The effects of repeated wet-dry cycles as a component of bone weathering

Subaerial weathering is a taphonomic process that affects many archaeological and paleontological bone assemblages and is characterized by surface bleaching, loss of organic component, and progressive cracking and splintering of the bones. Although the mechanisms of such changes are not well understood, previous research has indicated that multiple processes contribute to weathering, including ultraviolet exposure, mineral leaching, mineral recrystallization, thermal expansion/contraction, freezing/thawing, and wetting/drying. In order to examine specifically how wetting/drying cycles can contribute to weathering, a laboratory sample (n = 100) of ribs, phalanges, vertebrae, and distal tibiae from white-tailed deer (Odocoileus virginianus) were subjected to 150 cycles of complete wetting and drying. The bone surfaces developed the characteristic surface cracking of subaerial weathering, with weathering stage 1 (WS 1) reached by 50 cycles on three bones. By 150 cycles, 27 bones had reached WS 1, with all but 15 bones exhibiting some kind of new cracking damage. One bone reached WS 2 by 125 cycles, with additional bones exhibiting beginning surface delamination. Wet-dry cycles in some environments are a potentially important component of the overall osseous subaerial weathering process and can on their own weather bone.