Air humidity and lake delta O-18 during the latest Paleocene-earliest Eocene in France from recent and fossil fresh-water and marine gastropod delta O-18, delta C-13, and Sr-87/Sr-86

Detailed isotopic (delta O-18, delta C-13, Sr-87/Sr-86) analyses have been performed on aragonitic fresh-water, brackish-water, and marine gastropod s hells of latest Paleocene-earliest Eocene age from northwestern Europe. Fre sh-water shells (e,g,, Viviparus, Lymnaea) from Sparnacian deposits in the Paris basin show relatively high delta O-18 values, in the range -4 parts p er thousand to -0.1 parts per thousand. Large intrashell delta O-18 variabi lity, typically 3 parts per thousand, is consistent with significant season al variation in precipitation and/or temperature. We also present intrashel l isotopic profiles for 22 recent fresh-water shells, mainly Viviparidae, r epresenting the major middle- to low-latitude climate zones (e,g,, Sweden, France, Portugal, Lake Chad, Ceylon, Gambia, Congo, Lake Victoria, New Guin ea). Distinct isotopic patterns, reflecting humidity and temperature, chara cterize each of the climate zones. Comparing the results for recent and fos sil shells suggests that the climate in northern France during Sparnacian t ime was warm subtropical with a pronounced seasonal drought, The delta O-18 composition of Sparnacian lake water has been estimated from the fossil fr esh-water shell delta O-18 and by using seasonal temperatures derived from delta O-18 profiles of fully marine shells. The best estimate of the delta O-18 composition of Sparnacian lake water (compared with Eocene mean ocean water) is -1 parts per thousand. This is consistent with paleorain delta O- 18 values of -3 parts per thousand, to -5 parts per thousand, similar to pr esent mean rain delta O-18 (standard mean ocean water) values close to -4 p arts per thousand in Portugal at similar to 40 degreesN, the paleolatitude of the Paris basin during earliest Eocene time. The evaporated nature of Sp arnacian lake water contradicts hypotheses of globally equable humid condit ions in the warm early Eocene and instead suggests that dry subtropical hig hs occurred over the eastern parts of the oceans, similar to today. The res ults of this study demonstrate the potential of fossil fresh-water carbonat es to reconstruct the development of subtropical highs and Hadley cell circ ulation in the past.