Orbitally driven east–west antiphasing of South American precipitation

precipitation changes in the region on orbital timescales. 22 The Nordeste, a semi-arid region in northeastern Brazil, 23 is known for its severe and recurrent droughts, which cause 24 socioeconomic problems for millions of people. Observational and 25 modelling studies have convincingly linked below-normal rainfall 26 in the Nordeste during the rainy season (February, March and 27 April) to periods of anomalously warm waters in the tropical 28 North Atlantic sector, a weakened interhemispheric sea-surface29 temperature gradient, an unusually far northward position of the 30 intertropical convergence zone (ITCZ) and El Niño conditions in 31 the tropical Pacific (for example refs 9,10). 32 Abrupt reduction of the Atlantic meridional overturning circu33 lation and sea-ice expansion in the North Atlantic are viewed to be 34 the cause of a southward displacement of the ITCZ (ref. 11), which 35 promoted wet conditions in the Nordeste12 and dry conditions in 36 Venezuela13,14 on millennial timescales. These episodic wet phases 37 extended to the interior of the Nordeste, where they are recorded by 38 short-lived speleothems/travertine growth phases15. 39 The long-term average climatic conditions in the Nordeste are 40 primarily a result of the subtropical anticyclone in the South 41 Atlantic and persistent subsidence related to the Nordeste Low in 42 the upper troposphere. Monsoon systems tend to influence the 43 equatorward portion of subtropical anticyclones to the east of 44