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Abstract Speleothems can provide high-quality continuous records of the direction and relative paleointensity of the geomagnetic field, combining high precision dating (with U-Th method) and rapid lock-in of their detrital magnetic particles during calcite precipitation. Paleomagnetic results for a mid-to-late Holocene stalagmite from Dona Benedita Cave in central Brazil encompass ~1900 years (3410 BP to 5310 BP, constrained by 12 U-Th ages) of paleomagnetic record from 58 samples (resolution of ~33 years). This dataset reveals angular variations of less than 0.06° yr −1 and a relatively steady paleointensity record (after calibration with geomagnetic field model) contrasting with the fast variations observed in younger speleothems from the same region under influence of the South Atlantic Anomaly. These results point to a quiescent period of the geomagnetic field during the mid-to-late Holocene in the area now comprised by the South Atlantic Anomaly, suggesting an intermittent or an absent behavior at the multi-millennial timescale. 

Abstract. The South American Summer Monsoon (SASM) is the maindriver of regional hydroclimate variability across tropical and subtropicalSouth America. It is best recorded on paleoclimatic timescales by stableoxygen isotope proxies, which are more spatially representative of regionalhydroclimate than proxies for local precipitation alone. Network studies ofproxies that can isolate regional influences lend particular insight intovarious environmental characteristics that modulate hydroclimate, such asatmospheric circulation variability and changes in the regional energybudget as well as understanding the climate system sensitivity to externalforcings. We extract the coherent modes of variability of the SASM over thelast millennium (LM) using a Monte Carlo empirical orthogonal function(MCEOF) decomposition of 14 δ18O proxy records and compare themwith modes decomposed from isotope-enabled climate model data. The twoleading modes reflect the isotopic variability associated with (1) thermodynamic changes driving the upper-tropospheric monsoon circulation(Bolivian High–Nordeste Low waveguide) and (2) the latitudinaldisplacement of the South Atlantic Convergence Zone (SACZ). The spatialcharacteristics of these modes appear to be robust features of the LMhydroclimate over South America and are reproduced both in the proxy dataand in isotope-enabled climate models, regardless of the nature of themodel-imposed external forcing. The proxy data document that the SASM wascharacterized by considerable temporal variability throughout the LM, withsignificant departures from the mean state during both the Medieval ClimateAnomaly (MCA) and the Little Ice Age (LIA). Model analyses during theseperiods suggest that the local isotopic composition of precipitation isprimarily a reflection of upstream rainout processes associated with monsoonconvection. Model and proxy data both point to an intensification of themonsoon during the LIA over the central and western parts of tropical SouthAmerica and indicate a displacement of the South Atlantic Convergence Zone(SACZ) to the southwest. These centennial-scale changes in monsoon intensityover the LM are underestimated in climate models, complicating theattribution of changes on these timescales to specific forcings and pointingtoward areas of important model development.