Phosphate delta O-18 determination of modern rodent teeth by direct laser fluorination: An appraisal of methodology and potential application to palaeoclimate reconstruction

A direct laser-fluorination (DLF) method is presented for phosphate delta O -18 analysis (mass 1 - 2 mg). The automated system heats samples in the pre sence of excess BrF5 using a 25 W CO2 laser, at 10.66 Am. delta O-18 ratios of the liberated O-2 were measured using a dual inlet Optima mass spectrom eter. As DLF measures whole apatite oxygen, non-phosphate bound oxygen must be removed by pre-treatment. Two methods were investigated: 1) heating to 1000 degreesC; and 2) beating to 400 degreesC followed by laser fusing. Met hod 2 is recommended as samples heated to 1000 degreesC showed evidence of oxygen exchange with atmospheric water. To validate the DLF method, and sho w the potential of rodent teeth in palaeoclimate reconstruction, modern rod ent teeth delta O-18 results from 2 species are presented (delta O-18(p)). Large inter- and intra-jaw heterogeneity indicates that single teeth cannot be used for palaeothermometry. However, the overall standard deviations we re low (Glis glis delta O-18(p) = + 10.4 +/- 0.7 parts per thousand n = 38 and Apodemus sylvaticus delta O-18(p) = + 14.4 +/- 1.3 parts per thousand n = 24). Using equations, derived from lab rodents, an ingested water value of -5.6 +/- 2.2 parts per thousand, was calculated for Apodemus sylvaticus, only - 1.3 parts per thousand lower than measured local water (-4.3 parts per thousand). This suggests that the phosphate delta O-18 of rodent teeth can be used as a proxy for palaeoclimate reconstruction. Copyright (C) 2001 Elsevier Science Ltd.