From Science Daily:
Our records reflect details of the climatic evolution in the Atlantic region since the end of the last Ice Age to the present day. We would have liked to compare our results to similar data sets from other parts of the South Atlantic, but no other records provide the same degree of resolution, says Professor Björck. After the end of the last Glacial both Hemispheres became warmer as a result of melting ice sheets, but during the last 9000 years we can identify a persistent "seesaw" pattern. When the South Atlantic was warm it was cold in the North Atlantic and vice versa.
This is most certainly related to large-scale ocean circulation in the Atlantic Ocean. The main current system - "the Great Ocean Conveyor" - is driven by sinking of dense, relatively cold and salty water in the northern North Atlantic. This results in southward-flowing deep-water that is replaced by warm surface water brought to high northern latitudes from the tropics and ultimately from the South Atlantic