珪藻温度指数 Td 値の特性について

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Diatom temperature index (Td) which was introduced by Kanaya and Koizumi (1966) as a proxy of sea surface temperature is discussed on its sensitivity to temperature. The Td value is calculated as Td=Xw/(Xw+Xc), where Xw and Xc are frequencies of warm and cold water species, respectively. The sensitivity of this index to temperature is not uniform, but greatly variable geographically; Within mixed water region, it is sensitive enough to be used as a reliable thermometer, but the Td value is much insensitive in warm or cold current region, not reflecting a temperature change. This variable sensitivity of the Td value inevitably deforms the signal of paleotemperature fluctuation when the signal is outputted as diatom temperature curves in analyses of piston cores. Td curves are contorted to a greater or less extent, producing characteristic patterns unique to the location of the cores. If the analyzed core is consistently located within the cold or warm water region, Td value records no paleotempereture signals and produces an almost flat Td curve. When the core is situated within the mixed water region throughout the time, the Td curve may well reflect a temperature oscillation. If the core is located near the northern front of the mixed water region, paleotemperature fluctuations may be slightly distorted and recorded as an alternation of pointed narrow peaks in warmer periods and truncated broad valleys in colder periods. On the contrary, if the core is near the southern limit of the mixed water region, Td curved may be a series of truncated broad hills in warmer periods and narrow troughs in colder periods. These characteristic patterns are clearly recognized in the Holocene Td curves of three piston cores obtained from Japan Sea. It should be remembered, when we interpret Td curves, that the signals of paleotemperature change are to a greater or less degree deformed in the Td curves.
日本古生物学会の論文
1993-11-30

珪藻温度指数 Td 値の特性について

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