Mean annual poleward energy transports by the oceans in the southern hemisphere

A survey is made of the published estimates of the components of the poleward flux of energy by the atmosphere in the Southern Hemisphere in order to determine the total atmospheric transport. Together with recent measurements by satellite of the Earth's radiation budget this allows a new estimate of the required poleward energy transport by the oceans in the Southern Hemisphere for mean annual conditions. Results show that the ocean and atmosphere each contribute similar amounts for 0–30°S and that the ocean probably also transports about one third of the total at 60°S. The latter is in contrast to similar latitudes in the Northern Hemisphere where the ocean transport is negligible, but consistent with the different distribution of land and sea in the two hemispheres.     

Lowland Maya water management practices: The household exploitation of rural wells

A hypothesis developed by Vernon Scarborough and endorsed and modified by Lisa Lucero and Anabel Ford proposes that lowland Maya elites centralized and coordinated political power by controlling access to water stored in large, centrally located reservoirs. The hypothesis presupposes that in the central and southern Maya lowlands, nonelites did not have access to viable alternative dry‐season water sources. This paper demonstrates that, in the east‐central and southwestern areas of the Maya lowlands, fault springs were an important source of water, particularly to rural peoples. After reviewing the evidence of Maya fault spring exploitation and documenting the hydrogeological conditions under which fault springs form, I describe wells that rural households built to expose fault springs and enhance their flow, including clay‐lined and stone‐lined shafts. Also documented are three well types found elsewhere in the Maya lowlands: (1) wells built to exploit permanent, generally shallow water tables; (2) wells dug to catch precipitation as it filtered down through bedrock; and (3) buk'teob, built to recover during the dry season the receding contents of pools that during the rainy season collect in aguadas. The dispersed distribution of Maya wells in rural settings and their frequent association with modest residential remains suggests that nonelite households managed them. The existence of Maya wells that supplied water to rural peoples through the dry season is inconsistent with the Scarborough‐Lucero‐Ford hypothesis. © 2004 Wiley Periodicals, Inc.     

Manganese and iron in hydrothermal plumes resulting from the 1996 Gorda Ridge Event

We sampled hydrothermal plumes over the N. Gorda Ridge four times between March and August 1996 to document Mn and Fe discharge resulting from a magmatic intrusion/seafloor eruption. Two separate event plumes, EP96A and B, and chronic hydrothermal emissions lasting 6 months were characterized. Shipboard time-series measurements of an event plume sample were used to calibrate an Fe phase clock useful for estimating sample age up to 6 days after fluid discharge. Samples collected from EP96A and B had Mn/heat (<0.15 nmol J^-1) and Fe/Mn (>2 mol mol^-1) ratios similar to historical event plume observations. We suggest these “signature” ratio values are generally characteristic of event plumes and hypothesize that Mn and Fe may be supplied to event plumes by different processes: Mn by entrainment of fluids from an extant shallow subseafloor reservoir, and Fe by short-lived, high-temperature water-rock reaction coincident with dike emplacement. Calculations based on the Fe phase clock indicate that the two event plumes were released more than a month apart. The largest event plume, EP96A (2.3×10⁶ M Mn and 13×10⁶ M Fe), formed 7 March soon after seismic activity began. The smaller EP96B (0.49×10⁶ M Mn and 3.5×10⁶ M Fe) was not discharged until 11 April, 3 weeks after the cessation of seismic activity detectable by SOSUS T-phase monitoring. We hypothesize that the subseafloor disturbance that triggered EP96B also resulted in the episodic flushing of a reservoir of chronic-plume-like fluids. Total event plume inventories of Mn and Fe at N. Gorda Ridge are much smaller than those associated with the 1986 event at N. Cleft segment of the Juan de Fuca Ridge, but comparable to event plume inventories at N. Cleft segment in 1987 and CoAxial segment in 1993. Mn/heat values for chronic plumes over the eruption site underlying EP96A evolved from moderate (0.25 oonmol J^-1, reflecting probable admixture with event plume formation fluids) to high (0.7 nmol J^-1, typical of chronic plumes) to low (0.1 nmol J^-1, similar to diffuse vent fluid values), marking a complete episode of intrusion/eruption-induced hydrothermal discharge.     

