Ancient Arctic Trees: A Memory-Morphic System of Recorded Climate in the Arctic
Anna Davidson
Global warming is currently causing Arctic temperatures to rise at two times the rate of lower latitudes. This is a trend that is predicted to continue well into the future (ACIA, 2005), which will eventually result in an ice-free environment causing a more temperate climate to occur.
The mild ice-free Arctic environments of the late Paleocene and early Eocene (~45 myo) up to the Pliocene represent one of the best deep-time analogues for evaluating a rapidly changing global climate on a high latitude system (Eberle and Greenwood 2012), or in other words, it is an important example of future climate conditions that could result should current warming trends continue (Haywood and Valdes, 2004; Jansen et al., 2007).
There are many fossilized remains of plants and animals in addition to unfossilized wood in many parts of the Canadian Arctic and Greenland. Exquisitely preserved wood dating back to the Pliocene has been found on Strathcona Fiord, Ellesmere Island, Canadian Arctic Archipelago, 78°29.271" N 82° 37.973" W (Csank et.al., 2011).
Perhaps even more impressive is the 45-million-year-old mummified wood forest found on Axelberg Island (Basinger, 1991) collectively and informally called the “fossil forest.” This forest was recognized during a Geological Survey of Canada field operations in the summer of 1985 (75 55’N, 88, 58’W). Although this is known as a “fossil forest” there are remnants of non-mineralized wood and in situ stumps. Intact un-mineralized 45-myo wood is difficult to find as one might imagine. This forest was once a boreal mixed evergreen coniferous /broad leafed deciduous forest comparable to modern northern mixed forests in North America today. At present, the Fossil Forest is located on Axel Heiberg Island, which is part of the Arctic Canadian Archipelago in the Nunavut territory of Canada. It is located at 79◦55N, 89◦02W (Geological Society of Canada Map 1301A), far above the Arctic circle.
These two locations are currently tundra, have very few plant species and is home to no tree species. However, during the late Paleocene and early Eocene this island and the surrounding area was once inhabited by lush swamp forests, and thermophilic fauna such as alligators and giant tortoises. The list of found plants includes ancient conifers, like hemlock, spruce, pine, larch and the dominant species Dawn Redwood (Metasequoia, once thought to be extinct but subsequently found in China), the broadleaf-conifer relative Ginkgo, plus deciduous broadleaf trees like birch, alder, oak and sycamore, and ferns. Upon isotopic, paleo botanical, and anatomical observation, one can study this wood in detail and piece together ancient climate and ecosystems.
I argue here, that the rings of these ancient trees are small units of stored memory. They reveal information about the past while at the same time, providing us clues of what the future may look like.
To make a ring, a tree’s cambium layer creates one phloem cell (bark) to the outside of itself to every three xylem cells (wood) to the inside of itself. If conditions are right, it will keep dividing over time making the growth ring bigger and bigger. When conditions are harsh and the tree can barely survive in an environment, it may make a ring as small as a single division of the cambium. The number of rings can tell us how old the tree is, and the thickness of the rings can tell us how fit the tree was in that environment. Additionally, the size of the cells themselves within the ring, tell us what kind of rainy season the tree experienced and how much rain or drought it experienced. Rings can tell us about the ecological changes the tree experienced in its lifetime, temperature changes during the growing seasons, distribution of precipitation, and information about photoperiod.
In essence, these xylem wood cells are an agent of memory that collectively make up a memory-morphic system as in, an entire tree or forest of trees. Like the ocean, these precious wood specimens are the keepers of the past. They have “memory.” Likewise, they are the fortune tellers of the future in terms of what future climatic conditions will exist in the Arctic and what types of species we expect to see in the future.
Acknowledgements:
Thanks to James Bassinger (geologist, University of Saskatchewan), Joel Barker (biogeochemist, Ohio State University), Anna Jacobson (anatomist, California State-Bakersfield), Brandon Pratt (ecophysiologist, California State-Bakersfield) and Maciej Zwieniecki (ecophysiologist, University of California, Davis).
References
ACIA, 2005. Arctic Climate Impact Assessment. Cambridge University Press.
Erberle, J.J. , Greenwod, D.R. 2012. Life at the top of the greenhouse Eocene world-a review of the Eocene Flora and vertebrae from Canada’s High Arctic. Geol. Sco. Am. Bil.124. 3-23
Basinger, 1991. The fossil forests of the Buchanan Lake Formation (Early Tertiary) Axel Heiberg Island, Canadian Arctic Archipelago: Preliminary Floristics and Paleoclimate.
A.Z. Csank a, W.P. Patterson b, c, B.M. Eglington c, N. Rybczynski d, J.F. Basinger, 2011. Climate variability in the Early Pliocene Arctic: Annually resolved evidence from stable isotope values of sub-fossil wood, Ellesmere Island, Canada Paleogeography, Paleoclimatology, Paleoecology