| Popis: |
Multi-element SRXRF of sediments of Lake Baikal (East Siberia) with samples taken at 10 cm intervals from a core spanning the last 250 ky revealed nine peaks of “warm” signals like Sr/Ba(Rb,Cs) and U/Th corresponding to Oceanic Isotope Stages 1,3,5a,5c,5e,7 and 9, and six peaks of “cold correlator” corresponding to OIS 2,4,5d,6 and 8. A slab (1500–2200 mm below the sediment surface) taken from another core was studied by scanning SRXRF. This interval corresponds to the Siberian Karga interstadial (OIS3, 24–58 ky BP). It hosted two peaks of diatom algae frustulles, indicators of warmer climates. The scanning was performed at a temporal resolution of ca. 50 yr. Ratios of concentrations like Sr/Rb(Ba,Cs,Ti,Fe) (Nucl. Instr. and Meth. A 448(1–2) (2000) 384; Nucl. Instr. and Meth. A 448 (1–2) (2000) 400) appeared to be more sensitive proxies of warm climates, compared to total diatoms, and revealed at least six pronounced cycles of abrupt warming and cooling episodes, each lasting a few millennia. These fluctuations may reflect a response of the catchment basin of the Lake Baikal to abrupt global climate cycles recorded in the ice of Greenland and in the sediments of North Atlantic (Nature 364 (1993) 142; Science 278 (1997) 1257; Science 288 (2000) 128). SRXRF applied to the sediments of Lake Teletskoye (West Siberia, Altai Mountains) of the last 600 yr provided a temporal resolution of 1.2–1.8 yr. The profiles of a few elements like K, Ca, Ti, Fe, V revealed oscillations with a periodicity of 9.4 yr over the time interval between years 1400 and 1600. Oscillations faded out after the cooling of 1600–1700 (The Maunder interval). Periodic oscillations between years 1400 and 1600 seem to correspond to periodic changes in the height of oceanic tides (9 yr (PNAS 94 (1997) 8321; PNAS 97 (2000) 3814)) rather than to the solar activity cycles (periodicity of 11 yr). |
Full Text from ScienceDirect