The large-scale context for the TOGA Coupled Ocean-Atmosphere Response Experiment

Summary The TOGA Coupled Ocean-Atmosphere Response Experiment (COARE) concentrated a variety of observational systems in the warm pool of the western equatorial Pacific for an Intensive Observation Period (IOP) November 1992 through February 1993. In this paper, aspects of the largescale variations of the tropical atmosphere and Pacific Ocean surrounding the observations of air-sea interaction in the Intensive Flux Array (IFA) during the IOP are described, with the objective of providing a context for the future analyses of these observations.The evolution of the 1991–1992 El Niño/Southern Oscillation event was unusual: Warm SST anomalies in the equatorial cold tongue region switched to colder than climatology in the last half of 1992, but waters warmer than 30°C remained displaced eastward just west of the dateline, coninuing to fuel anomalous convection there during the IOP. Fortunately, SST in the IFA remained warmer than 29°C during most of the IOP, and convective activity was observed over the IFA. The Southern Oscillation Index, which had relaxed to near zero prior to the experiment, decreased during the IOP, reflecting sea level presure changes associated with renewed westerly wind activity. In response to these westerly wind events, the warm pool migrated back into the central equatorial Pacific, leading to a reintensification of the ENSO warm SST anomalies east of the dateline.With 10 Figures     

The sedimentary signature of ice-contact sedimentation and deformation at macro- and micro-scale: A case study from NW Scotland

Studies on the genesis of subaerial debris flows and associated deposits are relatively rare in the literature, especially in an ice-marginal context of moraine formation. The present contribution reports results from both the macro- and micro-scales of a subaerial depositional setting in order to contribute to closing this gap. At the macroscale, alternating loose, stratified, clast- and matrix-supported diamicts and finely laminated sand units indicate deposition of debris flows and fluvial units in a subaerial, ice-marginal setting that were stacked up to form a terrestrial ice-contact fan. Macroscale and micromorphological analyses show that this fan displays evidence of a three-phased formation: (a) overriding and glaciotectonisation of pre-existing sediments followed by retreat and burial of this core by (b) ice-contact fan deposition dominated by water-rich fluvial deposition with relatively little debris flow activity and (c) a switch to a gravitational sedimentation style with dominantly debris flow deposition and fewer and thinner fluvial units. Thin sections of both the diamict and laminated sand units show evidence of deposition of a mud and fine sand-rich slurry being expelled from the tops of advancing mass flows. Water-rich fine-grained slurries appear to have been progressively overridden and deformed in response to ductile shear occurring at the base of individual flows. Liquefaction and remobilisation of sand within laminated deposits occurred during such basal shear events, resulting in the injection of liquefied sediments into variably deformed laminated sands and clays. Deformation is more likely to have taken place through internal movement of the sediment due to changing porewater conditions and loading upon emplacement. Our approach confirms previous results that highlight the possibilities of increasing the accuracy of sedimentological investigations through combined sedimentological analyses at varying scales.     

Processes of annual moraine formation at a temperate alpine valley glacier: insights into glacier dynamics and climatic controls

This paper presents the first detailed sedimentological study of annual moraines formed by an alpine valley glacier. The moraines have been forming since at least AD 1980 by a subsidiary lobe of Gornergletscher, Switzerland that advances up a reverse bedrock slope. They reach heights of 0.5–1.5 m, widths of up to 6 m and lengths of up to several hundreds of metres. Sediments in these moraines are composed of proglacial outwash and debris flow units; subglacial traction till is absent entirely. Based on four representative sections, three genetic process combinations have been identified: (i) inefficient bulldozing of a gently sloping ice margin transfers proglacial sediments onto the ice, causing differential ablation and dead‐ice incorporation upon retreat; (ii) terrestrial ice‐contact fans are formed by the dumping of englacial and supraglacial material from point sources such as englacial conduit fills; debris flows and associated fluvial sediments are stacked against a temporarily stationary margin at the start, and deformed during glacier advance in the remainder, of the accumulation season; (iii) a steep ice margin without supraglacial input leads to efficient bulldozing and deformation of pre‐existing foreland sediments by wholesale folding. Ice‐surface slope appears to be a key control on the type of process responsible for moraine formation in any given place and year. The second and third modes result in stable and higher moraines that have a higher preservation potential than those containing dead ice. Analysis of the spacing and climatic records at Gornergletscher reveals that winter temperature controls marginal retreat and hence moraine formation. However, any climatic signal is complicated by other factors, most notably the presence of a reverse bedrock slope, so that the extraction of a clear climatic signal is not straightforward. This study highlights the complexity of annual moraine formation in high‐mountain environments and suggests avenues for further research.     

