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81.
Thomas Soltwedel Nina Jaeckisch Nikolaus Ritter Christiane Hasemann Melanie Bergmann Michael Klages 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1856-1872
Five photographic transects, covering some 830 m2 of seafloor in total, were analyzed to characterize the megabenthic community along a bathymetric gradient covering water depths from 1200 to 5500 m in the eastern Fram Strait. Megafaunal densities ranged between 11 and 38 ind. m−2. The highest densities were found at 1650 m and the lowest densities occurred at 3000 m depth. The number of taxa and morphotypes ranged between 4 at 5500 m and 27 at 1650 m water depth. Ophiocten gracilis, a small white unidentified amphipod, Kolga hyalina, and Bathycrinus carpenteri were the dominant and characteristic species on the slope and continental rise. Elpidia heckeri dominated in the Molloy Hole, the deepest depression known in the Arctic Ocean. Megafaunal zonation patterns appeared to be mainly controlled by food availability, as indicated by phytodetrital matter measured at the seafloor, and by benthic biomass in the sediments, as indicated by sediment-bound particulate proteins and phospholipids. By contrast, physical factors, including water depth and seabed properties such as sediment porosity and hard substrata (e.g., dropstones), appear to play a secondary role in determining megabenthic zonation patterns along the bathymetric HAUSGARTEN gradient. 相似文献
82.
Consulting type specimens is a necessary element of taxonomic research in palaeontology. Every taxonomist from time to time has to examine the types to make sure that the identifications are correct. This can be a difficult proposition when the fossils in question were collected in the early nineteenth century. But just because a historical fossil collection is said to be 'lost', doesn't mean it cannot be found. 相似文献
83.
We report here on cirque infills mapped in the Khibiny Mountains, Kola Peninsula, Russia. Cirque infills are morainic deposits located near the headwalls of valleys and cirques. Their location and shape, often with concave margins towards the valley side, indicate that they were deposited by ice flowing up‐valley, into the mountains, rather than by local glaciers. We suggest that they formed during the last deglaciation, when Khibiny was a nunatak and Fennoscandian ice sheet lobes extended into valleys and cirques of the massif. The formation of cirque infills is probably more related to ice sheet dynamic factors, occurring when the ice margin retreated from the cirques, than to climate‐driven interruption in the ice‐marginal retreat. Glacial conditions similar to those prevalent when the Khibiny cirque infills were formed, occur today in Antarctica where the ice sheets engulf nunatak ranges. In Heimefrontfjella, Antarctica, the formation of supraglacial moraines at the head of cirques are linked to blue‐ice conditions, indicating locally low accumulation rates, a dry continental climate and sublimation dominated ablation. We suggest that these Antarctic moraines are modern analogues of cirque infills on the Kola Peninsula, and possibly, that the cirque infills may be used as palaeoenvironmental indicators. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
84.
Shao-Yi Huang Yue-Gau Chen George S. Burr Manoj K. Jaiswal Yunung Nina Lin Gongming Yin Jingwei Liu Shujun Zhao Zhongquan Cao 《Quaternary Research》2014
We present a reconstructed lithologic column compiled from a series of lacustrine outcrops along a tributary of the Nyang River, a major tributary of the Yarlung-Tsangpo in southeast Tibet. The deposits were preserved between terraces at altitudes of 2950–3100 m asl. The stratigraphic record features at least two sets of coarsening-upward sequences depicting episodic aggradation and progradation of a glacially dammed lake related delta. Recognized facies changes illustrate the evolution cycles of depositional environments from pro-delta, delta front, to delta plain. Radiocarbon and optically stimulated luminescence dates reveal an aging-downward trend in stratigraphic order and provide an approximate timeline for the formation of glacially dammed lakes in late Pleistocene. This result reflects that the Zelunglung Glacier had progressively advanced to block the Yarlung-Tsangpo river and the dam materials had stepwise stacked up to an altitude of 3095 m asl during Marine Oxygen Isotope Stages 4 to 2. 相似文献
85.
Journal of Geographical Systems - Scale effects are pervasive in geospatial modeling and affect the reliability of analysis results. This paper examines the neighborhood scale effects on the... 相似文献
86.
Amphipoda are a diverse and important faunal component of deep‐sea habitats worldwide. However, relatively little is known about species that are associated with cold‐water corals, in particular concerning their genetic diversity, population genetic processes, population differentiation, and potential host specificity. We exemplarily investigate these questions studying three pleustid species—Stenopleustes aff. malmgreni (Boeck, 1871), Stenopleustes aff. nodifera (Sars, 1883) and Neopleustes aff. boecki (Hansen, 1888)—that are associated with cold‐water corals and polychaete assemblages along the Reykjanes Ridge southwest of Iceland. We sequenced mitochondrial COI and performed ddRAD to study thousands of nuclear loci. These species and a pair of morphologically cryptic species within Stenopleustes aff. nodifera were consistently delimited by COI and ddRAD. We conclude that all of our studied species are new to science, raising the number of pleustids reported from cold‐water corals to six. Two species were collected only once, and these species exhibited high levels of inbreeding, suggesting little exchange with other populations, which might be a result of strong host specificity. The other two species were wider distributed, with very low differentiation among populations, even between populations separated by 130 km. These species showed signs of recent population expansions, possibly in relation to changes in the cold‐water coral associated ecosystem (e.g., due to glacial cycles and/or volcanic or geothermal activities). They had lower levels of inbreeding and were each associated with three different host coral species, which might facilitate dispersal and gene flow. Our results show divergent population genetic patterns for the studied pleustid species. These might be attributed to the species’ host specificity and highlight important differences among species with seemingly similar life‐styles. Species diversities appear to be greatly underestimated, limiting our abilities to truly assess the vulnerability of the fauna living in these threatened cold‐water coral habitats. 相似文献
87.
