Research Articles (DES)

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14C dating of organic residue and carbonate from stromatolites in Etosha Pan, Namibia: 14C reservoir effect, correction of published ages, and evidence of >8-m-deep lake during the late pleistocene
(2013) Hipondoka, Martin; Brook, George A.; Railsback, Bruce L.; Marais, Eugene
Lacustrine stromatolites are layered accretionary structures formed in shallow water by cyanobacteria. They are a precise indicator of high lake limits and their morphology and structure provide an insight into paleoenvironments of the time. Previous research on lacustrine stromatolites from Etosha Pan in Namibia based on radiocarbon ages of carbonates were close to the limit of the method and did not account for any possible 14C reservoir effect. The ages were used to suggest that the basin was not extensively flooded during the last 40,000 yr. To assess the reservoir effect, the age characteristics of a stromatolite from Poacher’s Point were investigated by 14C dating both carbonate and organic residue from samples at different depths in the deposit. The ~15-cm-diameter stromatolite was separated into 12 zones from the center to the edge and block samples were cut from each zone; the carbonate and residual organic residue were dated separately. The carbonate ages ranged from 34,700 to 24,700 14C yr BP and the organic ages from 15,700 to 2500 14C yr BP. Ages generally increased with increasing distance from the surface of the deposit. We believe that the organic ages are an accurate estimate of the stromatolite’s age, while the much older carbonate ages reflect incorporation of old carbon from limestone bedrock and ancient calcrete introduced by stream and spring flow. Excluding the 2 oldest organic ages (15,700 and 13,600 14C yr BP), which may reflect contamination by older organic material washed into the lake during flooding, a linear regression relationship between carbonate and organic ages indicates that the reservoir effect on carbonate ranges up to ~24,000 14C yr BP but decreases slightly as the true age of the deposit increases. This regression relationship was used to correct 2 finite carbonate ages for stromatolites from Pelican Island obtained in the early 1980s, which together with our new organic age for a stromatolite from Andoni Bay, document a >8-m-deep lake in Etosha Pan during the Late Pleistocene, at and prior to ~34,000–26,000 cal yr BP. The organic carbon ages from the Poacher’s Point stromatolite suggest prolonged lacustrine conditions during the early to middle Holocene (8000–6600 cal yr BP) but not to the extent seen during the Late Pleistocene
A CFD study of wind patterns over a desert dune and the effect on seed dispersion
(Springer Netherlands, 2012) Joubert, Eugene C.; Harms, Thomas M.; Muller, Annethea A.; Hipondoka, Martin; Henschel, Joe R.
In the Namib Desert seed distribution is greatly influenced by wind patterns. Existing literature regarding wind patterns over dunes focuses on two-dimensional simulations of flow over simplified dune structures. The three-dimensional geometries of the sand dunes suggests far more complex flow features exist, which are not captured by two-dimensional simulations. Computational fluid dynamics (CFD) was used to reproduce the three-dimensional near surface wind patterns around a dune with the aim to learn more about seed distribution. Field work included terrain mapping, wind speed, direction and temperature metering. The CFD results show the expected two-dimensional flow features of high pressure at the dune toe, low pressure at the crest and flow acceleration up windward slope. Also observed are some three-dimensional flow features such as a spiral vortex near the crest and transverse flow due to crest-line curvature of the dune. It was also observed how the wall shear stress differs due to the three-dimensional shape of the dune. The wall shear stress suggests that seed accumulation is more likely to occur behind trailing (down-wind) crest edges. Particle tracking showed how seeds tend to move over the dune crest and recirculate towards the crest on the lee-side. The study showed that adding the third dimension makes the simulations more complex, adds to computational requirements and increases simulation time but also provides vital flow information which is not possible with two-dimensional simulations.
Chronology of sand ridges and the Late Quaternary evolution of the Etosha Pan, Namibia
(2014) Hipondoka, Martin; Mauz, B.; Kempf, Jurgen; Packman, S.; Chiverrell, R.C.; Bloemendal, J.
