Nitrogen cycling in the southern North Sea: consequences for total nitrogen transport     

K. Weston  T. D. Jickells  L. Fernand  E. R. Parker 《Estuarine, Coastal and Shelf Science》2004,59(4):559-573

Nitrate and ammonium uptake rates were measured during a series of cruises in the well-mixed region of the southern North Sea from February to September. Water column-integrated uptake rates ranged between 0.01 and 8.7 mmol N m⁻² d⁻¹ and 0.01 and 12.2 mmol N m⁻² d⁻¹ for nitrate and ammonium, respectively, with ammonium uptake dominating after the phytoplankton spring bloom in May. A moored buoy continuously measuring nitrate and chlorophyll a and seabed current meters were also deployed in the central southern North Sea in the region of the East Anglian plume—a permanent physical feature which transports nutrients towards continental Europe. This enabled the flux of water and hence of nutrients across the southern North Sea to be determined and an assessment of the contribution of freshwater nutrients to the flux to be made. A simple box model is developed to relate the phytoplankton uptake of nitrate and ammonium to the transport of nitrate, ammonium and particulate organic matter (POM) across the southern North Sea. This showed the importance of the plume region of the North Sea in the processing of nitrogen, with nitrate dominating total nitrogen transport prior to the spring bloom (10 340×10³ kg N inflow to the plume in March) and transport of nitrogen as ammonium, nitrate and POM in approximately equivalent amounts during summer (2560, 2960 and 2151×10³ kg N inflow to the plume, respectively, in July). The box model also demonstrates more generally the need to assess nitrogen transport as nitrate, ammonium and POM if an improved understanding of the impact of nutrient input in shelf seas is to be achieved.  相似文献   

Application of in situ target-strength estimations in lakes: examples from rainbow-smelt surveys in Lakes Erie and Champlain   总被引：1，自引：0，他引：1  

Rudstam  L.G; Parker  S.L; Einhouse  D.W; Witzel  L.D; Warner  D.M; Stritzel  J.L; Parrish  D.L; Sullivan  P.J 《ICES Journal of Marine Science》2003,60(3):500-507

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Effects of a crude oil and an oil dispersant (Corexit 9527) on populations of the littleneck clam (protothaca staminea)     

E. B. Hartwick  R. S. S. Wu  D. B. Parker 《Marine environmental research》1982,6(4):291-306

Field and laboratory experiments were carried out to investigate the effects of Alberta crude oil and an oil dispersant (Corexit 9527) on the larval settlement, survival, siphon activities and behaviour of the littleneck clam (Protothaca staminea). Corexit 9527 was much more toxic than crude oil, and the highest toxicity was obtained when Corexit 9527 was mixed with crude oil. Siphon activities were impaired and abnormal behaviour was exhibited when adult clams were treated with 100 ppm Corexit 9527, 1000 ppm crude oil or a combination of both. Larval settlement was not affected when the substratum was treated with 1000ppm crude oil but was retarded when the substratum was treated with a mixture of 1000 ppm oil and 100 ppm Corexit 9527. Gas chromatograms also showed that the retention time and depth of penetration of hydrocarbons in the substratum was increased when Corexit 9527 was used with crude oil.  相似文献   

Modelling the effects and economics of managed realignment on the cycling and storage of nutrients, carbon and sediments in the Blackwater estuary UK     

D. Shepherd  D. Burgess  T. Jickells  J. Andrews  R. Cave  R.K. Turner  J. Aldridge  E.R. Parker  E. Young   《Estuarine, Coastal and Shelf Science》2007,73(3-4):355-367

A hydrodynamic model is developed for the Blackwater estuary (UK) and used to estimate nitrate removal by denitrification. Using the model, sediment analysis and estimates of sedimentation rates, we estimate changes in estuarine denitrification and intertidal carbon and nutrient storage and associated value of habitat created under a scenario of extensive managed realignment. We then use this information, together with engineering and land costs, to conduct a cost benefit analysis of the managed realignment. This demonstrates that over a 50–100 year timescale the value of the habitat created and carbon buried is sufficient to make the large scale managed realignment cost effective. The analysis reveals that carbon and nutrient storage plus habitat creation represent major and quantifiable benefits of realignment. The methodology described here can be readily transferred to other coastal systems.  相似文献   

Stable nitrogen and carbon isotope ratios of beach tars on South Texas barrier islands     

Stephen A Macko  Patrick L Parker 《Marine environmental research》1983,10(2):93-103

Stable nitrogen and carbon isotope analyses have been used to characterize two major oil spills in the northwestern Gulf of Mexico. Stable isotope ratios were determined on both the crude material and on discrete chemical fractions of the whole oil (aliphatic, aromatic and NOS). A comparison of these isotopic compositions, of the crude materials and their chemical fractions, with those from samples of beach tars collected from south Texas barrier islands has indicated at least sixteen distinct isotopic signatures in the beach tars, excluding those resembling the major spills. This variation may be indicative of multiple sources of oils stemming from exploration and transport activities. Multiple isotope analysis can be a useful tool in the resolution of origins of spilled oils and tars.  相似文献   

The dust distribution within the inner coma of comet P/Halley 1982i: encounter by Giotto's impact detectors     

McDonnell JA  Alexander WM  Burton WM  Bussoletti E  Evans GC  Evans ST  Firth JG  Grard RJ  Green SF  Grun E  Hanner MS  Hughes DW  Igenbergs E  Kissel J  Kuczera H  Lindblad BA  Langevin Y  Mandeville JC  Nappo S  Pankiewicz GS  Perry CH  Schwehm GH  Sekanina Z  Stevenson TJ  Zarnecki JC et AL 《Astronomy and Astrophysics》1987,187(1-2):719-741

Analysis of the data from Giotto's Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (>10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.  相似文献   

The propagation of torsion along flux tubes subject to dynamical nonequilibrium     

E. N. Parker 《地球物理与天体物理流体动力学》2013,107(4):245-272

Abstract

The dynamical nonequilibrium of close-packed flux tubes is driven by the torsion in the individual tubes so that, wherever tubes with the same sense of twisting come into contact, there is reconnection of their azimuthal field components. The reconnection consumes the local torsion, causing the propagation of torsional Alfven waves into the region from elsewhere along the tubes.

