Neogene fluvial landscape evolution in the hyperarid core of the Atacama Desert

Dating of extensive alluvial fan surfaces and fluvial features in the hyperarid core of the Atacama Desert, Chile, using cosmogenic nuclides provides unrivalled insights about the onset and variability of aridity. The predominantly hyperarid conditions help to preserve the traces of episodic climatic and/or slow tectonic change. Utilizing single clast exposure dating with cosmogenic 10Be and 21Ne, we determine the termination of episodes of enhanced fluvial erosion and deposition occurring at ~19, ~14, ~9.5 Ma; large scale fluvial modification of the landscape had ceased by ~2–3 Ma. The presence of clasts that record pre-Miocene exposure ages (~28 Ma and ~34 Ma) require stagnant landscape development during the Oligocene. Our data implies an early onset of (hyper-) aridity in the core region of the Atacama Desert, interrupted by wetter but probably still arid periods. The apparent conflict with interpretation that favour a later onset of (hyper-) aridity can be reconciled when the climatic gradients within the Atacama Desert are considered

Staurosporine induces necroptotic cell death under caspase-compromised conditions in U937 cells

For a long time necrosis was thought to be an uncontrolled process but evidences recently have revealed that necrosis can also occur in a regulated manner. Necroptosis, a type of programmed necrosis is defined as a death receptor-initiated process under caspase-compromised conditions. The process requires the kinase activity of receptor-interacting protein kinase 1 and 3 (RIPK1 and RIPK3) and mixed lineage kinase domain-like protein (MLKL), as a substrate of RIPK3. The further downstream events remain elusive. We applied known inhibitors to characterize the contributing enzymes in necroptosis and their effect on cell viability and different cellular functions were detected mainly by flow cytometry. Here we report that staurosporine, the classical inducer of intrinsic apoptotic pathway can induce necroptosis under caspase-compromised conditions in U937 cell line. This process could be hampered at least partially by the RIPK1 inhibitor necrotstin-1 and by the heat shock protein 90 kDa inhibitor geldanamycin. Moreover both the staurosporine-triggered and the classical death ligand-induced necroptotic pathway can be effectively arrested by a lysosomal enzyme inhibitor CA-074-OMe and the recently discovered MLKL inhibitor necrosulfonamide. We also confirmed that the enzymatic role of poly(ADP-ribose)polymerase (PARP) is dispensable in necroptosis but it contributes to membrane disruption in secondary necrosis. In conclusion, we identified a novel way of necroptosis induction that can facilitate our understanding of the molecular mechanisms of necroptosis. Our results shed light on alternative application of staurosporine, as a possible anticancer therapeutic agent. Furthermore, we showed that the CA-074-OMe has a target in the signaling pathway leading to necroptosis. Finally, we could differentiate necroptotic and secondary necrotic processes based on participation of PARP enzyme

Comparison of BES measurements of ion-scale turbulence with direct, gyrokinetic simulations of MAST L-mode plasmas

Observations of ion-scale (k_y*rho_i <= 1) density turbulence of relative amplitude dn_e/n_e <= 0.2% are available on the Mega Amp Spherical Tokamak (MAST) using a 2D (8 radial x 4 poloidal channel) imaging Beam Emission Spectroscopy (BES) diagnostic. Spatial and temporal characteristics of this turbulence, i.e., amplitudes, correlation times, radial and perpendicular correlation lengths and apparent phase velocities of the density contours, are determined by means of correlation analysis. For a low-density, L-mode discharge with strong equilibrium flow shear exhibiting an internal transport barrier (ITB) in the ion channel, the observed turbulence characteristics are compared with synthetic density turbulence data generated from global, non-linear, gyro-kinetic simulations using the particle-in-cell (PIC) code NEMORB. This validation exercise highlights the need to include increasingly sophisticated physics, e.g., kinetic treatment of trapped electrons, equilibrium flow shear and collisions, to reproduce most of the characteristics of the observed turbulence. Even so, significant discrepancies remain: an underprediction by the simulations of the turbulence amplituide and heat flux at plasma periphery and the finding that the correlation times of the numerically simulated turbulence are typically two orders of magnitude longer than those measured in MAST. Comparison of these correlation times with various linear timescales suggests that, while the measured turbulence is strong and may be `critically balanced', the simulated turbulence is weak.Comment: 27 pages, 11 figure

