Weakening of the Florida Current during 1909-2018

The Florida Current marks the beginning of the Gulf Stream at Florida Straits, and plays an important role in climate. But, its temporal evolution over the last century has been unclear, due to a lack of sustained circulation measurements. Here I reconstruct annual Florida Current transport at 27ºN over 1909-2018 using probabilistic methods and principles of ocean dynamics applied to shorter observations of the transport and longer coastal sea-level data. Florida Current transport very likely (probability P=0.93) has weakened since the 1920s such that modern measurements in the Florida Straits since 1982 likely (P=0.87) depict the Florida Current in a reduced transport state. The weakest decadally averaged transport over the last 110 y probably (P=0.74) occurred sometime during the last two decades. The weakening of the Florida Current transport is consistent with sea-surface cooling observed over the subpolar Atlantic and a hypothesized slowing of the deep Atlantic meridional overturning circulation over the last century, and corroborates model predictions that a slowdown of the deep overturning circulation under climate change is compensated mostly by a reduced surface western boundary current.