Propagation pathways of classical Labrador Sea Water from its source region to 26°N

More than two decades of hydrography on the Abaco line east of the Bahamas at 26°N reveals decadal variability in the salinity of classical Labrador Sea Water (cLSW), despite the long distance from its source region in the North Atlantic Ocean. Hydrographic time series from the Labrador Sea and from the Abaco line show a pronounced step-like decrease in salinity; between 1985 and 1995 in the Labrador Sea and between 1995 and 2010 at the Abaco line, suggesting a time lag between the two locations of approximately 9 years. The amplitude of the anomaly at the Abaco line is 50% of the amplitude in the Labrador Sea. A similar time lag and reduction of amplitude is found in the high-resolution OFES model, in which salinity anomalies can be observed propagating through the Deep Western Boundary Current as well as through a broad interior pathway. On its way south to the Abaco line, the cLSW becomes 8 standard deviations saltier due to isopycnal mixing with Mediterranean Outflow Water (MOW). Climatological data in the North Atlantic suggests that the mixing ratio of MOW to cLSW at the Abaco line is 1:4 and that no variability in MOW is required to explain the observed variability at the Abaco line. The data studied here suggest that decadal cLSW anomalies stay relatively coherent while getting advected, despite the important role of interior pathways.

Figure 14: Advection time scales in the OFES model to (a) the Abaco line and from (b) the Labrador Sea, determined from the lag at which correlation is highest between the time series of salinity at the base point (the black circles) and the time series of salinity at any other point in the North Atlantic in the cLSW density range. Areas where the correlation is lower than 0.75 are shaded light gray and areas where no correlations have been computed are shaded dark gray. In the model, the lag between the Labrador Sea and the Abaco line is 10 - 12 years.