The El Niño Southern Oscillation (ENSO) is a climatic disturbance that affects climate patterns on a global scale. El Niño is a wind-driven reversal of the Pacific Ocean equatorial currents resulting in the movement of warm water towards the coast of the Americas. Severe El Niño conditions occurred in 1953, 1957-58, 1965, 1972-1973, 1976-77, 1982-83, 1986-87, 1991-92 and 1994-95 (Duxbury and Duxbury, 1994). The El Niño event is so named because the effects generally develop just after Christmas.

The distribution of warm ocean water strongly affects climate. In the 1982-83 ENSO, the polar jet stream was displaced southward over the Pacific, bringing unusually dry conditions to Hawaii and very high winds and precipitation along the west coast of the United States. Heavy rains occurred in Ecuador, Peru and Polynesia, while droughts struck Australia, the Sahel of Africa, southern India, and Indonesia (Duxbury and Duxbury, 1994). At the same time, cooler temperatures in the North Atlantic made the 1982-83 hurricane season the quietest in over fifty years as hurricanes require warm ocean temperatures to form.

During the 1991-92 ENSO event, the southern displacement of the polar jet stream over the Pacific brought heavy winter rains and coastal flooding to southern California and the U.S. Gulf Coast and a mild, low-precipitation winter to the coastal regions of the northwest. Extremely heavy snowfall in the Sierra Nevada of California was also a result. At the same time, New England and the maritime provinces of Canada had an extremely cold and snowy winter.

The exact cause of El Niño is still in doubt, but has become an important area of research because of the widespread impacts of ENSO climate shifts to society. There has been a great deal of research attempting to document the periodicity (time between the onset) of ENSO events. A large proportion of the research on ENSO periodicity has, however, focused on oceanic records. Recent research on marine sediment records from off the coast of California has suggested that the periodicity of ENSO events has decreased slightly from 7.0 years during 200-300 years before present to 5.2 years during 0-100 years before present (Christensen et. al., 1994). Coral banding records indicate ENSO disturbances have been occurring since at least the 1600's (Druffel, 1985), but there currently are no data to determine the timing of the onset of ENSO events. Correlations between marine records and terrestrial impacts are not well constrained, but are critical because of the immediate impact ENSO climate shifts have on population centers and global agricultural productivity.

Long term terrestrial records of ENSO disturbance events may be recorded in lake sediments, particularly in areas where precipitation patterns are strongly influenced by ENSO climate patterns. One such area is the high peaks area of the San Gorgonio Wilderness of southern California. A series of glacial-sediment dammed lakes (Dry, Baldwin, Erwin, Lucerne and Rabbit Lakes) are present in the region. The history of sediments in these lakes may yield important climate information from this southernmost site of glaciation in the United States. A core taken in Dry Lake recovered layered sediments recording sedimentation for the last 13,000 years (Doug Clark, University of Washington, personal communication, 1996). Sedimentation patterns in the lakes should consist of an annual layered couplet that records spring melt water and coarser-grained sediment influxes followed by finer-grained sediment settle out during the summer. During the winter, sedimentation in the frozen lakes will stop. These coarse/fine sediment layer couplets therefore record lake deposition on an annual basis. During ENSO years, snowfall, and precipitation in this region, is greatly increased. As a result, melt water sedimentation events should be significantly larger and ENSO layering should be distinctly coarser and thicker than non-ENSO year layering.

I propose to evaluate the lake sediment records in the high peaks area of southern California to determine the history of lake sedimentation. The sedimentation in these lakes has been continuous, or nearly so, we believe since at least 13,000 - 18,000 years ago and likely records climate information throughout the last deglaciation. Lake sedimentation in this area is strongly tied to precipitation events and snow melt. ENSO disturbances result in increased precipitation and heavy snowfalls and strongly control sedimentation patterns in lakes in the proposed study area. Detailed analysis of sedimentation patterns should result in recognition of variations in sedimentation rates and pattern that reflect periods of increased precipitation that can be directly correlated to ENSO disturbance events. A variety of sedimentological parameters (e.g. sedimentation rates, grain size, grain composition and mineralogy) have the potential for reconstructing temporal trends in sediment fluxes to a lake, which can then be tied to precipitation and run-off events. Rhythmic layering in sediment cores from lakes faithfully record changes in precipitation patterns. A series of methods will be used to determine rhythmicity patterns in lake sediment layering in order to determine periodicities in changes in lake sediment flux.

This study will integrate the terrestrial record of ENSO disturbances with marine sediment records and extend the record of ENSO climatic disturbances back at least 10,000 years, and potentially further. This long-term record will allow us to evaluate the periodicities of ENSO events to determine a) if there are changes in the periodicity of ENSO events, b) what the trends in changes may be, and finally, c) if sedimentation rates are high enough, the timing of the onset of ENSO events.

We will core several lakes in the high peaks area of the San Gorgonio Wilderness in southern California. Coring was done with 3" diameter aluminum tubing and driven into the sediment by hand. We recoverd greater than 6 meters of sediment from Dry Lake.

Cores will subjected to x-radiography at the sedimentology facility at the National Oceanographic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratories in Miami. Dr. Terry Nelsen is enthusiastic about the project and has offered use of his facilities (support letter is attached). X-radiographs clearly show banding and layering of sediments in cores. The x-radiographs illuminate subtle banding in sediments related to visually indistinct features such as changes in water content or organic matter content. X-radiographs will be digitally scanned and processed with programs developed at NOAA for image analysis of this type of layering. Digital scans will then be subjected to densitometer analysis (which assigns values to relative transparency of the lamination). The internal consistency of the information represented by the laminae will be examined using Auto and Cross-Correlation Analysis and by a Multivariate Analysis of Variance. Following this examination to establish error bounds, the lamina will be subjected to Fourier Analysis. This procedure should elucidate the statistically significant periodicities of sediment lamination in the lake sediments. Dr. Pascal de Caprariis of the Department of Geology will perform the data analyses of densitometer records for this project.

Following x-radiography of cores, cores will be subsampled for sedimentologic analysis. X-radiography films will be used to guide sediment sampling relative to layering. A variety of sedimentological parameters (e.g. sedimentation rates, grain size, grain composition and mineralogy) will be measured. Sediment analysis equipment is a standard component of my laboratory facilities and methodology, and procedures are well established in the Department of Geology's Sedimentology Lab.

Sedimentation rates will be determined utilizing ²¹⁰Pb analysis. ²¹⁰Pb is a naturally occurring radionucleid that is delivered to sedimentation sites by atmospheric influx. Once in the water (either lakes or oceans), it is quickly adsorbed onto fine-grained sediment particles and delivered to the lake or ocean bottom. Upon burial of the sediment particle, ²¹⁰Pb decays away from surficial input values. Concentrations of ²¹⁰Pb relative to its granddaughter particle ²¹⁰Po are then determined by alpha spectroscopy. Sediment burial rate (sedimentation rate) can then be determined for about the last 100 years. This technique will allow determination of the time equivalent of individual laminations so that real time can be assigned to the periodicities recorded in the sediment laminae.

In addition to ²¹⁰Pb, ¹³⁷Cs decay rates will also be measured. ¹³⁷Cs has a shorter half-life than ²¹⁰Pb and is used to calibrate the ²¹⁰Pb by verifying surficial fluxes to determine the starting points for ²¹⁰Pb. Alpha and gamma spectroscopy on lake sediment subsamples will be performed by Dr. John Trefry at the geochemistry laboratory at Florida Institute of Technology in Melbourne, Florida.