The impacts of climate change on North Atlantic nutrient chemistry remain poorly understood, as there exist a multitude of rapidly-changing biological and physical drivers of nutrient conditions throughout the region. Here, we present nitrogen isotope measurements derived from a six-hundred-year-old crustose coralline alga (δ15Nalgal) to elucidate historic and contemporary trends in Labrador Shelf nitrate utilization, defined as the degree of biological nitrate uptake relative to supply. Prior to ~1800, periods during which utilization approached completion corresponded to neutral modes of the Atlantic Multidecadal Oscillation, which we argue promoted favorable oceanographic conditions for simultaneous phytoplankton growth and reduced nitrate input. More recently, nearly-complete utilization occurred concomitantly with a weakened Labrador Current, suggesting reduced nutrient inflow from eastern subpolar waters. These results highlight the role of ongoing climate-induced circulation changes in driving nutrient distributions throughout the subpolar North Atlantic, which may have implications for future fisheries and oceanic carbon storage.