Excessive Southwest Greenland Ice Sheet Melting Between 4.4 and 3.2 ka BP Documented by Fjord Sediments: Implications for N-Atlantic Ocean Circulation and AMOC

Greenland Ice Sheet (GrIS) melting occurred during the later part of the Holocene Thermal Maximum (HTM) with a well-documented significant GrIS retreat between 7 and 3 ka. However, less is known about the immediate melt water impact on Greenland fjord hydrography and more distant ocean circulation. A compilation of published sediment records from southwest Greenland fjords and Disko Bay, West Greenland, demonstrates marked local erosional events and deposition of extensive (silty) melt water sediments within the period 4.4 to 3.2 ka BP. The termination of fjord perturbation in this region is dated at c. 3.2 ka and closely corresponds to the reported timing of minimum GrIS extent. As an ocean response, an increased freshening and enhanced melt water transport by the Labrador Current (LC) between 4.4 and 4.0 ka are concluded to signal the most prominent melt water discharge events in the southwest Greenland fjords. The latter melt water pulses were coeval with a marked warming episode and negative surface mass balance peak recorded in ice cores. As suggested by modelling and paleo-oceanographic records from the North Atlantic subpolar gyre, temporarily enhanced GrIS melting and increased LC freshwater release into the North Atlantic around 4.2 ka may have led to destabilization of the AMOC. The GrIS melt water surges associated with an anomalous atmospheric (Greenland blocking) regime are proposed to reflect a regional climate anomaly related to the so-called ‘4.2 ka BP event’.