A HYDROLOGICAL BUDGET FOR THE OKEFENOKEE SWAMP WATERSHED, 1981-82

Previous hydrological models of the Okefenokee Swamp watershed were developed without the benefit of accurate empirical data on surface runoff into and out of the swamp, and without data on direct ground water flow into the swamp. Data from a network of ground water observation wells during 1981-82 have revealed that ground water amounted to only 1.3% of total swamp inputs. This figure is much lower than had been expected and confirms that the swamp portion of the Okefenokee watershed is predominantly a surface-water system. A simple conceptual model of the watershed hydrology with upland and swamp compartments, and upland wetland, upland terrestrial, swamp prairie-marsh, and swamp forest-shrub subcompartments, indicates that in 1981-82 actual evapotranspiration from uplands and swamp was 78% and 84% of precipitation, respectively, and that upland surface runoff contributed only 13% of swamp inputs. Significant differences between the long-term and 1981-82 hydrological budgets emphasize that the Okefenokee Swamp is a dynamic hydrological system.     

DOUBLE FOURIER SERIES ANALYSIS OF COCKPIT AND DOLINE KARST NEAR BROWNS TOWN,JAMAICA

Double Fourier series models of two doline and two cockpit landscapes in northern Jamaica, each 2 × 2 km in area, explained 92% and 90%, and 73% and 58% of the variance in the topographic data. The ten most significant waves accounted for 74% and 76%, and 61% and 58% of the variance in each model. The greater importance of frequency pairs of longer wavelength in the doline karst models suggests that there are fewer horizontally and vertically persistent bedrock fractures controlling topographic development in the doline areas than in the cockpit terrains—a fact confirmed by fracture-trace mapping. Frequency pair orientations and powers indicate that north-west- and northeast-trending fractures exert a major influence on topographic development in the cockpit terrains and that east-trending fractures are relatively more important in the doline areas. Further studies are needed to determine if Fourier models of the doline, cockpit, and tower karst styles differ in a consistent fashion and to find out to what extent these differences are related to the bedding, fracture, and relief characteristics of the karst bedrock. [Key words: Jamaica, karst, morphometry, double Fourier series, dolines, cockpits.]     

Forming a large disc galaxy from a z < 1 major merger

Using high-resolution SPH simulations in a fully cosmological Λ cold dark matter context, we study the formation of a bright disc-dominated galaxy that originates from a 'wet' major merger at   z = 0.8  . The progenitors of the disc galaxy are themselves disc galaxies that formed from early major mergers between galaxies with blue colours. A substantial thin stellar disc grows rapidly following the last major merger and the present-day properties of the final remnant are typical of early-type spiral galaxies, with an i -band bulge-to-disc ratio ∼0.65, a disc scalelength of 7.2 kpc,   g − r = 0.5 mag  , an H  i linewidth ( W ₂₀/2) of 238 km s⁻¹ and total magnitude   i =−22.4  . The key ingredients for the formation of a dominant stellar disc component after a major merger are (i) substantial and rapid accretion of gas through cold flows followed at late times by cooling of gas from the hot phase, (ii) supernova feedback that is able to partially suppress star formation during mergers and (iii) relative fading of the spheroidal component. The gas fraction of the progenitors' discs does not exceed 25 per cent at   z < 3  , emphasizing that the continuous supply of gas from the local environment plays a major role in the regrowth of discs and in keeping the galaxies blue. The results of this simulation alleviate the problem posed for the existence of disc galaxies by the high likelihood of interactions and mergers for galaxy-sized haloes at relatively low z .     

Assessment of agricultural drought using a simple water balance model in the Free State Province of South Africa

Water Requirement Satisfaction Index (WRSI) at three different probability levels (20%, 50%, and 80%) was used to quantify drought affecting rain-fed maize production in the Free State Province of South Africa based on climate data from 227 weather stations. Results showed high spatial variability in the suitability of different areas: the southern and southwestern localities are unsuitable due to high drought incidences; the northern, central, and western regions are marginally suitable; the eastern, northerneastern areas and a few patches in the northwest are highly suitable with relatively low drought severity. Proper choice of maize varieties to suit conditions at different localities is crucial. The Mann–Kendall test and coefficient of variation were further used to determine trends and temporal variability, respectively, in the WRSI, seasonal rainfall, and seasonal maize water requirements. Results of this analysis revealed no significant positive trends in the WRSI, no significant negative trends in seasonal rainfall, and no significant positive trends in maize water requirements, contradicting previous findings of increased drought severity. Seasonal rainfall and the WRSI showed high interseasonal variability, while seasonal maize water requirements showed low variability. In view of these observations, it is apparent that realignment of management practices is an overdue prerequisite for sustainable maize production.     

Late Pleistocene eolian features in southeastern Maryland and Chesapeake Bay region indicate strong WNW–NW winds accompanied growth of the Laurentide Ice Sheet

Inactive parabolic dunes are present in southeastern Maryland, USA, along the east bank of the Potomac River. More elongate and finer-grained eolian deposits and paha-like ridges characterize the Potomac River–Patuxent River upland and the west side of Chesapeake Bay. These ridges are streamlined erosional features, veneered with eolian sediment and interspersed with dunes in the low-relief headwaters of Potomac- and Patuxent-river tributaries. Axis data for the dunes and ridges indicate formation by WNW–NW winds. Optically stimulated luminescence and radiocarbon age data suggest dune formation from  33–15 ka, agreeing with the 30–13 ka ages Denny, C.S., Owens, J.P., Sirkin, L., Rubin, M., 1979. The Parsonburg Sand in the central Delmarva Peninsula, Maryland and Delaware. U.S. Geol. Surv. Prof. Pap. 1067-B, 16 pp. suggested for eolian deposits east of Chesapeake Bay. Age range and paleowind direction(s) for eolian features in the Bay region approximate those for late Wisconsin loess in the North American midcontinent. Formation of midcontinent loess and Bay-region eolian features was coeval with rapid growth of the Laurentide Ice Sheet and strong cooling episodes (δ¹⁸O minima) evident in Greenland ice cores. Age and paleowind-direction coincidence, for eolian features in the midcontinent and Bay region, indicates strong mid-latitude WNW–NW winds for several hundred kilometers south of the Laurentide glacial terminus that were oblique to previously simulated anticyclonic winds for the last glacial maximum.     

