Changes in Bottom Water Physical Properties Above the Mid‐Atlantic Ridge Flank in the Brazil Basin

Warming of abyssal waters in recent decades has been widely documented around the global ocean. Here repeat hydrographic data collected in 1997 and 2014 near a deep fracture zone canyon in the eastern Brazil Basin are used to quantify the long‐term change. Significant changes are found in the Antarctic Bottom Water (AABW) within the canyon. The AABW in 2014 was warmer (0.08 ± 0.06 °C), saltier (0.01 ± 0.005), and less dense (0.005 ± 0.004 kg m−3) than in 1997. In contrast, the change in the North Atlantic Deep Water has complicated spatial structure and is almost indistinguishable from zero at 95% confidence. The resulting divergence in vertical displacement of the isopycnals modifies the local density stratification. At its peak, the local squared buoyancy frequency ( N2) near the canyon is reduced by about 20% from 1997 to 2014. Similar reduction is found in the basinwide averaged profiles over the Mid‐Atlantic Ridge flank along 25 °W in years 1989, 2005, and 2014. The observed changes in density stratification have important implications for internal tide generation and dissipation. Key Points Significant long‐term changes of deep water properties are identified in and above deep fracture zone canyons in the eastern Brazil Basin Between 1989 and 2014, the isopycnals in the bottom water moved downward whereas a small upward trend occurred in the overlying deep water The mean vertical divergence in density has reduced the stratification by about 20% in a 500‐m‐thick deep layer in the eastern Brazil Basin