The village of Barrow, Alaska, is the northernmost settlement in the USA and the largest native community in the Arctic. The population has grown from about 300 residents in 1900 to more than 4600 in 2000. In recent decades, a general increase of mean annual and mean winter air temperature has been recorded near the centre of the village, and a concurrent trend of progressively earlier snowmelt in the village has been documented. Satellite observations and data from a nearby climate observatory indicate a corresponding but much weaker snowmelt trend in the surrounding regions of relatively undisturbed tundra. Because the region is underlain by ice-rich permafrost, there is concern that early snowmelt will increase the thickness of the thawed layer in summer and threaten the structural stability of roads, buildings, and pipelines. Here, we demonstrate the existence of a strong urban heat island (UHI) during winter. Data loggers (54) were installed in the ∼150 km 2 study area to monitor hourly air and soil temperature, and daily spatial averages were calculated using the six or seven warmest and coldest sites. During winter (December 2001-March 2002, the urban area averaged 2.2°C warmer than the hinterland. The strength of the UHI increased as the wind velocity decreased, reaching an average value of 3.2°C under calm (<2 m s −1 ) conditions and maximum single-day magnitude of 6°C. UHI magnitude generally increased with decreasing air temperature in winter, reflecting the input of anthropogenic heat to maintain interior building temperatures. On a daily basis, the UHI reached its peak intensity in the late evening and early morning. There was a strong positive relation between monthly UHI magnitude and natural gas production/use. Integrated over the period September-May, there was a 9% reduction in accumulated freezing degree days in the urban area. The evidence suggests that urbanization has contributed to early snowmelt in the village.

No abstract

Differential cement mineralogy is influenced by depositional textures, structural deformation, pore fluid chemistry, and ultimately influences landscape evolution by introducing heterogeneities in erodibility. In Southern Utah, the region West of the Kaibab uplift known as Mollies Nipple (Mollies) in Grand Staircase-Escalante National Monument exhibits a complex history of fluid-sediment interactions, which has resulted in a localized zone of anomalous diagenetic iron sulfate (jarosite) mineralogy in a well-exposed dune-interdune deposit within the Navajo Sandstone. Mineralogy and geochemistry of cements within this region are examined using reflectance and imaging spectroscopy, field investigations, microscopy, and whole-rock geochemical analyses. These data show that the in-situ jarosite cement is localized to a plane along the highest ridge of the butte, providing an armor along with other secondary cements, which controls the butte's geomorphic evolution. The jarosite cement is associated with other mineralogies suggesting that the sulfate was one of the latest fluid-related precipitates in the paragenetic sequence. It was preceded by a regional bleaching event, precipitation of clay cements, some localized concretionary iron oxide precipitation, and formation of deformation bands. At least one generation of dense iron oxide mineralization is associated with cataclastic brittle deformation predating the sulfate precipitation. Trace element geochemistry of cements shows certain metal oxide populations associated with extremely high (>2000 ppm) arsenic values. We interpret the combination of spatial mineral distribution, observed paragenetic sequence, and trace element geochemistry to suggest this region experienced acid sulfate diagenesis along fracture-controlled fluid conduits related to weathering of proximal, unidentified, sulfides, or H 2 S associated with deep source beds. Jarosite is highly soluble, and its presence suggests that abundant fluid flow has not occurred in this region since its formation. This terminal cement-forming event must have occurred prior to sandstone exhumation and erosion to form the current extreme landscape at Mollies. This site exhibits the influence that fluid geochemistry, sedimentary mineralogy, and structural fabric have on geomorphic evolution.

No abstract