8000 year marine record of climate variability and fjord dynamics from Southern Greenland

Abstract

Holocene sediment records of glacio-marine environmental and climatic changes from Ikersuaq Fjord and Narsaq Sound in southern Greenland have been studied. The Ikersuaq Fjord record representing the last c. 500 years is dominated by turbidite sedimentation and very high sedimentations rates of up to 1 cm/yr. The adjacent Narsaq Sound site, on the other hand, represents a continuous and more slowly accumulating sedimentation record of the last c. 8000 years. The Narsaq record reveals changes in position and melting rates of glacier termini of the nearby Greenland Ice Sheet from the Holocene Thermal Optimum period terminating at about 5.0 ka to the Neoglaciation period during the late Holocene. From 8.0 ka to 4.8 ka, ice-rafted debris (IRD) influx progressively became reduced, supporting a landward retraction of glacier termini. Neoglaciation of the region appears to have been initiated at about 4.8 ka, with a culmination of IRD rain at about 4.6 ka, 3.6 ka, 2.2 ka, 1.0 ka, 0.7 ka, and 0.5 ka and onward. Some of these IRD events appear to be associated with enhanced melting and glacier instability during warming episodes. However, at the transition to the ‘Little Ice Age’ at about 1450 years AD, a marked increase in IRD influx took place. The bottom water of Narsaq Sound appears to have been dominated by modified Irminger Water (Atlantic) during most of the Holocene. Bottom current flow was quite sluggish before 3.2 ka, whereas the late Holocene period appears to have been characterised by three pronounced episodes of increased bottom current velocity and increased calcareous benthic foraminifera productivity. The long term climate pattern in the Narsaq Sound record follows climate changes consistent with patterns of East Greenland Current variability, which is partly related to dominant North Atlantic Oscillation forcing of wind and ice drift patterns.