Meridional Shifts in the Marine ITCZ and the Tropical Hydrologic Cycle Over the Last Three Glacial Cycles

Paleoproxy studies show a strong correlation between tropical climate and high-latitude temperature variability recorded in the Greenland ice cores over the last glacial cycle. In particular, abrupt cooling events in the Greenland Ice Sheet Project II δ18O ice record appear synchronous with a southward migration of the Intertropical Convergence Zone (ITCZ) in the Atlantic, a weakening of the Indian and East Asian monsoon systems, and a strengthening of the South American monsoon system. Because this high-to-low-latitude climate teleconnection significantly alters the tropical hydrologic cycle around the globe, it plays a critical role in regulating global climate on glacial-interglacial time scales. We compare δ18Oseawater reconstructions (a salinity proxy generated from previously published Mg/Ca and oxygen isotope data on Globigerinoides ruber (white var.)) obtained from western Caribbean core ODP 999A and western equatorial Pacific core 806B across the last three glacial cycles to show that systematic variations in surface salinity at these sites suggest the tropical Hadley cell hydrologic system undergoes systematic reorganizations that differ dramatically between warm interglacial and cold glacial periods. Furthermore, cross-spectral and phase angle analyses of the ice-volume-corrected Caribbean and western Pacific δ18O SW records reveal a 100 kyr frequency in both records that is almost 180 degrees out of phase and a 23 kyr frequency that is nearly in phase. This results in the development of a very large δ18OSW gradient between the Caribbean and the western equatorial Pacific on glacial-interglacial time scales that is best explained by a southward shift in both the Atlantic and Pacific ITCZ during North Atlantic cold phases