Tracking the lives of glaciers

Glacier Bay researchers are working to reconstruct the history of glaciers over the last 10,000 years

Posted: Sunday, January 21, 2001

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When Daniel Lawson looks out over the icebergs bobbing in Glacier Bay's Johns Hopkins Inlet, he observes more than the calving of a tidewater glacier.

Though he takes a moment to enjoy the show as large blocks of ice break loose and crash into the water, he's in the park to conduct studies of glacial and marine physical systems. His goal is to learn about the glaciers and glacial-marine systems and their response to climate while reconstructing the glacial history and the climate of the park over the past 10,000 years.

"The only constant in Glacier Bay is change," Lawson said on a recent trip to the park, one of many he's made over the past 11 years.

"Glacier Bay is a unique laboratory," he said. "The past several hundred years have been well-documented, the terrestrial and tidewater glaciers remain active in today's environment and the region is a dynamic environment, sensitive to subtle changes in climate."

This sensitivity provides a wealth of basic information about the response of glaciers to climate change in the present. Lawson and others use these clues to reconstruct how glaciers responded in the past and affected the current state of the land and to predict the response of natural systems in the future.

 

"To understand the environment, you need to go there and observe it, touch it, feel it, be a part of it. In geology, the present is the key to the past. The present and the past together hold the key to the future," Lawson said.

A resident of Palmer, Lawson is a research physical scientist for the Cold Regions Research and Engineering Laboratory, known as CRREL. With offices in Anchorage and Fairbanks and based in Hanover, N.H., CRREL is one of the laboratories of the U.S. Army Engineer Research and Development Center.

One of Lawson's ongoing projects in Alaska is to lead teams of researchers into Glacier Bay National Park and Preserve to gather data and observations of how glaciers respond to climate change. As a national park also designated as a World Heritage Site and Biosphere Reserve, the area has been protected from most development. To support this research the Park Service provides its vessel, Nunatak, and crew, Capt. Jim Luthy of Auke Bay and First Mate Chris Frary of Douglas Island.

As the team travels from a rainy inlet into one with filtered sun, Lawson looks beyond the casual observation of "change." He wants to document the variability in climate across the park by collecting precipitation and temperature data in various locations. Though he enjoys watching the ice chunks calving from the face of a tidewater glacier, he is more interested in using lasers to measure the advancing or retreating ice margins that end in the sea, and a fathometer (sonar) to map the topography of the inlet's seabed.

On shore, Lawson searches the valleys and streams for logs and stumps from the ancient forests that grew between previous ice advances and were preserved beneath sediments.

 

The ice sheet that filled what is now Glacier Bay was first noted in 1794 by British Capt. George Vancouver. Icebergs then choked Icy Strait, the northern entrance to the Inside Passage. Over the next century, this massive ice sheet retreated more than 35 miles, leaving a natural laboratory for the study of glaciers, past and present. Through maps, notes and photographs, the past 200 years of change have been documented by explorers and scientists.

Explorer and naturalist John Muir came to Glacier Bay in 1879 seeking knowledge to support a theory that modern-day landforms were created by worldwide glaciation, not the biblical flood. In his memoir, "Travels in Alaska," Muir described "the crystal bluffs of the vast glacier, the intensely white, far-spreading fields of ice."

Today, more than a century after Muir built his cabin at the glacier margin, the view shows a deep fjord flanked by sheer cliffs and the beginnings of revegetation. The glacier that bears his name is now more than 25 miles away and no longer touches tidewater. The inlet revealed by the retreating glacier was the site of study several days into one of Lawson's trips.

In calm waters, the Nunatak ventured up Muir Inlet in the East Arm of the park past the jagged, blue spires of the 200-foot-high face of McBride Glacier and the curving 15-mile descent of Riggs Glacier. Luthy, the ship's captain, said that in the early 1970s when the Muir Glacier was active, icebergs as big as moderate-sized houses filled the inlet.

 

In the morning, one crew boarded a skiff and slowly motored back and forth across the upper inlet to survey and map the seabed. Surveys done over several years will be compared to determine sedimentation and erosion rates. Sediment deposits vary depending on the distance from the glacier. It can total several feet per day near the ice face and only a few inches per day down the inlet. Submarine slumps along the ice margin can suddenly send thousands of cubic yards of material down the inlet, redistributing the sediment and reshaping the sea floor.

"With this basic research, we begin to understand what occurs in the natural systems, glacial and land, and the interaction of these with the marine systems of the fjords," Lawson said.

He shares this research with marine biologists to help in their research.

"Where is the sediment moving and how will it affect the marine environment? Where does the material end up? If it is redeposited offshore along the continental margin, we can study these sequences of material and possibly learn what happened within Glacier Bay over 12,000 to perhaps 60,000 or more years ago during the last major glaciation."

