Loading ...
Sorry, an error occurred while loading the content.

9439Ma: Drought and the Maya Collapse

Expand Messages
  • jbaker@email.arizona.edu
    Jan 24, 2003
      >Jeff Baker said:
      >"There is one major problem with both Gill's book and the O-18
      >studies. Both Gill and the researcher's studying the oxygen
      >isotopes place the drought in the 9th and 10th centuries, yet the
      >population decline in the southern lowlands occurred in the 8th
      >century.
      >
      >"And, in regard to the isotope data, the isotope information is
      >all from the northern lowlands, and pinpoints to a "drought" in
      >the 9th and 10th centuries in the north. Yet, the north was
      >undergoing a resurgence at this time. The Puuc was seeing a
      >population explosion, Chichen was seeing large scale building
      >going on, Dzibilchaltun was undergoing a population explosion.
      >
      >"The data on population changes in the 8th, 9th and 10th centuries
      >simply does not fit the drought model."

      Martin Peach said:

      >I disagree.
      >Hodell et al (Science 292 p1367) have the major drought starting
      >around AD 750, ie the 8th century, in the central Yucatan. One
      >might expect that the main population effects of a severe drought
      >would show up at the beginning of the period as the system was
      >caught off guard with several failed harvests in succession, and
      >that after no more than a few decades, the survivors would have
      >learned to live under the new regime, for instance by learning to
      >use the groundwater aquifers instead of rainfall to irrigate
      >crops.
      >
      >It also seems to me that the climate data from lake cores is
      >likely more accurate than current population estimates. It may be
      >for instance that as the climate dried out, scattered farmers
      >moved to locations with cenotes, giving rise a population
      >increase at these centres, while the corresponding depopulation
      >of the hinterland would go unnoticed using current archaological
      >methods.
      >
      >Martin

      This is the first chance I've had to respond to the many comments
      on this topic.

      Subsequent work by Curtis, Hodell and company has placed a peak
      in the drought at A.D. 862, with a peak in humidity (i.e. high
      rainfall) 50 - 75 years before the drought, or at the end of the
      8th century (Curtis et al. 1996).

      This underscores another problem with the isotopic studies, the
      inconsistency in the climatic data coming from different lakes.
      The extreme example of this can be found in a comparison of Lakes
      Coba and Punta Laguna, which are separated by a mere 20 km. Over
      the last 1500 years, the isotopic data from Lake Coba appears to
      show a drying trend (Whitmore et al. 1996), while the last 1000
      years of oxygen isotope data from Punta Laguna seems to indicate
      a period of increasing humidity (Curtis 1996).

      An examination of modern rainfall and the O-18 ratios of modern
      lakewater does not provide support for a relationship between
      O-18 ratios and precipitation. The following presents several
      Yucatecan lakes, modern rainfall levels and the O-18 ratio of the
      modern rainfall:
      San Jose Chulchaca: 500 - 900 mm/yr; 0.5 ppt.
      Lake Sayaucil: 1000 mm/yr; 5.3 ppt.
      Lake Chichancanab: 1300 mm/yr; 3.5 -5.4 ppt.
      Punta Laguna: 1519 mm/yr; 0.93 ppt.
      Lake Coba: >1500 mm/yr; 1.18 ppt.

      Based upon the oxygen isotope ratios, one would assume that Lake
      Sayaucil would have the highest rainfall of any of the lakes, yet
      it has the second lowest rainfall total. Punta Laguna, with one
      of the highest rainfall totals, has the second lowest isotopic
      ratio, not one of the highest. It is clear that there is no
      correlation between modern rainfall and the O-18 levels of modern
      lakewater (Whitmore et al. 1996: 285), yet researchers assume
      that there is a correlation between rainfall and O-18 levels in
      the past.

      I think much of the problem stems from the number of variables
      that can influence the O-18 of ostracod and gastropod shells. A
      total of 13 variables can influence the O-18 in the shells, yet
      researchers assume that the only significant variable is the
      Evaporation/Precipation ratio (E/P) (Baker 2002). Even if the
      other 12 variables are relatively minor by themselves, combined
      they could have a significant effect on the fossil O-18 signal.

      Turning specifically to surveys in the northern Yucatan:

      Current archaeological methods do study rural households. There
      have been numerous surveys over the past thirty years on
      hinterland areas in both the northern and southern lowlands (see
      Culbert and Rice 1990). In the Puuc area, Dunning's (1992) work
      did involve an examination of rural households. Similarly, Vlcek
      et al.'s (1978) work at Dzibilchaltun extended outside of the
      urban area into the rural areas surrounding Dzibilchaltun. The
      population patterns I mentioned above are not based solely upon
      site center studies, a point supported by Jerry Ek, David Hixson
      and Clifford Brown. The evidence we have for the northern Yucatan
      clearly indicates that the countrysides were NOT abandoned in the
      9th and 10th centuries.

