Astrodynamical Space Test of Relativity using Optical Devices I (ASTROD I)—a class-M fundamental physics mission proposal for cosmic vision 2015–2025: 2010 Update

ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test General Relativity with an improvement in sensitivity of over 3 orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals.For this mission, accurate pulse timing with an ultra-stable clock, and a drag-free spacecraft with reliable inertial sensor are required. T2L2 has demonstrated the required accurate pulse timing; rubidium clock on board Galileo has mostly demonstrated the required clock stability; the accelerometer on board GOCE has paved the way for achieving the reliable inertial sensor; the demonstration of LISA Pathfinder will provide an excellent platform for the implementation of the ASTROD I drag-free spacecraft. These European activities comprise the pillars for building up the mission and make the technologies needed ready. A second mission, ASTROD or ASTROD-GW (depending on the results of ASTROD I), is envisaged as a three-spacecraft mission which, in the case of ASTROD, would test General Relativity to one part per billion, enable detection of solar g-modes, measure the solar Lense-Thirring effect to 10 parts per million, and probe gravitational waves at frequencies below the LISA bandwidth, or in the case of ASTROD-GW, would be dedicated to probe gravitational waves at frequencies below the LISA bandwidth to 100?nHz and to detect solar g-mode oscillations. In the third phase (Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD bandwidth. This paper on ASTROD I is based on our 2010 proposal submitted for the ESA call for class-M mission proposals, and is a sequel and an update to our previous paper (Appouchaux et al., Exp Astron 23:491?C527, 2009; designated as Paper I) which was based on our last proposal submitted for the 2007 ESA call. In this paper, we present our orbit selection with one Venus swing-by together with orbit simulation. In Paper I, our orbit choice is with two Venus swing-bys. The present choice takes shorter time (about 250?days) to reach the opposite side of the Sun. We also present a preliminary design of the optical bench, and elaborate on the solar physics goals with the radiation monitor payload. We discuss telescope size, trade-offs of drag-free sensitivities, thermal issues and present an outlook.     

Slope‐to‐basin stratigraphic evolution of the northwestern Great Bahama Bank (Bahamas) during the Neogene to Quaternary: interactions between downslope and bottom currents deposits

Multichannel high‐resolution seismic data along the northwestern margin of the Great Bahama Bank (GBB), Bahamas, detail the internal geometry and depositional history of a Neogene‐Quaternary carbonate slope‐to‐basin area. The stratigraphic architecture through this period evolves from (i) a mud‐dominated slope apron during the Miocene, (ii) a debris‐dominated base‐of‐slope apron during the Late Pliocene and then (iii) return to a slope apron with very short prograding clinoformal aprons during the Pleistocene. This geometric evolution was broadly constrained by the development of the Santaren Drift by bottom current since the Langhian. The drift expands along the northwestern GBB slope, forming a continuous correlative massive feature that shows successive phases of growth and retreat and influenced the downslope sediments distribution. Indeed, Late Pliocene deposits are confined into the moat, forming a strike‐continuous coarse debrites belt along the mid‐slope, preventing their free expansion into the basin. The occurrence of basinal drift that operated since 15 Ma showed a significant upslope growth around 3.6 Ma and is interpreted as resulting from the closure of the Central American Seaway which also coincides with a global oceanographic re‐organization and climate changes in the Northern Hemisphere.     

Seismic stratigraphy and paleogeographic evolution of Fairway Basin,Northern Zealandia,Southwest Pacific: from Cretaceous Gondwana breakup to Cenozoic Tonga–Kermadec subduction

We present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.     

The extent of chronic marine oil pollution in southeastern Newfoundland waters assessed through beached bird surveys 1984-1999

The Grand Banks south of Newfoundland provide year-round feeding habitat for tens of millions of seabirds of numerous species, an abundance and diversity unparalleled in the North Atlantic. Dense ship traffic routes traverse this productive environment as vessels travel the Great Circle Route between Europe and North America. Oiled seabirds have washed up on beaches in Newfoundland for many decades. Most oil on their feathers is heavy fuel oil mixed with lubricants, the mixture found in bilges of large vessels. Beached bird surveys conducted between 1984 and 1999 indicate that chronic oil pollution along the southeast coast of Newfoundland is among the highest in world. Sixty two percent of all dead birds found over the 16-year period had oil on their feathers; 74% during the last five years. Auks, especially Thick-billed Murres (Uria lomvia), are the most affected. The mean number of oiled birds per kilometer was 0.77 and thus higher than in other regions of the world during a comparable time period (0.02-0.33). Oiling rates correlated with weather patterns and degree of the regional murre hunt, indicate that illegal dumping of oil may occur year round, and point out that it is critical to assess all possible environmental and anthropogenic factors influencing the number of clean and oiled dead birds found on beaches before inferring trends in oiling rates over time.     

