Abstract
Changes in ocean dynamics in the northern North Atlantic affect the thermohaline circulation that controls global climate. During glacial and deglaciation periods these dynamics are enhanced due to large variations in the surface ocean density caused by changes in glacier volumes. During full interglacial conditions, the dominant role of the northern North Atlantic on global climate is limited due to the reduced discharge of freshwater to the ocean, causing other regional dynamics to gain importance. Here we present a speleothem delta O-18 record from the Iberian Peninsula that supports that the northern North Atlantic and tropical North Atlantic were both source regions of millennial climate oscillations during the Holocene. The speleothem delta O-18 signal records millennial time-scale changes in the hydrological cycle as a result of persistent anomalies of the Gulf Stream-North Atlantic Current dynamics. In addition, the speleothem delta O-18 record shows synchronous variability with records from the eastern Pacific region though the entire Holocene, whereas records from western Pacific region have limited or no correlation beyond periods of major instability of the northern North Atlantic. The discontinuous climate connection among the studied records is the result of different mechanisms affecting the climate system that originated in distant regions. We suggest that two regions, the tropical North Atlantic and northern North Atlantic, alternate their dominance as source regions causing millennial climate anomalies in large planetary regions. The duration of these persistent climate changes and the extension of the regions affected depend on the region triggering the anomaly because different mechanisms affecting the climate system are involved.