Sedimentation and subsidence history of the Lomonosov Ridge

During the first scientific ocean drilling expedition to the Arctic Ocean (Arctic Coring Expedition [ACEX]; Integrated Ocean Drilling Program Expedition 302), four sites were drilled and cored atop the central part of the Lomonosov Ridge in the Arctic Ocean at ~88°N, 140°E (see Fig. F18 in the "Sites M0001–M0004" chapter). The ridge was rifted from the Eurasian continental margin at ~57 Ma (Fig. F1) (Jokat et al., 1992, 1995). Since the rifting event and the concurrent tilting and erosion of this sliver of the outer continental margin, the Lomonosov Ridge subsided while hemipelagic and pelagic sediments were deposited above the angular rifting unconformity (see Fig. F7A in the "Sites M0001–M0004" chapter).The sections recovered from the four sites drilled during Expedition 302 can be correlated using their seismic signature, physical properties (porosity, magnetic susceptibility, resistivity, and P-wave velocity), chemostratigraphy (ammonia content of pore waters), lithostratigraphy, and biostratigraphy. The lithostratigraphy of the composite section combined with biostratigraphy provides an insight into the complex history of deposition, erosion, and preservation of the biogenic fraction. Eventually, the ridge subsided to its present water depth as it drifted from the Eurasian margin. In this chapter, we compare a simple model of subsidence history with the sedimentary record recovered from atop the ridge

Accidental Degeneracy and Berry Phase of Resonant States

We study the complex geometric phase acquired by the resonant states of an open quantum system which evolves irreversibly in a slowly time dependent environment. In analogy with the case of bound states, the Berry phase factors of resonant states are holonomy group elements of a complex line bundle with structure group C*. In sharp contrast with bound states, accidental degeneracies of resonances produce a continuous closed line of singularities formally equivalent to a continuous distribution of "magnetic" charge on a "diabolical" circle, in consequence, we find different classes of topologically inequivalent non-trivial closed paths in parameter space.Comment: 23 pages, 2 Postscript figures, LaTex, to be published in: Group 21: Symposium on Semigroups and Quantum Irreversibility (Proc. of the XXI Int. Colloquium on Group Theoretical Methods in Physics

A dedicated haem lyase is required for the maturation of a novel bacterial cytochrome c with unconventional covalent haem binding

In bacterial c-type cytochromes, the haem cofactor is covalently attached via two cysteine residues organized in a haem c-binding motif. Here, a novel octa-haem c protein, MccA, is described that contains only seven conventional haem c-binding motifs (CXXCH), in addition to several single cysteine residues and a conserved CH signature. Mass spectrometric analysis of purified MccA from Wolinella succinogenes suggests that two of the single cysteine residues are actually part of an unprecedented CX15CH sequence involved in haem c binding. Spectroscopic characterization of MccA identified an unusual high-potential haem c with a red-shifted absorption maximum, not unlike that of certain eukaryotic cytochromes c that exceptionally bind haem via only one thioether bridge. A haem lyase gene was found to be specifically required for the maturation of MccA in W. succinogenes. Equivalent haem lyase-encoding genes belonging to either the bacterial cytochrome c biogenesis system I or II are present in the vicinity of every known mccA gene suggesting a dedicated cytochrome c maturation pathway. The results necessitate reconsideration of computer-based prediction of putative haem c-binding motifs in bacterial proteomes

The phase-space structure of a dark-matter halo: Implications for dark-matter direct detection experiments

