Hyperarid Core Research Articles

Endolithic Cyanobacteria in Halite Rocks from the Hyperarid Core of the Atacama Desert

In the driest parts of the Atacama Desert there are no visible life forms on soil or rock surfaces. The soil in this region contains only minute traces of bacteria distributed in patches, and conditions are too dry for cyanobacteria that live under translucent stones. Here we show that halite evaporite rocks from the driest part of the Atacama Desert are colonized by cyanobacteria. This colonization takes place just a few millimeters beneath the rock surface, occupying spaces among salt crystals. Our work reveals that these communities are composed of extremely resistant Chroococcidiopsis morphospecies of cyanobacteria and associated heterotrophic bacteria. This newly discovered endolithic environment is an extremely dry and, at the same time, saline microbial habitat. Photosynthetic microorganisms within dry evaporite rocks could be an important and previously unrecognized target for the search for life within our Solar System.

Holocene pollen spectra from Oyo, northwestern Sudan: problems of interpretation in a hyperarid environment

The Oyo site is in the hyperarid core of the eastern Sahara. A 3.4 m core of lake sediment yielded a continuous pollen record for the period 9 to 4.5 ka BP. The lower, regularly-laminated carbonate sediments (9-6 ka) show a pollen assemblage with the tropical taxa dominated by plants of Sudanian and Sahelian affinity, and the local taxa dominated by grass and Typha. The upper sediments (6-4.5 ka), grading from laminated carbonates to coarsely bedded and massive layers with aeolian sands, have reduced frequencies of Sudanian pollen taxa, and increases in Saharan types and sedge-dominated local pollen spectra. A possible vegetational reconstruction is a mosaic of savanna woodlands associated with groundwater-supported lakes and marshes between 9 and 6 ka BP, and sparser cover of steppe and semidesert communities between 6 and 4.5 ka BP as water tables dropped and hyperarid conditions were restored.

Holocene palaeoecology of the eastern Sahara; Selima Oasis

Buried lake sediments and tufa strandlines of Holocene age provide evidence of a former lake in the Selima Oasis depression, northwest Sudan, near the hyperarid core of the eastern Sahara Desert. A 1.6 m section through laminated lake muds and precipitates has been analysed in detail, and 30 radiocarbon dates, geochemical, sedimentological, diatom and pollen analyses indicate that the unit dated from approximately 8.4 ka BP to <6 ka BP, and was deposited in an environment that passed through one arid-to-humid-to-arid cycle. The arid episodes, from prior to 8.4 ka BP, and subsequent to 7 ka BP, are characterized by high CaCO 3 deposition, abundant diatom indicators of relatively high salinity and well developed periphytic communities, and pollen spectra dominated by desert-grassland indicators. A humid period centered on 8 ka BP is indicated by low CaCO 3 deposition, high organic rich mud and Al and Si oxide deposition, diatoms indicating a fresh, deep (20 m) lake, and a pollen assemblage with maximum values for Sahelo-Sudanian tree taxa suggesting a thorn tree and shrub savanna vegetational mosaic. This reconstruction, concordant with higher groundwater table and precipitation between 9.3 and 7 ka BP, agrees with palaeoecological inferences from other sites in North Africa.

Sediment and pollen evidence for an early to mid-Holocene humid period in the eastern Sahara

A major problem in the study of Holocene palaeoenvironments of the arid and wind-deflated Sahara is the low preservation potential of sediments from which a record of past climatic change can be established. Several indirect and imprecisely dated pieces of evidence have suggested humid episodes in the Holocene that may have supported more productive ecosystems and denser human populations than today. Searches for reliable proxy data on past climates, however, have failed to yield satisfactory results. We report here the discovery of buried lake muds in north-west Sudan, in the hyperarid core of the Eastern Sahara, which yield sedimentological and palynological data clearly interpretable as recording an early to mid-Holocene humid episode that supported a relatively-deep stratified lake surrounded by tropical savanna woodland vegetation.