Karoo Desert Research Articles

Towards New Proximities: A Conversation on Photographic Encounters Between Southern Africa and Mexico

This dialogue between South African photographer Jo Ractliffe and Mexican art historian Daniela Montelongo draws upon conversations initiated during Ractliffe’s exhibition Hay tiempo, no hay tiempo at the Centro Fotográfico Manuel Álvarez Bravo in Oaxaca, Mexico, in November 2018. The exhibition formed part of Hacer Noche, a project exploring rituals and practices around death and the afterlife in artworks from southern Africa. Hacer Noche also included artists’ residencies, workshops and a conference that aimed to connect guest artists, curators, art historians and the broader Oaxacan community. Hay tiempo, no hay tiempo comprised photographs taken from Ractliffe’s negative files from the mid 1980s to the present, and included images that have been widely circulated in exhibitions and books, alongside previously unpublished images. When conceptualising the Hacer Noche exhibition, Ractliffe proposed Manuel Álvarez Bravo’s (Mexico City, 1902–2002) photograph Striking Worker, Assassinated (1934) as the starting point for selecting works. In so doing, Ractliffe sought a fluid, associative process, engaging individual images, rather than a particular photo-essay. Unhinged from their originating intentions, groupings and contexts, the images could be encountered in new and unexpected proximities, not least in their physical relocation from southern Africa to Mexico for the exhibition. A year later, in August 2019, Ractliffe and Montelongo resumed their exchange during a research trip to South Africa undertaken by Montelongo. They continued their conversation during a road trip across the Western Cape, from the coast, across the mountains and into the Karoo desert. Reflecting on these two transnational encounters and their attendant discussions in the aftermath of a global pandemic generated a reconsideration of the role of photography in mediating such encounters, especially when international travel can no longer be taken for granted and communication faces a profound restructuring.

‘If the desert could speak’: The karretjiemense of the Karoo in My Children Have Faces

Both film-maker Timothy Gabb and anthropologist Michael de Jongh have noticed the disappearance of the karretjiemense, a marginalised people who travel the Karoo desert using donkey carts or karretjies. Having run a petrol station in Prince Albert in the Eastern Cape, author Carol Campbell’s debut novel My Children Have Faces features a family of karretjiemense who wander the Karoo desert and in real ways ‘belong to’ it. This belonging is reflected in the novel through the ‘interchanges and interconnections between [their] human corporeality and the more-than-human’, which ecocritic Stacey Alaimo calls ‘transcorporeality’. It is an engagement that enables the resilience of the tight-knit family to the vulnerabilities of living in the desert in order to escape the pursuit of the murderous Miskiet. Campbell reflects this transcorporeality, fictionally, through naming, through animal imagery and through the motifs of smell and of movement. She also registers how transcorporeality dwindles and family unity breaks down once they leave the desert. Having sold their donkeys and killed Miskiet, they apply for the formal identities they have lacked and head towards a settled life in the village very different to the nomadic life that has defined them up to now.Contribution: This article adds to the emerging field of ecocriticism in South Africa by using the concept of ‘transcorporeality’ to explore the connections between the karretjiemense and the desert Karoo environment in Carol Campbell’s My Children Have Faces (2013).

Physiological Plasticity as a Strategy to Cope with Harsh Climatic Conditions: Ecophysiological Meta-Analysis of the Cosmopolitan Moss Ceratodon purpureus in the Southern Hemisphere.

Determining the physiological tolerance ranges of species is necessary to comprehend the limits of their responsiveness under strong abiotic pressures. For this purpose, the cosmopolitan moss Ceratodon purpureus (Hedw.) Brid. is a good model due to its wide geographical distribution throughout different biomes and habitats. In order to disentangle how this species copes with stresses such as extreme temperatures and high radiation, we designed a meta-analysis by including the main photosynthetic traits obtained by gas exchange measurements in three contrasting habitats from the Southern Hemisphere. Our findings highlight that traits such as respiration homeostasis, modulation of the photosynthetic efficiency, adjustment of the optimal temperature, and switching between shade and sun-adapted forms, which are crucial in determining the responsiveness of this species. In fact, these ecophysiological traits are in concordance with the climatic particularities of each habitat. Furthermore, the photosynthetic trends found in our study point out how different Livingston Island (Maritime Antarctica) and Granite Harbour (Continental Antarctica) are for plant life, while the population from the Succulent Karoo Desert (South Africa) shares traits with both Antarctic regions. Altogether, the study highlights the high resilience of C. purpureus under abrupt climate changes and opens new perspectives about the wide spectrum of physiological responses of cryptogams to cope with climate change scenarios.

