Dynamic Uplift Research Articles

Numerical investigation on aerodynamic performance of a ducted fan under interferences from the ground, static water and dynamic waves

Ducted fans have been widely applied in various VTOL (vertical takeoff and landing) vehicles due to their high efficiency and low noise. By using the sliding mesh technique to simulate propeller rotation, a ducted fan system is chosen and the effects of the ground, static water and dynamic waves on its aerodynamic performance are evaluated, thereby exploring the adaptability of the system to complicated environments. The ground is set to slip wall moving with the same speed as the free stream and the static water surface is identified by using the VOF model. To generate dynamic waves, the open channel wave boundary is investigated to simulate a Stokes wave combined with the VOF model. A series of calculation cases consisting of free space, the ground effect, the static water effect and the wave effect are observed and analyzed in detail. The results indicate that ground, water surface and wave can strongly affect the aerodynamic performance of the ducted fan, as they interrupt the jet flow from the outlet of the duct and further pull the rebounded flow into the system. A decrease in the height between the system and the surface leads to a greater influence on the ducted fan. The strong effect obtained by the rigid ground benefits the lift of the propeller the most but also greatly weakens the lift of the duct; ultimately, the total lift of the system is lost. The torque changes by a law similar to that of the lift. The soft water surface is impacted to form a “drainage area”, which can be considered to increase the distance between the system and the water. Therefore, the water effect is not as strong as the ground effect. However, the change rules of the lift and the torque are nearly the same as those for the ground effect. The dynamic wave has the most complicated effect on the system. The periodic wave causes unpredictable periodic changes on the lift and the torque of the duct and the propeller, which may be related to numerical wave attenuation and the real-time changes in the soft wave surface. A larger wave height and a shorter distance between the wave and the system lead to a greater influence on the ducted fan. Moreover, the dynamic wave can induce “dynamic uplift” and hysteresis phenomena on the aerodynamic performance of the system.

Dissolved inorganic nitrogen and particulate organic nitrogen budget in the Yucatán shelf: driving mechanisms through a physical–biogeochemical coupled model

Abstract. Continental shelves are the most productive areas in the seas with the strongest implications for global nitrogen cycling. The Yucatán shelf (YS) is the largest shelf in the Gulf of Mexico (GoM); however, its nitrogen budget has not been quantified. This is largely due to the lack of significant spatio-temporal in situ measurements and the complexity of the shelf dynamics, including coastal upwelling, coastal-trapped waves (CTWs), and influence of the Yucatán Current (YC) via bottom Ekman transport and dynamic uplift. In this paper, we investigate and quantify the nitrogen budget of dissolved inorganic nitrogen (DIN) and particulate organic nitrogen (PON) in the YS using a 9-year output from a coupled physical–biogeochemical model of the GoM. The sum of DIN and PON is here referred to as total nitrogen (TN). Results indicate that the main entrance of DIN is through its southern (continental) and eastern margins. The TN is then advected to the deep oligotrophic Bay of Campeche and central GoM. It is also shown that the inner shelf (bounded by the 50 m isobath) is “efficient” in terms of TN, since all DIN imported into this shelf is consumed by the phytoplankton. Submarine groundwater discharges (SGDs) contribute 20 % of the TN, while denitrification removes up to 53 % of TN that enters into the inner shelf. The high-frequency variability of the TN fluxes in the southern margin is modulated by fluxes from the YC due to enhanced bottom Ekman transport when the YC leans against the shelf break (250 m isobath) on the eastern margin. This current–topography interaction can help to maintain the upwelling of Cape Catoche, uplifting nutrient-rich water into the euphotic layer. The export of TN at both western and northwestern margins is modulated by CTWs with a mean period of about 10 d in agreement with recent observational and modelling studies.