Etosha Pan, situated at the southern border of tropical Africa, is a vast endorheic plain in Namibia's semi-arid north. The most recent studies agree that the pan was the floor of a former lake with varying water levels. Here we explored this idea further by investigating the link between lake-level change and records of late Pleistocene and Holocene climate change. The varying lake levels were inferred through sediment analysis and optical dating of sand deposits that form ridges parallel to the current shore along the northern and western margins of the pan. Our results support the view that the sand ridges are shoreline deposits of an evaporitic lake. The ridges result from the interplay between intermittent river discharge and riverine sediment supply from the north, prevailing north-easterly wind and shore-parallel waves. Therefore they are a proxy for former levels of a perennial lake. We infer higher levels during the late Pleistocene and a drastic drop shortly after 10 ka. Since around 8 ka Etosha Pan was covered by a shallow water body. This lake water-level reconstruction is not in line with the histories of ITCZ migration and strength of Benguela current upwelling. We confirm that the linkages between the evolution of the Etosha Pan and the climate mechanisms driving hydrological changes in subtropical southwest Africa are poorly resolved and need further investigation.
Etosha Pan: Dust source characteristics and emission controls
(Southern African Association of Geomorphologists, 2012) Bryant, R.G.; Eckardt, F.G.; Vickery, K.; Hipondoka, Martin; Murray, J.E.; Abrahams, D.
Fossil evidence for perennial lake conditions during the Holocene at Etosha Pan, Namibia
(2006) Hipondoka, Martin; Jousse, H.; Kempf, Jurgen; Busche, Detlef
ETOSHA PAN, A LARGE (4760km2), ENDORheic depression situated in north-central Namibia, has been claimed to be essentially a wind-deflated landform. The pan was assumed by some researchers to have developed under persistent semi-arid conditions,which were alleged to have prevailed in the region for at least the last 140 000 years. Recent field evidence points to the contrary. This evidence includes a significant number of fossils belonging to, amongst others, semi-aquatic antelopes such as sitatunga, which are diagnostically indicative of perennial lake conditions in the area. These species have previously never been reported from Etosha National Park, either as fossils or extant. Here we indicate the significance of these findings and their implications for the palaeo-environment of the Etosha region.
The potential of rainwater harvesting: A case of the City of Windhoek, Namibia
(2013) Nashima, Festus P.; Hipondoka, Martin; Iiyambo, Inekela; Hambia, Johannes
Windhoek, Namibia’s capital has experience for more than 25 years of novel approaches in integrated water management largely driven by the scarcity of water in the area. Notably absent in their approaches how ever, is the rooftop rainwater harvesting which is regarded as one of the viable alternative sources of water for domestic use. This paper assesses the potential economic benefits for rooftop rainwater harvesting for the City of Windhoek. Th e rooftop areas from four representative formal suburbs of Okuryangava ( low income) in the north, Academia (middle income) in the south-central, Pioneers Park (middle income) in the south-west and Ludwigsdorf (high income) in the east, were estimated from high resolution satellite images captured from Google Earth. These estimates were used to extrapolate for the potential amount of rainwater that can be harvested in an average rainy season (i.e. December to April) in the study area. The estimated harvestable amount for each residential area was developed using a simple model that incorporates total rooftop area and estimated rainwater. The derived figure was then expressed in terms of cost per unit prices charged by the City of Windhoek. Pioneers Park attests to have the highest (134 m3) potential harvestable rainwater per household, while Okuryangava is estimated to harvest the least amount of 36 m3 per raining period. Given the high density of erven, however, Okuryangava has a potential to harvest approximately 920484 m3 of water per hectare, ranking this suburb second after Academia, which stands at 1120716 m3. This is a significant amount of water effectively taken from rainwater rooftop that could also provide justifiable saving to residents if used instead of tap water. It is therefore recommended that the City of Windhoek actively promotes rooftop rainwater harvesting for the benefit of residents and also as a measure to reduce storm-water runoff due to urban development.
