MIGRATION OF THE ITCZ DURING THE HOLOCENE: EVIDENCE FROM THE CARIBBEAN-GULF OF MEXICO REGION

Proxy records of Holocene climate variability from Lake Miragoane, Haiti, marine core RC 12-10 from the western Gulf of Mexico, and radiocarbon dated charcoal and packrat middens from New Mexico show similar structure and trends. We interpret the similarities as evidence for a regional scale driver that has varied in strength through the Holocene. The ostracod oxygen isotope record from Haiti (Hodell et al., 1991) which reflects changing ration of evaporation to precipitation, shows increasing, though variable precipitation between 10.5 and 6 ka (14C years). Precipitation then decreases toward the present. In the Gulf core, the overall relative abundance of the planktic foraminifer Globigerinoides sacculifer, an indicator of westward transport of Caribbean surface waters into the Gulf of Mexico, increases in early Holocene toward a maximum at 6 ka and then decreases toward the present. Radiocarbon dated charcoal and packrat midden occurrences in New Mexico increase significantly after 6 ka. The charcoal and midden records show correlative millennial scale variations between 0 and 4 ka. We conclude that all of these records are related to changes in the average position of the ITCZ. In the early Holocene, up to 6 ka, increased warming of the Northern Hemisphere resulted in northward movement of the average position of the ITCZ. The northward movement strengthened easterly winds increasing transport of Caribbean surface waters, delivering greater precipitation to Haiti, and strengthening the North American Monsoon. After the mid-Holocene insolation maximum, the average position of the ITCZ moved south weakening easterly winds and thus resulting in decreased precipitation in Haiti, waning of westward transport of Caribbean surface waters, and weakening of the monsoon. Millennial scale variability in the late Holocene is particularly pronounced in the terrestrial records, possibly reflecting the dominance of monsoon precipitation on surface processes in semi-arid New Mexico.