Search and identification of transient and variable radio sources using MeerKAT observations: a case study on the MAXI J1820+070 field

ABSTRACT Many transient and variable sources detected at multiple wavelengths are also observed to vary at radio frequencies. However, these samples are typically biased towards sources that are initially detected in wide-field optical, X-ray, or gamma-ray surveys. Many sources that are insufficiently bright at higher frequencies are therefore missed, leading to potential gaps in our knowledge of these sources and missing populations that are not detectable in optical, X-rays, or gamma-rays. Taking advantage of new state-of-the-art radio facilities that provide high-quality wide-field images with fast survey speeds, we can now conduct unbiased surveys for transient and variable sources at radio frequencies. In this paper, we present an unbiased survey using observations obtained by MeerKAT, a mid-frequency (∼GHz) radio array in South Africa’s Karoo Desert. The observations used were obtained as part of a weekly monitoring campaign for X-ray binaries (XRBs) and we focus on the field of MAXI J1820+070. We develop methods to efficiently filter transient and variable candidates that can be directly applied to other data sets. In addition to MAXI J1820+070, we identify four likely active galactic nuclei, one source that could be a Galactic source (pulsar or quiescent XRB) or an AGN, and one variable pulsar. No transient sources, defined as being undetected in deep images, were identified leading to a transient surface density of <3.7 × 10−2 deg−2 at a sensitivity of 1 mJy on time-scales of 1 week at 1.4 GHz.

MID-Radio Telescope, Single Pixel Feed Packages for the Square Kilometer Array: An Overview

The Square Kilometre Array (SKA) project is an international effort to build the world s largest radio telescope, enabling science with unprecedented detail and survey speed. The project spans over a decade and is now at a mature stage, ready to enter the construction and integration phase. In the fully deployed state, the MID-Telescope consists of a 150-km diameter array of offset Gregorian antennas installed in the radio quiet zone of the Karoo desert (South Africa). Each antenna is equipped with three feed packages, that are precision positioned in the sub-reflector focus by a feed indexer platform. The total observational bandwidth (0.35-15.4GHz) is segmented into seven bands. Band 1 (0.35-1.05GHz) and Band 2 (0.95-1.76GHz) are implemented as individual feed packages. The remaining five bands (Bands 3, 4, 5a, 5b, and 6) are combined in a single feed package. Initially only Band 5a (4.6-8.5GHz) and Band 5b (8.3-15.4GHz) will be installed. This paper provides an overview of recent progress on design, test and integration of each feed package as well as project and science goals, timeline and path to construction.

Developing a Real-Time Processing System for HERA

The Hydrogen Epoch of Reionization Array (HERA) is a radio telescope in the Karoo desert of South Africa endeavoring to observe Cosmic Dawn and the Epoch of Reionization. When fully constructed, it will consist of 350 antennas and generate over 60 terabytes (TB) of data each night. In order to keep pace with the relatively large rate of data, we have developed the real-time processing (RTP) system for HERA. The RTP is responsible for inspecting data for acceptable levels of quality and flagging unusable data, as well as providing an initial calibration solution. The RTP system consists of the pipeline management system, called the hera_opm package, and the data management system, called the librarian. Though the systems have been developed in the context of analyzing HERA data, they feature public and open source software, and have been designed to be adapted and used in other contexts as necessary.

POSTCOLONIAL LITERATURE AND LAND ART IN THE ANTHROPOCENE

This paper analyses the relationships between literature and land art, in a comparative and cooperative perspective. A feeble monument in Kenya, erected by Karen Blixen and dedicated to her beloved, finds echoes in a paper installation by Canadian artist Marlene Creates. Both monuments present a strong gender signature. J.M. Coetzee's novel In the Heart of the Country (1976) includes writing with stones in the Karoo desert not dissimilarly from what children do in a popular game, where they draw with stones. Finally, Margaret Atwood provides a memorable example of bioart and ecoart in her novel The Year of the Flood (2009), where insects co-participate in the artistic project, right as South African artist William Kentridge managed to produce drawings and a film with ants. All these examples show a cooperative approach to art between humans and non-humans, be they rocks, insects, bones.

