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We report the first direct turbulence observations in the Samoan Passage (SP), a 40 km wide notch in the South Pacific bathymetry through which flows most of the water supplying the North Pacific abyssal circulation. The observed turbulence is 1000 to 10,000 times typical abyssal levels —strong enough to completely mix away the densest water entering the passage—confirming inferences from previous coarser temperature and salinity sections. Accompanying towed measurements of velocity and temperature with horizontal resolution of about 250 m indicate the dominant processes responsible for the turbulence. Specifically, the flow accelerates substantially at the primary sill within the passage, reaching speeds as great as 0.55 m s−1. A strong hydraulic response is seen, with layers first rising to clear the sill and then plunging hundreds of meters downward. Turbulence results from high shear at the interface above the densest fluid as it descends and from hydraulic jumps that form downstream of the sill. In addition to the primary sill, other locations along the multiple interconnected channels through the Samoan Passage also have an effect on the mixing of the dense water. In fact, quite different hydraulic responses and turbulence levels are observed at seafloor features separated laterally by a few kilometers, suggesting that abyssal mixing depends sensitively on bathymetric details on small scales.

Surface reflectance/albedo is important for many geophysical applications, atmospheric circulation, and climate modeling (Henderson-Sellers et al. 1993). It is a key input parameter for land type classification and serves as a major boundary condition in surface-atmosphere radiative transfer modeling, which determines the distribution of solar energy between the surface and the atmosphere. Surface reflective properties can be retrieved from satellite observations. A surface target may be observed by satellite from different viewing directions. Due to the anisotropy of surface reflection, this leads to diversity of surface properties retrieved from satellite composite images (Li et al. 1996). To address this problem, one needs to determine the surface bidirectional reflectance distribution function (BRDF) properties and correct for them in the final product. Integrals of BRDF functions result in the so-called black-sky and white-sky albedos that convey important information concerning the inherent properties of surface albedo (Wanner et al. 1997).

AbstractThe Olorgesailie Formation (1.2–0.49 Ma) consists of fluvial and lacustrine rift sediments that have yielded abundant Acheulean artifacts and a fossil hominin (Homo cf. erectus). In testing prior understandings of the paleoenvironmental context, we define nine new geochemical zones. A Chemical Index of Alteration suggests increased catchment weathering during deposition of Members 1, 2, 7, 11, and 13. Biophile elements (Br, S) peak in M8–9 and lower M13 possibly reflecting increased input from soil erosion. REE data show that the Magadi Trachytes supplied most siliciclastic grains. Sixteen diatom stages indicate conductivities of 200–16,000 μS cm− 1 and pH of 7.5–9.5 for five deep-water lakes, ten shallow lakes and sixteen wetlands. These results are compared with diatom data from other sections in the basin and show aquatic spatial variability over km-scale distances. Similar floras are traceable over several kilometers for M2, M3 and M9, indicating broadly homogeneous lacustrine conditions during these times, but diatoms in other members imply variable conditions, some related to local tectonic controls. This lateral and temporal variability emphasizes the importance of carrying out stratigraphic sampling at multiple sites within a basin in efforts to define the environmental context relevant to human evolution.

Multicomponent seismic recordings are currently being analyzed in an attempt to improve conventional P‐wave sections and to find and use rock properties associated with shear waves (e.g. Dohr, 1985; Danbom and Dominico, 1986). Mode‐converted (P-SV) waves hold a special interest for several reasons: They are generated by conventional P‐wave sources and have only a one‐way travel path as a shear wave through the typically low velocity and attenuative near surface. For a given frequency, they will have a shorter wavelength than the original P wave, and thus offer higher spatial resolution; this has been observed in several vertical seismic profiling (VSP) cases (e.g., Geis et al., 1990). However, for surface seismic data, converted waves are often found to be of lower frequency than P-P waves (e.g., Eaton et al., 1991).

The mechanics associated with forepoling structures explicitly, has never been fully investigated in order to determine the associated support mechanics when installed in isolation and/or in groups as an umbrella arch. Further, numerically, these support structures cannot be modelled using the commonly used, industry standard, two-dimensional (2D) numerical software packages. In numerical software using three-dimensional (3D) codes, these support elements are commonly standardized using pile or rockbolt simplified noded elements that do not truly describe their behaviour when subjected to the true 3D stress conditions that result at face or near the face due to the tunnel or mining excavation process. As such, a deficiency exists with regards to prediction of the interaction of umbrella arch support systems with forepoles element for tunnelling practices within weak rock masses. Methods have been developed in order to predict the behaviour of radial support systems to include temporary support elements such as rock bolts, steel sets, and liners such as the convergence-confinement method. However, these tools do not have the ability to capture the influence of support systems installed longitudinally at the face of tunnel such as forepole, and core reinforcement elements. In an attempt to improve tunnel design strategies, this paper will focus on the mechanical response of the application of the forepole element as part of the umbrella arch method installed in deep and shallow excavations; As well, other issues associated (influences) with the use of forepoles are also highlighted and discussed.

Long-term monitoring data of total gaseous mercury (TGM) concentrations from the Canadian Atmospheric Mercury Measurement Network (CAMNet) were analysed for temporal trends, seasonality and comparability within the network and compared to other network and model results. Data collected from 11 Canadian measurement sites between 1995 and 2005 were analysed. Sites within CAMNet were characterized by principle component analysis (PCA) into four main categories. For the first time since automated TGM measurements have been made within CAMNet, this paper reveals statistically significant decreasing TGM concentrations from rural locations in Canada during this time period. The largest declines were observed close to the urban areas of Toronto and Montreal, where levels fell by 17% at Point Petre, and 13% at St. Anicet, respectively. Many of the TGM changes are comparable with the overall trends observed in total mercury concentrations in precipitation, for similar time periods, at co-located or nearby National Atmospheric Deposition programme's Mercury Deposition Network (NADP-MDN) sites. The results show that these changes are mostly driven by local or regional changes in mercury emissions. Other sites within CAMNet reflect reported changes in hemispherical global background concentrations of airborne mercury, where slight decreases or no statistically significant trend in TGM concentrations exist over the same time period.

Abstract Recent LiDAR (Light Detection and Ranging) survey in Tonga has documented a dense and complex archaeological landscape, particularly on the principal island of Tongatapu. Among the features revealed by the LiDAR are a profusion of earthen mounds, most of which are associated with residence, sporting, or burial in the period 1000–1850 CE. For identification and mapping of the mounds we use and evaluate two automated feature extraction (AFE) techniques, object-based image analysis and an inverted pit-filling algorithm (“iMound”). Accuracy of these methods was measured using an F1-score (harmonic mean of precision and recall). Variable AFE results indicate that continual and iterative fine-tuning is required. Successful mapping of some 10,000 mounds on Tongatapu reveals a distinct spatial structure that relates to traditional land division and tenure.