Decadal water mass variations along 20°W in the Northeastern Atlantic Ocean

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Author(s) Johnson, Gregory C., Gruber, Nicolas
Publication Type Journal Items, Publication Status: Published
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Title Decadal water mass variations along 20°W in the Northeastern Atlantic Ocean
Author(s) Johnson, Gregory C.
Gruber, Nicolas
Journal or Series Title Progress in oceanography
Volume Number 73
Issue Number 3-4
Start Page 227
End Page 295
ISSN 0079-6611
Publisher Elsevier
Publication Place Amsterdam
Publication Date 2007
Keyword(s) Dissolved oxygen
Heat storage
Ocean–atmosphere system
Ocean circulation
Temporal variations
Water masses
Eastern subpolar North Atlantic ocean
Abstract Water mass variations in the northeastern Atlantic Ocean along 20°W are analyzed with pentadal resolution over the past 15 years using data from four repeat occupations of a meridional hydrographic section running south from Iceland. The section was sampled in 1988, 1993, 1998, and 2003. The results are interpreted in the context of changes in air–sea forcing, ocean circulation, and water properties associated with the North Atlantic Oscillation (NAO). The NAO index oscillated around zero from 1984 to 1988, was strongly positive from 1989 to 1995, after which it shifted to lower positive, and occasionally negative values from 1996 to 2003. Previously published studies suggest that after the 1995–1996 shift of the NAO, the subpolar gyre largely retreated to the northwest in the northeastern Atlantic Ocean, resulting in an increasingly southeastern character of local water masses with time. Water property changes extending from the SubPolar Mode Water (SPMW) just below the seasonal pycnocline through the density range shared by Mediterranean Outflow Water and SubArctic Intermediate Water (SAIW) along 20°W are consistent with changes in wind-driven ocean circulation and air–sea heat flux associated with shifts in the NAO, especially after accounting for ocean memory. After periods of lower NAO index the SPMW is warmer, saltier, and lighter. At these same times, large increases of apparent oxygen utilization (AOU) and potential vorticity are found at the SPMW base, consistent with SPMW ventilation to lighter densities during lower NAO index periods. Deeper and denser in the water column, the cold, fresh, and dense SAIW signature within the permanent pycnocline that was most strongly present in 1993, near the culmination of a period of high NAO index, is much reduced in 1988 and 1998. In 2003, after a prolonged period of lower NAO index, increasing influence of warmer, saltier subtropical waters is clear within the permanent pycnocline. The deep penetration of the changes implies that they are caused primarily by circulation changes resulting from NAO-associated wind shifts, but changes in air–sea heat flux could also have played a role.
DOI 10.1016/j.pocean.2006.03.022
Additional Notes Received 25 February 2005, Revised 8 September 2005, Accepted 23 March 2006, Available online 4 May 2007
Document Type Article
Publication Status Published
Language English
Assigned Organisational Unit(s) 03267
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NEBIS System Number 000035650
Source Database ID PP-38840
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  author = "Johnson, Gregory C. and Gruber, Nicolas",
  title = "{D}ecadal water mass variations along 20{\textdegree}{W} in the {N}ortheastern {A}tlantic {O}cean",
  journal = "Progress in oceanography",
  year = 2007,
  volume = "73",
  number = "3-4",
  pages = "227--295",

E-Citations record created: Thu, 01 Apr 2010, 21:27:14 CET