Reconstruction of the main modes of variability in the North Atlantic over the past 600 years using a collection of high-resolution paleoceanographic proxy data

A collection of 37 near-annually-resolved proxy records is used to evaluate the main modes of marine variability in the North Atlantic for the past 600 years. The temporal gaps in the proxy data are first filled in using a nesting procedure, and the 19 longest proxy time series are used to derive the modes of variability linked to the instrumental sea surface temperature (SST) data. By comparing with other indices and reconstructions, the four main modes of variability in the North Atlantic appear most closely related to 1) the North Atlantic subtropical/subpolar SST dipole (often used as an indicator for Atlantic Meridional Overturning Circulation [AMOC] variability), 2) the Atlantic Multidecadal Variability (AMV), 3) the North Atlantic Tripole/Oscillation, and 4) the East Atlantic Pattern. Modes 1 and 2 show a significant change in variability during the historical period, whereas modes 3 and 4 show more high frequency variability. This change is also observed in the correlations between modes during the historical and pre-industrial periods. The AMV mode published here is the first to be reconstructed exclusively using multi-proxy marine data from across the North Atlantic. The suitability of the spatial fingerprint representative of AMOC dynamics is investigated from simulations of a large climate model ensemble, and results show that the derived AMOC trends are overestimated. Our analysis suggests that multiple dynamical/thermodynamical processes influence the SST-dipole mode commonly used to reconstruct AMOC behavior. The implications of this result may provide avenues for future research and should act as a cautionary note.