Stratigraphy of the mid-Holocene black bands in Lakes Michigan and Huron: Evidence for possible basin-wide anoxia

The post-glacial history of the Great Lakes has involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, outlet incision and isostatic rebound. The final lowering of lake levels occurred at approximately 7600 ¹⁴C yr BP, after which lake levels began to rise again to the Nipissing highstand at approximately 4700 ¹⁴C yr BP. During this time of rising lake levels, black bands of iron sulfide were being formed in the sediments of all five of the Great Lakes. These bands signify suboxic to anoxic conditions, at least within the sediments and possibly at the sediment-water interface, during the middle Holocene warm interval. During this interval, the climate was warmer and drier than present, possibly resulting in the occasional absence of seasonal turnover in the lakes. We examined a series of piston cores from northern Lakes Michigan and Huron and found that the black bands are correlatable among cores taken from within the same basin. The observation that the banding can be correlated suggests a basin-wide cause, near-bottom or sub-bottom anoxia in the northern Michigan and northern Huron sediments during the mid-Holocene warm period. The sedimentary and geochemical processes in the Great Lakes during the middle Holocene warm interval are good indicators of possible future scenarios for the lakes as a result of global warming, as 21^st-century temperatures are predicted to reach similar levels due to increased concentrations of greenhouse gases.     

Evaluating trophic status and restoration procedures of a polluted lake,Lake Kastoria,Greece

Lake Kastoria is a shallow lake with many anthropogenic activities concentrated in its catchment area. Surficial runoff rich in agricultural waste and underground seepage from urban and rural areas enrich the lake with nutrients intensifying the eutrophication problem of the water.Restoration techniques, with different approach, each one are proposed to restore the lake water. Treatment with alum is very effective but needs special care during the application. Reeds harvesting is an inexpensive and effective way and in combination with the city sewage redirection will improve the water quality and the trophic status of the lake sufficiently.     

Genetic implications of minor-element and Sr-isotope geochemistry of alkaline rock complexes in the Wet Mountains area,Fremont and Custer counties,Colorado

Concentrations of Rb, Sr, and REE (rare earth elements), and Sr-isotopic ratios in rocks of the Cambrian alkaline complexes in the Wet Mountains area, Colorado, show that rocks formed as end-products of a variety of magmas generated from different source materials. The complexes generally contain a bimodal suite of cumulus mafic-ultramafic rocks and younger leucocratic rocks that include nepheline syenite and hornblende-biotite syenite in the McClure Mountain Complex, nepheline syenite pegmatite in the Gem Park Complex, and quartz syenite in the complex at Democrat Creek. The nepheline syenite and hornblende-biotite syenite at McClure Mountain (535±5m.y.) are older than the syenitic rocks at Democrat Creek (511±8m.y.). REE concentrations indicate that the nepheline syenite at McClure Mountain cannot be derived from the hornblende-biotite syenite, which it intrudes, or from the associated mafic-ultramafic rocks. REE also indicate that mafic-ultramafic rocks at McClure Mountain have a source distinct from that of the mafic-ultramafic rocks at Democrat Creek.In the McClure Mountain Complex, initial⁸⁷Sr/⁸⁶Sr ratios for mafic-ultramafic rocks (0.7046±0.0002) are similar to those of hornblende-biotite syenite (0.7045±0.0002), suggesting a similar magmatic source, whereas ratios for carbonatites (0.7038±0.0002) are similar to those of nepheline syenite (0.7038±0.0002). At Democrat Creek, initial ratios of syenitic rocks (0.7032±0.0002) and mafic-ultramafic rocks (0.7028±0.0002) are different from those of corresponding rocks at McClure Mountain.     

The dynamics of conservative mixing in estuaries

Mixing plots, in which a dissolved constituent is plotted against salinity or chlorinity, are commonly used to interpret conservative and non-conservative processes in estuarine systems. A bend in the resulting curve is generally interpreted as indicative of the reactive or non-conservative nature of the constituent or the presence of multiple sources or sinks within the estuary. This paper demonstrates analytically that bends in mixing curves may also result from temporal variations in end-member (river or ocean) constituent concentrations even for conservative constituents. A one-dimensional dispersion equation is used to calculate the distribution of salinity and a conservative constituent in a model estuary. Both straight and bent mixing curves are shown resulting simply from changing the variability of the river constituent concentration. For no variability the curve is straight. For variability with a period much less than the flushing time, the average curve for a general data set straight, whereas the curve for a synoptic data set is bent. For variability with a period greater than the flushing time a bent curve results. Since bent mixing curves can occur for conservative properties, the use of these curves for interpretation of estuarine processes must be undertaken with an understanding of the temporal variability of the river and ocean constituents and their relationship to the estuary mixing properties and flushing time.     

Evidence for extensive diagenesis,Madagascar Basin,Deep Sea Drilling Site 245

Deep Sea Drilling Hole 245 (31°32′S, 52° 18′E) in the southwest Indian Ocean shows pronounced linear concentration-depth gradients in interstitial dissolved Ca, Mg and Sr. Electrical conductivity tests enable us to make the estimate of a constant diffusion coefficient with depth of about 2 × 10^?6 cm²/sec. The shapes of the concentration-depth gradients suggest that the major reaction sites in this hole are situated in the basal sediments and/or underlying basalts. It is proposed that observed interstitial water concentration changes in Ca and Mg are related to alteration of basaltic material, whereas those in Sr are due to calcium carbonate recrystallization processes. Support for the basaltic material alteration hypothesis comes from petrochemical and mineralogical data. Geochemical data also indicate that the high contents in Fe and Mn of the basal sediments can be related to low temperature alteration of basaltic glass and not necessarily to ‘hydrothermal’ activity.     

