Abrupt deglaciation events and Holocene palaeoceanography from high-resolution cores,Cartwright Saddle,Labrador Shelf,Canada     

J. T. Andrews  L. Keigwin  F. Hall  Anne E. Jennings 《第四纪科学杂志》1999,14(5):383-397

The uppermost Quaternary sediments in Cartwright Saddle, Labrador Shelf, are acoustically laminated, with reflectors that can be traced over long distances. Two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the Laurentide Ice Sheet (LIS) during deglaciation. Variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr. The temporal sampling interval reaches decadal resolution in the last deglacial period 7–9 ka. Analyses of total carbonate content, sediment magnetic variables, foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca. 10.9, 9.2, 8.8, 7.9 and 7 ka (with 450 yr correction). There was no distinct change in sediment character during much of the Younger Dryas chronozone. In the δ¹⁸O record, the 8.8 ka event is a dramatic 1‰ shift toward lower values, which we associate with the Noble Inlet glacial event within Hudson Strait. We do not see the pronounced low δ¹⁸O event at 7.1 ka reported off Nova Scotia, but surprisingly, neither the Nova Scotia records nor other records in the Labrador Sea capture the impressive 8.8 ka change. Serious consideration must be given to the final collapse of the LIS as the cause of the 8.2 cal. ka cold event recorded in Greenland and northwest Europe. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

The influence of underwater data transmission sounds on the displacement behaviour of captive harbour seals (Phoca vitulina)     

Kastelein RA  van der Heul S  Verboom WC  Triesscheijn RJ  Jennings NV 《Marine environmental research》2006,61(1):19-39

To prevent grounding of ships and collisions between ships in shallow coastal waters, an underwater data collection and communication network (ACME) using underwater sounds to encode and transmit data is currently under development. Marine mammals might be affected by ACME sounds since they may use sound of a similar frequency (around 12 kHz) for communication, orientation, and prey location. If marine mammals tend to avoid the vicinity of the acoustic transmitters, they may be kept away from ecologically important areas by ACME sounds. One marine mammal species that may be affected in the North Sea is the harbour seal (Phoca vitulina). No information is available on the effects of ACME-like sounds on harbour seals, so this study was carried out as part of an environmental impact assessment program. Nine captive harbour seals were subjected to four sound types, three of which may be used in the underwater acoustic data communication network. The effect of each sound was judged by comparing the animals' location in a pool during test periods to that during baseline periods, during which no sound was produced. Each of the four sounds could be made into a deterrent by increasing its amplitude. The seals reacted by swimming away from the sound source. The sound pressure level (SPL) at the acoustic discomfort threshold was established for each of the four sounds. The acoustic discomfort threshold is defined as the boundary between the areas that the animals generally occupied during the transmission of the sounds and the areas that they generally did not enter during transmission. The SPLs at the acoustic discomfort thresholds were similar for each of the sounds (107 dB re 1 microPa). Based on this discomfort threshold SPL, discomfort zones at sea for several source levels (130-180 dB re 1 microPa) of the sounds were calculated, using a guideline sound propagation model for shallow water. The discomfort zone is defined as the area around a sound source that harbour seals are expected to avoid. The definition of the discomfort zone is based on behavioural discomfort, and does not necessarily coincide with the physical discomfort zone. Based on these results, source levels can be selected that have an acceptable effect on harbour seals in particular areas. The discomfort zone of a communication sound depends on the sound, the source level, and the propagation characteristics of the area in which the sound system is operational. The source level of the communication system should be adapted to each area (taking into account the width of a sea arm, the local sound propagation, and the importance of an area to the affected species). The discomfort zone should not coincide with ecologically important areas (for instance resting, breeding, suckling, and feeding areas), or routes between these areas.  相似文献   

The role of marine protected areas in environmental management   总被引：1，自引：0，他引：1  

Jennings  Simon 《ICES Journal of Marine Science》2009,66(1):16-21

  相似文献   

Stable isotopes in juvenile marine fishes and their invertebrate prey from the Thames Estuary,UK, and adjacent coastal regions     

Chris D.B. Leakey  Martin J. Attrill  Simon Jennings  Mark F. Fitzsimons 《Estuarine, Coastal and Shelf Science》2008

Estuaries are regarded as valuable nursery habitats for many commercially important marine fishes, potentially providing a thermal resource, refuge from predators and a source of abundant prey. Stable isotope analysis may be used to assess relative resource use from isotopically distinct sources. This study comprised two major components: (1) development of a spatial map and discriminant function model of stable isotope variation in selected invertebrate groups inhabiting the Thames Estuary and adjacent coastal regions; and (2) analysis of stable isotope signatures of juvenile bass (Dicentrarchus labrax), sole (Solea solea) and whiting (Merlangius merlangus) for assessment of resource use and feeding strategies. The data were also used to consider anthropogenic enrichment of the estuary and potential energetic benefits of feeding in estuarine nursery habitat.  相似文献   