Back aboard the Nunatak, a second crew lowered a conductivity-temperature-depth instrument to the seabed to profile the water characteristics in Muir Inlet. Long-term, site-specific oceanographic surveys examine tidal, seasonal and annual changes in fjord waters, including temperature and water quality. Measurements are also made in the streams discharging from the glaciers into the inlets. Together the information will be used to analyze seasonal and annual changes in sediment discharge from the tidewater glaciers in an effort to understand the subglacial processes that shape the landscape and produce the sediments that affect the marine environment. Sediment discharge can have a significant effect on marine conditions because the tidewater glaciers of Glacier Bay produce extremely high volumes of material.

In the afternoon, the first crew reinstalled a tide gauge after retrieving a year's worth of data, then hiked to Muir Photographic Station 37. Photographic stations throughout the park, marked by cairns, were established by scientist William Field after his first trip to Glacier Bay in 1929. Field noticed the dramatic changes in the ice positions relative to those recorded by pioneering glaciologist Harry Fielding Reid in 1890. Where Reid's maps showed solid ice, Field found water. Official photographers continue Field's record with the help of unofficial photographers who document the changing ice positions.

 

In a nearby valley, the other crew hiked in search of ancient logs and stumps for radiocarbon dating and tree-ring analysis. As the sediments erode, trees buried by the glacier are uncovered. By collecting, dating and studying the tree rings of numerous samples from each time period of ice advance and retreat, Lawson hopes to develop a continuous record dating back more than 9,000 years. This would be the only such record in sub-arctic North America and would be invaluable to understanding the climate through that time. This information would also allow researchers to reconstruct the park's glacial history and paleoclimate during Native habitation. Knowledge of ice advance and retreat and the associated climate could help identify the probable locations and duration of Native settlements and camps in the park.

"It's a race against time," said Lawson of his search for ancient wood.

In the East Arm, Lawson's team found wood near the present margin of Muir Glacier dating to nearly 9,000 years ago. Stumps still rooted in Wachusett Inlet have dates that may represent two periods of time when trees grew on the landscape: 2,400 to 3,600 years ago and 6,700 to 8,900 years ago. Investigations are just beginning in Adams Inlet with evidence of a 1,500- to 1,800-year-old rain forest of large Sitka spruce, some over 6 feet in diameter, similar to the forest growing today in Bartlett Cove near park headquarters.

In the West Arm, in Reid Inlet, evidence of two periods of interstadial forests have been found near the ice margin, suggesting Reid Glacier advanced through the inlet 7,500 years ago, retreated, then advanced again around 4,500 years ago. Last summer, peat some 12,000 years old was found. This organic material was produced from plants growing after the last major period of glaciation that covered much of North America, known as the Laurentide, ended. Further up the West Arm, only fragments of wood had been found in Tarr Inlet and Johns Hopkins Inlet until a discovery last summer of 8,800-year-old logs being pushed out from beneath Grand Pacific Glacier by a glacial stream.

"There is an urgency to this research. We need to repeatedly get to as many valleys and mountain slopes as we can to sample the wood just as it is uncovered by erosion of the sediments. If the wood is left exposed it will rot and the tree-ring record is lost. If we wait, wood samples that could be dated will be hidden by the encroaching vegetation."

Three days later, in the West Arm, the Nunatak continued to enjoy calm weather with an anchorage in the shadow of Reid Glacier. As the sun worked its way in and out of the scarf of clouds encircling the mountains, one team skiffed to Johns Hopkins Inlet around car-sized icebergs, past the tall, jagged face of Lamplugh Glacier and along the valley below Topeka Glacier. The team had scoured this valley for ancient wood earlier in the trip but had had no luck.

Johns Hopkins Inlet was barely passable due to ice, but Lawson's team could get to the recording gauges for the first time in over a year of trips. The team collected data from existing water-level and rain gauges and added a recording temperature gauge. There's little information on the current climate of the park and its glaciated fjords, but it is essential to interpreting past glacial activity and climate changes.

Though Lawson has a jump start on collecting weather, water and ice data, his vision includes small, unobtrusive permanent weather stations with remote access via satellite for scientific as well as park ranger use. In his search for keys to the past, his team has only just begun to acquire wood samples for tree-ring analysis.

His goal would be to send teams of researchers to collect and analyze the rings to create a 9,000-year record of the climatic conditions during the advances and retreats of the glaciers. All this basic research, he hopes, will lead to an understanding of Glacier Bay National Park's physical environment and glacial systems from the mountaintops through the ice margins down to the bottom of the inlets and out to the edge of the continental margin.

"The more often you go to Glacier Bay, the more you can learn. Yes, you can use computers and remote sensing to measure and model, but it is the direct observation that validates the models," Lawson said. "Every day in Glacier Bay, we learn or discover something new as we try to understand the world we live in. In Glacier Bay, we can observe changes during a lifetime, instead of on a geologic time scale."

Kirsten Gehlbach is a freelance writer living in Vermont.



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