The Summer of the Bear: A snapshot of climate change in Southeast Alaska


Standing on top of one of the Pyramid mountains, gloved hands stuffed into my orange raincoat, I look out over a sea of pink and yellow clouds as the sun sets on the low evening ceiling that settles over Sitka Sound. Alaska is not always the easiest place to call home, but moments like these make me forget the rain and cold. They fill me with awe that presses out against my ribs, bringing up a line from a James Wright poem, A Blessing: "Suddenly I realize that if I stepped out of my body I would break into blossom."

When the sun shines in my hometown, Sitka, I know I am in the most beautiful place on earth. Sitka is a bustling rural metropolis hugging twenty miles of shoreline on Baranof Island, in Southeast Alaska. The southeast "panhandle," sandwiched between British Columbia and the Gulf of Alaska, is made up of eleven hundred islands called the Alexander Archipelago. Baranof is one of the largest, reaching one-hundred miles long and thirty miles across at its widest point. Like almost all of the other large islands, Baranof is covered in mountains and has year-round ice fields at high elevations.

Southeast Alaska is in the Tongass National Forest. Just shy of seventeen million acres, the Tongass is the largest national forest in the country, and is part of the largest area of temperate rainforest on the planet. Temperate rainforest is a very specific and interesting ecosystem, defined by high annual precipitation, mild climate, and tree populations that do not require fire to regenerate.

Fifty degrees and overcast with a seventy percent chance of rain could be the forecast any day of the year in Sitka. Sitka gets about eighty seven inches of rain per year, and there are other towns, both north and south of us, that get up to one hundred-fifty inches annually. Rainfall varies throughout the region due to mountains and wind patterns.

Climate also varies throughout Southeast, but in general it is pretty mild. The ocean keeps the islands cool and wet in the summer, and warm and wet in the winter. Air temperatures range between forty and sixty degrees fahrenheit in the summer and twenty to forty degrees in the winter. Warm Japanese ocean currents keep the water around forty-five to fifty-five degrees, depending on the season.

Finally, temperate rainforests have little to no forest fires. In some places, like California, fire is part of the life cycle of the forest that allows plants to regenerate and be productive. In Southeast Alaska, wind is the change agent that keeps the forest going. In October and November, our stormiest months, straight winds of up to eighty or ninety miles per hour sweep through Southeast, taking out power lines, keeping people off the water, and blowing down trees. When trees get knocked over, the canopy opens up, allowing young trees to grow and providing light to the ground cover plants. The fallen trees themselves become "nursery logs," providing nutrients to new trees and plants.

While Southeast is not the dramatic icy tundra that many people imagine when they think of Alaska, its majestic mountainous islands make it beautiful in its own way. The mountains are one of my favorite features of the islands, and they have an interesting history. The islands did not all form in the same way, but are the result of a few different geological processes that gathered together over millions of years. At one point, the whole area was covered by glaciers, resulting in the topography we see today.

The Alexander Archipelago is made up of three different types of islands called Wrangellia, Stikine, and Alexander. Two-hundred and twenty million years ago, all three "terranes" were scattered off-shore, separate from each other. The Stikine terrane, made up of volcanic flow, paleozoic sedimentary rocks, and marine sandstone, probably started out as a chain of volcanic islands much like Hawaii. As the plates shifted 200 million years ago, the chain collided with ancient North America at what is now British Columbia. Wrangellia also started as a volcanic chain, but these islands sank below the surface and became a shallow reef covered by marine shale. After a while a rift in the ocean floor produced a large amount of volcanic basalt that covered the reef. Later still, copper was deposited on Wrangellia, and that is why today, the Wrangell mountains have copper deposits. The Alexander terrane, distinguished by its marble and limestone, joined up with Wrangellia off shore in the Middle Jurassic period. Together they made a subterrane that collided with the North American plate in a region of subduction. The collision caused metamorphic and igneous rocks to be formed, and the was begining of the region's mountains. Over the next 200 million years the land continued to shift, with rocks being added, and some rocks breaking off, forming the archipelago. Today the mountains are still growing, possibly rebounding from ancient glaciation or as a result of continued subduction. [2]

The Alexander Archipelago is defined by its deep channels and steep mountainous islands. The channels, like Chatham Strait, often mark fault lines between chunks of islands. Their depth, and the dramatic contrast with the mountains, is a result of ancient glaciation. At the height of the ice age, Southeast Alaska was covered in thick glaciers that scoured the islands down to bedrock. The only exposed habitat, called refugia, were small areas of coastline and rocky nunataks that stuck up above the ice at high elevations. Both types of refugia were islands of rock in a sea of ice, and supported life, including mountain goats and bears that still inhabit the islands today [9]. When the glaciers melted, the channels flooded and the tops of the mountains became islands. Looking across Baranof Island on a clear day, you can pick out the sharp rocky peaks that must have survived above the ice, as well as the rounded mountains that were scoured down and made smooth by the heavy ice. There is a lake south of town, Blue Lake, where the deepest point is actually below sea level, probably because the valley was once hollowed out by ice.

It used to be believed that the islands were totally inhospitable during the ice age (Wisconsin glaciation), and all flora and fauna populations arrived and spread in the past 10,000 years [5]. However, because of fossil findings, we are now fairly confident that refugia supported life during the ice age. Sea level was about 300 feet lower, and the coastline was lifted in response to the pressing down of the ice. This created the coastal refugia where plants and animals survived. These areas existed on islands we still see today, but it also connected some landforms that