Shrinking and Splitting of drainage basins in orogenic landscapes from the migration of the main drainage divide

International audienceClimate, and in particular **the spatial pattern of precipitation, is thought to affect* *the topographic and tectonic evolution of mountain belts through erosion. Numerical model simulations of landscape erosion controlled **by horizontal tectonic motion or orographic precipitation result in the asymmetric topography that characterizes most natural mountain belts, and in a continuous migration of the main drainage divide. The effects of such a migration have, however, been challenging to observe in natural settings. Here I document the effects of a lateral precipitation gradient on a landscape undergoing constant uplift in a laboratory modelling experiment. In the experiment, the drainage divide migrates towards the drier, leeward side of the mountain range, causing the drainage basins on the leeward side to shrink and split into* *smaller basins. This mechanism results in a progressively increasing number of drainage basins on the leeward side of the mountain range as the divide migrates, such that the expected relationship between the spacing of drainage basins and the location of the main drainage divide is maintained. I propose that this mechanism could clarify the drainage divide migration and topographic asymmetry found in active orogenic mountain ranges, as exemplified by the Aconquija Range of Argentin

Soliton pair dynamics in patterned ferromagnetic ellipses

Confinement alters the energy landscape of nanoscale magnets, leading to the appearance of unusual magnetic states, such as vortices, for example. Many basic questions concerning dynamical and interaction effects remain unanswered, and nanomagnets are convenient model systems for studying these fundamental physical phenomena. A single vortex in restricted geometry, also known as a non-localized soliton, possesses a characteristic translational excitation mode that corresponds to spiral-like motion of the vortex core around its equilibrium position. Here, we investigate, by a microwave reflection technique, the dynamics of magnetic soliton pairs confined in lithographically defined, ferromagnetic Permalloy ellipses. Through a comparison with micromagnetic simulations, the observed strong resonances in the subgigahertz frequency range can be assigned to the translational modes of vortex pairs with parallel or antiparallel core polarizations. Vortex polarizations play a negligible role in the static interaction between two vortices, but their effect dominates the dynamics.Comment: supplemental movies on http://www.nature.com/nphys/journal/v1/n3/suppinfo/nphys173_S1.htm

Analysis of urinary oligosaccharides in lysosomal storage disorders by capillary high-performance anion-exchange chromatography–mass spectrometry

Many lysosomal storage diseases are characterized by an increased urinary excretion of glycoconjugates and oligosaccharides that are characteristic for the underlying enzymatic defect. Here, we have used capillary high-performance anion-exchange chromatography (HPAEC) hyphenated to mass spectrometry to analyze free oligosaccharides from urine samples of patients suffering from the lysosomal storage disorders fucosidosis, α-mannosidosis, GM1-gangliosidosis, GM2-gangliosidosis, and sialidosis. Glycan fingerprints were registered, and the patterns of accumulated oligosaccharides were found to reflect the specific blockages of the catabolic pathway. Our analytical approach allowed structural analysis of the excreted oligosaccharides and revealed several previously unpublished oligosaccharides. In conclusion, using online coupling of HPAEC with mass spectrometric detection, our study provides characteristic urinary oligosaccharide fingerprints with diagnostic potential for lysosomal storage disorders

Quaternary depositional systems in Northern Lake Baikal, Siberia

New high-resolution seismic reflection data from northern Lake Baikal and detailed land-based morphological and sedimentological data reveal a variety of coarse-grained deposits in the northern Baikal Rift. Each depositional facies is assigned to a specific structural domain. Alluvial fans (onshore) and small fan deltas (offshore) dominate the western border-fault flank. Glacial deposits (onshore) and large glacio-lacustrine fans (offshore) characterize the eastern flexural margin. In the north, the axial rift termination comprises a large fluvial delta. This distinct pattern of depositional environments reflects the pronounced asymmetry of the rift and emphasizes the role of rift structure in controlling drainage and the location and type of rift-basin fill. Climate, however, exerts a profound influence on the generation and availability of coarse-grained material. This is best documented along the eastern rift margin where Pleistocene valley glaciers advanced at >50, 40-35, and 26-13 ka from the high rift shoulders down to, and beyond, the present shore into the Baikal Basin. During these phases, large volumes of glacial sediment were introduced into the basin, accumulating in extensive glacio-lacustrine outwash fans. About one-third of the seismically penetrated rift fill is glacial-outwash material derived from the eastern shoulder. Under present-day nonglacial conditions, however, the fans are inactive because of insufficient sediment supply; this documents the importance of major climatic fluctuations with respect to the magnitude of sediment discharge and accumulation. The sedimentary history also underscores the modifying effects of climate-driven processes on the typical structure-dominated aspects of rift sedimentation

Middle to late Miocene Middle Eastern climate from stable oxygen and carbon isotope data, southern Alborz mountains, N Iran

The Alborz mountains of northern Iran intercept and divert the northern hemisphere westerlies carrying moisture from the Mediterranean and Black Sea, and form an orographic barrier to moisture sourced to the north in the Caspian Sea. This implies that terrestrial deposits along the southern Alborz mountains (leeward side of northerly winds and windward side of westerlies with the respect to Tibet and other mountainous terrain in the Himalayan-Karakoram realm) potentially track changes in past moisture and erosional regimes and mirror rainfall patterns. Here, we present results of a stable isotope analysis and clay mineral study of the Miocene (ca. 17.5-7.6 Ma) Upper Red Formation in the foreland of the southern Alborz mountains. The changes recorded by stable oxygen and carbon isotope data from pedogenic and lacustrine/palustrine carbonate in the southern Alborz mountains suggest: 1) an increase in aridity possibly related to the evolution of the Alborz orographic rain shadow, which became more efficient between 17.5 and 13.2 Ma; 2) a steady increase in precipitation between 13.2 and 10.3 Ma with a significant increase in rainout along the southern slope of the Alborz mountains between 11 and 10.3 Ma, possibly related to perturbations in atmospheric circulation pattern in the northern hemisphere as suggested by coeval wetter phases in southern Europe; and 3) a decrease in aridity from ca. 9.6 to 7.6 Ma, possibly reflecting an increase in the seasonality of precipitation. Based on environmental and climatic changes observed across southern Asia and India starting from ca. 10 Ma, we speculate that the topographic evolution of the Himalayan-Tibetan system might have affected the late Miocene climate in Middle East