Session: Warm Climates (Mid-Holocene, Last interglacial, Deep-time, Pliocene)
Author: Kyle Niezgoda / email@example.com / CEOAS, Oregon State University
Co-author: David Noone, CEOAS, Oregon State University;
Bronwen Konecky, CIRES, University of Colorado Boulder;
Despite successes in evaluating variability in precipitation patterns over the Holocene, significant uncertainties remain in interpretations of rain intensity, domain, and frequency from the diverse proxy records available. To reconcile point-wise proxies with spatially constrained circulation in the tropics, we used an AMIP-style run of the isotope-enabled Community Earth System Model (iCESM) to study the atmosphere and land components of the mid-Holocene (6.2 ka) hydrological cycle. We forced the simulation with SST and sea ice data from a fully-coupled simulation of the mid-Holocene using CCSM4, the predecessor to iCESM. All other forcings, including orbital parameters and greenhouse gas concentrations, were prescribed in accordance with PMIP4 specifications. Here, we present findings from the mid-Holocene simulation with respect to a control simulation of the pre-industrial period (PI). In agreement with previous studies, our simulation produced a wetter Sahara and Arabian Peninsula during the mid-Holocene. Using simulated water isotopes as a tracer of atmospheric transport processes, we found evidence that increased convergence of Atlantic evaporation was the primary source of increased moisture availability over the Sahara. In the maritime continent, precipitation stable isotope ratios were depleted relative to the PI, especially over land masses such as the Malaysian Peninsula, Sumatra, and Borneo. These depletions spatially correspond with lower troposphere water vapor isotope ratios more accurately than with precipitation rate. This provides evidence that moisture source was a more important factor for precipitation stable isotope ratios than, for instance, convection strength or precipitation amount. The results of this study allow for interpretations of proxy data in the context of the regional atmospheric hydrologic cycle rather than local first order variables such as precipitation amount and highlight the value of using direct simulation of isotope ratios when evaluating model performance.