Four decades of dense water formation in the Iceland Sea

Dense water masses formed in the Nordic Seas flow across the Greenland-Scotland Ridge and provide a major contribution to the lower limb of the Atlantic Meridional Overturning Circulation. Originally considered an important source of dense water, the Iceland Sea regained focus when the North Icelandic Jet - a current transporting dense water from the Iceland Sea into Denmark Strait - was discovered in the early 2000s. Here we use recent hydrographic data to quantify water mass transformation in the Iceland Sea and contrast present conditions with measurements from hydrographic surveys conducted four decades earlier. We demonstrate that substantial changes in the large-scale hydrographic structure and in the properties of the locally formed dense waters have taken place over this period in concert with a retreating ice edge and diminished ocean-to-atmosphere heat fluxes. This development has impacted the properties of the dense water masses available to supply the North Icelandic Jet.