Lithospheric thinning and dynamic uplift effects during slab window formation, southern Patagonia (45˚-55˚ S)

The southernmost South America has been affected by the subduction of an oceanic seismic ridge, which began to subduct below southern Patagonia at ∼14 Ma. This scenario led to the formation of a slab window, which is still active and where hot buoyant asthenospheric mantle produced thermal anomalies and modifications in the lithospheric thicknesses. Meanwhile, from the Patagonian Andes to the Atlantic coast, an outstanding regional surface uplift took place, conducting to a moderated-elevation plateau formation. In this work we analyzed the causes of this long-wavelength surface elevation change using residual topography and uplift rate calculations, considering paleo-lithospheric states. We achieved this considering that the study area underwent a lithospheric thickness changes through time, before and after the slab window formation. This allowed us to estimate the isostatic and dynamic adjustment over time and their influences on the surface elevation changes. These rates were compared with geological and stratigraphic observations derived from a key elevation marker bed: The modern altitudes of Oligo-Miocene marine strata top, originally deposited close or below sea level, and placed at Present at hundreds of meters above sea level. Our residual topography calculations, that result from comparing isostatic and observed topography, indicates the dynamic topography contribution in the study region was very minor (if so) to null. The isostatic uplift, in turn, shows a remarkable fitting with the reconstruction of marine marker bed, suggesting a causative relationship. We can assert that Patagonian lithospheric thinning, particularly of the lithospheric mantle, by slab window formation, would have been enough to reproduce the modern elevations and surface uplift across the plateau from the Miocene to Present day. Our work opens a question on the model that connect slab windows, asthenospheric upwelling flows with surface uplifting. However, as shown by recent works, lithospheric changes might trigger small convection cells, which might produce local and small dynamic topography.

Uplift of Trail Ridge, Florida, by Karst Dissolution, Glacial Isostatic Adjustment, and Dynamic Topography

AbstractThe present elevation of Trail Ridge, a purported Pleistocene paleoshoreline (2.21 ± 0.38 Ma) up to ~70 m high, is attributed to isostatic uplift from karst‐induced mass loss of the underlying Florida Platform. However, glacial isostatic adjustment, dynamic topography (DT), and elastic flexure also contribute to the observed topography. We investigated the combined contribution of these geophysical processes to the elevation of Trail Ridge by adapting a numerical model of karst‐induced Airy isostatic uplift that is driven by sea level change since ~3 Ma with a gravitationally self‐consistent glacial isostatic adjustment model. We treat DT as a free parameter and explore a spectrum of scenarios, from dynamic subsidence (−25 m/Myr) to dynamic uplift (+25 m/Myr), with values consistent with mantle convection simulations for the region. We demonstrate a trade‐off between the age of Trail Ridge, karstification efficiency, and DT rate that necessitates robust estimates of two of these variables when solving for the third. For example, adopting spring‐efflux‐derived estimates of subsurface carbonate dissolution (1 m/38,000 yr) and a 10 m/Myr dynamic topographic uplift for the northern Florida Platform predicts an age of ~2.1 Ma for a model 70 m elevation marker, consistent with the bounds of the electron spin resonance optical dating geochronology. In contrast, by assuming a more rapid carbonate dissolution efficiency (1 m/11,000 yr) and dynamic subsidence of −15 m/Myr predicts a similar age. A refined karst‐induced isostatic uplift model age for Trail Ridge requires both improved rates of regional karst dissolution, dynamic topographic change, and elastic flexure.

Dynamic Topography Development North of Iceland from Subaerial Exposure of the Igneous Logi Ridge, NE Atlantic

