Mechanisms forcing abrupt fluctuations of the indian ocean summer monsoon during the last deglaciation
Abstract
A piston core from the Somali upwelling area has been studied at high resolution for its dinoflagellate cyst content. Variations in cyst association are inferred to reflect changes in Indian Ocean summer monsoon intensity. Several abrupt fluctuations in monsoon intensity are detected for the interval between 20 and 10 ka BP. Comparison of these fluctuations with changes in contrast between 30°N and 30°S July insolation and the δ18O GRIP ice-core values suggests that different mechanisms influenced monsoon intensity at different time intervals. A general trend in monsoon intensity follows variations in insolation contrast, lagging minimum contrast by 7.5 ka and maximum contrast by 4 ka. This phase lag difference can be explained by assuming the existence of an ice/snow cover over central Asia/Tibet during glacial times. Between 18.7 and 12.5 ka BP fluctuations in SW-monsoon intensity may be forced by variations in the thermohaline ocean circulation. A rapid transition. towards strong SW-monsoons at 12.5 ka BP is possibly the result of variations in atmospheric circulation and melting of the snow/ice fields in central Asia/Tibet. Variations in glacial-interglacial boundary conditions related to temperature change at northern latitudes are likely to have influenced SW-monsoon intensity between 12.5 and 10 ka BP, whereas after 10 ka BP variations in tropical land surface boundary conditions may be the dominant forcing factor. 0 1997 Elsevier Science Ltd.
- Publication:
-
Quaternary Science Reviews
- Pub Date:
- 1997
- DOI:
- 10.1016/S0277-3791(96)00049-2
- Bibcode:
- 1997QSRv...16..187Z