainwater spiked with H2O2 in the light or in dark controls suggesting that the loss was not due to direct photolysis or dark mediated reactions. There was a significant correlation between pseudo-first order rate constants of H2O2 decay and initial H2O2 concentrations. There was also a significant correlation between the rate constant and the abundance of DOC suggesting that rainwater organic carbon plays an important role during photolytic decay either via direct reaction or indirectly through production of peroxide reactive species or scavenging of peroxide generating radicals. Several rain samples exhibited an initial increase in H2O2 during the first 2 h of irradiation. These increases were generally small and most likely do not represent a significant input of peroxide in precipitation. The photo-induced destruction of H2O2 is important because it may partly explain the late afternoon decrease of peroxide concentrations observed in earlier field studies and the substantial under saturation (<10%) of this oxidant in rainwater compared with gas phase concentrations. 相似文献
69.
William L. Balsam Brooks B. Ellwood Junfeng Ji Earle R. Williams Xiaoyong Long Ahmed El Hassani 《Quaternary Science Reviews》2011,30(19-20):2732-2744
The magnetic susceptibility of soils has been linked with climate, mainly through rainfall, by numerous investigators. For this study we assembled a worldwide dataset of 272 samples, both published and new, to determine the nature of the relationship between MS and rainfall. On a worldwide basis there is a crude relationship (r2 = 0.265) between MS and rainfall. MS increases with increasing rainfall from about 200 mm/yr to 1000–1200 mm/yr. Above 1200 mm/yr, MS decreases as rainfall increases up to about 2000 mm/yr. Under arid and semi-arid conditions, below about 200 mm/yr of rainfall, MS and rainfall exhibit no relationship, likely the result of limited pedogenic activity.When tropical and temperate localities are analyzed separately, the correlation between MS and rainfall exhibits a dramatic improvement, r2 = 0.568 and 0.520, respectively. For similar amounts of rainfall tropical localities generally exhibit lower MS values which may be related to differences in the seasonal variation of rainfall. Because the soil environment is highly variable, it is unlikely that a global or even regional equation could accurately estimate rainfall from MS. Using data from Morocco and Mali we demonstrate that local equations using only MS to estimate rainfall produce reasonable results, r2 = 0.700 for Morocco and 0.611 for Mali. However, a single independent variable is unlikely to capture the variability of the complex soil system. To the local equations described above we experimented with adding several independent variables in addition to MS including diffuse reflectance spectral data (DRS), x-ray diffraction (XRD), and x-ray fluorescence (XRF). For DRS data, % reflectance and red, yellow, and near-infrared wavelengths appear important; for XRD illite and kaolinite counts are important whereas for XRF Fe2O3 is important. The addition of these other independent variables dramatically improves prediction quality. In the case of the Mali transect, estimating rainfall from these variables produces an r2 that exceeds 0.9. Based on these data we conclude that MS has the potential to be a reasonable proxy of rainfall for mean annual precipitation values from 200 to 2000 mm/yr, especially if local equations are used. Predictions can be improved by including other independent variables that show sensitivity to climate and are related to MS through the chemistry of the weathering process; we included DRS, XRD, and XRF data with good results. 相似文献
70.
A.E. Self S.J. Brooks H.J.B. Birks L. Nazarova D. Porinchu A. Odland H. Yang V.J. Jones 《Quaternary Science Reviews》2011,30(9-10):1122-1141
The large landmass of northern Russia has the potential to influence global climate through amplification of climate change. Reconstructing climate in this region over millennial timescales is crucial for understanding the processes that affect the global climate system. Chironomids, preserved in lake sediments, have the potential to produce high resolution, low error, quantitative summer air temperature reconstructions. Canonical correspondence analysis of modern surface sediments from high-latitude lakes, located in northern European Russia and central Siberia, suggests that mean July air temperature is the most significant variable explaining chironomid distribution and abundance. This strong relationship enabled the development of a chironomid-based mean July air temperature-inference model based on 81 lakes and 89 taxa which has a rjack2 = 0.92 and RMSEP = 0.89 °C. Comparison of taxon responses to July temperature between this Russian and existing Norwegian data-sets shows that the temperature optima of individual taxa were between 1 and 3 °C higher in the Russian data regardless of modelling technique. Reconstructions based on fossil assemblages from a Russian tundra lake core (VORK5) using a Norwegian chironomid-based inference model provide mean July air temperature estimates that are 1.0–2.7 °C colder than from the 81-lake Russian model and are also lower than the instrumental record from a nearby meteorological station. The Norwegian model also did not reconstruct decadal-scale fluctuations in temperature seen in the instrumental record. These observations suggest that chironomid-based inference models should only be applied to sediment cores which have similar climate regimes to the geographic area of the training set. In addition a 149 lake, 120 taxa chironomid-based continentality inference model was also developed from the modern Norwegian and Russian training sets. A 2-component WA-PLS model was the minimal adequate model with rjack2 = 0.73 and RMSEP = 9.9 using the Gorczynski continentality index. Comparison of reconstructed continentality indices from the tundra lake, VORK5, show close agreement with local instrumental records over the past 70 years and suggest that the model is reliable. Recent warming in the Arctic has been spatially and seasonally heterogeneous; in many areas warming is more pronounced in the spring and autumn leading to a lengthening of the summer, while summer temperatures have remained relatively stable. A continentality inference model has the potential to detect these seasonal changes in climate. 相似文献