AbstractThe Logi Ridge, located north of the West Jan Mayen Fracture Zone, is E‐W oriented and 140–150 km long. The seafloor surrounding the Logi Ridge is ∼0.65 km shallower than the conjugate seafloor east of the Mohn's Ridge, attributed to asymmetry in the regional NE Atlantic dynamic uplift. Eight reflection seismic lines across the Logi Ridge constrain its development. Both the western and eastern parts have flat tops, indicating erosion at sea level. Three different basement types surrounding the Logi Ridge are observed: rough basement represents abyssal hills original or reactivated by later magmatic/tectonic events; smooth basement caused by basalt flows overprinting early sediments; and irregular basement formed by later basalt flows and intrusions. The surrounding sediments have two distinct units, where the unit boundary is Middle Miocene (12–14 Ma). Mass transport from the Logi Ridge appears episodically throughout Late Oligocene to Middle Miocene, when development ends. The end of erosion age can also be estimated from seamount height, or present top seamount depth. In the west there is agreement with the age constrained by the sedimentation, proving little dynamic topography change. In the east, discrepancies between the methods are explained by 0.15–0.3 km dynamic uplift after submergence. Hence, most of the regional dynamic uplift occurred before the end of the Logi Ridge development in the Middle Miocene, suggesting a causative relationship. Minor recent magmatic growth and seafloor uplift over a ∼100 km wide zone southeast of the Logi Ridge may be tied to the younger dynamic uplift in the east.

Decompensative Gravity Anomalies Reveal the Structure of the Upper Crust of Antarctica

As Antarctica is almost entirely covered by thick ice shields impeding in situ measurements, information about upper crustal structures and sedimentary basins is still sparse and the analysis of the gravity anomalies offers new insights. Isostatic gravity anomalies are often used to investigate upper crust structures. However, compensating masses significantly reduce the gravity effect of unknown sedimentary and upper crustal structures. To separate these effects, we apply so-called decompensative corrections to the isostatic anomalies for the Antarctic continent, which reach values of up to ± 70 mGal. The obtained decompensative anomalies well correspond to the known sedimentary basins, such as in the areas of the Filchner-Ronne Ice Shelf and Lambert Graben, and also suggest the existence of other large sedimentary deposits both in West and East Antarctica, which are not or only sparsely mapped by existing seismic surveys, e.g. in coastal Dronning Maud Land and Enderby Land. A dipole-like structure exists at the Transantarctic Mountains and the Wilkes Subglacial Basin, suggesting the presence of isostatic disturbances linked to the dynamic uplift of the Transantarctic Mountains and thick sedimentary accumulations in the east. Extended positive anomalies in East Antarctica are likely related to the old and dense cratonic crust as well as to isostatic disturbances caused by the transition from local to regional compensation around the Lambert Graben.

An Unusual Extreme Rainfall Event in Canberra Australia on February 2018

AbstractA case of an extreme rainfall event in Canberra, the capital city of Australia, on 24–25 February 2018 is investigated. Canberra received more than the long‐term statistical February total rainfall within 6 hr on that day, causing overwhelming flash flooding in the city. In contrast to many coastal cities or tropical regions, Canberra is located at the boundary between the tropics and extratropics and is usually dry and warm in February. The diagnostic analysis shows that this relatively rare brief heavy rainfall was the joint effects of lower‐level warm, moist conveyor belts, the remnants of tropical cyclone Kelvin, surface cold fronts, and a midlatitude trough at middle to upper levels. The lower‐level northeast and west conveyor belts of water vapor contributed to the accumulation of moisture and created favorable conditional instability over Canberra by transporting tropical moist and warm air from Coral Sea and from the Kelvin remnant to Canberra prior to and during the rainfall period. Enhanced uplift was triggered by the arrival of a cold front in the warm, moist unstable air. The rainfall reached a peak 13.6 mm in 30 min soon after a low‐level frontal updraft coupled with middle‐ to upper‐level dynamical uplift ahead of the midlatitude trough. After the passage of the upper‐level trough, the dry, cold air in the rear of the trough stabilized and dried the atmosphere above Canberra. The rainfall decreased and ended rapidly.

