Surface reflectance characteristics of Langjökull, Iceland

ATM, ETM+ and MODIS radiance data collected for the surface of Langjokull during August 2007. Radiance data from the three different instruments was then converted to surface broadband albedo using a number of different methods. The differences between the methods used to derive the surface albedo were then compared, followed by an analysis of the impact of spatial resolution and sample size on the differences between the derived surface albedo. Analysis of the different datasets combined with transect sample analyses of the derived surface albedos indicated that the most precise methods of deriving albedo from the ATM and ETM+ instruments was through the use of FLAASH for the ATM and dark pixel atmospheric correction or 6S atmospheric correction for the ETM+. These first analyses also indicated that the MODIS data was broadly in agreement with these two datasets. However, analysis of the differences between the different spatial resolution datasets across the three different spatial extents revealed a number of differences between the datasets. At the smallest scale the lower resolution datasets were shown to contain a bias towards representing certain areas in individual pixels. Consequently, the correlation between the datasets was reduced across greater sample sizes. Moreover, this bias was shown to prevent the ETM+ and MODIS imagery from averaging highly variable surfaces. The result of these measurement characteristics was for the low resolution instruments to overestimate the albedo value of snow in the accumulation area, greatly underestimate the albedo in the firn zone and struggle to capture the spatial variability in the ablation zone. The implications of these characteristics for lower resolution data have consequently been outlined, with the extent of the differences between both the low resolution datasets and the ATM dataset, indicating that where possible ETM+ imagery should be used to monitor surface albedo characteristics as it was the most closely correlated with the ATM data

Are large submarine landslides in Polar Regions temporally random, or do current observations and age constraint make it impossible to tell?

Submarine landslides are one of the major mechanisms through which sediment is transported across our planet, and it has been proposed that they can generate exceptionally damaging tsunamis. Polar margins represent one of the environmental settings where these events have been identified. A large number of triggers and preconditioning factors have been proposed as possible causes for these events; including earthquakes, rapid sedimentation and gas hydrate dissociation. Rapid climate change in the Arctic has the potential to impact on these preconditioning and triggering factors. First, crustal rebound associated with ice melting is likely to produce larger and more frequent earthquakes. Second, Arctic Ocean warming over the next few decades may lead to dissociation of methane hydrates in marine sediments, thereby weakening sediment. In order to better understand whether landslide frequency will increase in the future, we need to determine whether landslide frequency has been affected by previous episodes of rapid climate or eustatic sea level change. Previous working whether landslide frequency is affected strongly by climatic change has been based predominantly on qualitative analysis, and has concluded that event clustering has occurred under specific environmental conditions. In contrast, two recent statistical investigations of submarine landslides have found events frequencies to follow a Poissonian distribution and thus are temporally random (Urlaub et al, 2013, QSR; Clare et al., Geology, Vol 42 (3)). However, these recent studies acknowledge the significant uncertainties in most landslide dates, and that these uncertainties could mask underlying relationships with climate or sea level. This presentation extends previous statistical work to assess whether landslide frequency is most likely temporally random, or whether the dating is just too uncertain to tell. Chi-Squared statistics are used to explore the extent to which we can be statistically sure that submarine landslides do indeed follow a Poissonian distribution. This is achieved by analysing the ease with which ordered frequency data can appear Poissonian according to the Chi-Squared statistic and the number of events needed before a certain distribution can be guaranteed. From this we are able comment on the extent to which we can use event frequency as a means with which to analyse triggers and preconditioning factors. We can also assess the implications for future submarine landslide risk analysis

Stratigraphic record reveals contrasting roles of overflows and underflows over glacial cycles in a hypersaline lake (Dead Sea)

In lakes and oceans, links between modern sediment density flow processes and deposits preserved in long-term geological records are poorly understood. Consequently, it is unclear whether, and if so how, long-term climate changes affect the magnitude/frequency of sediment density flows. One approach to answering this question is to analyze a comprehensive geological record that comprises deposits that can be reliably linked to modern sediment flow processes. To address this question, we investigated the unique ICDP Core 5017-1 from the Dead Sea (the largest and deepest hypersaline lake on the Earth) depocenter covering MIS 7-1. Based on an understanding of modern sediment density flow processes in the lake, we link homogeneous muds in the core to overflows (surface flood plumes, ρflowρwater). Our dataset reveals (1) overflows are more prominent during interglacials, while underflows are more prominent during glacials; (2) orbital-scale climate changes affected the flow magnitude/frequency via changing salinity and density profile of lake brine, lake-level, and source materials

Re-channelization of turbidity currents in South China Sea abyssal plain due to seamounts and ridges

Turbidity currents can be characterized as net-erosive, net-depositional or net-bypassing. Whether a flow is erosive, depositional or bypasses depends on the flow velocity, concentration and size but these can also be impacted by external controls such as the degree of confinement, slope gradient and substrate type and erodibility. Our understanding of the relative importance of these controls comes from laboratory experiments and numerical modelling, as well as from field data due to the proliferation of high-resolution 3D seismic and bathymetric data, as well as the outcrop and rock record. In this study, based on extensive multibeam and seismic reflection surveys in combination with International Ocean Discovery Program cores from the South China Sea, we document a new mechanism of turbidity current transformation from depositional to erosive resulting in channel incision. We show how confinement by seamounts and bedrock highs of previously unconfined turbidity currents has resulted in the development of seafloor channels. These channels are inferred to be the result of confinement of flows, which have traversed the abyssal plain, leading to flow acceleration allowing them to erode the seafloor substrate. This interpretation is further supported by the coarsening of flow deposits within the area of the seamounts, indicating that confinement has increased flow competency, allowing turbidity currents to carry larger volumes of coarse sediment which has been deposited in this region. This basin-scale depositional pattern suggests that pre-established basin topography can have an important control on sedimentation which can impact characteristics such as potential hydrocarbon storage

