Femke de Jong, Royal Netherlands Institute for Sea Research & Utrecht University, Ocean Science Systems, Texel, Netherlands and Daphne van Zanten, Utrecht University, IMAU, Utrecht, Netherlands
Dense waters overflow the Denmark Strait sill into the North Atlantic subpolar gyre and contribute to the deep southward limb of the Atlantic Meridional Overturning Circulation. There are several sources proposed to contribute to the dense water overflowing the sill; the East Greenland Current (EGC), the separated East Greenland Current (sEGC) and the North Icelandic Jet (NIJ). An observational Lagrangian study using RAFOS floats by de Jong et al (2018) mainly found contributions from the EGC and sEGC. In their tracks the NIJ seemed to originate from the EGC and they did not find a strong eastern connection to the Iceland Sea. However, model studies have suggested that these pathways may vary in time. Therefore, this study investigated time variability of pathways in 10-year time series of a 1/12° model of the Iceland Sea. Virtual particles were released monthly between February 2005 and August 2015 at two locations, particles were tracked forward from a section at 70°N in the EGC and backward from the sill of Denmark Strait. In the mean, the forward trajectories show a clear splitting of the EGC into three branches, towards the east through the Spar Fracture Zone, southwards towards Iceland along the western flank of the Kolbeinsey Ridge and southwestward along the eastern continental shelf of Greenland. This last branch shows another bifurcation further downstream in the Blosseville Basin into the mean EGC and the separated EGC. The backward trajectories show a main contribution from the Icelandic shelf west of the Kolbeinsey Ridge, which appears similar to the NIJ, but the connection is mostly to the EGC at 70°N rather to the east of the Kolbeinsey Ridge. While some interannual variability was expected, we mainly found large variability on monthly time scales. The pathways just upstream of Denmark Strait appear to be determined by an anti-cyclonic meso-scale eddy or lens (visible as a thickening of the layer between 27.5 and 27.8 kg/m3), in the southern end of the Blosseville Basin, with the volume transport along the Iceland shelf strongly correlated with the density anomaly of the eddy. A cyclonic eddy just west of the Spar Fracture Zone strongly influences the direction of forward particles released at 70°N, either steering particles into the East Icelandic Current when the cyclone is strong or not when the cyclone is weak.