Evidence of climatic changes is recorded in the salt content of the surface sediments in arid zones. In wetter periods airborne salts are removed downward by leaching to the groundwater, whereas in drier periods they accumulate. The period of salt accumulation in the loessial sediments of the northern Negev is about 10,000 yr. This period represents the recent aridification phase. The beginning of this stretch of time followed the last humid period in the region. Top paleo soil (calcic horizon) found in the region and dated 12,000 yr B.P. is an indicator of this humid period.