Mechanisms of Tropical Pacific Climate Change During the Holocene

• Main Author: Atwood, Alyssa
• Other Authors: Sachs, Julian P
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: ENSO; Holocene; ITCZ; paleoclimate; tropical Pacific; Paleoclimate science; Climate change; oceanography; Arctic; Pacific; albedo; North Atlantic; Sea ice
• Online Access: http://hdl.handle.net/1773/34109

Thesis (Ph.D.)--University of Washington, 2015 A novel set of hydroclimate reconstructions is presented from the eastern equatorial Pacific that spans the last 9100 years. Past changes in total climatological rainfall and rainfall associated with El Niño events were reconstructed using the sedimentary distribution, accumulation rate, and hydrogen isotope composition of four lipid biomarkers in the sediment of El Junco Lake, San Cristóbal Island. Possible mechanisms of the multi-decadal to millennial scale rainfall variations inferred at El Junco Lake are evaluated in light of tropical hydroclimate and global climate reconstructions through the Holocene. Tropical hydroclimate changes are further investigated during the so-called “8.2 ka event” and the Little Ice Age (LIA) using climate model simulations. We propose that rainfall changes at El Junco Lake ca. 8500-8000 yr BP were produced by a large meltwater pulse in the North Atlantic that caused a southward shift of the ITCZ (via reduced northward ocean heat transport and expanded Arctic sea ice) and weakened El Niño/Southern Oscillation (ENSO) variability (via tropical Pacific mean state changes that increased the stability of the coupled ocean-atmosphere system). We provide support for this concept using simulations with a fully coupled global climate model (CESM) and a linearized ocean-atmosphere model of the tropical Pacific (LOAM), Tropical hydroclimate changes and their mechanisms during the LIA were investigated in the CMIP5/PMIP3 last millennium simulations. Climate forcings and feedbacks were quantified using the Approximate Partial Radiative Perturbation and radiative kernel methods, highlighting the role of volcanic forcing and the water vapor, lapse rate, and surface albedo feedbacks during the LIA. A weak southward shift in zonally averaged tropical precipitation was found during the LIA in the model simulations in association with anomalous northward cross-equatorial atmospheric energy transport that was driven by greater volcanic forcing and ...