The interplay of dynamic topography and eustasy on continental flooding in the late Paleozoic

Global sea level change can be inferred from sequence stratigraphic and continental flooding data. These methods reconstruct sea level from peri-cratonic and cratonic basins that are assumed to be tectonically stable and sometimes called reference districts, and from spatio-temporal correlations across basins. However, it has been understood that long-wavelength (typically hundreds of km) and low-amplitude (<2 km) vertical displacements of the Earth's surface due to mantle flow, namely dynamic topography, can occur in the absence of crustal deformation. Dynamic topography can drive marine inundation or regional emergence of continents and must be taken into consideration for eustasy estimates. Our analysis indicates that the long-term trend in global-scale maximum flooding over the late Paleozoic generally correlates with global sea level curves. The first-order flooding history of North America correlates with some estimates of eustasy. The Paleozoic inundation of South America does not follow long-term sea level variations. The flooding lows during the Early Carboniferous and high during the Late Carboniferous are at odds with estimates of eustasy and can be explained by dynamic uplift and subsidence, respectively. Our dynamic topography models indicate that the Yangtze Platform of South China experienced significant dynamic subsidence during the transition from Permian to Triassic largely due to proto-Pacific subduction and its northward motion to collide with North China. The reference districts – Western New York, Oklahoma and Kansas, and West Texas in North America – were to some degree affected by dynamic uplift and subsidence associated with long-lived Panthalassa subduction zones, closure of the Rheic Ocean and large-scale upwelling above the African deep-mantle structure during late Paleozoic times. This indicates that some published global sea level curves may include non-eustatic signals such as dynamic uplift or subsidence. The interpretation of stratigraphic data gathered from these reference districts should be treated with caution to estimate global sea level variations.

Petroleum tectonic comparison of fold and thrust belts: the Zagros of Iraq and Iran, the Pyrenees of Spain, the Sevier of Western USA and the Beni Sub-Andean of Bolivia

Abstract The genetic analysis of fold and thrust belts is facilitated by tracking the evolution of their organic endowment (petroleum tectonics). Petroleum tectonic analysis of convergent orogenic systems provides an audit of the processes that control the deformation and kinematics of orogenic belts. The distribution and deformation paths of the organic endowment intervals are key factors in determining the petroleum system evolution of fold and thrust belts. This comparison of orogenic systems illustrates the importance of flexural v. dynamic processes, orogenic wedge taper, mechanical stratigraphy and inherited architecture on the creation, preservation and destruction of petroleum accumulations. The Zagros, Pyrenees, Sevier and Beni Sub-Andean convergent systems share key characteristics of fold and thrust belts, with major differences in scale, degree of incorporation of organic endowment in evolution of the fold and thrust belt and its foreland, and preservation of fold and thrust belt wedge-top deposits. The Zagros is an orogen dominated by flexural processes that is a perfect storm for hydrocarbon generation and preservation. Its multiple stacked sources ensure continuous hydrocarbon generation while stacked detachments foster a low taper and thick wedge-top basins. The Pyrenees is also a flexurally dominated orogen, but the early consumption of its source rocks led to minimal survival of hydrocarbon accumulations during exhumation in a long lasting, high-taper orogenic wedge. The Sevier was initially a flexural orogen that was later dominated by dynamic uplift of the fold and thrust belt and distal foreland subsidence with foreland deformation. The consumption of its pre-orogenic sources during the early low-taper phase indicates a probable robust petroleum system at that time. However, the late high-taper phase exhumed and destroyed much of the early petroleum system. The addition of syntectonic foreland sources to be matured by both local and dynamic subsidence created an additional later set of petroleum systems. Post-orogenic events have left only remnants of world-class petroleum systems. The Beni segment of the Sub-Andean Orogen is a flexural system with probable dynamic overprints. Its most robust petroleum system probably occurred during its early low-taper flexural phase, with dynamic subsidence enhancement. Its late high-taper phase with possible dynamic uplift shuts down and stresses the petroleum systems. Comparison of these orogenic systems illustrates the importance of flexural v. dynamic processes, orogenic wedge taper kinematics, mechanical stratigraphy, distribution of source rocks relative to shortening and inherited architecture on the creation, preservation and destruction of petroleum accumulations in fold and thrust belts.

