Bruce D. Allen

A continuous, high-resolution record of late Pleistocene climate variability from the Estancia basin, New Mexico

Lake sediments that accumulated in the Estancia basin, central New Mexico, provide a detailed record of submillennial latest Pleistocene climatic oscillations. Sedimentologic, biologic, and geochemical proxies for changes in salinity and lake level were used to identify episodes of wet and dry climate that occurred between 24 and 12 k.y. B.P., as dated by 14C by means of accelerator mass spectrometry from shoreline and basin-center deposits. These dates determine the timing and duration of the episodes of wet and dry climate. The lake expanded and contracted repeatedly during the last glacial maximum and fluctuated near its highest elevation several times during the interval ca. 20 to 15 k.y. B.P. A pronounced lowstand lasting ∼1 k.y. occurred between ca. 15 and 14 k.y. B.P., followed by two more highstands of the lake between ca. 14 and 12.5 k.y. B.P. Desiccation of the perennial lake after 12 k.y. B.P. was followed by a final, poorly dated highstand at ca. 10 k.y. B.P. The record of lake-level fluctuations from the Estancia basin provides a high-resolution record of changes in water budget in a basin, the comparatively simple physiography and hydrogeology of which ensured a direct response to the strong climatic fluctuations that occurred during the last glacial maximum and termination.

Evidence from Western North America for Rapid Shifts in Climate During the Last Glacial Maximum

The Estancia basin in southwestern United States contains evidence for strong and rapid pulsations in the supply of moisture brought into the region during the last ice age. The pulses were recorded during episodes of stream discharge that spread plumes of fresh water laden with quartz sand over the saline lake. The largest pulses in stream discharge lasted only a few decades, were organized into cycles that were spaced approximately 200 to 250 and 2000 years apart, and were of sufficient magnitude to freshen and maintain the lake at its maximum recorded elevation.

Evaporation from groundwater discharge playas, Estancia Basin, central New Mexico.

Abstract Bowen ratio meteorological stations have been deployed to measure rates of evaporation from groundwater discharge playas and from an adjacent vegetated bench in the Estancia Basin, in central New Mexico. The playas are remnants of late Pleistocene pluvial Lake Estancia and are discharge areas for groundwater originating as precipitation in the adjacent Manzano Mts. They also accumulate water during local precipitation events. Evaporation is calculated from measured values of net radiation, soil heat flux, atmospheric temperature, and relative humidity. Evaporation rates are strongly dependent on the presence or absence of standing water in the playas, with rates increasing more than 600% after individual rainstorms. Evaporation at site E-12, in the southeastern part of the playa complex, measured 74 cm over a yearlong period from mid-1997 through mid-1998. This value compares favorably to earlier estimates from northern Estancia playas, but is nearly three times greater than evaporation at a similar playa in western Utah. Differences in geographical position, salt crust composition, and physical properties may explain some of the difference in evaporation rates in these two geographic regions.

Footprints preserve terminal Pleistocene hunt? Human-sloth interactions in North America

Contemporaneous sloth and human footprints from the terminal Pleistocene at White Sands National Monument suggest stalking. Predator-prey interactions revealed by vertebrate trace fossils are extremely rare. We present footprint evidence from White Sands National Monument in New Mexico for the association of sloth and human trackways. Geologically, the sloth and human trackways were made contemporaneously, and the sloth trackways show evidence of evasion and defensive behavior when associated with human tracks. Behavioral inferences from these trackways indicate prey selection and suggest that humans were harassing, stalking, and/or hunting the now-extinct giant ground sloth in the terminal Pleistocene.

Poster 043. Ability of a Priority Dispatch System to Respond Appropriately to Victims of Cardiac Arrest

Purpose: To evaluate die accuracy of die Emergency Medical Priority Dispatch System (EMPDS) with respect to response level for cardiac arrest cases, and to compare response times for delta versus other response levels. The study setting was an urban ALS system that adopted a priority dispatch system 2.5 years ago. The sensitivity of the EMPDS has not been evaluated with regard to cardiac arrest cases since its implementation. We hypothesized that 99% of cardiac arrest cases would receive the highest level of response. Methods: We retrospectively reviewed 1994 emergency medical services (EMS) atraumatic cardiac arrest incident reports. We compared response time to response level using a subsample of 230 cases for which complete data were available. We used ANOVA and chi-square tests in our analyses. Results: Of 284 cardiac arrest cases, 258 (90.8%) were classified as delta, 17 (6.0%) as charlie, eight (2.8%) as bravo, and one (0.4%) as alpha. More cases were misclassified as charlie or lower than expected ( p p = 0.25). Conclusion: The EMPDS has high sensitivity in identifying and responding to cardiac arrest calls. The highest priority calls had, on average, approximately one minute faster response times than the lower priority calls. This reflects the importance of accuracy in this system, particularly with regard to conditions, such as cardiac arrest where response time is highly correlated with survival. The results of this study support the use of the EMPDS, and indicate the need for more specific analyses of the causes and consequences of misclassification of cardiac arrest cases.