Wind as a cooling agent: substrate temperatures are responsible for variable lithobiont-induced weathering patterns on west- and east-facing limestone bedrock of the Negev

Spatial variability in lithobiont-induced weathering patterns on desert rocks is aspect-dependent. While differences between the northern and southern aspects have been extensively studied, little is known concerning the differences between east-facing (EF) and west-facing (WF) aspects in deserts, including the Negev Desert. Whereas cobbles on both slopes are inhabited by endolithic lichens, epilithic lichens, which render the bedrock a smooth appearance, and free-living cyanobacteria, which give the bedrock a rugged microrelief, predominate on WF and EF bedrock, respectively. Following previous research that regarded dew as the principal factor that determines lithobiont distribution, measurements of radiation, temperature, wind and dew were carried out during 2008–2009 in the Negev Desert. The data indicated that albeit slightly higher midday surface temperatures that characterize WF surfaces (cobbles and bedrock), nocturnal temperatures on these surfaces were significantly lower, therefore facilitating higher dew condensation. High amounts of dew result from the relatively rapid drop in temperatures (14:00–20:00) due to the afternoon northwesterly sea-breeze wind (with a cooling rate of the WF bedrock being 52.9% higher than on EF bedrock, 2.6 °C h⁻¹ in comparison to only 1.7 °C h⁻¹), and facilitate the growth of high-chlorophyll dew-fed (and rain-fed) epilithic lichens, which may act as bio-protectors on WF bedrock. Lack of condensation on EF bedrock results in turn in the growth of rain-fed free-living cyanobacteria, responsible for high rock dissolution and subsequently for a rugged microrelief. By affecting the nocturnal bedrock temperatures, wind acts as a cooling agent, impacting in turn the amount of dew, and subsequently lithobiont composition and weathering patterns in the Negev Desert.