TUFA RECORDS OF HOLOCENE CLIMATE CHANGE IN HIGHLAND SOUTHERN YEMEN

As a paleoclimatic recorder tufa can be instrumental in reconstructing the mid-Holocene paleoclimate and paleohydrology in Wadi Idim and Wadi Sana, which are north flowing tributaries to Wadi Hadramawt, in the highlands of southern Yemen. Based on preliminary age estimates, tufa formation began around 10,000 14C yr B.P., when a stronger summer monsoon brought increased precipitation across the southern Arabian peninsula. Approximately 5,000 14C yr B.P. formation of major tufa mounds ceased, as the monsoon weakened and shifted southward, leading to an increasingly arid climate in the region. Radiocarbon age estimates recovered from sand lenses in the tufa deposits indicate a possible north to south headward migration of the tufa source through Wadi Idim and Wadi Sana. Ages on tufa deposits from both wadis correspond with evidence from other paleoclimate proxies in eastern Africa, the Arabian Sea, western India, and elsewhere in southern Arabia, that indicate increased moisture availability from about 10,000 to 5,000 years ago.

In our study area, increased precipitation contributed to enhanced meteoric recharge of shallow aquifers discharging as springs, which served as point-sources for tufa formation. More active spring discharge led to the formation of expansive marsh and wetland environments, which are indicated by organic-rich lacustrine sediments grading from the tufa mounds to the wadi center. Fossil aquatic gastropods and plant impressions are abundant in the tufa sediments, providing additional evidence for the extensive riparian environment adjacent to the spring sources.

Radiocarbon age estimates determined on charcoal recovered from sand lenses within the tufa deposits are correlated with periods of more extensive human occupation in the region, as documented by the RASA (Roots of Agriculture in Southern Arabia) team. Evidence suggests that early farmers may have been exploiting water resources discharging from these fossil springs during the mid-Holocene humid phase. Subsequent aridification has led to abandonment of agricultural subsistence and return to pastoralism in much of the region.