Local and regional variation of MORB parent magmas: evidence from melt inclusions from the Endeavour Segment of the Juan de Fuca Ridge

The development of petrogenetic models of igneous processes in the mantle is dependent on a detailed knowledge of the diversity of magmas produced in the melting regime. These primary magmas, however, undergo significant mixing and fractionation during transport to the surface, destroying much of the evidence of their primary diversity. To circumvent this problem and to determine the diversity of melts produced in the mantle, we used melt inclusions hosted in primitive plagioclase phenocrysts from eight mid-ocean ridge basalts from the axial and West Valleys of the Endeavour Segment, Juan de Fuca Ridge. This area was selected for study because of the demonstrated close association of enriched (E-MORB) lavas and incompatible element enriched depleted (N-MORB) lavas. Rehomogenized melt inclusions from E-MORB, T-MORB, and N-MORB lavas have been analyzed by electron and ion microprobe for major and trace elements. The depleted and enriched lavas, as well as their melt inclusions, have very similar compatible element concentrations (major elements, Sr, Ni and Cr). Inclusion compositions are more primitive than, yet collinear with, the host lava suites. In contrast, the minor and trace element characteristics of melt inclusions from depleted and enriched lavas are different both in range and absolute concentration. N-MORB lavas contain both depleted and enriched melt inclusions, and therefore exhibit the largest compositional range (K₂O: 0.01 to 0.4 oxide wt%, P₂O₅: <0.01 to 0.2 oxide wt%, La_N: 7 to 35, Yb_N: 1 to 13, and Ti/Zr: <100 to 1300). E-MORB lavas contain only enriched inclusions, and are therefore relatively homogeneous (K₂O: 0.32 to 0.9 oxide wt %, P₂O₅: 0.02 to 0.35 oxide wt%, La_N: 11 to 60, Yb_N: 4 to 21, and Ti/Zr: ∼100). In addition, the most primitive E-32 inclusions are similar in composition to the most enriched inclusions from the depleted hosts. Major element data for melt inclusions from both N-MORB and E-MORB lavas suggest that the magmas lie on a low pressure cotectic, consistent with a petrogenesis including fractional crystallization. However, the minor and trace element compositions in melt inclusions vary independently of the major element composition implying an alternative history. When fractionation-corrected, inclusion compositions correlate with their host glass composition. Hence, the degree of enrichment of the lavas is a function of the composition of aggregated melts, not of processing in the upper mantle or lower crust. Based on this fact, the lava suites are not produced from a single parent magma, but from a suite of primary magmas. The chemistry of the melt inclusions from the enriched lavas is consistent with a derivation from variable percentages of partial melting within the spinel stability field by a process of open system (continuous or critical) melting assuming a depleted lherzolite source veined with clinopyroxenite. The low percentage melts are dominantly enriched melts of the clinopyroxenite. In contrast, the depleted lavas were created by melting of a harzburgite source, possibly fluxed with a fluid enriched in K, Ba and the LREE. Such a source was likely melted up to or past the point at which all of its clinopyroxene was consumed. This set of characteristics is consistent with a scenario by which diverse melts produced at different depths travel through the melting regime to the base of the crust without homogenizing en route. The homogeneous major element characteristics are created in the lower crust by fractional crystallization and reaction with lower crustal gabbros. Therefore, the degree of decoupling between major and trace element characteristics of the melt inclusions (and lavas) is dictated by the reaction rate of the melts with the materials in the conduit walls, as well as the residence times and flux rate, in the upper mantle and lower crust. Received: 2 December 1997 / Accepted: 27 August 1998     

Conceptual Framework for Changes of Extremes of the Hydrological Cycle with Climate Change

A physically based conceptual framework is put forward that explains why an increase in heavy precipitation events should be a primary manifestation of the climate change that accompanies increases in greenhouse gases in the atmosphere. Increased concentrations of greenhouse gases in the atmosphere increase downwelling infrared radiation, and this global heating at the surface not only acts to increase temperatures but also increases evaporation which enhances the atmospheric moisture content. Consequently all weather systems, ranging from individual clouds and thunderstorms to extratropical cyclones, which feed on the available moisture through storm-scale moisture convergence, are likely to produce correspondingly enhanced precipitation rates. Increases in heavy rainfall at the expense of more moderate rainfall are the consequence along with increased runoff and risk of flooding. However, because of constraints in the surface energy budget, there are also implications for the frequency and/or efficiency of precipitation. It follows that increased attention should be given to trends in atmospheric moisture content, and datasets on hourly precipitation rates and frequency need to be developed and analyzed as well as total accumulation.     