Intra-annual variability of extremely rapid sedimentation onto Gardar Drift in the northern North Atlantic

North Atlantic sediment drifts are valuable archives for paleoceanographic reconstructions spanning various timescales. However, the short-term dynamics of such systems are poorly known, and this impinges on our ability to quantitatively reconstruct past change. Here we describe a high-resolution 319-day time-series of hydrodynamics and near-bottom (4 m) particulate matter flux variability at a 2600 m deep site with an extremely high sediment accumulation rate on the southern Gardar Drift in the North Atlantic. We compare our findings with the actual deposits at the site. The total annual particle flux amounted to ～360 g m^?2 yr^?1, varied from ～0.15 to >5.0 g m^?2 day^?1 and displayed strong seasonal compositional changes, with the highest proportion of fresh biogenic matter arriving after the spring bloom in June and July. Flux variability also depended on the changing input of lithogenic matter that had been (re)suspended for a longer time (decades). Active focussing of material from both sources is required to account for the composition and the magnitude of the total flux, which exceed observations elsewhere by an order of magnitude. The enhanced focussing or increased delivery appeared to be positively related to current velocity. The intercepted annual particle flux accounted for only 60% of the sediment accumulation rate of 600±20 g m^?2 yr^?1 (0.20±0.07 cm yr^?1), indicating higher intra- and inter-annual variability of both the biogenic and lithogenic fluxes and/or advection of additional sediment closer to the seafloor (i.e. <4 m). This temporal variability in the composition and amount of material deposited highlights intra-annual changes in the flux of lithogenic material, but also underscores the importance of (reworked) sediment focussing and seasonality of the biogenic flux. All should be taken into account in the interpretation of the paleorecord from such depositional settings.     

Impact lithologies and their emplacement in the Chicxulub impact crater: Initial results from the Chicxulub Scientific Drilling Project,Yaxcopoil, Mexico

Abstract— The Chicxulub Scientific Drilling Project (CSDP), Mexico, produced a continuous core of material from depths of 404 to 1511 m in the Yaxcopoil‐1 (Yax‐1) borehole, revealing (top to bottom) Tertiary marine sediments, polymict breccias, an impact melt unit, and one or more blocks of Cretaceous target sediments that are crosscut with impact‐generated dikes, in a region that lies between the peak ring and final crater rim. The impact melt and breccias in the Yax‐1 borehole are 100 m thick, which is approximately 1/5 the thickness of breccias and melts exposed in the Yucatán‐6 exploration hole, which is also thought to be located between the peak ring and final rim of the Chicxulub crater. The sequence and composition of impact melts and breccias are grossly similar to those in the Yucatán‐6 hole. Compared to breccias in other impact craters, the Chicxulub breccias are incredibly rich in silicate melt fragments (up to 84% versus 30 to 50%, for example, in the Ries). The melt in the Yax‐1 hole was produced largely from the silicate basement lithologies that lie beneath a 3 km‐ thick carbonate platform in the target area. Small amounts of immiscible molten carbonate were ejected with the silicate melt, and clastic carbonate often forms the matrix of the polymict breccias. The melt unit appears to have been deposited while molten but brecciated after solidification. The melt fragments in the polymict breccias appear to have solidified in flight, before deposition, and fractured during transport and deposition.     

Improving trajectory estimation using 3D city models and kinematic point clouds

Accurate and robust positioning of vehicles in urban environments is of high importance for autonomous driving or mobile mapping. In mobile mapping systems, a simultaneous mapping of the environment using laser scanning and an accurate positioning using global navigation satellite systems are targeted. This requirement is often not guaranteed in shadowed cities where global navigation satellite system signals are usually disturbed, weak or even unavailable. We propose a novel approach which incorporates prior knowledge (i.e., a 3D city model of the environment) and improves the trajectory. The recorded point cloud is matched with the semantic city model using a point‐to‐plane iterative closest point method. A pre‐classification step enables an informed sampling of appropriate matching points. Random forest is used as classifier to discriminate between facade and remaining points. Local inconsistencies are tackled by a segmentwise partitioning of the point cloud where an interpolation guarantees a seamless transition between the segments. The general applicability of the method implemented is demonstrated on an inner‐city data set recorded with a mobile mapping system.     

Breakout of squeezed stocks: dispersal of roof fragments,source of extrusive salt and interaction with regional thrust faults

