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A 1300-Year History of West-Central Mexican Cloud Forest Climate
Figueroa-Rangel, B.L., Willis, K.J. and Olvera-Vargas, M. 2010. Cloud forest dynamics in the Mexican neotropics during the last 1300 years. Global Change Biology 16: 1689-1704.

What was done
Working in the Sierra de Manantlan Biosphere Reserve (SMBR) in west-central Mexico, the authors constructed a 1300-year history of the reserve's cloud forest vegetation dynamics via analyses of fossil pollen, microfossil charcoal and organic and inorganic sediment data obtained from a 96-cm core of black organic material retrieved from a small forest hollow (19°35'32"N, 104°16'56"W).

What was learned
Figueroa-Rangel et al. note that "during intervals of aridity, cloud forest taxa tend to become reduced," while, in contrast, "during intervals of increased humidity, the cloud forest thrives." And based on these facts, they determined from their data that there was a major dry period that lasted from approximately AD 800 to 1200 in the SMBR.

What it means
Quoting the four researchers, "results from this study corroborate the existence of a dry period from 1200 to 800 cal years BP in mountain forests of the region (B.L. Figueroa-Rangel, unpublished data); in central Mexico (Metcalf and Hales, 1994; Metcalfe, 1995; Arnauld et al., 1997; O'Hara and Metcalfe, 1997; Almeida-Lenero et al., 2005; Ludlow-Wiechers et al., 2005; Metcalfe et al., 2007); lowlands of the Yucatan Peninsula (Hodell et al., 1995, 2001, 2005a,b) and the Cariaco Basin in Venezuela (Haug et al., 2003)." In addition, they write that "the causes associated to this phase of climate change have been attributed to solar activity (Hodell et al., 2001; Haug et al., 2003), changes in the latitudinal migration of the Intertropical Convergence Zone (ITCZ, Metcalfe et al., 2000; Hodell et al., 2005a,b; Berrio et al., 2006) and to ENSO variability (Metcalfe, 2006)."

We additionally note that the time frame of this significant dry period coincides extremely well with the broad central portion of the Medieval Warm Period, as may be seen by viewing the Interactive Map and Time Domain Plot of our Medieval Warm Period Project. And this correspondence further harmonizes with the dry period's temporal association with enhanced solar activity and a southward shift of the ITCZ.

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.

Arnauld, C., Metcalfe, S. and Petrequin, P. 1997. Holocene climatic change in the Zacapu Lake Basin, Michoacan: synthesis of results. Quaternary International 43/44: 173-179.

Berrio, J.C., Hooghiemstra, H., van Geel, B. and Ludlow-Wiechers, B. 2006. Environmental history of the dry forest biome of Guerrero, Mexico, and human impact during the last c. 2700 years. The Holocene 16: 63-80.

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: 1731-1725.

Hodell, D.A., Brenner, M. and Curtis, J.H. 2005a. Terminal classic drought in the northern Maya lowlands inferred from multiple sediment cores in Lake Chichancanab (Mexico). Quaternary Science Reviews 24: 1413-1427.

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.

Hodell, D.A., Brenner, M., Curtis, J.H., Medina-Gonzalez, R., Can, E. I.-C., Albornaz-Pat, A. and Guilderson, T.P. 2005b. Climate change on the Yucatan Peninsula during the Little Ice Age. Quaternary Research 63: 109-121.

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

Ludlow-Wiechers, B., Almeida-Lenero, L. and Islebe, G. 2005. Paleoecological and climatic changes of the Upper Lerma Basin, Central Mexico during the Holocene. Quaternary Research 64: 318-332.

Metcalfe, S.E. 1995. Holocene environmental change in the Zacapu Basin, Mexico: a diatom based record. The Holocene 5: 196-208.

Metcalfe, S.E. 2006. Late Quaternary environments of the northern deserts and central transvolcanic belt of Mexico. Annals of the Missouri Botanical Garden 93: 258-273.

Metcalfe, S.E., Davies, S.J., Braisby, J.D., Leng, M.J., Newton, A.J., Terrett, N.L. and O'Hara, S.L. 2007. Long-term changes in the Patzcuaro Basin, central Mexico. Palaeogeography, Palaeoclimatology, Palaeoecology 247: 272-295.

Metcalfe, S.E. and Hales, P.E. 1994. Holocene diatoms from a Mexican crater lake -- La Piscina Yuriria. In: Proceedings of the 11th International Diatom Symposium, San Francisco, USA, 1990 17: 155-171. California Academy of Sciences, San Francisco, California, USA.

Metcalfe, S.E., O'Hara, S.L., Caballero, M. and Davies, S.J. 2000. Records of Late Pleistocene-Holocene climatic change in Mexico -- a review. Quaternary Science Reviews 19: 699-721.

O'Hara, S.L. and Metcalfe, S.E. 1997. The climate of Mexico since the Aztec period. Quaternary International 43/44: 25-31.

Reviewed 13 October 2010