Variation and uncertainty in evaporation from a subtropical estuary: Florida Bay     

René M. Price  William K. Nuttle  Bernard J. Cosby  Peter K. Swart 《Estuaries and Coasts》2007,30(3):497-506

Variation and uncertainty in estimated evaporation was determined over time and between two locations in Florida Bay, a subtropical estuary. Meteorological data were collected from September 2001 to August 2002 at Rabbit Key and Butternut Key within the Bay. Evaporation was estimated using both vapor flux and energy budget methods. The results were placed into a long-term context using 33 years of temperature and rainfall data collected in south Florida. Evaporation also was estimated from this long-term data using an empirical formula relating evaporation to clear sky solar radiation and air temperature. Evaporation estimates for the 12-mo period ranged from 144 to 175 cm yr⁻¹, depending on location and method, with an average of 163 cm yr⁻¹ (±9%). Monthly values ranged from 9.2 to 18.5 cm, with the highest value observed in May, corresponding with the maximum in measured net radiation. Uncertainty estimates derived from measurement errors in the data were as much as 10%, and were large enough to obscure differences in evaporation between the two sites. Differences among all estimates for any month indicate the overall uncertainty in monthly evaporation, and ranged from 9% to 26%. Over a 33-yr period (1970–2002), estimated annual evaporation from Florida Bay ranged from 148 to 181 cm yr⁻¹, with an average of 166 cm yr⁻¹. Rainfall was consistently lower in Florida Bay than evaporation, with a long-term average of 106 cm yr⁻¹. Rainfall considered alone was uncorrelated with evaporation at both monthly and annual time scales; when the seasonal variation in clear sky radiation was also taken into account both net radiation and evaporation were significantly suppressed in months with high rainfall.  相似文献   

The isotopic composition of respired carbon dioxide in scleractinian corals: Implications for cycling of organic carbon in corals     

Peter K. Swart  Alina Szmant  Richard E. Dodge  John R. Southam 《Geochimica et cosmochimica acta》2005,69(6):1495-1509

The origin of δ¹³C variations within the skeletons of zooxanthellate scleractinian corals is still a matter of considerable debate. In particular, the role respired CO₂ plays in controlling the eventual δ¹³C of the skeleton remains unclear. In this study, the temporal variability of the δ¹³C of respired CO₂ produced by Montastraea faveolata has been measured at approximately monthly intervals over a 1-year period. In these experiments, three corals maintained on a platform at 8 m depth near Molasses Reef in the Florida Keys were incubated in closed chambers for 24-h periods and samples of the incubation water analyzed for the δ¹³C of the dissolved inorganic carbon (ΣCO₂) at ∼3-h intervals. Throughout the incubation, the concentration of O₂ was measured continuously within the chamber. Our results show that during daylight, the δ¹³C of the ΣCO₂ in the incubation water becomes enriched in ¹³C as a result of fractionation during the fixation of C by photosynthesis, whereas at night the δ¹³C of the ΣCO₂ becomes more negative. The δ¹³C of the respiratory CO₂ ranges from −9‰ in the late spring to values as low as −17‰ in the autumn. The lighter values are significantly more negative than those reported by previous workers for coral tissue and zooxanthellae. An explanation for this discrepancy may be that the corals respire a significant proportion of isotopically negative substances, such as lipids, which are known to have values up to 10‰ lighter compared to the bulk δ¹³C of the tissue. The clear seasonal cycle in the δ¹³C of the respiratory CO₂ suggests that there is also seasonal variability in either the δ¹³C of the coral tissue or the type and/or amount of organic material being respired. A similar temporal pattern and magnitude of change was observed in the δ¹³C of the coral tissue samples collected from a nearby reef at monthly intervals between 1995 and 1997. These patterns are similar in timing to the δ¹³C measured in the coral skeletons. We have also calculated an annual mean value for the fractionation factor between dissolved CO₂⁻ in the external environment and photosynthate fixed by the zooxanthellae of 1.0121 (±0.003). This value is inversely correlated with the ratio of photosynthesis to respiration (P/R) of the entire organism and shows the highest values during the summer months.  相似文献   

Vertical structure of residual slope circulation driven by JEBAR and tides: an idealised model     

Meinte Blaas  Huib E. de Swart   《Continental Shelf Research》2002,22(18-19)

The residual circulation over the continental slope, and in particular, its vertical structure, is analysed by means of an idealised hydrodynamic model. The model is based on the depth-dependent shallow-water equations under uniform along-isobath conditions and is forced by a prescribed meridional density gradient and tidal velocities. By means of expansion in the small Rossby number solutions are analysed for conditions representative for the continental slopes off the Hebrides and in the Bay of Biscay. The steady solution at zeroth order consists of a linear density-driven flow. At order a tidally rectified flow is found and a stationary flow due to self-interaction of the zeroth-order density-driven flow. At order ² the leading-order effect of the interaction between the zeroth-order density-driven flow and the tides is found: the ‘interaction current’. The solutions up to and including order ² constitute an along-isobath steady slope current which is comparable to field data. The slope current and the accompanying cross-shelf circulation depend strongly on the shelf and flow characteristics. For the Hebridean case the density forcing predominates, but for the Biscay case the tidal effects are of the same order of magnitude as the density effects. Under those conditions the interaction current is significant which implies that linear superposition of density and tidal effects differs from the non-linear combination of both. It is also shown that the depth-average of the interaction current differs essentially from the solution obtained from a depth-averaged model.  相似文献   

