| Summary: | This thesis presents late Cenozoic reconstructions of hydrogen isotope ratios in mean annual precipitation (dDMAP) from fossil plant waxes (n-C28 alkanoic acids) and hydrated volcanic glass shards in tephra that are archived in sediments in south-east Alaska and central Yukon. The leaf wax dDMAP estimates, spanning 6.2 to 2.8 Ma, are negative compared to modern which is unexpected for a warmer-than-modern climate as indicated by other proxies. Tephra-dDMAP estimates spanning 6.7 to 0.025 Ma are consistent with North Pacific sea surface temperatures, documenting low dDMAP values during the latest Miocene, peak values during high pCO2 warm intervals (~5 and 3 Ma), and transition to the lowest values on record in the Late Pleistocene. The difference in trends between the two dDMAP reconstructions most likely owes to an inappropriate net-fractionation assumption associated with the leaf wax proxy which remains one of the largest uncertainties in fossil leaf wax derived paleoclimate reconstructions. M.Sc.
|
|---|