We used seven scaled physical models to explore the near‐surface structural evolution of shallowly buried, actively rising salt stocks. The models consisted of dry sand, ceramic microspheres and silicone. Previously dormant stocks rose because of lateral squeezing or pumping of salt from below. The pressure of rising salt created a dynamic bulge in the crest of the diapir, which arched the overlying roof sediments. Eventually this dynamic bulge collapsed and its overlying roof broke into rafts along subradial grabens. The rafts were dispersed outwards by shear traction of spreading salt, surmounting an upturned collar of country rock and eventually grounding at the front of the extrusive flow. Flow of salt around these stranded fragments created a lobate extrusion front, common in submarine salt sheets in the Gulf of Mexico and subaerial salt glaciers in Iran. Stock geometry, regional dip and roof density affected extrusion rates and spreading directions. Stocks leaning seaward extruded salt faster and farther than did upright stocks. Dense roofs foundered and plugged the vent, limiting surface extrusion. In tilted models, broad salt sheets spread asymmetrically downslope. Stock contents were inverted within the extruded salt sheet: successively deeper parts of the stock's core rose to the surface and overran salt extruded from the shallower parts of the diapir. As shortening continued, salt from the source layer reached the surface after being driven out by thrusting. A central thrust block, or primary indenter, moved ahead of surrounding thrust blocks, impinging against and squeezing the stock into an elliptical planform. After high shortening, secondary indenters converged obliquely into the salt stock, expelling salt from the periphery of the diapir. The models shed light on (1) the origin and fate of large rafts or carapace blocks atop allochthonous salt, (2) cuspate margins of salt sheets and (3) interaction of thrusting, diapir pinch‐off and emplacement of allochthonous salt sheets.     

Acoustic telemetry system for underwater control

Underwater acoustic communication in the multipath environment encountered in shallow water is restricted mostly by signal fading. It degrades the signal detection and time synchronization required for reliable acoustic communication. An approach to time synchronization and to the frequency diversity method is presented. A communication algorithm for obtaining a reliable acoustic underwater link, and offering an easy-to-implement decoding scheme is introduced, and system realization is described     

MicroRaman spectroscopy of diamond and graphite in Almahata Sitta and comparison with other ureilites

This work is the first detailed study of carbon phases in the ureilite Almahata Sitta (sample #7). We present microRaman data for diamond and graphite in Almahata Sitta, seven unbrecciated ureilites, and two brecciated ureilites. Diamond in Almahata Sitta was found to be distinct from that in unbrecciated and brecciated ureilites, although diamond in unbrecciated and brecciated ureilites is indistinguishable. Almahata Sitta diamond shows a peak center range of 1318.5–1330.2 cm^?1 and a full width at half maximum (FWHM) range of 6.6–17.4 cm^?1, representing a shock pressure of at least 60 kbar. The actual peak shock pressure may be higher than this due to postshock annealing, if shock synthesis is the source of ureilite diamonds. Diamond in unbrecciated and brecciated ureilites have peak center wave numbers closer to terrestrial kimberlite diamond, but show a wider range of FWHM than Almahata Sitta. The larger peak shift observed in Almahata Sitta may indicate the presence of lonsdaleite. Alternatively, the lower values in brecciated ureilites may be evidence of an annealing step either following the initial diamond‐generating shock or as a consequence of heating during reconsolidation of the breccia. Graphite in Almahata Sitta shows a G‐band peak center range of 1569.1–1577.1 cm^?1 and a G‐band FWHM range of 24.3–41.6 cm^?1 representing a formation temperature of 990 ± 120 °C. Amorphous carbon was also found. We examine the different theories for diamond formation in ureilites, such as chemical vapor deposition and shock origin from graphite, and explore explanations for the differences between Almahata Sitta and other ureilites.     

Sequence stratigraphy of a Paleogene coal bearing rim syncline: interplay of salt dynamics and sea‐level changes,Schöningen,Germany

Salt rim synclines contain important hydrocarbon and coal resources in central Europe. The Schöningen salt rim syncline is filled with >300 m of Early to Middle Eocene unconsolidated clastics with interbedded lignitic coal seams that are mined at the surface. In this study, 357 lithologic logs are integrated with measured outcrop sections and paleo‐botanical data to interpret the depositional environments and sequence stratigraphic framework of the rim syncline fill. As salt withdrew, it generated an elongate mini‐basin that mimicked an incised valley. The sustained accommodation and slow broadening of the syncline affected the stratigraphic architecture and contributed to the preservation of coal units. The clastic units in the syncline filled in seven depositional stages: (1) tidally influenced fluvial estuarine channels; (2) mixed tide‐ and wave‐ dominated estuaries; (3) prograding wave dominate deltas; (4) transgressive shoreline deposits; (5) braided fluvial channels; (6) estuaries; and (7) prograding tide‐dominated channels. The succession defines four 3rd order sequences and several higher order sequences that are possibly related to Milankovitch cycles. The higher order sequences are dominantly characterized by stacked transgressive cycles of thick, lowstand coals overlain by estuarine sands. The nearly continuous warm and wet Eocene climate was conducive to continuous peat production with a climatic overprint recorded in the mire type: ombrotrophic mires developed in wetter times and rheotrophic mires developed in relatively drier conditions pointing to the presence of orbitally controlled seasonality. Both mire types were impacted by the interplay of subsidence and base‐level. The continuous dropping of the mires below base‐level via subsidence protected the mires against erosion and may account for the absence of coals outside of the rim synclines in the region.