The hydrogen epoch of reionization array dish III: measuring chromaticity of prototype element with reflectometry

The experimental efforts to detect the redshifted 21 cm signal from the Epoch of Reionization (EoR) are limited predominantly by the chromatic instrumental systematic effect. The delay spectrum methodology for 21 cm power spectrum measurements brought new attention to the critical impact of an antenna's chromaticity on the viability of making this measurement. This methodology established a straightforward relationship between time-domain response of an instrument and the power spectrum modes accessible to a 21 cm EoR experiment. We examine the performance of a prototype of the Hydrogen Epoch of Reionization Array (HERA) array element that is currently observing in Karoo desert, South Africa. We present a mathematical framework to derive the beam integrated frequency response of a HERA prototype element in reception from the return loss measurements between 100-200 MHz and determined the extent of additional foreground contamination in the delay space. The measurement reveals excess spectral structures in comparison to the simulation studies of the HERA element. Combined with the HERA data analysis pipeline that incorporates inverse covariance weighting in optimal quadratic estimation of power spectrum, we find that in spite of its departure from the simulated response, HERA prototype element satisfies the necessary criteria posed by the foreground attenuation limits and potentially can measure the power spectrum at spatial modes as low as $k_{\parallel} > 0.1h$~Mpc$^{-1}$. The work highlights a straightforward method for directly measuring an instrument response and assessing its impact on 21 cm EoR power spectrum measurements for future experiments that will use reflector-type antenna.

Reproductive ecology of Aloe plicatilis, a fynbos tree aloe endemic to the Cape Winelands, South Africa

While the pollination ecology of many Aloe species is well-documented, knowledge on aloe seed ecology, and hence aloe reproductive ecology in its entirety is limited. The aim of this study was to investigate the reproductive ecology of Aloe plicatilis, a Cape fynbos tree aloe endemic to the Cape Winelands, South Africa. Results from a pollinator exclusion experiment conducted at an A. plicatilis population on Paarl mountain suggests pollination primarily by insects, although bird visitation significantly increased seed set/fruit indicating possible co-pollination with insects. The species' long-tubed flowers and production of concentrated nectar, with observations of malachite sunbirds as the most common avian visitors to A. plicatilis flowers indicate the importance of long-billed specialist avian nectarivores as floral visitors. Analysis of the relationship between plant size and inflorescence production for five populations combined revealed a significant, positive linear relationship between plant size and the logarithm of the number of inflorescences/plant. Natural fruit and seed set determined for three populations (1325, 27,930 and 251,616 seeds/population) suggests low reproductive output compared to several other Aloe species. The smallest (31 individuals) and least dense (75plants/ha) A. plicatilis population produced the lowest seed set/plant (128 seeds) and per population (1325 seeds), suggesting an Allee effect. Evaluation of seed dispersal potential showed that potential dispersal distances were approximately three times the canopy height; however, the occurrence of A. plicatilis on mountains isolated from more continuous mountain ranges on which the species also occurs suggests the possibility of long-distance dispersal by strong, gusty, summer winds. Soil seed bank samples collected from 13 populations yielded close to zero seedling emergence, indicating the absence of persistent seed banks. A. plicatilis seeds stored under ambient laboratory conditions for 3, 18 and 24months were germinated in an environmental control chamber and a laboratory. High percentage germination was recorded for 18- and 24-month-seed (86 and 80%, respectively), while germination of 3-month-old seeds was three times lower, suggesting the need for after-ripening. Germination of fresh and one-year-old seed under ambient nursery conditions at the Karoo Desert National Botanical Garden in Worcester yielded emergence percentages of 67 and 44%, respectively, and were therefore less successful than germination under more controlled conditions. This is the first known study to investigate the reproductive ecology of a tree aloe species and that of a Cape fynbos aloe. The study highlights the importance of further studies on aloe seed ecology, particularly for rare and threatened species.

