Contents lists available at ScienceDirect Journal of Archaeological Science: Reports journal homepage: www.elsevier.com/locate/jasrep The effects of repeated wet-dry cycles as a component of bone weathering James T. Pokines a,b, ⁎ , Katie Faillace a , Jacqueline Berger a , Danea Pirtle a , Megan Sharpe a , Ashley Curtis a , Kimberly Lombardi a , James Admans a a Forensic Anthropology Program, Boston University School of Medicine, Department of Anatomy and Neurobiology, 72 East Concord Street, L1004, Boston, MA 02118, USA b Office of the Chief Medical Examiner, 720 Albany Street, Boston, MA 02118, USA ARTICLE INFO Keywords: Taphonomy Bone weathering Wet-dry cycles ABSTRACT Subaerial weathering is a taphonomic process that affects many archaeological and paleontological bone as- semblages 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. 1. Introduction Subaerial weathering is a taphonomic process whereby bones ex- posed on the surface undergo gradual breakdown, including bleaching, loss of organic content, and cracking and flaking, leading to eventual splintering apart into fragments (Behrensmeyer, 1978; Miller, 1975). These changes generally take years, and their timing has been de- monstrated to vary greatly by environment (Andrews and Armour- Chelu, 1998; Andrews and Cook, 1985; Andrews and Whybrow, 2005; Junod and Pokines, 2014; Miller, 2009, 2011, 2012; Pokines and Ames, 2015; Tappen, 1992, 1994, 1995), indicating that variables including moisture regime may play a large role. The weathering processes in- clude the overall breakdown of the organic content/grease, leaving bone more brittle and thus more prone to fracturing (Collins et al., 2002; Symes et al., 2014). The loss of grease content also will affect the ability of transient water content to bring about weathering or related changes, including recrystallization (Prassack, 2011; Trueman et al., 2004), demineralization through acidic dissolution, and expansion and contraction caused by wet-dry cycles. Loss of organic content and the incidence of UV light cause bone bleaching (Beary, 2005). Crack propagation often parallels the osteon structure (Tappen and Peske, 1970), following the weaker planes in the bone, and cracking may be enhanced by thermal expansion-contraction from daily sun exposure (Conard et al., 2008). Cracking also is caused in part by freeze-thaw cycles, where expanding ice crystals force the bone apart and form cracks (Guadelli, 2008, 2015; Guadelli and Ozouf, 1994; Mallye et al., 2009; Pokines et al., 2016; Texier et al., 1998; Todisco and Monchot, 2008). With the exception of freeze-thaw cycles, the physical and chemical mechanisms of bone weathering have undergone relatively little research in settings that isolated the effects of these different processes. The present research examines one environmental process, wet-dry cycles, and their cumulative effect upon bone macroscopic characteristics (surface cracking) as a component of the overall weathering process. The six-stage system of Behrensmeyer (1978) is standard in os- teology/taphonomy to describe weathering changes in megafaunal (average adult body mass > 5 kg) bones. These stages start at weath- ering stage 0 (WS 0), where the bone is unweathered and displays no fine surface cracking. At WS 1, the bone has begun to display fine surface cracking, and the surface starts to delaminate and flake away in https://doi.org/10.1016/j.jasrep.2017.11.025 Received 19 July 2017; Received in revised form 18 November 2017; Accepted 20 November 2017 ⁎ Corresponding author at: Forensic Anthropology Program, Boston University School of Medicine, Department of Anatomy and Neurobiology, 72 East Concord Street, L1004, Boston, MA 02118, USA. E-mail address: jpokines@bu.edu (J.T. Pokines). Journal of Archaeological Science: Reports 17 (2018) 433–441 2352-409X/ © 2017 Elsevier Ltd. All rights reserved. T