Topographic evolution of the western United States since the early Miocene

The origin of the high topography within the western United States has been attributed to either crustal/lithospheric isostasy or dynamic topography, but their relative contributions remain unconstrained. Here we investigate this problem using gravity, residual topography and geodynamic modeling. We first evaluate two end-member scenarios of isostatic balance: crustal isostasy and lithospheric isostasy. Both cases lead to prominent negative mantle residual gravity within the tectonically active western U.S. and unrealistic crustal/lithospheric density structures, requiring the presence of low-density mantle underneath. The negative mantle residual gravity is consistent with both the estimated positive residual topography and calculated dynamic uplift due to the presence of hot asthenospheric mantle underneath. Geodynamic modeling further reveals that this landward migrating dynamic uplift originates from the eastward intrusion of the hot Pacific mantle through tears and edges of the Juan de Fuca slab since middle Miocene. The estimated paleotopography maps by combining dynamic topography and lithosphere isostasy over the western U.S. are consistent with several observational constraints, including episodic uplifts of the Sierra Nevada, post-mid-Miocene uplift of the Idaho batholith, the sustaining subsidence within most of the B&R, and the largely stable topography of central Colorado Plateau since 20 Ma.

Mapping the bathymetric evolution of the Northern North Sea: from Jurassic synrift archipelago through Cretaceous–Tertiary post-rift subsidence

The post-rift history of the North Viking Graben has been backstripped in 3D, producing a sequence of palaeobathymetric maps that culminates at the Late Jurassic synrift stage. The backstripping takes into account the three main processes which drive post-rift basin development: thermal subsidence, flexural-isostatic loading and sediment compaction. Before backstripping was performed, the Norwegian Trench, a bathymetric feature within the present-day seabed, was smoothed in order to remove associated decompaction artefacts within the backstripping results. Palaeobathymetric restorations at the top and base of the Paleocene take into account regional transient dynamic uplift, probably related to the Iceland Plume. 350 m of uplift is incorporated at the Base Tertiary (65 Ma) and 300 m at the Top Balder Formation (54 Ma), followed by rapid collapse of this same uplift. At the top of the Lower Cretaceous (98.9 Ma), very localized fault-block topography, inherited from the Jurassic rift, is predicted to have remained emergent within the basin. At the Base Cretaceous (140 Ma), the fault-block topography is much more prominent and numerous isolated footwall islands are shown to have been present. At the Late Jurassic synrift stage (155 Ma), these islands are linked to form emergent island chains along the footwalls of all of the major faults. This is the Jurassic archipelago, the islands of which were the products of synrift footwall uplift. The predicted magnitude and distribution of footwall emergence calibrates well against available well data and published stratigraphic information, providing important constraints on the reliability of the results.

Phytoplankton blooms associated with upwelling at Cabo Catoche

In this work, the spatial and temporal implications of the Non-Eastern Boundary Upwelling (Non-EBUS) on the bio-productivity from coastal shallow waters have been studied. At the coast of Cabo Catoche, on the Yucatán shelf, two 12-day field campaigns (April and July) were conducted. Cross-shore CTD-fluorescence profiles, water samples, and plankton were collected each day. Nutrients, ocean temperature and currents times series from two moorings (8 and 12 m depth) were analyzed, as were temperature and chlorophyll (Chl-a) from satellite data. The water masses from the Yucatan channel reached the coast of Cabo Catoche in both study periods. The Yucatan Upwelling Water (YUW, ~ 19.6–22.5 °C) supplied the surface and subsurface water, up to 6 km offshore, with nutrients during the upwelling pulses from 2 to 5 days. Nutrients were higher in April (nitrate, ammonium < 5, 18 μmol L−1), but the phytoplankton bloom was more consistent in July (Chl-a mean, 1.45 mg m−3) showing greater distribution across the coast. The steady upwelling plume (cold water, high nutrients) recorded in Cabo Catoche and observed on the north shelf, could have been the result of dynamic uplift in the Yucatan Channel prior to the field campaign. Through the way to the shelf, the plankton increased, explaining the high temporal association between low temperatures and the phytoplankton bloom at the coast. The Non-EBUS has strong implications for the pelagic ecosystem from Cabo Catoche, enhancing productivity and triggering energy flow by the physical process.

