5 NATURAL ABUNDANCE OF THE STABLE ISOTOPES ... - Falw.vu

Chapter 7isotope depletion of precipitation is studied in detail as a function of latitude and thus of airtemperature, a relation can be derived (Volume 2) which comes to the temperaturedependence:d 18 / dt +0.7‰ / C (7.30)(Dansgaard, 1964; Van der Straaten and Mook, 1983). By this relation it is possible totranslate isotope variations into climatic variations during geologic times. Records have beenobtained on ice cores from Greenland and the Antarctic, showing the alternation of low- 18 (or low- 2 ) and high- 18 (or high- 2 ) periods, respectively cold and warm periods (Eq.7.30).18 marine Arctic Antarcticcarbonate+1.5 0 40 36 49 45020406080100120140Time (10 3 years BP)Fig.7.14Palaeotemperature records represented by 18 variations in time in the CaCO 3 fractionfrom foraminifera shells in deep-sea core sediments (left), in glacier ice of a NorthernGreenland glacier (at Summit), and in glacier ice of an Antarctic ice core (at Vostok),respectively from left to right (figure modified from Lorius and Oeschger, 1994). In eachrecord the left side indicates the lower temperatures, for instance, at 20 000 years BP eachcurve shows the most recent glacial maximum. The upper 10 000 years contain thepresent warm interglacial, the Holocene.114