GROUNDWATER FLOW SYSTEM RESPONSES TO PALEOCLIMATIC CHANGES DURING LATE PLEISTOCENE AND HOLOCENE, BLACK MESA BASIN, ARIZONA

New noble gas data confirm the paleorecharge and paleo-groundwater flow pattern reconstruction for the past 31 k.y. for the N aquifer in the Black Mesa basin, Arizona. Paleorecharge rates varied significantly in late Pleistocene and Holocene, which were estimated, independently, by numerical simulation of groundwater flow and ¹⁴C transport and Chloride Mass Balance on Cl and ³⁶Cl. The temporal variations correlate well with paleoclimate changes delineated by our noble gas data of paleo-recharge temperatures as well as by other climate proxies in the Four Corner area. Recharge rates were two to three times higher than today during the late Wisconsin when inferred annual mean temperatures were 5-6 ^oC cooler, but about 50% lower during early to mid-Holocene when inferred summer temperatures were 2-4 ^oC warmer. The pulse of the highest estimated recharge between 14 and 17 ka coincided with the northward migration of the southern branch of the split jet stream in late Pleistocene, and is associated with ~300% excess Δ Ne. The existence of independent estimates of water table levels and recharge rates from ¹⁴C and ³⁶Cl/Cl data-based methods allows us to evaluate excess Ne as a proxy for groundwater water table fluctuations. Model simulations suggest that thousands of years are required for water levels to fully respond to the changes in climate and recharge, and that water levels fluctuated from 60 m higher to 6 m lower than today.