Tectonics and geodynamics of the eastern Tethys and northern Gondwana since the Jurassic

Southeast Asia experienced a complex tectonic and geodynamic history related to the subduction of the eastern Tethyan ocean basins, resulting from the long-term convergence between the Indo-Australian, Eurasian, and Pacific plates since Pangea breakup. The complex collage of continental and island arc terranes can be reconstructed into an estimated ancient arrangement using plate tectonic reconstruction approaches based on a synthesis of continental and marine geological and geophysical data. We use the open-source and cross-platform software GPlates (www.gplates.org) to refine the evolution of the eastern Neo-Tethys since the latest Jurassic rifting episodes along northern Gondwana. We apply the resulting plate motions to drive numerical models of mantle flow in order to predict the evolving mantle structure. New Guinea’s northward motion over subducted slabs, related to the Sepik back-arc basin and the Maramuni subduction system, resulted in long-term flooding of the margin since ~20 Ma, despite falling long-term global sea levels. The Sundaland continental promontory experienced dynamic uplift in the latest Cretaceous to Eocene times due to the accretion of the Woyla Arc at ~80 Ma, leading to slab breakoff and a temporary interruption of subduction. However, renewed subduction along the Sunda margin resulted in renewed dynamic subsidence from ~30 Ma, which was amplified by regional basin rifting events. In addition, the sinking Sunda slab likely triggered a mantle slab avalanche, resulting in a counterintuitive combination of contemporaneous basin inversion and strong dynamic subsidence from ~15 Ma. The evolution of the eastern Tethyan oceanic gateway provides an important framework for understanding the role of plate tectonics in controlling long-term oceanic circulation and climate, as well as shedding light on the complex interplay between deep Earth and surface processes in driving basin formation and evolution. These results provide new avenues for reconciling stratigraphic and tectonic processes, as well as contributing new approaches for basin analysis and hydrocarbon exploration.

Simulation of High-Speed Pantograph Dynamic Performance Based on Finite Element Model and Aerodynamic Pantograph Model

A coupled finite element model for the pantograph-catenary system and an aerodynamic pantograph model were built. Based on the models, the dynamic current collection and aerodynamic performances of the pantograph were studied using MSC-Marc and STAR-CD simulations of software. In the finite element model, the pantograph and catenary subsystems are integrated into a whole system through contact coupling between them to simulate the dynamic behavior of the pantograph-catenary system. Then, the aerodynamic performance of the high-speed pantograph was simulated on the three-Dimensional aerodynamic pantograph model. The simulation results show that the dynamic uplift and average contact force of simple suspension are smaller than those of stitched suspension.

The Dynamic Topography of Eastern China Since the Latest Jurassic Period

AbstractSome changes in the topography of eastern China since Late Jurassic times cannot be well explained by lithospheric deformation. Here we analyze global mantle flow models to investigate how mantle‐driven long‐wavelength topography may have contributed to shaping the surface topography of eastern China. Paleodrainage directions suggest that a southward tilted topography once existed in eastern north China in the latest Jurassic Period, which is different from that at present day (southeastward tilting). Our model dynamic topography reveals a southward tilting topography between 160 and 150 Ma, followed by southeastward tilting and rapid subsidence, which is compatible with paleodrainage directions and tectonic subsidence of the Ordos Basin. The Cretaceous anomalous subsidence of the Songliao and North Yellow Sea basins, as well as the Cenozoic anomalous subsidence of the East China Sea Shelf Basin, can also be explained by dynamic topography. An apatite fission track study in the Taihang Mountains reveals four stages of evolution: Late Jurassic fast unroofing, Cretaceous slow unroofing, early Cenozoic fast unroofing, and late Cenozoic slow unroofing. We propose that mantle flow influenced this surface unroofing because the model predicts Late Jurassic dynamic uplift, Cretaceous dynamic subsidence, early Cenozoic dynamic uplift, and late Cenozoic dynamic subsidence. Apatite fission track data from northern south China are also in reasonable agreement with predicted dynamic topography between 80 and 30 Ma. The spatial and temporal agreement between geological observations and model dynamic topography indicates that mantle flow has had a significant influence in shaping the surface topography of eastern China.