The application of an innovative inverse model for understanding and predicting landslide movements (Salazie cirque landslides,Reunion Island)

The prediction of landslide movement acceleration is a complex problem, among others identified for deep-seated landslides, and represents a crucial step for risk assessment. Within the scope of this problem, the objective of this paper is to explore a modelling method that enables the study of landslide function and facilitates displacement predictions based on a limited data set. An inverse modelling approach is proposed for predicting the temporal evolution of landslide movement based on rainfall and displacement velocities. Initially, the hydrogeology of the studied landslides was conceptualised based on correlative analyses. Subsequently, we applied an inverse model with a Gaussian-exponential transfer function to reproduce the displacements. This method was tested on the Grand Ilet (GI) and Mare-à-Poule-d’Eau (HB) landslides on Reunion Island in the Indian Ocean. We show that the behaviour of landslides can be modelled by inverse models with a bimodal transfer function using a Gaussian-exponential impulse response. The cumulative displacements over 7 years of modelling (2 years of calibration period for GI, and 4 years for HB) were reproduced with an RMSE above 0.9. The characteristics of the bimodal transfer function are directly related to the hydrogeological functioning demonstrated by the correlative analyses: the rapid reaction of a landslide can be associated with the effect of a preferential flow path on groundwater level variations. Thus, this study shows that the inverse model using a Gaussian-exponential transfer function is a powerful tool for predicting deep-seated landslide movements and for studying how they function. Beyond modelling displacements, our approach effectively demonstrates its ability to contribute relevant data for conceptualising the sliding mechanisms and hydrogeology of landslides.     

228Ra, 226Ra, 224Ra and 223Ra in potential sources and sinks of land-derived material in the German Bight of the North Sea: implications for the use of radium as a tracer

Activities of the naturally occurring radium nuclides ²²⁸Ra, ²²⁶Ra, ²²⁴Ra and ²²³Ra were determined in waters of the open German Bight and adjacent nearshore areas in the North Sea, in order to explore the potential use of radium isotopes as natural tracers of land–ocean interaction in an environment characterised by extensive tidal flats, as well as riverine and groundwater influx. Data collected at various tidal phases from the Weser Estuary (²²⁸Ra: 46.3 ± 4.6; ²²⁶Ra: 17.1 ± 1.1; ²²⁴Ra: 26.1 ± 8.2 to 36.5 ± 6.1; ²²³Ra: 1.8 ± 0.1 to 4.0 ± 0.4), tidal flats near Sahlenburg (²²⁸Ra: 39.3 ± 3.8 to 46.0 ± 4.5; ²²⁶Ra: 15.5 ± 1.5 to 16.5 ± 1.7; ²²⁴Ra: 34.3 ± 2.2 to 85.3 ± 6.3; ²²³Ra: 3.6 ± 0.5 to 8.0 ± 1.2), freshwater seeps on tidal flats near Sahlenburg (²²⁸Ra: 42.1 ± 4.1; ²²⁶Ra: 21.3 ± 2.2; ²²⁴Ra: 5.1 ± 0.9; ²²³Ra: 2.6 ± 1.3) and also in permanently inundated parts of the North Sea (²²⁸Ra: 23.0 ± 2.3 to 28.2 ± 2.8; ²²⁶Ra: 8.2 ± 0.8 to 11.8 ± 1.2; ²²⁴Ra: 3.1 ± 1.0 to 10.1 ± 0.9; ²²³Ra: 0.1 ± 0.02 to 0.9 ± 0.05; units: disintegrations per minute per 100 kg water sample) reveal that, except for the fresh groundwater, the potential end-members of nearshore water mass mixing have quite similar radium signatures, excluding a simple discrimination between the sources. However, the decreasing activities of the short-lived ²²⁴Ra and ²²³Ra isotopes recorded towards the island of Helgoland in the central German Bight show a potential to constrain fluxes of land-derived material to the open North Sea. The largest source for all radium isotopes is generally found on the vast tidal flats and in the Weser Estuary. Future work could meaningfully combine this so-called radium quartet approach with investigations of radon activity. Indeed, preliminary data from a tidal flat site with fresh groundwater seepage reveal a ²²²Rn signal that is clearly lower in seawater.     

