Diversity of bathyal macrofauna on the northeastern Pacific margin: the influence of methane seeps and oxygen minimum zones     

Lisa A. Levin  Guillermo F. Mendoza  Jennifer P. Gonzalez  rew R. Thurber  & Erik E. Cordes 《Marine Ecology》2010,31(1):94-110

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Habitat heterogeneity and its influence on benthic biodiversity in oxygen minimum zones     

Andrew J. Gooday  Brian J. Bett  Elva Escobar  Baban Ingole  Lisa A. Levin  Carlos Neira  Akkur V. Raman  & Javier Sellanes 《Marine Ecology》2010,31(1):125-147

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Modeling and interpreting the seismic-reflection expression of sandstone in an ancient mass-transport deposit dominated deep-water slope environment     

Dominic A. Armitage  Lisa Stright 《Marine and Petroleum Geology》2010

Subsurface mass-transport deposits (MTDs) commonly have a chaotic seismic-reflection response. Synthetic seismic-reflection profiles, created from a precise lithological model, are used to interpret reflection character and depositional geometries at multiple frequencies. The lithological model was created from an outcrop of deep-water lithofacies where sandstone deposition was influenced by mass-transport deposit topography. The influence of MTD topography on sandstone distribution should be considered in reservoir characterization and modeling when MTDs underlie the reservoir, especially if the reservoir is thin relative to the scale of the topography. MTD topography up to several tens of meters in both the horizontal and vertical dimensions (relative to local elevation) compartmentalizes significant quantities of sandstone and is not resolved at lower seismic-reflection frequencies. The resolvability of thick (up to 70 m) sandstone packages is hindered when they are encased in MTDs of at least equivalent thickness. Lateral and vertical changes in seismic-reflection character (e.g., amplitude, polarity, geometry) of sandstone packages in the synthetic profiles are due to lithology changes, tuning effects, resolution limits, and depositional geometries, which are corroborated by the lithological model. Similar reflection-character changes are observed in an actual seismic-reflection profile, of comparable scale to the synthetic profiles, from the Gulf of Mexico, which demonstrates similar lithofacies distributions. Synthetic profiles, when constrained by a precise lithological model, are particularly useful analogues for interpretation of lithofacies relationships, and depositional geometries, in complicated depositional environments, such as deep-water slope deposits.  相似文献   

The 20th-century development and expansion of Louisiana shelf hypoxia,Gulf of Mexico     

Lisa E. Osterman  Richard Z. Poore  Peter W. Swarzenski  David B. Senn  Steven F. DiMarco 《Geo-Marine Letters》2009,29(6):405-414

Since systematic measurements of Louisiana continental-shelf waters were initiated in 1985, hypoxia (oxygen content <2 mg L⁻¹) has increased considerably in an area termed the dead zone. Monitoring and modeling studies have concluded that the expansion of the Louisiana shelf dead zone is related to increased anthropogenically derived nutrient delivery from the Mississippi River drainage basin, physical and hydrographical changes of the Louisiana Shelf, and possibly coastal erosion of wetlands in southern Louisiana. In order to track the development and expansion of seasonal low-oxygen conditions on the Louisiana shelf prior to 1985, we used a specific low-oxygen foraminiferal faunal proxy, the PEB index, which has been shown statistically to represent the modern Louisiana hypoxia zone. We constructed a network of 13 PEB records with excess ²¹⁰Pb-derived chronologies to establish the development of low-oxygen and hypoxic conditions over a large portion of the modern dead zone for the last 100 years. The PEB index record indicates that areas of low-oxygen bottom water began to appear in the early 1910s in isolated hotspots near the Mississippi Delta and rapidly expanded across the entire Louisiana shelf beginning in the 1950s. Since ~1950, the percentage of PEB species has steadily increased over a large portion of the modern dead zone. By 1960, subsurface low-oxygen conditions were occurring seasonally over a large part of the geographic area now known as the dead zone. The long-term trends in the PEB index are consistent with the 20th-century observational and proxy data for low oxygen and hypoxia.  相似文献   

Holocene evolution of Apalachicola Bay,Florida     

Lisa E. Osterman  David C. Twichell  Richard Z. Poore 《Geo-Marine Letters》2009,29(6):395-404

A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS ¹⁴C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 ¹⁴C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ∼6,400 and ∼2,500 ¹⁴C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ∼5,800 and 5,100 ¹⁴C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 ¹⁴C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay.  相似文献   

Metal-catalyzed degradation and racemization of amino acids in iron sulfate brines under simulated martian surface conditions     

Adam P. Johnson  Lisa M. Pratt 《Icarus》2010,207(1):124-603

Recent lines of evidence indicate that Mars may have been substantially warmer and wetter, raising questions about whether the planet’s surface was once more conducive to the possibility of life. To better constrain the extent of preservation of ancient amino acid biosignatures, the effects of metal ions and UV radiation were investigated with respect to the rates of diagenesis of amino acids in metal-rich sulfate brines. Individual experimental results indicate that the oxidation rates of amino acids loosely followed trends characteristic of a radiolytic oxidation mechanism that is dependent on variations in side-chain constituents. Relative rates of racemization only show a limited dependence on the presence of metals; overall, rates of racemization in the presence of metals in solution are an order of magnitude slower than oxidation and both are several orders of magnitude faster than previously reported. This increase in rate constant is indicative of an extremely efficient catalytic enhancement of this destructive diagenetic pathway. These findings imply that chiral life-detection strategies should focus on specific geochemical environments that exhibit relatively slow rates of both degradation and racemization. Episodic liquid water during periods of increased water activity on the martian surface may have significant implications for the oxidation of organic matter through secondary diagenetic reactions and may act as a leveling mechanism for organic compounds.  相似文献   

