A sedimentological record of fluvial-aeolian interactions and climate variability in the hyperarid northern Namib Desert, Namibia

2021 ◽  
Author(s):  
R. McG. Miller ◽  
C. Krapf ◽  
T. Hoey ◽  
J. Fitchett ◽  
A-K. Nguno ◽  
...  
Keyword(s):  
Rainfall Regime ◽  
Namib Desert ◽  
Free Standing ◽  
Winter Rainfall ◽  
Climatological Data ◽  
Salt Pans ◽  
Mass Flows ◽  
Wind Sea ◽  
Glacial Periods ◽  
Fine Gravel

Abstract The aeolian regime of the 100 km wide, hyperarid Namib Desert has been sporadically punctuated by the deposition of fluvial sediments generated during periods of higher humidity either further inland or well within the desert from Late Oligocene to Late Holocene. Four new Late Cenozoic formations are described from the northern Skeleton Coast and compared with formations further south: the Klein Nadas, Nadas (gravels, sands), Vulture’s Nest (silts) and Uniab Boulder Formations. The Klein Nadas Formation is a trimodal mass-flow fan consisting of thousands of huge, remobilised, end-Carboniferous Dwyka glacial boulders, many >3 m in length, set in an abundant, K-feldspar-rich and sandy matrix of fine gravel. Deluge rains over the smallest catchments deep within the northern Namib were the driving agent for the Klein Nadas Fan, the termination of which, with its contained boulders, rests on the coastal salt pans. These rains also resulted in catastrophic mass flows in several of the other northern Namib rivers. The Uniab Boulder Formation, being one, consists only of huge free-standing boulders. Gravelly fluvial deposition took place during global interglacial and glacial events. The Skeleton Coast Erg and other smaller dune trains blocked the rivers at times. The low-energy, thinly bedded silt deposits of the central and northern Namib are quite distinctive from the sands and gravels of older deposits. Their intermittent deposition is illustrated by bioturbation and pedogenesis of individual layers. Published offshore proxy climatological data (pollens, upwelling, wind, sea surface temperatures) point to expansion of the winter-rainfall regime of the southern Cape into southwestern Angola during strong glacial periods between the Upper Pleistocene and Holocene. In contrast to deposition initiated by short summer thunder storms, we contend that the silt successions are river-end accumulations within which each layer was deposited by runoff from comparatively gentle winter rains that lasted several days.

Impact of changing rainfall conditions on surface and groundwater resources in an experimental watershed in Greece

2013 ◽  
Vol 12 (2) ◽  
pp. 119-125
Keyword(s):  
Groundwater Resources ◽  
Annual Runoff ◽  
Annual Rainfall ◽  
Rainfall Regime ◽  
Winter Rainfall ◽  
Rainfall Depth ◽  
Rainfall Volume ◽  
The Mean ◽  
Groundwater Reserves ◽  
The Impact

The present study concerns the impact of a change in the rainfall regime on surface and groundwater resources in an experimental watershed. The research is conducted in a gauged mountainous watershed (15.18 km2) that is located on the eastern side of Penteli Mountain, in the prefecture of Attica, Greece and the study period concerns the years from 2003 to 2008. The decrease in the annual rainfall depth during the last two hydrological years 2006-2007, 2007-2008 is 10% and 35%, respectively, in relation to the average of the previous years. In addition, the monthly distribution of rainfall is characterized by a distinct decrease in winter rainfall volume. The field measurements show that this change in rainfall conditions has a direct impact on the surface runoff of the watershed, as well as on the groundwater reserves. The mean annual runoff in the last two hydrological years has decreased by 56% and 75% in relation to the average of the previous years. Moreover, the groundwater level follows a declining trend and has dropped significantly in the last two years.

Topography and recent winter rainfall regime change in temperate Western European areas: a case study in the Rhine-Meuse basin

2006 ◽  
Vol 26 (6) ◽  
pp. 785-796 ◽  
Author(s):  
Drogue Gilles ◽  
Wagner Christian ◽  
Mahr Nicole ◽  
Hoffmann Lucien ◽  
Pfister Laurent
Keyword(s):  
Regime Change ◽  
Rainfall Regime ◽  
Winter Rainfall ◽  
Western European

scholarly journals Metaviromics of Namib Desert Salt Pans: A Novel Lineage of Haloarchaeal Salterproviruses and a Rich Source of ssDNA Viruses

