A tropical speleothem record of glacial inception, the South American Summer Monsoon from 125 to 115 ka

Abstract

Abstract. Relatively few marine or terrestrial paleoclimate studies have focused on glacial inception, the transition from an interglacial to a glacial climate state. As a result, neither the timing and structure of glacial inception nor the spatial pattern of glacial inception in different parts of the world is well known. Here we present results of a study of a speleothem from the Peruvian Andes that records changes in the intensity of South American Summer Monsoon (SASM) rainfall over the period from 125 to 115 ka. The results show that late in the last interglacial period, at 123 ka, SASM rainfall decreased, perhaps in response to a decrease in temperature and ice cover in the high northern latitudes and associated changes in atmospheric circulation. Then at 120.8 ka, a rapid increase in SASM rainfall marks the end of the last interglacial. After a more gradual increase between 120 and 117 ka, a second abrupt increase occurs at 117 ka. This pattern of change is mirrored to a remarkable degree by changes in the East Asian Monsoon. It is interpreted to reflect both a long-term gradual response of the monsoons to orbitally driven insolation changes and to rapid changes in Northern Hemisphere ice volume and temperature. Both monsoon systems are close to their full glacial conditions by 117 ka, before any significant decrease in atmospheric CO 2 .

Monsoon Responses to Climate Changes—Connecting Past, Present and Future

“…However, the external forcing for the Eemian is the insolation change due to orbital forcing which has a different seasonal response (more warming in boreal summer) than the greenhouse gas forcing of the present and future (more warming in the winters of the two hemispheres). While the LIG is not an exact analog for future warming, proxy reconstructions reveal wetter summer monsoons in East Asia and South Asia [57], West Africa [58], and a drier South American monsoon [59,60]. Various modeling studies support the hypothesis that insolation-driven latitudinal temperature gradients drive monsoon intensity, simulating increased West African, South Asian, and East Asian precipitation during the LIG [61,62].…”