AbstractPrecise measurements of dissolved noble gases along the GP15 GEOTRACES Pacific Meridional Transect reveal the oldest northern bottom waters equilibrated with the atmosphere at a higher barometric pressure than more recent waters. Here, using a radiocarbon-calibrated multi-tracer-based diagnostic model, we reconstruct the magnitude and timing of this palaeo-barometric pressure anomaly. We hypothesize this multi-millennial trend in sea-level pressure results from local and regional processes extant in Antarctic Bottom Water formation regions.