Water mass transport

Here are represented classical θ-S diagrams of  water masses encountered along the Ovide section in the subpolar gyre. The gyre was divided in three areas : the Western Boundary Current (left column), the central and esatern Irminger Sea (central column), and the Iceland Basin (right column).

Typical water masses are : 

  • DSOW : Denmark Strait Overflow Water
  • ISOW : Iceland-Scotland Overflow Water
  • lLSW : lower Labrador Sea Water
  • uLSW : upper Labrador Sea Water
  • ISW : Icelandic Slope Water
  • SAIW : Sub-Arctic Intermediate Water

Coloured squares represent the transports (in Sverdrups) that were binned according to water properties. Some specifics isopycnal lines are drawn :

  • σMOC separates the upper from the lower branch of the Meridional Overturning Circulation (32.1 ≤ σ1≤ 32.2);
  • σD is the upper limit of the deep waters (σ2 = 36.94)
  • σB is the upper limit of the DSOW (σ2 = 37.1)

 

 

Western Boundary Current

Central and Eastern Irminger Sea

Iceland Basin

2002

2004

2006

2008

2010

 

These diagrams appear as a concise way to gain knowledge on the water masses transported by the main currents, and on the associated variability from year to year. Here are a few results deduced from these figures, reported by Lherminier et al. (2010):

  • The lLSW, formed in the Labrador Sea in the mid 1990s, is disappearing progressively from the eastern subpolar gyre, while the lighter uLSW, formed at the beginning of the 2000s, gains in volume. Both vintages are advected northwards in the Iceland Basin and in the central and eastern Irminger Sea; they are exported southwards in the Western Boundary Current but loss their θ-S signature in the swiftest part of the current inshore.
  • Depending on the years, some water of Atlantic origin is advected in the East Greenland-Irminger Current (i.e. the Western Boundary Current above σD), but has lost enough heat and salt to belong to the lower branch of the MOC, denser than σMOC. Salinities are found greater than 35.05 in 2004, 2008 and 2010.