Sand-ridge dynamics and the evolution of the Etosha Pan, Namibia
(2012) Hipondoka, Martin; Mauz, B.; Packman, S.; Bloemendal, J.; Kempf, Jurgen; Chiverrell, R.C.
Source of lunette dune sediments: A geomorphic terrain analysis approach in Etosha National Park, Namibia
(2004) Hipondoka, Martin; Busche, Detlef; Kempf, Jurgen
The presence of so-called lunette dunes in the lee of pans in northern Namibia sprouted a discussion on the formation of the shallow basins related to them. These lunette dunes are made up of larger particles than those found in the pans, from which the sediments are thought to have originated. At Etosha Pan, this contradiction is compounded by the fact that the dunes are found on the northwestern and western side of the pan, whilst the prevailing dominant wind, believed to have played a formative role in their development, blows from the northeast. Ancillary data, in concert with high-resolution, multi-date satellite imagery were examined through the prism of geomorphic terrain analysis. The resultant indicators unequivocally point to the Ekuma delta, on the northwestern rim of the pan, in direct opposition to the pan floor proper, as the source of these dune sediments. It is therefore probable that coarser sediments found on the lee side of similar pans can be similarly explained as originating from former inlet deposition and not from wind excavation in the process of pan initiation as popularly held.
Spatio-temporal characterization of surface water dynamics with Landsat in endorheic Cuvelai-Etosha Basin (1990–2021)
(Elsevier, 2022) Hamunyela, Eliakim; Hipondoka, Martin; Persendt, Frans; Nghiyalwa, Hilma Sevalia; Thomas, Chris; Matengu, Kenneth
Socio-economic damages caused by extreme floods have been increasing rapidly in recent years, mainly driven by changes in the climate and modulated by increasing human population in deltic areas and floodplains. The Cuvelai-Etosha Basin (CEB) in southern Africa, covering southern Angola and northern Namibia, experiences socially and economically devastating extreme floods. Yet, accurate information on past and current surface water changes and dynamics is lacking. Here, we estimate and map the surface water extents in the CEB and its surroundings (CEB + S) for 32 years (1990–2021) from Landsat data using random forest models to provide long-term baseline information on surface water changes and dynamics. Based on the reference data, a total of 15,677 ± 1080 km2 have been inundated by surface water in the CEB + S during 1990–2021. This extent was accurately mapped by our local water extent product (mapped area = 16,273 km2, user’s accuracy = 91.5 ± 2.5%, producer’s accuracy = 91.1 ± 6%). With user’s and producer’s accuracy of 91%, our overall water extent provides the first most accurate long-term baseline information on surface water inundation in CEB + S necessary for local spatial planning processes to minimise future negative impacts of floods in the basin. Interannual variability of surface water extent is, however, high, with water extent ranging from 520.8 ± 375.7 km2 to 12372.3 ± 1154.7 km2 during the 1990–2021 period. The largest annual water extents (>10,000 km2) were recorded in 2006, 2008, 2009, 2011, and 2017, whereas the smallest extents (<1000 km2) were recorded in 1992 and 2019. We found that over 40% of the area inundated in the CEB + S during 1990–2021 was inundated less than 9 times. With human population increasing rapidly in the CEB + S, rarely inundated areas with short water residence could become a prime target for human settlements, which may lead to huge socio-economic damages during extreme floods if no preventive measures are put in place. Globally available surface water maps from the Global Land Analysis and Discovery (GLAD) and European Commission’s Joint Research Centre (JRC) did not provide realistic surface water extent for CEB + S, especially during years with extreme floods. Therefore, locally adopted product for operational monitoring of surface water in the CEB + S is needed to provide accurate information for informing spatial planning processes and surface water resource management strategies in this endorheic basin and help minimise future negative impacts of floods.

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