Reconstruction of the late-Holocene changes in the Sub-Arctic Front position at the Reykjanes Ridge, north Atlantic
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Changes in the dynamics of the North Atlantic subpolar gyre are involved in the modulation of the northward salinity and heat transport in the northern North Atlantic via the North Atlantic Current (NAC). Variations in the strength of the East Greenland Current (EGC) can influence the gyre dynamics by impacting deep convection in the Labrador Sea. Oxygen isotope data of three planktonic foraminiferal species (surface water Neogloboquadrina pachyderma dextral coiling and Globigerina bulloides; thermocline recorder Globorotalia inflata) from a site located close to the present Sub-Arctic Front at the Reykjanes Ridge suggest significant strengthening or shifting of the Sub-Arctic Front throughout the late Holocene. The oxygen isotope based inferences are supported by Mg/Ca-derived temperature reconstructions from Neogloboquadrina pachyderma dextral coiling, alkenone-derived sea surface temperature and other paleoclimatic proxy data. The late-Holocene strengthening/shift of the Sub-Arctic Front appears caused by an increasingly more defined and fresher EGC. The proposed subpolar gyre changes may modulate the northward heat transport, and explain the geographically different long-term climatic trends in the North Atlantic during the late Holocene, i.e. a cooling of the EGC-influenced regions and a warming of the NAC-influenced areas from c. 4 to 5 ka. This mechanism cannot, however, explain the simultaneous occurrence of millennial-scale events at c. 5.6, 3.9, 2.7, 1.3 ka and the ‘Little Ice Age’ in both areas. Noteworthy is the steadily increasing amplitude of these cold events at the Reykjanes Ridge, likely induced by drift ice and/or EGC-influence culminating in the ‘Little Ice Age’. A widespread pronounced warming at 2.0 ka seems to represent the ‘Roman Warm Period’ and reflects the warmest period of the late Holocene.