Looking at the distant universe with the MeerKAT Array (LADUMA)

AbstractThe MeerKAT (64 x 13.5m dish radio interferometer) is South Africa's precursor instrument for the Square Kilometre Array (SKA), exploring dish design, instrumentation, and the characteristics of a Karoo desert site and is projected to be on sky in 2016. One of two top-priority, Key Projects is a single deep field, integrating for 5000 hours total with the aim to detect neutral atomic hydrogen through its 21 cm line emission out to redshift unity and beyond. This first truly deep HI survey will help constrain fueling models for galaxy assembly and evolution. It will measure the evolution of the cosmic neutral gas density and its distribution over galaxies over cosmic time, explore evolution of the gas in galaxies, measure the Tully-Fisher relation, measure OH maser counts, and address many more topics. Here we present the observing strategy and envisaged science case for this unique deep field, which encompasses the Chandra Deep Field-South (and the footprints of GOODS, GEMS and several other surveys) to produce a singular legacy multi-wavelength data-set.

Basking is affected by season and influences oxygen consumption in desert‐living striped mice

Small mammals that inhabit arid and temporally unproductive environments use several methods to conserve energy. Here, we investigate the energetic role of sun basking in striped mice Rhabdomys pumilio from the Succulent Karoo desert in South Africa. We observed mice in front of their nests for 140 h and recorded the time they spent basking during the non-breeding (dry) and the breeding (wet) seasons. We measured temperature changes in model mice to provide an indication of the heat that can be absorbed from the sun. Finally, we measured the oxygen consumption (V̇O2) of mice at their basking sites in the field both in the sun and in the shade. This was accomplished using a portable respirometry system with a metabolism chamber, which could be placed in and out of the sun. Observations showed that mice basked more often during the non-breeding than during the breeding season. During the former season, mice spent an average of 11.9 ± 1.1 min (se) in the morning and 5.5 ± 0.5 min in the afternoon per day basking. Within the metabolism chamber, V̇O2 decreased when the animal was in the sunshine compared with the shade. This effect occurred independent of the ambient temperature (Ta), indicating that a significant amount of radiant energy was absorbed from the sun. Basking may be an alternative to other energy-acquisition behaviours, such as foraging, which might be particularly useful at times when food is scarce.

Regulation of Activity in Desert‐Living Striped Mice: The Importance of Basking

AbstractDeserts represent challenging, energy restricted environments for small mammals, but offer ample exposure to sunlight that might be used for energy saving during basking. The Succulent Karoo desert in southern Africa is a seasonal environment with cold moist winters, followed by maximum food availability in spring and dry hot summers with food shortage. The striped mouse (Rhabdomys pumilio) from the Succulent Karoo desert is diurnal and its activity is influenced by photoperiod in captivity. However, in contrast to standardized laboratory conditions, it can be expected that several factors other than photoperiod influence its activity pattern in the field. We expected that striped mice behave in a way that indicates that they use basking to passively warm up and thus reduce endogenous energy expenditure. We studied activity and basking patterns in 56 social groups of striped mice for a period of 4 yr, comprising 1534 observation sessions at their nests. Mice generally started activity around the time the sun illuminated their nest and terminated activity when their nest was no longer sunlit, i.e. they were strictly diurnal. The onset of activity was delayed on days when ambient temperature was colder and when group sizes were smaller. During the breeding season when food availability was high, striped mice usually left the nest before it was sunlit without basking. Outside the breeding season, they emerged and basked in front of nests mainly after nests were sunlit. These findings concur with the view that striped mice trade‐off between active energy gain via foraging and passive energy acquisition by sun basking.

Rapid cold‐hardening in a Karoo beetle, Afrinus sp.

Abstract. In the insect rapid cold‐hardening response, survival at subzero temperatures is greatly improved by a brief pre‐exposure at a milder temperature. It is predicted that insects with minimal cold tolerance capabilities living in variable environments should use rapid cold‐hardening to survive sudden cold snaps. This is tested in Afrinus sp., a beetle that lives in an exposed habitat on rock outcrops in the Karoo Desert, South Africa, where microclimate temperatures drop infrequently to below freezing. Afrinus sp. shows a significant rapid cold‐hardening response: survival of a 2‐h exposure to −6.5 °C is much improved after pre‐exposure to −2 °C, to 0 °C with a 2‐h return to the rearing temperature, and to 40 °C, but not after pre‐exposure to 0 °C. Little is known about the mechanism of the rapid cold‐hardening response, although the data suggest that rapid cold‐hardening may be mediated via several different mechanisms.

Climatic variability and hemispheric differences in insect cold tolerance: support from southern Africa

SummaryInsects generally survive subzero temperatures by utilizing either freeze tolerance or freeze avoidance. Comparative analyses from a limited data set have indicated that freeze tolerance may be predominant among species at temperate latitudes in the southern hemisphere, while freeze avoidance dominates in the north.We investigated the cold tolerance strategies of cockroaches and beetles from cold regions in southern Africa, including the Cederberg mountains, the Karoo desert and the Drakensberg mountains.We found that 8 of 11 species are freeze tolerant.Overall, 77% of species investigated in the southern hemisphere (n = 27) were freeze tolerant, which is significantly different from the 29% (n = 258) in the north (P < 0·001).There are regular, unpredictable subzero temperature events in the southern African habitats; such variability appears to be a general feature of many cold habitats in the southern hemisphere, which may lead to the observed interhemispheric discrepancies in cold‐tolerance strategies.

Effects of Multispecies Clumping on Survival of Three Succulent Plant Species Translocated onto Mine Spoil in the Succulent Karoo Desert, South Africa

Abstract Salvaging from premining areas and translocation of succulent plants has been investigated for the revegetation of gypsiferous mine spoil in an arid region of South Africa. Given that facilitation effects are thought to outweigh competition effects in harsh environments, we hypothesized that the survival of translocated succulents would be higher when planted in multispecies clumps than alone and that the growth rate (measured as stem extension) and fruit‐set would be greater for plants in clumps than for those planted alone. Two leaf‐succulent species (Aridaria noctiflora ssp. noctiflora and Drosanthemum deciduum) and one stem‐succulent species (Psilocaulon dinteri) were salvaged from the area destined for mining and translocated onto the mine spoil. These plants were planted either in a multispecies clump of the three species together or alone. One year after translocation, 67% of the plants survived. It was also found that the succulents used in these experiments survived in higher numbers when planted alone. Due to the similar root morphology of D. deciduum and P. dinteri, they competed for resources instead of facilitating each other's establishment. The results were variable for each of the species used, and neither growth nor seed‐set was improved by clumping. These findings would also possibly vary from year to year with different abiotic conditions.

Aerosol optical depth over a remote semi-arid region of South Africa from spectral measurements of the daytime solar extinction and the nighttime stellar extinction

Spectral daytime aerosol optical depths have been measured at Sutherland, South Africa (32°22′S, 20°48′E), from January 1998 to November 1999. Sutherland is located in the semi-arid Karoo desert, approximately 400-km northeast from Cape Town. The site, remote from major sources of aerosols, hosts the South African Astronomical Observatory (SAAO), where nighttime stellar extinction is being measured. The comparison of daytime and nighttime measurements for the years 1998–1999 makes it possible to validate the astronomical dataset of aerosol optical depth ( τ a) dating back to 1991. The 1998 and 1999 annually averaged daytime τ a at 500 nm are 0.04±0.04 and 0.06±0.06, respectively. Half-day averages vary between 0.03 and 0.44, with peak values in August–September. This pronounced seasonality is linked to the biomass-burning season in the Southern Hemisphere. Smoke haze layers transported to Sutherland originated primarily on the African landmass at latitudes between 10° and 20°S and passed over Namibia and Angola. On one occasion, aerosols from fires in Brazil transported across the Atlantic Ocean were likely detected. The haze layers reaching Sutherland are therefore at least 2–3 days old. The spectral dependence of the aerosol optical depth for the smoke layers supports the bimodality of the volume size distribution for biomass burning aerosols. The accumulation mode has a volume modal diameter of 0.32 μm, consistent with the hypothesis of aged haze. The stellar measurements (1991–2001) show that, due to the eruption of Mt. Pinatubo, the atmospheric extinction depth at 550 nm in the years 1991–1993 increased by 33% with respect to the average value (0.14±0.03) for the period 1994–2001. Outside the Pinatubo event, extinction is largest in the period 1997–1999.