Climate Change and the Arctic

The fossils shown in the images were found near Buchanan Lake, which is at the mouth of Mokka Fjord on the east coast of Axel Heiberg Island in the Arctic. The site lies on the edges of Quttinirpaaq National Park. There are no communities nearby as the Island is uninhabited, except for seasonal research stations.

In the late Early Eocene Epoch, about 50 mya, the Earth’s climate was the warmest it had been for 65 million years. In the Arctic, lush swamps teemed with crocodiles, turtles, garfish and insects. Large land tortoises roamed nearby. Flying lemurs glided from tree to tree; tapirs and the large, hippo-like Coryphodon browsed on rich plant life.

In addition to the fossils shown, fossils of soft-shelled turtles, alligators, Coryphodon (rhinoceros-like creatures) and a variety of smaller mammals (rodents) were also found. Metasequoia (Dawn Redwood) and Glyptostrobus (Swamp Cypress) dominated the treed landscape supplemented with Gingko trees and ancient ferns. Broad-leafed deciduous trees included oak, birch, sycamore and walnuts. Pinecones, spruce cones and woody nuts of walnut have also been found.

The fossils have been dated using a variety of methods, including relative dating (compare the known age of the layers where the fossils are found with the fossils themselves), and absolute dating (based on potassium-argon and rubidium-strontium decay rates). Time period can also be roughly inferred from knowledge of past climates, which might have made such forests possible.

When leaves fall to a forest floor, organisms in the soil break them down, turning the leaf litter into new soil. At Axel Heiberg, a flash flood may have buried the forest in fine sand that cut off the organic matter from oxygen needed for decomposition. By the time erosion had un-buried the ancient forest, the climate had changed. The frigid arctic temperatures and permafrost kept the forest preserved until today.

Animation

During the time period shown in the animation, the conditions which allowed a sub-tropical climate and ecosystem to flourish were replaced with a colder, harsher climate regime. Two notable changes that can be observed in the animation include the development of ice cover in the Arctic, and the connecting of North and South America by a land bridge.

Some possible reasons for the dramatic difference in climate in this high Arctic region today compared to 45 million years ago include:

• Weather patterns may have shifted from the currently predominant west-east axis to a south-axis, bringing warm, moist air to the arctic regions.
  
• The land bridge between North and South America not yet having formed might have allowed warm oceanic currents to overwhelm arctic waters, creating a system similar to the current gulf stream which brings warmer temperatures to northern Europe from the Gulf of Mexico.
  
• In the absence of the albedo effect¹ caused by the ice today, the level of ambient temperature in the Polar Regions would be much greater, perhaps even sufficient to support the Eocene forest on its own.
  
• A period of intense greenhouse gas emissions from volcanic eruptions and carbon-rich rock decay or even massive methane emissions from the oceans might have contributed to a sharp increase in global temperatures, most extreme increases being concentrated near the poles and tapering off in equatorial regions, much like is suggested by current climatic observations.
  
• Perhaps the warmer regimes dictated by the Milankovitch² cycles coincided with one or more of the cases described above.