Coherent response of Arabian Sea upwelling and pollen transport to late Quaternary monsoonal winds

Abstract

The Indian summer monsoon causes large seasonal changes in the environments of both eastern Africa and the Arabian Sea. Here we compare time series (140 kyr long) of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments, to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation. During interglacial intervals, the pollen and upwelling records of the western Arabian Sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the Earth's rotational axis (23 kyr). We conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals. Low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records. These data indicate that two distinct modes of monsoon variability may exist: an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records, and a glacial mode with both weaker monsoons and decreased linkage between Arabian Sea pollen and upwelling records.