STABLE OXYGEN ISOTOPE ANALYSIS OF THE FRESHWATER GASTROPOD PACHYCHILUS SPP. AND ITS POTENTIAL USE FOR SEASONALITY STUDIES AT THE LOWLAND MAYA SITE OF PACBITUN, BELIZE

Shells of the freshwater prosobranch gastropod Pachychilus spp. (jute) are ubiquitous in lowland Maya archaeological sites and may be a useful proxy not only for paleoclimate studies of northern Central America and the impact climate may have had on ancient Maya populations, but they may also be a source of information pertaining to human subsistence behavior. Jute snails can still be found today in streams and rivers of southern Mexico, Guatemala, Honduras, and Belize. This talk will present results from a three-year investigation into the viability of this gastropod as a potential climate proxy for northern Central America.

In the Maya lowlands, seasonal climate variation is principally expressed as cycles in rainfall, as opposed to air temperature, with pronounced rainy and dry seasons present. However, water temperature data collected from Roaring Creek and Barton Creek in the Cayo District of Belize, have revealed that there is, to a lesser extent, some seasonal water temperature variation that coincides with seasonal creek water δ¹⁸O variation observed in water samples collected on a bi-weekly basis from October 2010 to October 2011 in Roaring Creek. Creek water δ¹⁸O appears to reflect meteorological activity in the area, although the amplitude of this variation is less than that of the annual meteorological δ¹⁸O variation obtained from modeled IAEA data. This “flattening” of creek water δ¹⁸O seasonal variation may be a consequence of surface and groundwater mixing in the karstic landscape of western central Belize. Therefore, δ¹⁸O variation observed in the carbonate of jute shells may reflect both seasonal temperature variability and seasonal fluctuations in stream water δ¹⁸O.

Analysis of shell carbonate oxygen isotope variation has revealed strong sinusoidal δ¹⁸O variation in specimens collected live from the Cayo District of Belize. Currently, work is being conducted in order to compare shell carbonate oxygen isotope variation with stream water δ¹⁸O and temperature variation. In addition to the study of modern jute and their aqueous environments, a seasonality study of Middle Preclassic jute from Plaza B in the site core of Pacbitun will also be discussed.