Transport and Modification of Water Masses within the Gulf Stream from Underwater Glider Observations

The Gulf Stream comprises the upper limb of the Atlantic Meridional Overturning Circulation in the subtropical gyre; it carries large amounts of heat and water from the tropics to higher latitudes and thus plays an important role in global climate. It is well known that Gulf Stream transport increases along the US East Coast through the entrainment of different water masses along the way. However, the details of the transport increase and the associated entrainment and water mass modification remain poorly resolved due to a 1500-km-long gap in sustained subsurface Gulf Stream measurements. Spray glider observations collected over more than 25 missions in the past several years are used to elucidate the evolution of Gulf Stream volume transport by water class. The repeated glider surveys span more than 15 degrees of latitude between the Florida Strait and New England and provide over 180 cross-Gulf Stream transects with concurrent measurements of hydrography and velocity. They are used to calculate the time-mean Gulf Stream transport as a function of along-stream distance. The advection and modification of remotely formed intermediate waters (such as upper Labrador Sea Water and Antarctic Intermediate Water) within the Gulf Stream are analyzed. The glider-based observations agree well with independent water class transport estimates in the Florida Strait, while also offering a first look at the entrainment further downstream.