3:30 PM - 3:52 PM
[MIS16-06] Today’s drought extremes, little ice age wet extremes, and quiet 3 centuries in between: observations from Guatemalan varves, 1413±4 to 2015±0 CE
★Invited Papers
Keywords:Extreme weather, Climatic stability, Itrax XRF scanner, Varve
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.