Identifying Environmental and Human Factors Associated With Tick Bites using Volunteered Reports and Frequent Pattern Mining   总被引：1，自引：0，他引：1       下载免费PDF全文

Irene Garcia‐Martí  Raul Zurita‐Milla  Arno Swart  Kees C. van den Wijngaard  Arnold J.H. van Vliet  Sita Bennema  Margriet Harms 《Transactions in GIS》2017,21(2):277-299

Tick populations and tick‐borne diseases like Lyme borreliosis have been steadily increasing since the mid‐1990s. Realizing the threat that ticks pose to public health, two Dutch citizen science projects have collected tick bite reports since 2006. This unique volunteered geographical dataset, which currently has nearly 35,000 reports, was used to identify environmental and other circumstantial factors associated with tick bites. For this, we first enriched the tick bite reports with temperature, precipitation, vegetation and volunteered data associated with the location of the tick bite. Using this enriched dataset, we then derived a series of features to characterize the environmental and volunteer‐related conditions in which each tick bite occurred. Next, we discretized these features using the Jenks Natural Breaks algorithm and, after that, we mined frequent environmental patterns associated with tick bites using the AprioriClose algorithm. Finally, we checked that these patterns are specifically associated with the tick bites by comparing them with the frequent patterns mined from pseudo‐random locations. The frequent patterns were visualized using heat maps and ring maps and two representative patterns associated with tick bites were projected into geographic space to study their spatio‐temporal distribution. Our results show that factors linked to human activity are more relevant to model tick bites than seasonal accumulations of temperature, vegetation or precipitation. In particular, the number of warm and dry days per season are present in a significant number of patterns and the majority of tick bites are produced within a distance of half a kilometer of a forest, recreational or built‐up area. The study of patterns in the time‐series revealed that there are several persistent patterns consistently occurring each year and the validation process showed that the volunteer tick bites collection is capturing environmental conditions associated with tick bites, suggesting that these reports have a high scientific value. These results support the creation of a Dutch tick bite risk map that, in turn, will open the door to the design of public health interventions to reduce the incidence of Lyme disease.  相似文献   

A comparison of ABL heights inferred routinely from lidar and radiosondes at noontime     

W. A. J. Van Pul  A. A. M. Holtslag  D. P. J. Swart 《Boundary-Layer Meteorology》1994,68(1-2):173-191

The height of the atmospheric boundary layer (ABL) obtained with lidar and radiosondes is compared for a data set of 43 noon (12.00 GMT) cases in 1984. The data were selected to represent the synoptic circulation types appropriately. Lidar vertical profiles at 1064 nm were used to obtain three estimates for the ABL height (h _lid), based on the first gradient in the back-scatter profile, namely, at the beginning, middle and top of the gradient. The boundary-layer height obtained with the radiosondes (h _s) was determined with the dry-parcel-intersection method in unstable conditions. As a first guess for near-neutral and stable conditions, the height of the first significant level in the potential temperature profile was taken. Overall, the boundary-layer thickness estimates agree surprisingly well (regression lineh _lidb=h_s:cc.=0.93 and the standard error=121 m). However, in 10% of the cases, the lidar estimate was significantly lower (difference>400 m) than the routinely inferredh _s. These outliers are discussed separately. For stable conditions, an estimate of ABL height (h _N) is also made based on the friction velocity and the Brunt-Väisälä frequency. The agreement betweenh _Nandh _lidbis good. Discrepancies between the two methods are caused by:

1. rapid growth of the boundary layer arround the measurement time;
2. the presence of a deep entrainment layer leading to a large zone in which quantities are not well mixed;
3. a large systematic error of 100–200 m in the estimate of boundary-layer height obtained from the radiosonde due to the way that profiles are recorded, as a series of significant points.

