By Dan May
On Our Land
Dan May
Among the many holiday movies on television this time each year are a few that depict Santa’s North Pole home against a background of the northern lights.
The flickering green and red light strands of this aurora are produced when charged particles emitted by the Sun collide with charged particles in the upper atmosphere. Both sets are brought together by the Earth’s magnetic field as it converges near the North Pole.
The magnetic field itself is generated by electromagnetic currents in the Earth’s metallic liquid outer core about 2,000 miles below the surface. The outer core in turn is the deepest of several separately layered fluid systems undergoing convection that characterize Earth’s planetary behavior.
This spectacular display is best seen in winter at high latitudes, but occasionally appears further south where it can be seen on clear nights in rural New England where light pollution from cities is low. However, to truly appreciate the beauty of this interaction between the Earth’s magnetic field and the solar wind, a winter visit to Iceland, Greenland or Svalbard is warranted.
Svalbard has been on my bucket list for years now, but I have yet to convince my spouse to visit this Arctic archipelago in mid-winter when views of the Northern Lights would be assured. Located in the Arctic Ocean about midway between Norway and the North Pole, this is likely the world’s most northerly populated community. And at nearly 80 degrees north latitude, at this time of year it’s nighttime all the time.
Norway annexed Svalbard about a century ago, partly for military reasons, but also because it hosts significant coal deposits. Scientific American once whimsically featured it in an article as the possible source of Santa’s coal for mischievous children. But geologically it’s not all that different from New England. The rocks in Svalbard formed mainly in mountain-building episodes called the Caledonide orogeny, which is the European name for similar episodes that gave rise to the Appalachian Mountains in North America more than 300 million years ago.
That extensive mountain chain originally extended from the Gulf of Mexico through New England, Nova Scotia, Scotland and Norway and exceeded the modern Alpine/Himalayan system in extent and height. Such mountain building is the product of another convecting system in the Earth, in this case slow viscous movement of Earth’s outer mantle that moves its cold rigid crust around at rates of several centimeters per year. When underlying mantle currents draw two continents toward each other, their slow collision slowly builds up mountain belts.
The subsequent opening of the Atlantic and Arctic oceans occurred when mantle currents later diverged beneath this extensive mountain belt and began to break it into what are now North American and European segments. Locally this started about 190 million years ago, leaving behind narrow rift valleys now occupied by the Hudson and Connecticut rivers. Over time, the modern Atlantic Ocean itself began to form, and stranded Svalbard as a small, partly submerged micro-continent surrounded by younger seafloor.
Svalbard’s coal deposits have attracted considerable scientific interest, as they formed at higher latitudes than most coal beds and are geologically younger than most as well. Svalbard coal formed during a period of accelerated global warming that records one of the few known natural analogs to rates of climate change of concern today. The source of that warming (officially called the Paleocene-Eocene thermal maximum) is thought to be due to marked changes in global oceanic circulation. Paleontologists studying this episode may find some indication of global warming impacts over many millennia, and/or how three-dimensional circulation of the oceans impact global climate zones.
Severe and unusual weather events like recent December tornadoes in Kentucky or grassfires in Colorado draw attention to warming of the atmosphere and changes in its circulation patterns, and certainly have the most direct human impacts. But among climate scientists, the main concerns are with how the oceans store and distribute heat within their circulation systems, including the deep circulation of cold Arctic waters beneath the warmer ocean currents to the south.
Svalbard is one of the few places where evidence of all of Earth’s circulating fluid systems (outer core, mantle, oceans and atmosphere) is on display. So maybe I will try once again to convince my wife it is worth a winter visit.
Dan May is a geologist and professor of environmental science at the University of New Haven. He can be contacted at dmay@newhaven.edu.