Lacustrine 87 Sr/ 86 Sr as a tracer to reconstruct Milankovitch forcing of the Eocene hydrologic cycle

摘要: Abstract The Green River Formation (GRF) provides one of the premier paleoclimate archives Early Eocene Climatic Optimum (∼50 Ma), representing apex early Cenozoic greenhouse climate. Rhythmic lake-level variability expressed in GRF has inspired numerous hypotheses for behavior hydrologic cycle, including its linkage to astronomical forcing, solar variability, and El Nino Southern Oscillation (ENSO). However, lack sufficient proxy data document atmospheric water-mass transport geographic pattern evaporation/precipitation/runoff made it difficult discriminate between different models forcing. Variable 87Sr/86Sr ratios bedrock that encompass provide an opportunity reconstruct spatial expression cycle lake level. Here Sr isotope from Wilkins Peak Member, a rhythmic succession been demonstrated record Milankovitch forcing levels, indicate high levels reflect increased proportion runoff less radiogenic rocks west basin, eliminating number existing astronomical-forcing hypotheses. is consistent with change mean ENSO state, which predicted by climate be linked orbital-insolation. Thus, reveal coupling frequency (ENSO) low (astronomical) also predict existence sizable astronomically-forced alpine snowpack during last More broadly, this study demonstrates utility as powerful tool reconstructing deep-time cycle.