Lozier, M., Bower, A., Furey, H., Drouin, K., Xu, X., & Zou, S., 2022. Overflow Water Pathways in the North Atlantic. Progress In Oceanography, 102874. https://doi.org/10.1016/j.pocean.2022.102874
Cumulative two-year probability distributions from the Markov chain (top panels), HYCOM (middle panels) and FLAME (bottom panels) simulations. Particles were released at the EG (left panels), WRR (middle panels) and ERR (right panels) sites in the subpolar North Atlantic. The probability distribution is shown as the percentage of particle positions such that the total value of all grid cells adds up to 100%. 200000, 200000, and 300,000 particles are launched from sites east of Greenland, west of the Reykjanes Ridge, and east of the Reykjanes Ridge (the EG, WRR, and ERR deployment sites, respectively), for the Markov chain. 11,820 (5940 in Northeast Atlantic Deep Water, or NEADW, and 5880 in Denmark Strait Overflow Water, or DSOW), 4320 (in NEADW), and 6600 (in ISOW) particles are launched from the EG, WRR, and ERR deployment sites, respectively, for HYCOM. 6236 (4670 in NEADW and 1566 in DSOW), 7286 (in NEADW) and 6236 (in ISOW) particles are launched from the EG, WRR, and ERR deployment sites, respectively, for FLAME. At each grid point, the particle count is inclusive of all layers defined as OW (see Supplementary Information). Bathymetry is contoured at 1000, 2000, and 3000 m. (Adapted from Figure 3 in Lozier et al 2022.)
As part of the international Overturning in the Subpolar North Atlantic Program (OSNAP), 135 acoustically-tracked deep floats were deployed to track the spreading pathways of Iceland-Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW) from 2014 to 2018. These water masses, which originate in the Nordic Seas, are transported by the deepest branch of the Atlantic Meridional Overturning Circulation (AMOC). The OSNAP floats provide the first directly-observed, comprehensive Lagrangian view of ISOW and DSOW spreading pathways throughout the subpolar North Atlantic. The collection of OSNAP float trajectories, complemented by model simulations, reveals that their pathways are (a) not restricted to western boundary currents, and (b) remarkably different from each other in character. The spread of DSOW from the Irminger Sea is primarily via the swift deep boundary currents of the Irminger and Labrador Seas, whereas the spread of ISOW out of the Iceland Basin is slower and along multiple export pathways. The characterization of these Overflow Water pathways has important implications for our understanding of the AMOC and its variability. Finally, reconstructions of AMOC variability from proxy data, involving either the strength of boundary currents and/or the property variability of deep waters, should account for the myriad pathways of DSOW and ISOW, but particularly so for the latter. https://doi.org/10.1016/j.pocean.2022.102874
This research was funded by the National Science Foundation (Grants OCE-2017522, OCE-1756361, OCE-1851075, and OCE-2038449) and published in the Journal of Physical Oceanography.