On the age and extent of the Serra da Peneda glaciation, NW Portugal

10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022.Geomorphological vestiges in the mountains of NW Portugal testify a low altitude, sheltered, and precipitation-driven glaciation. These vestiges have already been characterised in several works, with emphasis on mapping and delimitation of the extent of glaciation, especially in the Serra do Gerês. In Serra da Peneda, the glacial reconstitution is not so comprehensive. Previous works have identified erosional and accumulation landforms, as well as various types of tills. However, the maximum extent of glaciation still raises some doubts and the spatial discontinuity of vestiges could suggest different episodes of glaciation. To detail the extent of the glaciation in the Serra da Peneda, an identification of glacial and periglacial landforms and deposits was performed, based on field surveys, aerial photography analysis, and LiDAR imagery processing and interpretation. Moreover, 10Be cosmogenic nuclide dating of moraine granite boulders exposure age was carried out in the Alto Vez valley, the area where the main glacial vestiges occur. Samples were collected from the uppermost erratic boulders of Senhora da Guia, at 1000 m asl., pointing to a Last Glaciation Maximum (LGM) age whereas the moraine boulders of the valley floor, at 900 m asl. indicate a Younger Dryas age. These are the first glacial dating results for this region and are in contrast to others previously published for exposure ages of glaciated surfaces in the Serra do Gerês, which raises the possibility that different Pleistocene glaciations may be represented in the mountains of NW Portugal. To reconstitute the history of glaciations in the region, similar dating in other moraines of the Peneda and Gerês mountains is in progress

Experimental Signatures of Critically Balanced Turbulence in MAST

Beam Emission Spectroscopy (BES) measurements of ion-scale density fluctuations in the MAST tokamak are used to show that the turbulence correlation time, the drift time associated with ion temperature or density gradients, the particle (ion) streaming time along the magnetic field and the magnetic drift time are consistently comparable, suggesting a "critically balanced" turbulence determined by the local equilibrium. The resulting scalings of the poloidal and radial correlation lengths are derived and tested. The nonlinear time inferred from the density fluctuations is longer than the other times; its ratio to the correlation time scales as $\nu_{*i}^{-0.8\pm0.1}$, where $\nu_{*i}=$ ion collision rate/streaming rate. This is consistent with turbulent decorrelation being controlled by a zonal component, invisible to the BES, with an amplitude exceeding the drift waves' by $\sim \nu_{*i}^{-0.8}$.Comment: 6 pages, 4 figures, submitted to PR

Evidence for multiple Plio-Pleistocene lake episodes in the hyperarid Atacama Desert

Cosmogenic nuclide exposure dating of ancient shoreline terraces of the Quillagua-Llamara Soledad Lake in the central Atacama Desert of northern Chile provides new insights in the paleohydrology of the driest desert on Earth. The lake developed in a paleo-endorheic drainage system in the Central Depression prior to draining into the Pacific due to incision of the Río Loa canyon. The durations of lake stages were sufficiently long to form wave-erosion induced shoreline terraces on the wind-exposed slopes of former islands. Successively younger shoreline levels are preserved over an elevation range of 250 m due to progressive uplift of the islands coeval with the lake stages. Cosmogenic 10Be- and 21Ne-derived exposure ages of the shorelines reveals that the hyperarid conditions in the Río Loa catchment were interspersed by several pluvial stages during the Pliocene and Pleistocene, which generated a large and persistent lake in the Quillagua-Llamara basin. The exposure ages of the final lake stage provide the maximum age for the incision of the Río Loa canyon (274 ± 74 ka) and the subsequent breaching of the Coastal Cordillera

The timing of formation of the Douro and Tejo rivers and implications for the evolution of the landscapes of central mainland Portugal

10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022.The formation and development of major rivers limits the overall pace of the surrounding landscape evolution and drives sediment delivery from source to sink. The timings and rates of river incision may be a response to external influences, such as tectonic or climate driven base-level changes, or alternatively they may be linked to the breaching of internal thresholds, for example, drainage capture events. The Tejo and Douro rivers (also known as Tagus and Duero rivers) each drain a significant portion of the Iberian Peninsula and much of their courses through Portugal are typified by v-shaped valleys that are deeply incised into the surrounding topography. Earlier work has dated fluvial terrace deposits, mostly by luminescence techniques, but also by electron spin resonance and cosmogenic nuclide exposure dating. This has provided constraints on the late Pleistocene histories of the Tejo and Douro rivers, however, the timing of their transition from endorheic to exorheic is not precisely known and whether or not their histories are linked to a common mechanism is unclear. This study aims to provide age constraints on the early history of the Tejo and Douro rivers, and to examine whether and to what degree the erosion rates of low relief, granite etchplain landscapes within the river’s catchment areas are responding to the trunk channel incision. We focus on reaches of the Tejo and Douro rivers located in the eastern sector of mainland Portugal. Samples were collected for cosmogenic nuclide (10Be and 26Al) surface exposure and burial dating to date upper fluvial terrace levels. In addition, a combination of cosmogenic nuclide exposure ages and depth profiles in bedrock outcrops, alongside basin-wide erosion rate determinations will be used constrain the pace of evolution of nearby granitic landscapes. Preparation of the samples for measurement is ongoing and we will present our initial findings