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Images: Transient Tracers Track Ocean Cimate Signals

A bird's eye view of the distribution of tritium in the North Atlantic. Picture yourself floating a few hundred miles above Norway, looking southwestward down at the North Atlantic. North America is in the top right corner of the view, Greenland to the lower right, and parts of Europe, Great Britain, and Africa are visible on the lower left. The spikes are ocean islands. The blue "blanket" is the 1 Tritium Unit isosurface (surface of constant tritium measured in 1981). (One Tritium Unit equals one tritium atom to 1018 hydrogen atoms.) Underneath this blanket lies water that has not been appreciably ventilated (in contact with the atmosphere) while water above this level has been ventilated since the 1960s

A time series of tritium in the Sargasso Sea near Bermuda. The plot of tritium vs. depth and time shows the sudden arrival of tritium at intermediate depths (1,000 to 1,500 meters) in the late 1970s, and at deeper depths (2,000 to 2,500 meters) in the late 1980s. These events correspond to the onset of cooling at these levels, and signal the arrival of newly ventilated waters in response to climate changes farther north.

Four chlorofluorocarbon (CFC) sections taken at various times along 55°W south of the Grand Banks. Note the absence of any significant CFC signal at the depth of the Labrador Sea Water (about 1,500 meters depth) in 1983, but the sudden flooding of these depths with CFCs in the later sections, as newly formed Labrador Sea Water flows around the Grand Banks and into the Sargasso Sea. These changes correspond to the tritium increases seen in the Bermuda time series (see previous figure).

The downstream evolution of tritium (upper panel, in tritium units) and tritium-helium age (lower panel, in years) vs. distance in the core of the deep western boundary current. Note the approximately tenfold reduction in tritium content in the Deep Western Boundary Current core due to dilution with older, surrounding deep water, and the linear increase in age downstream. The age increase is consistent with a mean speed of about 1.5 centimeters per second