We study the phase-space structure of a dark-matter halo formed in a high resolution simulation of a Lambda CDM cosmology. Our goal is to quantify how much substructure is left over from the inhomogeneous growth of the halo, and how it may affect the signal in experiments aimed at detecting the dark matter particles directly. If we focus on the equivalent of ``Solar vicinity'', we find that the dark-matter is smoothly distributed in space. The probability of detecting particles bound within dense lumps of individual mass less than 10^7 M_\sun h^{-1} is small, less than 10^{-2}. The velocity ellipsoid in the Solar neighbourhood deviates only slightly from a multivariate Gaussian, and can be thought of as a superposition of thousands of kinematically cold streams. The motions of the most energetic particles are, however, strongly clumped and highly anisotropic. We conclude that experiments may safely assume a smooth multivariate Gaussian distribution to represent the kinematics of dark-matter particles in the Solar neighbourhood. Experiments sensitive to the direction of motion of the incident particles could exploit the expected anisotropy to learn about the recent merging history of our Galaxy.Comment: 13 pages, 13 figures, Phys. Rev. D in press. Postscript version with high resolution figures available from http://www.mpa-garching.mpg.de/~ahelmi/research/lcdm_dm.html; some changes in the text; constraints on the effect of bound dark-matter lumps revised; remaining conclusions unchange

The use of synchrotron edge topography to study polytype nearest neighbour relationships in SiC

A brief review of the phenomenon of polytypism is presented and its prolific abundance in Silicon Carbide discussed. An attempt has been made to emphasise modern developments in understanding this unique behaviour. The properties of Synchrotron Radiation are shown to be ideally suited to studies of polytypes in various materials and in particular the coalescence of polytypes in SiC. It is shown that with complex multipolytypic crystals the technique of edge topography allows the spatial extent of disorder to be determined and, from the superposition of Laue type reflections, neighbourhood relationships between polytypes can be deduced. Finer features have now been observed with the advent of second generation synchrotrons, the resolution available enabling the regions between adjoining polytypes to be examined more closely. It is shown that Long Period Polytypes and One Dimensionally Disordered layers often found in association with regions of high defect density are common features at polytype boundaries. An idealised configuration termed a "polytype sandwich" is presented as a model for the structure of SiC grown by the modified Lely technique. The frequency of common sandwich edge profiles are classified and some general trends of polytype neighbourism are summarised

Expedition 302 geophysics: integrating past data with new results

In preparation for IODP Expedition 302, Arctic Coring Expedition (ACEX), a site survey database comprising geophysical and geological data from the Lomonosov Ridge was compiled. The accumulated database includes data collected from ice islands, icebreakers, and submarines from 1961 to 2001. In addition, seismic reflection profiles were collected during Expedition 302 that complement the existing seismic reflection data and facilitate integration between the acoustic stratigraphy and the Expedition 302 drill cores. An overview of these data is presented in this chapter.It is well recognized that collecting geophysical data in ice-covered seas, in particular the Arctic Ocean, is a challenging endeavor. This is because much of the Arctic Ocean is continuously covered with ice thicknesses that vary from 1 to 6 m. Over the continental shelves, sea ice can be absent during summer months, but it is present year-round in the central basins. This ice cover is the most dominant feature of the Arctic Ocean environment. It circulates in the ocean basin in two main circulation patterns: the Transpolar Drift and the Beaufort Gyre (see the "Expedition 302 summary" chapter; Rudels et al., 1996).Expedition 302 sites are located within the less severe of these two ice circulation systems, the Transpolar Drift, which primarily moves sea ice from the shelves where it is formed (the Laptev and East Siberian Seas) across the basin and exits through the Fram Strait. During late summer, concentrations of Arctic sea ice can be <100% (10/10 ice cover), making it possible for icebreakers to operate. Average ice concentrations in the central Arctic Ocean during summer months can locally vary from partially open water (6/10) to completely ice covered (10/10). This sea-ice cover can move at speeds up to 0.5 kt.Early Arctic Ocean geophysical exploration was performed from ice-drift stations (Weber and Roots, 1990). However, the tracks from these drifting ice stations were controlled "by the whims of nature" (Jackson et al., 1990), preventing detailed, systematic surveys of predetermined target areas. These ice-drift stations were set up on stable icebergs that were trapped in sea ice and moved generally with the large drift patterns, but locally they were erratic, so preselected locations could not be surveyed. In the late 1980s, single icebreakers began to be used for oceanographic survey work in the Arctic Ocean. Between 1991 and 2001, four scientific icebreaker expeditions to the Lomonosov Ridge took place. These cruises all experienced local sea-ice conditions varying between 8/10 and 10/10. During these expeditions, towed geophysical equipment was occasionally damaged or lost, either because of a rapidly closing wake caused by local ice pressure or because ice had cut the air gun array.Conventionally powered icebreakers reached as far as the North Pole for the first time during the 1991 Expedition (Andersen and Carlsonn, 1992; Fütterer, 1992). Geophysical results from this expedition collected two important reflection profiles, AWI-91090 and AWI-91091, that crossed the Lomonosov Ridge between 87° and 88°N. These profiles imaged a ~450 m thick, well-stratified and apparently undisturbed drape of sediments overlying a prominent acoustic unconformity (Jokat et al., 1992) that spawned the idea to conduct a paleoceanographic drilling expedition to this Ridge.The use of US Navy nuclear submarines for geophysical mapping was implemented through the Science Ice Exercise program (SCICEX) (Newton, 2000). The development of the Seafloor Characterization and Mapping Pods (SCAMP), which hold a Chirp subbottom profiler, swath bathymetric profiler, and side scan sonar, was an essential part of the SCICEX program (Chayes et al., 1996). In 1999, the Lomonosov Ridge geophysical database was augmented with acoustic data acquired during the SCICEX program using the SCAMP system mounted on the US nuclear submarine USS Hawkbill (Edwards and Coakley, 2003)

