Changes in bottom water physical properties above the mid-Atlantic ridge flank in the Brazil Basin

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Zhao, Jian, Thurnherr, Andreas M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: John Wiley & Sons 2018
• Subjects: AABW; Decadal change; Abyssal stratification; Antarctic; The Antarctic; Mid-Atlantic Ridge; Antarc*; North Atlantic Deep Water; North Atlantic
• Online Access: https://hdl.handle.net/1912/9636

Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 708–719, doi:10.1002/2017JC013375. 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 inline image), saltier (0.01 ± 0.005), and less dense (0.005 ± 0.004 inline image) 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 ( inline image) 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 inline imageW in years 1989, 2005, and 2014. The observed changes in density stratification have important implications for internal tide generation and dissipation. NSF Grant Number: OCE-1235094 2018-07-30