No abstract

9951. 15. A Bax and N. Tjandra, J. Biomol. NMR 10, 289 (1 997). 15, In the LC terature, ths agnment tensor IS usually referred to as S (8), but to avod confuson w~th the order parameter for Internal moton, commonly also denoted S (7 7), we refer to t as A. 17. G. L~par and A. Szabo, J. Am. Chem. Soc. 104. 4545 (1 982). 18. J. R. Toman J. M. Flanagan. M. A. Kennedy J. H.Prestegard, Nature Struct. Biol. 4. 292 (1997). 19 One-bond J spl!tt~ngs are measured n the unorlented phase at 25°C-just below the temperature of the phase transton from gel to q u d crystal-and In the LC phase at 38°C.

Here we discuss paleoenvironmental evolution in the Baikal region during the Holocene using new records of aquatic (diatom) and terrestrial vegetation changes from Hovsgol, Mongolia's largest and deepest lake. We reconcile previous contradictory Baikal timescales by constraining reservoir corrections of AMS dates on bulk sedimentary organic carbon. Synthesis of the Holocene records in the Baikal watershed reveals a northward progression in landscape/vegetation changes and an anti-phase behavior of diatom and biogenic silica proxies in neighboring rift lakes. In Lake Baikal, these proxies appear to be responsive to annual temperature increases after 6 ka, whereas in Lake Hovsgol they respond to higher precipitation/runoff from 11 to 7 ka. Unlike around Lake Baikal, warmer summers between 6 and 3.5 ka resulted in the decline, not expansion, of forest vegetation around Lake Hovsgol, apparently as a result of higher soil temperatures and lower moisture availability. The regional climatic proxy data are consistent with a series of 500-yr time slice Holocene GCM simulations for continental Eurasia. Our results allow reevaluation of the concepts of ‘the Holocene optimum’ and a ‘maximum of the Asian summer monsoon’, as applied to paleoclimate records from continental Asia.