Complex structure moduli stability in toroidal compactifications

In this paper we present a classification of possible dynamics of closed string moduli within specific toroidal compactifications of Type II string theories due to the NS-NS tadpole terms in the reduced action. They appear as potential terms for the moduli when supersymmetry is broken due to the presence of D-branes. We particularise to specific constructions with two, four and six-dimensional tori, and study the stabilisation of the complex structure moduli at the disk level. We find that, depending on the cycle on the compact space where the brane is wrapped, there are three possible cases: i) there is a solution inside the complex structure moduli space, and the configuration is stable at the critical point, ii) the moduli fields are driven towards the boundary of the moduli space, iii) there is no stable solution at the minimum of the potential and the system decays into a set of branes.Comment: 24 pages, JHEP3.cls, 19 figures. A few references adde

M-Theory Moduli Space and Cosmology

We conduct a systematic search for a viable string/M-theory cosmology, focusing on cosmologies that include an era of slow-roll inflation, after which the moduli are stabilized and the Universe is in a state with an acceptably small cosmological constant. We observe that the duality relations between different cosmological backgrounds of string/M-theory moduli space are greatly simplified, and that this simplification leads to a truncated moduli space within which possible cosmological solutions lie. We review some known challenges to four dimensional models in the "outer", perturbative, region of moduli space, and use duality relations to extend them to models of all of the (compactified) perturbative string theories and 11D supergravity, including brane world models. We conclude that cosmologies restricted to the outer region are not viable, and that the most likely region of moduli space in which to find realistic cosmology is the "central", non-perturbative region, with coupling and compact volume both of order unity, in string units.Comment: 42 pages, 3 figure

Expedition 302 summary

The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole.Expedition 302's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship.The biggest challenge during Expedition 302 was maintaining the drillship's location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as "mare incognitum" within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions.Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, spanning a 25 m.y. interval from the early Miocene to the middle Eocene between ~18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water setting dominated the region during this time period. Although predrilling predictions based on geophysical data had placed the base of the sediment column at 50 Ma, drilling revealed that the uppermost Paleocene to lowermost Eocene boundary interval, well known as the Paleocene/Eocene Thermal Maximum (PETM), was recovered. During the PETM, the temperature of the Arctic Ocean surface waters exceeded 20°C.Drilling during Expedition 302 also penetrated into the underlying sedimentary bedrock, revealing a shallow-water depositional environment of Late Cretaceous age

Methods

Information assembled in this chapter will help the reader understand the basis for the preliminary conclusions of the Expedition 302 Scientists and will also enable the interested investigator to select samples for further analyses. This information concerns offshore and onshore operations and analyses described in the "Sites M0001–M0004" chapter. Methods used by various investigators for shore-based analyses of Expedition 302 samples will be described in the individual contributions published in the Expedition Research Results and in various professional journals