15:30 〜 15:52
[MIS16-06] 現代と小氷期の暴れる気候、およびその間にある「おだやかな300年」：グアテマラから得られた602±4年分の年縞の記録
★招待講演
キーワード：極端気象、気候の安定性、Itrax蛍光X線スキャナ、年縞
Increased frequency of extreme weather events is considered to be closely linked to recent global warming. However, reliable meteorological data are available only since the industrial revolution, i.e., after the beginning of the present global warming. Before that, it is generally difficult to find geological archives that enable us to detect extreme weather events, which, in turn, prevents us from assessing the relationship between present global warming and instability of weather.
Sediment cores recovered from Lake Petexbatún (Guatemala) in 2015 (GPB15) are ideal materials for this purpose. Counts of their clear varves (annual laminae) and 29 14C dates for the last 600 years enabled us to establish a chronology with exceptionally high precision and accuracy. We then performed ultra-high resolution (on average, ca. 180 data points per varve, i.e. ca. 2 days interval) X-ray fluorescence scans of the cores. Changes in the Ca/Fe ratio, a proxy for precipitation – evaporation balance, show that long-term drying proceeded in parallel with contemporary warming. More importantly, amplitude of the estimated dryness has increased during the same interval, suggesting a dramatic change in the instability of the climate system. On the other hand, during the Little Ice Age (LIA, ca. 16th to 17th century CE), rainfall increased and became unstable (the frequency of extreme rainfall events increased). During the 300 year period from the LIA to the 1970’s, we were in the narrow window of the ‘stable’ climatic mode.
A clear increase of the both dryness and wetness oscillation amplitudes is only visible, and is very visible, in monthly data because impacts of spiky events are not suitably represented in long-term means. Strong weather extremes included in the climatic oscillation cannot be seen in the geo-archives at annual or lower resolution.
Sediment cores recovered from Lake Petexbatún (Guatemala) in 2015 (GPB15) are ideal materials for this purpose. Counts of their clear varves (annual laminae) and 29 14C dates for the last 600 years enabled us to establish a chronology with exceptionally high precision and accuracy. We then performed ultra-high resolution (on average, ca. 180 data points per varve, i.e. ca. 2 days interval) X-ray fluorescence scans of the cores. Changes in the Ca/Fe ratio, a proxy for precipitation – evaporation balance, show that long-term drying proceeded in parallel with contemporary warming. More importantly, amplitude of the estimated dryness has increased during the same interval, suggesting a dramatic change in the instability of the climate system. On the other hand, during the Little Ice Age (LIA, ca. 16th to 17th century CE), rainfall increased and became unstable (the frequency of extreme rainfall events increased). During the 300 year period from the LIA to the 1970’s, we were in the narrow window of the ‘stable’ climatic mode.
A clear increase of the both dryness and wetness oscillation amplitudes is only visible, and is very visible, in monthly data because impacts of spiky events are not suitably represented in long-term means. Strong weather extremes included in the climatic oscillation cannot be seen in the geo-archives at annual or lower resolution.