Construction of the casa grande by sequential high precision C-14 dating

Two composite radiocarbon dates on wood beams from a unique, prehistoric building in southern Arizona are the result of growth series subsampling of the beams and statistical evaluation of radiocarbon dates on the subsamples. This procedure avoids some of the problems caused by secular variations in the biospheric ¹⁴C activity and by the dating of specimens grown over a range of years. This procedure yields results similar to more precise tree-ring dates from other sites in the southwestern United States. The procedure illustrated here is applicable to any archaeological tree specimen consisting of at least the last 40 growth rings.     

An improved model for the dielectric constant of sea water at microwave frequencies

The advent of precision microwave radiometry has placed a stringent requirement on the accuracy with which the dielectric constant of sea water must be known. To this end, measurements of the dielectric constant have been conducted atS-band andL-band with a quoted uncertainty of tenths of a percent. These and earlier results are critically examined, and expressions are developed which will yield computations of brightness temperature having an error of no more than 0.3 K for an undisturbed sea at frequencies lower thanX-band. At the higher microwave and millimeter wave frequencies, the accuracy is in question because of uncertainties in the relaxation time and the dielectric constant at infinite frequency.     

Effects Of Changing Surface Heat Flux On Atmospheric Boundary-Layer Flow Over Flat Terrain

We examine the unsteady response of a neutral atmospheric boundary layer (ABL) of depth h and friction velocity u _* when a uniform surface heat flux is applied abruptly or decreased rapidly over a time scale t<inf>θ</inf> less than about h /(10u _*). Standard Monin–Obukhov (MO) relationships are used for the perturbed eddy viscosity profile in terms of the changes to the heat flux and mean shear. Analytical solutions for changes in temperature, mean wind and shear stress profile are obtained for the surface layer, when there are small changes in h /|L_MO| over the time scale t_MO~|L _MO|/(10u_*) (where L _MO and t _MO are the length and time scales, respectively). They show that a maximum in the wind speed profile occurs at the top of the thermal boundary layer for weak surface cooling, i.e. a wind jet, whereas there is a flattening of the profile and no marked maximum for weak surface heating. The modelled profiles are approximately the same as those obtained from the U.K. Met Office Unified Model when operating as a mesoscale model at 12-km horizontal resolution. The theoretical model is modified when strong surface heating is suddenly applied, resulting in a large change in h /|L _MO| (>>1), over the time scale t _MO. The eddy structure is predicted to change significantly and the addition of convective turbulence increases the shear turbulence at the ground. A low-level wind jet can form, with convective turbulence adding to the mean momentum of the flow. This was verified by our laboratory experiment and direct numerical simulations. Additionally, it is shown that the effects of Coriolis acceleration diminish (rather than as suggested in the literature, amplify) the formation of the wind jets in the situations considered here. Hence, only when the surface heat flux changes over time scales greater than 1/f (where f is the Coriolis parameter) does the ABL adjust monotonically between its equilibrium states. These results are also applicable to the ABL passing over spatially varying surface heat fluxes.     

Research planning in the face of change: the human role in reindeer/caribou systems

Reindeer/caribou ( Rangifer tarandus ) constitute a biological resource of vital importance to the physical and cultural survival of Arctic residents since time immemorial. Recent and possible future economic, social and ecological changes raise concern for sustainability of these resources and the well-being of those who depend on them. In February 1999 eighty scientists, reindeer/caribou users and resource managers gathered in Rovaniemi, Finland, for an interdisciplinary workshop to develop a circumpolar research plan that addressed the sustainability of humanreindeer/caribou systems. Small working groups addressed six themes: hunting systems, herding systems, rengeland/habitat protection, minimizing industrial impacts, maintaining the strength of indigenous cultures, and responding to global change. The resulting Research Plan cells for interdisciplinary comparative studies, advancement of tools for assessing cumulative effects, implementation of regional and a circumpolar monitoring and assessment programmes, and cultural studies on the transmission of knowledge. Cross-cutting directives for future research include:
• improving humans'ability to anticipate and respond to change;
• understanding better the dynamics of human-reindeer/caribou systems;
• developing research methods that are both more instructive and less intrusive;
• facilitating open communication among groups with interests in reindeer/caribou resources;
• organizing researchers into a strong, coordinated network;
• re-framing the conventional research paradigm to be more inclusive of differing cultural perspectives.
Three follow-up initiatives are proposed: 1) development of a web-based resource on the human role in reindeer/caribou systems (www.rangifer.net); establishment of a Profile of Herds database to support comparative research; and 3) convening of working groups to address specific problems identified by workshop participants.     

Arctic grazing systems and industrial development: can we minimize conflicts?

