Atlantic Water (AW) is the largest reservoir of heat in the Arctic Ocean, isolated from the surface and sea-ice by a strong halocline. In recent years AW shoaling and warming are thought to have had an increased influence on sea-ice in the Eurasian Basin. In this study we analyse 59000 profiles from across the Arctic from the 1970s to 2018 to obtain an observationally-based pan-Arctic picture of the AW layer, and to quantify temporal and spatial trends. The potential temperature maximum of the AW (the AW core) is found to be an easily detectable, and generally effective metric for assessments of AW properties, although its depth is not always a good indicator of the depth of the AW layer. In contrast to the Eurasian Basin, where the AW warms in a pulse-like fashion and has an increased influence on upper ocean heat content, AW heat in the Canadian Basin became more isolated from the surface due to the intensification of the Beaufort Gyre and an influx of Pacific Water. The increase in density of the AW core suggests an increasing interaction between cold dense shelf flows and the AW during its advection, consistent with the enhanced brine rejection expected from decreases in summer sea-ice extent. This process could play an important role in AW cooling west of the Lomonosov Ridge. The differences in AW trends in the Eurasian and Canadian Basins of the Arctic over the period studied suggest that these two regions may evolve differently over the coming decades.