OCR Text |
Show occurred during a near desiccation of Owens Lake. Additional information on the relationship between Heinrich events and change in the hydrologic balance of Great Basin lakes can be obtained from the Mono Lake record ( Fig. 3). The multi- millennial ( Heinrich) scale in hydrologic variance is evidenced by persistent ( 1000 to 2000 year) lowstands ( L1 through L4) of Mono Lake which occurred every 6000 to 7000 years. Given the 14C- based chronologies of the Heinrich events and Mono Lake lowstands, it appears that lowstands L1 through L4 occurred at nearly the same times as Heinrich events H1 through H4. However, 14C reservoir effects are neither constant nor easily quantified in either marine or lacustrine environments and lacustrine carbonates exposed to the subaerial environment do not always remain closed systems with respect to carbon. The likelihood that lowstands of Mono Lake were synchronous with Heinrich events was further tested using paleomagnetic secular variation ( PSV) data from two deep- sea sediment cores from the western North Atlantic that contain Heinrich events. A magnetic chronostratigraphy was developed in which each Atlantic Heinrich event and each Mono Lake lowstand was associated with directional features of their magnetic records. Using the PSV data sets, we found that Heinrich events H1, H2, and H4 and Mono Lake lowstands L1, L2, and L4 are nearly synchronous ( within 100 to 200 years); however, Heinrich event H3 does not correlate with any Mono Lake lowstand. Lowstand L1 is of particular interest because it occurred at very nearly the same time ( 15.5 to 14 kyr) as the desiccation of Owens Lake ( Fig. 2). The 103- year ( Dansgaard- Oescheger) scale in hydrologic variance is evidenced by 500- to 1500- year oscillations in the size ( S180 value) of Mono Lake. The oscillations are most clearly displayed in the plot that represents the running mean of three successive measurements of 5180 ( Fig. 3). 8180(% o) Fig. 3. 8180 record from Wilson Creek sediments compared with the 5180 record from G1SP2 ice core, Greenland. H1- H4 refer to North Atlantic Heinrich events; L1 to L4 refer to principal lowstands of Mono Lake; D2 to D8 refers to Dansgaard- Oeschger interstadials. |