The industrialized world is expanding its search for energy, minerals, timber and other resources into the Arctic and adjacent higher latitudes. Up to now, large-scale development projects in the Arctic and sub-Arctic have been few. We can, however, profit from experiences gained from several of these, including oil and gas exploration and development in Alaska and on Russia's Yamal Peninsula, the Norilsk metalurgical complex of Siberia, Alaska's Red Dog mine and others. Conclusions drawn from these experiences are that industrial impacts on Arctic grazing systems can be minimized if the following considerations guide their planning: 1) most of the large development projects that have been undertaken in the North have lacked adequate background information on the grazing systems that they might impact; 2) there needs to be recognition by industry and governments for the amount of time required to gather such information and provision made for this; 3) because types of impacts on northern grazing systems that may result from development projects vary depending on whether they involve mining, oil or gas, hydroelectric or other activities, each proposed project must be assessed independently; 4) cumulative effects of multiple projects, often sequentially developed, are seldom addressed by the responsible governments, thus planning for development of an individual project should be within the context of regional and long-range development planning; and 5) types and sources of contaminants entering northern ecosystems, threatening the health of northern residents, must also be a major focus of project assessment.     

Collocation of hydrological and biological attenuation of nitrate in an urban stream

The hydrologic and biogeochemical processes that control nutrient export in urban streams are not well understood. Attenuation can occur by tributary dilution, groundwater discharge, and biological processing both in the water column and the hyporheic zone. A wastewater treatment plant on Pennypack Creek, an urban stream near Philadelphia, PA, provided high nitrate concentrations for analysis of downstream attenuation processes. Longitudinal sampling for an 8‐km reach revealed decreases in nitrate concentration of 2 mg l^?1 at high flow and 4.5 mg l^?1 during low flow. During high flow, δ¹⁵N‐NO₃ increased from 9.5 to 10.5‰ and during low flow increased from 10.1 to 11.1‰. Two reaches were sampled at fine spatial intervals (approximately 200 m) to better identify attenuation processes. Mixing analysis indicated that groundwater discharge and biological processing both control nitrate concentration and isotope signatures. However, fine‐scaled sampling did not reveal spatially discrete zones; instead, these processes were occurring simultaneously. While both processes attenuate nitrate, they have opposite isotope signatures, which may have muted changes in δ¹⁵N‐NO₃. At high flow, a decrease in Cl/NO₃ ratios helped distinguish groundwater discharge occurring along both finely sampled reaches. At low flow, biological processing seemed to be occurring more extensively, but the δ¹⁵N‐NO₃ signature was not consistent with either a single process or a sequential combination of groundwater dilution and biological nitrate attenuation. The collocation of processes makes it more difficult to assess biological processing hot spots and predict how urbanization and subsequent stream restoration influence nitrate attenuation. Copyright © 2016 John Wiley & Sons, Ltd.     

RCP2.6: exploring the possibility to keep global mean temperature increase below 2��C

The RCP2.6 emission and concentration pathway is representative of the literature on mitigation scenarios aiming to limit the increase of global mean temperature to 2°C. These scenarios form the low end of the scenario literature in terms of emissions and radiative forcing. They often show negative emissions from energy use in the second half of the 21st century. The RCP2.6 scenario is shown to be technically feasible in the IMAGE integrated assessment modeling framework from a medium emission baseline scenario, assuming full participation of all countries. Cumulative emissions of greenhouse gases from 2010 to 2100 need to be reduced by 70% compared to a baseline scenario, requiring substantial changes in energy use and emissions of non-CO₂ gases. These measures (specifically the use of bio-energy and reforestation measures) also have clear consequences for global land use. Based on the RCP2.6 scenario, recommendations for further research on low emission scenarios have been formulated. These include the response of the climate system to a radiative forcing peak, the ability of society to achieve the required emission reduction rates given political and social inertia and the possibilities to further reduce emissions of non-CO₂ gases.     

Size-dependent uptake of nitrate and ammonium as a function of light in well-mixed temperate coastal waters

The effect of light on nitrate (NO₃⁻) and ammonium (NH₄⁺) uptake by natural communities was investigated in relation to cell size (<10 and >10 μm) in the well-mixed coastal waters of the English Channel. Nitrogen (N) uptake kinetics as a function of irradiance were assessed using ¹⁵N tracer techniques, for a seasonal cycle of populations collected at 50% and 1% light penetration depth. The nitrogen uptake responses to irradiance can be represented by the formulation used to describe the photosynthesis versus irradiance relationships and modified by the addition of a dark uptake parameter. The response curves of two size fractions of phytoplankton collected at 50% and 1% of incident light did not differ significantly, which suggested that the physiological characteristics of N uptake were not affected by the light intensity at which the phytoplankton assemblages were sampled. The kinetics parameters indicated that the NO₃⁻ uptake system was more strongly dependent on light than the NH₄⁺ uptake system. They also showed that N uptake was less limited by the light intensity in the small size fraction than it was in the large size fraction. At the mean light intensity in the water column, kinetics analysis predicted a NH₄⁺ uptake that was on average 1.8 (±0.6) and 2.4 (±1.0) times greater than the NO₃⁻ uptake, for <10 and >10 μm size fractions, respectively. The kinetics also predicted, at the in situ mean light intensity, that the mean ability to take up nitrogen was twice as high (1.8±0.5) for the small than for the large cells when the N substrate was NH₄⁺ and more than twice as high (2.6±1.5) when the substrate was NO₃⁻. These results added to our understanding of the light effect on N uptake processes in well-mixed waters, and can largely explain the phytoplankton production, mainly regenerated and dominated by small cells, that has been observed in these waters.