Variable Response of Rainfall in the Western Pacific Warm Pool at Orbital and Millennial Timescales over the Last 1.5 My
Abstract
The Western Pacific Warm Pool (WPWP) is a major source of heat and moisture to the atmosphere and a location of deep convection and heavy rainfall. However, the causes and extent of past precipitation changes in the WPWP are not well constrained in terms of the relative importance of extra-tropical (e.g., equator-to-pole temperature gradient) vs. tropical controls (e.g. SST patterns and zonal winds). Changes in Earth's orbital configuration, which alter the spatial and temporal distribution of solar insolation, offer the means to test the relative importance of tropical vs. extratropical forcing on rainfall in the heart of the WPWP. Using x-ray fluorescence core scanning we generated a 1.5 Myr record of paleo-runoff from IODP Site U1486 (02°22.34'S, 144°36.08'E, 1332 m), recovered offshore of two major rivers draining the northern highlands of Papua New Guinea. The carbonate free basis Ti concentration (Ticfb), an indicator of the coarse river particulate fraction, displays significant power at 23, 41, and 100 ky, reflecting the persistent influence of precession, obliquity, and eccentricity cycles on runoff and rainfall over northern PNG across the mid-Pleistocene transition. Peak Ticfb, and thus rainfall over northern PNG, is 180° out of phase with precipitation records from China at the precession timescale, underscoring the role of the Intertropical Convergence Zone (ITCZ) and the global monsoon in linking the northern and southern hemispheres over the last 1.5 My. In contrast, on millennial timescales rainfall over PNG is in phase with records north of the equator. During Heinrich events, we suggest the ITCZ was displaced further south relative to its maximum southward migration during a precession cycle, likely in response to reduced North Atlantic deepwater formation and thus a stronger cross-equatorial pressure gradient.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP51C1386B
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICS