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Changes in Bottom Water Physical Properties Above the Mid‐Atlantic Ridge Flank in the Brazil Basin
Author(s) -
Zhao Jian,
Thurnherr Andreas M.
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2017jc013375
Subject(s) - canyon , geology , oceanography , hydrography , stratification (seeds) , ridge , antarctic bottom water , abyssal zone , bottom water , bathymetry , structural basin , internal tide , circumpolar deep water , climatology , thermohaline circulation , north atlantic deep water , geomorphology , internal wave , paleontology , seed dormancy , botany , germination , dormancy , biology
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 k g 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 ( N 2 ) 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.