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Morphodynamics of ebb-tidal deltas: a model approach   总被引：1，自引：0，他引：1  

S. M. van Leeuwen  M. van der Vegt  H. E. de Swart 《Estuarine, Coastal and Shelf Science》2003,57(5-6):899-907

The results of 2DH numerical models of the Frisian Inlet (located in the Dutch Wadden Sea) are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb-tidal deltas and of channels and shoals in tide-dominated inlet systems. A hydrodynamic model, extended with sediment transport formulations, was used to verify earlier conceptual models that deal with ebb-tidal delta characteristics. The model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb-tidal deltas and suggests that long-term morphological simulations are needed to understand this aspect. Furthermore, the model indicates that the initial formation of the ebb-tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents, whilst the net sediment transport in the basin is mainly caused by tidal asymmetry. A second model (accounting for feedbacks between tidal motion and the erodible bottom) was used to simulate the long-term bathymetric evolution of the Frisian Inlet under fair weather conditions. This model reproduces the gross characteristics of the observed morphology: the presence of a double-inlet system with two distinct ebb-tidal deltas having different sizes and the presence of channels and shoals. The role of the ‘Engelsmanplaat’, a consolidated shoal in the middle of the Frisian Inlet, was not found to be crucial for the morphodynamic stability of this inlet system.  相似文献   

Editorial: Citations and other musings     

Peter Swart  Paul Carling 《Sedimentology》2008,55(5):1115-1116

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Carbon and oxygen isotope fractionation in scleractinian corals: a review     

Peter K. Swart 《Earth》1983,19(1):51-80

The present theories on the fractionation of stable isotopes in scleractinian corals are critically discussed in the light of data available on primary productivity, respiration and stable isotope chemistry. These data support a model of fractionation in which the carbon and oxygen isotopes are decoupled. Calcification occurs from a reservoir of carbon dioxide derived from both organic and inorganic sources. Photosynthesis preferentially fixes¹³C and thereby leaves behind¹³C. Increases in the rate of photosynthesis therefore also enrich the carbon isotope ratio of the skeleton. From theoretical considerations, photosynthesis has little effect on the oxygen isotope ratio of the skeleton, a fact confirmed by available data. The process of respiration adds depleted carbon and oxygen to the calcification reservoirs. The varying correlations between carbon and oxygen isotopes seen in hermatypic corals are caused by changes in the relationship between photosynthesis and respiration at different geographical localities. The isotopic compositions in the skeletons of non-zooxanthellate corals, which show a consistent positive correlation, can also be explained by the above scenario.  相似文献   

The carbon and nitrogen isotopic composition of ureilites: Implications for their genesis     

M.M. Grady  I.P. Wright  P.K. Swart  C.T. Pillinger 《Geochimica et cosmochimica acta》1985,49(4):903-915

Fourteen ureilites were analyzed for stable C isotopic composition using stepped combustion. The δ¹³C values over the temperature range 500 to 1000°C are fairly constant for any particular meteorite although there are differences between samples. The similarity in combustion temperatures of pure diamond (600–1000δC) and pure graphite (600–800°C) makes it difficult to ascertain the relative proportions of either component within each sample. However, the constant δ¹³C values observed over the range 500 to 1000°C strongly suggests that ureilite diamond and graphite have the same isotopic composition. This would seem to confirm that the diamond in ureilites formed from the graphite during a process, presumably an impact event, which did not fractionate C isotopes.There is a variation in C isotopic composition of graphite/diamond intergrowths among ureilites, which is not continuous—the samples fall into two groups, with δ¹³C values clustered around ?10%. and ?2%. PDB. These groups are also distinguishable on the basis of the Fe content of their olivines, which may reflect the existence of more than one ureilite parent body. The brecciated ureilite North Haig has a δ¹³C value of ?6.5%. and it is thus possible that this sample contains components from mixed parent materials.Nitrogen abundance and stable isotope measurements were made on five samples using stepped combustion analysis. Nitrogen concentrations range from 25 to 150 ppm and $\text{C}\text{N}$ ratios are substantially less than for carbonaceous chondrites. Variation in N isotopic composition is wide and there is evidence of different ratios in diamond/graphite, silicate and metal.  相似文献   

An integrated model for the assessment of the greenhouse effect: The Dutch approach   总被引：1，自引：0，他引：1  

Jan Rotmans  Hans De Boois  Robert J. Swart 《Climatic change》1990,16(3):331-356

This paper describes a simulation policy model of the combined greenhouse effects of trace gases. With this model, the Integrated Model for the Assessment of the Greenhouse Effect (IMAGE) scenarios for the future impact of the greenhouse effect can be made, based on different assumptions for technological and socio-economic developments. The contribution of each trace gas can be estimated separately.Basically the model, consisting of a number of coupled modules, gives policy makers a concise overview of the problem and enables them to evaluate the impact of different strategies. Because the model covers the complete cause-effect relationship it can be utilized to derive allowable emission rates for the different trace gases from set effect related targets. Regular demonstration sessions with the simulation model have proven the importance of such science based integrated models for policy development.Four different scenarios are worked out for the most important trace gases (CO₂, CH₄, N₂O, CFC-11 and CFC-12). One of these scenarios can be regarded as a growth scenario unrestricted by environmental concerns. The others are based on different strategic policies. After the simulation of future trace gas concentrations global equilibrium temperature increases are computed. Finally the sea level rise, the most threatening effect of the greenhouse problem for the Netherlands, is estimated.Simulation results so far emphasize the importance of trace gases other than CO₂. The Montreal Protocol on reduction of CFC is found to stabilize the relative contribution of these substances to the greenhouse effect.  相似文献