Sediment disturbance caused by a suspension-feeding tubular agglutinated foraminifer

We report the occurrence of in-situ sediment disturbance caused by a specimen of Rhabdammina observed in life position on the 1991 Mt. Pinatubo ash layer in the abyssal South China Sea. The specimen extracts sediment grains from the ash layer to build its agglutinated test, causing a depression, or “moat” to form around the base of the specimen. We suspect that such fine-scale disturbance caused by large, erect tubular foraminifera is a common feature of the fossil record in deep-sea settings

Bolboforma from Leg 105, Labrador Sea and Baffin Bay, and the chronostratigraphy of Bolboforma in the North Atlantic

The genus Bolboforma, first described by Daniels and Spiegler (1974), is a problematic group of calcareous microfossils. Solbaforma is most probably a planktonic cyst (Rogl and Hochuli, 1976) having protozoan or algal affinities (Poag and Karowe, 1986). Its known distribution at present suggests that various species may have potential for becoming good stratigraphic indicators. Bolboforma also may be useful in areas where other calcareous planktonic microfossils are poorly preserved, i.e., the North Sea, the Norwegian-Greenland Sea, and Baffin Bay. This report summarizes the known occurrences of Bolboforma in the North Atlantic and correlates them with a standard geochronology (Berggren et al., 1985a, 1985b). In addition, further occurrences of Bolboforma are reported from Sites 645, 646, and 647 (Fig. 1)

A tubular protozoan predator: a burrow selectively filled with tubular agglutinated protozoans (Xenophyophorea, Foraminifera) in the abyssal South China Sea

We report the occurrence of an unusual agglutinated protozoan-filled burrow recovered in a box core collected in 1998 from a depth of 2496 m in the South China Sea. The onion-shaped burrow occurring some 8 cm beneath the sediment surface was packed full with specimens of xenophyophoreans and foraminifera dominated by a single genus (Aschemonella) that had been living on the surface of the 1991 Mt. Pinatubo ash layer. This selective scavenging of epibenthic tubular agglutinated protozoans contributes to the patchiness of the benthic fauna on the sea floor. Because the tubular protozoans selectively agglutinate mafic mineral grains from the volcanic ash, two levels of biological scavenging are involved with the redistribution of these volcanic grains

Taxonomy and biostratigraphy of new and emended species of Cenozoic deep-water agglutinated foraminifera from the Labrador and North Seas

Deep marine, fine grained sedimentary strata of Maastrichtian through Miocene age in the Labrador and North Sea sedimentary basins are rich in agglutinated benthic foraminifera. Six new taxa have been found in these regions, several of which also extend to other circum-Atlantic Paleogene localities. The new taxa are: Ammomarginulina aubertae, n. sp. (Maastrichtian to Eocene), Adercotryma agterbergi, n. sp. (middle Eocene to lower Oligocene), Reticulophragmoides jarvisi (Thalmann) emended herein (Paleocene to lower Oligocene), Reticulophragmoides sp. 5 (Oligocene to Miocene), and Spiroplectammina navarroana Cushman emended herein (Maastrichtian to lower middle Eocene). The last occurrences of these taxa are important elements in the high-resolution probabilistic biozonations for the Labrador and North Sea basins

Early to middle Miocene foraminifera from the deep-sea Congo Fan, offshore Angola

Analysis of a 630m section of an exploration well penetrating the distal part of the Congo Fan (~2000m water depth) yielded high abundance and diversity assemblages of agglutinated and calcareous benthic foraminifera. Planktonic foraminifera constrain the age to Early – Middle Miocene, and \delta 18O records reveal the Mi1 (~16.3 Ma) isotopic shift. Relatively few taxonomic studies of deep-water calcareous and agglutinated benthic foraminifera exist from this time period in this locality. All species encountered are therefore taxonomically described and documented using SEM photography (over 170 species), along with 27 species of planktonic foraminifera. Faunas show close affinities to those of the eastern Venezuela Basin, Gulf of Mexico and Central Paratethys. Seven assemblages are defined and analysed using morphogroup analysis and Correspondence Analysis, documenting the response of benthic foraminifera to three primary environmental-forcing factors; energy levels in the benthic boundary layer, oxygen levels relating to changing surface water productivity, and fluctuations in the level of the CCD. Near the top and bottom of the studied section both foraminiferal abundance and diversity decrease, corresponding with increased sand content implying greater energy levels and environmental disturbance. The majority of the section consists of shales with very low percentage sand, high foraminiferal abundance and diversity, and high sedimentation rates of ~10cm/kyr. Morphogroup analysis reveals a major switch in the fauna at around oxygen isotope event Mi1, with the transition from an epifaunal-dominated Cibicidoides assemblage to shallow infaunal-dominated Bulimina assemblage. We regard this as likely due to expansion of the oxygen minimum zone (paleobathymetric estimates are ~1000m) related to increased surface-water productivity and global cooling. Shifts in calcareous foraminiferal percentage over the studied interval overprint these signals and are believed to be related to a shoaling CCD, linked to reduced oceanic acidity and global atmospheric CO2 levels during the early Middle Miocene Monterey Carbon Isotope Excursion

Universality of the Kondo Effect in a Quantum Dot out of Equilibrium

We study the Kondo effect in a quantum dot driven out of equilibrium by an external ac field. The Kondo effect can be probed by measuring the dc current induced by an auxiliary dc bias $V_{dc}$ applied across the dot. In the absence of ac perturbation, the corresponding differential conductance $G(V_{dc})$ is known to exhibit a sharp peak at $V_{dc}=0$, which is the manifestation of the Kondo effect. In the equilibrium, there exists only one energy scale, the Kondo temperature $T_K$, which controls all the low-energy physics of the system; $G$ is some universal function of $eV_{dc}/T_K$. We demonstrate that the dot out of equilibrium is also characterized by a universal behavior: conductance $G$ depends on the ac field only through two dimensionless parameters, which are the frequency $\omega$ and the amplitude of the ac perturbation, both divided by $T_K$. We find analytically the large- and small-frequency asymptotes of the universal dependence of $G$ on these parameters. The obtained results allow us to predict the behavior of the conductance in the crossover regime $\hbar\omega\sim T_K$.Comment: 18 pages, 5 figure

How to make semiconductors ferromagnetic: A first course on spintronics

The rapidly developing field of ferromagnetism in diluted magnetic semiconductors, where a semiconductor host is magnetically doped by transition metal impurities to produce a ferromagnetic semiconductor (e.g. Ga_{1-x}Mn_xAs with x ~ 1-10 %), is discussed with the emphasis on elucidating the physical mechanisms underlying the magnetic properties. Recent key developments are summarized with critical discussions of the roles of disorder, localization, band structure, defects, and the choice of materials in producing good magnetic quality and high Curie temperature. The correlation between magnetic and transport properties is argued to be a crucial ingredient in developing a full understanding of the properties of ferromagnetic semiconductors.Comment: 8 pages; to appear in the special issue 'Quantum Phases at Nanoscale' of Solid State Communication