Description and Mechanisms of the Mid-Year Upwelling in the Southern Caribbean Sea from Remote Sensing and Local Data

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period.

Dynamic uplift, recycling, and climate control on the petrology of passive-margin sand (Angola)

The subequatorial Angolan continental margin offers excellent conditions to test textbook theories on the composition of passive-margin sediments generated in different climatic and tectonic regimes. We use here comprehensive petrographic, heavy-mineral, geochemical and zircon-geochronology datasets on modern fluvial, beach, shelfal, and deep-marine sands and muds collected from hyperarid northern Namibia to hyperhumid Congo to investigate and assess: a) how faithfully sand mineralogy reflects the lithological and time structures of source rocks in a tectonically active rifted margin; b) in what climatic and geomorphological conditions the mark of chemical weathering becomes strong and next overwhelming; and, c) to what extent the effect of weathering can be isolated from quartz dilution by recycling of older siliciclastic strata and other physical controls including hydraulic sorting and mechanical wear. A new refined classification of feldspatho-quartzose and quartzose sands and sandstones is proposed.First-cycle quartzo-feldspathic to feldspar-rich feldspatho-quartzose sand eroded from mid-crustal granitoid gneisses of the Angola Block exposed in the dynamically uplifted Bié-Huila dome is deposited in arid southern Angola, whereas quartz-rich feldspatho-quartzose to quartzose sand characterizes the lower-relief, less deeply dissected, and more intensely weathered rifted margin of humid northern Angola. Pure quartzose, largely recycled sand is generated in the vast, low-lying hyperhumid continental interiors drained by the Congo River. The progressive relative increase of durable minerals toward the Equator results from three distinct processes acting in accord: active tectonic uplift in the arid south, and progressively stronger weathering coupled with more extensive recycling in the humid north. The quartz/feldspar ratio increases and the plagioclase/feldspar ratio decreases rapidly in first-cycle sand generated farther inland in the Catumbela catchment, reflecting stronger weathering in wet interior highlands. Discriminating weathering from recycling control is difficult in northern Angola. Although textural features including deep etch pits even on relatively resistant minerals such as quartz and microcline or rounded outline and abraded overgrowths provide valuable independent information, recycling remains as a most elusive problem in provenance analysis of terrigenous sediments.

Impacts of Mt Pinatubo volcanic aerosol on the tropical stratosphere in chemistry–climate model simulations using CCMI and CMIP6 stratospheric aerosol data

Abstract. To simulate the impacts of volcanic eruptions on the stratosphere, chemistry–climate models that do not include an online aerosol module require temporally and spatially resolved aerosol size parameters for heterogeneous chemistry and aerosol radiative properties as a function of wavelength. For phase 1 of the Chemistry-Climate Model Initiative (CCMI-1) and, later, for phase 6 of the Coupled Model Intercomparison Project (CMIP6) two such stratospheric aerosol data sets were compiled, whose functional capability and representativeness are compared here. For CCMI-1, the SAGE-4λ data set was compiled, which hinges on the measurements at four wavelengths of the SAGE (Stratospheric Aerosol and Gas Experiment) II satellite instrument and uses ground-based lidar measurements for gap-filling immediately after the 1991 Mt Pinatubo eruption, when the stratosphere was too optically opaque for SAGE II. For CMIP6, the new SAGE-3λ data set was compiled, which excludes the least reliable SAGE II wavelength and uses measurements from CLAES (Cryogenic Limb Array Etalon Spectrometer) on UARS, the Upper Atmosphere Research Satellite, for gap-filling following the Mt Pinatubo eruption instead of ground-based lidars. Here, we performed SOCOLv3 (Solar Climate Ozone Links version 3) chemistry–climate model simulations of the recent past (1986–2005) to investigate the impact of the Mt Pinatubo eruption in 1991 on stratospheric temperature and ozone and how this response differs depending on which aerosol data set is applied. The use of SAGE-4λ results in heating and ozone loss being overestimated in the tropical lower stratosphere compared to observations in the post-eruption period by approximately 3 K and 0.2 ppmv, respectively. However, less heating occurs in the model simulations based on SAGE-3λ, because the improved gap-filling procedures after the eruption lead to less aerosol loading in the tropical lower stratosphere. As a result, simulated tropical temperature anomalies in the model simulations based on SAGE-3λ for CMIP6 are in excellent agreement with MERRA and ERA-Interim reanalyses in the post-eruption period. Less heating in the simulations with SAGE-3λ means that the rate of tropical upwelling does not strengthen as much as it does in the simulations with SAGE-4λ, which limits dynamical uplift of ozone and therefore provides more time for ozone to accumulate in tropical mid-stratospheric air. Ozone loss following the Mt Pinatubo eruption is overestimated by up to 0.1 ppmv in the model simulations based on SAGE-3λ, which is a better agreement with observations than in the simulations based on SAGE-4λ. Overall, the CMIP6 stratospheric aerosol data set, SAGE-3λ, allows SOCOLv3 to more accurately simulate the post-Pinatubo eruption period.

