Thursday, April 19, 2012, 4:30PM - 5:30PM
RL-1 room 269
The Mississippi River responded to the end of the last glacial cycle by changing its discharge and draiange basin area in response to the waning Laurentide Ice Sheet and adjusting its long profile to match isostatic adjustment and sea level change as it routed meltwater floods to the ocean. Earlier in the last glacial cycle, the Laurentide Ice Sheet crossed into Illinois and pushed the Upper Mississippi out of its former course (the modern Illinois River and Princeton valleys) and into its modern path down the Ancestral Iowa River. It then incised and later aggraded through this new reach in response to uplift and subsidence of the Laurentide forebulge, leaving a distinctive overdeepening in its bedrock long profile. In addition to these upstream geomorphic impacts, the Laurentide Ice Sheet expanded the Last Glacial Maximum Mississippi River drainage basin to double its current size and sent large volumes of meltwater through the Mississippi to the Gulf of Mexico. We model the combined evolution of the Mississippi drainage basin, the Laurentide Ice Sheet, and δ18O in the Gulf. The coincidence of large modeled and measured δ18O excursions at ~14.5 ka, during a period of rapid global sea level rise (~20 meters in 500 years) known as Meltwater Pulse 1A (MWP-1A), shows that the timing of the model is correct. However, the magnitude of the modeled δ18O excursion is much greater than the measured δ18O excursion, indicating that the widely-used ICE-5G global ice sheet reconstruction overestimates the Laurentide Ice Sheet contribution to this sea level rise by a factor of two and placing more weight behind a potential Antarctic meltwater source.
If time permits, Andy will also touch on development of field sensor systems, cliff retreat around the Grand Canyon, and/or maybe something to do with tectonics and model coupling.