Scientists can learn about past climates and environments by studying the insect species composition found in dated layers of sediment. This isn’t possible in most parts of the world because of poor preservation processes, but it is in the Yukon were rapid sedimentation combined with permafrost conditions have preserved insect remains for the past 250,000 years in some localities. This includes 2 full glacial and interglacial climate phases. Today, the Old Crow River valley consists of coniferous forest, wetlands, and wet tundra; but in the past the environment has fluctuated between dry desert grassland during Ice Ages, and open spruce parkland during Interglacial periods. (This region was north of the massive glaciers that covered most of Canada when Ice Ages occurred.) The present day Interglacial is different from previous Interglacial periods because forests are thicker. The extinction of megafauna likely explains why denser forests predominate today. During past Interglacial times herds of horses, camels, mastodons, mammoths, and ground sloths kept woodlands more open.
Location of study area from the below referenced paper.
Insect remains found in sedimentary cores from the Yukon.
A specimen of Dyschirius laevifasciatus was found in a Yukon sediment core. It no longer lives this far north.
A species of rove beetle (not the one in the above photo) that today is only known from the Pacific Coast formerly lived in the Yukon interior. It probably lived on a glacial lake shoreline, similar to the beach zones it occurs in today.
Some fossil insect remains suggests previous Interglacial periods were warmer than the present day Interglacial. Scientists found remains of Dyschirius laevifasciatus, a species of ground beetle that lives much farther south today in sediment layers dating to the Sangamonian Interglacial. Beetles in this genus prefer wet sand habitats, and these remains indicate a glacial lake beach occurred here. They also found remains of a species of rove beetle (Kallisus nitodus) that not only doesn’t live this far north but is today only known from the Pacific Coast. This species formerly was able to range into drier inland habitats. Why its range has contracted is a mystery. Perhaps, it never recolonized the region after a glacial lake dried up.
The insect species composition during previous Interglacial periods differs from present day species composition. There were some species that live in wooded areas–bark beetles, a species of weevil, and a few ant species–but much fewer than today. Even though the climate was warmer and probably wetter than today, forests weren’t as dense, and trees grew farther apart, like a parkland. Steppe grassland species still occurred.
The scientists who authored the below referenced study took sample cores from 4 sites in the Old Crow River Valley. They often encountered ice wedges marking areas when the permafrost melted during previous Interglacial periods. Then the water refroze. The insects were buried in sediment when rivers flooded and when glacial lake levels rose as temperatures increased. The scientists used wet screening to find the subfossil insect parts. Insect exoskeletons float to the surface when sediment is immersed in water. From dozens of sample cores they collected thousands of specimens from over 100 species. Radiocarbon dating can only be used for organic material that is younger than 50,000 years, but insect species composition can be used in conjunction with other methods to date sedimentary layers older than this. Layers with mostly steppe grassland species indicate Ice Ages, and layers with some woodland species indicate Interglacial periods.
Though climate changed in the Yukon, evidence from this study suggests it has changed less here than in other regions of the world. The Yukon is near the Arctic Circle and has remained cold for millions of years.
Kazima, S. et. al.
“Middle Pleistocene (MIS 5) to Holocene Fossil Insect Assemblages from the Old Crow Basin, Northern Yukon, Canada”
Quaternary International 341 August 2014
GeorgiaBeforePeople 