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common ground

Investigating Ecosystems
Spring 1995, vol. 8(1)

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*  View from the Top of the Planet

(photo) Archeologist in the field.

"The public has spoken: save our forests for future generations. At the U.S. Forest Service, that means taking a more holistic view of America's woodlands-their past as well as their present. Enter archeology."

Sandra Jo Forney

by Michael Kunz and Robert King

The Mesa, as the plateau is now known, rises 200 feet above a roadless expanse of tundra the size of Indiana, accessible only by helicopter. During the field season, the flights are frequent. The Mesa site is yielding evidence with potential far-reaching implications for the planet's future.

The story of the site began in the mid-1970s, when the Interior Department was charged with managing oil and gas exploration in the National Petroleum Reserve on the north slope of Alaska's Brooks Range, a barren chain of jagged peaks 500 miles north of Anchorage. In 1978, archeologists with the Bureau of Land Management, surveying the Mesa and its environs in advance of drilling, discovered stone projectile points that bore a striking resemblance to Paleoindian-style points of the American high plains and southwest.

"Paleoindians," the name given to the first Americans, occupied North America during the Pleistocene-Holocene transition, a period of extensive climate change 12,500 to 8,500 years ago. Before the discovery of the Mesa site, no scientifically accepted Paleoindian sites had been discovered in the Arctic, much less near the Bering land bridge.

The BLM archeologists excavated the remains of three ancient campfires; each contained chipping waste, stone tools, and at least one projectile point. None of the hearths had the minimum amount of charcoal required for radiocarbon dating, so their charcoal was combined, yielding a date of 7620 B.P. (years before present)—about 1,000 years too recent to be considered "Paleoindian."

Jump forward a decade to 1989, when accelerator mass spectrometry, a new radiocarbon dating technique that can be used on very small amounts of organic material, became commercially available. Tested with the new method, the Mesa charcoal yielded a date of 9730 B.P. Since then, charcoal from 14 Mesa hearths has yielded dates ranging from 11,660 to 9730 B.P. In 1992 the uncertainty concerning the validity of the site's original date was resolved when the first sample was re-tested and dated to 10,060 B.P.

The Mesa is by most standards an archeologist's dream. Unlike most Arctic sites, it is basically uncontaminated by the remains of more recent cultures. The Mesa itself has been mostly undisturbed by the harsh Arctic environment, making excavation and analysis relatively uncomplicated. The site is exceptionally well dated and its distinctive projectile points now serve to indicate the presence of Paleoindians when found at other Alaskan sites. Because of these attributes, the Mesa has played a paramount role in defining the Northern Paleoindian Tradition.

However, because the site was only a hunting lookout, not a settlement, it has produced no plant or animal remains, which could supply information about the climate and environment during the time the site was occupied. These kinds of remains—which provide insights into residents' daily and seasonal activities—are usually found at encampments or where game was killed and butchered. Doubtless these activities were associated with the Mesa; however, they likely were confined to the valley floor and thus their remains may have been either eroded or buried by the meanderings and fluctuations of Iteriak Creek.

Research elsewhere in the world indicates that the Mesa was occupied during a time of radical global change. However, it requires data from non-archeological contexts to understand how people using the Mesa were affected by the rapidly changing ecosystem.

Late Pleistocene fossil remains—including those of mammoth, bison, and antelope—are found throughout the region, demonstrating that until about 11,000 years ago the ecology of northern Alaska was quite different than it is today. Many of these extinct animals, grass-eaters with small hooves adapted for travel across firm, dry ground, were not well suited to digging through more than a thin snow cover for food. Their presence suggests a grassland ecosystem, best termed a steppe-tundra.

Preliminary research suggests that this ecosystem had a climate that was windier, colder, and drier than today. Braided streams probably served as sources of sand and loess, which the wind transported across the region. Unstable soils, the result of the wind-born sediment and minimal precipitation, prevented the accumulation of peat, probably keeping the summer-thaw layer in the soil thick, encouraging the growth of grasses.