A Holocene record of endogenic iron and manganese precipitation and vegetation history in a lake-fen complex in northwestern Minnesota     

Walter E. Dean  Lisa A. Doner 《Journal of Paleolimnology》2012,47(1):29-42

Little Shingobee Lake and Fen are part of the extensive network of lakes and wetlands in the Shingobee River headwaters of northwestern Minnesota, designed to study the interactions between surface and ground waters. Prior to about 11.2 cal. ka, most of these lakes and wetlands were interconnected to form glacial Lake Willobee, which apparently formed when a debris flow dammed the Shingobee River. Between 11.2 and 8.5 cal. ka, the level of Lake Willobee fell as a result of breaching of the dam, transforming the deep lake into the existing lakes and wetlands. Analyses of a 9-m core from Little Shingobee Lake (LSL-B), and lacustrine sediments under 3.3 m of peat in a 17-m core from Little Shingobee Fen (LSF-10), show that the dominant components are allogenic clastic material, and endogenic CaCO₃ and organic matter. In both cores almost all of the iron (Fe) and manganese (Mn) are incorporated in endogenic minerals, presumed to be X-ray amorphous oxyhydroxide minerals, that occur in significant quantities throughout the cores; almost no Fe and Mn are contributed from detrital aluminosilicate minerals. This suggests that, for most of the Holocene, the allogenic watershed contributions to lake chemistry were minor compared to the dissolved mineral load. In addition, prior to 3.5 cal. ka, pollen zone boundaries coincide with large changes in lake-sediment mineralogy, indicating that both landscape and climate processes were linked to early- and mid-Holocene lake chemistry. The pollen time series, with sequential domination by spruce, pine, sagebrush-oak, birch-oak and, finally, white pine is typical of the region and reflects the changing location of the prairie-forest transition zone over time. These changes in vegetation had some profound effects on the geochemistry of the lake waters.  相似文献   

Evaluating the impact of visualization of risk upon emergency route-planning     

Lisa Cheong  Christoph Kinkeldey  Ingrid Burfurd  Susanne Bleisch 《International journal of geographical information science》2020,34(5):1022-1050

ABSTRACT

This paper reports on a controlled experiment evaluating how different cartographic representations of risk affect participants’ performance on a complex spatial decision task: route planning. The specific experimental scenario used is oriented towards emergency route-planning during flood response. The experiment compared six common abstract and metaphorical graphical symbolizations of risk. The results indicate a pattern of less-preferred graphical symbolizations associated with slower responses and lower-risk route choices. One mechanism that might explain these observed relationships would be that more complex and effortful maps promote closer attention paid by participants and lower levels of risk taking. Such user considerations have important implications for the design of maps and mapping interfaces for emergency planning and response. The data also highlights the importance of the ‘right decision, wrong outcome problem’ inherent in decision-making under uncertainty: in individual instances, more risky decisions do not always lead to worse outcomes.  相似文献   

From green spaces to vital places: connection and expression in urban greening     

Lisa de Kleyn  Laura Mumaw  Helen Corney 《The Australian geographer》2020,51(2):205-219

ABSTRACT

Urban greening, the improvement or increase of green spaces in cities, has purported environmental, individual, social and cultural benefits. The extent and qualities of urban green spaces, and our opportunities to engage with them, reflect and shape human responses to those spaces. Planning scholars recognise the traditional role and obligation of planning to help reduce social problems and see the potential for the public to be leaders in defining responses. However, use of technical, scientific and economic approaches by urban land managers can limit recognition of diverse connections to urban green and advance narrow conceptions of nature. We sample people’s responses to different forms of urban green and greening in three case studies from Melbourne, Australia. We show that modern connections and expressions are personal, social and dynamic. Human experiences are embedded in nature and connections develop from interactions with and about nature, in formal and informal spaces. Diverse connections prompt responses to nature, and actions affecting nature itself. Accordingly, we propose ways to develop more receptive, responsive, inclusive and connected forms of urban greening. These include recognising diverse connections and expressions, encouraging dynamic relationships with nature, and providing varied ways of engaging with urban green spaces that foster stewardship.  相似文献   

Multidecadal simulation of coastal fog with a regional climate model     

Travis A. O’Brien  Lisa C. Sloan  Patrick Y. Chuang  Ian C. Faloona  James A. Johnstone 《Climate Dynamics》2013,40(11-12):2801-2812

In order to model stratocumulus clouds and coastal fog, we have coupled the University of Washington boundary layer model to the regional climate model, RegCM (RegCM-UW). By comparing fog occurrences observed at various coastal airports in the western United States, we show that RegCM-UW has success at modeling the spatial and temporal (diurnal, seasonal, and interannual) climatology of northern California coastal fog. The quality of the modeled fog estimate depends on whether coast-adjacent ocean or land grid cells are used; for the model runs shown here, the oceanic grid cells seem to be most appropriate. The interannual variability of oceanic northern California summertime fog, from a multi-decadal simulation, has a high and statistically significant correlation with the observed interannual variability (r = 0.72), which indicates that RegCM-UW is capable of investigating the response of fog to long-term climatological forcing. While RegCM-UW has a number of aspects that would benefit from further investigation and development, RegCM-UW is a new tool for investigating the climatology of coastal fog and the physical processes that govern it. We expect that with appropriate physical parameterizations and moderate horizontal resolution, other climate models should be capable of simulating coastal fog. The source code for RegCM-UW is publicly available, under the GNU license, through the International Centre for Theoretical Physics.  相似文献