Structure, transport, and vertical coherence of the Gulf Stream from the Straits of Florida to the Southeast Newfoundland Ridge

• Analysis of new and historical data sets along the length of the Gulf Stream pathway allows for the development of a consistent understanding of the flow and property changes as the current evolves downstream.
• Surface and deep flows within the Gulf Stream are generally incoherent for most time scales between one day and one year, regardless of the location along the Gulf Stream pathway.
• The Gulf Stream flow at 27°N and 42°N appears to operate in two independent layers, whereas at 38°N the Gulf Stream flow exists as three independent layers.
• Proper understanding of Gulf Stream variability requires simultaneous observations throughout the water column.
• Transport exchange between the Gulf Stream and the bounding recirculations to the north and south appears to have a maximum for inflow near 68°W based on analysis of data sets in the region.

Data from three independent and extensive field programs in the Straits of Florida, the Mid-Atlantic Bight, and near the Southeast Newfoundland Ridge are reanalyzed and compared with results from other historical studies to highlight the downstream evolution of several characteristics of the Gulf Stream's mean flow and variability. The three locations represent distinct dynamical regimes: a tightly confined jet in a channel; a freely meandering jet; and a topographically controlled jet on a boundary. Despite these differing dynamical regimes, the Gulf Stream in these areas exhibits many similarities. There are also anticipated and important differences, such as the loss of the warm core of the current by 42°N and the decrease in the cross-frontal gradient of potential vorticity as the current flows northward. As the Gulf Stream evolves it undergoes major changes in transport, both in magnitude and structure. The rate of inflow up to 60°W and outflow thereafter are generally uniform, but do exhibit some remarkable short-scale variations. As the Gulf Stream flows northward the vertical coherence of the flow changes, with the Florida Current and North Atlantic Current segments of the Gulf Stream exhibiting distinct upper and deep flows that are incoherent, while in the Mid-Atlantic Bight the Gulf Stream exhibits flows in three layers each of which tends to be incoherent with the other layers at most periods. These coherence characteristics are exhibited in both Eulerian and stream coordinates. The observed lack of vertical coherence indicates that great caution must be exercised in interpreting proxies for Gulf Stream structure and flow from vertically-limited or remote observations.