Inverse phase oscillations between the East Asian and Indian Ocean summer monsoons during the last 12 000 years and paleo-El Niño

Abstract

The inverse phase variations between the East Asian and Indian Ocean summer monsoons on the interannual timescale result from the El Niño-Southern Oscillation activity in the tropical Pacific, which potentially provides a new way for studying paleo-ENSO. Here we reconstruct a 12 000-yr proxy record for the East Asian summer monsoon from δ 13C time series of the plant cellulose of the Hani peat bog in the northeastern China. The comparison of it with the peat proxy record of the Indian Ocean summer monsoon suggests that the El Niño conditions are coincident with strong East Asian summer monsoons, weak Indian summer monsoons, and drift ice events in the North Atlantic at both orbital and millennial time scales. The orbital-scale inverse phase relationships between the monsoons indicate the occurrence of a long-term ENSO-like pattern, confirming the sensitivity of the monsoon systems associated with ENSO to insolation forcing. The nine inverse phase variations on the millennial time scales may suggest the nine El Niño-like patterns superimposing the long-term ENSO-like pattern. The inverse phase variations between the monsoons also show close correspondence to the drift ice events at high northern latitudes. In every case when the abrupt ice-rafted debris events occurred in the North Atlantic, the inverse phase relationship established, and the El Niño-like pattern occurred in the tropical Pacific correspondingly. The discussions on the influence of ocean thermohaline circulation on these global linkages have been made.