The formal problem of the propagation of the torsion along twisted flux tubes is presented and some of the basic physical properties worked out in the limit of small torsion.

It is pointed out that in tubes with finite twisting the propagation of torsional Alfven waves can be a more complicated phenomenon.

Application to the sun suggests that the propagation of torsion from below the visible surface up into the corona is an important energy supply to the corona for a period of perhaps 10–20 hours after the emergence of the flux tubes through the surface of the sun, bringing up torsion from depths of 10⁴km or more. Torsion is continually supplied by the manipulation and shuffling of the field by the convection, of course.  相似文献   

The oil spill behaviour model of the canadian atmospheric environment service. Part II: Evaluation of model guidance for emergency response     

S. Venkatesh  V.R. Neralla  W. Hume  N. Parker  B. Thomson 《大气与海洋》2013,51(1):109-117

Abstract

In a companion paper the theoretical basis for the Canadian Atmospheric Environment Service oil spill behaviour model was discussed along with its evaluation, in non‐real time, using data collected from field experiments and a real spill. This paper deals with the use of the model in real time to provide guidance in support of the emergency created by an oil spill in the Canadian Beaufort Sea. The spill of about 2440 barrels of diesel oil occurred in September 1985, the result of storm damage to an artificial island used for hydrocarbon exploration.

Model simulations were carried out for two time periods while the spill was being tracked. These simulations identified the marked shifts in the direction of movement of the spill. While the predictive skills for the two time periods varied, with re‐initialization the final observed slick location was predicted to within 2 km. This model prediction was used by the regulatory authorities as guidance information in locating the slick when it could not be easily spotted from the air. The prediction of the size of the slick 27 h after initial time was in very good agreement with observations. A qualitative evaluation of the model‐simulated weathering of the oil was also carried out.  相似文献   

A temperature‐precipitation‐based model of thirty‐year mean snowpack accumulation and melt in Oregon,USA     

Scott G. Leibowitz  Parker J. Wigington Jr.    Randy L. Comeleo  Joseph L. Ebersole 《水文研究》2012,26(5):741-759

High‐resolution, spatially extensive climate grids can be useful in regional hydrologic applications. However, in regions where precipitation is dominated by snow, snowmelt models are often used to account for timing and magnitude of water delivery. We developed an empirical, nonlinear model to estimate 30‐year means of monthly snowpack and snowmelt throughout Oregon. Precipitation and temperature for the period 1971–2000, derived from 400‐m resolution PRISM data, and potential evapotranspiration (estimated from temperature and day length) drive the model. The model was calibrated using mean monthly data from 45 SNOTEL sites and accurately estimated snowpack at 25 validation sites: R² = 0·76, Nash‐Sutcliffe Efficiency (NSE) = 0·80. Calibrating it with data from all 70 SNOTEL sites gave somewhat better results (R² = 0·84, NSE = 0·85). We separately applied the model to SNOTEL stations located < 200 and ≥ 200 km from the Oregon coast, since they have different climatic conditions. The model performed equally well for both areas. We used the model to modify moisture surplus (precipitation minus potential evapotranspiration) to account for snowpack accumulation and snowmelt. The resulting values accurately reflect the shape and magnitude of runoff at a snow‐dominated basin, with low winter values and a June peak. Our findings suggest that the model is robust with respect to different climatic conditions, and that it can be used to estimate potential runoff in snow‐dominated basins. The model may allow high‐resolution, regional hydrologic comparisons to be made across basins that are differentially affected by snowpack, and may prove useful for investigating regional hydrologic response to climate change. Published in 2011 by John Wiley & Sons, Ltd.  相似文献   

Microvertebrates from the Rhaetian basal bone bed of Saltford,near Bath,SW England     

Matthieu Moreau  Christopher J. Duffin  Claudia Hildebrandt  Deborah Hutchinson  Adam Parker  Simon Carpenter  Michael J. Benton 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(2):174-187

The famous Rhaetian bone bed (Late Triassic, 205 Ma) is well known because it marks a major switch in depositional environment from terrestrial red beds to fully marine conditions throughout the UK and much of Europe. The bone bed is generally cemented and less than 10 cm thick. However, we report here an unusual case from Saltford, near Bath, S.W. England where the bone bed is unconsolidated and up to nearly 1 m thick. The exposure of the basal beds of the Westbury Formation, Penarth Group includes a bone bed containing a diverse Rhaetian marine microvertebrate fauna dominated by sharks, actinopterygian fishes and reptiles. Despite the unusual sedimentary character of the bone bed, we find similar proportions of taxa as in other basal Rhaetian bone beds (55–59 % Lissodus teeth, 13–16 % Rhomphaiodon teeth, 12–14 % Severnichthys teeth, 6–9% Gyrolepis teeth, 3–4% undetermined sharks’ teeth, 1–3% undetermined bony fish teeth, and < 1% of each of Hybodus, Parascylloides, and Sargodon), the only differences being in the proportions of Rhomphaiodon teeth, which can represent 30–40 % of specimens elsewhere. This suggests that taphonomic bias of varying Rhaetian bone beds may be comparable despite different sedimentary settings, and that the proportions of taxa say something about their original proportions in the ecosystem.  相似文献