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Alumni Profiles - Ann Dieffenbacher-Krall

Ice age pests

Chironomids, or midge flies, begin their lives as larvae in lake sediment. As they grow, they shed their skin four times, then pupate.

When they emerge as a swarm of adults, they mate, lay eggs and die. The extent of their adult lives occurs within a few days, but the lessons they can teach us about climate change endure, according to University of Maine researcher Ann Dieffenbacher-Krall.

Dieffenbacher-Krall has spent the last several years extracting and classifying chironomid head capsules – the only part of the insect that preserves – from cores of lake sediment in New Zealand.

“We’re using them as a thermometer, basically,” Dieffenbacher-Krall says, to help determine what was going on in the Southern Hemisphere at the end of the last ice age.

Different types of chironomids exist in different ecological conditions, but the dominant variable is a lake’s mean summer temperature.

Comparing chironomid research data with pollen-based studies of temperature change, Dieffenbacher-Krall and her Climate Change Institute colleagues George Denton and Marcus Vandergoes have painted a more complete picture of climate change in the late glacial period.

The findings from their research, which were recently published in Quaternary Science Reviews, indicate stronger seasonality, which could have broader implications for understanding the differences between proxy records for abrupt climate change.

Image Description: Ann Dieffenbacher-Krall

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