Mercury after the MESSENGER flybys: An introduction to the special issue of Planetary and Space Science     

Sean C. Solomon  Ralph L. McNutt Jr.  Louise M. Prockter 《Planetary and Space Science》2011,59(15):1827-1828

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Rotating micro-structures in Antarctic cold basal ice: implications for glacier flow and its interpretation     

Denis Samyn  Sean J. Fitzsimons  Reginald D. Lorrain 《International Journal of Earth Sciences》2010,99(8):1849-1857

Structural analyses were conducted in the basal zone of an Antarctic glacier. The studied basal ice sequence was retrieved from a 20-m-long subglacial tunnel dug at the margin of the glacier and is at the temperature of −17°C. For the first time, rotating clast systems embedded within debris-rich ice were thin-sectioned using specially designed cutting techniques. The observed structures reflect the occurrence of pervasive shearing at the base of the glacier, and can be used as shear sense indicators. In addition, some of these structures provide evidence for the presence of thin liquid films at the time of formation despite the marked freezing temperature of the ice. It is showed here that cautious analysis of deformation structures present in debris-bearing ice may bring insights not only into the flow dynamics of the embedding matrix, but also into the behaviour of the interstitial fluid network at the base of cold glaciers and ice sheets.  相似文献   

Impacts of Oyster Reef Restoration on Primary Productivity and Nutrient Dynamics in Tidal Creeks of the North Central Gulf of Mexico     

Rochelle Plutchak  Kelly Major  Just Cebrian  C. Drew Foster  Mary-Elizabeth C. Miller  Andrea Anton  Kate L. Sheehan  Kenneth L. HeckJr.  Sean P. Powers 《Estuaries and Coasts》2010,33(6):1355-1364

The ability of oysters to remove large quantities of particulates from the water column, thereby potentially improving water quality, has been cited as one of the reasons for oyster reef restoration. However, this ability has not yet been effectively demonstrated in the field. As part of the Alabama Oyster Reef Restoration Project, this study was designed to assess impacts of restored eastern oyster (Crassostrea virginica) reefs on primary production, nutrient dynamics, and water quality in shallow tidal creeks. Using a Before–After-Control–Impact (BACI) design, we monitored tidal creeks around Dauphin Island, AL, for changes induced by the introduction of oyster reefs. Reef placement resulted in increased ammonium (NH₄⁺) in two of the three experimental creeks. Interestingly, oyster reefs did not seem to reduce water column particulates or have an impact on phytoplankton or microphytobenthic biomass or productivity. We do not believe that our data discount the importance and/or usefulness of oysters in modifying the water column. Rather, we acknowledge that it is difficult to detect these impacts/environmental services in this type of system (i.e., a tidal creek system), because they seem to be very localized and short-lived (i.e., not ecologically relevant on a creek-wide scale). This study highlights the need to consider location and habitat in planning oyster restoration projects. Also, it demonstrates that the types, magnitudes, and spatial extent of changes in ecosystem services that should be expected after reef restoration might need to be re-evaluated.  相似文献   

Marine and estuarine reservoir effects in central Queensland,Australia: Determination of ΔR values     

Sean Ulm 《Geoarchaeology》2002,17(4):319-348

As a component of archaeological investigations on the central Queensland coast, a series of five marine shell specimens live‐collected between A.D. 1904 and A.D. 1929 and 11 shell/charcoal paired samples from archaeological contexts were radiocarbon dated to determine local ΔR values. The object of the study was to assess the potential influence of localized variation in marine reservoir effect in accurately determining the age of marine and estuarine shell from archaeological deposits in the area. Results indicate that the routinely applied ΔR value of −5 ± 35 for northeast Australia is erroneously calculated. The determined values suggest a minor revision to Reimer and Reimer's (2000) recommended value for northeast Australia from ΔR = +11 ± 5 to +12 ± 7, and specifically for central Queensland to ΔR = +10 ± 7, for near‐shore open marine environments. In contrast, data obtained from estuarine shell/charcoal pairs demonstrate a general lack of consistency, suggesting estuary‐specific patterns of variation in terrestrial carbon input and exchange with the open ocean. Preliminary data indicate that in some estuaries, at some time periods, a ΔR value of more than −155 ± 55 may be appropriate. In estuarine contexts in central Queensland, a localized estuary‐specific correction factor is recommended to account for geographical and temporal variation in ¹⁴C activity. © 2002 Wiley Periodicals, Inc.  相似文献