Long-term subsurface observations are essential for detecting oceanic changes in the Arctic Ocean, where severe sea-ice conditions limit ship-based hydrographic surveys. Arctic Atlantification, characterized by the increasing influence of Atlantic Water (AW), provides a significant subsurface heat source and can affect upper-ocean and sea-ice conditions. In this study, we deployed three current- and pressure-recording inverted echo sounders (CPIES) from 2017 to 2026 in the Northwind Abyssal Plain (NAP) of the western Arctic Ocean to continuously monitor changes in the intermediate and deep water column. The CPIES measured vertical round-trip acoustic travel time between the seafloor and sea surface, providing a long-term proxy for water-column thermal variability. The observed acoustic travel time decreased at an average rate of approximately 0.42 ms yr⁻¹, indicating subsurface warming during the observation period. Hydrographic CTD data collected during summer surveys suggest that this decrease was primarily associated with an enhanced influence of AW, defined here as θ > 0 °C and σ > 27.4 kg m⁻³. Between 2017 and 2026, the temperature of the 250–1000 m layer increased by approximately 0.038 °C/yr, and the AW layer thickened by about 22.1m/yr. These changes contrast with trends observed from 2002 to 2016 and were particularly evident at CPIES sites influenced by the AW boundary current. The post-2017 warming and thickening of AW in the NAP appear to be linked to changes in the AW boundary current system and Beaufort Gyre (BG) circulation, particularly the eastward displacement of the Beaufort High after 2016. Correlations between meridional current velocity and BG strength suggest that the Beaufort High–BG circulation can oppose the AW boundary current and modulate AW accumulation in the NAP. This displacement, together with a recent weakening of the BG, may have reduced the opposing meridional flow, enhanced AW accumulation, and accelerated Atlantification along the AW boundary current. These results demonstrate that long-term CPIES observations are a useful tool for detecting subsurface Atlantification in the western Arctic Ocean. They further suggest that variations in the coupled Beaufort High–BG system may regulate how AW is transported into and accumulated within the western Arctic interior.