Sedimentation processes on the antarctic continental margin at Kapp Norvegia during the late Pleistocene

Sedimentological analyses concerning ice rafted debris, grain size distribution, biogenous components, and clay mineral composition of four sediment cores from the Antarctic continental margin off Kapp Norvegia reveal a cyclical pattern of three different sediment facies. These are classified into warm and cold types representing warm and cold a climatic periods and short transition period from cold to warm events.The sedimentological parameters reflect the variations within the cryosphere and the hydrosphere, which are directly influenced by the climatic fluctuations. The unusually high content of carbonaceous planktonic and benthonic foraminifera in these polar sediments, as well as the interfingering of terrigeneous and biogeneous-rich sediments with increasing distance from the continent, might reflect the influence of the Weddell Sea Polynya and the oscillations of polynya, pack ice and ice shelf extent during the late Pleistocene.

---

Zusammenfassung An vier Sedimentkernen eines Profils am antarktischen Kontinentalhang vor Kapp Norvegia wurden Eisfracht, biogene Komponenten, Korngrößenverteilungen und Tonmineralvergesellschaftungen bestimmt. Die Verteilung der sedimentologischen Parameter zeigt eine zyklische Abfolge von drei verschiedenen Sedimentfazies, die die klimatisch gesteuerten Veränderungen innerhalb der Hydrossphäre und der Kryossphäre widerspiegeln.Die drei Sedimentfazies werden warmen und kalten Klimaperioden sowie einer kurzen Übergangszeit zugeordnet. Der für polare Sedimente ungewöhnlich hohe Gehalt an kalkigen benthonischen und planktonischen Foraminiferen sowie die Verzahnung vorwiegend terrigener mit biogenreichen Sedimenten bei zunehmender Entfernung vom Kontinent lassen den Einfluß der Weddell See-Polynya und die Oszillationen von Schelfeiskante und Packeisbildung während des späten Pleistozäns erkennen.

---

Résumé Des analyses sédimentologiques ont été effectuées sur 4 carottes prélevées le long d'un profil dans les sédiments de la marge continentale antarctique au large du cap Norvegia. Elles ont porté sur les débris amenés par les glaces, la granulométrie, les composants biogéniques et la composition des constituants argileux. Ces analyses révélent une succession cyclique de 3 facies sédimentaires; ceux-ci correspondent à des périodes climatiques chaudes et froides, ainsi qu'à de courtes périodes de transition du froid vers le chaud.Les paramètres sédimentologiques reflètent des variations de l'hydrosphère et de la cryosphère, directement influencées par les fluctuations climatiques. La teneur anormalement élevée de ces sédiments polaires en foraminif ères carbonatés planctoniques et benthoniques, ainsi que l'indentation de sédiments terrigènes et de sédiments riches en éléments biogéniques, peuvent traduire l'influence de la polyme de la Mer de Weddell, ainsi que les oscillations des surfaces occupées par la polynie, le pack et l'iceshelf, au cours du Pleistocène tardif.

---

. , . , , . , , , , Weddell See-Polynya , .

     

Tholeiitic Aleutian arc plutonism: The Finger Bay pluton,Adak, Alaska

The earliest representatives in the sequence of Tertiary to Recent magmatic rocks on Adak island in the central Aleutians, are the Finger Bay Volcanics and associated small shallow-level gabbroic intrusives. The tholeiitic Finger Bay pluton (gabbro to quartz monzodiorite) is among the least altered representatives of this earliest period. The field relations, mineralogy, and geochemistry of the Finger Bay pluton contrast with the more recent calcalkaline plutons in the arc (e.g. on Adak, Hidden Bay pluton: 33 m.y. and on Kagalaska, Kagalaska pluton: 15 m.y.). Compared with the Hidden Bay pluton, the Finger Bay pluton is smaller (8 km² versus 100 km²), has a greater proportion of gabbro (84% versus 5%), has a somewhat different mineralogy, and has higher whole rock and mafic mineral FeO/MgO ratios, higher K₂O, and higher concentrations of incompatable elements in rocks of equivalent SiO₂ (particularly for the more siliceous units). Magmatic amphibole occurs only in the most siliceous units in the Finger Bay pluton, whereas it is common in the calc-alkaline plutons. Except for the size, these differences parallel those between tholeiitic and calc-alkaline volcanic rocks from the active Aleutian volcanic centers. Textural, miner-alogical, and trace element analyses indicate that mixing of magmas and gabbros generated some of the rocks of intermediate (monzodiorite) composition in the Finger Bay pluton. Most of the differences in magmatic trends between the calc-alkaline and tholeiitic plutons are attributed to the physical conditions of magmatic evolution in the crust, rather than to differences in initial magmatic types. This conclusion rests on the similarity of fractionation-independent isotope ratios and trace element ratios in Aleutian magmas of all ages. In particular, compared to magmas of the north Pacific ocean basin (MORB, oceanic islands), Aleutian magmas show excess enrichment of Ba, K, Rb, and U relative to REE and high ²⁰⁷Pb/²⁰⁴Pb ratios for a given ²⁰⁶Pb/²⁰⁴Pb ratio. Recognition of tholeiitic series plutons in the arc provides direct evidence for magmatic conditions accompanying fractionation, and serves to emphasize the diversity of magmatic trends that are found over time and space at convergent plate margins.     

