Effect of bed surface roughness on longitudinal dispersion in artificial open channels

In several empirical and modelling studies on river hydraulics, dispersion was negatively correlated to surface roughness. In this study, it was aimed to investigate the influence of surface roughness on longitudinal dispersion under controlled conditions. In artificial flow channels with a length of 104 m, tracer experiments with variations in channel bed material were performed. By use of measured tracer breakthrough curves, average flow velocity, mean longitudinal dispersion, and mean longitudinal dispersivity were calculated. Longitudinal dispersion coefficients ranged from 0·018 m² s^?1 in channels with smooth bed surface up to 0·209 m² s^?1 in channels with coarse gravel as bed material. Longitudinal dispersion was linearly related to mean flow velocity. Accordingly, longitudinal dispersivities ranged between 0·152 ± 0·017 m in channels with smooth bed surface and 0·584 ± 0·015 m in identical channels with a coarse gravel substrate. Grain size and surface roughness of the channel bed were found to correlate positively to longitudinal dispersion. This finding contradicts several existing relations between surface roughness and dispersion. Future studies should include further variation in surface roughness to derive a better‐founded empirical equation forecasting longitudinal dispersion from surface roughness. Copyright © 2011 John Wiley & Sons, Ltd.     

Provenance of deep-water reservoir sandstones from the Jubarte oil field,Campos Basin,Eastern Brazilian Margin

The provenance of the Maastrichtian deep-water reservoir sandstones from the Jubarte oil field (Campos Basin, eastern Brazil), was studied using an integrated approach that included quantitative petrography, conventional heavy mineral analysis, garnet mineral chemistry and zircon geochronology. The reservoirs are predominantly coarse, poorly-sorted sandstones with feldspathic composition derived from uplifted basement terrains. The fourth- and fifth-order depositional sequences analyzed show no major variations in composition or in provenance through time. However, variations in apatite:tourmaline presents potential to be used as a parameter for sandstone correlation within the field. The composition of heavy minerals indicates derivation from high temperature and low-to-medium pressure aluminous metapelitic rocks, from granites and subordinate mafic rocks, derived from the Cabo Frio Tectonic Domain and the Oriental terrain of Ribeira orogen, characterizing a supply route from SW to NE. The low ZTR index, as well as the absence of low-grade stable heavy minerals and of metasedimentary rock fragments, suggest that by the end of Cretaceous all supracrustal, low-grade terrains had already been totally eroded, and that plutonic, infracrustal rocks were exposed, similarly to the present situation.     

The <Emphasis Type="Italic">Wind</Emphasis>/EPACT Proton Event Catalog (1996 – 2016)

We present the finalized catalog of solar energetic proton events detected by the Wind/EPACT instrument over the period 1996?–?2016. Onset times, peak times, peak proton intensity and onset-to-peak proton fluence are evaluated for the two available energy channels, at about 25 and 50 MeV. We describe the procedure utilized to identify the proton events and to relate them to their solar origin (in terms of flares and coronal mass ejections). The statistical relationships between the energetic protons and their origin (linear and partial correlation analysis) are reported and discussed in view of earlier findings. Finally, the different trends found in the first 8 years of Solar Cycles 23 and 24 are discussed.     

Differences in trace metal concentrations among fluvial morphologic units and implications for sampling

 This study examines the segregation of trace metals within and between fluvial morphologic units in sand-sized and finer bed sediments in a cobble bed stream. The types of fluvial morphologic units sampled are low gradient riffles, high gradient riffles, glides, eddy drop zones, lateral scour pools, attached bars, and detached bars. Three to nine samples were collected from ten of each type of morphologic unit. All 12 metals show significantly different concentrations between some morphologic units in sediments smaller than 2 mm. Eddy drop zones and attached bars consistently have the highest metal concentrations, while low gradient riffles, high gradient riffles, and glides typically have the lowest concentrations. Metals showing the greatest between-unit variability are Al, Cr, Fe, Cu, and Ti, followed by Co, Mn, and Pb, while Mg, Mn, V, and Zn display relatively few differences between units. Lateral and longitudinal variations of metals within units are not significant, and there was no consistent, predictable variation in metal concentrations with distance downstream. Results indicate that metal studies in other gravel- and cobble-bed streams should include a reconnaissance survey to determine variations between morphologic units, stratify sampling by morphologic unit, and analyze spatial autocorrelation to determine sample spacing. Received: October 1997 · Accepted: 23 March 1998     

The activities of potassium chloride and of water in Dead Sea brine

The activities of KCl and of H₂O in Dead Sea water were estimated according to several approaches dealing with multicomponent electrolyte solutions. The activity of H₂O, both measured directly via its vapor pressure and calculated theoretically, is 0.754 ± 0.004 for brine of density 1.207 ± 0.003gcm^?3 at 25°C. The mean ionic activity of KCl in this brine ranges from 0.876 to 1.199 according to various treatments. These correspond to binary aqueous solutions 8.6–12.1 times richer than the brine. The brine cannot be simultaneously in equilibrium with respect to both H₂O and KCl with such binary solutions, so a hypothetically perfect semipermeable membrane cannot lead to a state of equilibrium between the brine and aqueous KCl of any concentration.     

Diapycnal heat flux and mixed layer heat budget within the Atlantic Cold Tongue

Sea surface temperatures (SSTs) in the eastern tropical Atlantic are crucial for climate variability within the tropical belt. Despite this importance, state-of-the-art climate models show a large SST warm bias in this region. Knowledge about the seasonal mixed layer (ML) heat budget is a prerequisite for understanding SST mean state and its variability. Within this study all contributions to the seasonal ML heat budget are estimated at four locations within the Atlantic cold tongue (ACT) that are representative for the western (0°N, 23°W), central (0°N, 10°W) and eastern (0°N, 0°E) equatorial as well as the southern (10°S, 10°W) ACT. To estimate the contribution of the diapycnal heat flux due to turbulence an extensive data set of microstructure observations collected during ten research cruises between 2005 and 2012 is analyzed. The results for the equatorial ACT indicate that with the inclusion of the diapycnal heat flux the seasonal ML heat budget is balanced. Within the equatorial region, the diapycnal heat flux is essential for the development of the ACT. It dominates over all other cooling terms in the central and eastern equatorial ACT, while it is of similar size as the zonal advection in the western equatorial ACT. In contrast, the SST evolution in the southern ACT region can be explained entirely by air-sea heat fluxes.     

Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)

It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.