Viruses ◽  
2016 ◽  
Vol 8 (1) ◽  
pp. 14 ◽  
Author(s):  
Evelien Adriaenssens ◽  
Leonardo van Zyl ◽  
Don Cowan ◽  
Marla Trindade
Keyword(s):  
Rich Source ◽  
Namib Desert ◽  
Salt Pans ◽  
Ssdna Viruses

Vegetation and Seasonality Shifts during the Late Quaternary Deduced from 13C/12C Ratios of Grazers at Equus Cave, South Africa

1995 ◽  
Vol 43 (3) ◽  
pp. 426-432 ◽  
Author(s):  
Julia A. Lee-Thorp ◽  
Peter B. Beaumont
Keyword(s):  
South Africa ◽  
Climate Models ◽  
Tooth Enamel ◽  
Late Quaternary ◽  
Relative Proportion ◽  
Major Influence ◽  
Rainfall Regime ◽  
Relative Distribution ◽  
Winter Rainfall ◽  
Recent Climate

AbstractSeason of rainfall can be a major influence on the relative proportions of C3 and C4 grasses in a landscape, since their relative distribution is essentially constrained by temperatures during the growing season; cool growing seasons favor C3 grasses, whereas warm ones favor C4 grasses. 13C/12C ratios in tooth enamel carbonate of grazers from the site of Equus Cave, northern Cape Province, South Africa, were used to determine vegetation and rainfall seasonality shifts during the late Quaternary. The results show shifts in the relative proportion of C3 and C4 grasses during the latter stages of the Pleistocene, and domination by C4 grasses in the Holocene. The data show that the northwestern Cape did not fall within a winter rainfall zone during this period as has been postulated in recent climate models. Instead, a more complex situation is suggested in which at least two periods of enhanced winter rainfall occurred within a predominantly summer rainfall regime.

scholarly journals Long-Term Population Dynamics of Namib Desert Tenebrionid Beetles Reveal Complex Relationships to Pulse-Reserve Conditions

Insects ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 804
Author(s):  
Joh R. Henschel
Keyword(s):  
Heavy Rain ◽  
Population Variation ◽  
Population Bottlenecks ◽  
Namib Desert ◽  
Winter Rainfall ◽  
Rainfall Events ◽  
High Species Diversity ◽  
Complex Relationships ◽  
Coleoptera Tenebrionidae

Noy-Meir’s paradigm concerning desert populations being predictably tied to unpredictable productivity pulses was tested by examining abundance trends of 26 species of flightless detritivorous tenebrionid beetles (Coleoptera, Tenebrionidae) in the hyper-arid Namib Desert (MAP = 25 mm). Over 45 years, tenebrionids were continuously pitfall trapped on a gravel plain. Species were categorised according to how their populations increased after 22 effective rainfall events (>11 mm in a week), and declined with decreasing detritus reserves (97.7–0.2 g m−2), while sustained by nonrainfall moisture. Six patterns of population variation were recognised: (a) increases triggered by effective summer rainfalls, tracking detritus over time (five species, 41% abundance); (b) irrupting upon summer rainfalls, crashing a year later (three, 18%); (c) increasing gradually after series of heavy (>40 mm) rainfall years, declining over the next decade (eight, 15%); (d) triggered by winter rainfall, population fluctuating moderately (two, 20%); (e) increasing during dry years, declining during wet (one, 0.4%); (f) erratic range expansions following heavy rain (seven, 5%). All species experienced population bottlenecks during a decade of scant reserves, followed by the community cycling back to its earlier composition after 30 years. By responding selectively to alternative configurations of resources, Namib tenebrionids showed temporal patterns and magnitudes of population fluctuation more diverse than predicted by Noy-Meir’s original model, underpinning high species diversity.

