A recent article appeared in Nature suggested that the AMOC has been very weak during the past 150 years since the end of the Little Ice Age (LIA) , and that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA weakened Labrador Sea convection and thus the AMOC. They also suggested that the lack of a subsequent recovery may have resulted from hysteresis (i.e., instability of thermohaline circulation) or from 21st century melting of the Greenland Ice Sheet.
Another recent Nature article developed (or improved) a SST-based proxy (or fingerprint) for AMOC strength. Their proxy AMOC fingerprint consists of a cooling in the subpolar gyre region due to reduced heat transport, and a warming in the Gulf Stream region due to a northward shift of the Gulf Stream, indicating that AMOC has been steadily weakening since around 1950, strengthened shortly during the 1990s and 2000s, then weakened again.
Nature news article about the above two papers:
A related paper recent published in the Geophysical Research Letters: