Climate change is triggering profound changes in the marine environment, especially in the Arctic Ocean (AO) and subpolar North Atlantic (SPNA), two key areas playing a crucial role in feeding the main engine of the global oceans: the Atlantic Meridional Overturning Circulation (AMOC). Despite the utmost importance of AMOC for the climate system, there are still many open fundamental questions regarding its physical mechanisms, water mass pathways, and transport or ventilation timescales. TITANICA aims to improve our understanding of AMOC on the basis of a new set of transient radionuclide tracers (129I, 236U, 39Ar and 14C), a quartet that will allow to study and constrain oceanographic processes on timescales of years to millennia. While the combination of the two nuclear reprocessing-derived 129I and 236U will investigate the shorter transport mechanisms (100 y). Newly available techniques will allow the implementation of 39Ar to unprecedented possibilities, closing the time gap between the artificial transient tracers (CFCs, SF6, 129I, 236U) and natural 14C. TITANICA goes beyond the state-of-the art as it combines cutting-edge analytical techniques (Accelerator Mass Spectrometry and Atom Trap Trace Analysis) with novel data analysis methods pioneered by the PI and supported by binary mixing models, transit time distributions, and regional ocean modeling. During the 5 years journey of TITANICA, two PhD students and two postdocs will join the PI embarking in a suit of ocean expeditions covering the Arctic Ocean, the SPNA and the subtropical Atlantic Ocean. The new data generated and the strong collaboration with European and International partners will combine with the PI unique expertise in this field, triggering a new era of transient tracers in the Arctic and Atlantic oceans.