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Primary Productivity Dynamics in the Sulu Sea
Reference
de Garidel-Thoron, T. and Beaufort, L. 2001. Millennial-scale dynamics of the East Asian winter monsoon during the last 200,000 years. Paleoceanography 16: 1-12.

What was done
The authors reconstructed a 200,000-year history of primary productivity (PP) in the Sulu Sea north of Borneo (847'N, 12117'E), based on abundances of the coccolithophore Florisphaera profunda measured in a 36-meter giant piston core retrieved from a depth of 3600 meters. Three time-slices were explored in particular detail in order to determine high-frequency cycles in the PP record: one from 160 to 130 ka, one from 60 to 30 ka, and one from 22 to 4.1 ka.

What was learned
The finest-scale repeatable feature observed in all three time-slices was a climate-driven PP oscillation that had a mean period of approximately 1500 years.

What it means
With respect to the ~1500-year PP cycle, the authors say its occurrence in the three different time-slices is suggestive of "a common origin and an almost stationary signal across different climatic conditions." They also point out the PP cycle's similarity to the 1470-year temperature cycle observed by Dansgaard et al. (1984) in the Camp Century δ18O ice core record, the ~1500-year δ18O and chemical markers cycles observed by Mayewski et al. (1997) in the Summit ice core, the 1470-year climate cycle found by Bond et al. (1997) in North Atlantic deep-sea cores, and the 1500-year climate cycle found by Campbell et al. (1998) in an Alaskan lake, which observations lead the authors to suggest there is also "a common origin" for the documented cyclicity in the climate of both high and low latitudes. (See also Bond et al., 2001.)

Once again, we thus have powerful evidence for a persistent, global, millennial-scale cycle of climate that occurs throughout glacial and interglacial periods alike, the most recent manifestations of which are the Medieval Warm Period and Little Ice Age. Projecting this cyclical behavior forward - which is about as sound a thing as one could ever do, based on hundreds of thousands of years of unfailing repetitive behavior - we see we are on the threshold of a several-hundred-year period of what we could well call the optimum climatic conditions of the Modern Warm Period. Hence, there is no compelling reason to believe that any of the warming of the past century is related to the historical and still-ongoing rise in the air's CO2 content. It is merely a continuation of what has happened over and over, again and again, throughout the history of the planet as far back in time as can be traced.

References
Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.

Bond, G., Showers, W., Chezebiet, M., Lotti, R., Almasi, P., deMenocal, P., Priore, P., Cullen, H., Hajdas, I. and Bonani, G. 1997. A pervasive millennial scale cycle in North-Atlantic Holocene and glacial climates. Science 278: 1257-1266.

Campbell, I.D., Campbell, C., Apps, M.J., Rutter, N.W. and Bush, A.B.G. 1998. Late Holocene ca.1500 yr climatic periodicities and their implications. Geology 26: 471-473.

Dansgaard, W., Johnsen, S.J., Clausen, H.B., Dahl-Jensen, N., Gundestrup, N. and Hammer, C.U. 1984. North Atlantic climatic oscillations revealed by deep Greenland ice cores. In: Hansen, J.E. and Takahashi, T. (Eds.), Climate Processes and Climate Sensitivity, American Geophysical Union, Washington, DC, pp. 288-298.

Mayewski, P.A., Meeker, L.D., Twickler, M.S., Whitlow, S., Yang, Q., Lyons, W.B. and Prentice, M. 1997. Major features and forcing of high-latitude Northern Hemisphere atmospheric circulation using a 110,000-year long glaciogeochemical series. Journal of Geophysical Research 102: 26,345-26,366.


Reviewed 27 March 2002