Wet Conditions during the Last Glaciation in the Chihuahuan Desert, Alta Babicora Basin, Mexico

2002 ◽  
Vol 57 (1) ◽  
pp. 91-101 ◽  
Author(s):  
Sarah Metcalfe ◽  
Alison Say ◽  
Stuart Black ◽  
Robert McCulloch ◽  
Sarah O'Hara
Keyword(s):  
Late Pleistocene ◽  
Chihuahuan Desert ◽  
Summer Rainfall ◽  
Sediment Chemistry ◽  
Carbonate Content ◽  
Rainfall Regime ◽  
Winter Rainfall ◽  
Northern Mexico ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractA 467-cm core (B94/3) from the Alta Babicora basin in the Chihuahuan Desert, northern Mexico (29°N, 108°W), documents lake-level and climate changes over the past ca. 65,000 yr. Chronological control is provided by four accelerator mass spectrometry 14C dates and five U-series dates on diatom silica. The core has been analyzed for magnetic susceptibility, loss-on-ignition, carbonate content, sediment chemistry and mineralogy, and pollen and diatom composition. The basin was occupied by a deep freshwater lake throughout the late Pleistocene which, based on shoreline evidence, was at least 19 m deeper than today. The lake shallowed after ca. 57,000 yr B.P. High variability typified the period between 54,600 and 38,000 yr B.P., probably with periodic desiccation and deflation. A deep-water lake was reestablished after 38,000 yr B.P. and persisted until ca. 29,000 yr B.P. Shallowing occurred through the last glacial maximum, although the lake was still deeper than at present. The Pleistocene–Holocene transition was marked by a distinctive change in the diatom flora. There is no diatom record for much of the Holocene, but other proxies indicate generally dry, stable catchment conditions. The Babicora record is more akin to those from the southwest United States than it is to Central America and northern South America. Wet conditions in the late Pleistocene are attributed to winter rainfall from midlatitudes in contrast to the modern, tropical, summer rainfall regime.

scholarly journals Implications of summer breeding frogs from Langebaanweg, South Africa: Regional climate evolution at 5.1 mya

2016 ◽  
Vol Volume 112 (Number 9/10) ◽  
Author(s):  
Thalassa Matthews ◽  
G. John Measey ◽  
David L. Roberts ◽  
◽  
◽  
...  
Keyword(s):  
South Africa ◽  
Southern Africa ◽  
West Coast ◽  
Regional Climate ◽  
Summer Rainfall ◽  
Rainfall Regime ◽  
The West ◽  
Winter Rainfall ◽  
Early Pliocene ◽  
Climate Evolution

Abstract No direct palaeoclimatic proxies have been available to indicate the seasonality or amount of rainfall on the west coast of southern Africa during the Early Pliocene. The Benguela Upwelling System (BUS) is today one of the factors responsible for the present-day aridity on the west coast of southern Africa. The initiation of the BUS is frequently linked to the entrenchment of aridity and the establishment of the current winter rainfall pattern on the west coast; however, marine proxies are inconclusive regarding the effects of past fluctuations in the BUS and sea surface temperatures on the rainfall regime. Neither the fossil evidence nor the fact that plants using the C3 photosynthetic pathway predominate at this time, provide direct evidence of winter rainfall at Langebaanweg. We challenge certain assumptions which are commonly made in the literature regarding the timing of inception of a winter rainfall regime on the west coast and the onset of aridity in the Langebaan region, and provide new evidence as to seasonality of rainfall at Langebaanweg in the Early Pliocene. Herein, the identification of frog species from the genus Ptychadena from Langebaanweg provides new and compelling evidence for a summer rainfall regime, or of at least significant summer rainfall, at 5.1 mya in the southwestern Cape of South Africa.

Structured methods for improving flow measurement accuracy in pipelines

2020 ◽  
pp. 30-35
Author(s):  
Gurami N. Akhobadze
Keyword(s):  
Flow Measurement ◽  
Measurement Accuracy ◽  
Directional Coupler ◽  
Signal To Noise Ratio ◽  
Scattered Wave ◽  
Orthogonal Polarization ◽  
Flow Sensors ◽  
Information Signal ◽  
Mass Flows ◽  
Processing Device

In the age of digital transformation of production processes in industry and science the development and design of intelligent flow sensors for granular and liquid substances transferring through pipelines becomes more important. With this in view new approaches for improving the accuracy of microwave flowmeters are proposed. Taking into account the characteristics ofelectromagnetic waves propagating through a pipeline, a wave scattered by inhomogeneities of the controlled medium is analyzed. Features of the transformation of the polarized scattered wave limiting the geometric dimensions of the pipeline and optimizing the values of the useful scattered signal are revealed. Expediency of collection of the information signal with orthogonal polarization of the scattered wave and through a directional coupler is substantiated. The method of estimating the measurement accuracy with reference to the signal-to-noise ratio at the input of the processing device is given. The research results can be used in cryogenic machine engineering to measure volume and mass flows of liquid cryogenic products.

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