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Pacific Water circulation (origin, forcing, pathways)

Ye. Aksenov, R. Gerdes, A. Nguyen, E. Watanabe, A. Proshutinsky

The circulation of Pacific Water may be coherent with the surface currents but its pathways are not known from direct observations. Recently the vertical structure of this layer and its properties have been revised by Shimada et al., (2001) and Steele et al., (2004)  where the presence of two types of summer Pacific halocline water and one type of winter Pacific halocline water in the Beaufort Gyre were reported. According to the Environmental Working Group analysis, the total thickness of the Pacific layer in the Beaufort Gyre is approximately 150 m. This thickness is subject to temporal variability (McLaughlin et al., 2003) depending on wind stress and circulation modes (Proshutinsky et al., 2002).  Steele et al. (2004) found similar evidence in their examination of data from the 1980s and 1990s.  Accordingly, it is important to investigate the variability of the different Pacific-origin water components, their circulation patterns and their role in stabilizing or destabilizing the Canada Basin and the Arctic Ocean climatic circulation. Conditions proposed for this experiment and model output parameters are presented below.

a.     Questions :

  • How PW crosses the Arctic Ocean during cyclonic and anti-cyclonic regimes of the circulation?
  • How much of FW associated with the PW is in the CAA/Fram Strait outflow; what caused the recent decline of the PW fraction east of Greenland?
  • How big was the change in the storage of the PW and associated FW in the Arctic Ocean over the last 50 years?

b.    Experiments :

  • Identify pathways of  the PW out of the Chukchi Sea into the Arctic Ocean: ideally we should  be able to detect the eastern route into the Beaufort Sea and the western route into the Makarov Basin. Relate the variability of the transports along the routes to the type of the circulation in the Western Arctic.
  • Assess variations of the PW fraction in the polar outflow west and east of Greenland. Compare simulated in models fractions of the PW and FW flux of PW on the main transects. Compare simulations with the observations where possible.
  • From sources and sinks of PW estimate the recent 2001-2008 change of the PW content.

c.    Which fields :

  • The model experiments require the PW tracer release in the Chukchi Sea, as close as possible to the Bering Strait. If PW tracer could not be included, TS or density classification for PW might be considered.
  • The standard period for the model fields is 1948-2008, although for some model it will be shorter
  • Monthly-mean depth-averaged 10-250 m horizontal distribution of the PW fraction For the Arctic Ocean.
  • Monthly-mean TS and PW tracer vertical distributions, monthly-mean timeseries of the total and PW-associated FW transports through the sides of  the ‘box’ bounded by meridional transects ~150°W and ~180°W, zonal ~75°N and ~80°N.
  • Monthly-mean TS and PW tracer vertical distributions, monthly-mean timeseries of the total and PW-associated FW transport for the transects across Fram Strait at ~79°N (coinciding with AWI transects) and Davis Strait at ~66.5°N.
  • Monthly-mean timeseries of the total and PW-associated FW transport for the transects across Nares Strait at ~81.5°N, Jones Sound ~80°W, Lancaster Sound at ~94°W, and Hudson Strait at ~70°W, provided the model resolution is high enough to resolve these passages.