1750?years of large rainfall events inferred from particle size at East Lake, Cape Bounty, Melville Island, Canada

Annual grain-size variation was measured on the varved (annually laminated) lacustrine sediment from Cape Bounty East Lake using an innovative image analysis system. About 7100 images were acquired using a scanning electron microscope and processed to obtain measurement of particles from 2845 varves. Several particle-size distributions indices were calculated and can be linked to high-energy sedimentary facies. Moreover, the coarse grain size (98th percentile) of these high-energy facies is strongly correlated with summer rainfall (and also summer temperature) of instrumental data from nearby stations. Particle-size distributions show a similar trend through time, especially for the standard deviation and the 98th percentile. Climatic reconstruction suggests that Cape Bounty recently experienced an unprecedented increase of rainfall events since ~AD 1920. On the other hand, changes in varve thickness are weakly correlated with the particle-size distribution. Altogether, these results highlight the need to obtain annual grain-size data to identify a meteorological signal.     

Giant submarine collapse of a carbonate platform at the Turonian–Coniacian transition: The Ayabacas Formation, southern Peru

The Ayabacas Formation of southern Peru is an impressive unit formed by the giant submarine collapse of the mid‐Cretaceous carbonate platform of the western Peru back‐arc basin (WPBAB), near the Turonian–Coniacian transition (～90–89 Ma). It extends along the southwestern edge of the Cordillera Oriental and throughout the Altiplano and Cordillera Occidental over >80 000 km² in map view, and represents a volume of displaced sediments of >10 000 km³. The collapse occurred down the basin slope, i.e. toward the SW. Six zones are characterised on the basis of deformational facies, and a seventh corresponds to the northeastern ‘stable’ area (Zone 0). Zones 1–3 display increasing fragmentation from NE to SW, and are composed of limestone rafts and sheets embedded in a matrix of mainly red, partly calcareous and locally sandy, mudstones to siltstones. In contrast, in Zones 4 and 5 the unit consists only of displaced and stacked limestone masses forming a ‘sedimentary thrust and fold system’, with sizes increasing to the southwest. In Zone 6, the upper part of the limestone succession consists of rafts and sheets stacked over the regularly bedded lower part. The triggering of this extremely large mass wasting clearly ensued from slope creation, oversteepening and seismicity produced by extensional tectonic activity, as demonstrated by the observation of synsedimentary normal faults and related thickness variations. Other factors, such as pore pressure increases or lithification contrasts probably facilitated sliding. The key role of tectonics is strengthened by the specific relationships between the basin and collapse histories and two major fault systems that cross the study area. The Ayabacas collapse occurred at a turning point in the Central Andean evolution. Before the event, the back‐arc basin had been essentially marine and deepened to the west, with little volcanic activity taking place at the arc. After the event, the back‐arc was occupied by continental to near‐continental environments, and was bounded to the southwest by a massive volcanic arc shedding debris and tuffs into the basin.     

Estimation of grain size variability with micro X-ray fluorescence in laminated lacustrine sediments,Cape Bounty,Canadian High Arctic

Finely laminated sediment cores from two Arctic lakes were investigated using the Itrax™ Core Scanner that provides micro X-ray fluorescence (μ-XRF) measurements with a spatial resolution of 100 μm. We compared these chemical measurements with standard geochemical methods using, at the macroscopic scale, inductively coupled plasma–atomic emission spectrometry (ICP-AES) and, at the microscopic scale, energy dispersive spectroscopy (EDS). We also investigated the relationship between the chemical profiles and the grain size of sediments at macro-scale using laser particle-size analysis, and at microscopic scale, using thin section image analysis techniques. Results show a link between grain size and the relative abundance of several elements. Silicon and zirconium are associated with very coarse silt and sand deposits, K and Fe with clay-rich layers, and Ti with silty facies. Four sedimentary facies are characterised based on sedimentary structure and texture, and interpreted in terms of known seasonal hydroclimatic processes. We show that is possible to identify these sedimentary facies using μ-XRF element abundance or ratio variations. The K/Ti ratio is the best marker of the upper varve boundary, and it might be used for varve identification and counting of Cape Bounty sediments in future. More generally, this study demonstrates new applications for paleohydrological reconstructions from laminated sediments.