Ice-albedo feedback in a CO2-doubling simulation

We estimate the feedback of sea-ice change to the warming from CO₂-doubling according to the simulation of Washington and Meehl (1984). Without ice-snow albedo feedback, their global warming of 3.5 °C would have been 2.2. °C according to our estimate of the ice-snow feedback. About 80% of the albedo change from ice and snow occurred in the Southern Hemisphere. Whether this change was an overestimate will require further study.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

An overview of the role of weathering in the production of quartz silt

Quartz silt is a widespread detrital sediment with large aeolian (loess) and alluvial silt deposits forming important components of many contemporary landscapes. Despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments (e.g. glacial grinding, fluvial comminution, aeolian abrasion, frost weathering, salt weathering, insolation weathering and deep weathering), the ‘glacial-aeolian’ hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a Quaternary phenomenon. As a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre-Quaternary environments. In particular, earth scientists may have considerably underestimated the role of weathering in global silt generation, as there are now many references to the existence of a patchy but widespread distribution of pre-Quaternary weathering profiles across the glacial and periglacial landscapes of the Northern Hemisphere (e.g. North America, British Isles, north and central Europe), landscapes within which many of the classical loess deposits are located. These observations suggest that weathering profiles may have covered large tracts of the Northern Hemisphere land surface prior to the Quaternary glaciations. This, in turn, may have important implications for quartz silt generation as: (1) experimental studies indicate that many weathering processes are capable of generating significant quantities of silt-sized debris, and (2) particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt-sized material, or quartz grains that are weakened by weathering derived microfractures. Thus, weathering profiles may represent ‘mines’ of actual and potential quartz silt, available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial, fluvial and aeolian erosion.     

Anthropogenic inputs of several heavy metals to nearshore basins off Los Angeles

Budgets of anthropogenically-derived Cr, Zn and Pb in the Santa Monica-San Pedro Basin and the Palos Verdes Shelf are estimated from profiles of these metals in a large number of sediment cores. Comparisons of inventories in the deep basin with combined emissions from the responsible sewage outfalls indicate that no more than 7% of the Cr, 2% of the Zn and 5% of the Pb derived from the sewage source are buried in the nearshore basin. A similar comparison of metal accumulation on the Palos Verdes Shelf with discharges from the nearby JWPCP outfall indicates that 12% of the Zn and 20% of the Cr and Pb are deposited locally. The annual percentages of sewage-derived Pb retained should be significantly lower, because surface runoff and atmospheric fallout are also important input pathways for anthropogenic Pb. Offshore variations in sediment metal composition suggest that Cr is most strongly attached to sewage particles while Zn and Pb are more labile. We conclude that the majority of anthropogenic metals are exported offshore beyond the inner basin.     

The Project for Intercomparison of Land-surface Parameterization Schemes (PILPS) phase 2(c) Red-Arkansas River basin experiment:: 2. Spatial and temporal analysis of energy fluxes

The energy components of sixteen Soil-Vegetation Atmospheric Transfer (SVAT) schemes were analyzed and intercompared using 10 years of surface meteorological and radiative forcing data from the Red-Arkansas River basin in the Southern Great Plains of the United States. Comparisons of simulated surface energy fluxes among models showed that the net radiation and surface temperature generally had the best agreement among the schemes. On an average (annual and monthly) basis, the estimated latent heat fluxes agreed (to within approximate estimation errors) with the latent heat fluxes derived from a radiosonde-based atmospheric budget method for slightly more than half of the schemes. The sensible heat fluxes had larger differences among the schemes than did the latent heat fluxes, and the model-simulated ground heat fluxes had large variations among the schemes. The spatial patterns of the model-computed net radiation and surface temperature were generally similar among the schemes, and appear reasonable and consistent with observations of related variables, such as surface air temperature. The spatial mean patterns of latent and sensible heat fluxes were less similar than for net radiation, and the spatial patterns of the ground heat flux vary greatly among the 16 schemes. Generally, there is less similarity among the models in the temporal (interannual) variability of surface fluxes and temperature than there is in the mean fields, even for schemes with similar mean fields.     

Microstructural study of micron‐sized craters simulating Stardust impacts in aluminum 1100 targets

Abstract— Various microscopic techniques were used to characterize experimental microcraters in aluminum foils to prepare for the comprehensive analysis of the cometary and interstellar particle impacts in aluminum foils to be returned by the Stardust mission. First, scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS) were used to study the morphology of the impact craters and the bulk composition of the residues left by soda‐lime glass impactors. A more detailed structural and compositional study of impactor remnants was then performed using transmission electron microscopy (TEM), EDS, and electron diffraction methods. The TEM samples were prepared by focused ion beam (FIB) methods. This technique proved to be especially valuable in studying impact crater residues and impact crater morphology. Finally, we also showed that infrared microscopy (IR) can be a quick and reliable tool for such investigations. The combination of all of these tools enables a complete microscopic characterization of the craters.     

