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Images: Labrador Sea Water Carries Northern Climate Signal South

A: Structure of the North Atlantic basins is defined by bathymetric contours (2,000, 3,000, and 4,000 meters) progressively shaded gray. The Mid-Atlantic Ridge separates the western and eastern basins. The dominant currents at mid depths (near 1,500 meters) are approximated by the pink lines (bringing relatively warm water northward) and the blue lines (transporting cold waters southward). B: Thickness in meters of the density layer corresponding to the Labrador Sea Water (LSW). C: Temperature, in degrees centigrade, of a density surface in the middle of the LSW layer. These maps highlight the geographical distribution of the Labrador Sea Water and the Mediterranean Outflow water masses that mix to produce Upper North Atlantic Deep Water. D: Temperature profiles from the Labrador Basin and the Mediterranean Outflow region (locations are shown by x in panel A). Green shading denotes the density layer that is mapped in panel B for each profile.

Time series of Labrador Sea Water properties in its source region. Thickness is the vertical distance (meters) between two density surfaces that bracket the Labrador Sea Water. The North Atlantic Oscillation index has been overplotted on the thickness axis with high index shaded red and low index blue. Years in which surface salinity anomalies occupied the Labrador Basin are shaded green.

Depth profiles of temperature for three different years contrasting the Labrador Sea Water temperature in its cool period before World War II (1935), the peak of warming (1971), and at its coldest point (1993).

Temperature changes recorded in the 1,500 to 2,500 meter layer near Bermuda. The top plots show time series of Bermuda temperature anomaly (red curve) lagged by 6 years, thickness of the Labrador Sea Water layer (blue curve) in its formation area, and temperature of the LSW core (green curve). The lower plot shows a lagged correlation analysis for Bermuda temperature and Labrador Sea Water (LSW) thickness, which is highest for lags of 5 to 7 years. The authors? interpretation is that subpolar thickness anomalies result in variability of the volume of LSW entering the subtropics. A large volume of LSW shifts the balance of influence between LSW and Mediterranean Outflow towards LSW. When the LSW is thick, Bermuda sees colder (and fresher) conditions about 6 years later, while a thin LSW source results in stronger Mediterranean Outflow influence and Bermuda sees warmer (and saltier) conditions after about 6 years.

Temperature changes recorded in the 1,500 to 2,500 meter layer near Bermuda. The top plots show time series of Bermuda temperature anomaly (red curve) lagged by 6 years, thickness of the Labrador Sea Water layer (blue curve) in its formation area, and temperature of the LSW core (green curve). The lower plot shows a lagged correlation analysis for Bermuda temperature and Labrador Sea Water (LSW) thickness, which is highest for lags of 5 to 7 years. The authors??A? interpretation is that subpolar thickness anomalies result in variability of the volume of LSW entering the subtropics. A large volume of LSW shifts the balance of influence between LSW and Mediterranean Outflow towards LSW. When the LSW is thick, Bermuda sees colder (and fresher) conditions about 6 years later, while a thin LSW source results in stronger Mediterranean Outflow influence and Bermuda sees warmer (and saltier) conditions after about 6 years.

Thickness difference fields (left column) and temperature difference fields (right column) were constructed by subtracting thickness or temperature in two consecutive time frames at each 1-degree square in the North Atlantic. The thickness represents the LSW density layer and temperature values are taken at a density surface in the middle of that layer. Green-blue colors indicate layer thickening and/or cooling in one time frame compared to the previous time frame; yellow-red colors indicate layer thinning and/or warming.