Forecasting and hindcasting waves with the SWAN model in the Southern California Bight

The Naval Research Laboratory created a wave forecasting system in support of the Nearshore Canyon Experiment (NCEX) field program. The outer nest of this prediction system encompassed the Southern California Bight. This forecasting system is described in this paper, with analysis of results via comparison to the extensive buoy network in the region. There are a number of potential errors, two of which are poor resolution of islands in the Bight—which have a strong impact on nearshore wave climate—and the use of the stationary assumption for computations. These two problems have straightforward solutions, but the solutions are computationally expensive, so an operational user must carefully consider their cost. The authors study the impact of these two types of error (relative to other errors, such as error in boundary forcing) using several hindcasts performed after the completion of NCEX. It is found that, with buoy observations as ground truth, the stationary assumption leads to a modest increase in root-mean-square error; this is due to relatively poor prediction of the timing of swell arrivals and local sea growth/decay. The model results are found to be sensitive to the resolution of islands; however, coarse resolution does not incur an appreciable penalty in terms of error statistics computed via comparison to buoy observations, suggesting that other errors dominate. Inaccuracy in representation of the local atmospheric forcing likely has a significant impact on wave model error. Perhaps most importantly, the accuracy of directional distribution of wave energy at the open ocean boundaries appears to be a critical limitation on the accuracy of the model-data comparisons inside the Bight.     

Dissolved iodine in waters overlying and in the Orca Basin,Gulf of Mexico

The distribution and speciation of iodine, a biophilic redox-sensitive trace element, in waters overlying and in the Orca Basin, Gulf of Mexico, which contains hypersaline, anoxic and yet non-sulfide-bearing brine have been determined. The distribution of iodate and iodide in the oxic waters overlying the anoxic brine are similar to those reported in other oceans. However, in the oxic-anoxic mixing zone, iodate disappears while the concentration of iodide reaches a maximum of 8.1 μM, the highest concentration ever reported in open oceans. There is also a maximum in specific iodine of 30.7 nM‰^?1 at this depth. Specific iodine in oxic seawater is only about 10–14 nM ‰^?1. These features may be explained by the preferential dissolution of biogenic particles that have accumulated in a strong pycnocline. In the anoxic brine proper, the concentration of iodide is 3.8 μM and can be explained almost entirely by the simultaneous mobilization of chloride and iodide during the dissolution of evaporite beds as the specific iodine of 14.5 nM‰^?1 is only slightly higher than those observed in the oxic waters.     

Dehydration melting of a basaltic composition amphibolite at 1.5 and 2.0 GPa: implications for the origin of adakites

This study presents the results of dehydration melting experiments on a basaltic composition amphibolite under conditions appropriate to a hot slab geotherm (1.5 and 2.0 GPa and temperatures of 850 to 1150° C). Dehydration melting produces an omphacitic augite and garnet bearing residue coexisting with rhyolitic to andesitic composition melts. At 1.5 GPa, the amphibolite melts in two stages between 800 and 1025° C. The 2.0 GPa data also define two melting stages. At 2.0 GPa, the first stage involves nearly modal melting of the original amphibolite minerals (qtz, pl, amp) to produce melt + cpx + grt. During the second stage, the eclogite restite melts non-modally (0.86 cpx + 0.14 grt = 1 melt). The experimental results were combined with data from the literature to generate a composite P-T phase diagram for basaltic composition amphibolites over the 800 to 1100° C temperature range for pressures up to 2.0 GPa. Comparison of the major element compositions of the experimentally produced melts with compositions of presumed slab melts (adakites) shows that partial melting of amphibolite at conditions appropriate to a hot-slab geotherm produces melts similar to andesitic and dacitic adakites except for significant MgO and CaO depletions. Trace element modelling of amphibolite dehydration melting using the 2.0 GPa melting reactions produces REE abundances similar to those of adakites at 10–15 wt% batch melting, but the models do not reproduce the high Sr/Y ratios characteristic of adakites. Taken together, the major and trace element results are not consistent with the derivation of adakites by dehydration melting of the subducted slab with little or no interaction with the mantle wedge or crust. If adakites are partial melts of the subducted slab, they must undergo significant interaction with the mantle and/or crust, during which they acquire a number of their distinctive characteristics.     

Errors due to random noise in velocity measurement using incoherent-scatter radar

The random-noise errors involved in measuring the Doppler shift of an incoherent-scatter spectrum are predicted theoretically for all values of T_e/T_i from 1.0 to 3.0. After correction has been made for the effects of convolution during transmission and reception and the additional errors introduced by subtracting the average of the background gates, the rms errors can be expressed by a simple semi-empirical formula. The observed errors are determined from a comparison of simultaneous EISCAT measurements using an identical pulse code on several adjacent frequencies. The plot of observed versus predicted error has a slope of 0.991 and a correlation coefficient of 99.3%. The prediction also agrees well with the mean of the error distribution reported by the standard EISCAT analysis programme.     

Hard and Soft Skills in Preparing GIS Professionals: Comparing Perceptions of Employers and Educators

Organizations that hire GIS professionals look for entry‐level employees with specialized technical skills but also other competencies such as effective communication and a capacity to think critically and creatively. Indeed, the success of GIS projects and initiatives often depends on individuals who possess a combination of specialized GIS skills and more general competencies that influence their ability to collaborate and manage resources. This article presents findings from a survey of GIS employers and educators concerning the importance of hard and soft skills among entry‐level GIS professionals. A key finding is the high level of consistency in ratings assigned by employers and educators concerning hard skills such as data editing and GIS analysis and soft skills including problem solving and adaptability. However, the groups were less similar in ratings assigned to data capture skills, project management, and written/verbal skills. GIS qualifications were also compared, revealing a greater emphasis on internships among educators and higher ratings assigned to academic GIS certificates among employers.     

Paleoindian environmental change and landscape response in Barger Gulch,Middle Park,Colorado

Middle Park, a high‐altitude basin in the Southern Rocky Mountains of north‐central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (˜10,500 ¹⁴C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest‐Pleistocene soil and a younger mollic epipedon formed between ˜6000 and 5200 ¹⁴C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ˜10,200 and 9700 ¹⁴C yr B.P., and that the erosion is likely related to truncation of the latest‐Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ˜10,000 and 9700 ¹⁴C yr B.P. was followed by rapid aggradation between ˜9700 and 9550 ¹⁴C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ˜11,000–10,000 ¹⁴C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ˜9500 and 8000 ¹⁴C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (˜11,000–10,000 ¹⁴C yr B.P., 76%) relative to late Paleoindian sites (˜10,000–8000 ¹⁴C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc.     

A study of dissipation of wind-waves by mud at Cassino Beach,Brazil: Prediction and inversion

The impact of a non-rigid seafloor on the wave climate at Cassino Beach, Brazil, May–June 2005 is studied using field measurements and a numerical wave model. The measurements consist of wave data at four locations; rheology and mud thickness from grab samples; and an estimate of the horizontal distribution of mud based on echo-soundings. The dissipation of waves by a non-rigid bottom is represented in the wave model by treating the mud layer as a viscous fluid. Applied for 431 time periods, the model without this type of dissipation has a strong tendency to overpredict nearshore wave energy, except during a period of large storm waves. Two model variations which include this dissipation have a modest tendency to underpredict the nearshore wave energy. An inversion methodology is developed and applied to infer an alternate mud distribution which, when used with the wave model, yields the observed waveheights.