Despite numerous investigations, the dynamical origins of the medieval Climate Anomalyand the Little Ice Age remain uncertain. A major unresolved issue relating to internal climatedynamics is the mode and tempo of Atlantic meridional overturning circulation variability, andthe significance of decadal-to-centennial scale changes in Atlantic meridional overturningcirculation strength in regulating the climate of the last millennium. Here we use the timeconstrained high-resolution local radiocarbon reservoir age offset derived from an absolutelydated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changesin surface ocean circulation and climate. The water mass tracer data presented here from thenorth Icelandic shelf, combined with previously published data from the Arctic and subtropicalAtlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplifiedthe relatively warm conditions during the medieval Climate Anomaly and the relatively coolconditions during the Little Ice Age within the north Atlantic sector.
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