A 145 kyr record of upstream changes in Indian monsoon circulation and its link to southern high-latitude climate

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The influence of northern high latitude climate variability on the South Asian Summer Monsoon has been extensively studied using both instrumental and proxy based climate data. In comparison, only a few studies have attempted to explore the southern high latitude association of the South Asian Summer Monsoon. Here we present a 145 kyr long new data (oxygen and carbon isotopic abundance of two depth-stratified species of foraminifera viz. Globigerinoides ruber and Globorotalia menardii) from a sediment core on sub-millennial to millennial scale resolution from the southwestern tropical Indian Ocean - a region swept by the southeasterly wind during boreal summer (referred to as ‘summer’ hereafter), which transforms to the southwest monsoon wind after crossing the equator. The available records of past summer monsoon variability are predominantly based on reconstruction of downstream hydrology, which is identifiable with the thermodynamics of the system. The present study is a reconstruction of the dynamics of the summer monsoon circulation from an upstream region which is ideally suited for exploring its link with the southern high-latitude climate. We identified several occurrences of interchanging intense and weak monsoon circulation events during the 145 kyr period. We further find that warm (cold) conditions in Antarctica show a near one-to-one coupling with weak (strong) monsoon phases, suggesting a strong mechanistic link between them during the period.