Timing of Sierra Nevadan stadial/interstadial variations from 15 to 56 ka

摘要

We summarize proxy evidence for stadial/interstadial variability recorded in sediments of three Great Basin lakes ? Owens, Mono, and Pyramid. These lakes lie along the eastern margin of the Sierra Nevada Ice Sheet and record environmental variability associated with it. We have applied new paleomagnetic secular variation measurements (PSV) to more carefully date the lake environmental variability. We have also used PSV to correlate the Great Basin environmental variability to North Atlantic records of oxygen isotope variability. We see evidence for 25 cycles in stadial/interstadial variability of the Great Basin lakes. These cycles can be correlated among all three lakes and are largely synchronous. We can also date the individual stadial and interstadial intervals present in the three lakes. They have an average cycle duration of 1430 ? 530 years. But, the cycle durations in all three lakes vary coherently from less than 1000 years to more than 2000 years between 20 and 56 ka. The variability in cycle duration suggests internal variability in the global climate engine as the cause of the observed variability rather than some (presumably more periodic) external forcing. We also correlate interstadial D/O cycles 2?16 recorded in the Atlantic Ocean region with interstadial intervals in the Great Basin lakes. These intervals are largely synchronous between the two regions. We see evidence of 5 more Great Basin lake interstadials synchronous with un-numbered light ?18O intervals in the Atlantic oxygen isotope stratigraphy. This suggests some kind of linkage between the North Atlantic and North Pacific climate variability during the period 15?56 ka.