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A Closer Look at Particle Exchange in the Gulf Stream

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  • 1 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
  • | 2 Ocean Sciences Program, Duke University, Durham, North Carolina
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Abstract

The trajectories of 95 isopycnal floats deployed in the Gulf Stream in the last decade have shown that a substantial amount of particle exchange takes place between the Gulf Stream and the surrounding fluid at the level of the main thermocline. This exchange is suggestive of significant cross-stream eddy mixing, but in order to accurately interpret the float exchange in terms of property exchange the location of float deployment was assessed relative to the strong potential vorticity front associated with the Gulf Stream. The basic result of this analysis is that most of the observed float exchange is not representative of cross-frontal exchange. At the level where a strong potential vorticity front is present, some fluid particles escape from the jet, but most of them stay on the same side of the front. In the deep main thermocline, significant particle exchange is observed between the Gulf Stream and fluid on both sides of the jet, but this exchange is indicative of particles circulating in a relatively homogeneous pool of potential vorticity and thus does not signify a cross-stream property flux. These characteristics of particle exchange in the Gulf Stream are found to be generally compatible with the results from a study of particle behavior in a quasigeostrophic eddy-resolving GCM.

Abstract

The trajectories of 95 isopycnal floats deployed in the Gulf Stream in the last decade have shown that a substantial amount of particle exchange takes place between the Gulf Stream and the surrounding fluid at the level of the main thermocline. This exchange is suggestive of significant cross-stream eddy mixing, but in order to accurately interpret the float exchange in terms of property exchange the location of float deployment was assessed relative to the strong potential vorticity front associated with the Gulf Stream. The basic result of this analysis is that most of the observed float exchange is not representative of cross-frontal exchange. At the level where a strong potential vorticity front is present, some fluid particles escape from the jet, but most of them stay on the same side of the front. In the deep main thermocline, significant particle exchange is observed between the Gulf Stream and fluid on both sides of the jet, but this exchange is indicative of particles circulating in a relatively homogeneous pool of potential vorticity and thus does not signify a cross-stream property flux. These characteristics of particle exchange in the Gulf Stream are found to be generally compatible with the results from a study of particle behavior in a quasigeostrophic eddy-resolving GCM.

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