Feedbacks between sea-floor spreading, trade winds and precipitation in the Southern Red Sea

Feedbacks between climatic and geological processes are highly controversial and testing them is a key challenge in Earth sciences. The Great Escarpment of the Arabian Red Sea margin has several features that make it a useful natural laboratory for studying the effect of surface processes on deep Earth. These include strong orographic rainfall, convex channel profiles versus concave swath profiles on the west side of the divide, morphological disequilibrium in fluvial channels, and systematic morphological changes from north to south that relate to depth changes of the central Red Sea. Here we show that these features are well interpreted with a cycle that initiated with the onset of spreading in the Red Sea and involves feedbacks between orographic precipitation, tectonic deformation, mid-ocean spreading and coastal magmatism. It appears that the feedback is enhanced by the moist easterly trade winds that initiated largely contemporaneously with sea floor spreading in the Red Sea

Tectonic geomorphology at small catchment sizes extensions of the stream-power approach and the method

Quantitative tectonic geomorphology hinges on the analysis of longitudinal river profiles. The model behind almost all approaches in this field originates from an empirical relationship between channel slope and catchment size, often substantiated in the form of the stream-power model for fluvial incision. Significant methodological progress was recently achieved by introducing the transform. It defines a nonlinear length coordinate in such a way that the inherent curvature of river profiles due to the increase of catchment sizes in the downstream direction is removed from the analysis. However, the limitation to large catchment sizes inherited from the stream-power approach for fluvial incision persists. As a consequence, only a small fraction of all nodes of a digital elevation model (DEM) can be used for the analysis. In this study we present and discuss some empirically derived extensions of the stream power law towards small catchment sizes in order to overcome this limitation. Beyond this, we introduce a simple method for estimating the adjustable parameters in the original method as well as in our extended approaches. As a main result, an approach originally suggested for debris flow channels seems to be the best approximation if both large and small catchment sizes are included in the same analysis.(VLID)214713

Enhanced Grid-Based Visual Analysis of Retinal Layer Thickness with Optical Coherence Tomography

Optical coherence tomography enables high-resolution 3D imaging of retinal layers in the human eye. The thickness of the layers is commonly assessed to understand a variety of retinal and systemic disorders. Yet, the thickness data are complex and currently need to be considerably reduced prior to further processing and analysis. This leads to a loss of information on localized variations in thickness, which is important for early detection of certain retinal diseases. We propose an enhanced grid-based reduction and exploration of retinal thickness data. Alternative grids are computed, their representation quality is rated, and best fitting grids for given thickness data are suggested. Selected grids are then visualized, adapted, and compared at different levels of granularity. A visual analysis tool bundles all computational, visual, and interactive means in a flexible user interface. We demonstrate the utility of our tool in a complementary analysis procedure, which eases the evaluation of ophthalmic study data. Ophthalmologists successfully applied our solution to study localized variations in thickness of retinal layers in patients with diabetes mellitus

A two phase escarpment evolution of the Red Sea margin of southwestern Saudi Arabia. Insights from low-temperature apatite thermochronology

International audienceRifting of the Red Sea resulted in the formation of one of the highest escarpments on our planet: the Great Escarpment of southwestern Saudi Arabia. Published low-temperature geochronology ages are around the Paleogene-Neogene transition, but geomorphic features like the height, the steepness and the preservation of the escarpment may indicate a younger aspect to the exhumation history. Here we use apatite fission track (AFT) and (U-Th-Sm)/He (AHe) cooling ages in combination with a geomorphic analysis of the region from Jeddah to Jizan to test this idea. Pooled AFT ages range from to Ma (1σ). The base of the AFT partial annealing zone prior to rock uplift is at ∼200 m elevation in most of the studied area, but track length data show that the amount of exhumation is insufficient to affect all coastal plain samples. Consistent with earlier estimates in the literature, the total amount of rock uplift is estimated to be ∼4 km. Single grain AHe ages range from to Ma (1σ) and do not have a clear trend with distance from the escarpment. Overall, the distribution of data appears to indicate widespread downwearing of the elevated topography around the rift flank. In contrast, geomorphic analysis that indicates escarpment retreat including a flexural uplift response. We suggest that the conflict between geomorphological and geochronological data can be resolved by invoking a two-stage erosion model. The first stage involved dome-shaped rift flank uplift since initiation of the Afar plume, downwearing of this topography and cooling recorded by the AFT ages. The second stage involved the massive erosion that excavated the present day Saudi escarpment and reset the AHe ages. We suggest that this second stage is related to the formation of oceanic lithosphere since 13 Ma in the Red Sea, associated downwarping of the margin and flexural updoming of the eastern rift flank. The consequential orographic precipitation initiated asymmetric erosion and formation of a retreating escarpment. This model is consistent with the large age difference between Miocene AFT and Pliocene AHe ages and the geomorphic metrics