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Fieldwork

Geophysical Studies of Lake Titicaca Provide Paleoclimate Insights


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Neecho scientific party
Fig. 1: Members of the R/V Neecho's scientific party included (from left): Ken Parolski, Rob Thieler, Paul Baker (Duke Unversity), Geoff Seltzer (Syracuse University), and Bolivian first mate Antonio Catari. Photograph by Steve Colman (not pictured).
Lake Titicaca in Bolivia/Peru contains what is believed to be one of the most significant climatic archives in all of South America and was the location of a recent cruise (07 Jan - 02 Feb 1999) to collect geophysical data for paleoclimate studies. The operation was based out of the Woods Hole Field Center and included Rob Thieler, Steve Colman, and Ken Parolski, along with collaborating scientists Paul Baker (Duke University) and Geoff Seltzer (Syracuse University) (Fig. 1).

At an elevation of 3,825 m above sea level, Lake Titicaca is the highest navigable lake in the world and presents a considerable technical challenge because of the high altitude and remote location. Given the scientific and technical experience of the USGS in large lakes, the technology development, and the capability of working in remote areas (Lake Baikal; Guatemala; Enewetak; etc.), Survey collaboration with the academic investigators working on the lake was a natural. The R/V Neecho (Fig. 2), formerly part of the USGS Coastal and Marine Geology Program, was used to conduct the seismic and sidescan sonar investigation.

Preliminary analyses of piston cores and reconnaissance CHIRP subbottom ata obtained by Baker and Seltzer demonstrated that the sedimentary components necessary for a successful paleoclimatic reconstruction are present and generally well preserved in the lake. However, detailed geophysical data that would provide the critical framework for the interpretation of existing data and planning of future work were lacking.

R/V Neecho
Fig. 2: The R/V Neecho at the dock on Lake Titicaca, Bolivia/Peru. Formerly part of WHFC, the boat was transferred to Duke University via WHOI in 1996 and had been used for piston coring since arriving at the lake in 1997.
The cruise collected 245 km of airgun seismic data that imaged bedrock beneath the entire sedimentary sequence-about 400 m thick-in the large basins of the lake. These data will be used to examine the record of lacustrine sedimentation, as well as to evaluate the neotectonic and structural evolution of the lake basin. In addition, sidescan and seismic data were collected on two of the major deltas in the lake. The sidescan mosaics coupled with the seismic data will be used to determine the impact of mid-Holocene climatic change on lake-level fall and on presently submerged drainage patterns. Initial results suggest that the deltaic sequences are graded to several Holocene lake-level stillstands.

Sidescan sonar and CHIRP data obtained in the small basin of the lake, Lago Hui–aimarca, revealed an outstandingly well-preserved fluvial system that probably records the initial flooding of the basin about 3,000 years ago and which may have submerged some of the early habitations around the lake. Bottom video and grab samples confirmed the presence of distinct sedimentary environments within this paleofluvial system.

Operations on the lake were hindered somewhat by an unexpectedly low lake level and some initial problems with the Neecho. Persistent work by Ken Parolski, however, got all systems working in short order. As a result of this and other feats (including fixing the generator in the tiny village of Challapampa), he will receive the coveted Golden Flashlight award from his Woods Hole Field Center-Marine Operations Facility colleagues.


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