Re con struct ing sea son al ity us ing d 18O in in cre men tal lay ers of hu man enamel: a test of the an a lyt i cal pro to col de vel oped for SHRIMP IIe/MC ion microprobe

Ox y gen iso tope anal y sis of den tal enamel is a pow er ful tool for palaeo bio logi cal and ar chae o log i cal stud ies as an in di ca tor of the pa ram e ters of phys i ol ogy, nat u ral en vi ron ment and hab i - tat pref er ences. A par tic u larly prom is ing ap proach is to mea - sure intra-tooth vari a tion (Ballase, 2003; Blaise and Balasse, 2011; Stevens et al., 2011), be cause teeth ac cu mu late a se - quence of sig nif i cant iso to pic in for ma tion cov er ing the short time of enamel bioapatite pro gres sive for ma tion. The ox y gen iso tope in ves ti ga tions of mam ma lian den tal enamel are based on a few gen eral as sump tions that: – the tis sues of or gan ism iso to pi cally equil i brated with their en vi ron ment will re flect the lo cal en vi ron men tal ox - y gen ra tio; – iso to pic sig na ture of skel e tal tis sues is di rectly re lated to that of the lo cal drink ing wa ter; – bioapatite, the main com po nent of teeth, is rel a tively most re sis tant to diagenetic pro cesses and pre serves its biogenic iso to pic sig na ture. Un der a con stant tem per a ture of 37°C of mam ma lian body, the ox y gen iso tope ra tio within den tal enamel es sen tially de - pends on the ox y gen iso tope com po si tion of wa ter in gested by the or gan ism. Be tween the wa ter and bioapatite, ox y gen iso - tope is frac tion ated in two steps, i.e. be tween en vi ron men tal and body wa ter and be tween body wa ter and bioapatite in teeth and bones (Bryant and Froelich, 1995). More over, the ox y gen iso tope com po si tion of enamel re mains fixed (i.e. enamel is no lon ger me tab o lized by the body), pro vid ing a nearly con tin u ous sta ble iso tope re cord that may cover a pe riod from months to years and that can be re tained for thou sands of years af ter fos - sil iza tion (Kohn and Cerling, 2002). The iso to pic anal y sis of enamel has been used to study sea sonal di etary hab its of both mod ern and ar chae o log i cal fauna (Fricke and O’Neil, 1996; Stu art-Wil liams and Schwarcz, 1997; Fricke et al., 1998; Balasse, 2003; Blaise and Balasse, 2011; Stevens et al., 2011), how ever, se quen tial intra-tooth iso - to pic vari a tion has re ceived lit tle at ten tion in the stud ies of ar - chae o log i cal hu man re mains. The ox y gen iso to pic com po si tion of hu man bioapatite is re - lated to the iso to pic com po si tion of lo cal drink ing wa ter (Longi - nelli, 1984