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Atlantic Water circulation

R. Gerdes, Ye. Aksenov, A. Nguyen, W. Maslowski, C. Postlethwaite, R. Gerdes

The cyclonic pattern of Atlantic water propagation along the continental slope, proposed by Rudels et al. (1994) is supported by some numerical models (Holland, Karcher, Holloway, AOMIP, pers. com.). However other models (Häkkinen, Maslowski, Zhang, AOMIP, pers. com.) show anticyclonic rotation of this “wheel”. McLauglin et al., (2004) showed that Atlantic Water as much as 0.5oC warmer than the historical record were observed in the eastern Canada Basin relatively recently. These observations signaled that warm-anomaly Fram Strait waters, first observed upstream in the Nansen Basin in 1990, had arrived in the Canada Basin.  The mechanisms that drive the mean and time-varying Atlantic Water circulation require further investigation. The major experiments for these studies can be subdivided on three categories reflecting a) the general circulation of the Atlantic Water layer and causes of its variability; b) investigation the Atlantic Water inflow via Fram Strait in via St. Anna Trough (the Kara and Barents Seas), and c) model validations based on observations from NABOS project along the Siberian continental slope. Major details and conditions for these experiments are summarized below.

AW circulation sense and variability: G. Holloway

a.    Questions :

  • Right direction of circulation? Build of previous papers on this topic

b.    Experiments :

  • Compare basin-scale AW circulation and topostrophy in the models (Greg Holloway might be interested in pursuing this.)

c.    Which fields :

  • Monthly-mean stream functions 1948-2008
  • Model topography
  • Wind curl 1948-2008
  • Momentum balance terms
  • Topostrophy

Model validation of AW circulation along Siberian Shelf: Ye. Aksenov, A. Nguyen

a.    Questions :

  • How well the AW flow along the shelf is simulated in the models?
  • What are routes of the AW flow into the Eurasian and Makarov basins?

b.    Experiments :

  • Assess strength, position/depth, TS of the AW flow along the shelf and estimate associated heat/salt fluxes and their variability for 1948-2008. Compare model results with observations.
  • Estimate partitioning of the flow along the Gakkel and Lomonosov ridges and inflow into the Makarov Basin,

c.    Which fields :

  • Monthly-mean timeseries of the total and AW-associated volume/heat/salt transports across specified sections (provisionally ~105°E, ~125°E, ~140°E, ~155°E), and through sides of two ‘boxes’, around the Siberian end of the Lomonosov Ridge and around the Eurasian end of the Gakkel Ridge. AW is specified with S>34.8 and T>0°C. Additionally, AW fraction, defined from tracers released in the Barents Sea and Fram Strait will be used.
  • CTD data and current meter data from moorings from the NABOS transects 2002-2008.

AW inflow: W. Maslowski, A. Nguyen, Ye. Aksenov, C. Postlethwaite, R. Gerdes

a.    Questions :

  • How well represented? Dependence on resolution and/or parameterizations. Effect of circulation of AW in the Arctic Ocean?
  • Change of the heat storage of the AW layer
  • How do tides affect Barents Sea Branch of AW inflow?
  • Relative contribution of AW inflow through Fram Strait and the Barents Sea; their dependence on atmospheric forcing, sea ice state, and upstream oceanic conditions
  • Relative role of buoyancy and wind forcing over the Arctic Ocean for the AW inflow

b.    Experiments :

  • Assess strength, position/depth, TS of the AW inflow through Fram Strait and estimate associated heat/salt fluxes and their variability for 1948-2008, compared model results to the published observational estimates.
  • Assess the contribution of heat and salt of the Barents Sea Branch of AW inflow 1948-2008.
  • Estimate heat content of the AW layer in the Arctic ocean
  • Assess impact of including tides in model on AW transport through Barents Sea
  • Compare model versions of different resolution and parameterizations regarding their representation of the AW inflow
  • Calculate time series of AW volume flux north through Fram strait and through the Barents Sea; relate timeseries to atmospheric forcing fields and sea ice fields
  • Modify atmospheric forcing over the subpolar North Atlantic and the Nordic Seas to assess impact of upstream oceanic conditions
  • Modify wind and buoyancy forcing over the Arctic Ocean to assess their respective role for the AW inflow.
  • Idealized experiments to elucidate the cause of AW flow into the Arctic Ocean

c.    Which fields :

  • Monthly-mean timeseries of the total and AW-associated volume/heat/salt transports across specified sections in Fram Strait and  Barents Sea (provisionally AWI transect, Norway-Bjornaya transect, St Anna Trough section, Spitsbergen - Franz Josef Land and Franz Josef Land - Novaya Zemlya sections). AW is specified with S>34.8 and T>0°C. Additionally, AW fraction, defined from tracers release in the Barents Sea and Fram Strait will be used.
  • Monthly-mean timeseries of the AW heat content calculated from aforementioned AW definition.
  • Monthly-mean TS and velocity fields in the Barents Sea for 2000-2001. Monthly timeseries of the cross-section velocity, T, S, volume, heat and salt transports for the same period across the frequently visited observational transects in the Barents Sea (e.g. Norway-Bjornoya, Vardo, Kola, Wilkitsky Strait, Spitsbergen- Franz-Josef Land, and Franz-Josef Land - Novaya Zemlya sections).
  • Monthly-mean sea ice fraction, thickness and sea ice melt fields
  • Monthly-mean wind, precipitation less evaporation, SSH