Near cessation of Eighteen Degree Water renewal in the western North Atlantic in the warm winter of 2011-2012

TitleNear cessation of Eighteen Degree Water renewal in the western North Atlantic in the warm winter of 2011-2012
Publication TypeJournal Article
Year of Publication2013
AuthorsBillheimer S., Talley LD
JournalJournal of Geophysical Research-Oceans
Volume118
Pagination6838-6853
Date Published2013/12
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000329926200035
Keywords18-degree water; Atlantic Oscillation; decadal; fluxes; Gulf Stream; gulf-stream; gyre; heat loss; heat-transport; north; North Atlantic; nutrient supply; oscillation; sea-surface temperature; southern-ocean; subtropical mode water; variability
Abstract

The winter of 2011-2012 was a particularly weak season for the renewal of "Eighteen Degree Water" (EDW), the Subtropical Mode Water of the western North Atlantic, as demonstrated by Argo and repeat hydrography. Weak, late winter buoyancy forcing produced shallower than usual winter mixed layers throughout the subtropical gyre, failing to thoroughly ventilate the underlying mode water, and can likely be attributed to the coinciding high, positive phase of the North Atlantic Oscillation (NAO). The only region where EDW was renewed was in the far northeastern Sargasso Sea where it is understood that the Gulf Stream plays a central role in formation; no EDW formed over the large regions of the gyre where deep winter mixed layers driven by surface buoyancy loss normally create EDW. The present investigation evaluates 2011-2012 winter buoyancy content anomalies, surface buoyancy fluxes, and advection of buoyancy via the Gulf Stream and compares them with the previous seven winters that exhibited more vigorous EDW formation. The weak 2011-2012 formation did not result from increased Gulf Stream heat advection, and was also not driven by preconditioning as the buoyancy content of the region prior to the onset of winter forcing was not unusually high. Rather, the weak formation resulted from climatologically weak surface cooling late in winter. The winter of 2007-2008 also experienced particularly weak EDW formation under similar conditions, including a high NAO and weak late winter surface cooling.

DOI10.1002/2013jc009024
Short TitleJ Geophys Res-Oceans
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