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Natural Climate Variability on Decade-to-Century Time Scales
(a) Annual runoff from the North American continent into the Arctic Basin, 1930-67, with mean (solid line) and ± 1 standard deviation (dashed line) indicated; (b) lagged cross-correlation between runoff (above) and Koch Index of ice severity (below) at the Icelandic coast, 1915-75; (c) the Koch sea-ice severity index for Iceland. (All from Mysak and Power, 1991; reprinted with permission of the Canadian Meteorological and Oceanographic Society.)
that is inherent in such processes. The approximately 14-year circulation period of the subpolar gyre is plainly one such control, but the decadal regimes in southeastern U.S. air temperature shown in Figure 11, the 6.7-year spectral maximum in the North Atlantic oscillation index (Rogers,
Anomalies of (a) temperature and (b) salinity in June at 25 m depth in a study area between Iceland and Jan Mayen (67- 69°N, 11-15°W). The long-term means, 1950-58, are also shown. (From Malmberg, 1973; reprinted with permission.)
Schematic diagram illustrating the suppression of convection north of Iceland as upper-ocean salinities decrease below 34.7. (From Dickson et al., 1988; reprinted with permission of Pergamon Press.)
1984), the multi-year advective time lag of ice drift from the Beaufort Sea to Greenland and Labrador (Mysak and Power, 1991; Mysak and Manak, 1989) plainly have the potential to lend a degree of periodicity to the process. Conceptual models for these periodic anomalies—some of great complexity (see Figure 3 of Mysak and Power, 1991)—have been proposed (see also Darby and Mysak, 1993; Ikeda, 1990). Under this rationale the Great Salinity Anomaly was merely a more obvious, high-amplitude iteration of a regular event.
THE GLOBAL SCALE: PRODUCTION OF NORTH ATLANTIC DEEP WATER AND THE THERMOHALINE CIRCULATION
To demonstrate a global role for Denmark Strait exchanges, there can be few more eloquent illustrations than Figure 16 (from Charles and Fairbanks, 1992), in which the d13C history in benthic forams from the sea-floor sedi-