Oxygen isotopic determination of climatic variation using phosphate from beaver bone, tooth enamel, and dentine

The delta(18)O Of Canadian beaver (Castor canadensis) teeth should reflect variations in the isotopic composition of the water in which the beavers live, as their incisors grow rapidly and continuously. We observe seasonal variations in phosphate delta(18)O using samples of enamel taken along the length of single teeth. In the spring the delta(18)O of the enamel being deposited gradually declines, reflecting a retarded input of O-18 depleted winter water. After mid-year, enamel delta(18)O is higher than average (as represented by the delta(18)O of bone phosphate from the same animal) and passes through a maximum in late summer or early fall. Overall, the amplitude of seasonal excursions in enamel delta(18)O (4 parts per thousand) is much smaller than the expected summer-winter range in the delta(18)O of meteoric water (>10 parts per thousand). This is because hydrologic mixing processes, gradual admiring of environmental water with beaver body water, long term plant growth, and oxygen inputs of relatively constant Value (particularly atmospheric oxygen) tend to even out summer-winter differences in the delta(18)O of oxygen inputs to the beaver. The delta(18)O of bone from adult beavers was uniform at 11.9 +/- 0.5 parts per thousand over the study area. Analyses of a Sangamon age giant beaver (Castoroides ohioensis) incisor from Hopwood Farm, Illinois, show a slightly larger 5.5 parts per thousand seasonal cycle of delta(18)O with an average enamel delta(18)O of 18 parts per thousand. This suggests that average temperatures were warmer during the Sangamon than today and that seasonal temperature differences and/or relative humidity variations were larger. Copyright (C) 1997 Elsevier Science Ltd.