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Late-Holocene Drought on Mexico's Yucatan Peninsula
Reference
Hodell, D.A., Brenner, M. and Curtis, J.H.  2005.  Terminal Classic drought in the northern Maya lowlands inferred from multiple sediment cores in Lake Chichancanab (Mexico).  Quaternary Science Reviews 24: 1413-1427.

Background
Based on a single sediment core retrieved in 1993 from Lake Chichanacanab in the center of the northern Yucatan Peninsula of Mexico (1950'-1957'N, 8845'-8846'W), Hodell et al. (1995) provided evidence for a protracted drought during the Terminal Classic Period of Mayan civilization (AD 800-1000).  Subsequently, based on two additional sediment cores retrieved from the same location in 2000, Hodell et al. (2001) determined that the massive drought likely occurred in two distinct phases (750-875 and 1000-1075).

What was done
In this most recent study, Hodell et al. (2005) returned to Lake Chichanacanab in March of 2004 and retrieved a number of additional sediment cores in some of the deeper parts in the lake, with multiple cores being taken from its deepest point.  Depth profiles of bulk density data were then obtained by means of gamma-ray attenuation, as were profiles of reflected red, green and blue light via a digital color line-scan camera.

What was learned
In the words of the researchers, "the data reveal in great detail the climatic events that comprised the Terminal Classic Drought and coincided with the demise of Classic Maya civilization."  In this regard, they report that "the Terminal Classic Drought was not a single, two-century-long megadrought, but rather consisted of a series of dry events separated by intervening periods of relatively moister conditions," and that it "included an early phase (ca 770-870) and late phase (ca 920-1100)."  Last of all, they say that "the bipartite drought history inferred from Chichancanab is supported by oxygen isotope records from nearby Punta Laguna," and that "the general pattern is also consistent with findings from the Cariaco Basin off northern Venezuela (Haug et al., 2003), suggesting that the Terminal Classic Drought was a widespread phenomenon and not limited to north-central Yucatan."

What it means
Based on proxy temperature data from several places in North America, it would appear that the Terminal Classic Drought that led to the demise of Mayan civilization likely occurred during the climatic transition between the Dark Ages Cold Period and Medieval Warm Period, when increasing temperatures may have exacerbated land water loss via evaporation in the midst of a prolonged period of significantly reduced precipitation.  See also, in this regard, our review of the study of Almeida-Lenero et al. (2005).

References
Almeida-Lenero, L., Hooghiemstra, H., Cleef, A.M. and Van Geel, B.  2005.  Holocene climatic and environmental change from pollen records of Lakes Zempoala and Quila, central Mexican highlands.  Review of Palaeobotany and Palynology 136: 63-92.

Haug, G.H., Gunther, D., Peterson, L.C., Sigman, D.M., Hughen, K.A. and Aeschlimann, B.  2003.  Climate and the collapse of Maya civilization.  Science 299: 1731-1735.

Hodell, D.A., Curtis, J.H. and Brenner, M.  1995.  Possible role of climate in the collapse of Classic Maya civilization.  Nature 375: 391-394.

Hodell, D.A., Brenner, M., Curtis, J.H. and Guilderson, T.  2001.  Solar forcing of drought frequency in the Maya lowlands.  Science 292: 1367-1369.

Reviewed 21 December 2005