The role of the Agulhas in the Benguela Current system: A numerical modeling approach

AbstractA modeling approach is used to investigate the influence of the Agulhas on the southern Benguela system. Two climatological ROMS simulations are run that are identical except that in one of them the effect of the Agulhas is removed. Comparing their outputs allows for a clear indication of the role of the Agulhas on both the large‐scale and shelf dynamics. About 15 Sv of the mean transport of the Benguela Current is shown to be contributed by Agulhas influx, with the most intense flow being associated with extreme turbulence and its meandering nature is a reflection of the passage of Agulhas Rings. The injection of warm water is particularly evident beyond the shelf‐edge, producing a perennially intense cross‐shelf density front that is enhanced during upwelling season. This gradient drives a jet that is fastest at the shelf‐edge but that extends from the midshelf to at least 100 km beyond it and is associated with dynamic uplift via vortex squashing. Similarly generated is the Good Hope Jet that extends northwestward from the western Agulhas Bank. Turbulence associated with Agulhas leakage increases rapidly beyond the shelf‐edge causing the upwelling front in the southern Benguela to be subject to intense mixing, leaving a relatively uniform front there. Locally generated regions of high turbulence exist in the vicinity of the shelf‐edge jets as well as further north in association with the large filaments that originate from the perennial Lüderitz upwelling cell, with or without the influence of the Agulhas.

Large fluctuations of shallow seas in low-lying Southeast Asia driven by mantle flow

The Sundaland continental promontory, as the core of Southeast Asia, is one of the lowest lying continental regions, with half of the continental area presently inundated by a shallow sea. The role of mantle convection in driving long-wavelength topography and vertical motion of the lithosphere in this region has often been ignored when interpreting regional stratigraphy, including a widespread Late Cretaceous-Eocene unconformity, despite a consensus that Southeast Asia is presently situated over a large-amplitude, dynamic topography low resulting from long-term post-Pangea subduction. We use forward numerical models to link mantle flow with surface tectonics, and compare predicted trends of dynamic topography with eustasy and regional paleogeography to determine the influence of mantle convection on regional basin histories. A Late Cretaceous collision of Gondwana-derived terranes with Sundaland choked the active margin, leading to slab breakoff and a ∼10-15 Myr-long subduction hiatus. Slab breakoff likely resulted in several hundred meters of dynamic uplift and emergence of Sundaland between ∼80 and 60 Ma, and may explain the absence of a Late Cretaceous-Eocene sedimentary record. Renewed subduction from ∼60 Ma reinitiated dynamic subsidence of Sundaland, leading to submergence from ∼40 Ma despite falling long-term global sea levels. Our results highlight a complete ‘down-up-down' dynamic topography cycle experienced by Sundaland, with transient dynamic topography manifesting as a major regional unconformity in sedimentary basins.