Shortly after the Mesa was first occupied, the climate changed to much like that of today. The change was abrupt and rapid, probably too fast for the plantlife to adapt. It became warmer and wetter, with more snow in winter and more rain summer. A resulting increase in vegetation probably restricted sediment runoff into streams, dampened flood events, and stabilized channels, fostering a switch from braided to predominantly meandering channels. This change removed sources of wind-born sediments and lessened disturbance to the surface of the land.

Together, the wetter climate, the stabilization of the floodplain, and the drop in wind-born sediments permitted a build-up of peat. Samples collected by coring through the modern tundra around the Mesa suggest that peat accumulation was region-wide by 8500 B.P., with the vegetation much like it is today.

As peat accumulated, the seasonal frost-free layers shrank, causing soil temperatures to drop and surface water to pond. This further encouraged peat accumulation, squeezing out the grasslands so that the vegetation could sustain only specially adapted broad-hoofed herbivores, such as moose, caribou, and muskox.

These changes probably devastated the large Ice Age herbivores and may have severely impacted humans as well. The changed ecosystem made overland travel difficult, as anyone who has hiked across the tussock-tundra can attest. Decreased mobility reduced the size of an area that could be depended on for subsistence at the very time when the ability to range over a large area was necessary, given the dwindling of game. Such circumstances may have provided the impetus for some of the people to move south.

Paleoecological research associated with the Mesa has led to some interesting new discoveries. There is tentative evidence for a Younger Dryas (YD) event—a time of radical and rapid climate fluctuations at the core of the changes just described—in Alaska from 11,000 to 10,000 B.P.

The Mesa project has dated defined stratigraphic profiles using accelerator mass spectrometry, which has yielded evidence supporting the occurrence of the YD in Alaska. Several stratigraphic sections indicate that prior to 11,000 B.P. the climate had moderated to the extent that peat build-up had begun in favorable locales. Sometime between then and 9500 B.P. the peat was overrun by solifluction, the thawed layer sliding downhill along the surface of the permafrost. This episode may represent a return to a full glacial climate, the YD, conducive to the spread of solifluction lobes.

One of the most exciting aspects of the paleoecological research is the discovery of the "Lake of the Pleistocene." Several hundred years ago, an ancient lake was breached and drained by a course change in the Nigu River 15 miles to the west of the Mesa. The lake's sedimentary record begins during full glacial times, spans the Pleistocene-Holocene transition, and extends up to the time of drainage. The frozen sediments of the drained lake are now exposed in a 150-meter-long, 5-meter-high cutbank of the river. The Pleistocene-Holocene transition is recorded by a stratigraphy change from sand to silt sediments. The lake sediments are finely laminated and contain a frozen archive of plant fossils. Because the lake cross-section is so large, study is not limited to core drilling as it would be if the lake had not been drained. This means that an immense amount of ancient information can be recovered.

This project promises to lead to new discoveries about the origins of the tussock-tundra ecosystem that blankets most of arctic Alaska, Canada, and Russia, which may play a key role in global budgets of carbon dioxide in the future. If the earth's climate warms up, vast amounts of peat may deteriorate, releasing large amounts of carbon dioxide into the atmosphere and increasing the greenhouse effect. This would feed a cycle of further peat deterioration, carbon dioxide release, and increasing global warming.

Studies of the Pleistocene-Holocene transition could provide valuable data for the critical debate over climate change. The effect of ancient warming episodes on permafrost may parallel what some scientists foresee as the result of global warming in the next century. Thus, the Mesa project can help identify processes and rates of change in Arctic ecosystems.

It is both fitting and ironic that research on the Mesa people, whose world changed so dramatically over 10,000 years ago, may help us deal with changes occurring to the Arctic ecosystem in our near future. To ignore this largely untapped source of information could eventually place us in the same category as the fauna of the late Ice Age.

For more information, contact Michael Kunz, BLM Arctic District, 1150 University Ave., Fairbanks, AK 99709-3844, (907) 474-2311, fax (907) 474-2280 or Robert King, BLM Alaska State Office (930), 222 West 7th Ave., #13, Anchorage, AK 99513-7599, (907) 271-5510.