Saturn's latitudinal C₂H₂ and C₂H₆ abundance profiles from Cassini/CIRS and ground-based observations     

Brigette E. Hesman  Donald E. Jennings  Gordon L. Bjoraker  Amy A. Simon-Miller  Robert J. Boyle  Leigh N. Fletcher 《Icarus》2009,202(1):249-259

Hydrocarbons in the upper atmosphere of Saturn are known, from Voyager, ground-based, and early Cassini results, to vary in emission intensity with latitude. Of particular interest is the marked increase in hydrocarbon line intensity near the south pole during southern summer, as the increased line intensity cannot be simply explained by the increased temperatures observed in that region since the variations between C₂H₂ and C₂H₆ emission in the south pole region are different. In order to measure the latitudinal variations of hydrocarbons in Saturn's southern hemisphere we have used 3 cm⁻¹ resolution Cassini CIRS data from 2006 and combined this with measurements from the ground in October 2006 at NASA's IRTF using Celeste, an infrared high-resolution cryogenic grating spectrometer. These two data sets have been used to infer the molecular abundances of C₂H₂ and C₂H₆ across the southern hemisphere in the 1-10 mbar altitude region. We find that the latitudinal acetylene profile follows the yearly average mean daily insolation except at the southern pole where it peaks in abundance. Near the equator (5° S) the C₂H₂ abundance at the 1.2 mbar level is (1.6±0.19)×¹⁰−7 and it decreases by a factor of 2.7 from the equator toward the pole. However, at the pole (∼87° S) the C₂H₂ abundance jumps to (1.8±0.3)×¹⁰−7, approximately the equatorial value. The C₂H₆ abundance near the equator at the 2 mbar level is (0.7±0.1)×¹⁰−5 and stays approximately constant until mid-latitudes where it increases gradually toward the pole, attaining a value of (1.4±0.4)×¹⁰−5 there. The increase in ethane toward the pole with the corresponding decrease in acetylene is consistent with southern hemisphere meridional winds [Greathouse, T.K., Lacy, J.H., Bézard, B., Moses, J.I., Griffith, C.A., Richter, M.J., 2005. Icarus 177, 18-31]. The localized increase in acetylene at the pole provides evidence that there is dynamical transport of hydrocarbons from the equator to the southern pole.  相似文献   

Titan's prolific propane: The Cassini CIRS perspective     

C.A. Nixon  D.E. Jennings  B. Bézard  P.G.J. Irwin  A. Coustenis  F.M. Flasar 《Planetary and Space Science》2009,57(13):1573-1585

Although propane gas (C₃H₈) was first detected in the stratosphere of Titan by the Voyager IRIS infrared spectrometer in 1980, obtaining an accurate measurement of its abundance has proved difficult. All existing measurements have been made by modeling the ν₂₆ band at : however, different analyzes over time have yielded quite different results, and it also suffers from confusion with the strong nearby ν₅ band of acetylene. In this paper we select large spectral averages of data from the Cassini Composite Infrared Spectrometer (CIRS) obtained in limb-viewing mode at low latitudes (30^°S-30^°N), greatly increasing the path length and hence signal-to-noise ratio for optically thin trace species such as propane. By modeling and subtracting the emissions of other gas species, we demonstrate that at least six infrared bands of propane are detected by CIRS, including two not previously identified in Titan spectra. Using a new linelist for the range 1300-1400 cm^-1, along with an existing GEISA list, we retrieve propane abundances from two bands at 748 and 1376 cm^-1. At 748 cm^-1 we retrieve 4.2±0.5×10^-7 (1-σ error) at 2 mbar, in good agreement with previous studies, although lack of hotbands in the present spectral atlas remains a problem. We also determine 5.7±0.8×10^-7 at 2 mbar from the 1376 cm^-1 band — a value that is probably affected by systematic errors including continuum gradients due to haze and also an imperfect model of the ν₆ band of ethane. This study clearly shows for the first time the ubiquity of propane's emission bands across the thermal infrared spectrum of Titan, and points to an urgent need for further laboratory spectroscopy work, both to provide the line positions and intensities needed to model these bands, and also to further characterize haze spectral opacity. The present lack of accurate modeling capability for propane is an impediment not only for the measurement of propane itself, but also for the search for the emissions of new molecules in many spectral regions.  相似文献   