      Regarding water tables in the Puuc:

      Martin Peach wrote:

      "In the context of a collapse of larger scale social organization,
      lowlands would not be safe places to live. Also, the water table,
      despite its name, is not flat, but follows the topography."

      There are places in the Puuc where the water table is close to
      the surface, but there are also many places where the water table
      is much deeper. However, this is similar to the situation in the
      Peten. Though everyone is aware of the failure of the Tikal
      project to dig a well deep enough to tap into the water table,
      most people are unaware of many handdug wells in the Peten
      physiographic region that tap into shallow water tables. There is
      one that is not far from the site of La Milpa at an elevation of
      app. 200 meters above sea level (while La Milpa is not the
      Department of the Peten, it is within the Peten physiographic
      region). In a presented at the SAA' several years ago, Hugh
      Robicheaux mentioned the presence of a series of wells in the
      Peten that were hand dug and tapped into shallow water tables.

      The water table in the Puuc does not seem to be significantly
      different from that in the Peten. And, despite being termed the
      lowlands, the Peten is far from a flat terrain. The Peten
      physiographic region is characterized by steep hills with
      interspersed flat land, similar to the Puuc. But, in the Peten,
      the sites are located on the hills, while the flat land is
      unoccupied. From my understanding of Dunning's work in the Puuc,
      the exact opposite situation is present there.

      A couple final points relate to Clifford Brown's e-mail:

      "There is no doubt that Jerry and David are right. The timing of
      the drought documented in the lake cores is now admitted by all
      to not correspond terribly well with the Collapse (if that's not
      a misnomer, and many think it is). It is also true that the Puuc
      region has the least surface water and the fewest water sources
      of any part of the Maya lowlands. Nevertheless, it was very
      densely populated during the Late and Terminal Classic periods.
      We need to be looking at other climate proxies, like stalactites,
      tree rings, and otoliths, to understand the climate patterns
      better."

      In research I've conducted at the site of Sierra de Agua in
      northwestern Belize, we cored a small, shallow aguada. This
      aguada was cleaned out during the Late Classic Period, but has a
      continuous pollen record for the last 1200+ years. During the
      drought years of 1995 and 1997, there was no surface water in the
      aguada during the dry season, but the sediments were moist.

      A prolonged, severe drought, such as that postulated for the 9th
      and 10th centuries would, I think, have dried these sediments out
      during the dry season.

      During the rainy season, the aguada would have filled with water.
      This alternating saturation desiccation would have destroyed
      pollen and organic matter within the aguada. There is no evidence
      for such an event occurring at Sierra de Aguada. I should note at
      this point, that the water table in the vicinity of the aguada is
      perched.

      Dr. Brown also indicated that the timing of the drought is "now
      admitted by all to not correspond terribly well with the Collapse."

      I wish this was true. At the recent AAA meetings (in mid-November),
      during one symposium, one researcher have another was mentioning
      the 'overwhelming' and/or 'conclusive' evidence for a drought at
      the end of the Late Classic.

      Jeff Baker

      References:

      Baker, Jeffrey L., 2002, Maya Wetlands: Ecology and Pre-hispanic
      Utilization of Wetlands in Northwestern Belize. Ph.D Dissertation,
      University of Arizona.

      Culbert, T. Patrick and Don S. Rice (eds), 1990, Precolumbian
      Population History in the Maya Lowlands. University of New Mexico
      Press, Albuquerque.

      Curtis, Jason H., David A. Hodell and Mark Brenner, 1996, Climate
      Variability on the Yucatan Peninsula (Mexico) during the Past 3500
      Years, and Implications for Maya Cultural Evolution. Quaternary
      Research 46: 37-47.

      Dunning, Nicholas, 1992 Lords of the Hills: Ancient Maya
      Settlement in the Puuc Region, Yucatan, Mexico. Prehistory Press,
      Madison.

      Vlcek, David T., Sylvia Garza de Gonzalez and Edward B. Kurjack,
      1978, Contemporary Farming and Ancient Maya Settlements: Some
      Disconcerting Evidence. In Pre-Hispanic Maya Agriculture, edited
      by Peter D. Harrison and B. L. Turner II, pp. 211 ? 223.
      University of New Mexico Press, Albuquerque.

      Whitmore, Thomas J., Mark Brenner, Jason H. Curtis, Bruce H.
      Dahlin and Barbara W. Leyden, 1996, Holocene Climatic and Human
      Influences on Lakes of the Yucatan Peninsula, Mexico: An
      Interdisciplinary Paleolimnological Approach. The Holocene 6:
      273 ? 287.


      Copyright � AZTLAN <AZTLAN@...> 2003
      All rights reserved.
    • Show all 13 messages in this topic