Dynamics of Atlantic water advection to the Norwegian-Greenland Sea — a time-slice record of carbonate distribution in the last 300 ky

Abstract

Short-term variability in volume and configuration of Atlantic water advection to the Norwegian-Greenland Sea (NGS) has recently been identified as a new and significant element for northern hemisphere glacial/interglacial climatic fluctuations. The amount of salt, heat and moisture transferred by Atlantic waters to the high Arctic effectively influences Northern Hemisphere climates and is critical for the overall oceanic turnover rate. In particular, determining the extent and duration of Atlantic Water intrusions in the NGS is essential because of: (1) its effect on the climate of the Nordic continents; and (2) its trigger function on the stability of the ice sheets with (a) weak inflows of Atlantic Water during glacials, promoting an increase in ice volume by moisture supply to polar areas; and (b) positive feed-back mechanisms of Atlantic water intrusions during ice sheet decay. In this study, the dynamics of surface water mass regimes in the NGS have been reconstructed for the past 300 ky by means of time-slice compilations of calcium carbonate distribution and micropaleontologic proxies. In addition, carbonate preservation records are used to quantify deep water ventilation and production rates. In contrast to the CLIMAP scenario, but in accordance with many recent publications, results of this study indicate that Atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration. Significant modes recognized are: (1) the full interglacial mode with a wide inflow of warm Atlantic waters covering a broad area in the eastern sector of the NGS and extending far north, combined with excellent carbonate preservation and very efficient deep water formation (stages 1 and 5.5.1); (2) the moderate interglacial mode with a rather small extension of Atlantic waters along a narrow corridor in the southeastern sector of the NGS but still very efficient deep water exchange (stages 9, isotopic events 7.5, 7.3–7.1, 5.3 and 5.1); (3) pronounced cool phases during interglacials with only a very narrow inflow of Atlantic waters into the southeastern NGS, while the coastal areas off Norway were still affected by iceberg drift (substages 7.4 and 5.2), carbonate preservation records indicate ongoing deep water formation in the NGS; (4) the normal glacial mode characterized by a variable but persistent inflow of cool-temperate Atlantic water (lower stage 8, repetitively during stages 6, 4, 3.1 and 2), carbonate preservation records indicate ongoing deep water formation in the NGS; (5) short glacial and deglacial periods characterized by episodic high inputs of IRD, evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution (e.g. episodically within stages 10, 6 and 2, the 6 5 , 4 3 and 2 1 transitions). Some of these NGS diamicton layers correlate with Heinrich layers in the North Atlantic, but generally NGS diamicton layers occur more frequently than Heinrich layers. The role of Atlantic water influence during these events remains enigmatic but Atlantic water influence is frequently found just above and below these sections. A scenario with rapid ice sheet disintegration induced by Atlantic water advection (via increase of the thermal regime along the ice margin, possibly triggered by small-scale sea level rise) might be envisaged. More obviously, the short-term cessation of deep-water formation in the NGS, as evidenced by the dissolution spikes, may be correlated with contemporaneous ventilation minima in the North Atlantic.