Theory and Practice in Mathematical Geology—Introduction and Discussion

Mathematical geology has developed into a very diverse system of mathematical models, algorithms and corresponding software. Experience shows that this diversification of approaches and methods was and is accompanied by an increasing gap between the availability of powerful tools and the continuation of many traditional working methods in the geosciences. Besides continuing to develop models, one of the basic functions of mathematical geology should be to introduce all new tools into practice and to aid non-specialized geoscientists to use them successfully and without bias. Some ways to do so will be briefly discussed here. Instructive and intelligible contributions towards attaining this goal were presented at the last (32nd) International Geological Congress held in Florence, Italy, in 2004. The intention of this present compilation is to suggest relevant discussions and conclusions. Mathematical geology should not be the domain of a few experts. It should be made accessible to all geologists and scientists in related fields.     

Routing of canopy drip in the snowpack below a spruce crown

Snow that is retained by a forest canopy may either sublimate or evaporate directly from the crown or drop as snow clumps or meltwater to the ground. Redistributed snow and meltwater affect the snow structure and prevent the formation of mechanically weak layers, which is the prerequisite for avalanche formation in forests. In this paper we describe the results of dye tracer experiments conducted in a subalpine forest near Davos, Switzerland. Before a snowfall event we stained snow‐free branches of a spruce with a dye tracer solution. After snowfall the coloured meltwater dripping from the branches down on to the snowpack stained the percolation pathways of the meltwater in the snowpack. Photographs of the snow profiles indicate that the meltwater seeped almost vertically through the isothermal snowpack to the soil surface not exceeding the projected crown edge. Meltwater of different events moves along different preferential flow channels in the snow suggesting that old channels are not non‐conducting and additional meltwater fronts create new channels. Copyright © 1999 John Wiley & Sons, Ltd.     

Voluminous lava flows at Oldoinyo Lengai in 2006: chronology of events and insights into the shallow magmatic system

The largest natrocarbonatite lava flow eruption ever documented at Oldoinyo Lengai, NW Tanzania, occurred from March 25 to April 5, 2006, in two main phases. It was associated with hornito collapse, rapid extrusion of lava covering a third of the crater and emplacement of a 3-km long compound rubbly pahoehoe to blocky aa-like flow on the W flank. The eruption was followed by rapid enlargement of a pit crater. The erupted natrocarbonatite lava has high silica content (3% SiO₂). The eruption chronology is reconstructed from eyewitness and news media reports and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data, which provide the most reliable evidence to constrain the eruption’s onset and variations in activity. The eruption products were mapped in the field and the total erupted lava volume estimated at 9.2 ± 3.0 × 10⁵ m³. The event chronology and field evidence are consistent with vent construct instability causing magma mixing and rapid extrusion from shallow reservoirs. It provides new insights into and highlights the evolution of the shallow magmatic system at this unique natrocarbonatite volcano.     

Reporting negative results to stimulate experimental hydrology: discussion of “The role of experimental work in hydrological sciences – insights from a community survey”*

Experimental work in hydrology is in decline. Based on a community survey, Blume et al. showed that the hydrological community associates experimental work with greater risks. One of the main issues with experimental work is the higher chance of negative results (defined here as when the expected or wanted result was not observed despite careful experimental design, planning and execution), resulting in a longer and more difficult publishing process. Reporting on negative results would avoid putting time and resources into repeating experiments that lead to negative results, and give experimental hydrologists the scientific recognition they deserve. With this commentary, we propose four potential solutions to encourage reporting on negative results, which might contribute to a stimulation of experimental hydrology.     

Urbanization in China from the end of 1980s until 2010 – spatial dynamics and patterns of growth using EO-data

Urbanization in China has been experiencing a remarkable dynamism in the past 40 years. The most evident implication of urbanization is the physical growth of cities. We analyze urban land growth rates and changes in spatial urban forms from the end of the 1980s to 2010 based on the authoritative National Land Use/Cover Database of China. We present new spatial measures that describe ‘urban land growth types’ and ‘fluctuations in urban land growth’ within the monitoring time span with a temporal interval of five-year steps. We evaluate the correlations between urban land growth rates and socioeconomic data. Results show that (1) distinct characteristics exist on the spatiotemporal evolutions of urban land growth rates in terms of area and perimeter, e.g. coastal areas exhibit the most dramatic growth rates; (2) the spatial distribution characteristics of ‘urban land growth types’ and ‘fluctuations in urban land growth’ follow similar spatial patterns across China, e.g. significant differences exist between the eastern region and other regions; and (3) a moderate correlation exists between urban area growth rate and urban population growth rate at an R² of 0.37. By contrast, we determine no significant correlation between urban area growth rate and tertiary industry value growth rate.