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  1. Abstract

    The Gulf Stream is the only pathway in the subtropical North Atlantic by which warm water flows poleward. This transport of warm water and return of cold water at depth is called the Atlantic Meridional Overturning Circulation (AMOC). The dynamic method is applied to hydrocasts collected since the 1930s to estimate upper‐ocean transport (0–1,000 m) between the U.S. Continental Slope and Bermuda and separately to Africa with focus on the longest directly observable timescale. Calculating transport between the Slope and Bermuda eliminates the Gulf Stream's northern and southern recirculation gyres, while calculations between the Slope and Africa remove all other recirculating geostrophic flow. The net Slope‐Bermuda upper‐ocean transport is estimated to be 41.1 ± 0.4 Sv, decreasing by 2.0 ± 0.8 Sv between 1930 and 2020. The AMOC contribution is 18.4 ± 0.6 Sv, decreasing by 0.4 ± 0.6 Sv between 1930 and 2020.

     
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  2. Abstract

    Past studies of dispersion with float‐pairs have indicated that they may remain close together for much longer when they equilibrate on the same isopycnal, presumably due to the reduced influence of vertical shear. To examine this question more closely, we use a set of 13 and 15 float pair combinations that equilibrated within 0.1 °C (∼σθ = 0.01 kg m−3) of each other on two density surfaces in the main thermocline in a Lagrangian dispersion study. Their average rate of separation after launch was 0.0021 ± 0.0014 ms−1(∼5.5 km after 30 days). Relative dispersion is accurately expressed by <D2> = 4•106exp (t/10.8) m2from start to about 30 days. Relative diffusivity (K) versus separation dropped well below the classical 4/3rds power law settling out at about 2–3 m2s−1for separations less than ∼6 km, far lower than results from other float studies, but in accord with dye dispersion estimates.

     
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  3. Abstract

    The flow of warm water into the Nordic Seas plays an important role for the mild climate of central and northern Europe. Here we estimate the stability of this flow thanks to the extensive hydrographic record that dates back to the early 1900s. Using all casts in two areas with little mean flow just south and north of the Greenland‐Scotland Ridge that bracket the two main inflow branches, we find a well‐defined approximately ±0.5 Sv volume transport (and a corresponding ±30 TW heat flux) variation in synchrony with the Atlantic multidecadal variability that peaked most recently around 2010 and is now trending down. No evidence is found for a long‐term trend in transport over the last 70 to 100 years.

     
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