New optically stimulated luminescence ages provide evidence of MIS3 and MIS2 eolian activity on Black Mesa, northeastern Arizona, USA

Eolian deposition on the semiarid southern Colorado Plateau has been attributed to episodic aridity during the Quaternary Period. However, OSL ages from three topographically controlled (e.g. falling) dunes on Black Mesa in northeastern Arizona indicate that eolian sediments there were deposited in deep tributary valleys as early as 35–30 ka, with most sand deposited before 20 ka. In contrast, the oldest OSL ages for sand sheets fall within the Pleistocene-Holocene climatic transition (~ 12–8 ka). Thus most eolian sediment accumulated on Black Mesa under climatic conditions that were in general cooler, moister, and more variable than today, not more arid, pointing to a considerable increase in sediment supply.     

Logjams as a driver of transient storage in a mountain stream

We use four stream segments along a wood-rich, pool–riffle mountain stream in the Southern Rockies of Colorado, USA to examine how spatial variations in wood load and variations in discharge during and after the snowmelt peak flow influence the magnitude of surface and subsurface transient storage. Segments range in complexity from a single channel with no large wood to an anabranching channel with closely spaced, channel-spanning logjams. Discharges at which transient storage was assessed range from base flow to snowmelt peak flow. To explore these relations, we used 10 geomorphic variables representing channel morphology and bed substrate, four wood-related variables representing wood load and associated backwater storage, and two measures of skewness from instream and bulk electrical conductivity breakthrough curves during tracer tests. Instream curves reflect surface and subsurface transient storage, whereas bulk curves primarily represent subsurface transient storage. Higher values of skewness indicate greater retention, and we used the values here as a metric of increased transient storage. Although limited sample size restricts the power of our results, our findings suggest that stream segments with greater instream large wood loads have more and larger pools, greater storage of fine sediment and particulate organic matter, and higher values of skew from instream conductivity. The results also suggest that the presence of instream wood, rather than changes in channel morphology associated with wood, is the most important driver of transient storage. This implies that river management designed to foster transient storage should focus on retaining instream large wood. We did not find significant correlations between geomorphic or wood-related variables and the skew estimated from bulk conductivity, which may reflect the relatively thin alluvium present in the field area and the prevalence of surface transient storage in this system.     

A threatened world city: the benefits of protecting London from the sea

This paper describes the options appraisal undertaken in the UK within the major TE2100 project to investigate the future of protecting London from flooding from the sea. An economic analysis, within a Benefit-Cost framework complemented by Multi-Criteria Analysis, shows that improving the existing flood defences and, in 2070, constructing a new Thames Barrier downstream from the existing one are the “front runner” options for tackling the increase in flood risk that is anticipated in the future. Both sensitivity and scenario analysis have little effect on option choice. Uncertainties inevitably remain, however, when looking so far ahead, but it is clear that continuing to protect this area from the sea is highly cost-beneficial. Also the very high standard of protection now, and the robustness of the existing flood defence assets, mean that major new interventions will not be needed for some time (i.e. until c. 2070). We therefore have time to monitor the situation, carefully plan measures to maintain and enhance the existing defences, and to seek to restrain the growth of risk in the Estuary and in London through carefully designed and implemented resilience-building flood plain management measures. Rather than having to rush to new engineering works, because we have not anticipated what is needed but are forced to respond hastily to a “crisis” situation, the adaptive approach that is now possible is a key legacy of the TE2100 project.     

Search for sulfates on the surface of Ceres

The formation of hydrated salts is an expected consequence of aqueous alteration of Main Belt objects, particularly for large, volatile‐rich protoplanets like Ceres. Sulfates, present on water‐bearing planetary bodies (e.g., Earth, Mars, and carbonaceous chondrite parent bodies) across the inner solar system, may contribute to Ceres’ UV and IR spectral signature along with phyllosilicates and carbonates. We investigate the presence and stability of hydrated sulfates under Ceres’ cryogenic, low‐pressure environment and the consequent spectral effects, using UV–Vis–IR reflectance spectroscopy. H₂O loss begins instantaneously with vacuum exposure, measured by the attenuation of spectral water absorption bands, and a phase transition from crystalline to amorphous is observed for MgSO₄·6H₂O by X‐ray powder diffraction. Long‐term (>40 h), continuous exposure of MgSO₄·nH₂O (n = 0, 6, 7) to low pressure (10^?3–10^?6 Torr) causes material decomposition and strong UV absorption below 0.5 μm. Our measurements suggest that MgSO₄·6H₂O grains (45–83 μm) dehydrate to 2% of the original 1.9 μm water band area over ~0.3 Ma at 200 K on Ceres and after ~42 Ma for 147 K. These rates, inferred from an Avrami dehydration model, preclude MgSO₄·6H₂O as a component of Ceres’ surface, although anhydrous and minimally hydrated sulfates may be present. A comparison between Ceres emissivity spectra and laboratory reflectance measurements over the infrared range (5–17 μm) suggests sulfates cannot be excluded from Ceres’ mineralogy.     

Geologic constraints on the origin of red organic‐rich material on Ceres

The geologic context of red organic‐rich materials (ROR) found across an elongated 200 km region on Ceres is evaluated with spectral information from the multispectral framing camera (FC) and the visible and near‐infrared mapping spectrometer (VIR) of Dawn. Discrete areas of ROR materials are found to be associated with small fresh craters less than a few hundred meters in diameter. Regions with the highest concentration of discrete ROR areas exhibit a weaker diffuse background of ROR materials. The observed pattern could be consistent with a field of secondary impacts, but no appropriate primary crater has been found. Both endogenic and exogenic sources are being considered for these distinctive organic materials.     

The fold test as an analytical tool

Two fold tests for palaeomagnetism have recently been proposed that rely on the assumption that the total population of magnetic vectors is most highly concentrated with the rocks in the orientation they had at the time of acquisition of the magnetization. This leads to appealing, simple tests based on parameter estimation. However, it is shown that the underlying assumption is flawed and can lead to incorrect conclusions. McFadden & Jones (1981 ) previously developed an inference test based on the concept that the between-group dispersion of magnetization should be consistent with the within-group dispersion when the rocks are in the orientation they had at the time of magnetic acquisition. That test made unrealistic demands upon the sampling scheme for typical, realistic folding geometries and so it has been under-utilized. The McFadden & Jones test is extended by recognizing that it is sufficient to use groups with similar bedding corrections and that it is not necessary to insist on groups with common bedding corrections. These groups may easily be determined with a clustering algorithm. The point is that with the rocks in the orientation at which the magnetization was acquired, it should be immaterial how the groups are chosen.     

Palaeomagnetism and the age of the Makapansgat hominid site

The time of deposition of the Makapansgat Limeworks site in South Africa, containing several hominid fossils, has an important bearing on hominid phylogeny in Africa. Hence, in an attempt to determine this age, a palaeomagnetic analysis of the site has been performed and the results are reported here. Member 3 (from which most of the important hominid fossils have been recovered) appears to have an age greater than 2.90 Ma and possibly greater than 3.06 Ma but less than 3.32 Ma. Previously it has not been possible to delineate the age of this important member with any degree of accuracy. The most likely position for the underlying Member 2 is in that section of the Gauss normal epoch predating the Mammoth event and having age limits of 3.06–3.32 Ma.