OCR Text |
Show magnetite and biotite) to greigite ( Fe3S4) in anoxic pore waters of Owens Lake. The cause for OWENS LAKE 81 ^ O TOO (% C) 18 20 22 24 26 28 4.0 3.0 2.0 1.0 0.0 0 20 40 60 80 2.0 1.0 0.0 XOO^ SI) 103UTHICS/ g Fig. 2. 8180, TOC and % records from cores OL90- 1 and - 2 compared with the lithic record from North Atlantic core V23- 81 for the period 52,500 to 12,500 yr B. P. Greenland Dansgaard- Oeschger ( D) warm events and Heinrich ( H) events are indicated. Selected maxima in 8180, %, and minima in TOC are shown in black; maxima in TOC and lithics ( from V23- 81) are indicated in gray. Sierran glacial advances ( magnetic susceptibility peaks) are labeled A,- Aia; Sierran glacial recessions ( peaks in TOC) between 39,000 and 24,000 14C yr B. P. are labeled R8- R19. Periods of hydrologic closure of Owens Lake prior to 40,000 yr B. P. are labeled CT- CS. Correlations between closed lakes and glacial advances are indicate by dashed lines. enhanced formation of greigite during glacial advances is not well understood; however, 87Sr values of Owens Lake carbonates indicate that Fe is released from biotites during glaciation. The eight oldest glacial advances ( A,- A8) occurred between 52.5 and 40 kyr when relatively heavy 5180 values indicate the lake was intermittently closed ( CrC8), suggesting that climate was cold and relatively dry when glaciers advanced ( Fig. 2). Between 40 and 23.5 kyr, Owens Lake also experienced closure during glacial advances ( A10- Al2 and A17- Al8) and the Tioga glaciation occurred during a relatively dry period ( 23.5 to 15.5 kyr). Between 52.5 and 23.5 kyr, maxima in % are coincident with minima in total organic carbon ( TOC) ( Fig. 2). The TOC minima resulted from decreases in biological productivity and dilution of the TOC fraction with glacially derived silt; e. g., TOC concentrations were reduced to < 0.3% during the Tioga glaciation. Between 39 and 24 kyr, maxima in TOC mark the occurrence of 12 glacial recessions ( R8 through R19, ( Fig. 2). One of our purposes was to determine whether records of climate change from the Owens basin could be objectively linked to North Atlantic climate events. Even though age controls for the marine and lacustrine records do not permit comparison between individual oscillations, it is apparent that the number of advances/ retreats of Sierran glaciers is similar to the number of North Atlantic iceberg discharge events ( Fig. 2). Heinrich event H2 occurred during a 5180 maxima ( dry period) that accompanied the most intense period of Tioga glaciation and H1 |