The subpolar North Atlantic is one of the key regions in the climate system because formation of deep waters contributes to the AMOC, as well as the uptake of CO2 from the atmosphere. Paleoceanographic reconstructions and climate model studies imply a key role of Labrador Sea circulation in driving millennial-scale climate variability. On shorter timescales, comprehensive hydrographic data also reveal considerable variations in convection and deep-water formation in the central Labrador Sea, which are only partly understood. Future changes in the strength of the AMOC depend critically on the distribution of heat and salt in the North Atlantic. ArcTrain projects will contribute to establish climatologies for the subpolar North Atlantic and extended time series from paleoclimate archives for benchmarking and improving ocean-circulation models and understanding the physical processes associated with heat and salt transfer in the ocean.