Nina Keul John W. Morse Rik Wanninkhof Dwight K. Gledhill Thomas S. Bianchi 《Aquatic Geochemistry》2010,16(3):337-351
This paper presents the results of two cruises in the Northern Gulf of Mexico in 2008 that investigated local and short-term
factors influencing the carbonate chemistry dynamics and saturation state with respect to aragonite (Ωaragonite) of surface seawater in this region. One cruise covered much of the northern half of the Gulf, and the other focused on
the coastal zone west of the Atchafalaya Bay outlet of the Mississippi River—the region where the hypoxic “dead zone” occurs
on the Louisiana shelf. Offshore waters (>100 m depth) exhibited only small variations in CO2 fugacity (fCO2), total alkalinity (TA) and Ωaragonite. Values were close to those typically observed in subtropical Atlantic Ocean and Caribbean Sea waters of similar salinity.
However, inner shelf waters (<50 m depth) exhibited large variations in fCO2, TA, and Ωaragonite that were not directly related to salinity or distance from the Mississippi River plume. Changes in TA values were not the
result of simple mixing of end-member freshwater and seawater TA concentrations but exhibited a minimum in values near salinity
of 25. This minimum could be the result of microbial recycling across salinity gradients, biological removal of alkalinity
by formation of calcium carbonate or mixing of a third end-member with a low alkalinity such as Terrebonne Bay. All waters
were supersaturated with respect to aragonite. Offshore waters had an average Ωaragonite of 3.86 with a standard deviation of only ±0.06 and inner shelf waters had a range in Ωaragonite values from 3.9 to 9.7 with a median of 4.3. Shelf water Ωaragonite values were elevated relative to the offshore as a consequence of both high TA input from Mississippi River and biological
drawdown of CO2. A dominant factor controlling Ωaragonite distribution in offshore waters with relatively constant temperatures was fCO2, with higher supersaturation occurring in areas with low fCO2. 相似文献
88.
Julia Semprich Nina S. C. Simon Yuri Yu. Podladchikov 《International Journal of Earth Sciences》2010,99(7):1487-1510
Constraints on density as a function of pressure, temperature, and composition are crucial to understand isostatic movements
during geodynamic processes. Here, we provide a systematic series of density diagrams extracted from thermodynamic calculations
for a variety of crustal compositions within a wide P–T range. We quantify systematic density changes in collisional settings for relevant compositional variations and attempt to
simplify the density–composition relationships. Rock densities depend strongly on pressure, temperature, and composition.
Densities at some selected pressure–temperature conditions increase linearly with increasing Al2O3 as well as MgO/FeO contents in pelitic rocks. Al- and Fe-rich pelites yield the highest densities, which is mostly due to
the formation of garnet but also depends on other minerals and changes of reactions. The effect of loading on densities is
investigated, and we show that for deep burial, a meta-pelite rich in Fe and Mg yields much larger density changes than a
dry basalt and that the burial of such a rock with a composition close to typical lower crust may result in significant negative
buoyancy. Metamorphism of hydrous lower crust due to pressurization and heating thus leads to densification of thickened lower
crust, while heating of dry crust leads to a decrease in density. Hence, water-loaded isostatic subsidence due to metamorphism
of water-saturated lower crust is substantial and increases with the thickness and depth of the reacting layer, while dry
compositions show much less or only transient densification and subsidence. The density change due to thermal expansion, an
extensively used concept in geodynamic models, predicts uplift under the same P–T conditions and is an order of magnitude smaller than the density variation calculated from petrologically consistent diagrams. 相似文献
89.
Presently, 235 submerged caves and pits have been recorded along the Croatian coast and islands, partly or completely submerged
by sea water. Contrary to the inland situation, recorded submerged features are predominantly horizontal (60%), though there
are indications that the real situation is similar to that of the continental part where 69% are vertical pits. Completely
marine conditions are established in 126 caves and the rest are anchihaline caves and submarine springs. Speleothems are found
in more than 140 caves. By their origin, the investigated caves are all continental features formed in Mesozoic and Palaeogene
carbonates, subsequently submerged owing to sea transgression. Due to the relatively low wave energy, rapid sea level rise
and maturity of the host rock, they do not fit into concepts of a sea cave or a flank margin cave development, but they fulfil
several conditions for being the blue holes. Since the term ‘blue hole’ is mainly associated with the Bahamian karst, our
attempt is only to show the possible similarities with no intention of ascribing that term to the Croatian caves. Beside karstological
issues, Croatian submerged caves are unique environmental, archaeological and tourism assets. 相似文献
90.
Nina D. ROSENBERG Lauren BROWNING William L. BOURCIER 《Meteoritics & planetary science》2001,36(2):239-244
Abstract— Results from an inorganic geochemical modeling study support a scenario in which low‐temperature aqueous alteration of an anhydrous CM asteroidal parent body and melt water from H2O and CO2 ices produces the altered assemblage observed in CM carbonaceous chondrites (chrysotile, greenalite, tochilinite, cronstedtite and minor calcite and magnetite). We consider a range of possible precursor mineral assemblages, varying with respect to the Fe‐oxidation state of the initial anhydrous phases. The aqueous solutions produced by this alteration are generally strongly basic and reducing and a large quantity of H2, and possible CH4, gas can be released during aqueous alteration. 相似文献