On the structure and transport of the separated Gulf Stream

Data from two long-term observational efforts, the Oleander and Line W programs, quantify the time averaged Gulf Stream structure and transport at 70.3W and 68.5W, respectively. The Oleander project acquires high-horizontal resolution, upper 600-m shipboard acoustic Doppler current profiles along weekly round-trip transits between New Jersey and Bermuda. Line W supported two tall current meter moorings with unprecedented coverage of the full-water column about the Gulf Stream axis. Time-averaged velocity sections are constructed from each data set in stream coordinates guided by satellite altimeter data and in situ velocity and temperature observations. The Line W analysis capitalizes on the mesoscale variability that sweeps the Gulf Stream laterally over the moorings. Upper-ocean (0-600 m) transport estimates from the two sites, averaged from 2010 to 2014, are in good agreement: 60.6 Sv for the Oleander and 59.9 Sv (with 95% statistical confidence bounds for each around +/- 2 Sv). The time-averaged full-ocean-depth Gulf Stream transport inferred from the Line W moorings is 102.1 Sv (with 95% confidence bounds between 99.1 and 106.3 Sv). This estimate is weaker by about 10% than the time-averaged full-ocean-depth transport reported for the late 1980s at the same location using similar methods. This difference likely manifests interannual variability as opposed to a secular trend. Satellite altimeter data show that the recirculation cells flanking the Gulf Stream in this region exhibit a strong interannual variability as well. The presence of these recirculation cells makes it difficult to disentangle Gulf Stream throughput from recirculation components.