Selectivity and efficiency of two otter trawls used to assess estuarine fish and macroinvertebrate populations in North Carolina

Otter trawl surveys are frequently used to assess estuarine fish and macroinvertebrate communities. Although these surveys may have similar objectives and sampling areas and seasons may overlap, the sampling gear is usually unique to the agency conducting the survey. An example of this is the North Carolina Division of Marine Fisheries (NCDMF) and Environmental Monitoring and Assessment Program-Estuaries (EMAP) surveys in North Carolinian estuaries. We estimated experimentally the selectivity and efficiency of the trawls used for these surveys to determine the comparability of data used to estimate community structure and the abundance of dominant species. The catch percent similarity of the trawls was low (12.0%). The NCDMF net (3.2-m flat otter trawl, 6.4-mm mesh body, 3.2-mm cod-end, plus tickle chain) precisely (11.7%) and accurately (4.5%) sampled brown shrimp, Penaeus aztecus, density but overestimated spot, Leiostomus xanthurus, densities (22.8% accuracy), possibly because these fishes had highly contagious distributions. The EMAP net (4.9-m high-rise otter trawl, 38.1-mm mesh body and cod-end) was precise (17.9–37.4%) but inaccurate (76.8–97.2%), probably because of the single large mesh size and the lack of a tickler chain. Our study suggests the EMAP and NCDMF surveys collect different subsamples of the same fish and macroinvertebrate estuarine populations, and therefore could deliver different results and conclusions.     

The nature of publishing and assessment in Geography and Environmental Studies: evidence from the Research Assessment Exercise 2008

We present a summary of the kinds of outputs submitted to the Geography and Environmental Studies sub-panel (H-32) for the 2008 Research Assessment Exercise (RAE), and examine the relationships between the peer assessment of research quality that the RAE process has typified, and alternative modes of assessment based on bibliometrics. This comparison is effected using (in aggregate form) some of the results from the RAE, together with citation data gathered after completion of the RAE assessment, specifically for the purpose of this paper. We conclude that, if it continues to be necessary and desirable to assess, in some measure and however imprecisely, research quality, then peer assessment cannot be replaced by bibliometrics. Bibliometrics permit measurement of something that may be linked to quality but is essentially a different phenomenon – a measure of 'impact', for example.     

A steady-state model of NEA binaries formed by tidal disruption of gravitational aggregates

We present results of a simulation of a steady-state binary near-Earth asteroid (NEA) population. This study combines previous work on tidal disruption of gravitational aggregates [Walsh, K.J., Richardson, D.C., 2006. Icarus 180, 201-216] with a Monte Carlo simulation of NEA planetary encounters. Evolutionary effects include tidal evolution and binary disruption from close planetary encounters. The results show that with the best known progenitor (small Main Belt asteroids) shape and spin distributions, and current estimates of NEA lifetime and encounter probabilities, that tidal disruption should account for approximately 1-2% of NEAs being binaries. Given the best observed estimate of a ∼15% binary NEA fraction, we conclude that there are other formation mechanisms that contribute significantly to this population. We also present the expected distribution of binary orbital and physical properties for the steady-state binary NEAs formed by tidal disruption. We discuss the effects on binary fraction and properties due to changes in the least constrained parameters, and other possible effects on our model that could account for differences between the presented results and the observed binary population. Finally, we model possible effects of a significant population of binaries migrating to the near-Earth population from the Main Belt.     

翼龙前肢元素的异速生长比率

Pterosaurs exhibit a large size range with the smallest approximately the size of a sparrow and the largest about the size of a small airplane. Based on studies of extant flying vertebrates and principles of allometry (Norberg & Rayner, 1987; Rayner, 1988), a reasonable assumption is that pterosaurs of different sizes used their wings differently during flight.     

Spatial variations in chemical compositions along Langtang–Narayani river system in central Nepal

Surface water samples were collected from Langtang Lirung glacier outlet point to the Narayani river system in central Nepal in order to investigate the role of elevation in the variation of chemistry along the drainage networks. The chemistry of Langtang–Narayani river system was dominated by sulfide oxidation coupled with carbonate dissolution and weathering of silicate minerals. Calcium and magnesium concentrations were relatively higher than other cations and the sum of both species strongly correlated with alkalinity, supporting the dissolution of carbonate and dolomite as the dominant source for these ions. Aluminosilicate minerals primarily as albite and anorthite appeared as dominant silicate minerals within the drainage basin. Bisiallitization was the dominant type of weathering within the entire drainage system. Hydrogen ion concentration was lower in the low elevation sites than in high elevation sites reflecting the more consumption of carbon dioxide in the low elevation sites due to enhanced chemical weathering rates. Furthermore, major solutes like sum of base cations, silicon as well as alkalinity increased in concentration in the lower elevation sites. All regulating factors appeared to be directly related to elevation and hence elevation appeared to be the prime factor for the variation in chemical species along the Langtang–Narayani river system. Toshiyuki Masuzawa: deceased.