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No evidence of Gulf Stream slow down!

In contrast to recent claims of a Gulf Stream slow-down (Sallenger et al., 2012; Ezer et al., 2013), two decades of Oleander-derived upper-layer Gulf Stream transport show no evidence of a decrease.

Using a well-constrained definition of Gulf Stream layer transport (Rossby et al. 2010), the linear least square fit yields a mean surface-layer transport = 1.35 x 105 m2 s-1 with a 0.13% negative trend per year. Assuming geostrophy these layer transports correspond to a mean cross-stream sea level difference of 1.17 m, with sea level decreasing 0.03 m over the 20-year period. Not only is this is not significant at the 95% confidence level, it is a factor of 2-4 less than that alleged from coastal sea-level rise.

Annually averaged layer transport stepped every half-year. The slope the linear least square fit is -173 ± 377 m2s-1yr-1, equivalent to a decrease in sea level difference of 1.5 ± 3.3 mm yr-1 or 0.03 m over the 20 year observing period. The dashed lines indicate the 95% confidence limits of the linear fit. The right axis shows 0-2000 m transport assuming a scale factor of 700 based upon the 1980-1983 Pegasus data set at 73°W (Halkin and Rossby, 1985).

Ezer, T., L. P. Atkinson, W. B. Cortlett, and J. L. Blanco (2013), Gulf Stream’s induced sea level rise and variability along the U.S. mid-Atlantic coast, J. Geophys. Res., 118, doi:10.1002/jgrc.20091.

Halkin, D. and H.T. Rossby (1985), The Structure and transport of the Gulf Stream at 73° W. J. Phys. Oceanogr., 15, 1439-1452.

Rossby, T., C. Flagg, and K. Donohue (2010), On the Variability of Gulf Stream transport from seasonal to decadal timescales. J. Mar. Res.,68,503-522.

Sallenger Jr, A. H., K. S. Doran, and P. A. Howd (2012), Hotspot of accelerated sea-level rise on the Atlantic coast of North America. Nature Clim. Ch., 2, 884-888.