Effects of fluids on the interaction of granites with limestones: The Notch Peak stock,Utah

In this paper we consider the mechanisms by which the mineralogy and composition of the margins of the Notch Peak granitic stock, Utah, were affected by calcareous argillite country rocks. The contact zone of the granite relative to the unaffected granite is enriched in: K₂O from about 4 to 10 wt.%, Rb from 250 to 510 ppm, Sr from 150 to 790 ppm and Ba from 250 to 2160 ppm. Locally, some of the intrusive rocks at the contact are nearly devoid of quartz and can be classified as syenites. The initial ⁸⁷Sr/⁸⁶Sr ratios range from 0.7069 in the unaffected rocks to 0.7100 in the potassium-enriched samples, approaching the values of the calc-silicate country rocks of about 0.7110.Calculations show that the characteristics of the contact zone near the top of the stock are the result of a number of sequential processes. CO₂-rich fluids derived from the heated calcareous argillites apparently caused a shift in the phase boundaries in the magma, enhancing accumulation of K-feldspar and high-Ca augite at the expense of other phases. The accumulation resulted in the high Ba and Sr concentrations in some samples. However, the high K₂O and Rb concentrations and magmatic ¹⁸O values indicate infiltration of magmatic fluid emanating from the solidifying lower portions of the pluton subsequent to solidification of the cap. The minimum fluid-rock ratios of 4.6 by mass, calculated on the basis of K₂O and Rb concentration shifts, indicate that a substantial amount of the fluid was channeled through this contact zone. The desilication of the rocks forming the syenitic samples at the contact apparently occurred when a chemical potential gradient of silica between the granite and wall-rocks was established as quartz was consumed in the wall-rocks during calc-silicate reactions. The infiltrating magmatic fluid probably acted as a medium for transport of silica across the contact and perhaps exchange of Sr between the country rocks and the intrusion where up to 30% of strontium in the granitic and syenitic samples from the contact zone was derived from the calc-silicates. The syenitic rocks cannot be explained by desilication reactions involving assimilation of the calc-silicates by the granite magma. The results of this study show that fluids interacting with the country rocks need to be considered to explain the effects of country rocks on the composition of the margins of granitic intrusions.     

Drainage basins as process-response systems: An example from Central Macedonia,North Greece

Study of two subareas of the same large basin in North Greece determined that differences in processes and form exist between the two subareas. These differences were brought on by man's interference upon one of the subareas. In area A, seminatural vegetation promotes throughflow and protects the surface from overland flow. Hence, natural erosion takes place primarily by channel deepening and infall of side slopes into the channels. In area B, clearing of the seminatural vegetation and the improper ploughing for cultivation increases the overland flow which promotes slope erosion but the augmented debris supply has checked channel erosion. These processes change the form of the drainage basins of the area.     

An error analysis of profile flux,stability, and roughness length measurements made in the marine atmospheric surface layer

An analytical error analysis of profile-derived fluxes of heat, moisture, and momentum, along with stability and roughness length, is performed using the accuracies of the constituent temperature, humidity, and wind speed measurements. Five experiments, representing more than two thirds of the existing marine profile data presently contained in the literature, are compared. Much of the profile data examined was used to develop the transfer coefficients presently employed by a large number of competing bulk aerodynamic flux schemes. Depending upon the experiment, typical profile-method measurement errors were found to range from 15 to 35% for a sensible heat flux of ± 10 W m^-2, from 15 to 105% for a latent heat flux of ± 100 W m^-2, from 10 to 40% for a stress of 0.05 N m^-2, from 15 to 60% for a Monin-Obukhov stability of ± 0.05, and from 25 to 100% for a roughness length of 2 × 10^-4 m. Smaller magnitude flux values were found to contain typical errors as large as 100% for sensible heat flux, 300% for latent heat flux, and 60% for stress.     

Intercomparison of Two Box Models of the Chemical Evolution in Biomass-Burning Smoke Plumes

Results from two independently developed biomass-burning smoke plume models are compared. Model results were obtained for the temporal evolution of two nascent smoke plumes originating from significantly different fire environments (an Alaskan boreal forest and an African savanna). The two smoke plume models differed by 1%–10% for [O₃], with similar differences for NO _x and formaldehyde (relative percent differences). Smaller intermodel differences were observed for the African savanna smoke plume as compared to the plume from the Alaskan boreal fire. Mechanistic differences between the models are heightened for the Alaskan smoke plume due to the higher VOC emission ratios as compared to the African savanna fire. The largest deviations result from the differences in oxidative photochemical mechanisms, with a smaller contribution attributable to the calculation of photolysis frequencies. The differences between the two smoke plume models are significantly smaller than the uncertainties of available photokinetic data or field measurements. Model accuracy depends most significantly on having the fullest possible VOC data, a requirement that is constrained by currently available instrumentation.