Irish peat slides 2006�C2010     

Michael Long  Paul Jennings  Roselyn Carroll 《Landslides》2011,8(3):391-401

The purpose of this paper is to present a review of peat landslide events in Ireland since 2003, when two significant events occurred. Since 2003, there have been at least 13 such events. Several of these events included more than one slide. It is also likely that there have been unrecorded slides. It seems that there is an increasing incidence of such events, but they seem to occur in clusters with intervening quiet periods. These clusters coincide with periods of intense rainfall. For many slides, at least two causal factors can be identified. Primarily these comprised intense rainfall but human activities such as road construction and peat cutting also contributed to the slides. Detailed geotechnical testing of the peat, including laboratory direct simple shear tests (DSS), is reported for two of the slides. Back-analysis of these two failures suggests that the mobilised strength of the material in the failure surface is similar to that measured in the DSS tests. However, conventional geotechnical analyses need to be treated with caution as they fail to account for the complex interactions in the sliding surface and in particular the lubricating role of water.  相似文献   

Processes and timescales by which a coastal gravel-dominated barrier responds geomorphologically to sea-level rise: Story head barrier,Nova Scotia     

J. D. Orford  R. W. G. Carter  S. C. Jennings  A. C. Hinton 《地球表面变化过程与地形》1995,20(1):21-37

Sea-level rise (SLR) is considered to be important for barrier behaviour when barriers are swash-aligned and single-crested, which is typical of only one part of a barrier's lifeterm. Under such conditions gravel-barrier retreat rate correlates with mesoscale (sub-decadal: <10¹ a) SLR rate. Barrier crest overwashing, depending on surge frequency/magnitude, is recognized as the dynamic element that controls barrier retreat rate. Surge characterization of the Halifax tide gauge (using an annual forcing coefficient derived from tide gauge surge residuals) is shown to have high correlation with Story Head (Nova Scotia) barrier retreat rate between 1945 and 1987. Barrier response appears to vary as a function of mesoscale (sub-decadal) SLR and antecedent barrier conditions in combination with the forcing coefficient. Mesoscale (10⁰ a–10² a) rather than macroscale (> 10² a) SLR rate is the critical control on barrier retreat, as mesoscale SLR variation in combination with surge potential is able to raise water level to the elevation threshold sufficient for barrier overwash and hence drive barrier retreat.  相似文献   

Relationship between low-grade gold disseminations and high-grade veins in the Quartz Mountain district,Oregon     

V. F. Hollister  D. S. Jennings 《Natural Resources Research》1993,2(4):284-291

Gold and mercury mineralization related to epithermal hot springs occurs spatially associated with rhyolite dome complexes in the Quartz Mountain district, Lake County, Oregon. Drilling of over 800 holes from 1983 to 1991, mostly by Quartz Mountain Gold Corp., has resulted in a mineral inventory of at least 100,000,000 tons, averaging 0.0255 ounce gold per ton in two near-surface, disseminated gold ore bodies, Quartz Butte and Crone Hill. Extensive gold disseminations are underlain by and include rare, higher-grade veins that could be feeders for the near-surface, quasi-horizontal, pervasively mineralized gold dissemination. The veins contain about 2,000,000 tons of ore, aver-aging 0.29 ounce gold per ton. Approximately 750,000 tons of this underlie Quartz Butte, and the remainder is included in the Crone Hill low-grade dissemination. With a mineral inventory of about 3,000,000 ounces, Quartz Mountain is currently the largest known gold deposit in Oregon.As now known, the veins seem too few in number and too sporadically positioned to account for the volume of near-surface gold disseminations. We offer hypotheses to explain the apparent anomaly between the volume of disseminated gold ore and the paucity of feeders. Quartz Mountain has numerous alteration and mineralization similarities with the well-studied Steamboat Springs district (White and others, 1964). Coincidences between the two districts are noted.  相似文献   

The age of Canberra landforms     

J. N. Jennings 《Australian Journal of Earth Sciences》2013,60(3):371-378

The interpretation of Canberra's landforms as unexhumed survivals from Bowning faulting and mid‐Devonian vulcanicity is opposed. Some major faults are truncated whereas sharp scarps coincide with others. In the nearby Taemas area, the Canberra‐Yass Plains cut across Tabberabberan folds. Summit surface remnants surviving high in the A.C.T. Ranges and discordant river gorges are incompatible with extreme age of the relief. River nick‐points and steps between surfaces are some related and some unrelated to faults, with like import. Stripping of the Murrumbidgee Batholith, also of Bowning age, would have caused substantial filling of the Canberra Rift; during subsequent removal, erosion would not have entirely respected Silurian rocks similar in resistance to Devonian fill. Permian rocks to the east must in part derive from erosion of the Canberra area. Local rates of denudation of 5 cm/1000 y. are hard to reconcile with survival of high steep relief from the mid‐Devonian.

Alternative explanations are given for those characters of the Fyshwick Gravels which led them to be regarded as Permian glaciofluvials.

The same evidence supports Browne's standpoint that the relief is polycyclic through epeirogenic uplift at intervals, together with posthumous movement along some old faults.  相似文献