A recent decline in North Atlantic subtropical mode water formation

• Published in: Nature Climate Change
• Main Authors: Stevens, Samuel W., Johnson, Rodney J., Maze, Guillaume, Bates, Nicholas R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Science and Business Media LLC 2020
• Subjects: North Atlantic
• Online Access: https://archimer.ifremer.fr/doc/00618/72973/72146.pdf; https://archimer.ifremer.fr/doc/00618/72973/77554.pdf; https://doi.org/10.1038/s41558-020-0722-3; https://archimer.ifremer.fr/doc/00618/72973/

As a manifestation of mixing dynamics in the upper ocean, interannual and decadal variability of subtropical mode water (STMW) properties in the North Atlantic Ocean provides a valuable insight into ocean–atmosphere interaction in a changing climate. Here, we use hydrographic data from the Bermuda Atlantic Time-Series Study and Hydrostation S sites near Bermuda, as well as various ocean reanalysis products, to evaluate the modern variability of STMW properties. Our study finds an 86–93% loss of STMW thickness at these sites between 2010 and 2018 and a comparable loss throughout the western subtropical gyre, culminating in the weakest STMW pentad on record. We correlate this decline with a reduction in the annual outcropping volume and northward excursions of the formation region, suggesting a gyre-wide signal of weakening STMW generation. The outcropping volume of STMW is anti-correlated with surface ocean heat content, foreshadowing future STMW loss in the face of continued warming.