PREDICTING WELL PRODUCTIVITY USING PRINCIPAL COMPONENTS ANALYSIS*

Principal components analysis of fracture trace and sinkhole characteristics near 33 wells drawing water from the Ocala aquifer identified three hydrogeologically significant components. Multiple regression analysis using these components as independent variables showed that the flow of water to a well bore is influenced in order of importance by (1) proximity to a zone of high secondary permeability; (2) average aquifer transmissivity near the well; and (3) degree of cavity development in the closest zone of high secondary permeability.     

A portable suction dredge for quantitative sampling in difficult substrates

A lightweight, portable suction dredge has been used for five bottom types which usually present problems to benthic investigators. Water depth ranged from 0.25 m to 5 m. By use of a 0.25 m² quadrat or using the suction end as a probe with the depth of penetration limited by a collar, quantitative samples were taken in coarse sand, fine flocculent mud, dense turtle grass (Thalassia testudinum), sparse turtle grass over coralline rubble (Porites sp.) and carbonate rock with an overlay of shell rubble. The samples consisted of the material retained by a collecting bag attached to the suction dredge. None of the commonly used benthic sampling devices could obtain samples at all stations.     

Glacial outlet valley size–ice drainage area relationships: some considerations

Previous work indicates that large variations in the power‐law relationship, relating glacial outlet valley size to ice drainage area, may occur between different glaciological settings. In this paper, we take issue with methods used to quantify the relationships of outlet valley size to drainage area size and propose a general method for comparing power‐law relationships between study areas, to determine whether or not such power‐law scalings are similar. Based on this method, we demonstrate that outlet valleys have a similar sensitivity to variation in ice‐contributing area irrespective of their glaciological setting, contrary to earlier findings. Minor variation in such relationships may reflect the different lithological and glaciological settings of the study sites and provide an insight into the physics of glacial erosional development of landscapes. Despite their limitations, we conclude that power‐law relationships are valid and, when interpreted carefully, provide a useful basis for comparing the efficiency of glacial erosion processes in different locations. Copyright © 2003 John Wiley & Sons, Ltd.     

The effect of metasomatism on the Cr-PGE mineralization in the Finero Complex, Ivrea Zone, Southern Alps

The magmatic metasomatism that was responsible for producing chromitite–dunite bodies in the unusual phlogopite peridotite of the Finero Complex in Permian to Triassic times also influenced the Cr-platinum group elements (PGE) mineralization. At least the end stages of this metasomatism are recorded in compositional zoning of chromite grains in the podiform chromitite. Metasomatic melt, with or without vapor, reacted with chromite to produce core-to-rim Cr enrichment of extant chromite grains and was concurrent with pyroxene crystallization. Under conditions of lower melt/rock ratio, metasomatism resulted in core-to-rim Al enrichment in chromite and crystallization of amphibole between chromite and clinopyroxene. This early, high-temperature metasomatism is unrelated to the later and pervasive K-metasomatism that crystallized phlogopite and was associated with the intrusion of clinopyroxenite dikes that cut the peridotite. Much later, serpentinization of olivine locally depleted chromite in Al and enriched it in Fe and formed minor amounts of magnetite.The PGE, which are present mainly as laurite inclusions in chromite, were remobilized by the early metasomatism. This resulted in substantial variation in the PGE contents of chromitites and imposed a characteristic PGE pattern in which chondrite-normalized Os, Ir, Ru and Rh contents are high but Pt and Pd contents are low. The slopes of PGE chondrite-normalized concentration patterns are systematically related to absolute PGE abundance and to rock mode. Chromitites with low modal orthopyroxene, clinopyroxene, and amphibole exhibit negative PGE slopes and contain relatively high PGE concentrations, whereas chromitites rich in these silicate minerals have positive slopes and low PGE contents.     

Cosmogenic Be dating of the Salpausselkä I Moraine in southwestern Finland

We determined in situ cosmogenic ¹⁰Be ages for nine boulders sampled on the Salpausselkä I (Ss I) Moraine. Previous dating of this moraine indicated that it formed during the Younger Dryas Stadial along the southern margin of the Scandinavian Ice Sheet in southern Finland. Our new exposure ages range from 10.9±1.0 to 13.5±1.2 ¹⁰Be ka, with an error-weighted mean age of 12.4±0.7 ¹⁰Be ka. Our results confirm four previous ¹⁰Be ages obtained 40 km northeast of our sample location. The combined data (n=13) indicate that retreat from the Ss I Moraine occurred at 12.5±0.7 ¹⁰Be ka, in excellent agreement with an age of 12.1 ka for retreat from the Ss I Moraine based on varve chronologies. These results identify the Ss I Moraine as among the best-dated margins associated with Late Quaternary ice sheets.