The hydrolgic balance of surface-water systems in the Great Basin of the western United States should have responded to the migration of the jet stream. When the jet stream was positioned over or south of a particular surface-water system, decreased evaporation and increased precipitation should have resulted in an increase in the effective wetness of the surface-water system. The Owens Lake basin is the first in a chain of once- connected basins located on the eastern side of the Sierra Nevada. When water in Owens lake exceeded a depth of ~60 m, it overflowed southward along a series of channels to China Lake.
When a lake changes from a closed to an open (spilling) condition, the residence time of water in the lake basin decreases. And as the rate of spill (throughput) of water increases, the residence time further decreases. The d18O and d13C values of lake water are a function of its residence time. Preferential loss of isotopically light oxygen during evaporation causes an increase in the d18O value of lake water. The d13C value of lake water increases with increasing carbon dioxide exchange between the lake and the atmosphere; therefore, the longer the residence time of water in a lake basin, the heavier the values of d18O and d13C.
We report here the d18O and d13C values of the total inorganic carbon fraction of channel samples taken from cores OL-92-2. The reader is referred to Bischoff and others (1993) for details of the coring, sampling, and sample preparation procedures.
Laboratory Procedures
Sediment samples were analyzed at the University of Michigan Stable
Isotope Laboratory using a Finnigan Mat 251 mass spectrometer equipped
with a Kiel carbonate-extraction device. Precision for d18O and d13C
was ±0.05 o/oo. Data are reported relative to the
Peedee Belemnite (PDB) standard.
Results and discussion
Analytical results are listed in Table 1 and plotted in Figure 1. Between
110 and 5 m (interval I), peaks and troughs in values of d18O and d13C
covary; this covariance is less pronounced between 190 and 110 m (interval
II) and is generally absent below 190 m (interval III).
If it is assumed that the d18O value of the uppermost sample (which integrates sediment deposited since about 11,000 yr B.P.) is representative of a closed-basin condition, then all samples having d18O values more negative than -4 o/oo were deposited in a spilling lake. The d18O maxima and minima that indicate open and closed lake conditions within intervals I and II (Fig. 1) correspond to glacial and interglacial periods that can also be defined on the basis of carbonate (CO2) and organic carbon (OC) variations (Bischoff and others, 1993).
The volume weighted d18O average of Sierra Nevadan precipitation at Tahoe Meadows (2525 m), located about 350 km NNW of Owens Lake, was -14.6 o/oo for 134 samples collected between September 1986 and January 1990 (Benson, 1993). If this value is indicative of d18O of precipitation in the Owens Lake catchment area in the past, Owens Lake was little more than a wide spot in the Owens River during times represented by depths of 25 and 97 m in core OL-92(Fig. 1).
The d13C-depth pattern is more difficult to interpret than the d18O-depth pattern in core OL-92 (Fig. 1). For interval I, the peak-to-peak and trough-to-trough covariance of d18O and d13C indicate that low values of d13C correspond to times of spill and high values correspond to a closed basin state. This covariance does not occur, however, in intervals II and III. The mean d13C value of 35 samples of Walker River water was -10.1 o/oo for the period February 1990 through December 1992 (unpublished data of L. Benson). The d13C values of OL-92 sediments are 15 to 20 o/oo more positive than water in present-day rivers that flow from the Sierra Nevada. The d13C of carbonate in lake water in equilibrium with atmospheric CO2 should have a value of about 1 o/oo at 20oC (Friedman and O'Neil, 1977). The higher values shown in Figure 1 indicates that some process other than gas exchange (e.g. variation in productivity) has affected the d13C value of Owens Lake water for much of the past.
Results of analyses are reported in parts per thousand relative to the Peedee Belemnite standard. Samples that lacked sufficient carbonate for analysis are indicated by --.
All values are given in parts per thousand relative to the VPDB (Vienna Peedee Belemnite) standard. Gaps in the data indicate samples that did not contain sufficient carbonate for analysis.
U.S. Department of Interior, U.S. Geological Survey
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