Focus, Vol. 1 No. 1

A literary magazine of student writing published by the Department of English of Stephen F. Austin State College.https://scholarworks.sfasu.edu/focus/1000/thumbnail.jp

Wacker-oxidation of Ethylene over Pillared Layered Material Catalysts

This paper concerns the Wacker oxidation of ethylene by oxygen in the presence of water over supported Pd/VOx catalysts. High surface area porous supports were obtained from layer-structured materials, such as, montmorillonite (MT), laponite (LT) (smectites), and hydrotalcite (layered double hydroxide, LDH) by pillaring. Before introduction of Pd, supports MT and LDH were pillared by vanadia. The laponite was used in titania-pillared form (TiO2-LAP) as support of Pd/VOx active component. Acetaldehyde (AcH), acetic acid (AcOH) and CO2 were the products with yields and selectivities, depending on the reaction conditions and the properties of the applied catalyst. Under comparable conditions the pillared smectite catalysts gave higher AcH yield than the pillared LDH catalyst. UV vis spectroscopic examination suggested that the pillared smectites contained polymeric chains of VO4, whereas only isolated monomeric VO4 species were present in the pillared LDH. The higher catalytic activity in the Wacker oxidation was attributed to the more favorable redox property of the polymeric than of the monomeric vanadia. The V3+ ions in the polymeric species can reduce O2 to O2- ions, whereas the obtained V5+ ions are ready to pass over O to Pd0 to generate PdO whereon the oxidation of the ethylene proceeds

Detailed monitoring reveals the nature of submarine turbidity currents

Seafloor sediment flows, called turbidity currents, form the largest sediment accumulations, deepest canyons, and longest channels on Earth. It was once thought that turbidity currents were impractical to measure in action, especially due to their ability to damage sensors in their path, but direct monitoring since the mid 2010s has measured them in detail. In this Review, we summarise knowledge of turbidity currents gleaned from this direct monitoring. Monitoring identifies triggering mechanisms from dilute river-plumes, and shows how rapid sediment accumulation can precondition slope failure, but the final triggers can be delayed and subtle. Turbidity currents are consistently more frequent than predicted by past sequence stratigraphic models, including at sites >300 km from any coast. Faster (>~1.5 m s–1) flows are driven by a dense near-bed layer at their front, whereas slower flows are entirely dilute. This frontal layer sometimes erodes large (>2.5 km3) volumes of sediment, yet maintains a near-uniform speed, leading to a travelling wave model. Monitoring shows that flows sculpt canyons and channels through fast-moving knickpoints, and how deposits originate. Emerging technologies with reduced cost and risk can lead to widespread monitoring of turbidity currents, so their sediment and carbon fluxes can be compared with other major global transport processes

A focus on L dwarfs with trigonometric parallaxes

This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. Under embargo until 14 May 2019. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1538-3873/aaacc5.We report new parallax measurements for ten L and early T type dwarfs, five of which have no previous published values, using observations over 3 years at the robotic Liverpool Telescope. The resulting parallaxes and proper motions have median errors of 2\,mas and 1.5\,mas/year respectively. Their space motions indicate they are all Galactic disk members. We combined this sample with other objects with astrometry from the Liverpool Telescope and with published literature astrometry to construct a sample of 260 L and early T type dwarfs with measured parallaxes, designated the Astrometry Sample. We study the kinematics of the Astrometry Sample, and derived a solar motion of $(U,V,W)_{\bigodot} = (7.9\pm1.7,13.2\pm1.2,7.2\pm1.0)$\,\kms~ with respect to the local standard of rest, in agreement with recent literature. We derive a kinematic age of 1.5-1.7\,Gyr for the Astrometry Sample assuming the age increases monotonically with the total velocity for a given disk sample. This kinematic age is less than half literature values for other low mass dwarf samples. We believe this difference arises for two reasons (1) the sample is mainly composed of mid to late L dwarfs which are expected to be relatively young and (2) the requirement that objects have a measured parallax biases the sample to the brighter examples which tend to be younger.Peer reviewedFinal Accepted Versio

Different frequencies and triggers of canyon filling and flushing events in Nazaré Canyon, offshore Portugal

Submarine canyons are one of the most important pathways for sediment transport into ocean basins. For this reason, understanding canyon architecture and sedimentary processes has importance for sediment budgets, carbon cycling, and geohazard assessment. Despite increasing knowledge of turbidity current triggers, the down-canyon variability in turbidity current frequency within most canyon systems is not well constrained. New AMS radiocarbon chronologies from canyon sediment cores illustrate significant variability in turbidity current frequency within Nazaré Canyon through time. Generalised linear models and Cox proportional hazards models indicate a strong influence of global sea level on the frequency of turbidity currents that fill the canyon. Radiocarbon ages from basin sediment cores indicate that larger, canyon-flushing turbidity currents reaching the Iberian Abyssal Plain have a significantly longer average recurrence interval than turbidity currents that fill the canyon. The recurrence intervals of these canyon-flushing turbidity currents also appear to be unaffected by long-term changes in global sea level. Furthermore, canyon-flushing and canyon-filling have very different statistical distributions of recurrence intervals. This indicates that the factors triggering, and thus controlling the frequency of canyon-flushing and canyon-filling events are very different. Canyon-filling appears to be predominantly triggered by sediment instability during sea level lowstand, and by storm and nepheloid transport during the present day highstand. Canyon-flushing exhibits time-independent behaviour. This indicates that a temporally random process, signal shredding, or summation of non-random processes that cannot be discerned from a random signal, are triggering canyon flushing events