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01.26.10: What has been done since Bower et al. (2009)?

Zhang (2010)

“a coupled climate model (GFDL CM2.1), with the existence of interior pathways of North Atlantic Deep Water (NADW) from Flemish Cap to Cape Hatteras as that observed recently”

The author shows that the NADW takes more time in migrating south than if it would have bee advected within the DWBC.

Lozier (2010)

A nice “remise en cause” of the paradigm of the conveyor belt.

She mentions Dengler et al. (2004) where eddies along the boundary, rather than a steady DWBC, transport water masses meridionally. What does she mean, then by “The ubiquity of this phenomenon remains unknown” (p. 4, end of second paragraph, left column)?

She synthesizes the Lagragian observations.

See the analysis of an ocean model of Getzlaff et al. (2006).

“The fact that these recent float observations and modeling results directly contradict the predicted dominance of the DWBC theorized by Stommel is reconciled by considering the effect of eddies on the deep flow.” See Holland and Lin (1975) which I had but never read –maybe a mistake.

  1. eddies can drive Eulerian-mean flow
  2. eddies can homogenized PV
  3. do we really have an interior branch separated from the western boundary or should we consider rather that the boundary within which the total transport occurs is wider and diffusive in nature due to the eddies than the boundary defined by the Eulerian-mean flow? In the first case, the timescale between the interior and boundary pathway can be different; not in the second case.

The question about the steadiness of transport is raised also for the surface ocean (see Brambilla and Talley 2006, followed by Hakkinen and Rhines 2009). There, it was recently found that the transport is variable and controlled by large-scale winds.

In summary, “[c]onsiderably less certain is the 3D structure of the overturning” and “[g]lobal pathways for the waters in the lower and upper limbs and the mechanisms governing their spatial and temporal variability remain unknown”.

Dengler et al. (2004)

Although the paper was written before that of Bower et al. (2009), it is relevant to the their work as described by Lozier (2010).

Observations show that south of 8S, the DBWC breaks up into eddies and the latter transport the water mass.

About the fact that overall transport in the Atlantic is considerably less that transport estimates from the DWBC: “The existence of deep recirculation gyres adjacent to the western boundary is conjectured to explain such locally increased DWBC transports” (see McCartney, M. S. Recirculation components to the deep boundary current of the northern North Atlantic. Prog. Oceanogr. 29, 1992; Hogg, N. G. On the transport of the Gulf Stream between Cape Hatteras and the Grand Banks. Deep-Sea Res. I 39, 1992).

“The NADW transport carried by the migrating eddies therefore corresponds roughly to the southward NADW transport determined at 5S”. Consistent with the picture that eddies do not change the overall transport, because the transport is fixed upstream.