Greenland (GISP2) ice core and historical indicators of complex North Atlantic climate changes during the fourteenth century

The paper uses Greenland GISP2 ice core data together with historical documentary information to investigate the nature of climate changes that took place between AD 1270 and 1450 across the North Atlantic region. Detailed Deuterium and deuterium excess time series resolved to c. 8-10 samples per year are used to reconstruct relative changes in Greenland air temperature and past changes in sea surface temperature across the western North Atlantic. The data show that sea surface temperatures during the late thirteenth century and the majority of the fourteenth century were characterized by relatively high-amplitude warming and cooling 'events'. These changes preceded a marked reduction in the amplitude of the sea surface temperature changes c. 30-40 years before the well-known change in Northern Hemisphere tropospheric circulation characterized by a marked increase in regional storminess that started between c. AD 1400 and 1420. The time interval between AD 1270 and 1450 also appears over Greenland to have featured several short-lived phases of marked air temperature lowering that were rarely ever equalled during succeeding centuries. We believe that the climate changes described here are of considerable importance in understanding climate dynamics of the North Atlantic region since they took place at a time when the North Atlantic Oscillation (NAO) may have been weak. The results also show that the marked change in atmospheric circulation coincident with a significant increase in North Atlantic storminess at c. AD 1400-1420, possibly the biggest such change in the Holocene, took place after the strong perturbations in North Atlantic sea surface temperature (both warming and cooling) described here as well as after several episodes of air temperature lowering over Greenland.