Deep circulation driven by strong vertical mixing in the Timor Basin

The importance of deep mixing in driving the deep part of the overturning circulation has been a long debated question at the global scale. Our observations provide an illustration of this process at the Timor Basin scale of ～1000 km. Long-term averaged moored velocity data at the Timor western sill suggest that a deep circulation is present in the Timor Basin. An inflow transport of ～0.15 Sv is observed between 1600 m and the bottom at 1890 m. Since the basin is closed on its eastern side below 1250 m depth, a return flow must be generated above 1600 m with a ～0.15 Sv outflow. The vertical turbulent diffusivity is inferred from a heat and transport balance at the basin scale and from Thorpe scale analysis. Basin averaged vertical diffusivity is as large as 1 × 10^?3 m² s^?1. Observations are compared with regional low-resolution numerical simulations, and the deep observed circulation is only recovered when a strong vertical diffusivity resulting from the parameterization of internal tidal mixing is considered. Furthermore, the deep vertical mixing appears to be strongly dependent on the choice of the internal tide mixing parameterization and also on the prescribed value of the mixing efficiency.     

A Preliminary Appraisal of Seven Natural Zircon Reference Materials for In Situ Hf Isotope Determination

There is a growing need for new zircon reference materials for in situ Hf-isotope analysis by laser ablation-multicollector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS). In this contribution we document the results of a preliminary investigation of seven natural zircons, conducted in order to test their suitability in this regard. Solution MC-ICP-MS data on separated Lu and Hf fractions provided reference compositional data while the results of ca. 750 in situ LA-MC-ICP-MS analyses allowed assessment of potential micrometre-scale heterogeneity. On the basis of these analyses and additional relevant considerations such as availability, size and (Lu)Yb/Hf ratio, we suggest that, of the currently available zircons, Temora-2 and Mud Tank are most likely to provide robust reference materials for Hf isotope determinations both at the present time and into the future. The former has the advantage of also being well-characterised for U-Th-Pb systematics and suitable for in situ age determination, while the latter is the most readily available and is of very large grain size. Additional materials such as BR266, and 91500, although limited in supply, show more consistent Lu/Hf ratios and are thus of use in monitoring elemental fractionation during ICP-MS analysis.     

Sourcing Olive Jars Using U‐Pb Ages of Detrital Zircons: A Study of 16th Century Olive Jars Recovered from the Solomon Islands

We present U‐Pb ages of zircons extracted from olive jars recovered from two sites associated with Alvaro de Mendaña y Neyra's colonising expedition to the Solomon Islands, c. 1595–1596 A.D. The olive jars were previously associated with Panamanian and Peruvian origins based on petrological and geochemical studies. To further define provenance, 143 zircons were extracted from five olive jar sherds, analyzed and dated. The resultant U‐Pb ages range from the Archaean to the Cenozoic (2977.2 ± 29.0–3.2 ± 4.0 Ma), but the dominance of Cretaceous and Palaeogene ages (∼ 90% of the total age population is between ∼ 145 and 23 Ma) supports a Peruvian origin based on comparative geology, with the Coastal Batholith of Peru a prime candidate area of ceramic production. These results are significant for the characterization of 16th Century Peruvian‐made pottery and our understanding of its production and trade.     

Urban heat island diagnosis using ASTER satellite images and ‘in situ’ air temperature

This study demonstrates that thermal satellite images combined with ‘in situ’ ground data can be used to examine models of heat island genesis and thus identify the main causes of urban heat islands (UHIs). The models, although proposed over 30 years ago, have not been thoroughly evaluated due to a combination of inadequate ground data and the low resolution of thermal satellite data. Also there has been limited understanding of the relevance of satellite-derived surface temperatures to local and regional scale air temperatures. A cloud-free ASTER thermal image of urban and rural areas of Hong Kong was obtained on a winter night with a well-developed heat island, accompanied by a 148 km vehicle traverse of air temperatures. Over the whole traverse a high R² of 0.80 was observed between surface and air temperatures, with the two datasets showing a similar amplitude and general trend, but with the surface exhibiting much higher local variability than air temperature. Gradients in both surface and air temperature could be related to differences in land cover, with little evidence of large scale advection, thus supporting the population/physical structure model of UHI causation, rather than the advection model. However, the much higher surface and air temperatures observed over the largest urban area, Kowloon, than over any smaller urban centre with similar physical structure in the New Territories, would seem more indicative of the advection model. The image and ground data suggest that Kowloon's urban canopy layer climate is mainly influenced by local city structure, but it is also modified by a strongly developed, regional scale urban boundary layer which has developed over the largest urban centre of Kowloon, and reinforces heating from both above and below.